Laura Hernández

Assessing changes in species distribution from sequential large-scale forest inventories

Abstract• ContextIt is assumed that global change is already affecting the composition, structure and distribution of forest ecosystems; however, detailed evidences of altitudinal and latitudinal shifts are still scarce.• AimsTo develop a method based on National Forest Inventory (NFI) to assess spatio-temporal changes in species distributions.• MethodsWe develop an approach based on universal kriging to compare species distribution models from the different NFI cycles and regardless of the differences in the sampling schemes used. Furthermore, a confidence interval approach is used to assess significant changes in species distribution. The approach is applied to some of the southernmost populations of Pinus sylvestris and Fagus sylvatica in the Western Pyrenees over the last 40xa0years.• ResultsAn increase of the presence of the two species in the region was observed. Scots pine distribution has shifted about 1.5xa0km northwards over recent decades, whereas the European beech has extended its distribution southwards by about 2xa0km. Furthermore, the optimum altitude for both species has risen by about 200xa0m. As a result, the zone in which the two species coexist has been enlarged.• ConclusionsThis approach provides a useful tool to compare NFI data from different sampling schemes, quantifying and testing significant shifts in tree species distribution over recent decades across geographical gradients.

Exploring range shifts of contrasting tree species across a bioclimatic transition zone

Bioclimatic transition zones are supposed to encompass sensitive areas to global change effects on forest ecosystems. In this study, we attempt to detect shifts in the ranges of contrasting Iberian tree species in the submediterranean transition zone in Navarra, northern Spain. These shifts are analysed in the context of a significant increase in temperature over recent decades along with moderate land use changes. Data from national forest inventories (1971 and 2010) are compared through universal kriging (UK) and block kriging models to assess the shifts in the ranges of Quercus subpyrenaica, Quercus ilex, Pinus sylvestris and Fagus sylvatica. UK results predicted an increase in the presence probability of the four target species for the whole Navarra region. However, in the submediterranean zone, the presence probability of Q. subpyrenaica, P. sylvestris and F. sylvatica shows a shrinking trend, whereas Q. ilex is expanding its range, supporting a previous hypothesis of a “mediterranization” of this bioclimatic transition region. These trends are concomitant with recent elevational shift patterns towards higher elevations in the case of Q. subpyrenaica, P. sylvestris and F. sylvatica in the transition zone. Moreover, the expected increase in species richness as a consequence of geographical shifts and vegetation recovery is identified. The moderate human influence detected in the study area confirms the major role of climate warming as driver of species range shifts over the period. The results of this study highlight the suitability of bioclimatic transition zones for monitoring the effects of global change on natural ecosystems, providing evidences of the complex mechanisms affecting the distribution of forests.