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Understanding Soil Time
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Efforts to maintain soils in a sustainable
manner are complicated by interactions among
soil components that respond to perturbation
at vastly different rates.
VOL 321 SCIENCE
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The influence of conversion of forest types on carbon sequestration and other ecosystem services in the South Central United States
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This paper develops a forestland management model for the three states in the South Central United States (Arkansas,
Louisiana, and Mississippi). Forest type and land-use shares are estimated to be a function of economic and physical variables.
The results suggest that while historically pine plantations in this region have been established largely on old agricultural land,
in the future pine plantations are likely to occur on converted hardwood-forest lands. This shift in the supply of land for
plantations could have large effects on above-ground carbon storage and other ecosystem services. Subsidies of approximately
$12–27 per ha per year would maintain the area of hardwood forests and reduce carbon emissions from the above-ground and
product pool carbon stocks over the next 30 years. Across the several scenarios considered, results suggest that maintaining
hardwoods could be an efficient carbon sequestration alternative.
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The Historical Dynamics of Socio-ecological Traps
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Environmental degradation is a typical unintended
outcome of collective human behavior. Hardin’s
metaphor of the ‘‘tragedy of the commons’’ has become a
conceived wisdom that captures the social dynamics leading
to environmental degradation. Recently, ‘‘traps’’ has gained
currency as an alternative concept to explain the rigidity of
social and ecological processes that produce environmental
degradation and livelihood impoverishment. The trap metaphor
is, however, a great deal more complex compared to
Hardin’s insight. This paper takes stock of studies using the
trap metaphor. It argues that the concept includes time and
history in the analysis, but only as background conditions and
not as a factor of causality. From a historical–sociological
perspective this is remarkable since social–ecological traps
are clearly path-dependent processes, which are causally
produced through a conjunction of events. To prove this point
the paper conceptualizes social–ecological traps as a process
instead of a condition, and systematically compares history
and timing in one classic and three recent studies of social–
ecological traps. Based on this comparison it concludes that
conjunction of social and environmental events contributes
profoundly to the production of trap processes. The paper
further discusses the implications of this conclusion for policy
intervention and outlines how future research might generalize
insights from historical–sociological studies of traps.
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Impact of disturbed desert soils on duration of mountain snow cover
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Snow cover duration in a seasonally snow covered
mountain range (San Juan Mountains, USA) was found to
be shortened by 18 to 35 days during ablation through
surface shortwave radiative forcing by deposition of
disturbed desert dust. Frequency of dust deposition and
radiative forcing doubled when the Colorado Plateau, the
dust source region, experienced intense drought (8 events
and 39–59 Watts per square meter in 2006) versus a year
with near normal precipitation (4 events and 17–34 Watts
per square meter in 2005). It is likely that the current
duration of snow cover and surface radiation budget
represent a dramatic change from those before the
widespread soil disturbance of the western US in the late
1800s that resulted in enhanced dust emission. Moreover,
the projected increases in drought intensity and frequency
and associated increases in dust emission from the desert
southwest US may further reduce snow cover duration
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Linking climate change to lemming cycles
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The population cycles of rodents at northern latitudes have puzzled
people for centuries1,2
, and their impact is manifest throughout the
alpine ecosystem2,3
. Climate change is known to be able to drive
animal population dynamics between stable and cyclic phases
4,5
,
and has been suggested to cause the recent changesin cyclic dynamics
of rodents and their predators
3,6–9
. But although predator–rodent
interactions are commonly argued to be the cause of the
Fennoscandian rodent cycles
1,10–13
, the role of the environment in
the modulation of such dynamics is often poorly understood in
natural systems
8,9,14
. Hence, quantitative links between climatedriven
processes and rodent dynamics have so far been lacking.
Here we show that winter weather and snow conditions, together
with density dependence in the net population growth rate, account
for the observed population dynamics of the rodent community
dominated by lemmings (Lemmus lemmus) in an alpine Norwegian
core habitat between 1970 and 1997, and predictthe observed absence
of rodent peak years after 1994. These local rodent dynamics are
coherentwith alpine bird dynamics both locally and over all ofsouthern
Norway, consistent with the influence of large-scale fluctuations
in winter conditions. The relationship between commonly available
meteorological data and snow conditions indicates that changes in
temperature and humidity, and thus conditions in the subnivean
space, seem to markedly affect the dynamics of alpine rodents and
their linked groups. The pattern of less regular rodent peaks, and
corresponding changes in the overall dynamics of the alpine ecosystem,
thusseemslikely to prevail over a growing area under projected
climate change.
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Soil Temperature following Logging-Debris Manipulation and Aspen Regrowth in Minnesota: Implications for Sampling Depth and Alteration of Soil Processes
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Soil temperature is a fundamental controller of processes influencing the
transformation and flux of soil C and nutrients following forest harvest. Soil
temperature response to harvesting is influenced by the amount of logging
debris (biomass) removal that occurs, but the duration, magnitude, and depth
of influence is unclear. Logging debris manipulations (none, moderate, and
heavy amounts) were applied following clearcut harvesting at four aspendominated
(Populus tremuloides Michx.) sites in northeastern Minnesota, and
temperature was measured at 10-, 30-, and 50-cm depths for two growing
seasons. Across sites, soil temperature was significantly greater at all sample
depths relative to uncut forest in some periods of each year, but the increase
was reduced with increasing logging-debris retention. When logging debris
was removed compared to when it was retained in the first growing season,
mean growing season soil temperatures were 0.9, 1.0, and 0.8°C greater at
10-, 30-, and 50-cm depths, respectively. These patterns were also observed
early in the second growing season, but there was no discernible difference
among treatments later in the growing season due to the modifying effect of
rapid aspen regrowth. Where vegetation establishment and growth occurs
quickly, effects of logging debris removal on soil temperature and the processes
influenced by it will likely be short-lived. The significant increase in
soil temperature that occurred in deep soil for at least 2 yr after harvest
supports an argument for deeper soil sampling than commonly occurs in
experimental studies.
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Illuminating the Modern Dance of Climate and CO2
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Records of Earth’s past climate imply higher atmospheric carbon dioxide concentrations in the future
19 SEPTEMBER 2008 VOL 321 SCIENCE
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Prolonged suppression of ecosystem carbon dioxide uptake after an anomalously warm year
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Terrestrial ecosystems control carbon dioxide fluxes to and from
the atmosphere1,2 through photosynthesis and respiration, a balance
between net primary productivity and heterotrophic respiration,
that determines whether an ecosystem issequestering carbon
or releasing it to the atmosphere. Global1,3–5 and site-specific6 data
sets have demonstrated that climate and climate variability influence
biogeochemical processes that determine net ecosystem carbon
dioxide exchange (NEE) at multiple timescales. Experimental
data necessary to quantify impacts of a single climate variable,
such as temperature anomalies, on NEE and carbon sequestration
of ecosystems at interannual timescales have been lacking. This
derives from an inability of field studies to avoid the confounding
effects of natural intra-annual and interannual variability in temperature
and precipitation. Here we present results from a fouryear
study using replicate 12,000-kg intact tallgrass prairie monoliths
located in four 184-m3 enclosed lysimeters7
. We exposed 6 of
12 monoliths to an anomalously warm year in the second year of
the study8 and continuously quantified rates of ecosystem processes,
including NEE. We find that warming decreases NEE in
both the extreme year and the following year by inducing drought
that suppresses net primary productivity in the extreme year and
by stimulating heterotrophic respiration of soil biota in the subsequent
year. Our data indicate thattwo years are required for NEE
in the previously warmed experimental ecosystems to recover to
levels measured in the control ecosystems. Thistime lag caused net
ecosystem carbon sequestration in previously warmed ecosystems
to be decreased threefold over the study period, compared with
control ecosystems. Our findings suggest that more frequent
anomalously warm years9
, a possible consequence of increasing
anthropogenic carbon dioxide levels10, may lead to a sustained
decrease in carbon dioxide uptake by terrestrial ecosystems.
Vol 455| 18 September 2008
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Politics for the day after tomorrow: The logic of apocalypse in global climate politics
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The recent global climate change discourse is a prominent example of a securitization of environmental
issues. While the problem is often framed in the language of existentialism, crisis or even apocalypse, climate
discourses rarely result in exceptional or extraordinary measures, but rather put forth a governmental
scheme of piecemeal and technocratic solutions often associated with risk management. This article argues
that this seeming paradox is no accident but follows from a politics of apocalypse that combines two logics
– those of security and risk – which in critical security studies are often treated as two different animals.
Drawing on the hegemony theory of Ernesto Laclau and Chantal Mouffe, however, this article shows
that the two are inherently connected. In the same way as the Christian pastorate could not do without
apocalyptic imageries, today’s micro-politics of risk depends on a series of macro-securitizations that
enable and legitimize the governmental machinery. This claim is backed up by an inquiry into current global
discourses of global climate change regarding mitigation, adaptation and security implications. Although
these discourses are often framed through the use of apocalyptic images, they rarely result in exceptional
or extraordinary measures, but rather advance a governmental scheme of risk management. Tracing the
relationship between security and risk in these discourses, we use the case of climate change to highlight
the relevance of our theoretical argument.
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Temperature control of larval dispersal and the implications for marine ecology, evolution, and conservation
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Temperature controls the rate of fundamental biochemical processes
and thereby regulates organismal attributes including development
rate and survival. The increase in metabolic rate with
temperature explains substantial among-species variation in lifehistory
traits, population dynamics, and ecosystem processes.
Temperature can also cause variability in metabolic rate within
species. Here, we compare the effect of temperature on a key
component of marine life cycles among a geographically and
taxonomically diverse group of marine fish and invertebrates.
Although innumerable lab studies document the negative effect of
temperature on larval development time, little is known about the
generality versus taxon-dependence of this relationship. We
present a unified, parameterized model for the temperature dependence
of larval development in marine animals. Because the
duration of the larval period is known to influence larval dispersal
distance and survival, changes in ocean temperature could have
a direct and predictable influence on population connectivity,
community structure, and regional-to-global scale patterns of
biodiversity.
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