Airborne LiDAR reveals context dependence in the effects of canopy architecture on arthropod diversity

• An application of LiDAR data to explain arthropod diversity in tree canopies.
• First step toward a unifying concept of biodiversity – forest growth models.
• Testing of ecological hypotheses which might drive the diversity of tree crowns.
• A study which might stimulate more forest ecologists to use publicly available LiDAR data.

Ecologists have long recognized the important role of canopy heterogeneity in structuring the diversity of animal communities. However, studies directly linking variation in the three-dimensional structure of forests to variation in biodiversity are still rare. For canopy arthropods representing a dominant component of forest biodiversity in montane spruce forests of Europe, we used publicly available airborne LiDAR measurements to test the premises of two existing hypotheses that resource concentration and habitat heterogeneity are potential drivers of faunal diversity at both the tree scale and stand scale. We sampled 391 arthropod species from the canopies of 60 trees; coverage-based rarefaction revealed high completeness of faunal sampling (93.7%). When we controlled for elevation and broadleaf tree cover, we found strong (tree and stand scale) context dependence in the response of arthropod diversity to variation in vegetation structure. Arthropod diversity increased with increasing canopy density at the tree scale and was positively associated only with vegetation heterogeneity at the tree scale, but decreased with increasing canopy density at the stand scale. These trends held across all levels of biological response from total richness to diversity measures to richness of different guilds. Our results showed that different components of vegetation structural complexity drive canopy arthropod biodiversity at different spatial scales. Highest canopy arthropod diversity can be expected in spruce forests with relatively open stands containing individual trees with dense and long crowns. Thus, LiDAR opens new avenues for testing ecological hypotheses and for forest-growth models to be linked with the canopy diversity of forests.