-
Regional vegetation die-off in response to global-change-type drought
-
uture drought is projected to occur under warmer temperature conditions as climate change progresses, referred to here as global- change-type drought, yet quantitative assessments of the triggers and potential extent of drought-induced vegetation die-off remain pivotal uncertainties in assessing climate-change impacts. Of par- ticular concern is regional-scale mortality of overstory trees, which rapidly alters ecosystem type, associated ecosystem properties, and land surface conditions for decades. Here, we quantify region- al-scale vegetation die-off across southwestern North American woodlands in 2002–2003 in response to drought and associated bark beetle infestations. At an intensively studied site within the region, we quantified that after 15 months of depleted soil water content, >90% of the dominant, overstory tree species (Pinus edulis, a pin ̃on) died. The die-off was reflected in changes in a remotely sensed index of vegetation greenness (Normalized Dif- ference Vegetation Index), not only at the intensively studied site but also across the region, extending over 12,000 km2 or more; aerial and field surveys confirmed the general extent of the die-off. Notably, the recent drought was warmer than the previous sub- continental drought of the 1950s. The limited, available observa- tions suggest that die-off from the recent drought was more extensive than that from the previous drought, extending into wetter sites within the tree species’ distribution. Our results quantify a trigger leading to rapid, drought-induced die-off of overstory woody plants at subcontinental scale and highlight the potential for such die-off to be more severe and extensive for future global-change-type drought under warmer conditions.
tree mortality vegetation dynamics climate change impacts woodlands Pinus edulis
Located in
Resources
/
Climate Science Documents
-
Vegetation synchronously leans upslope as climate warms
-
Ecologists have long sought to understand how vegetation re- lates to climate (1, 2). Such knowledge underlies effective mitigation and adaptation to contempo- rary climate change (3). Warming tem- peratures associated with anthropogenic increases in greenhouse gases have led ecologists to predict that vegetation gra- dients will ‘‘march’’ up the hill as cli- mate envelopes shift with elevation, at a lag that scales with species’ generation times (4, 5). This prediction derives from the hypothesis that low-temperature constraints relax in association with warming climate, resulting in more fa- vorable conditions for establishment and growth at the leading edge of a species’ range (e.g., the upper elevation bound- ary on a mountain) (6, 7). Because of competition and change in plant-available water, the trailing edge is expected to track the leading edge (5) with the cen- tral tendency expected to concurrently ‘‘march’’ upslope. This type of response has important implications for predict- ing and mitigating climate change impacts, particularly for vegetation span- ning elevation gradients. If, rather than collectively moving with climate change, responses of dominant species assem- bled along an elevation gradient are highly individualistic, there is greater potential for more novel, nonanalog veg- etation assemblages.
Located in
Resources
/
Climate Science Documents
-
Global evidence that deforestation amplifies flood risk and severity in the developing world
-
With the wide acceptance of forest-protection policies in the developing world comes a requirement for clear demonstrations of how deforestation may erode human well-being and economies. For centuries, it has been believed that forests provide protection against flooding. However, such claims have given rise to a heated polemic, and broad-scale quantitative evidence of the possible role of forests in flood protection has not been forthcoming. Using data collected from 1990 to 2000 from 56 developing countries, we show using generalized linear and mixed-effects models contrasted with information- theoretic measures of parsimony that flood frequency is negatively correlated with the amount of remaining natural forest and positively correlated with natural forest area loss (after controlling for rainfall, slope and degraded landscape area). The most parsimo- nious models accounted for over 65% of the variation in flood frequency, of which nearly 14% was due to forest cover variables alone. During the decade investigated, nearly 100 000 people were killed and 320 million people were displaced by floods, with total reported economic damages exceeding US$1151 billion. Extracted measures of flood severity (flood duration, people killed and displaced, and total damage) showed some weaker, albeit detectable correlations to natural forest cover and loss. Based on an arbitrary decrease in natural forest area of 10%, the model-averaged prediction of flood frequency increased between 4% and 28% among the countries modeled. Using the same hypothetical decline in natural forest area resulted in a 4–8% increase in total flood duration. These correlations suggest that global-scale patterns in mean forest trends across countries are meaningful with respect to flood dynamics. Unabated loss of forests may increase or exacerbate the number of flood-related disasters, negatively impact millions of poor people, and inflict trillions of dollars in damage in disadvantaged economies over the coming decades. This first global-scale empirical demonstration that forests are correlated with flood risk and severity in developing countries reinforces the imperative for large-scale forest protection to protect human welfare, and suggests that reforestation may help to reduce the frequency and severity of flood-related catastrophes.
Keywords: conservation, damage, flooding events, forest loss, generalized linear mixed-effects models, generalized linear models, human displacement, projected costs, rainfall
Located in
Resources
/
Climate Science Documents
-
Thriving Arctic Bottom Dwellers Could Get Strangled by Warming
-
Many biologists hypothesize that climate change could hurt the Arctic benthos and the large creatures that live off it by wiping out ice (and hence ice algae), lengthening growing seasons for zooplankton, and giving warm- water species a foothold. “The way the system works now is very much in favor of the benthos,” says UAF polar ecologist Rolf Gradinger. “If the sys- tem changes, things could go downhill fast.”
Located in
Resources
/
Climate Science Documents
-
The Evolution and Distribution of Species Body Size
-
The distribution of species body size within taxonomic groups exhibits a heavy right tail extending over many orders of magnitude, where most species are much larger than the smallest species. We provide a simple model of cladogenetic diffusion over evolutionary time that omits explicit mechanisms for interspecific competition and other microevolutionary processes, yet fully explains the shape of this distribution. We estimate the model’s parameters from fossil data and find that it robustly reproduces the distribution of 4002 mammal species from the late Quaternary. The observed fit suggests that the asymmetric distribution arises from a fundamental trade-off between the short-term selective advantages (Cope’s rule) and long-term selective risks of increased species body size in the presence of a taxon-specific lower limit on body size
Located in
Resources
/
Climate Science Documents
-
Grassland Vegetation Changes and Nocturnal Global Warming
-
Global minimum temperatures (TMIN) are increasing faster than maximum temperatures, but the ecological consequences of this are largely unexplored. Long-term data sets from the shortgrass steppe were used to identify corre- lations between TMIN and several vegetation variables. This ecosystem is po- tentially sensitive to increases in TMIN. Most notably, increased spring TMIN was correlated with decreased net primary production by the dominant C4 grass (Bouteloua gracilis) and with increased abundance and production by exotic and native C3 forbs. Reductions in B. gracilis may make this system more vulnerable to invasion by exotic species and less tolerant of drought and grazing.
Located in
Resources
/
Climate Science Documents
-
Integrating multiple lines of evidence into historical biogeography hypothesis testing: a Bison bison case study
-
One of the grand goals of historical biogeography is to understand how and why species’ population sizes and distributions change over time. Multiple types of data drawn from disparate fields, combined into a single modelling framework, are necessary to document changes in a species’s demography and distribution, and to determine the drivers responsible for change. Yet truly integrated approaches are challenging and rarely performed. Here, we discuss a modelling framework that integrates spatio-temporal fossil data, ancient DNA, palaeoclimatological reconstruc- tions, bioclimatic envelope modelling and coalescence models in order to statistically test alternative hypotheses of demographic and potential distri- butional changes for the iconic American bison (Bison bison). Using different assumptions about the evolution of the bioclimatic niche, we generate hypothetical distributional and demographic histories of the species. We then test these demographic models by comparing the genetic signature pre- dicted by serial coalescence against sequence data derived from subfossils and modern populations. Our results supported demographic models that include both climate and human-associated drivers of population declines. This synthetic approach, integrating palaeoclimatology, bioclimatic envel- opes, serial coalescence, spatio-temporal fossil data and heterochronous DNA sequences, improves understanding of species’ historical biogeography by allowing consideration of both abiotic and biotic interactions at the population level
Located in
Resources
/
Climate Science Documents
-
Global Biodiversity Conservation and the Alleviation of Poverty
-
Poverty and biodiversity loss are two of the world’s dire challenges. Claims of conservation’s contribution to poverty alleviation, however, remain controversial. Here, we assess the flows of ecosystem services provided to people by priority habitats for terrestrial conservation, considering the global distributions of biodiversity, physical factors, and socioeconomic context. We estimate the value of these habitats to the poor, both through direct benefits and through payments for ecosystem services to those stewarding natural habitats. The global potential for biodiversity conservation to support poor communities is high: The top 25% of conservation priority areas could provide 56%–57% of benefits. The aggregate benefits are valued at three times the estimated opportunity costs and exceed $1 per person per day for 331 million of the world’s poorest people. Although trade-offs remain, these results show win–win synergies between conservation and poverty alleviation, indicate that effective financial mecha- nisms can enhance these synergies, and suggest biodiversity conservation as a fundamental component of sustainable economic development.
Keywords: ecosystem service flows, poverty alleviation, biodiversity conservation priorities, natural capital, valuation
Located in
Resources
/
Climate Science Documents
-
The bigger they come, the harder they fall: body size and prey abundance influence predator −prey ratios
-
Large carnivores are highly threatened, yet the processes underlying their population declines are still poorly understood and widely debated. We explored how body mass and prey abundance influence carnivore density using data on 199 populations obtained across multiple sites for 11 carnivore species. We found that relative decreases in prey abundance resulted in a five- to sixfold greater decrease in the largest carnivores compared with the smallest species. We discuss a number of possible causes for this inherent vulnerability, but also explore a possible mechanistic link between predator size, ener- getics and population processes. Our results have important implications for carnivore ecol- ogy and conservation, demonstrating that larger species are particularly vulnerable to anthropo- genic threats to their environment, especially those which have an adverse affect on the abundance of their prey.
Keywords: carnivore ecology; predator–prey relationships; abundance scaling; climate change; metabolism
Located in
Resources
/
Climate Science Documents
-
Predicting ecosystem shifts requires new approaches that integrate the effects of climate change across entire systems
-
Most studies that forecast the ecological conse- quences of climate change target a single species and a single life stage. Depending on climatic impacts on other life stages and on interacting species, however, the results from simple exper- iments may not translate into accurate predictions of future ecological change. Research needs to move beyond simple experimental studies and environmental envelope projections for single species towards identifying where ecosystem change is likely to occur and the drivers for this change. For this to happen, we advocate research directions that (i) identify the critical species within the target ecosystem, and the life stage(s) most susceptible to changing conditions and (ii) the key interactions between these species and components of their broader ecosystem. A combined approach using macroecology, experimentally derived data and modelling that incorporates energy budgets in life cycle models may identify critical abiotic conditions that disproportionately alter important ecological processes under forecasted climates.
Keywords: climate change; ocean acidification; global warming; species interactions; ecosystem shift; productivity and consumption
Located in
Resources
/
Climate Science Documents
