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Four-year response of underplanted American chestnut (Castanea dentata) and three competitors to midstory removal, root trenching, and weeding treatments in an oak-hickory forest
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American chestnut (Castanea dentata) has been killed or reduced to recurrent stump sprouts throughout its range following the importation of multiple pathogens in the 19th and early 20th centuries. Under- standing what drives chestnut growth and survival would aid the development of appropriate silvicultural guidelines for restoring the species once blight resistant stock is available. Here we compare the response of planted American and hybrid chestnut seedlings to that of important competitors, northern red oak (Quercus rubra), sugar maple (Acer saccharum) and red maple (A. rubrum), under treatments designed to evaluate the effects of various sources of competition on seedling growth and survival. After four years, American and hybrid chestnut was significantly taller in trenched plots (181.8 ± 12.4 cm; mean ± SE) compared to untrenched plots (127.5 ± 7.9 cm), weeded plots (174.5 ± 12.7 cm) compared to unweeded plots (130.1 ± 6.5 cm) and in midstory removal plots (156.6 ± 7.8) versus full canopy (88.8 ± 11.7 cm), and had outperformed the other species in most competitive environments. Chestnut was the only species to respond to every treatment with significant growth increases, displaying a nota- ble ability to capture growing space when it became available. We suggest that American chestnut res- toration may be more successful where early stand management provides chestnut a brief period of reduced competition. Specifically, midstory removal can increase survival and growth of underplanted American chestnut, and when combined with multi-stage shelterwood removals of the overstory and some amount of competition control, may constitute a viable restoration strategy for chestnut in many of the eastern oak-hickory forests where it was originally dominant.
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Long-term aspen cover change in the western US
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Quaking aspen (Populus tremuloides Michx.) is one of the most important tree species in the western United States due to its role in biodiversity, tourism, and other ecological and aesthetic values. This paper provides an overview of the drivers of long-term aspen cover change in the western US and how these drivers operate on diverse spatial and temporal scales. There has been substantial concern that aspen has been declining in the western US, but trends of aspen persistence vary both geographically and tem- porally. One important goal for future research is to better understand long-term and broad-scale changes in aspen cover across its range. Inferences about aspen dynamics are contingent on the spatial and temporal scales of inquiry, thus differences in scope and design among studies partly explain varia- tion among conclusions. For example, major aspen decline has been noted when the spatial scale of inquiry is relatively small and the temporal scale of inquiry is relatively short. Thus, it is important to consider the scale of research when addressing aspen dynamics.
Successional replacement of aspen by conifer species is most pronounced in systems shaped by long fire intervals and can thus be seen as part of a normal, long-term fluctuation in forest composition. Aspen decline was initially reported primarily at the margins of aspen’s distribution, but may be becoming more ubiquitous due to the direct effects of climate (e.g. drought). In contrast, the indirect effects of recent climate (e.g. forest fires, bark beetle outbreaks, and compounded disturbances) appear to favor aspen and may facilitate expansion of this forest type. Thus, future aspen trends are likely to depend on the net result of the direct and indirect effects of altered climate.
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PHENOLOGY OF MIXED WOODY–HERBACEOUS ECOSYSTEMS FOLLOWING EXTREME EVENTS: NET AND DIFFERENTIAL RESPONSES
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We present responses of a mixed woody–herbaceous ecosystem type to an extreme event: regional-scale pinon pine mortality following an extended drought and the subsequent herbaceous green-up following the first wet period after the drought. This example highlights how reductions in greenness of the slower, more stable evergreen woody component can rapidly be offset by increases associated with resources made available to the relatively more responsive herbaceous component. We hypothesize that such two-phase phenological responses to extreme events are characteristic of many mixed woody– herbaceous ecosystems.
Key words: die-off; disturbance; drought; extreme events; fire; Mesita del Buey; mortality; normalized difference vegetation index; phenology; pin ̃on; semiarid woodlands; woody and herbaceous plants.
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Impacts of the EU biofuel policy on agricultural markets and land use
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The European Union's Renewable Energy Directive (RED)1 sets an overall target of 20% of the EU's energy used to come from renewable sources by 2020. As part of this target, at least 10% of total transport fuel consumption is to come from renewable energies (RE). In parallel, the Fuel Quality Directive (FQD)2 requires fuel suppliers to reduce the carbon intensity of road fuels they supply by 6% in 2020. The EU Member States were required to report their expectations and plans on how to meet these targets in National Renewable Energy Action Plans (NREAP) by 30 June 2010, including the technology mix and the trajectory to reach them.
However, in the end the extent to which the 2020 mandate will be met is uncertain. During the 2012 Workshop on 'Commodity Market Development in Europe – Outlook'3, held in Brussels, many participants highlighted the difficulty to reach such a level of biofuel consumption. In addition, according to the 2012 ECOFYS report on renewable energy progress and biofuels' sustainability, in 2012 the objectives for transport were already not being met. The European car industry is indeed not ready to use blends with high shares of biodiesel and ethanol. Moreover the contribution of second-generation biofuels towards meeting the target is expected to remain small.
Furthermore the repeated droughts in recent years have put pressure on food prices and put forward the world food security debate. The use of food crops to produce biofuels instead of feeding the world has been criticised. Sustainability of biodiesel is especially questioned. In order to reduce the indirect land use change (ILUC) which may be caused by higher demand for food and feed crops for biofuel, on 17 October 2012 the European Commission (EC) published a proposal to amend the RED (COM(2012)595). It proposed to cap the amount of first-generation biofuels that can count towards the 10% renewable energy target at 5%4. In addition, the use of advanced biofuels, with no or low ILUC emissions, would be promoted by weighting their contribution towards fulfilling the target more favourably. The estimated ILUC emissions are also included in the greenhouse gas balance of biofuels for the purpose of compliance with the reporting obligations under the RED and FQD.
Therefore the development of the biofuel market is highly uncertain, especially in the European Union (EU). This report aims to analyse different scenarios that could occur in the EU in the years to come.
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Top 10 Places to Save for Endangered Species in a Warming World
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If your house were on fire, what would you save? Would it be the precious items passed down in your family from genera- tion to generation? Or would you choose the irreplaceable photos that would disappear forever? Where do you even start? What if it wasn’t just your house, but your whole planet that was on fire?That is the scenario we face today. Climate change has arrived. No longer clouds gathering in the distance, the storm is here now—melting our titanic glaciers, drying our mighty rivers and setting our deserts ablaze. What do we save? For the Endangered Species Coalition, the answer is easy: we start with our endangered species. They are already on the brink of extinction, so vulnerable that a stressor such as climate change acts as a bulldozer, steaming full force ahead with the potential to shove them right over the edge of extinction.And where do we begin? We asked our member groups and our scientists, “If we want to save endangered species from climate change, what habitats do we need to protect?” Together, they identified ten ecosystems that are critical to conserve if we are to protect our nation’s endangered species from the ravages of climate change.
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Sediment Trapping by Dams Creates Methane Emission Hot Spots
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Inland waters transport and transform sub- stantial amounts of carbon and account for ∼18% of global methane emissions. Large reservoirs with higher areal methane release rates than natural waters contribute significantly to freshwater emissions. However, there are millions of small dams worldwide that receive and trap high loads of organic carbon and can therefore potentially emit significant amounts of methane to the atmosphere. We evaluated the effect of damming on methane emissions in a central European impounded river. Direct comparison of riverine and reservoir reaches, where sedimentation in the latter is increased due to trapping by dams, revealed that the reservoir reaches are the major source of methane emissions (∼0.23 mmol CH4 m−2 d−1 vs ∼19.7 mmol CH4 m−2 d−1, respectively) and that areal emission rates far exceed previous estimates for temperate reservoirs or rivers. We show that sediment accumulation correlates with methane production and subsequent ebullitive release rates and may therefore be an excellent proxy for estimating methane emissions from small reservoirs. Our results suggest that sedimentation- driven methane emissions from dammed river hot spot sites can potentially increase global freshwater emissions by up to 7%.
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Increased River Alkalinization in the Eastern U.S.
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The interaction between human activities and watershed geology is accelerating long-term changes in the carbon cycle of rivers. We evaluated changes in bicarbonate alkalinity, a product of chemical weathering, and tested for long-term trends at 97 sites in the eastern United States draining over 260 000 km2. We observed statistically significant increasing trends in alkalinity at 62 of the 97 sites, while remaining sites exhibited no significant decreasing trends. Over 50% of study sites also had statistically significant increasing trends in concentrations of calcium (another product of chemical weathering) where data were available. River alkalinization rates were significantly related to watershed carbonate lithology, acid deposition, and topography. These three variables explained ∼40% of variation in river alkalinization rates. The strongest predictor of river alkalinization rates was carbonate lithology. The most rapid rates of river alkalinization occurred at sites with highest inputs of acid deposition and highest elevation. The rise of alkalinity in many rivers throughout the Eastern U.S. suggests human-accelerated chemical weathering, in addition to previously documented impacts of mining and land use. Increased river alkalinization has major environmental implications including impacts on water hardness and salinization of drinking water, alterations of air−water exchange of CO2, coastal ocean acidification, and the influence of bicarbonate availability on primary production.
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Linking primary production, climate and land use along an urban–wildland transect: a satellite view
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Variation of green vegetation cover influences local climate dynamics, exchange of water–heat between land and atmosphere, and hydrological processes. However, the mechanism of interaction between vegetation and local climate change in subtropical areas under climate warming and anthropogenic disturbances is poorly understood. We analyzed spatial–temporal trends of vegetation with moderate-resolution imaging spectroradiometer (MODIS) vegetation index datasets over three sections, namely urban, urban–rural fringe and wildland along an urban–wildland transect in a southern mega-city area in China from 2000–2008. The results show increased photosynthetic activity occurred in the wildland and the stable urban landscape in correspondence to the rising temperature, and a considerable decrease of vegetation activity in the urban–rural fringe area, apparently due to urban expansion. On analyzing the controlling factors of climate change and human drivers of vegetation cover change, we found that temperature contributed to vegetation growth more than precipitation and that rising temperature accelerated plant physiological activity. Meanwhile, human-induced dramatic modification of land cover, e.g. conversion of natural forest and cropland to built-up areas in the urban–rural fringe, has caused significant changes of green vegetation fraction and overall primary production, which may further influence local climate.
Keywords: vegetation greenness, environmental gradients, urban, transect, climate change, remote sensing, rural
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Rethinking wedges
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Stabilizing CO2 emissions at current levels for fifty years is not consistent with either an atmospheric CO2 concentration below 500 ppm or global temperature increases below 2 ◦C. Accepting these targets, solving the climate problem requires that emissions peak and decline in the next few decades, and ultimately fall to near zero. Phasing out emissions over 50 years could be achieved by deploying on the order of 19 ‘wedges’, each of which ramps up linearly over a period of 50 years to ultimately avoid 1 GtC y−1 of CO2 emissions. But this level of mitigation will require affordable carbon-free energy systems to be deployed at the scale of tens of terawatts. Any hope for such fundamental and disruptive transformation of the global energy system depends upon coordinated efforts to innovate, plan, and deploy new transportation and energy systems that can provide affordable energy at this scale without emitting CO2 to the atmosphere.
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Sectoral contributions to surface water stress in the coterminous United States
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Here, we assess current stress in the freshwater system based on the best available data in order to understand possible risks and vulnerabilities to regional water resources and the sectors dependent on freshwater. We present watershed-scale measures of surface water supply stress for the coterminous United States (US) using the water supply stress index (WaSSI) model which considers regional trends in both water supply and demand. A snapshot of contemporary annual water demand is compared against different water supply regimes, including current average supplies, current extreme-year supplies, and projected future average surface water flows under a changing climate. In addition, we investigate the contributions of different water demand sectors to current water stress. On average, water supplies are stressed, meaning that demands for water outstrip natural supplies in over 9% of the 2103 watersheds examined. These watersheds rely on reservoir storage, conveyance systems, and groundwater to meet current water demands. Overall, agriculture is the major demand-side driver of water stress in the US, whereas municipal stress is isolated to southern California. Water stress introduced by cooling water demands for power plants is punctuated across the US, indicating that a single power plant has the potential to stress water supplies at the watershed scale. On the supply side, watersheds in the western US are particularly sensitive to low flow events and projected long-term shifts in flow driven by climate change. The WaSSI results imply that not only are water resources in the southwest in particular at risk, but that there are also potential vulnerabilities to specific sectors, even in the ‘water-rich’ southeast.
Keywords: water resources, surface water, water stress
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