Light interception in experimental forests affected by tree diversity and structural complexity of dominant canopy

Alain Paquette,Anne-Sophie Riopel-Bouvier,Marc-Olivier Martin-Guay,Kaisa Rissanen

doi:10.1016/j.agrformet.2019.107655

Abstract

Biodiversity affects ecosystem functioning in forests by, for example, enhancing growth and altering the forest structure towards greater complexity with cascading effects on other processes and trophic levels. Complexity in forest canopy could enhance light interception and form a link between diversity and productivity in polyculture forests, but the effect of canopy structure on light interception is rarely directly measured.We modelled the canopy surface structure of a tree diversity experiment by photographing it using unmanned aerial vehicle (UAV) and combining the photos into a digital elevation model with photogrammetry tools. We analysed the effects of tree diversity and functional diversity on canopy structural complexity and light interception with a structural equation model.Our results show that: a) increased structural complexity of the canopy reduces light interception, whereas b) tree diversity increases the structural complexity of the canopy, and has a dual impact on light interception. Tree diversity decreased light interception through the structural complexity of the canopy but increased it probably through canopy packing and crown complementarity. However, the effects of both tree diversity and structural complexity of canopy were smaller than the effect of the functional identities of the tree species, especially the differences between deciduous and evergreen trees.We conclude that more complexity in canopy structure can be gained through increased tree diversity, but complex canopy structure does not increase light interception in young forests.

Highlights

Studies on biodiversity and ecosystem functioning (BEF) in forests have shown that forests with diverse tree species are often more efficient in providing ecosystem services than monocultures
The digital elevation model (DEM) that was built based on unmanned aerial vehicle (UAV) aerial photos had a high resolution and its accuracy was on average 0.1 m horizontally and 0.07 m vertically, compared to the georeferenced ground control points (GCPs)
We found that UAV photogrammetry tools are useful in describing the height and structural complexity of dominant canopy of young forest and could provide a cost-effective alternative to airborne LiDAR

Summary

Introduction

Studies on biodiversity and ecosystem functioning (BEF) in forests have shown that forests with diverse tree species are often more efficient in providing ecosystem services than monocultures. Polyculture forests can be more resilient to changes in environment (Morin et al, 2014; Pretzsch, 2014) and provide more habitats for other organisms, such as berries and game animals (Gamfeldt et al, 2013) They can have higher productivity and capacity to store carbon in biomass (Paquette and Messier, 2011; Vilà et al, 2013; Ruiz-Benito et al, 2014), which was lately confirmed in a large worldwide analysis (Liang et al, 2016). Tree diversity experiments have shown that, for example, the presence of species with certain functional identities (Tobner et al, 2016) and functional diversity or species richness (Grossman et al, 2017) can increase productivity in young tree communities and that spatial crown complementarity in polycultures can increase light interception and productivity (Williams et al, 2017)

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