Understanding the effects of anthropogenic impacts on biodiversity and ecosistems' tipping points at different spatial and temporal scales

Human activities are reshaping forest ecosystems through interacting stressors (e.g., climate change, resource extraction, altered disturbance regimes), raising concerns that ecological change may be non-linear and difficult to anticipate. This thesis addresses the challenge of assessing ecosystem condition and resilience loss using indicators relevant for management, while recognising that ecological processes and the evidence used to observe them are uneven, scale-dependent, and uncertain. To build a coherent cross-scale framework, the thesis combines complementary data streams and response dimensions. First, as a methodological foundation, I quantified how taxonomic, spatial, and temporal biases, together with information decay, affect the reliability of large biodiversity databases, providing tools to diagnose where inference is most fragile. Second, I assessed global forest condition by adapting the abundance–biomass comparison (ABC) framework to derive the W index from the GFBI network. Relating W to climate, anthropogenic pressure, disturbance proxies, and protection status shows that disturbance signals are pervasive and closely linked to human pressure, especially resource extraction. Consistent differences among management regimes also emerge, with strict protection more often associated with higher integrity than many multi-use categories. Third, I tested whether temporal early warning signals from annual NDVI can anticipate bark beetle outbreaks in Germany. These signals are generally weak and spatially patchy, and do not clearly distinguish disturbed from undisturbed forests, highlighting limits to operational early warning under noisy and heterogeneous conditions. Finally, I examined long-term community reorganisation by quantifying temporal biotic homogenisation of German forest understorey vegetation. Homogenisation is widespread, but its magnitude and direction depend on spatial scale and vary across protection regimes. Overall, anthropogenic pressures reshape forests through multiple, partly decoupled pathways, often even where forest cover persists, underscoring the need for scale-aware, outcome-focused conservation under accelerating global change.