Global warming levels exceeding 2 ​℃ may cause tipping point of low elevation forests in a peri-urban forest of the black forest foothills

Climate change is impacting forests in Central Europe, causing increased mortality and degradation of forest ecosystem services (FES). As global warming intensifies, these effects are likely to worsen, particularly through more severe droughts and increased biotic disturbances. Understanding how forests respond to different levels of warming is essential for adaptation planning. Therefore, this study analyzed changes in forest structure and FES, including timber production, climate change mitigation, recreation, and structural diversity, under three global warming scenarios. Using the LandClim model, we compared warming levels of 1.5, 2, and 3 ​℃ above pre-industrial temperatures, based on 30-year periods from RCP data, to historical climate. Our research focused on Freiburg's forests in southwestern Germany, characterized by diverse tree species and an elevation range of 200–1,250 ​m a.s.l. A warming of 1.5 ​℃ could temporarily increase productivity, but at 2 ​℃, biomass losses of up to 10% would occur below elevations of 450 ​m due to drought mortality. Under 3 ​℃, losses would intensify below 650 ​m up to 40%, with even drought-resistant species like pedunculate oak experiencing mortality. At higher elevations, bark beetle outbreaks caused mortality of Norway spruce, while European beech capitalized on the changing ecological conditions. Higher warming levels significantly deteriorated FES, particularly timber production, climate change mitigation, and structural diversity, while recreation was less affected. These findings emphasize the urgency of meeting Paris Agreement targets, as limiting warming below 2 ​℃ can reduce severe impacts. If warming exceeds this critical threshold, even species presently considered drought-resistant, such as native sessile and pedunculate oaks and non-native red oak, could face serious threats at lower elevations. This would undermine the effectiveness of current management strategies, as these tree species are key to providing multiple FES.