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Holocene vegetation succession and degradation as responses to climatic change and human activity in the Serra de Estrela, Portugal

1995; Elsevier BV; Volume: 89; Issue: 3-4 Linguagem: Inglês

10.1016/0034-6667(95)00048-0

1879-0615

Willem O. van der Knaap, J. F. N. van Leeuwen,

Aeolian processes and effects

The Holocene vegetation history in the Serra da Estrela, a granitic mountain range in east-central Portugal, is reconstructed from a pollen diagram for Charco da Candieira, a small lake at 1400 m asl. The reconstruction is based on knowledge of the flora, the ecology of plant species in the region, and modern representation of pollen types. 207 pollen types were encountered in 245 samples. Macroanalysis, mainly of seeds, was carried out on twelve samples. Twenty-four levels were radiocarbon-dated. The dominant factors determining the vegetation succession appear to be climatic change in the earlier phases, gradually overshadowed by human activity in later phases, resulting in accelerated landscape degradation and soil erosion. Five main periods of vegetation succession are distinguished: (c. 10,350-8700 BP, 5 zones): Late-Glacial steppe succeeds to xerothermic forests under warm and rather dry climatic conditions and without human interference. (c. 8700-5670 BP, 6 zones): Climate turning moister and cooler is the main factor determining the forest dynamics. Eight climatic cycles consisting of a wet and a dry phase each were inferred. The forest changes from xerothermic to mesothermic c. 8240 BP. The anthropogenic factor starts to play a minor but increasing role. (c. 5670-3220 BP, 7 zones): The area covered by forests is hardly affected by human activity, but the inferred forest dynamics predominantly reflect human impact: some grazing occurred in the forests, with small-scale local deforestation. Local over-grazing with soil erosion starts c. 4550 BP. (c. 3220-955 BP, 9 zones): Large-scale deforestation, but the forests retain their capacity to regenerate. Deforestation phases, stable phases, and forest-regeneration phases succeed each other in response to changing patterns and intensity of human pressure. (c. 955 BP-present day, 5 zones): Anthropogenic pressure increases to such an extent that the forests virtually disappear and organic soils are for the greater part eroded and washed away. The main agents are grazing, burning, agriculture, and large-scale plantation of pines.