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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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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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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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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.
20
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When It Rains, It Pours Global Warming and the Increase in Extreme Precipitation from 1948 to 2011
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Global warming is happening now and
its effects are being felt in the United
States and around the world. Among
the expected consequences of global warming
is an increase in the heaviest rain and
snow storms, fueled by increased evaporation
and the ability of a warmer atmosphere
to hold more moisture.
An analysis of more than 80 million daily
precipitation records from across the contiguous
United States reveals that intense
rainstorms and snowstorms have already
become more frequent and more severe.
Extreme downpours are now happening
30 percent more often nationwide than
in 1948. In other words, large rain or
snowstorms that happened once every
12 months, on average, in the middle of
the 20th century now happen every nine
months. Moreover, the largest annual
storms now produce 10 percent more
precipitation, on average.
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Projections of Future Drought in the Continental United States and Mexico
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Using the Palmer drought severity index, the ability of 19 state-of-the-art climate models to reproduce observed
statistics of drought over North America is examined. It is found that correction of substantial biases in
the models’ surface air temperature and precipitation fields is necessary. However, even after a bias correction,
there are significant differences in the models’ ability to reproduce observations. Using metrics based on the
ability to reproduce observed temporal and spatial patterns of drought, the relationship between model performance
in simulating present-day drought characteristics and their differences in projections of future drought
changes is investigated. It is found that all models project increases in future drought frequency and severity.
However, using the metrics presented here to increase confidence in the multimodel projection is complicated
by a correlation between models’ drought metric skill and climate sensitivity. The effect of this sampling error
can be removed by changing how the projection is presented, from a projection based on a specific time interval
to a projection based on a specified temperature change. This modified class of projections has reduced
intermodel uncertainty and could be suitable for a wide range of climate change impacts projections.
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Safe Havens, Safe Passages for Vulnerable Fish and Wildlife
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Some of the best-known and most-cherished mountains on Earth are set in the
Canadian Rockies of British Columbia and Alberta. Indeed, the mention of
Banff, Jasper, Kootenay or Yoho National Parks evokes images of snow-capped
peaks, thundering falls and turquoise waters, numerous natural wonders and
majestic wildlife. The adjoining Provincial Parks in British Columbia – Mount
Robson, Mount Assiniboine, and Hamber – are just as spectacular, if not quite
as renowned. Waterton Lakes National Park in Alberta and Glacier National
Park in Montana – brought together in 1931 as an International Peace Park by
the respective Rotary Clubs – exemplify international cooperation and wilderness
and wildlife without borders. All 9 of these parks have been designated as
World Heritage Sites in recognition of their outstanding natural importance to
the common heritage of humanity.
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Spatial patterns and policy implications for residential water use
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The front yard makes a powerful visual statement about the
occupants of the residence. As visible statements, yards are likely
to induce a behavioral response on the part of neighboring
residents. As an example, residents may strive to keep their
yard as green and lush as their neighbors. For Kelowna, British
Columbia, a highly significant positive spatial lag for summer
water use implies some degree of spatial emulation in water using
behavior. Other variables such as lot size, building size, assessed
value, presence of a pool, etc. impact on water use as expected. The
presence of a spatial lag implies a spatial multiplier for water
saving innovations. If local water managers and policy makers can
influence the spatial pattern of water saving innovations, they may be
able to increase the size of the multiplier effect. Similar spatial policies
may also be applicable to other socially influenced behaviors that
leave a spatial signature, such as protecting ecologically significant
habitats in urban areas
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Slowly Warming
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A chart about global Warming
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How Much More Rain Will Global Warming Bring?
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Climate models and satellite observations both indicate that the total amount of water in the
atmosphere will increase at a rate of 7% per kelvin of surface warming. However, the climate
models predict that global precipitation will increase at a much slower rate of 1 to 3% per kelvin. A
recent analysis of satellite observations does not support this prediction of a muted response of
precipitation to global warming. Rather, the observations suggest that precipitation and total
atmospheric water have increased at about the same rate over the past two decades.
SCIENCE VOL 317 13 JULY 2007
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