Impactos da fragmentação de habitat sobre o clima: uma análise global

Abstract

Habitat fragmentation may make landscapes drier and hotter due to increases in the amount of habitat edges. The process, however, can also reduce temperatures and raise humidity at the landscape-level, as described in the "vegetation breeze" phenomenon. The plausibility of these two alternative hypotheses is still unclear, since the magnitude of the effects of habitat fragmentation on climate has rarely been quantified. This is an important limitation, since habitat fragmentation can affect the structure of biological communities and ecosystems functioning. The objective of this study was to quantify, for the first time, the impacts of habitat fragmentation at the landscape-level climate on a global scale. Satellite data were obtained for forest cover (year 2000) and five climatic variables: daytime temperature, nighttime temperature, daily temperature (daytime and nighttime), albedo and evapotranspiration. The analyses were performed separately for each climatic region (tropical = 20° S-20° N, temperate = 20° S-50° S and 20° N-50° N, boreal &#8805; 50° S and &#8805; 50 ° N). Using a "moving window" approach, we compared pairs of landscapes with similar amount of forest cover (difference <5%), but different levels of fragmentation (number of forest patches). Each pair contained one relatively more fragmented (<10 patches) and one more continuous (>10 patches) landscape. We controlled the effect of altitude (<50m) and calculated the difference of each climatic variable between the cells of each pair of landscapes. We used path analysis to investigate the relationships between the variables. Habitat fragmentation has reduced daily and daytime temperatures in the three climatic regions across the world. On the other hand, the fragmentation reduced the nocturnal temperature in the tropics, but increased in the temperate and boreal regions. In all climatic regions, habitat fragmentation increases the contact area between the forest and the matrix, resulting in final cooling due to increased evapotranspiration, the distribution of moisture in the landscape, and turbulent air fluxes. In temperate and boreal regions, however, nocturnal warming is probably due to the reduction of the antagonistic effect of evapotranspiration on the albedo in forest patches. The results indicate an unexpected effect of habitat fragmentation on temperature on the landscape-level, bringing new theoretical implications on a global scale. For this reason, a new conceptual model was proposed to unify the effects of habitat fragmentation on both local and landscape scale