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Highlights • Temperatures and summer aridity are increasing in southern forests of Pinus nigra. • The species' regeneration niche is consequently leaning upslope in these forests. • A significant seedling bank useful to restock harvested stands is present. • Water, irradiation and factors acting at the microhabitat scale affect recruitment. • Continuous cover forestry is recommended. Abstract Although typically considered shade-intolerant, Mediterranean pine species may form seedling banks due to the existence of facilitative interactions between seedlings and canopy trees. Consequently, seedling banks could be considered as part of the seedling pool that should restock managed Mediterranean pinewoods, thus increasing the resistance of these forests to climate change. The study investigated the characteristics of the seedling bank in a silviculturally undisturbed forest of Pinus nigra subsp. salzmanii exposed to increasingly arid conditions. The study site was located in the southernmost range limit of the species. The dynamics of the seedling bank was studied by comparing current seedling (height < 1.30 m, age < 2 yr) and pole tree (height ≥ 1.30 m and diameter at breast height < 12.5 cm) altitudinal distributions, using altitude as a proxy of aridity. Aridity was proved to have increased in the study area along the last four decades. These climatic trends were identified by means of Mann-Kendall tests for trend. Additionally, the effects of summer drought, light availability, soil compaction, litter layer and micro-slope as explanatory variables of the recruitment outcome were analysed by means of Generalized Linear Mixed Models and survival analysis. Altitude affected positively seedling establishment, but had no effect on the current abundance of pole trees, indicating a recent upwards displacement of the regeneration niche due to increasingly arid conditions. Water and light availability, the latter at intermediate levels of irradiance, affected tree recruitment positively, whereas the effects of soil compaction, litter layer depth and micro-slope were negative. Implementing extended rotation periods and maintaining intermediate values of tree cover are proposed as important management recommendations to achieve successful natural regeneration in Mediterranean pinewoods. [ABSTRACT FROM AUTHOR]

Since climate change projections contain many uncertainties and are normally unable to predict the direction and magnitude of change at the small scale needed by forest managers, some understanding about the functioning of the target forest should be obtained before a robust management strategy can be applied. Structure and regeneration patterns are related to key ecosystem processes which, on the other hand, can be modified by silvicultural treatments. In this research, the structure and recruitment dynamics of two stands with different histories of management were investigated in the southern limit of the range of Pinus nigra subsp. salzmannii (Southeast Spain). We described forest structure and facilitation effects by forest canopies and nurse shrubs, and quantified the processes affecting each stage of regeneration (dispersed seed, first year seedling and second year seedling) in different microhabitats. Forest structure was more complex in the stand scarcely influenced by human activities. Juniperus communis shrubs seemed to facilitate the establishment of tree saplings. Most seedlings died of desiccation during their first summer. At best, 190 out of 10,000 emerged seedlings survived the first summer. In light of these results, the possibilities of applying close-to-nature forestry in the study forests and other aspects of silviculture under a frame of adaptive forest management are discussed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]