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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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An Uncertain Future for Soil Carbon
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Predictions of how rapidly the large amounts of carbon stored as soil organic matter will respond to warming
are highly uncertain (1). Organic matter plays a key role in determining the physical and chemical properties of soils and is a major reservoir for plant nutrients. Understanding how fast organic matter in soils can be built up and lost is thus critical not just for its net effect on the atmospheric CO2 concentration but for
sustaining other soil functions, such as soil fertility, on which societies and ecosystems rely. Recent analytic advances are rapidly improving our understanding of the complex and interacting factors that control the age
and form of organic matter in soils, but the processes that destabilize organic matter in response to disturbances (such as warming or land use change) are poorly understood
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Impact of terrestrial biosphere carbon exchanges on the anomalous CO2 increase in 2002–2003
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Understanding the carbon dynamics of the terrestrial
biosphere during climate fluctuations is a prerequisite for
any reliable modeling of the climate-carbon cycle feedback.
We drive a terrestrial vegetation model with observed
climate data to show that most of the fluctuations in
atmospheric CO2 are consistent with the modeled shift in
the balance between carbon uptake by terrestrial plants and
carbon loss through soil and plant respiration. Simulated
anomalies of the Fraction of Absorbed Photosynthetically
Active Radiation (FAPAR) during the last two El Nin˜o
events also agree well with satellite observations. Our
model results suggest that changes in net primary
productivity (NPP) are mainly responsible for the
observed anomalies in the atmospheric CO2 growth rate.
Changes in heterotrophic respiration (Rh) mostly happen in
the same direction, but with smaller amplitude. We attribute
the unusual acceleration of the atmospheric CO2 growth rate
during 2002–2003 to a coincidence of moderate El Nin˜o
conditions in the tropics with a strong NPP decrease at
northern mid latitudes, only partially compensated by
decreased
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Emerging Techniques for Soil Carbon measurements
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Soil carbon sequestration is one approach to mitigate greenhouse gases. However, to reliably
assess the quantities sequestered as well as the chemical structure of the soil carbon, new
methods and equipment are needed. These methods and equipment must allow large scale
measurements and the construction of dynamic maps. This paper presents results from some
emerging techniques to measure carbon quantity and stability. Each methodology has specific
capabilities and their combined use along with other analytical tools will improve soil organic
matter research. New opportunities arise with the development and application of portable
equipment, based on spectroscopic methods, as laser-induced fluorescence, laser-induced
breakdown spectroscopy and near infrared, for in situ carbon measurements in different
ecosystems. These apparatus could provide faster and lower cost field analyses thus
improving soil carbon contents and quality databases. Improved databases are essential to
model carbon balance, thus reducing the uncertainties generated through the extrapolation of
limited data.
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Protected Areas as Frontiers for Human Migration
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Causes of human population growth near protected areas have been much debated. We conducted
821 interviews in 16 villages around Budongo Forest Reserve, Masindi district, Uganda, to explore the causes of
human migration to protected areas and to identify differences in forest use between migrant and nonmigrant
communities. We asked subjects for information about birthplace, migration, household assets, household
activities, and forest use. Interview subjects were categorized as nonmigrants (born in one of the interview
villages), socioeconomic migrants (chose to emigrate for economic or social reasons) from within Masindi
district (i.e., local migrants) and from outside the Masindi district (i.e., regional migrants), or forced migrants
(i.e., refugees or internally displaced individuals who emigrated as a result of conflict, human rights abuses,
or natural disaster). Only 198 respondents were born in interview villages, indicating high rates of migration
between 1998 and 2008. Migrants were drawn to Budongo Forest because they thought land was available
(268 individuals) or had family in the area (161 individuals). A greater number of regional migrants settled
in villages near Lake Albert than did forced and local migrants. Migration category was also associated with
differences in sources of livelihood. Of forced migrants 40.5% earned wages through labor, whereas 25.5% of
local and 14.5% of regional migrants engaged in wage labor. Migrant groups appeared to have different effects
on the environment. Of respondents that hunted, 72.7% were regional migrants. Principal component analyses
indicated households of regional migrants were more likely to be associated with deforestation. Our results
revealed gaps in current models of human population growth around protected areas. By highlighting the
importance of social networks and livelihood choices, our results contribute to a more nuanced understanding
of causes of migration and of the environmental effects of different migrant groups.
Conservation Biology, Volume 26, No. 3, 547–556
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Barking up the Wrong Tree? Forest Sustainability in the wake of Emerging Bioenergy Policies
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The spotted owl controversy revealed that federal forest management policies alone could not guarantee functioning forest ecosystems. At the same time as the owl’s listing, agreements made at the 1992 Rio Earth Summit highlighted the mounting pressures on natural systems, thus unofficially marking the advent of sustainable forestry management (SFM).2 While threats to forest ecosystems from traditional logging practices certainly remain,3 developed and developing countries have shifted generally toward more sustainable forest management, at least on paper, including codifying various sustainability indicators in public laws.4 Nevertheless, dark policy clouds are gathering on the forest management horizon. Scientific consensus has grown in recent years around a new and arguably more onerous threat to all of the world’s ecosystems—climate change. Governments’ responses have focused on bioenergy policies aimed
at curtailing anthropogenic greenhouse gas (GHG) emissions, and mandatesfor renewables in energy supplies now abound worldwide.
[Vol. 37:000
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Rebuilding Soils on Mined Land for Native Forests in Appalachia
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The eastern U.S. Appalachian region supports the world’s most extensive
temperate forests, but surface mining for coal has caused forest loss. New
reclamation methods are being employed with the intent of restoring native
forest on Appalachian mined lands. Mine soil construction is essential to
the reforestation process. Here, we review scientific literature concerning
selection of mining materials for mine soil construction where forest
ecosystem restoration is the reclamation goal. Successful establishment and
productive growth of native Appalachian trees has been documented on mine
soils with coarse fragment contents as great as 60% but with low soluble salt
levels and slightly to moderately acidic pHs, properties characteristic of the
region’s native soils. Native tree productivity on some Appalachian mined
lands where weathered rock spoils were used to reconstruct soils was found
comparable to productivity on native forest sites. Weathered rock spoils,
however, are lower in bioavailable N and P than native Appalachian soils and
they lack live seed banks which native soils contain. The body of scientific
research suggests use of salvaged native soils for mine soil construction when
forest ecosystem restoration is the reclamation goal, and that weathered rock
spoils are generally superior to unweathered rock spoils when constructing
mine soils for this purpose.
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Amazon Basin climate under global warming: the role of the sea surface temperature
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The Hadley Centre coupled climate–carbon cycle model (HadCM3LC) predicts loss of the Amazon
rainforest in response to future anthropogenic greenhouse gas emissions. In this study, the
atmospheric component of HadCM3LC is used to assess the role of simulated changes in midtwenty-first
century sea surface temperature (SST) in Amazon Basin climate change. When the full HadCM3LC SST anomalies (SSTAs) are used, the atmosphere model reproduces the Amazon Basin climate change exhibited by HadCM3LC, including much of the reduction in Amazon Basin rainfall. This rainfall change is shown to be the combined effect of SSTAs in both thetropical Atlantic and the Pacific, with roughly equal contributions from each basin. The greatest rainfall reduction occurs from May to October, outside of the mature South American monsoon (SAM) season. This dry season response is the combined effect of a more rapid warming of the tropical North Atlantic relative to the south, and warm SSTAs in the tropical east Pacific. Conversely,
a weak enhancement of mature SAM season rainfall in response to Atlantic SST change is suppressed
by the atmospheric response to Pacific SST. This net wet season response is sufficient to prevent dry
season soil moisture deficits from being recharged through the SAM season, leading to a perennial
soil moisture reduction and an associated 30% reduction in annual Amazon Basin net primary
productivity (NPP). A further 23% NPP reduction occurs in response to a 3.58C warmer air
temperature associated with a global mean SST warming.
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Allowable carbon emissions lowered by multiple climate targets
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Climate targets are designed to inform policies that would limit the
magnitude and impacts of climate change caused by anthropogenic
emissions of greenhouse gases and other substances. The target
that is currently recognized by most world governments1 places a
limit of two degrees Celsius on the global mean warming since
preindustrial times. This would require large sustained reductions
in carbon dioxide emissions during the twenty-first century and
beyond2–4. Such a global temperature target, however, is not sufficient
to control many other quantities, such as transient sea level
rise5
, ocean acidification6,7 and net primary production on land8,9.
Here, using an Earth system model of intermediate complexity
(EMIC) in an observation-informed Bayesian approach, we show
that allowable carbon emissions are substantially reduced whenmultiple
climate targets are set. We take into account uncertainties in
physical and carbon cycle model parameters, radiative efficiencies10,
climate sensitivity11 and carbon cycle feedbacks12,13 along with a
large set of observational constraints. Within this framework, we
explore a broad range of economically feasible greenhouse gas scenarios
from the integrated assessment community14–17 to determine
the likelihood of meeting a combination of specific global
and regional targets under various assumptions. For any given
likelihood of meeting a set of such targets, the allowable cumulative
emissions are greatly reduced from those inferred from the temperature
target alone. Therefore, temperature targets alone are unable
to comprehensively limit the risks from anthropogenic emissions.
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Managing Forests and Fire in Changing Climates
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With projected climate change, we
expect to face much more forest
fi re in the coming decades. Policymakers
are challenged not to categorize all
fires as destructive to ecosystems simply
because they have long fl ame lengths and kill
most of the trees within the fi re boundary. Ecological
context matters: In some ecosystems,
high-severity regimes are appropriate, but climate
change may modify these fi re regimes
and ecosystems as well. Some undesirable
impacts may be avoided or reduced through
global strategies, as well as distinct strategies
based on a forest’s historical fi re regime.
SCIENCE VOL 342 4 OCTOBER 2013
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