Vegetation‐atmosphere‐soil nutrient feedbacks in the Amazon for different deforestation scenarios

Abstract

[1] In recent decades, large areas of the Amazon forest have been deforested and the rainforest's future may be dependent on climate and soil nutrient feedbacks associated with deforestation. This is a two-way biosphere-atmosphere interaction problem: the response of the regional climate system to the land cover varies with the forest growth, which, in turn, depends on climate and nutrient stress. Nutrient stress also varies with forest age, being most severe for young forests and declining as forests mature. Here we use a coupled climate-biosphere model to investigate how these feedbacks interact to control the secondary forest recovery after different deforestation scenarios, looking for a threshold of deforestation that could cause dangerous interference on the Amazon recovery. Results show that the reduction in rainfall is proportional to the amount of deforestation and is more drastic when the deforested area is higher than 40% of the original forest extent. In addition, this simulated precipitation reduction alone is not sufficient to prevent the rainforest regrowth. However, when the precipitation reduction is associated with a soil nutrient stress, a savannization process may start over southern Amazonia (northern Mato Grosso state), no matter how much is deforested. In this region, a large precipitation reduction in the transition from the dry to the rainy season and an increase in the dry season duration are favorable to the savanna maintenance on nutrient-limited simulations. These results may be a valuable tool for prioritizing forest conservation in this region, which presently has the highest clearing rate in Amazonia.

Modeling the impact of net primary production dynamics on post-disturbance Amazon savannization

“…For a dynamic nutrient stress, the NPP was reduced according to an empirical relation that reflects a NPP decrease of 50% for trees biomass equal to zero, and no NPP decrease when the trees biomass reaches 10 kg-C m -2 or more (typical values of a mature forest). This assumption reproduced the capacity of the secondary forest to rebuild nutrient stocks in mature stages (Davidson et al 2007, Senna et al 2009a, considering a smaller magnitude of human pressures than the previous scenario. CCM3-IBIS was calibrated against Large Scale Biosphere-Atmosphere Experiment in Amazonia (LBA) tower results, and extensively validated against spatial fields of incident solar radiation, precipitation, land cover patterns, heterotrophic and root respiration, total NPP, aboveground NPP, wood NPP, leaf area index, and aboveground live biomass.…”

“…The Amazon helps fuel the Hadley and Walker circulations in the tropical atmosphere. Several climate modeling experiments indicate that as deforestation increases, the subsequent reductions in evapotranspiration and atmospheric heating may weaken moisture recycling and deep convection over the Amazon, thus lowering precipitation (Shukla et al 1990, Nobre et al 1991, Sampaio et al 2007, Senna et al 2009a.…”

“…Here, we investigate how the climate feedback and the nutrient feedback may affect the Amazon rainforest regrowth after a full deforestation. In a previous study (Senna et al 2009a), we evaluated these feedbacks considering a gradual deforestation, however the nutrient limitation due to frequent fires was not considered. The fire feedback is not directly included in this study, but it is indirectly considered by a scenario that constantly penalizes the NPP of the regrowth forest.…”

Representação Dos Padrões Atmosféricos Relacionados À Zona De Convergência Do Atlântico Sul Através De Um Modelo Acoplado Atmosfera-Biosfera

“…Nos últimos anos o CCM3-IBIS foi recalibrado usando dados do experimento LBA (Experimento de Grande Escala da Biosfera-Atmosfera na Amazônia) e de sensoriamento remoto. Sendo testado extensivamente em cenários de clima atual e futuro, como é possível observar nos trabalhos de Pereira (2006), Yanagi (2006), Senna et al (2009), e Senna et al (2009b.…”

Impacto Do Aumento Da Concentração Atmosférica De Co2 No Balanço Hídrico Climatológico Do Cerrado

“…Desta forma, faz-se necessário avaliar a intensidade destas mudanças, prevendo assim, cenários possíveis e futuros que mostrarão que tipos de problemas serão enfrentados em virtude destas transformações. Pesquisas mostram que o cenário mais provável nas próximas décadas inclui modificações intensas no meio ambiente global, principalmente o aumento da concentração atmosférica de CO2 proveniente das ações antrópicas (COSTA et al, 2009). …”