Land-Use Legacies and Climate Change as a Double Challenge to Oak Forest Resilience: Mismatches of Geographical and Ecological Rear Edges

Ecological Diversity within Rear-Edge: A Case Study from Mediterranean Quercus pyrenaica Willd.

“…The different clusters of oak populations are supported both by discriminant analysis of environmental variables and by ordination analysis based on the floristic composition in the target populations. Our results show that the diversity in the ecological conditions within these populations results from both the environmental heterogeneity created by the slopes and the contrasting exposures of the valleys they inhabit, and also the anthropic use of these ecosystems e.g., [11,111]. The confluence of these factors generates a multitude of environmental conditions on a fine scale, which are reflected in the distribution, composition, and functioning of the Quercus pyrenaica forests.…”

“…The differences among populations based on environmental variables obtained in our study are in line with differential ecological dynamics reported for Q. pyrenaica forests in the Sierra Nevada by other studies. For instance, primary productivity of these forest measured using remote sensing showed a heterogeneous spatial behavior, with oak woodlands of the southern slopes displaying a greater annual vegetation greenness than those from the northern slopes [11,77,78]. In addition, differences have been found in both seasonal dynamics of greenness [77], and in temporal trends for primary productivity in the last few years related with differential snow-cover trends in contrasting slopes [78,79].…”

“…On the other hand, the populations of the southern slopes of Sierra Nevada get an extra supply of water from moist air from the neighboring Alborán sea [102]. The differences in water availability among oak populations could affect several ecological processes such as tree-growth [5,11], seedling germination and survival [103][104][105], and the regeneration of the species [106], mainly due to the key role of water availability in the microsites facilitating the germination and establishment of seedlings.…”

“…The confluence of these factors generates a multitude of environmental conditions on a fine scale, which are reflected in the distribution, composition, and functioning of the Quercus pyrenaica forests. Quercus pyrenaica woodlands are highly diverse at all organization levels, from a genetic perspective, i.e., high levels of genetic differentiation within species [43] and differences between populations [86]-to ecosystem-functioning level, i.e., diversity in terms of primary production and growth [78,79], and diversity of resilience to disturbances e.g., [11]. Such ecological heterogeneity is also made evident by the accompanying plant communities, which are very different depending on the oak population considered, such differences being correlated with the differences in environmental conditions among populations.…”

“…Local responses to environmental changes may differ from the species mean response [3][4][5][6], and such differences may either promote or hamper the survival of edge populations under global change [7]. Furthermore, the heterogeneity in the response to climate change observed across ecological and geographical gradients [8][9][10][11], justifies the need to incorporate fine-scale variation of environment variables throughout species ranges to better understand species responses to global change [12,13]. This is particularly important for mountain landscapes, where the topographic complexity may cause a decoupling between the climate and the geographic spaces [14,15].…”