Does the disturbance hypothesis explain the biomass increase in basin‐wide Amazon forest plot data?

4 de setembro de 2009

set 4, 2009

Manuel Gloor, Oliver Phillips, J. J. Lloyd, S. L. Lewis, Y. Malh, T. R. Baker, G. López‐Gonzalez, J. Peacock, S. Almeida A. C. Alves De Oliveira E. Alvarez I. Amaral L. Arroyo G. Aymard O. Banki L. Blanc D. Bonal P. Brando, K.‐J. Chao, J. Chave, N. Dávila, T. Erwin, J. Silva, A. Di Fiore, T. R. Feldpausch, A. Freitas, R. Herrera, N. Higuchi, E. Honorio, E. Jiménez, T. Killeen, W. Laurance, C. Mendoza, A. Monteagudo, A. Andrade, D. Neill, D. Nepstad, P. Núñez Vargas, M. C. Peñuela, A. Peña Cruz, A. Prieto, N. Pitman, C. Quesada, R. Salomão, Marcos Silveira, M. Schwarz, J. Stropp, F. Ramírez, H. Ramírez, A. Rudas, H. Ter Steege, N. Silva, A. Torres, J. Terborgh, R. Vásquez, G. Van Der Heijden

Positive aboveground biomass trends have been reported from old‐growth forests across the Amazon basin and hypothesized to reflect a large‐scale response to exterior forcing. The result could, however, be an artefact due to a sampling bias induced by the nature of forest growth dynamics. Here, we characterize statistically the disturbance process in Amazon old‐growth forests as recorded in 135 forest plots of the RAINFOR network up to 2006, and other independent research programmes, and explore the consequences of sampling artefacts using a data‐based stochastic simulator.

Over the observed range of annual aboveground biomass losses, standard statistical tests show that the distribution of biomass losses through mortality follow an exponential or near‐identical Weibull probability distribution and not a power law as assumed by others. The simulator was parameterized using both an exponential disturbance probability distribution as well as a mixed exponential–power law distribution to account for potential large‐scale blowdown events. In both cases, sampling biases turn out to be too small to explain the gains detected by the extended RAINFOR plot network. This result lends further support to the notion that currently observed biomass gains for intact forests across the Amazon are actually occurring over large scales at the current time, presumably as a response to climate change.

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Nota técnica – Amazônia em chamas

Nota técnica – Amazônia em chamas

O fogo é um elemento comum na paisagem rural brasileira. Usado para limpar áreas recém-desmatadas e outros tipos de terreno, como pasto, frequentemente escapa ao controle e queima o que não deveria queimar (Nepstad et al., 1999). Na Amazônia não é diferente. Sua incidência na região está diretamente relacionada à ação humana e as chamas costumam seguir o rastro do desmatamento: quanto mais derrubada, maior o número de focos de calor.