Springer 2006
Landscape Ecology (2006) 21:1061–1073 DOI 10.1007/s10980-006-6913-0
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Research Article
Thresholds in landscape structure for three common deforestation patterns in the Brazilian Amazon Francisco Jose´ Barbosa de Oliveira Filho and Jean Paul Metzger* Department of Ecology – Bioscience Institute, University of Sa˜o Paulo, Rua do Matao, 321, travessa 14, 05508–900 Sao Paulo, SP, Brazil; *Author for correspondence (e-mail:
[email protected]) Received 30 May 2005; accepted in revised form 20 January 2006
Key words: Brazilian Amazon, Connectivity, Deforestation patterns, Fragmentation, Landscape dynamics, Structural threshold, Tropical forests
Abstract Although abrupt changes (i.e. thresholds) have been precisely defined in simulated landscapes, such changes in the structure of real landscapes are not well understood. We tested for threshold occurrence in three common deforestation patterns in the Brazilian Amazon: small properties regularly distributed along roads (fishbone), irregularly distributed small properties (independent settlements), and large properties. We analyzed differences between real deforestation patterns, and tested the capacity of simulated landscape with different aggregation degrees to predict threshold occurrence. Three 8 · 8 km sites (replicates) with more than 90% of forest in 1984 and less than 30% in 1998 were selected/simulated for each deforestation pattern. Thresholds were observed for fishbone and large property patterns, especially when considering the connectivity index, although threshold incidences were more frequently observed in simulated landscapes. The capacity of simulated landscapes to predict the exact threshold point in real landscapes was limited, even when considering highly aggregate simulations. However, the general trend in landscape structural changes was similar in real and simulated landscapes. Thresholds occurred at the beginning of the deforestation for mean patch size and at an intermediate stage, corresponding to the percolation threshold, for connectivity, isolation and fragmentation. Threshold behavior for connectivity index might suggest that the survival of strictly forest species will sharply decrease when the proportion of forest reach values
