Vol.: (0123456789) Aerobiologia (2025) 41:441–460 https://doi.org/10.1007/s10453-025-09860-2 ORIGINAL PAPER Ragweed (Ambrosia) pollen transport and seed production in Finland during 1990–2022 Maria Louna‑Korteniemi  · Sanna Pätsi  · Pasi Ahola · Agneta Ekebom  · Maiju Kyyhkynen · Linnea Toiviainen · Marika Viljanen · Annika Saarto Received: 19 December 2024 / Accepted: 13 April 2025 / Published online: 5 May 2025 © The Author(s) 2025 Keywords Ragweed · Ambrosia artemisiifolia · Invasive alien species · Aeroallergen · Climate change 1 Introduction Allergenic pollen season in Europe is characterized by deciduous trees flowering in the spring, grasses (Poaceae) from late spring to early autumn, and weeds such as mugworts (Artemisia spp.) and rag- weeds (Ambrosia spp.) from late summer to autumn. Common ragweed (Ambrosia artemisiifolia L., Aster- aceae; henceford referred to as ragweed) is an annual, herbaceous, wind-pollinated plant native to North America, but invasive around the world, especially in Europe (Bassett & Crompton, 1975; Essl et al., 2015; Smith et al., 2013). It is a short-day plant, with flow- ering governed by photoperiod: flowering is induced after summer solstice when the day-length has short- ened sufficiently (Allard, 1943, 1945; Deen et  al., 1998a; Leiblein-Wild & Tackenberg, 2014). After ripening, ragweed seeds will enter a dormant state and require specific conditions to break the dormancy (Baskin & Baskin, 1977, 1980; Bazzaz, 1970). Ragweed grows in anthropogenic environments in a wide range of open habitats associated with frequent soil disturbance, such as cultivated fields, roadsides and urban wastelands, and is highly inva- sive around the world in areas with temperate, conti- nental climates (Bassett & Crompton, 1975; Bullock et al., 2012; Essl et al., 2015; Montagnani et al., 2017; Abstract Common ragweed (Ambrosia artemisiifo- lia) is one of the most harmful alien invasive species in Europe. Ragweed pollen is a potent aeroallergen, and can travel long distances in the atmosphere. In this research we studied pollen samples collected in Turku, Finland, during 1990–2022, to identify when ragweed pollen was first transported to the country and how frequently it has happened since, how much pollen has been transported to the country yearly, and whether it is possible to observe trends in airborne ragweed pollen occurrence in Finland during the past decades. We show that (1) ragweed pollen has been transported to Finland since the 1990’s, significantly earlier than previously thought, and (2) the long-dis- tance transport episodes have often been more intense in the recent years. Ragweed pollen transports occur in the late summer or in the autumn, thus lengthening the pollen season in Finland. We also describe a case study where we show that ragweed is able to produce mature viable seeds in Finland. Our conclusion is that the significance of ragweed as an aeroallergen in Fin- land is increasing, and thus the situation needs to be regularly monitored. M. Louna-Korteniemi (*) · S. Pätsi · P. Ahola · M. Kyyhkynen · L. Toiviainen · M. Viljanen · A. Saarto  Biodiversity Unit, University of Turku, Turku, Finland e-mail: amlouna@gmail.com A. Ekebom  Palynological Laboratory, Swedish Museum of Natural History, Stockholm, Sweden 442 Aerobiologia (2025) 41:441–460 Vol:. (1234567890) Smith et al., 2013). It is a noxious weed that can grow up to 250  cm high, it causes significant crop losses in agriculture, and its pollen is a potent aeroallergen causing respiratory problems and asthma; thus, the species has harmful impacts on human health, agri- culture and economy (Bullock et al., 2012; Essl et al., 2015; Montagnani et  al., 2017, 2023; Smith et  al., 2013). One ragweed plant produces an average of 1.19 ± 0.14 billion pollen grains per year, and the pol- len production correlates with the size of the plant (Fumanal et  al., 2007). Ragweed pollen is highly allergenic and a significant health hazard both in North America and in the areas where the species is invasive (Bassett & Crompton, 1975; Arbes et al., 2005; Oswalt & Marshall, 2008; Bullock et al., 2012; Smith et al., 2013; Salo et al., 2014; Essl et al., 2015; Montagnani et al., 2017). The incidence of ragweed allergy has increased in Europe in the past decades (Bullock et  al., 2012) and sensitization to ragweed has been proposed to increase by over 100% in the next few decades (Lake et al., 2016). Geographical differences in sensitization rates are high, and the choice of methods in studying sensitization rates creates variation between different studies (NHANES III; Arbes et al., 2005; NHANES, 2005–2006; Bousquet et al., 2007; Heinzerling et al., 2009; Bullock et  al., 2012; Ruëff et  al., 2012; Salo et  al., 2014; Grewling et  al., 2018, Stepalska et  al., 2020 and references therein). Various threshold values for ragweed pollen that are likely to induce allergy symptoms have been mentioned in several studies, usually ranging from 5 pollen grains per m3 of air (pollen/m3) daily average up to 20 pollen/m3, but both lower and higher thresh- old values have also been proposed (Solomon, 1984; Comtois & Gagnon, 1988; Juhász, 1995, according to Makra et al., 2005; Makra et al., 2005; Bullock et al., 2012; Stepalska et  al., 2020 and references therein). However, in a systematic review by Steckling- Muschack et al. (2021) no universal clinical threshold could be identified, and the authors concluded that sensitivity to ragweed pollen is strongly dependent on the individuals. 1.1 Ragweed distribution in Europe In Europe, ragweed was first recorded in botanical gardens in the eighteenth century (Chauvel et  al., 2006; Essl et  al., 2015). In nature, its early invasive history began in the nineteenth century when it was inadvertently introduced into Europe with imported agricultural products from North America (Essl et al., 2015; Montagnani et  al., 2017, 2023; Smith et  al., 2013). It began spreading more rapidly around the mid-twentieth century by repeated introductions and the process of naturalization, and has now colonized large areas in South-Eastern, Southern and Central Europe (Bullock et  al., 2012; Chauvel et  al., 2006; Essl et  al., 2015; Montagnani et  al., 2017, 2023; Smith et al., 2013). It is also invasive in many parts of Asia, Australia, Africa and South America (Cher- rez-Ojeda et al., 2024; Montagnani et al., 2017, 2023; Prank et al., 2013; Smith et al., 2013). The spreading mechanisms of ragweed (both from native sources and from invaded areas) include dispersal through contaminated seed for crops, con- taminated bird seeds, transport along roads and on agricultural machinery, and—with minor impor- tance—natural seed dispersal e.g., by birds or wind (Bullock et al., 2012; Chapman et al., 2016; Chauvel et al., 2006; Essl et al., 2015; Lemke et al., 2019). Temperature is an important limiting factor for the spread of ragweed (Cunze et al., 2013; Essl et al., 2015). The seedlings are sensitive to frost, and it is widely believed that in the northern reaches of the distribution area the first autumn frosts terminate the flowering and kill the plants before the seeds mature, if the plants even have time so start flowering (Allard, 1943; Deen et  al., 1998b; Bullock et  al., 2012; Essl et al., 2015; Petrova, 2019). However, there are some indications that the frost tolerance of mature plants may be slightly better than often thought. According to Dahl et al. (1999), the killing frost for ragweed is − 5 °C. In Europe, ragweed’s main area of distribution lies in the southern parts of Eastern and Central Europe, with largest populations especially in the Rhône valley (France), the Pannonian plains (Hun- gary), Po valley (Italy), Croatia and Serbia, and smaller established populations in, e.g., Belgium, the Netherlands, Germany and Poland (Bullock et  al., 2012; Buters et  al., 2015; Essl et  al., 2015 and references therein). The species is also tak- ing a foothold in the Nordic and Baltic countries. In Denmark, ragweed is systematically flowering although its ability to produce mature seeds has been uncertain (Skjøth et  al., 2009; Ministeriet for 443Aerobiologia (2025) 41:441–460 Vol.: (0123456789) Fødevarer, Landbrug og Fiskeri, 2010). However, Bullock et al. (2012) report that it is spreading there from established areas. In Southern Sweden, a few cases have been reported during the 1990’s when, during warm years, ragweed produced germinative seeds (Dahl et al., 1999), but, according to Scalone et al. (2016), there were no established populations in Sweden in 2016, as the plants did not have time to produce seeds before they were killed by frost. In Latvia, ragweed plants are observed yearly and the number of observations is rising, but there is no information about their possible seed produc- tion (Titane & Sozinova, 2023). Saar et  al. (2000) reported that ragweed could produce seeds in Lithu- ania but not in Estonia, and in 2016 the situation in Estonia remained unchanged (Elvisto et  al., 2016). Thus, the northern populations are mostly ephem- eral and dependent on repeated seed introductions (Cunze et  al., 2013; Dahl et  al., 1999; Saar et  al., 2000; Smith et  al., 2013). However, some of the information available on ragweed occurrence and reproduction at the northern reaches of its distribu- tion area is somewhat outdated, and newer assess- ments on the situation may be needed. The current distribution of ragweed is smaller than its potential range, and several studies have predicted that the range will shift northwards and uphill in the future due to the ongoing naturalization process, cli- mate change, seed dispersal and changes in land-use, aided by phenotypic plasticity and adaptive potential (e.g., Battlay et  al., 2023; Cunze et  al., 2013; Essl et al., 2015; Gallien et al., 2016; Gentili et al., 2021; Leiblein-Wild et  al., 2016; Rasmussen et  al., 2017; Scalone et al., 2016; Storkey et al., 2014). Anthropogenic climate change has already altered the biosphere. The global surface tempera- ture in 2011–2020 was ca. 1.1 °C higher than during 1850–1900, climate zones have shifted polewards, the growing season has lengthened, and there are observ- able changes in weather patterns and precipitation. Globally, warming in the long term (2081–2100) is projected to be from 1.0  °C in the best-case sce- nario (SSP1-1.9), to 5.7 °C in the worst-case scenario (SSP5-8.5). (IPCC, 2021.) The higher latitudes are expected to experience more warming than the south- ern regions (Lee et  al., 2021), and the ragweed dis- tribution area is expected to spread northwards under all climate scenarios (Cunze et al., 2013; Essl et al., 2015; Rasmussen et  al., 2017; Storkey et  al., 2014). Warmer autumns and longer growing season will lengthen the pollen season (Ziska et al., 2011). Different aspects of climate change, such as ele- vated CO2 and elevated temperature, enhance the photosynthesis of ragweed and affect its growth, spread, flowering phenology, pollen and seed pro- duction and the allergenicity of pollen, but there may be differences in how different ecotypes react to the changes in their environment (Cheng et  al., 2023; Gentili et  al., 2019; Hamaoui-Laguel et  al., 2015; Lake et al., 2016; Leiblein-Wild & Tackenberg, 2014; Montagnani et  al., 2023; Rauer et  al., 2020; Stinson et al., 2017; Wayne et al., 2002; Ziska & Beggs, 2012 and references therein). Abiotic factors that remain constant even in a changing climate, such as photo- period, also pose challenges to species’ capabilities to spread northwards and to adapt to a changing climate (Saikkonen et al., 2012). For short-day plants such as ragweed this is especially important. 1.2 Ragweed in Finland Several studies have shown that ragweed pollen grains can be transported over long distances in the atmos- phere (Belmonte et  al., 2000; Cecchi et  al., 2007; Smith et al., 2008; Kasprzyk et al., 2011; Šikoparija et  al., 2013; Makra et  al., 2016; Weger et  al., 2016; Bilińska et  al., 2017; Stepalska et  al., 2020). Thus, ragweed pollen may cause allergic symptoms and sensitization even outside of the species’ distribution area. Finland is located in the north of Europe, but even so, ragweed pollen is occasionally observed in the air with the routine monitoring of airborne pol- len. To date, the first mention of long-distance trans- ported (LDT) ragweed pollen in Finland is from 2005 (Saarinen & Jantunen, 2017), when ragweed pollen was detected at several measuring stations in central and northern Finland. Ragweed is botanically classified in Finland as an ephemeral alien, i.e., a taxon that has not been able to persist or create populations (Kurtto et  al., 2019), unlike Montagnani et  al. report (2017), and officially classified as an “invasive alien to be moni- tored” (Niemivuo-Lahti, 2012). According to the Finnish Biodiversity Information Facility (https:// laji. fi), a few to a few dozens of plant individuals are reported around the country every year, mostly in gardens and near bird feeding sites, but also on road- sides and wastelands. Observational bias may affect 444 Aerobiologia (2025) 41:441–460 Vol:. (1234567890) our knowledge on the sites of ragweed occurrence in Finland, as the reports are often provided by garden and nature enthusiasts and not verified by experts, and gardens and bird feeding sites are one of the more typical places where people tend to make nature observations. An important route for ragweed seeds to Finland seems to be via birdseed, as reflected by the sites where they frequently occur, but this has not been systematically studied, and as the numbers of ragweed individuals are small, strong inferences on the routes are hard to make. Until recently it has been thought that ragweed is not able to reproduce in Fin- land as the first autumn frosts terminate the growing season before the plants have time to produce mature seeds (Kurtto, s.a.; Essl et al., 2015). Local ragweed plants are so few and so far apart in Finland that they do not contribute to the overall pol- len levels. However, the transported ragweed pollen may pose an allergy risk at least to some individuals, although little is known of its significance for autum- nal allergy symptoms in Finland. 1.3 Purpose of the study Although LDT ragweed pollen does occasionally reach Finland, its significance as part of the late pol- len season and airborne allergenic load in the coun- try has not been systematically studied. Information on ragweed phenology in the northern conditions in Finland is also scant. The aim of this study is to fill that void, to clarify the picture of the occurrence of ragweed pollen in Finland from the early 1990’s to the early 2020’s, and to acquire more information on ragweed seed production in Finland via a case study. The main study questions are: (a) since when and how often has ragweed pollen been transported to Finland, (b) how much pollen has been transported to the country yearly, (c) can ragweed produce mature seeds in Finland? 2 Materials and methods 2.1 Long-distance pollen transport We analyzed air samples collected with Hirst-Burk- ard volumetric spore sampler (Hirst, 1952) in Turku, Southwest Finland, between 1990 and 2022, in the months of August, September, and October (Fig. 1). At different times during the study period, the sampler was located on two different roofs at the University of Turku (UTU; 60.45521028N, 22.28512644E), all within 100  m from each other. Until 2012, the sampler was located 50 m above sea level (15  m above ground level), 2012–2016 42  m above sea level (10 m above ground level), and from 2016 onwards 51  m above sea level (16  m above ground level). The samplings –2012 and 2016–22 are Fig. 1 The locations from where pollen data was ana- lyzed in the present study (Turku, Finland), and the locations from where it was used as an aid in identify- ing possible LDT days in Finland (Kuopio in Finland, Stockholm and Borlänge in Sweden, and Tallinn, Jõhvi and Kuressaare in Estonia) 445Aerobiologia (2025) 41:441–460 Vol.: (0123456789) from the same roof; the difference in height is due to structural changes of the roof and the setting of the sampler (to the rail), the site of the trap on the roof was moved by approx. 5–10  m. The tapes from the sampler had been cut into pieces so that each piece equaled one day (24  h; henceforth “sample”). The pieces were mounted on microscopic slides with Gel- vatol. All the samples had been previously analyzed at UTU as part of the standard pollen monitoring rou- tine, in which pollen grains are counted with a light microscope using 400 × magnification on 48 random fields on the microscopic slides (Mäkinen, 1981). For the present study, we analyzed the entire collec- tion area of the slides (14 mm × 48 mm) with a light microscope using 200 × magnification, and identified and counted all ragweed pollen grains. The number of pollen grains was converted to the daily average pol- len concentration per cubic meter of air (pollen/m3). Due to limited resources, it was not possible to analyze all the samples in the August–October time- frame between 1990 and 2022. Consequently, we applied the following methods to identify days with likely long-distance transport episodes (LDTs). We analyzed all the samples that fulfilled one or more of the following criteria: (a) Ragweed pollen had been detected in Turku or Kuopio with the standard monitoring routine described above. Kuopio is a city in Eastern Finland (Fig.  1), and was chosen as a reference point as it is part of the routine pollen monitoring network in Finland, and as ragweed pollen trans- ported from Eastern Europe may occasionally have been detected there, even when it was not detected in Turku in Western Finland; (b) Non-specified Asteraceae pollen had been detected in Turku or Kuopio with routine moni- toring: during the 1990’s and early 2000’s rag- weed pollen was not routinely identified to the genus level but to family level Asteraceae. Therefore, some ragweed pollen may have been recorded as Asteraceae; (c) Ragweed pollen had been detected in the air at least at one of the following nearby aerobiologi- cal stations: Stockholm and Borlänge in Swe- den, or Jõhvi, Kuressaare and Tallinn in Estonia (Fig.  1), based on the data available at Euro- pean Aeroallergen Network (EAN). These were selected as reference sites due to their relative proximity to Turku and as airmasses moving from south to north will likely reach at least one of them before reaching Turku; (d) High amount of non-specified Asteraceae pol- len was detected in different aerobiological sta- tions in Sweden (selected with the same criteria as above) during 1990–1999, as during that time some ragweed pollen may have been recorded as Asteraceae. After analyzing the samples identified using the above criteria, we analyzed all the previous and fol- lowing samples in relation to the samples when rag- weed pollen was detected in Turku, until a sample with zero ragweed pollen was reached. This enabled us to pinpoint the start and end dates of each LDT episode. Furthermore, in order to control whether our screening methods were indeed able to find all or most of the LDT episodes, we analyzed all the sam- ples in August and September from the year 2017. The year 2017 was chosen as control because during the process of analyses we noticed that the same cri- teria indicated markedly less potential LDT days for 2017 than for 2018–2022. After analyzing the sam- ples that were indicated by the criteria, we also found that the number of LDT days in 2017 was consider- ably lower than in 2018–2021. We wanted to ascer- tain that the differences between the years reflected the actual pollen situation, and were not the result of inadequate or biased criteria. Some of the samples, especially the older ones, exhibited signs of deterioration, and, in some cases, it was difficult or impossible to analyze the entire col- lection area of the microscopic slide. These partly damaged samples were excluded from the calcula- tions of daily pollen concentrations, and in cases where no ragweed pollen was found on the preserved part of the sample, it was also excluded from the anal- yses of LDT days. If ragweed pollen was detected on the preserved part of the sample, that day was treated as an LDT day, even though its daily pollen concen- tration could not be calculated. Consequently, 28 samples were excluded from the calculations of con- centrations, 23 samples were excluded from the study completely, and 5 partially degraded samples contain- ing ragweed pollen were treated as LDT days. We analyzed 494 days in total. The number of days analyzed per year varied from 0 (1998) to 62 (2017). From 1998 no samples were analyzed, as we could 446 Aerobiologia (2025) 41:441–460 Vol:. (1234567890) not identify any possible LDT days using the criteria described above. The number of days analyzed from 2017 was higher than from any other year, as we ana- lyzed all the samples from August to September, and not just the samples for possible LDT days that were indicated by the criteria described above. 2.2 Case study: seed germination in Finland The case study was conducted in Turku area. The cli- mate is hemiboreal, characterized by warm summers and cold winters, subgroup Dfb in the Köppen climate classification system (Kottek et al., 2006). In August 2021, we observed by chance five naturally growing ragweed plants at a roadside wasteland in Auran- laakso, Kaarina, near the border of Turku (60.4684 N, 22.353  E). The plants were not sown there for the purpose of this study, but had grown from seeds of unknown origin. We wanted to test the belief that ragweed is not able to produce mature seeds in Fin- land, and started to monitor the plants regularly. At the beginning of November, seeds were observed on the plants. 70 seeds were collected and a laboratory growth experiment was conducted to test their viabil- ity. It is worth noting that during the following win- ter the ragweed-infested site was destroyed by exten- sive roadwork and construction, and that no ragweed plants have been observed growing at the site in the following years. Ragweed seeds become dormant upon maturation and require exposure to winter temperatures (strati- fication) to break the dormancy. In our study, these conditions were simulated by conducting the seed collection, storage, wet-stratification and growth experiment based on methods and results described in previous studies on ragweed life cycles, seed dor- mancy or germination. (See e.g., Bazzaz, 1970; Picket & Baskin, 1973; Willemsen, 1975; Baskin & Baskin, 1980; Leiblein-Wild et  al., 2014; Fogliatto et al., 2019.) 3 Results 3.1 Long-distance pollen transport No ragweed pollen was detected in the majority of the analyzed samples (Fig.  2), and when ragweed pollen was present, the daily average concentrations were mostly low (< 5 pollen/m3) (Fig.  3; Table 1). The number of LDT episodes per year varied from 0 to 5 (average 1.6), and the length of episodes varied from 1 to 13 days (average 3.2 days) (Fig. 4). The first ragweed pollen grain reaching Finland was found in a sample collected in 1991 (Fig.  2; Table 1). The first LDT episode with more than one pollen grain per sample occurred in 1995, and the first episode that lasted more than one day occurred in 1996 (Fig.  4). The first episode with average daily pollen concentration exceeding the often-used low-end clinical threshold of 5 pollen/m3 occurred in 1997 (12.2 pollen/m3) (Fig. 3; Table 1). This epi- sode was also the longest until that point, lasting six days (Fig. 4). The average daily pollen concentration exceeded the threshold of 20 pollen/m3 only four times during the study period, three of those occurring after 2018 (Table 1). The first time when pollen concentration exceeded 50 pollen/m3 occurred in 2020. The number of LDT days and the amount of transported pollen has varied a lot in the studied years, but the year 2020 was a record year in many ways. It had the maximum number of LDT days, with 23  days (Fig.  2), separated into two distinct episodes. 2020 also exhibited the highest daily pol- len concentration, 64 pollen/m3, as well as the high- est amount of transported pollen during the whole season (109 pollen/m3) (Fig. 3). No ragweed pollen was found in 1990, 1992–1994, and 2003–2004 (Fig.  2). This may be partly due to the low number of analyzed samples, as our methods identified only a few possible days to be analyzed. However, during the control year 2017, all the found LDT days were already indicated as potential LDT days by the selection criteria described above. No ragweed pollen was found from the samples that were not indicated as potential LDT days. Most LDT days occurred between the last week of August and the end of September. The earliest calendar day with LDT pollen was 3 August (2014), and the latest 18 October (2018). However, in 2021, the first ragweed pollen grains of the year were captured with the routine monitoring already on July 21, but as July was not included in the present study, that observation is not part of this dataset. 447Aerobiologia (2025) 41:441–460 Vol.: (0123456789) Fig. 2 The number of analyzed samples: Samples when rag- weed pollen was detected (black bars); samples when no rag- weed pollen was detected (dotted bars); and samples that could not be completely analyzed as part of the sample was either missing or too degraded (“miss”; striped bars). No samples were analyzed from year 1998, as we could not identify any possible LDT days using the criteria described in the methods section Fig. 3 Total amount of LDT ragweed pollen in Turku per year (grey bars) and the highest daily pollen concentration per year (black bars) (pollen/m3) 448 Aerobiologia (2025) 41:441–460 Vol:. (1234567890) 3.2 Case study: seed germination In August 2021 we observed five ragweed plants growing at a roadside wasteland nearby Turku, and monitored them from August to November 2021. On 28 August the first male flowers were observed to be open and pollinating. On 19 September several female flowers were open, but the exact date of the first female flowers opening is unknown. On 6 November, seeds were observed on three of the five plants. On 6 November, 52 seeds were collected, on 12 November the plants were visited again, and 18 more seeds were collected. In total 70 seeds were obtained. Only the seeds that seemed ripe or nearly ripe were collected. Most seeds on the plants were green, or soft and hollow. Green seeds were consid- ered unripe and the soft seeds dead, and were not collected. The observed plant individuals differed consider- ably in size and in the way they reacted to air tem- peratures as the autumn progressed. On 6 Novem- ber, two of the largest individuals had already wilted and did not produce any seeds. Two other plants were mostly green and had produced some seeds, but were beginning to show early signs of wilting. One plant, the one producing most seeds, seemed to be thriving. On 12 November, three of the five plants were dead, and the two remaining ones were wilting. From 13 November onwards the air temperatures remained mostly below freezing, there were no more seeds to collect, and the monitoring was discontinued. After the monitoring and seed collection, the growth experiment was started. The duration of the wet-stratification treatment was 12 weeks, after which the seeds were transferred to the climatic chamber. Some seeds germinated within two days of the trans- fer, and more continued to germinate during the next weeks. The experiment was terminated when no new seedlings had appeared during the previous two weeks. At that time, the seeds had been in the cli- matic chamber for approximately 6 weeks. It should be noted that a single seed provided an anomaly to this setup: This seed germinated already during wet- stratification treatment, after the treatment had con- tinued for only 7  weeks. It was transferred to the climatic chamber already at that time, meaning that it spent in the chamber ca. 5  weeks longer than the other seeds. Of the 52 seeds collected on 6 November, 7 seeds germinated (~ 13%). Of the 18 seeds collected on 12 November, 10 seeds germinated (~ 56%) (Fig. 5). The anomalous seed that germinated during the wet-strat- ification was from the set collected on 6 November. Table 1 The distribution of days with different daily ragweed pollen concentrations (pollen/m3) during the study period Year 0.1-4.9 5-9.9 10-19.9 20-50 > 50 1990 0 0 0 0 0 1991 1 0 0 0 0 1992 0 0 0 0 0 1993 0 0 0 0 0 1994 0 0 0 0 0 1995 1 0 0 0 0 1996 2 0 0 0 0 1997 5 0 1 0 0 1998 - - - - - 1999 3 1 0 0 0 2000 5 0 0 0 0 2001 10 0 3 0 0 2002 10 1 1 0 0 2003 0 0 0 0 0 2004 0 0 0 0 0 2005 8 0 1 1 0 2006 6 0 0 0 0 2007 9 1 2 0 0 2008 3 1 0 0 0 2009 3 0 0 0 0 2010 2 0 0 0 0 2011 2 1 0 0 0 2012 2 0 0 0 0 2013 4 0 0 0 0 2014 7 0 0 0 0 2015 8 0 0 0 0 2016 1 0 0 0 0 2017 7 0 0 0 0 2018 12 1 2 0 0 2019 8 1 0 1 0 2020 20 1 0 1 1 2021 8 0 0 1 0 2022 8 0 0 0 0 Concentration pollen/m3 Bolding indicates the first year when the daily concentration fell within each range. No samples were analyzed from year 1998, as we could not identify any possible LDT days using the criteria described in the methods section 449Aerobiologia (2025) 41:441–460 Vol.: (0123456789) 4 Discussion 4.1 Long-distance pollen transport We studied the incidence of LDT ragweed pollen in Finland during 1990–2022 by reanalyzing old sam- ples collected in Turku, Finland, with Hirst-Burkard pollen traps. Our results show that ragweed pollen has been transported to Finland earlier than previ- ously thought and that the most intense LDT epi- sodes have occurred toward the end of the study era (seen as the number of LDT days and the amount of transported pollen per year). The earliest ragweed pollen grain transported to Finland that we found was in a sample from 1991. This pushes the occurrence of ragweed pollen in Finland back at least 14  years from what was pre- viously known. Prior to our study, the first identi- fied ragweed pollen grains were observed in Finland as part of routine monitoring (Mäkinen, 1981) in 2005, when LDT pollen reached Kuopio and Vaasa 0 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14 1 9 9 0 1 9 9 1 1 9 9 2 1 9 9 3 1 9 9 4 1 9 9 5 1 9 9 6 1 9 9 7 1 9 9 8 1 9 9 9 2 0 0 0 2 0 0 1 2 0 0 2 2 0 0 3 2 0 0 4 2 0 0 5 2 0 0 6 2 0 0 7 2 0 0 8 2 0 0 9 2 0 1 0 2 0 1 1 2 0 1 2 2 0 1 3 2 0 1 4 2 0 1 5 2 0 1 6 2 0 1 7 2 0 1 8 2 0 1 9 2 0 2 0 2 0 2 1 2 0 2 2 L en g h t o f L D T e p is o d es ( d ay s) N u m b er o f L D T e p is o d es p er y ea r Fig. 4 Number of LDT episodes in (grey bars) in Turku, the average length of LDT episodes (large black dots) and the range between the shortest and longest episode of the year (small black dots) Fig. 5 Number of non- germinated (black bars) and germinated (grey bars) ragweed seeds by collec- tion date. ~ 13% of the seeds collected on 6 November germinated, and ~ 56% of the seeds collected on 12 November germinated 450 Aerobiologia (2025) 41:441–460 Vol:. (1234567890) in central Finland, and Oulu and Kevo (Utsjoki) in northern Finland (Saarinen & Jantunen, 2017). When re-examining the routine monitoring data (i.e., tables of identified pollen but not the physical samples) for 2005, we confirmed that ragweed pol- len was indeed recorded in Kuopio (25–27 August), Vaasa (25–26 August), Oulu (25–27 August), and Kevo (24–27 August), but not at the monitor- ing stations in southern Finland (Turku, Helsinki and Joutseno). In Helsinki, however, non-specified Asteraceae pollen was recorded 25–26 August, with concentrations 5 pollen/m3 and 23 pollen/m3, respectively. It is rare for Asteraceae pollen, other than Artemisia, to reach such a high level as 23 pol- len/m3 in Finland at any time of the year, let alone so late in the summer, and we believe that this has most likely been ragweed pollen. Unfortunately, the physical samples do not exist anymore, so this can- not be ascertained. In the present study, we found that ragweed pollen also reached Turku 25–27 August, with daily concentrations 24 pollen/m3, 19 pollen/m3 and < 1 pollen/m3. The measurements in Turku highlight the fact that small pollen amounts easily go undetected with routine pollen monitoring methodology (Mäkinen, 1981). Our results show that, prior to the 2005 episode described above, pollen amounts above or around 10 ragweed pollen/m3 daily average reached Turku already 5 September 2002 (19 pollen/m3), 21 Sep- tember 2001 (19.1 pollen/m3), 6 September 1999 (9.5 pollen/m3) and 28 August 1997 (12.2 pollen/ m3; the first episode in Finland with pollen concen- tration > 10 pollen/m3). The same LDT episodes were observed also in Sweden, where ragweed pollen was recorded in Stockholm 5 September 2002 (72 pollen/m3), 21 September 2001 (20 pollen/m3) and 6 September 1999 (62 pollen/m3). 28 August 1997, no ragweed pollen was recorded in Sweden, but indetermined pollen was observed in Stockholm (11 pollen/m3), and Asteraceae pollen in Eskilstuna (41 pollen/m3) and Uppsala (22 pollen/m3). It is very likely that these pollen grains recorded as Asteraceae or as indetermined were actually ragweed. The first epi- sode in Finland lasting more than one day occurred 28–29 August 1996 (1.4 pollen/m3), and 28 August 10 pollen/m3 of Asteraceae pollen was recorded in Stockholm, which may also have been ragweed. The above described LDT episodes in 1997 and 1996 were also recorded in Tartu and Kuressaare in Estonia (Saar et al., 2000). All in all, more LDT days were discovered in the present study where the entire collection area of the microscopic slide was analyzed, than with routine monitoring utilizing 48 random fields (Fig. 6). There was a lot of interannual variation in the amount of LDT pollen. The amounts were relatively high in 2018–2021, and 2020 was a record year in many ways. During 2022, the last year of the dataset, the pollen amounts were again lower. Based on later routine monitoring data, ragweed pollen was scarce also during 2023, but a new record was made again in 2024, when the total amount of LDT pollen reached 231 pollen/m3 (highest daily concentration 69 pollen/ m3; analyzed according to Mäkinen, 1981). As the sampler was located on two different roofs during the study period, it is possible that the differ- ent sampling heights may have had an effect on how much ragweed pollen was sampled. The amounts measured during 2012–2016, when the sampler was located lower, were quite small (highest daily count 4 pollen/m3, 20 September 2014). However, these amounts did not differ markedly from the amounts measured on the other roof, as the daily counts were mostly below 5 pollen/m3 throughout the entire study period. It was not possible to analyze all the days in August–October 1990–2022. Also, the clues we used for identifying potential LDT days for the analysis were more scattered the further back in time we go during the study period, and fewer days were ana- lyzed from the 1990’s than from the 2010’s. Some of the older microscopic slides were partly degraded and analyzing them was difficult. Thus, it is possi- ble that some minor LDT episodes were left out, and finding less transported pollen during the 1990’s may partly be a result of a collection bias. However, we are confident that the majority of the LDT days were discovered. One must also consider whether it is meaningful to treat days with pollen concentrations of 1 pollen/ m3 or below as LDT days. As ragweed can grow and some individuals also pollinate in Finland, it is possi- ble that some of the ragweed pollen on the tapes may be from local sources. However, local plants are rare, and the days with pollen concentrations at or below 1 pollen/m3 are the most numerous within the dataset, 451Aerobiologia (2025) 41:441–460 Vol.: (0123456789) so we believe that most of the detected ragweed pol- len is transported to the country from elsewhere. No correlations or causal relationships between the occurrence of LDT pollen and environmental factors were examined in this study. However, our observa- tions on the amounts of transported pollen fit the pic- ture of what is known of ragweed spread and changes in its pollen production and pollen transports under the changing climate, other anthropogenic factors, and the naturalization process (Cheng et  al., 2023; Gentili et  al., 2019; Hamaoui-Laguel et  al., 2015; Lake et al., 2016; Leiblein-Wild & Tackenberg, 2014; Montagnani et  al., 2023; Rauer et  al., 2020; Stinson et al., 2017; Wayne et al., 2002; Ziska & Beggs, 2012 and references therein). As the distribution area is expected to shift northwards in the future, new pol- len sources closer to Finland may increase both the amount of LDT pollen and the number and frequency of LDT episodes reaching the country. More ragweed growing in the source areas and the increases in pol- len production may also lead to more pollen to be transported. Back trajectory analyses would provide important information on the source areas from where ragweed pollen is transported to Finland, and they are a crucial next step in further studies on this subject. It would be highly useful to track possible changes in the source areas over the years. Knowledge on possible changes in ragweed populations or its pollen production in the source areas, and on the factors driving these changes (e.g., changes in land use, or in the weather patterns under climate change) might help to predict future trends in ragweed pollen transports to Finland. There are no studies estimating how many people in the general population of Finland are sensitized to ragweed pollen. According to Burbach et al. (2009), 2.4% of the routine out-patients at Helsinki Univer- sity Hospital with allergic symptoms were sensitized to ragweed. However, people sensitized to mugworts (Artemisia vulgaris, A. campestris and other Arte- misia species) pollen may be especially susceptible to show symptoms when exposed to ragweed pollen (Asero et al., 2006, 2014; Cecchi et al., 2010; Grewl- ing et  al., 2018; Ruëff et  al., 2012). It is still unre- solved how much of this is due to cross-reactivity and how much is caused by co-sensitization, at least from the viewpoint of clinical practice (Asero et al., 2014; Canis et  al., 2012). Common mugwort, or simply Fig. 6 Number of observed LDT days when using the random fields method of the routine monitoring system (light grey bars), and when analyzing the entire collection area of the microscopic slides (dark grey bars) 452 Aerobiologia (2025) 41:441–460 Vol:. (1234567890) mugwort (A. vulgaris), is a late-flowering plant native to Finland and its pollen is considered one of the major outdoor allergens in the country. According to Heinzerling et al. (2009), mugwort sensitization rate in Finland is 17.6% within the atopic population. In North Karelia, 16.9% of randomly selected school- children showed positive sIgE-results to mugwort allergens and 7.3% reacted to skin prick tests (Pekka- rinen et al., 2007). The mothers of the same children showed slighty different numbers: 6.1% gave positive sIgE test results and 9.0% reacted to skin prick tests. According to Jantunen and Saarinen (2008) there are approximately 100 000 people sensitized to mugwort in Finland (~ 1.9% of the population). These numbers are estimates, but based on them tens of thousands of people in Finland may react to transported ragweed pollen. According to our study, ragweed pollen is trans- ported to Finland in late summer and early autumn, the majority of it in late August and early September. Usually, as observed with the routine pollen moni- toring, the peak of mugwort flowering is reached at the end of July or the first half of August. This means that ragweed pollen reaches Finland at the end of the mugwort season, or well after mugwort flowering is already over, thus lengthening the overall pollen sea- son in Finland. However, the ragweed pollen concen- trations measured in Finland are small in comparison to concentrations elsewhere in Europe. The daily mean values are usually < 5 pollen/m3, only occasion- ally exceeding 20 pollen/m3, and as yet have never exceeded 100 pollen/m3. In the more heavily infested areas in Europe the daily mean concentrations can reach several hundreds of pollen grains per cubic meter of air (e.g., Makra et al., 2016; Stepalska et al., 2020; Melnychenko et al., 2021). Autumnal allergic symptoms in Finland are usu- ally attributed to airborne fungal spores, such as Cladosporium spp. and Alternaria spp., as the spore concentrations of these genera in the air are at their highest in the late summer and in the early autumn (e.g., Koivikko et  al., 1972, 1976; Rantio-Lehtimäki et  al., 1985). It would be interesting to study the interaction between the occurrence of fungal spores and ragweed pollen in the air, as ragweed pollen is typically transported to Finland during the same time period when fungal spores are abundant. At least dur- ing the days when ragweed pollen concentrations in the air exceed 5 pollen/m3 it may also cause allergic symptoms on some individuals. LDT ragweed pollen can also be accompanied by fungal spores as well as anthropogenic air pollutants (Grewling et  al., 2019), and the co-occurrence of allergenic pollen and fungal spores in the air may increase the severity of allergic symptoms and complicate their interpretation (Mysz- kowska et al., 2023). 4.2 Seed germination in Finland Our observations and growth experiment showed that, in favorable conditions, ragweed is able to pro- duce viable seeds in Finland. The development of ragweed plants and the timing of their flowering is an interplay of photoperiod, tem- perature and the accumulation of heat sum (Bullock et  al., 2012; Cunze et  al., 2013; Deen et  al., 1998b; Essl et  al., 2015). Ragweed flowering is said to be induced when the duration of daylight has shortened to ~ 14  h (Deen et  al., 1998a; Bullock et  al., 2012), though other studies indicate that earlier flowering is possible (Essl et al., 2015; Leiblein-Wild & Tack- enberg, 2014; Magyar et  al., 2022). Milakovic et  al. (2014) assume the time between flowering and seed ripening to be 4–6 weeks, and the same numbers are reported by Essl et  al. (2015). According to Beres (1994) the time for seed maturation is longer, 64 days on average (~ 9  weeks), and Scalone et  al. (2016) report an even longer time of 10–12 weeks. Knolma- jer et al. (2024) write that ragweed needs 40–60 days (~ 6–9 weeks) after fertilization to produce fully ripe seeds, but the source they give (Makra et  al., 2015) does not mention the time needed for seed ripening. Thus, the origin of the statement in Knolmajer et al. remains unknown, but the numbers do fall between the other estimates given in other studies. In southern parts of Europe, the flowering usually starts in late July or early August (Essl et al., 2015), and the seeds ripen sometime in September. In Finland, lower tem- peratures slow down the development of the plants, and the flowering usually starts in the beginning of September (personal observations). The seeds would then be predicted to ripen between mid-October and mid-November. In our case study, the first female flowers were observed 19 September, and seeds were collected on 6 and 12 November, giving them roughly 7–8 weeks to ripen on the plants. It is believed that the first autumn frosts end the period for the development of viable ragweed seeds 453Aerobiologia (2025) 41:441–460 Vol.: (0123456789) (e.g., Essl et  al., 2015; Solomon, 1984), but in our case study some of the seeds were collected after sev- eral night frosts, and they actually germinated better than the seeds that were collected before the cold- est temperatures. This observation suggests that the first frosts may not immediately terminate the devel- opment of viable seeds, giving the plants a longer- than-previously-thought window to reproduce in the northern parts of their distribution area. Also, the frost tolerance of ragweed plants may be slightly bet- ter than often reported. Several researches state that the first frosts kill ragweed (Deen et al., 1998b; Essl et al., 2015; Ziska et al., 2011), but Dahl et al. (1999) reported that plants die in temperatures below – 5 °C. Our observations in the field confirm that some rag- weed individuals can tolerate  at least approximately – 4 °C before they die. In southern Finland, it is pos- sible that the autumn temperatures keep mostly above freezing well into November, giving the seeds more time to mature. During our study, some nighttime frosts occurred in September, October and November, measured in Turku airport, ~ 6.5  km from the location where the ragweed plants of this study were found (Fig.  7). The coldest temperatures before collecting seeds were – 3.9  °C (19 October) and – 3.3  °C (24 Octo- ber). These temperatures were measured 2  m above ground; at ground level where the plants grow the temperatures are usually 1–2 °C lower. At least three of the plants seemed to survive these frosts. During the first days of November, the temperatures remained several degrees above 0 °C. After collecting the first set of seeds on 6 November, the nighttime tempera- tures fell below 0 °C for three nights in a row, ranging from – 2.0 to – 8.6 °C. The latest, on 9 November, was the coldest night during the study period, and killed all the remaining plants. The second set of seeds was collected three days after this. There was a marked difference between the germi- nation rates of the seeds collected on different days, with the germination rate of the seeds collected later being higher than that of the seeds collected earlier. Considering the possible reasons for this result, there were three obvious differences between the different sets of seeds. First, the later set of seeds were attached to the plants approximately one week longer than the earlier set; second, during that extra week in the field the later seeds were exposed to more frosts than the Fig. 7 Miniand maximum daily temperatures during 1.8.– 15.11.2021, measured in Turku airport, ~ 6.5 km from the loca- tion where the ragweed plants of this study were found. These measurements were made 2 m above ground; at ground level the temperatures are typically 1–2 °C lower (Finnish Meteoro- logical Institute, weather observations, CC BY 4.0.) 454 Aerobiologia (2025) 41:441–460 Vol:. (1234567890) earlier; and third, between harvesting and the wet stratification, the later set of seeds was stored one week less than the earlier set. It is possible for ragweed seeds to continue ripen- ing on cut branches after harvesting (Karrer & Pixner, 2012). But as most of the seeds in our study seemed already ripe at the time of collection, as they were detached from the branches completely, and as the set of seeds that was collected later germinated better than the earlier set, we believe the possibility of post- harvest ripening does not affect our results in any meaningful way. If frost terminated the development of viable seeds, the opposite result in the germination rates would have been expected – the germination rate of the later set of seeds would have been lower – but this was not the case. It also seems unlikely that the difference in storage time would have had such an influence in the germination rates. Then the possible explanation that remains is that the set of seeds that were collected later may have germinated better than the earlier set of seeds because they had had more time to mature on the plants in the field. However, as the number of plants and seeds in our case study was low, no definite conclusions can be drawn from the seed germination experiment. Especially the number of seeds collected later was so small, that the relative abundances of the germinated and non-germinated seeds within that set may have been the result of chance. Hall et al. (2021) also show that the results of seed viability tests are affected not only by the properties of the seeds, but also by the testing methods and laboratories. However, our results are interesting, and indicate that further sys- tematic studies with more plant individuals and a larger number of seeds would be useful in examining how much frost the plants tolerate at the end of the growing season, how frost affects ragweed seed mat- uration and germination, and how much variation is there between individuals considering these aspects. It has been shown that there is phenological vari- ation between plants from different populations, both in North America and Europe: plants from more northerly populations tend to flower earlier than plants from southerly areas, and may be pre-adapted to the thermal conditions and light-environment in the higher latitudes, which gives the seeds more time to mature in the autumn, and may facilitate the spread of ragweed to Fennoscandia (Basset & Crompton, 1975; Solomon, 1984; Scalone et  al., 2016; Krale- mann et  al., 2018; McGoey et  al., 2020). Bullock et al. (2012) report that the minimum necessary mean July temperature for ragweed to naturalize in an area is 15–20  °C. During the normal period 1991–2020 defined by Finnish Meteorological Institute (FMI) the mean July temperature in Turku was 17.6 °C. In 2021, the average temperature in July was 20.3  °C. Also, June and October 2021 were warmer than average, although August and September were cooler (Table 2). The warm temperatures in June and July 2021 may have enhanced the vegetative growth of the ragweed plants that were observed in the pre- sent study, and the warm temperature in October may have given the seeds more time to mature. Our study shows that one reproductive barrier preventing ragweed from naturalizing in Finland can be overcome, at least during years with especially favorable temperatures. Due to the warming caused by climate change, conditions favoring the reproduc- tion of ragweed in Finland are becoming more com- mon. McGoey and Stinchcombe (2021) also show that ragweed will be able to respond quickly to selec- tion pressures in changing environments. Thus, it is important to monitor ragweed plants and their pos- sible seed production in Finland so that measures to prevent the species from forming established popula- tions in Finland can be undertaken as soon as possi- ble, if needed. 5 Conclusions In our study we find that ragweed pollen has occurred in Finland since early 1990’s, much earlier than previ- ously thought, and that the LDT episodes have been Table 2 Average temperatures in Turku during the normal period 1991–2020 and in 2021 (Finnish Meteorological Institute, weather observations, CC BY 4.0.) Average temperature °C in Turku Year Jun Jul Aug Sep Oct Nov 1991–2020 5.8 14.7 17.8 16.6 11.8 6.2 2.1 2021 6.8 18.4 20.3 15.2 9.7 8.1 1.4 455Aerobiologia (2025) 41:441–460 Vol.: (0123456789) more intense in the recent years. Our germination experiment shows that ragweed plants are able to pro- duce viable seeds during the warmest autumns in Fin- land, and that freezing temperature during the matu- ration of seeds may not be an immediate killing factor neither for the plants nor their seeds. With climate change the significance of ragweed as an aeroallergen in Finland may be increasing. It is also possible that ragweed may eventually naturalize as part of the Finnish flora as the plants are able to produce viable seeds during warm autumns. Further studies are needed, and it is important to continue monitoring ragweed pollen transports and possible seed production in Finland. Acknowledgements The authors wish to thank the Research Council of Finland for funding this research as part of the All- Impress project; TOP-Säätiö for funding the PhD research of M. Louna-Korteniemi; Estonian Environmental Research Centre for access to the Estonian pollen data; J. Korteniemi for the map of locations of pollen measurements and for thor- ough proofreading of the manuscript; A.-M. Pessi for her insights and comments; K. Saikkonen for good discussions; and M. Mäkelä for his valuable comments around the subject of mugwort. Author contributions M.L.-K. Conceptualization, meth- odology, data analysis, writing – original draft and the main manuscript, review and editing, funding acquisition. S.P. Con- ceptualization, methodology, material preparation, data collec- tion, writing – review and editing. P.A., M.K., L.T. and M.V. Material preparation and data collection. A.E. Data collection, writing – review and editing. A.S. Conceptualization, method- ology, writing – review and editing, funding acquisition, super- vision. All authors read and approved the final manuscript. Funding Open Access funding provided by University of Turku (including Turku University Central Hospital). This work was supported by the Research Council of Finland (329217) and TOP-säätiö (20200637). Data availability Pollen data used in this study is avail- able on request by contacting Pollen forecasting, University of Turku. Declarations Competing interests The authors declare no competing inter- ests. Open Access This article is licensed under a Creative Com- mons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Crea- tive Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. References Allard, H. A. (1943). The North American ragweeds and their occurrence in other parts of the world. Science, 98(2544), 292–294. Allard, H. A. (1945). Flowering behavior and natural distri- bution of the eastern ragweeds (Ambrosia) as affected by length of day. Ecology, 26(4), 387–394. https:// doi. org/ 10. 2307/ 19316 60 Arbes, S. J., Jr., Gergen, P. J., Elliot, L., & Zeldin, D. C. (2005). Prevalences of positive skin test responses to 10 common allergens in the US population: Results from the third National Health and Nutrition Examina- tion Survey. Journal of Allergy and Clinical Immunol- ogy, 116, 337–383. Asero, R., Bellotto, E., Ghiani, A., Aina, R., Villalta, D., & Cit- terio, S. (2014). Concomitant sensitization to ragweed and mugwort pollen: Who is who in clinical allergy? Annals of Allergy, Asthma & Immunology, 113, 307–313. https:// doi. org/ 10. 1016/j. anai. 2014. 06. 009 Asero, R., Wopfner, N., Gruber, P., Gadermaier, G., & Ferreira, F. (2006). Artemisia and Ambrosia hypersensitivity: Co- sensitization or co-recognition? Clinical and Experimen- tal Allergy, 36, 658–665. https:// doi. org/ 10. 1111/j. 1365- 2222. 2006. 02477.x Baskin, J. M., & Baskin, C. C. (1977). Role of Temperature in the Germination Ecology of Three Summer Annual Weeds. Oecologia, 30, 377–382. https:// doi. org/ 10. 1007/ BF003 99768 Baskin, J. M., & Baskin, C. C. (1980). Ecophysiology of sec- ondary dormancy in seeds of Ambrosia artemisiifolia. Ecology, 61(3), 475–480. https:// doi. org/ 10. 2307/ 19374 10 Bassett, I. J., & Crompton, C. W. (1975). The biology of Cana- dian weeds.11. Ambrosia artemisiifolia L. and A. psilos- tachya DC. Canadian Journal of Plant Science, 55, 463– 476. https:// doi. org/ 10. 4141/ cjps75- 072 Battlay, P., Wilson, J., Bieker, V. C., Lee, C., Prapas, D., Petersen, B., Craig, S., van Boheemen, L., Scalone, R., de Silva, N. P., Sharma, A., Konstantinović, B., Nurkowski, K. A., Rieseberg, L. H., Connallon, T., Mar- tin, M. D., & Hodgins, K. A. (2023). Large haploblocks underlie rapid adaptation in the invasive weed Ambrosia artemisiifolia. Nature Communications, 14, 1717. https:// doi. org/ 10. 1038/ s41467- 023- 37303-4 Bazzaz, F. A. (1970). Secondary dormancy in the seeds of the common ragweed Ambrosia artemisiifolia. Bulletin of the Torrey Botanical Club, 97(5), 302–305. https:// doi. org/ 10. 2307/ 24836 50 456 Aerobiologia (2025) 41:441–460 Vol:. (1234567890) Belmonte, J., Vendrell, M., Roure, J. M., Vidal, J., Botey, J., & Cadahia, A. (2000). Levels of Ambrosia pollen in the atmospheric spectra of Catalan aerobiological stations. Aerobiologia, 16, 93–99. https:// doi. org/ 10. 1023/A: 10076 49427 549 Beres, I. (1994). New investigations on the biology of Ambro- sia artemisiifolia L. Mededelingen Faculteit Landbou- wkundige En Toegepaste Biologische Wetenschappen, Universiteit Gent, 59(3b), 1295–1297. Bilińska, D., Skjøth, C. A., Werner, M., Kryza, M., Malk- iewicz, M., Krynicka, J., & Drzeniecka-Osiadacz, A. (2017). Source regions of ragweed pollen arriving in south-western Poland and the influence of meteorologi- cal data on the HYSPLIT model results. Aerobiologia, 33, 315–326. https:// doi. org/ 10. 1007/ s10453- 017- 9471-9 Bousquet, P.-J., Chinn, S., Janson, C., Kogevinas, M., Burney, P., & Jarvis, D. (2007). Geographical variation in the prevalence of positive skin tests to environmental aeroal- lergens in the European Community Respiratory Health Survey I. Allergy, 62, 301–309. https:// doi. org/ 10. 1111/j. 1398- 9995. 2006. 01293.x Bullock, J.M., Chapman, D., Schafer, S., Roy, D., Girardello, M., Haynes, T., Beal, S., Wheeler, B., Dickie, I., Phang, Z., Tinch, R., Čivić, K., Delbaere, B., Jones‐Walters, L., Hilbert, A., Schrauwen, A., Prank, M., Sofiev, M., Nie- melä, S., et  al. (2012). Assessing and controlling the spread and the effects of common ragweed in Europe. Final report: ENV.B2/ETU/2010/0037: Natural Environ- ment Research Council, UK. 456 pp. Burbach, G. J., Heinzerling, L. M., Röhnelt, C., Bergmann, K.-C., Behrendt, H., & Zuberbier, T. (2009). Ragweed sensitization in Europe – GA2LEN study suggests increasing prevalence. Allergy, 64, 664–665. https:// doi. org/ 10. 1111/j. 1398- 9995. 2009. 01975.x Buters, J. T. M., Alberternst, B., Nawrath, S., Wimmer, M., Traidl-Hoffmann, C., Starfinger, U., Behrendt, H., Schmidt-Weber, C., & Bergmann, K. C. (2015). Ambro- sia artemisiifolia (ragweed) in Germany. Current pres- ence, allergologic relevance and containment procedure. Allergo Journal International, 24, 108–120. https:// doi. org/ 10. 1007/ s40629- 015- 0060-6 Canis, M., Becker, S., Gröger, M., & Kramer, M. F. (2012). IgE reactivity patterns in patients with allergic rhinoconjunc- tivitis to ragweed and mugwort pollens. American Jour- nal of Rhinology & Allergy, 26, 31–35. https:// doi. org/ 10. 2500/ ajra. 2012. 26. 3698 Cecchi, L., Testi, S., Campi, P., & Orlandini, S. (2010). Long- distance transport of ragweed pollen does not induce new sensitizations in the short term. Aerobiologia, 26, 351– 352. https:// doi. org/ 10. 1007/ s10453- 010- 9164-0 Cecchi, L., Torrigiani Malaspina, T., Albertini, R., Zanca, M., Ridolo, E., Usberti, I., Morabito, M., Dall’ Aglio, P., & Orlandini, S. (2007). The contribution of long-distance transport to the presence of Ambrosia pollen in central northern Italy. Aerobiologia, 23, 145–151. https:// doi. org/ 10. 1007/ s10453- 007- 9060-4 Chapman, D. S., Makra, L., Albertini, R., Bonini, M., Páldy, A., Rodinkova, V., Šikoparija, B., Weryszko- Chmielewska, E., & Bullock, J. M. (2016). Modelling the introduction and spread of non-native species: Interna- tional trade and climate change drive ragweed invasion. Global Change Biology, 22, 3067–3079. https:// doi. org/ 10. 1111/ gcb. 13220 Chauvel, B., Dessaint, F., Cardinal-Legrand, C., & Bretagnolle, F. (2006). The historical spread of Ambrosia artemisiifo- lia L. in France from herbarium records. Journal of Bio- geography, 33, 665–673. https:// doi. org/ 10. 1111/j. 1365- 2699. 2005. 01401.x Cheng, X., Frank, U., Zhao, F., Ruiz Capella, J., Winkler, B., Schnitzler, J.-P., Ghirardo, A., Bertić, M., Estrella, N., Durner, J., & Pritsch, K. (2023). Plant growth traits and allergenic potential of Ambrosia artemisiifolia pollen as modified by temperature and NO2. Environmental and Experimental Botany, 206, Article 105193. https:// doi. org/ 10. 1016/j. envex pbot. 2022. 105193 Cherrez-Ojeda, I., Robles-Velasco, K., Ramon, G. D., et  al. (2024). Ragweed in South America: The relevance of aerobiology stations in Latin America. Aerobiologia, 40, 343–351. https:// doi. org/ 10. 1007/ s10453- 024- 09825-x Comtois, P., & Gagnon, L. (1988). Concentration pollinique et fréquence des symptôms de pollinose: Une méthode pour determiner des seuils cliniques. Revue Française D’allergologie Et D’immunologie Clinique, 28(4), 279– 286. https:// doi. org/ 10. 1016/ S0335- 7457(88) 80046-7 Cunze, S., Leiblein, M. C., & Tackenberg, O. (2013). Range expansion of Ambrosia artemisiifolia in Europe is pro- moted by climate change. ISRN Ecology, 2013, 1–9. https:// doi. org/ 10. 1155/ 2013/ 610126 Dahl, Å., Stranhede, S.-O., & Wihl, J. -Å. (1999). Ragweed— An allergy risk in Sweden? Aerobiologia, 15, 293–297. https:// doi. org/ 10. 1023/A: 10076 78107 552 de Weger, L. A., Pashley, C. H., Šikoparija, B., Skjøth, C. A., Kasprzyk, I., Grewling, L., Thibaudon, M., Magyar, D., & Smith, M. (2016). The long distance transport of air- borne Ambrosia pollen to the UK and the Netherlands from Central and south Europe. International Journal of Biometeorology, 60, 1829–1839. https:// doi. org/ 10. 1007/ s00484- 016- 1170-7 Deen, W., Hunt, T., & Swanton, C. J. (1998a). Influence of temperature, photoperiod, and irradiance on the pheno- logical development of common ragweed (Ambrosia artemisiifolia). Weed Science, 46, 555–560. https:// doi. org/ 10. 1017/ S0043 17450 00910 98 Deen, W., Hunt, T., & Swanton, C. J. (1998b). Photothermal time describes common ragweed (Ambrosia artemisii- folia L.) phenological development and growth. Weed Science, 46(5), 561–568. https:// doi. org/ 10. 1017/ S0043 17450 00911 04 Elvisto, T., Pensa, M., & Paluoja, E. (2016). Indigenous and alien vascular plant species in a northern European urban setting (Tallinn, Estonia). Proceedings of the Estonian Academy of Sciences, 65(4), 431–441. https:// doi. org/ 10. 3176/ proc. 2016.4. 09 Essl, F., Biro, K., Brandes, D., Broennimann, O., Bullock, J. M., Chapman, D. S., Chauvel, B., Dullinger, S., Fuma- nal, B., Guisan, A., Karrer, G., Kazinczi, G., Kueffer, C., Laitung, B., Lavoie, C., Leitner, M., Mang, T., Moser, D., Müller-Schärer, H., … Follak, S. (2015). Biological Flora of the British Isles: Ambrosia artemisiifolia. Jour- nal of Ecology, 103, 1069–1098. https:// doi. org/ 10. 1111/ 1365- 2745. 12424 457Aerobiologia (2025) 41:441–460 Vol.: (0123456789) Fogliatto, S., Milan, M., De Palo, F., & Vidotto, F. (2019). The effect of various after-ripening temperature regimens on the germination behaviour of Ambrosia artemisiifolia. Plant Biosystems, 154(2), 165–172. https:// doi. org/ 10. 1080/ 11263 504. 2019. 15782 82 Fumanal, B., Chauvel, B., & Bretagnolle, F. (2007). Estimation of pollen and seed production of common ragweed in France. Annals of Agricultural and Environmental Medi- cine, 14, 233–236. Gallien, L., Thuiller, W., Fort, N., Boleda, M., Alberto, F. J., Rioux, D., et  al. (2016). Is there any evidence for rapid, genetically-based, climatic niche expansion in the invasive common ragweed? PLoS  One, 11(4), Article e0152867. https:// doi. org/ 10. 1371/ journ al. pone. 01528 67 Gentili, R., Ambrosini, R., Augustinus, B. A., Caronni, S., Cardarelli, E., Montagnani, C., Müller-Schärer, H., Schaffner, U., & Citterio, S. (2021). High phenotypic plasticity in a prominent plant invader along altitudinal and temperature gradients. Plants, 10, 2144. https:// doi. org/ 10. 3390/ plant s1010 2144 Gentili, R., Asero, R., Caronni, S., Guarino, M., Montagnani, C., Mistrello, G., & Citterio, S. (2019). Ambrosia arte- misiifolia L. temperature responsive traits influencing the prevalence and severity of pollinosis: a study in con- trolled conditions. BMC Plant Biology, 19, 155. https:// doi. org/ 10. 1186/ s12870- 019- 1762-6 Grewling, L., Bogawski, P., Kryza, M., Magyar, D., Šikoparija, B., Skjøth, C. A., Udvardy, O., Werner, M., & Smith, M. (2019). Concomitant occurrence of anthropogenic air pollutants, mineral dust and fungal spores during long- distance transport of ragweed pollen. Environmental Pollution, 254, Article 112948. https:// doi. org/ 10. 1016/j. envpol. 2019. 07. 116 Grewling, L., Jenerowicz, D., Bogawski, P., Smith, M., Nowak, M., Frątczak, A., & Czarnecka-Operacz, M. (2018). Cross-sensitization to Artemisia and Ambrosia pollen allergens in an area located outside of the current distri- bution range of Ambrosia. Advances in Dermatology and Allergology, 35(1), 83–89. https:// doi. org/ 10. 5114/ ada. 2018. 73167 Hall, R. M., Urban, B., Skálová, H., Moravcová, L., Sölter, U., Starfinger, U., Kazinczi, G., van Valkenburg, J., Fenesi, A., Konstantinovic, B., Uludag, A., Lommen, S., & Karrer, G. (2021). Seed viability of common ragweed (Ambrosia artemisiifolia L.) is affected by seed origin and age, but also by testing method and laboratory. Neo- Biota, 70, 193–221. https:// doi. org/ 10. 3897/ neobi ota. 70. 66915 Hamaoui-Laguel, L., Vautard, R., Liu, L., Solmon, F., Viovy, N., Khvorostyanov, D., Essl, F., Chuine, I., Colette, A., Semenov, M. A., Schaffhauser, A., Storkey, J., Thibau- don, M., & Epstein, M. M. (2015). Effects of climate change and seed dispersal on airborne ragweed pollen loads in Europe. Nature Climate Change, 5, 766–772. https:// doi. org/ 10. 1038/ nclim ate26 52 Heinzerling, L. M., Burbach, G. J., Edenharter, G., Bachert, C., Bindslev-Jensen, C., Bonini, S., Bousquet, J., Bous- quet-Rouanet, L., Bousquet, P. J., Bresciani, M., Bruno, A., Burney, P., Canonica, G. W., Darsow, U., Demoly, P., Durham, S., Fokkens, W. J., Giavi, S., Gjomarkaj, M., et  al. (2009). GA2LEN skin test study I: GA2LEN harmonization of skin prick testing: novel sensitization patterns for inhalant allergens in Europe. Allergy, 64, 1498–1506. https:// doi. org/ 10. 1111/j. 1398- 9995. 2009. 02093.x Hirst, J. M. (1952). An automatic volumetric spore trap. Annals of Applied Biology, 39(2), 257–265. https:// doi. org/ 10. 1111/j. 1744- 7348. 1952. tb009 04.x IPCC (2021). Summary for Policymakers. In: Masson-Del- motte, V., Zhai, P., Pirani, A., Connors, S.L., Péan, C., Berger, S., Caud, N., Chen, Y., Goldfarb, L., Gomis, M.I., Huang, M., Leitzell, K., Lonnoy, E., Matthews, J.B.R., Maycock, T.K., Waterfield, T., Yelekçi, O., Yu, R., & Zhou, B. (eds.) Climate Change 2021: The Physi- cal Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. (2391 pp.) Cambridge Univer- sity Press. https:// doi. org/ 10. 1017/ 97810 09157 896. 001 Jantunen, J., & Saarinen, K. (2008). Pujo taajama-alueiden allergiakasvina. Loppuraportti. Etelä-Karjalan Aller- gia-ja Ympäristöinstituutti. Joutseno. 31 pp. ISBN: 978-952-5156-52–2. Juhász, M. (1995). New results of aeropalynological research in Southern Hungary. Hungarian Academy of Sciences Regional Committee Szeged, 5, 17–30. Karrer, G., & Pixner, T. (2012). The contribution of post- harvest ripened ragweed seeds after cut for control. In: GEIB (eds.), Neobiota (p. 229). 7th European Confer- ence on Biological Invasions. Kasprzyk, I., Myszkowska, D., Grewling, L., Stach, A., Šikoparija, B., Skjøth, C. A., & Smith, M. (2011). The occurrence of Ambrosia pollen in Rzeszów, Kraków and Poznań, Poland: Investigation of trends and possible transport of Ambrosia pollen from Ukraine. International Journal of Biometeorology, 55, 633–644. https:// doi. org/ 10. 1007/ s00484- 010- 0376-3 Knolmajer, B., Jócsák, I., Taller, J., Keszthelyi, S., & Kazinczi, G. (2024). Common Ragweed—Ambrosia artemisiifolia L.: a review with special regards to the latest results in biology and ecology. Agronomy, 14, 497. https:// doi. org/ 10. 3390/ agron omy14 030497 Koivikko, A., Mäkinen, Y., Rantio-Lehtimäki, A., & Kupias, R. (1976). Aerobiologia ja allergia. In (anon.), Allergia- tutkimussäätiön vuosikirja 1976 (1st ed., pp. 14–19). Allergiatutkimussäätiö. Koivikko, A., Käpylä, M., & Mäkinen, Y. (1972). Siitepölyt ja sieni-itiöt allergioiden aiheuttajina. Suomen Lääkärilehti, 27, 1711. Kottek, M., Grieser, J., Beck, C., Rudolf, B., & Rubel, F. (2006). World Map of the Köppen-Geiger climate clas- sification updated. Meteorologische Zeitschrift, 15(3), 259–263. https:// doi. org/ 10. 1127/ 0941- 2948/ 2006/ 0130 Kralemann, L. E. M., Scalone, R., Andersson, L., & Hennig, L. (2018). North European invasion by common ragweed is associated with early flowering and dominant changes in FT/TFL1 expression. Journal of Experimental Botany, 69(10), 2647–2658. https:// doi. org/ 10. 1093/ jxb/ ery100 Kurtto, A. (s.a.). Marunatuoksukki – Ambrosia artemisiifolia. Suomen lajitietokeskus. Retrieved 9 March, 2022, from https:// laji. fi/ taxon/ MX. 39794. 458 Aerobiologia (2025) 41:441–460 Vol:. (1234567890) Kurtto, A., Lampinen, R., Piirainen, M., & Uotila, P. (2019). Checklist of the vascular plants of Finland. Suomen put- kilokasvien luettelo. Norrlinia, 34, 1–206. Lake, I. R., Jones, N. R., Agnew, M., Goodess, C. M., Giorgi, F., Hamaoui-Laguel, L., Semenov, M. A., Solomon, F., Storkey, J., Vautard, R., & Epstein, M. M. (2016). Cli- mate change and future pollen allergy in Europe. Envi- ronmental Health Perspectives, 125(3), 385–391. https:// doi. org/ 10. 1289/ EHP173 Lee, J.-Y., Marotzke, J., Bala, G., Cao, L., Corti, S., Dunne, J.P., Engelbrecht, F., Fischer, E., Fyfe, J.C., Jones, C., Maycock, A., Mutemi, J., Ndiaye, O., Panickal, S., & Zhou, T. (2021). Future Global Climate: Scenario- Based Projections and Near-Term Information. In Mas- son-Delmotte, V., Zhai, P., Pirani, A., Connors, S.L., Péan, C., Berger, S., Caud, N., Chen, Y., Goldfarb, L., Gomis, M.I., Huang, M., Leitzell, K., Lonnoy, E., Mat- thews, J.B.R., Maycock, T.K., Waterfield, T., Yelekçi, O., Yu, R., & Zhou, B. (Eds.), Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Inter- governmental Panel on Climate Change (pp. 553–672). Cambridge University Press. https:// doi. org/ 10. 1017/ 97810 09157 896. 006 Leiblein-Wild, M. C., Kaviani, R., & Tackenberg, O. (2014). Germination and seedling frost tolerance dif- fer between the native and invasive range in common ragweed. Oecologia, 174, 739–750. https:// doi. org/ 10. 1007/ s00442- 013- 2813-6 Leiblein-Wild, M. C., Steinkamp, J., Hickler, T., & Tacken- berg, O. (2016). Modelling the potential distribution, net primary production and phenology of common rag- weed with a physiological model. Journal of Biogeog- raphy, 43, 544–554. https:// doi. org/ 10. 1111/ jbi. 12646 Leiblein-Wild, M. C., & Tackenberg, O. (2014). Phenotypic variation of 38 European Ambrosia artemisiifolia pop- ulations measured in a common garden experiment. Biological Invasions, 16, 2003–2015. https:// doi. org/ 10. 1007/ s10530- 014- 0644-y Lemke, A., Kowarik, I., & von der Lippe, M. (2019). How traffic facilitates population expansion of invasive species along roads: The case of common ragweed in Germany. Journal of Applied Ecology, 56, 413–422. https:// doi. org/ 10. 1111/ 1365- 2664. 13287 Magyar, D., Novák, R., Udvardy, O., Páldy, A., Szigeti, T., Stjepanović, B., Hrga, I., Večenaj, A., Vucić, A., Peroš Pucar, D., Šikoparija, B., Radišić, P., Škorić, T., Ščevková, J., Simon-Csete, E., Nagy, M., & Leelőssy, Á. (2022). Unusual early peaks of airborne ragweed (Ambrosia L.) pollen in the Pannonian Bio- geographical Region. International Journal of Biom- eteorology, 66, 2195–2203. https:// doi. org/ 10. 1007/ s00484- 022- 02348-5 Mäkinen, Y. (1981). Random sampling in the study of micro- scopic slides. Reports from the Aerobiology Laboratory, University of Turku, 5, 27–43. Makra, L., Juhász, M., Béczi, R., & Borsos, E. (2005). The his- tory and impacts of airborne Ambrosia (Asteraceae) pol- len in Hungary. Grana, 44(1), 57–64. https:// doi. org/ 10. 1080/ 00173 13051 00105 58 Makra, L., Matyasovszky, I., Hufnagel, L., & Tusnády, G. (2015). The history of ragweed in the world. Applied Ecology and Environmental Research, 13(2), 489–512. https:// doi. org/ 10. 15666/ aeer/ 1302_ 489512 Makra, L., Matyasovszky, I., Tusnády, G., Wang, Y., Csépe, Z., Bozóki, Z., Nyúl, L. G., Erostyák, J., Bodnár, K., Sümeghy, Z., Vogel, H., Pauling, A., Páldy, A., Mag- yar, D., Mányoki, G., Bergmann, K.-C., Bonini, M., Šikoparija, B., Radišíc, et  al. (2016). Biogeographical estimates of allergenic pollen transport over regional scales: Common ragweed and Szeged, Hungary as a test case. Agricultural and Forest Meteorology, 221, 94–110. https:// doi. org/ 10. 1016/j. agrfo rmet. 2016. 02. 006 McGoey, B. V., Hodgins, K. A., & Stinchcombe, J. R. (2020). Parallel flowering time clines in native and introduced ragweed populations are likely due to adaptation. Ecol- ogy and Evolution, 10, 4595–4608. https:// doi. org/ 10. 1002/ ece3. 6163 McGoey, B. V., & Stinchcombe, J. R. (2021). Introduced popu- lations of ragweed show as much evolutionary potential as native populations. Evolutionary Applications, 14, 1436–1449. https:// doi. org/ 10. 1111/ eva. 13211 Melnychenko, H., Hrushka, V., & Ivanova, O. (2021). Dynam- ics of ragweed pollen concentration in the air of Ivano- Frankivsk. Journal of Vasyl Stefanyk Precarpathian National University, 8(4), 45–51. https:// doi. org/ 10. 15330/ jpnu.8. 4. 45- 51 Milakovic, I., Fiedler, K., & Karrer, G. (2014). Management of roadside populations of invasive Ambrosia artemisiifolia by mowing. Weed Research, 54, 256–264. https:// doi. org/ 10. 1111/ wre. 12074 Ministeriet for Fødevarer, Landbrug og Fiskeri, (2010). Rap- port over undersøgelse af vildtfugle-blandinger for ind- hold af bynkeambrosie frø (Ambrosia artemisiifolia L.) – vinter 2009–2010. Ministeriet for Fødevarer, Landbrug og Fiskeri. Denmark. ISBN 978-87-7083-727-9. Montagnani, C., Gentili, R., & Citterio, S. (2023). Ragweed in the air: Ambrosia L. (Asteraceae) and pollen allergens in a changing world. Current Protein and Peptide Sciences, 24, 98–111. https:// doi. org/ 10. 2174/ 13892 03724 66622 11211 63327 Montagnani, C., Gentili, R., Smith, M., Guarino, M. F., & Citterio, S. (2017). The worldwide spread, success, and impact of ragweed (Ambrosia spp.). Critical Reviews in Plant Sciences, 36(3), 139–178. https:// doi. org/ 10. 1080/ 07352 689. 2017. 13601 12 Myszkowska, D., Bogawski, P., Piotrowicz, K., Bosiacka, B., Grinn-Gofrón, A., Berger, U. E., Bonini, M., Ceriotti, V., Charalampopoulos, A., Galán, C., Gedda, B., Iano- vici, N., Kloster, M., Oliver, G., Pashley, C. H., Pätsi, S., Pérez-Badia, R., Puc, M., Rodinkova, V., et  al. (2023). Co-exposure to highly allergenic airborne pollen and fungal spores in Europe. Science of the Total Environ- ment, 905(2023), Article 167285. https:// doi. org/ 10. 1016/j. scito tenv. 2023. 167285 Niemivuo-Lahti, J. (ed.), (2012). Kansallinen vieraslajis- trategia. Maa-ja metsätalousministeriö. 126 pp. ISBN 978-952-453-725-4 Oswalt, M. L., & Marshall, G. D., Jr. (2008). Ragweed as an example of worldwide allergen expansion. Allergy, 459Aerobiologia (2025) 41:441–460 Vol.: (0123456789) Asthma, and Clinical Immunology, 4(3), 130–135. https:// doi. org/ 10. 1186/ 1710- 1492-4- 3- 130 Pekkarinen, P. T., von Hertzen, L., Laatikainen, T., Mäkelä, M. J., Jousilahti, P., Kosunen, T. U., Pantelejev, V., Varti- ainen, E., & Haahtela, T. (2007). A disparity in the asso- ciation of asthma, rhinitis, and eczema with allergen-spe- cific IgE between Finnish and Russian Karelia. Allergy, 62, 281–287. https:// doi. org/ 10. 1111/j. 1398- 9995. 2006. 01249.x Petrova, S. E. (2019). Development of invasive weeds Ambro- sia artemisiifolia L. and A. trifida L. (Asteraceae) in Moscow oblast. Russian Journal of Biological Invasions, 10(4), 370–381. https:// doi. org/ 10. 1134/ S2075 11171 90400 88 Pickett, S. T., & Baskin, J. M. (1973). The role of temperature and light in the germination behavior of Ambrosia arte- misiifolia. Bulletin of the Torrey Botanical Club, 100(3), 165–170. https:// doi. org/ 10. 2307/ 24846 28 Prank, M., Chapman, D. S., Bullock, J. M., Belmonte, J., Berger, U., Dahl, Å., Jäger, S., Kovtunenko, I., Magyar, D., Niemelä, S., Rantio-Lehtimäki, A., Rodinkova, V., Šaulienė, I., Severova, E., Šikoparija, B., & Sofiev, M. (2013). An operational model for forecasting ragweed pollen release and dispersion in Europe. Agricultural and Forest Meteorology, 182–183, 43–53. https:// doi. org/ 10. 1016/j. agrfo rmet. 2013. 08. 003 Rantio-Lehtimäki, A., Mäkinen, Y., & Pohjola, A. (1985). Sea- sonal variations in airborne fungus spore frequencies in Finland. Reports from the Aerobiology Laboratory, Uni- versity of Turku. ISSN 0356-8598. Rasmussen, K., Thyrring, J., Muscarella, R., & Borchsenius, F. (2017). Climate-change-induced range shifts of three allergenic ragweeds (Ambrosia L.) in Europe and their potential impact on human health. PeerJ, 5, Article e3104. https:// doi. org/ 10. 7717/ peerj. 3104 Rauer, D., Gilles, S., Wimmer, M., Frank, U., Mueller, C., Musiol, S., Vafadari, B., Aglas, L., Ferreira, F., Schmitt- Kopplin, P., Durner, J., Winkler, J. B., Ernst, D., Behrendt, H., Schmidt-Weber, C. B., Traidl-Hoffmann, C., & Alessandrini, F. (2020). Ragweed plants grown under elevated CO2 levels produce pollen which elicit stronger allergic lung inflammation. Allergy, 76, 1718– 1730. https:// doi. org/ 10. 1111/ all. 14618 Ruëff, F., Przybilla, B., Walker, A., Gmeiner, J., Kramer, M., Sabanés-Bové, D., Küchenhoff, H., & Herzinger, T. (2012). Sensitization to common ragweed in southern bavaria: Clinical and geographical risk factors in atopic patients. International Archives of Allergy and Immunol- ogy, 159, 65–74. https:// doi. org/ 10. 1159/ 00033 5192 Saar, M., Gudžinskas, Z., Ploompuu, T., Linno, E., Minkienė, Z., & Motiekaitytė, V. (2000). Ragweed plants and air- borne pollen in the Baltic states. Aerobiologia, 16, 101– 106. https:// doi. org/ 10. 1023/A: 10076 70229 308 Saarinen, K. & Jantunen, J. (2017). Siitepölyä ilmassa! Aller- giaa aiheuttavat siitepölyt Suomessa 1980–2015. Etelä- Karjalan allergia- ja ympäristöinstituutti. Imatra. 101 pp. Saikkonen, K., Taulavuori, K., Hyvönen, T., Gundel, P. E., Hamilton, C. E., Vänninen, I., Nissinen, A., & Helander, M. (2012). Climate change-driven species’ range shifts filtered by photoperiodism. Nature Climate Change, 2, 239–242. https:// doi. org/ 10. 1038/ nclim ate14 30 Salo, P. M., Arbes, S. J., Jaramillo, R., Calatroni, A., Weir, C. H., Sever, M. L., Hoppin, J. A., Rose, K. M., Liu, A. H., Gergen, P. J., Mitchell, H. E., & Zeldin, D. C. (2014). Prevalence of allergic sensitization in the U.S.: Results from the National Health and Nutrition Examination Survey (NHANES) 2005–2006. Journal of Allergy and Clinical Immunology, 134(2), 350–359. https:// doi. org/ 10. 1016/j. jaci. 2013. 12. 1071 Scalone, R., Lemke, A., Štefanić, E., Kolseth, A.-K., Rašić, S., & Andersson, L. (2016). Phenological variation in Ambrosia artemisiifolia L. facilitates near future estab- lishment at northern latitudes. PLoS ONE, 11(11), Arti- cle e0166510. https:// doi. org/ 10. 1371/ journ al. pone. 01665 10 Šikoparija, B., Skjøth, C. A., Alm Kübler, K., Dahl, Å., Som- mer, J., Grewling, L., Radišić, P., & Smith, M. (2013). A mechanism for long distance transport of Ambrosia pollen from the Pannonian Plain. Agricultural and For- est Meteorology, 180, 112–117. https:// doi. org/ 10. 1016/j. agrfo rmet. 2013. 05. 014 Skjøth, C. A., Petersen, H., Sommer, J., & Smith, M. (2009). Copenhagen: A harbinger for ragweed (Ambrosia) in Northern Europe under climate change? IOP Confer- ence Series: Earth and Environmental Science, 6, Article 142031. https:// doi. org/ 10. 1088/ 1755- 1307/6/ 14/ 142031 Smith, M., Cecchi, L., Skjøth, C. A., Karrer, G., & Šikoparija, B. (2013). Common ragweed: A threat to environmental health in Europe. Environment International, 61, 115– 126. https:// doi. org/ 10. 1016/j. envint. 2013. 08. 005 Smith, M., Skjøth, C. A., Myszkowska, D., Uruska, A., Puc, M., Stach, A., Balwierz, Z., Chlopek, K., Piotrowska, K., Kasprzyk, I., & Brandt, J. (2008). Long-range transport of Ambrosia pollen to Poland. Agricultural and Forest Meteorology, 148, 1402–1411. https:// doi. org/ 10. 1016/j. agrfo rmet. 2008. 04. 005 Solomon, W. R. (1984). Aerobiology of pollinosis. Journal of Allergy and Clinical Immunology, 74(4), 449–461. https:// doi. org/ 10. 1016/ 0091- 6749(84) 90376-2 Steckling-Muschack, N., Mertes, H., Mittermeier, I., Schutzmeier, P., Becker, J., Bergmann, K.-C., Böse- O’Reilly, S., Buters, J., Damialis, A., Heinrich, J., Kabesch, M., Nowak, D., Walser-Reichenbach, S., Weinberger, A., Zamfir, M., Herr, C., Kutzora, S., & Heinze, S. (2021). A systematic review of threshold val- ues of pollen concentrations for symptoms of allergy. Aerobiologia, 37, 395–424. https:// doi. org/ 10. 1007/ s10453- 021- 09709-4 Stępalska, D., Myszkowska, D., Piotrowicz, K., Kluska, K., Chłopek, K., Grewling, L., Lafférsová, J., Majkowska- Wojciechowska, B., Malkiewicz, M., Piotrowska- Weryszko, K., Puc, M., Rodinkova, V., Rybníček, O., Ščevková, J., & Voloshchuk, K. (2020). High Ambrosia pollen concentrations in Poland respecting the long dis- tance transport (LDT). Science of the Total Environment, 736, Article 139615. https:// doi. org/ 10. 1016/j. scito tenv. 2020. 139615 Stinson, K. A., Albertine, J. M., Seidler, T. G., Christine, A., & Rogers, C. A. (2017). Elevated CO2 boosts reproduction and alters selection in northern but not southern ecotypes of allergenic ragweed. American Journal of Botany, 104(9), 1313–1322. https:// doi. org/ 10. 3732/ ajb. 17002 22 460 Aerobiologia (2025) 41:441–460 Vol:. (1234567890) Storkey, J., Stratonovitch, P., Chapman, D. S., Vidotto, F., & Semenov, M. A. (2014). A process-based approach to predicting the effect of climate change on the distribu- tion of an invasive allergenic plant in Europe. PLoS One, 9(2), Article e88156. https:// doi. org/ 10. 1371/ journ al. pone. 00881 56 Titane, P.E., & Sozinova, O. (2023). Distribution of com- mon ragweed (ambrosia artemisiifolia) plant and pollen in Latvia and factors affecting them. Current stage and future perspectives of bioaerosol research in Europe. Book of abstracts. 81th International Scientific Confer- ence of the University of Latvia 2023. 10 pp. Wayne, P., Foster, S., Connolly, J., Bazzaz, F., & Epstein, P. (2002). Production of allergenic pollen by ragweed (Ambrosia artemisiifolia L.) is increased in CO2-enriched atmospheres. Annals of Allergy, Asthma & Immunology, 88, 279–282. https:// doi. org/ 10. 1016/ S1081- 1206(10) 62009-1 Willemsen, R. W. (1975). Effect of stratification temperature and germination temperature on germination and the induction of secondary dormancy in common ragweed seeds. American Journal of Botany, 62(1), 1–5. https:// doi. org/ 10. 1002/j. 1537- 2197. 1975. tb123 33.x Ziska, L. H., & Beggs, P. J. (2012). Anthropogenic climate change and allergen exposure: The role of plant biology. The Journal of Allergy and Clinical Immunology, 129, 27–32. https:// doi. org/ 10. 1016/j. jaci. 2011. 10. 032 Ziska, L., Knowlton, K., Rogers, C., Dalan, D., Tierney, N., Elder, M. A., Filley, W., Shropshire, J., Ford, L. B., Hed- berg, C., Fleetwood, P., Hovanky, K. T., Kavanaugh, T., Fulford, G., Vrtis, R. F., Patz, J. A., Portnoy, J., Coates, F., Bielory, L., & Frenzo, D. (2011). Recent warming by latitude associated with increased length of ragweed pollen season in central North America. PNAS, 108(10), 4248–4251. https:// doi. org/ 10. 1073/ pnas. 10141 07108