Climate change impacts and vulnerability of the southern populations of Pinus nigra subsp. salzmannii.

The understanding of regional vulnerability to climate change in Mediterranean mountain forests is not well developed. Climate change impacts on tree growth should be strongly related to the steep environmental gradients of mountainous areas, where a temperature-induced upward shift of the lower elevation limit is expected, particularly amongst drought-sensitive species. Trees will adapt not only to changes in mean climate variables but also to increased extreme events such as prolonged drought. In this paper, we investigate the sub-regional temperature and precipitation trends and measure the basal area increment (BAI) in Pinus nigra subsp. salzmannii (Dunal) Franco. Significant differences related to altitudinal and latitudinal gradients and stand-age structure were found in response to long-term trends in climate dryness. Old trees growing at higher elevations showed similar extreme drought sensitivity but maintained almost steady BAI. Declining BAI found in trees at lower elevations and drier sites may imply a higher vulnerability to temperature-induced drought stress, suggesting an impending growth decline and an enhanced die-off risk. Our results illustrate how the effects of long-term warming and short-term drought on tree BAI are influenced by both site conditions and mean stand age in a drought-sensitive Mediterranean pine.