Estimating potential vegetation distribution and restoration in a biodiversity hotspot region under future climate change

Potential Natural Vegetation (PNV) represents the climax of vegetation succession in a natural environment, free from significant disturbances. The reconstruction of PNV is widely used to study climate-vegetation relationships and predict future vegetation distributions. However, fine-scale PNV maps with high accuracy are still rare in biodiversity hotspots due to the complexity of ecosystems and limited field observations. In this study, we mapped the spatiotemporal distribution of 16 PNV types using adequate field and literature data, and an improved Comprehensive and Sequential Classification System (CSCS) approach under current (2005-2016) and future (2021-2080) climate scenarios in Yunnan province, Southwest China. We found that 1) from T0 (2005-2016) to T3 (2021-2080), regions with cold alpine PNV types, such as mid-mountain humid evergreen broad-leaved forests (EBLF), are projected to experience more significant temperature increases compared to regions with warm PNV types, like tropic rainforests and monsoon rainforests. High-emission scenarios (SSP585) are expected to result in temperature increases approximately 2 degrees C higher than low-emission scenarios (SSP126). Precipitation is projected to increase for water-deficient PNV types (e.g., monsoon rainforest and semi-humid EBLF) but decrease for humid PNV types (e.g., rainforest and mountain mossy EBLF). The SSP370 scenario predicts a slightly smaller increase in precipitation compared to other scenarios. 2) All PNV types are expected to shift to higher latitudes (by an average of 0.86 degrees) and higher elevations (by an average of 454 m) by T3, based on their current niches. Alpine PNV types are more sensitive to climate change and are projected to shift more prominently than other types. For example, mountain mossy EBLF is expected to move 1.78 degrees northward, while mid-mountain moist EBLF is projected to rise by 578 m. 3) Cold PNV types are likely to be replaced by warm types both in latitude and altitude. Semi-humid EBLF is projected to shrink the most, by 57,984 km2 (51.5% of its present range), while monsoon EBLF is expected to expand the most, by 44,881 km2 (64.7% of its present range). The suitable habitat for cold-temperate sclerophyllous EBLF and temperate shrublands may disappear entirely in Yunnan. Given the over-estimate of the projected PNV shift without accounting for the lag effects, these findings are still useful in planning future conservation and management efforts, which should prioritize PNV types experiencing drastic changes in temperature (e.g., mid-mountain moist EBLF), precipitation (e.g., mountain mossy EBLF), and distribution area (e.g., semi-humid EBLF and cold-temperate sclerophyllous EBLF).