Efeitos da urbanização e do clima na produtividade primária de florestas urbanas no Sul e Sudeste do Brasil

Abstract

Cities are social and ecological systems characterized by the high human demographic rate, which wields dominance on the structure and functioning of natural and semi natural ecosystems. The urban ecosystems interact substantially with regional and global ecological processes, and it is therefore important to know about the urbanization of the landscape process and its relation with the environment. The urbanization of the landscape is the process by which the urban ecosystems become the landscape matrix, going through phases of expansion and consolidation, and it has brought considerable degradation to the ecosystems of support in the regions and places it is inserted, negatively affecting the efficiency of environmental services. It is imperative to develop and apply urbanization models reconciled with the conservation and functional maintenance of the ecosystems support, and to this end, it is essential to be aware of its dynamic and functioning. In this regard, it is highlighted the studies about urban forests that are the isolated forest areas of the urbanized landscapes, originated from natural ecosystems and that are of great benefit to the local populations, fostering several ecosystem services. The primary productivity is an ecosystem function widely studied in natural and semi natural landscape contexts, and recently in urban landscapes as well where it is, usually, negatively correlated. Besides that, the productivity may further be influenced directly and indirectly by geographical, vegetational and climatic features of a particular region. With this in mind, studies that simultaneously evaluate urbanization effects and climatic changes in the productivity of urban forests are still necessary. Therefore, the present study aims at describing (1) the urban landscape expansion and consolidation patterns and (2) primary productivity of its forests, in nine urban landscapes in this region (two cities and seven metropolitan localities) between 1980 and 2010, as well as (3) testing possible causative variation mechanisms in the productivity of these urban forests, related to urbanization, climatic, vegetational and geographical factors. If the urban forests of the southern and the southeastern regions of Brazil follow the 6 observed patterns in other parts of the world, the primary productivity is temporarily affected by the urbanization process and by the climatic variations. Through the images of the Landsat 5 and Landsat 8 satellites, forests of nine urban regions of this region were monitored as to the changes in the land use and cover (urbanization, vegetation and water), climatic variations and NDVI (Normalized Difference Vegetation Index) since 1980. The average NDVI of the urban forests was calculated for each one of the analyzed decades. Pathways were elaborated to determine which geographical, climatic, vegetal and urban descriptors affect the primary productivity of these forests over time. The NDVI outcomes reported a 35% reduction on the primary productivity of the urban forests in the southern and southeastern cities of Brazil. From the Path Analysis test, it was noticed that the height (β = - 0,71) and the continental area (β = 0,47) indirectly influenced the productivity through the temperature rise (β = - 0,47), the urbanization (β = - 0,39), thus confirming the studies of many regions. If the predictions for urban expansion, vegetation loss and climatic changes for southern and southeastern Brazil hold true, we can expect the forests to be less productive, and possible profound changes in the carbon cycle, in the ecosystem services and in the life quality of the population itself