Investigating Influential Factors and Effects of Inter-Individual Variability in Silver Birch Phenology with Dense Lidar Time-Series

Abstract

Comprehending and quantifying local variability in plant phenology, alongside its impacts on tree growth, is challenging due to spatially and temporally heterogeneous environmental factors that interact to affect phenological events. Previous studies have focused on the climatic factors driving phenological events at the stand level, however the influences of competition, neighborhood characteristics, species richness, and water availability on plant phenology remain unclear. We used terrestrial LiDAR surveys every hour for one year between April 2020 and April 2021 to investigate the influence of local factors on the phenology of silver birch trees (Betula pendula Roth.). We also examined how phenological events affect growth in tree height and crown area. Our findings demonstrate a high within-species variability in plant phenology that is controlled by biotic and abiotic characteristics of the ecosystem. We found that between tree variation in leaf burst, completion of the leaf growth and length of canopy growth period were affected by tree size, neighborhood species richness, level of suppression and competition, which potentially indicate plant responses to light availability. The beginning of senescence, completion of leaf drop, and length of autumn phenology were mostly affected by topographic water index, which reflects water availability and can be linked to nutrient availability and exposure to wind. Furthermore, we demonstrated that an earlier leaf burst, and delayed beginning of senescence were associated with larger absolute growth in canopy area but found no clear relationship between height growth and phenology.

Keywords: LiDAR time-series, permanent laser scanning system, tree vertical and horizontalgrowth, tree neighborhood.