Prolonged tropical forest degradation due to compounding disturbances: Implications for CO and H O fluxes.

Drought, fire, and windstorms can interact to degrade tropical forests and the ecosystem services they provide, but how these forests recover after catastrophic disturbance events remains relatively unknown. Here, we analyze multi-year measurements of vegetation dynamics and function (fluxes of CO and H O) in forests recovering from 7 years of controlled burns, followed by wind disturbance. Located in southeast Amazonia, the experimental forest consists of three 50-ha plots burned annually, triennially, or not at all from 2004 to 2010.

Ecophysiological plasticity of Amazonian trees to long-term drought.

Episodic multi-year droughts fundamentally alter the dynamics, functioning, and structure of Amazonian forests. However, the capacity of individual plant species to withstand intense drought regimes remains unclear. Here, we evaluated ecophysiological responses from a forest community where we sampled 83 woody plant species during 5 years of experimental drought (throughfall exclusion) in an eastern Amazonian terra firme forest.

Abrupt increases in Amazonian tree mortality due to drought-fire interactions.

Interactions between climate and land-use change may drive widespread degradation of Amazonian forests. High-intensity fires associated with extreme weather events could accelerate this degradation by abruptly increasing tree mortality, but this process remains poorly understood. Here we present, to our knowledge, the first field-based evidence of a tipping point in Amazon forests due to altered fire regimes.

Dependence of hydropower energy generation on forests in the Amazon Basin at local and regional scales.

Tropical rainforest regions have large hydropower generation potential that figures prominently in many nations' energy growth strategies. Feasibility studies of hydropower plants typically ignore the effect of future deforestation or assume that deforestation will have a positive effect on river discharge and energy generation resulting from declines in evapotranspiration (ET) associated with forest conversion. Forest loss can also reduce river discharge, however, by inhibiting rainfall.

Testing the Amazon savannization hypothesis: fire effects on invasion of a neotropical forest by native cerrado and exotic pasture grasses.

Changes in climate and land use that interact synergistically to increase fire frequencies and intensities in tropical regions are predicted to drive forests to new grass-dominated stable states. To reveal the mechanisms for such a transition, we established 50 ha plots in a transitional forest in the southwestern Brazilian Amazon to different fire treatments (unburned, burned annually (B1yr) or at 3-year intervals (B3yr)). Over an 8-year period since the commencement of these treatments, we documented: (i) the annual rate of pasture and native grass invasion in response to increasing fire frequency; (ii) the establishment of Brachiaria decumbens (an African C4 grass) as a function of decreasing canopy cover and (iii) the effects of grass fine fuel on fire intensity.

Responding to climate change and the global land crisis: REDD+, market transformation and low-emissions rural development.

Climate change and rapidly escalating global demand for food, fuel, fibre and feed present seemingly contradictory challenges to humanity. Can greenhouse gas (GHG) emissions from land-use, more than one-fourth of the global total, decline as growth in land-based production accelerates? This review examines the status of two major international initiatives that are designed to address different aspects of this challenge. REDD+ is an emerging policy framework for providing incentives to tropical nations and states that reduce their GHG emissions from deforestation and forest degradation.

Defending public interests in private lands: compliance, costs and potential environmental consequences of the Brazilian Forest Code in Mato Grosso.

Land-use regulations are a critical component of forest governance and conservation strategies, but their effectiveness in shaping landholder behaviour is poorly understood. We conducted a spatial and temporal analysis of the Brazilian Forest Code (BFC) to understand the patterns of regulatory compliance over time and across changes in the policy, and the implications of these compliance patterns for the perceived costs to landholders and environmental performance of agricultural landscapes in the southern Amazon state of Mato Grosso. Landholdings tended to remain in compliance or not according to their status at the beginning of the study period.

Effects of high-frequency understorey fires on woody plant regeneration in southeastern Amazonian forests.

Anthropogenic understorey fires affect large areas of tropical forest, yet their effects on woody plant regeneration post-fire remain poorly understood. We examined the effects of repeated experimental fires on woody stem (less than 1 cm at base) mortality, recruitment, species diversity, community similarity and regeneration mode (seed versus sprout) in Mato Grosso, Brazil. From 2004 to 2010, forest plots (50 ha) were burned twice (B2) or five times (B5), and compared with an unburned control (B0).

Comment on "The incidence of fire in Amazonian forests with implications for REDD".

Aragão and Shimabukuro (Reports, 4 June 2010, p. 1275) reported that fires increase in agricultural frontiers even as deforestation decreases and concluded that these fires lead to unaccounted carbon emissions under the United Nations climate treaty's tropical deforestation and forest degradation component. Emissions from post-deforestation management activities are, in fact, included in these estimates--but burning of standing forests is not.

Seasonal and interannual variability of climate and vegetation indices across the Amazon.

Drought exerts a strong influence on tropical forest metabolism, carbon stocks, and ultimately the flux of carbon to the atmosphere. Satellite-based studies have suggested that Amazon forests green up during droughts because of increased sunlight, whereas field studies have reported increased tree mortality during severe droughts. In an effort to reconcile these apparently conflicting findings, we conducted an analysis of climate data, field measurements, and improved satellite-based measures of forest photosynthetic activity.

Soil moisture depletion under simulated drought in the Amazon: impacts on deep root uptake.

*Deep root water uptake in tropical Amazonian forests has been a major discovery during the last 15 yr. However, the effects of extended droughts, which may increase with climate change, on deep soil moisture utilization remain uncertain. *The current study utilized a 1999-2005 record of volumetric water content (VWC) under a throughfall exclusion experiment to calibrate a one-dimensional model of the hydrologic system to estimate VWC, and to quantify the rate of root uptake through 11.

Drought effects on litterfall, wood production and belowground carbon cycling in an Amazon forest: results of a throughfall reduction experiment.

The Amazon Basin experiences severe droughts that may become more common in the future. Little is known of the effects of such droughts on Amazon forest productivity and carbon allocation. We tested the prediction that severe drought decreases litterfall and wood production but potentially has multiple cancelling effects on belowground production within a 7-year partial throughfall exclusion experiment.

Interactions among Amazon land use, forests and climate: prospects for a near-term forest tipping point.

Some model experiments predict a large-scale substitution of Amazon forest by savannah-like vegetation by the end of the twenty-first century. Expanding global demands for biofuels and grains, positive feedbacks in the Amazon forest fire regime and drought may drive a faster process of forest degradation that could lead to a near-term forest dieback. Rising worldwide demands for biofuel and meat are creating powerful new incentives for agro-industrial expansion into Amazon forest regions.

Mortality of large trees and lianas following experimental drought in an Amazon forest.

Severe drought episodes such as those associated with El Niño Southern Oscillation (ENSO) events influence large areas of tropical forest and may become more frequent in the future. One of the most important forest responses to severe drought is tree mortality, which alters forest structure, composition, carbon content, and flammability, and which varies widely. This study tests the hypothesis that tree mortality increases abruptly during drought episodes when plant-available soil water (PAW) declines below a critical minimum threshold.

Globalization of the Amazon soy and beef industries: opportunities for conservation.

Amazon beef and soybean industries, the primary drivers of Amazon deforestation, are increasingly responsive to economic signals emanating from around the world, such as those associated with bovine spongiform encephalopathy (BSE, "mad cow disease") outbreaks and China's economic growth. The expanding role of these economic "teleconnections" (coupled phenomena that take place in distant places on the planet) led to a 3-year period (2002-2004) of historically high deforestation rates. But it also increases the potential for large-scale conservation in the region as markets and finance institutions demand better environmental and social performance of beef and soy producers.

Modelling conservation in the Amazon basin.

Expansion of the cattle and soy industries in the Amazon basin has increased deforestation rates and will soon push all-weather highways into the region's core. In the face of this growing pressure, a comprehensive conservation strategy for the Amazon basin should protect its watersheds, the full range of species and ecosystem diversity, and the stability of regional climates. Here we report that protected areas in the Amazon basin--the central feature of prevailing conservation approaches--are an important but insufficient component of this strategy, based on policy-sensitive simulations of future deforestation.

Hydraulic redistribution in three Amazonian trees.

About half of the Amazon rainforest is subject to seasonal droughts of 3 months or more. Despite this drought, several studies have shown that these forests, under a strongly seasonal climate, do not exhibit significant water stress during the dry season. In addition to deep soil water uptake, another contributing explanation for the absence of plant water stress during drought is the process of hydraulic redistribution; the nocturnal transfer of water by roots from moist to dry regions of the soil profile.

Rainfall exclusion in an eastern Amazonian forest alters soil water movement and depth of water uptake.

Deuterium-labeled water was used to study the effect of the Tapajós Throughfall Exclusion Experiment (TTEE) on soil moisture movement and on depth of water uptake by trees of Coussarea racemosa, Sclerolobium chrysophyllum, and Eschweilera pedicellata. The TTEE simulates an extended dry season in an eastern Amazonian rainforest, a plausible scenario if the El Niño phenomenon changes with climate change. The TTEE excludes 60% of the wet season throughfall from a 1-ha plot (treatment), while the control 1-ha plot receives precipitation year-round.