Elevational Shifts in the Topographic Position of Polylepis Forest Stands in the Andes of Southern Peru

Abstract

<p> The patchy distribution of high-Andean treeline forests has provoked discussion about</p><p>the relative importance of anthropogenic and climatic causes of this pattern, both of which</p><p>vary with topography. We aimed to understand the topographic controls on the distribution of</p><p>Polylepis subsericans treeline forests in the Andes of southern Peru, and the changes in these controls</p><p>along an elevational gradient. We mapped Polylepis forests in the Cordillera Urubamba, Cusco,</p><p>using high-resolution aerial images and related forest cover to topographic variables extracted from a</p><p>digital terrain model (30-m resolution). The variables were selected based on their expected biological</p><p>relevance for tree growth at high elevations. We constructed logistic regression models of forest</p><p>cover, separately for each of five 100-m elevational belts. To deal with spatial autocorrelation, models</p><p>were based on randomized 10% subsampling of the data with 1000 repetitions. The results suggest a</p><p>consistent shift in topographic preference with elevation, with forests at lower elevations showing</p><p>a preference for topographically protected sites near rivers and forests at higher elevations being</p><p>increasingly restricted to north-facing and well-drained sites. Our study offers the first indication of</p><p>the ability of Andean treeline forests to benefit from the topographic heterogeneity of the high-Andes.</p><p>Providing that dispersal and establishment are possible, local relocation between microsites could</p><p>

</p><p>help these forests to persist regionally in spite of changing climatic conditions.</p>