Age structure of Juniperus communis L. in the Iberian peninsula: conservation of remnant populations in Mediterranean mountains.

摘要

The demographic structure of Juniperus communis populations in the Mediterranean high mountains of southern Spain were examined in order to analyse its population viability. The age structure of these Mediterranean populations was compared with those of northern Spain (Atlantic), and, on a local scale, the populations of different habitats within the Sierra Nevada. The populations from northern Spain showed age structures with high proportions at young stages. In contrast, the Mediterranean populations were dominated by adult and senescent individuals, except for the few habitats with higher water availability during the summer, which had larger proportions of seedlings and juveniles. Dry habitats showed a lower seedling survival rate than wet habitats, mainly owing to summer drought. The differences between Atlantic and Mediterranean categories, and the habitats in the Sierra Nevada reflect a serious limitation on recruitment of J. communis in Mediterranean mountains due to climatic stress imposed by summer drought. The Mediterranean populations provide a clear example of remnant dynamics, surviving for long periods due to great individual longevity which partially offset losses to unfavourable environmental conditions. The low ability to recover after anthropic disturbances emphasized the need for conservation of J. communis populations in south-eastern Spain.