Follow-Up Study; Understanding Crown shyness at Tree Community Level in a Malaysian Tropical Forest Stand from a 3D Perspective

By Daan Ligtenberg

Abstract
Crown shyness is a phenomenon where puzzle-like patterns of openings are present between tree crowns. It has captured scientific interest as the understanding of the governing factors remain unclear. Existing research has primarily focused on pair-wise interactions within the uppermost canopy layer. Leaving the interactions among trees within entire networks and across different heights to be explored. This research expands the methodology presented by van der Zee et al. (2021) to examine the relationship between tree-structural parameters and crown shyness at a community level and among different height classes. The methodology employs surface complementarity as a measure of crown shyness. Applied within an old-growth lowland dipterocarp rainforest, the pair-wise and neighbourhood results revealed that overlapping trees exhibit significantly (α = 0.05) lower surface complementarity values, indicative of direct competition and suboptimal growth space utilization. Non-overlapping trees, in contrast, avoid direct competition, shedding light on crown shyness as a consequence of spatial niche partitioning, these findings are in accordance with previous research. Of the tree structural parameters, crown shape in neighbourhoods negatively correlates with surface complementarity (R2 = 0.061, p = 0.001), underscoring the role of crown morphology in crown shyness dynamics, which is in line with previous research. Between different height classes, slenderness and surface complementarity showed a significant negative relationship in the understorey (R2 = 0.046, p = 0.015) and canopy layer (R2 = 0.178, p = 0.001) and a significant positive relationship in the emergent layer (R2 = 0.373, p = 0.016). This suggests a diverse influence of environmental factors, such as wind exposure, on the degree of crown shyness within the lower forest layers compared to the more exposed emergent layer. This study advances the understanding of crown shyness, highlighting the need to integrate environmental influences and tree height. The expanded methodology enables a comprehensive examination of interactions among trees within the entire network and offers a valuable contribution to future research, with implications for comprehending ecological interactions in forest ecosystems.

Keywords: crown shyness, complementarity, neighbourhood interactions, terrestrial LiDAR, forest canopy, crown shape, tree slenderness