Quantifying changes in forest structural complexity using bi-temporal airborne laser scanning

Abstract

<p>Structural complexity is an important forest characteristic for habitat assessment, forest management<br>and planning. However, monitoring how forest structural complexity evolves over<br>time in various forest types has not been widely explored. In this study we investigate the<br>feasibility of bi-temporal low-density airborne laser scanning (ALS) for the assessment of<br>changes in light availability conditions within forest canopy, considered to imply changes in<br>forest structural complexity. We used ALS data acquired in 2012 and 2019 to generate canopy<br>vertical profiles by slicing the point clouds into 4 × 4 ×1 m voxels which were then rasterized<br>and reclassified into four light availability categories. To understand structural development<br>over time in different forest types we used field-measured tree heights and tree species<br>information to stratify sample plots in different stand complexity categories. Stands with higher<br>structural complexity represented increased proportions of space occupied by vegetation as<br>well as decreased proportions of empty space below the canopy. The experiments showed the<br>ability of low-density ALS to characterize the dynamics in canopy layering structure, implying<br>changes in forest structural complexity. The presented methodology could potentially be<br>upscaled and applied in the landscape-level monitoring of the development of boreal forest<br>structural characteristics.<br></p>