TY - JOUR

T1 - Effects of tree diversity on canopy space occupation vary with tree size and canopy space definition in a mature broad-leaved forest

AU - Georgi, Louis

AU - Kunz, Matthias

AU - Fichtner, Andreas

AU - Bienert, Anne

AU - Maas, Hans-Gerd

AU - von Oheimb, Goddert

N1 - Publisher Copyright: © 2022

PY - 2022/8/15

Y1 - 2022/8/15

N2 - A more efficient use of limited canopy space and, thus, a higher canopy space occupation (CSO) in forests can result in an increased absorption of photosynthetically active radiation, which in turn can promote productivity. Although there is some evidence for a positive relationship between tree diversity (TD) and CSO, the generality of this hypothesis is still under debate. Here, we propose a conceptual framework that accounts for both the spatial complexity of canopy space and size-dependent interspecific tree interactions and tested it using mobile laser scanning data across larger spatial scales. We assessed the CSO at high resolution with two diversity indices, tree species richness (TSR) and the effective number of species (ENS) along a TSR gradient ranging from monocultures to 8-species mixtures in a mature and structurally complex mixed-species temperate forest. We found that the direction and strength of the TD-CSO relationship largely depended on the way how canopy space is defined and which tree size classes are considered to calculate TSR. Using an broad deliniation of canopy space no significant relationship between TD and CSO was evident. In contrast, when considering only the upper canopy space, a significant effect of TSR on CSO emerged. Importantly, the direction of this relationship was critically dependent on the tree size threshold underlying the TSR determination. For all trees with a diameter at breast height > 7 cm, we observed a significant negative relationship, while the opposite was the case when considering only large-sized trees. Our novel conceptual framework demonstrates that accurate estimation of canopy space complexity and tree size dependence is key to better understanding the processes underlying CSO. However, further information on diversity-canopy space occupation relationships from studies in different forests and forest types is needed.

AB - A more efficient use of limited canopy space and, thus, a higher canopy space occupation (CSO) in forests can result in an increased absorption of photosynthetically active radiation, which in turn can promote productivity. Although there is some evidence for a positive relationship between tree diversity (TD) and CSO, the generality of this hypothesis is still under debate. Here, we propose a conceptual framework that accounts for both the spatial complexity of canopy space and size-dependent interspecific tree interactions and tested it using mobile laser scanning data across larger spatial scales. We assessed the CSO at high resolution with two diversity indices, tree species richness (TSR) and the effective number of species (ENS) along a TSR gradient ranging from monocultures to 8-species mixtures in a mature and structurally complex mixed-species temperate forest. We found that the direction and strength of the TD-CSO relationship largely depended on the way how canopy space is defined and which tree size classes are considered to calculate TSR. Using an broad deliniation of canopy space no significant relationship between TD and CSO was evident. In contrast, when considering only the upper canopy space, a significant effect of TSR on CSO emerged. Importantly, the direction of this relationship was critically dependent on the tree size threshold underlying the TSR determination. For all trees with a diameter at breast height > 7 cm, we observed a significant negative relationship, while the opposite was the case when considering only large-sized trees. Our novel conceptual framework demonstrates that accurate estimation of canopy space complexity and tree size dependence is key to better understanding the processes underlying CSO. However, further information on diversity-canopy space occupation relationships from studies in different forests and forest types is needed.

KW - Biodiversity

KW - Canopy packing

KW - Canopy space occupation

KW - Mobile laser scanning

KW - Near-natural forests

KW - Voxel

KW - Biology

UR - http://www.scopus.com/inward/record.url?scp=85132746335&partnerID=8YFLogxK

U2 - 10.1016/j.agrformet.2022.109055

DO - 10.1016/j.agrformet.2022.109055

M3 - Journal articles

AN - SCOPUS:85132746335

VL - 323

JO - Agricultural and Forest Meteorology

JF - Agricultural and Forest Meteorology

SN - 0168-1923

M1 - 109055

ER -