Abstract
ContextStructural diversity strongly influences habitat quality and the functioning of forest ecosystems. An important driver of the variation in forest structures are disturbances. As disturbances are increasing in many forest ecosystems around the globe, it is important to understand how structural diversity responds to (changing) disturbances.ObjectivesOur aim was to quantify the relationship between forest disturbances and structural diversity with a focus on diversity in canopy height.MethodsWe assessed diversity in canopy height for two strictly protected Central European forest landscapes using lidar data. We used a multi-scale framework to quantify within-patch (α), between-patch (β), and overall (γ) diversity. We then analysed the variation in canopy height diversity over an extensive gradient of disturbance rates.ResultsDiversity in canopy height was strongly driven by disturbance rate, with highest overall diversity between 0.5 and 1.5% of the forest area disturbed per year. The unimodal responses of overall diversity to disturbance emerged from contrasting within- and between-patch responses, i.e., a decrease in within-patch diversity and an increase in between-patch diversity with increasing disturbance. This relationship was consistent across study landscapes, spatial scales, and diversity indicators.ConclusionThe recent wave of natural disturbances in Central Europe has likely fostered the structural diversity of forest landscapes. However, a further increase in disturbance could result in the crossing of a tipping point (at ~ 1.5% of forest area disturbed per year), leading to substantial structural homogenization.
Highlights
Halting the loss of global biodiversity is one of the current challenges faced by humanity (Steffen et al 2015)
We focus on one important dimension of structural diversity, the diversity in canopy height classes (Kuuluvainen et al 1996), by answering the following three questions: (1) What is the effect of natural disturbance rates on canopy height diversity? (2) What is the contribution of patch-scale diversity versus landscape-scale diversity on overall diversity in canopy height classes? (3) At which disturbance rates is diversity in canopy height maximized? We quantify canopy height diversity using Light Detection and Ranging (Lidar) data and a multi-scale framework that partitions canopy height diversity into three components describing within-patch, between-patch and overall diversity
For richness in canopy classes (0D), we found an exponentially increasing pattern, indicating that the number of canopy classes on the landscape continuously increased within the range of observed disturbance rates
Summary
Halting the loss of global biodiversity is one of the current challenges faced by humanity (Steffen et al 2015). Structural diversity, here defined as the variability in the dominant canopy layer, is tightly related to ecosystem functioning. High structural diversity at the patch scale is typical for late-successional ecosystems (Franklin et al 2002), which harbour high levels of biodiversity, but are important contributors to global forest carbon storage (Carey et al 2001; Zhou et al 2006; Luyssaert et al 2008). Structural diversity can increase the resilience of forest ecosystems (Seidl et al 2014, 2016a), which is increasingly important as both the environment and society change rapidly (Seidl et al 2016b). As such, understanding the drivers of structural diversity is of crucial importance
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