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Wildfire and fuel treatment effects on forest carbon dynamics in the western United States
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Sequestration of carbon (C) in forests has the potential to mitigate the effects of climate change by offsetting
future emissions of greenhouse gases. However, in dry temperate forests, wildfire is a natural disturbance
agent with the potential to release large fluxes of C into the atmosphere. Climate-driven
increases in wildfire extent and severity are expected to increase the risks of reversal to C stores and
affect the potential of dry forests to sequester C. In the western United States, fuel treatments that
successfully reduce surface fuels in dry forests can mitigate the spread and severity of wildfire, while
reducing both tree mortality and emissions from wildfire. However, heterogeneous burn environments,
site-specific variability in post-fire ecosystem response, and uncertainty in future fire frequency and
extent complicate assessments of long-term (decades to centuries) C dynamics across large landscapes.
Results of studies on the effects of fuel treatments and wildfires on long-term C retention across large
landscapes are limited and equivocal. Stand-scale studies, empirical and modeled, describe a wide range
of total treatment costs (12–116 Mg C ha1
) and reductions in wildfire emissions between treated and
untreated stands (1–40 Mg C ha1
). Conclusions suggest the direction (source, sink) and magnitude of
net C effects from fuel treatments are similarly variable (33 Mg C ha1 to +3 Mg C ha1
). Studies at large
spatial and temporal scales suggest that there is a low likelihood of high-severity wildfire events interacting
with treated forests, negating any expected C benefit from fuels reduction. The frequency, extent,
and severity of wildfire are expected to increase as a result of changing climate, and additional information
on C response to management and disturbance scenarios is needed improve the accuracy and usefulness
of assessments of fuel treatment and wildfire effects on C dynamics.
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The anatomy of predator–prey dynamics in a changing climate
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1. Humans are increasingly influencing global climate and regional predator assemblages,
yet a mechanistic understanding of how climate and predation interact to affect
fluctuations in prey populations is currently lacking.
2. Here we develop a modelling framework to explore the effects of different predation
strategies on the response of age-structured prey populations to a changing climate.
3. We show that predation acts in opposition to temporal correlation in climatic
conditions to suppress prey population fluctuations.
4. Ambush predators such as lions are shown to be more effective at suppressing
fluctuations in their prey than cursorial predators such as wolves, which chase down
prey over long distances, because they are more effective predators on prime-aged adults.
5. We model climate as a Markov process and explore the consequences of future
changes in climatic autocorrelation for population dynamics. We show that the presence
of healthy predator populations will be particularly important in dampening prey
population fluctuations if temporal correlation in climatic conditions increases in the
future.
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Animal Versus Wind Dispersal and the Robustness of Tree Species to Deforestation
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Studies suggest that populations of different species do not decline equally after habitat loss. However, empirical tests have been confined to fine spatiotemporal scales and have rarely included plants. Using data from 89,365 forest survey plots covering peninsular Spain, we explored, for each of 34 common tree species, the relationship between probability of occurrence and the local cover of remaining forest. Twenty-four species showed a significant negative response to forest loss, so that decreased forest cover had
a negative effect on tree diversity, but the responses of individual species were highly variable. Animal-dispersed species were less vulnerable to forest loss, with six showing positive responses to decreased forest cover. The results imply that plant-animal interactions help prevent the collapse of forest communities that suffer habitat destruction.
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Large in-stream wood studies: a call for common metrics
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During the past decade, research on large in-stream wood has expanded beyond North America’s Pacifi c Northwest
to diverse environments and has shifted toward increasingly holistic perspectives that incorporate processes of wood recruitment,
retention, and loss at scales from channel segments to entire watersheds. Syntheses of this rapidly expanding literature can be
facilitated by agreement on primary variables and methods of measurement. In this paper we address these issues by listing the
variables that we consider fundamental to studies of in-stream wood, discussing the sources of variability in their measurement,
and suggesting more consistency in future studies. We recommend 23 variables for all studies of in-stream wood, as well as
another 12 variables that we suggest for studies with more specifi c objectives. Each of these variables relates either to the size
and characteristics of in-stream wood, to the geomorphic features of the channel and valley, or to the ecological characteristics
of the riparian zone adjacent to the study reach. The variables were derived from an overview of those cited in the literature and
from our collective fi eld experiences.
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Landscape-scale carbon storage associated with beaver dams
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Beaver meadows form when beaver dams promote
prolonged overbank flooding and floodplain retention of
sediment and organic matter. Extensive beaver meadows form
in broad, low-gradient valley segments upstream from glacial
terminal moraines. Surveyed sediment volume and total
organic carbon content in beaver meadows on the eastern side
of Rocky Mountain National Park are extrapolated to create a
first-order approximation of landscape-scale carbon storage in
these meadows relative to adjacent uplands. Differences in
total organic carbon between abandoned and active beaver
meadows suggest that valley-bottom carbon storage has
declined substantially as beaver have disappeared and
meadows have dried. Relict beaver meadows represent ~8%
of total carbon storage within the landscape, but the value was
closer to 23% when beaver actively maintained wet meadows.
These changes reflect the general magnitude of cumulative
effects in heterotrophic respiration and organic matter
oxidation associated with historical declines in beaver
populations across the continent
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Carbon sequestration in the U.S. forest sector from 1990 to 2010
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From 1990 through 2005, the forest sector (including forests and wood products) sequestered an average 162 Tg C year1 . In 2005, 49% of the total forest sector sequestration was in live and dead trees, 27% was
in wood products in landfills, with the remainder in down dead wood, wood products in use, and forest floor and soil. The pools with the largest carbon stocks were not the same as those with the largest sequestration rates, except for the tree pool. For example, landfilled wood products comprise only 3% of total stocks but account for 27% of carbon sequestration. Conversely, forest soils comprise 48% of total stocks but account for only 2% of carbon sequestration. For the tree pool, the spatial pattern of carbon stocks was dissimilar to that of carbon flux. On an area basis, tree carbon stocks were highest in the Pacific Northwest, while changes were generally greatest in the upper Midwest and the Northeast. Net carbon sequestration in the forest sector in 2005 offset 10% of U.S. CO2 emissions. In the near future, we project that U.S. forests will continue to sequester carbon at a rate similar to that in recent years. Based on a comparison of our estimates to a compilation of land-based estimates of non-forest carbon sinks from the literature, we estimate that the conterminous U.S. annually sequesters 149–330 Tg C year1. Forests, urban trees, and wood products are responsible for 65–91% of this sink.
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A new, global, multi-annual (2000–2007) burnt area product at 1 km resolution Vol. 35
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This paper reports on the development and validation
of a new, global, burnt area product. Burnt areas are
reported at a resolution of 1 km for seven fire years (2000 to
2007). A modified version of a Global Burnt Area (GBA)
2000 algorithm is used to compute global burnt area. The
total area burnt each year (2000– 2007) is estimated to be
between 3.5 million km2 and 4.5 million km2
. The total
amount of vegetation burnt by cover type according to the
Global Land Cover (GLC) 2000 product is reported.
Validation was undertaken using 72 Landsat TM scenes
was undertaken. Correlation statistics between estimated
burnt areas are reported for major vegetation types. The
accuracy of this new global data set depends on vegetation
type.
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Animal migration amid shifting patterns of phenology and predation: lessons from a Yellowstone elk herd
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Migration is a striking behavioral strategy by which many animals enhance resource acquisition while reducing predation risk. Historically, the demographic benefits of such movements made migration common, but in many taxa the phenomenon is considered globally threatened. Here we describe a long-term decline in the productivity of elk (Cervus elaphus) that migrate through intact wilderness areas to protected summer ranges inside Yellowstone National Park, USA. We attribute this decline to a long-term reduction in the
demographic benefits that ungulates typically gain from migration. Among migratory elk, we observed a 21-year, 70% reduction in recruitment and a 4-year, 19% depression in their pregnancy rate largely caused by infrequent reproduction of females that were young or lactating. In contrast, among resident elk, we have recently observed increasing recruitment and a high rate of pregnancy. Landscape-level changes in habitat quality and predation appear to be responsible for the declining productivity of Yellowstone migrants. From 1989 to 2009, migratory elk experienced an increasing rate and shorter duration of green-up coincident with
warmer spring–summer temperatures and reduced spring precipitation, also consistent with observations of an unusually severe drought in the region. Migrants are also now exposed to four times as many grizzly bears (Ursus arctos) and wolves (Canis lupus) as resident elk. Both of these restored predators consume migratory elk calves at high rates in the Yellowstone wilderness but are maintained at low densities via lethal management and human disturbance in the year-round habitats of resident elk. Our findings suggest that large-carnivore recovery and drought, operating simultaneously along an elevation gradient, have disproportionately influenced the demography of migratory elk. Many migratory animals travel large geographic distances between their seasonal ranges. Changes in land use and climate that disparately
influence such seasonal ranges may alter the ecological basis of migratory behavior, representing an important challenge.
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LCC Coordinator is Invited Speaker at Tennessee Fish and Wildlife Commission Meeting
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