Effects of forest fragmentation on the biomass of tropical forests

Abstract

The edge effect promotes microclimate changes that increase the mortality of large trees - i.e., individuals typical of advanced stages of succession - and the density of pioneer species. Thus, the edge effect leads to the process of "retrograde succession" during which the vegetation is simplified in structure and composition, leading to fragments dominated by pioneer species. This proliferation of pioneer species does not compensate for the loss of biomass caused by the mortality of large trees, which are the major biomass stocks in forests. Forests are among the most important carbon stocks and also the main targets of deforestation in the world. Due to the high rates of deforestation and fragmentation of tropical forests this study aims to determine the extent of the biomass collapse in tropical forest remnants. We performed a systematic review of the literature to assess the edge effect's impact on the vegetation biomass of tropical forest. The limited number of studies (N=9) did not allow us to establish the role of edges in determining biomass stocks. Thus, we proposed a conceptual model connecting spatial configuration and composition on biomass amount and a practical guide to test it. With this, we formulated two chapters to test our conceptual model. In one of the chapters we will determine the local factors that affect biomass stocks using collected data from Atlantic and Amazonian forests. We will evaluate how edge's distance, multiple edges and time since edge formation affect plant biomass and biomass by functional groups (based on regeneration strategy). In the other chapter we will test how landscape factors impact plant biomass and biomass by functional groups from Atlantic Forest. Associating secondary data with satellite images we will determine the focal landscapes and then calculate the metrics of the spatial composition (matrix type) and configuration (habitat amount, declivity and altitude). Thus, this study will be important to determine the extent of the collapse of biomass in tropical forests. Moreover, our results would allow the identification of which landscape configuration is favorable to the preservation of this essential ecosystem service.