Impact of Climate Change on Tree Species Distribution and Vulnerability in Key Protected Forest Ecosystems in Serbia

(1) Background: The recent decade appears to be the hottest since the beginning of modern measurements. Changes in climate patterns related to extreme events and disturbances in forest ecosystems are well documented. Six prominent protected areas (PAs), mountainous forest ecosystems in Serbia, were assessed from the perspective of species potential distribution and vulnerability. (2) Methods: Seven different machine learning models were employed, evaluated using AUC, the maximum F-measure, and TSS and joined into an ensemble model for each of the eight tree species/groups taken from the National Forest Inventory. Representatives from four groups of environmental variables were included: 1. climate (Ellenberg’s Climate Quotient), 2. soil (soil organic carbon), 3. topography (elevation), and 4. remotely sensed indices (NDVI). Future climate was derived from four scenarios (SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5). Stable/gain/loss areas and species vulnerability were calculated with a focus on the end of the 21st century. (3) Results: By the 2090s, generally, contraction of Silver fir, Norway spruce, and European beech is expected, together with the promotion of Downy oak and Sessile oak, in all climate scenarios at all PAs. Two high-mountain PAs expect to see promotions in average forest suitability, one PA both a promotion and a reduction in two scenarios, and three PAs reductions in forest ecosystems in general. (4) Conclusions: National parks “Kopaonik” and “Tara” appear to be the least endangered, followed by “Golija”, while “Stara planina”, “Djerdap”, and “Fruska gora” are expected to experience overall reductions in forest habitats.