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Drought Sensitivity of the Amazon Rainforest
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Amazon forests are a key but poorly understood component of the global carbon cycle. If, as
anticipated, they dry this century, they might accelerate climate change through carbon losses and
changed surface energy balances. We used records from multiple long-term monitoring plots across
Amazonia to assess forest responses to the intense 2005 drought, a possible analog of future events.
Affected forest lost biomass, reversing a large long-term carbon sink, with the greatest impacts
observed where the dry season was unusually intense. Relative to pre-2005 conditions, forest subjected
to a 100-millimeter increase in water deficit lost 5.3 megagrams of aboveground biomass of carbon per
hectare. The drought had a total biomass carbon impact of 1.2 to 1.6 petagrams (1.2 × 1015 to
1.6 × 1015 grams). Amazon forests therefore appear vulnerable to increasing moisture stress, with the
potential for large carbon losses to exert feedback on climate change.
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Climate Science Documents
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Drought, disease, defoliation and death: forest pathogens as agents of past vegetation change
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The temperate and boreal forests of Europe and North America have been subject to repeated pathogen (fungal disease and phytophagus insect) outbreaks over the last 100 years. Palaeoecology can, potentially, offer a long-term perspective on such disturbance episodes, providing information on their triggers, frequency and impact. Mid-Holocene declines in Tsuga and Ulmus pollen dominate the Quaternary literature on forest pathogens, yet the role of pathogens, and even the presence of pathogenic fungal diseases, during these events has yet to be established. Pathogen-focused research strategies, informed by the sequence of events documented in modern outbreaks, and undertaken at high temporal resolution using a multi-proxy approach, are required. It is argued that forest pathogens are likely to have been significant agents of past vegetation change, even in cases where climate change was the primary stress factor.
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Climate Science Documents
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Drought’s legacy: multiyear hydraulic deterioration underlies widespread aspen forest die-off and portends increased future risk
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Forest mortality constitutes a major uncertainty in projections of climate impacts on terrestrial ecosystems and car- bon-cycle feedbacks. Recent drought-induced, widespread forest die-offs highlight that climate change could acceler- ate forest mortality with its diverse and potentially severe consequences for the global carbon cycle, ecosystem services, and biodiversity. How trees die during drought over multiple years remains largely unknown and pre- cludes mechanistic modeling and prediction of forest die-off with climate change. Here, we examine the physiological basis of a recent multiyear widespread die-off of trembling aspen (Populus tremuloides) across much of western North America. Using observations from both native trees while they are dying and a rainfall exclusion experiment on mature trees, we measure hydraulic performance over multiple seasons and years and assess pathways of accumu- lated hydraulic damage. We test whether accumulated hydraulic damage can predict the probability of tree survival over 2 years. We find that hydraulic damage persisted and increased in dying trees over multiple years and exhibited few signs of repair. This accumulated hydraulic deterioration is largely mediated by increased vulnerability to cavita- tion, a process known as cavitation fatigue. Furthermore, this hydraulic damage predicts the probability of interyear stem mortality. Contrary to the expectation that surviving trees have weathered severe drought, the hydraulic deteri- oration demonstrated here reveals that surviving regions of these forests are actually more vulnerable to future droughts due to accumulated xylem damage. As the most widespread tree species in North America, increasing vul- nerability to drought in these forests has important ramifications for ecosystem stability, biodiversity, and ecosystem carbon balance. Our results provide a foundation for incorporating accumulated drought impacts into climate–vege- tation models. Finally, our findings highlight the critical role of drought stress accumulation and repair of stress- induced damage for avoiding plant mortality, presenting a dynamic and contingent framework for drought impacts on forest ecosystems.
Keywords: biosphere–atmosphere interactions, climate change, ecosystem shift, forest mortality, vegetation model, xylem cavitation, dieoff
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Eastern Forest Environmental Threat Assessment Center
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The Eastern Forest Environmental Threat Assessment Center is an interdisciplinary resource that is actively developing new technology and tools to anticipate and respond to emerging eastern forest threats.
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GIS & Planning
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Other Conservation & Planning Tools
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Eastern Forest Environmental Threat Assessment Center
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The Eastern Forest Environmental Threat Assessment Center is an interdisciplinary resource that is actively developing new technology and tools to anticipate and respond to emerging eastern forest threats.
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Planning In Practice
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Conservation Planning Projects
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Eastern redcedar burning tips
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Landowners and forest managers are welcomed to learn about how to clear and Eastern redcedar and maintain their lands and forests with prescribed burns.
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Training
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Videos, podcasts, multimedia
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Ecologists Report Huge Storm Losses in China’s Forests
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From delicate orchids and magnolias to rare Chinese yews and Kwangtung pines, the flora of Guangdong
Nanling National Nature Reserve is considered so precious that ecologists call the reserve “a treasure trove of species.” But winter storms have reduced the biological hot spot to a splintered ruin. Snow, sleet, and ice laid waste to 90% of the 58,000- hectare reserve’s forests, says He Kejun, director of Guangdong Forestry
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Climate Science Documents
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Ecosystem carbon stocks and sequestration potential of federal lands across the conterminous United States
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Federal lands across the conterminous United States (CONUS) account for 23.5% of the CONUS terrestrial area but have received no systematic studies on their ecosystem carbon (C) dynamics and contribution to the national C budgets. The methodology for US Congress-mandated national biological C sequestration potential assessment was used to evaluate ecosystem C dynamics in CONUS federal lands at present and in the future under three Intergovernmental Panel on Climate Change Special Report on Emission Scenarios (IPCC SRES) A1B, A2, and B1. The total ecosystem C stock was estimated as 11,613 Tg C in 2005 and projected to be 13,965 Tg C in 2050, an average increase of 19.4% from the baseline. The projected annual C sequestration rate (in kilograms of carbon per hectare per year) from 2006 to 2050 would be sinks of 620 and 228 for forests and grasslands, respectively, and C sources of 13 for shrublands. The federal lands’ contribution to the national ecosystem C budget could decrease from 23.3% in 2005 to 20.8% in 2050. The C sequestration potential in the future depends not only on the footprint of individual ecosystems but also on each federal agency’s land use and management. The results presented here update our current knowledge about the baseline ecosystem C stock and sequestration potential of federal lands, which would be useful for federal agencies to decide management practices to achieve the national greenhouse gas (GHG) mitigation goal.
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Ecosystem Disturbance, Carbon, and Climate
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Models of climate change effects should incorporate land-use changes and episodic disturbances such as fires and insect epidemics.
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Climate Science Documents
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Effect of per-capita land use changes on Holocene forest clearance and CO2 emissions
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The centerpiece of the early anthropogenic hypothesis is the claim that humans took control of greenhouse-gas trends thousands of years ago because of emissions from early agriculture (Ruddiman, 2003, 2007). A common reaction to this claim is that too few people lived thousands of years ago to have had a major effect on either land use or greenhouse-gas concentrations. Implicit in this view is the notion that per-capita land clearance has changed little for millennia, but numerous field studies have shown that early per-capita land use was large and then declined as increasing population density led to more intensive farming. Here we explore the potential impact of changing per-capita land use in recent millennia and conclude that greater clearance by early agriculturalists could have had a disproportionately large impact on CO2 emissions.
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Climate Science Documents
