Long-term variation in Amazon forest dynamics

Laurance, Susan G.W., Laurance, William F., Nascimento, Henrique E.M., Andrade, Ana, Fearnside, Phillip M., Rebello, Expedito R.G., and Condit, Richard (2009) Long-term variation in Amazon forest dynamics. Journal of Vegetation Science, 20 (2). pp. 323-333.

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Questions: Have forest dynamics changed significantly in intact Amazon rainforests since the early 1980s? If so, what environmental drivers might potentially be responsible?

Location: Central Amazonia, north of Manaus, Brazil.

Methods: Within 20 1-ha plots scattered over ∼300 km², all trees (≥10 cm diameter at breast height) were marked, identified, and measured five times between 1981 and 2003. We estimated stand-level dynamics (mortality, recruitment, and growth) for each census interval and evaluated weather parameters over the study period.

Results: We observed a widespread, significant increase in tree mortality across our plots. Tree recruitment also rose significantly over time but lagged behind mortality. Tree growth generally accelerated but varied considerably among census intervals, and was lowest when mortality was highest. Tree basal area rose 4% overall, but stem number exhibited no clear trend. In terms of climate variation, annual maximum and minimum temperatures increased significantly during our study. Rainfall anomalies were strongly and positively associated with ENSO events.

Conclusions: The increasing forest dynamics, growth, and basal area observed are broadly consistent with the CO₂ fertilization hypothesis. However, pronounced shorter-term variability in stand dynamics might be associated with climatic vicissitudes. Tree mortality peaked, and tree recruitment and growth declined during atypically wet periods. Tree growth was fastest during dry periods, when reduced cloudiness might have increased available solar radiation. Inferences about causality are tenuous because tree data were collected only at multi-year intervals. Mean temperatures and rainfall seasonality have both increased over time in central Amazonia, and these could potentially have long-term effects on forest dynamics and carbon storage.

Item ID: 23662
Item Type: Article (Research - C1)
ISSN: 1654-1103
Keywords: Amazon; climatic trends; El Niño; forest dynamics; permanent plots; rainforest; tree growth; tree mortality; tree recruitment; tropical forests; weather variation
Funders: NASA-LBA, A. W. Mellon Foundation, US National Science Foundation
Projects and Grants: Biological Dynamics of Forest Fragments Project
Date Deposited: 17 Oct 2012 06:17
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060299 Ecology not elsewhere classified @ 30%
05 ENVIRONMENTAL SCIENCES > 0501 Ecological Applications > 050102 Ecosystem Function @ 20%
05 ENVIRONMENTAL SCIENCES > 0501 Ecological Applications > 050101 Ecological Impacts of Climate Change @ 50%
SEO Codes: 96 ENVIRONMENT > 9603 Climate and Climate Change > 960310 Global Effects of Climate Change and Variability (excl. Australia, New Zealand, Antarctica and the South Pacific) @ 100%
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