Estimated degradation of the Caatinga based on modern pollen rain deposited in reservoirs

Abstract

The vegetation cover is the result of many biological and abiotic interactions. To identify the different factors that cause changes is crucial when defining future sustainable development and protection of natural resources. In the Brazilian semiarid region, the vegetation cover has been subjected to drastic deforestation and land use at centennialscale that has led to desertification. Pollen analysis is an efficient tool to reconstruct the different processes of degradation of the vegetation cover over time. We built a referential data set for the vegetation cover using 48 pollen surface samples collected in the reservoirs of the Ceará. We used satellite images for comparison with the pollen signatures and defined an alteration score to express the correlation between terrestrial pollen and anthropic cover. Our results showed our surface samples to be generally representative of the vegetation cover and of the general degradation of the landscape. Our study areas can be considered as degraded as the initial categories "preserved" or "intermediary" are not reflected in the pollen assemblages, in agreement with results of botanical surveys and the historical background. The on-going process of desertification is climate-independent and was initiated many decades or centuries ago by intensive land use for agriculture and grazing.