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Indian-Set Fires in the Forests of the Northeastern United States
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The historical evidence for the Indians' burning the forests of the northeastern United
Abstract. States is reevaluated. Of 35 documents that describe vegetation or Indian life in the 16th or 17th centuries, only half mention any use of fire except for cooking. Only six purportedly first-hand accounts might refer to purposeful, widespread, and frequent use of fire. These six are all consistent with use of fire only locally near camps or villages, or with accidentally escaped fires. It is concluded that the frequent use of fires by the Indians to burn the forests was probably at most a local occurrence. The Indians' presence in the region and their use of fire for many purposes did, however, increase the frequency of fires above the low levels caused by lightning, and thus had some effect on the vegetation; for example, grasses characterized the ground cover at small, local, frequently burned sites.
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Desert grassland responses to climate and soil moisture suggest divergent vulnerabilities across the southwestern United States
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Climate change predictions include warming and drying trends, which are expected to be particularly pronounced in the southwestern United States. In this region, grassland dynamics are tightly linked to available moisture, yet it has proven difficult to resolve what aspects of climate drive vegetation change. In part, this is because it is unclear how heterogeneity in soils affects plant responses to climate. Here, we combine climate and soil properties with a mecha- nistic soil water model to explain temporal fluctuations in perennial grass cover, quantify where and the degree to which incorporating soil water dynamics enhances our ability to understand temporal patterns, and explore the potential consequences of climate change by assessing future trajectories of important climate and soil water variables. Our analyses focused on long-term (20–56 years) perennial grass dynamics across the Colorado Plateau, Sonoran, and Chihuahuan Desert regions. Our results suggest that climate variability has negative effects on grass cover, and that precipitation subsidies that extend growing seasons are beneficial. Soil water metrics, including the number of dry days and availability of water from deeper (>30 cm) soil layers, explained additional grass cover variability. While individual climate variables were ranked as more important in explaining grass cover, collectively soil water accounted for 40–60% of the total explained variance. Soil water conditions were more useful for understanding the responses of C3 than C4 grass species. Projections of water balance variables under climate change indicate that conditions that currently support perennial grasses will be less common in the future, and these altered conditions will be more pronounced in the Chihuahuan Desert and Colorado Plateau. We conclude that incorporating multiple aspects of climate and accounting for soil variability can improve our ability to understand patterns, identify areas of vulnerability, and predict the future of desert grasslands.
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Preemptive and Salvage Harvesting of New England Forests: When Doing Nothing Is a Viable Alternative
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Oneunexpectedconsequenceofnaturaldisturbancesinforestedareasisthatmanagersofteniniti- ate activities that may impose greater ecosystem impacts than the disturbances themselves. By salvage logging areas affected by windstorms or other impacts, by harvesting host trees in advance of insect infestation or disease, or by preemptively harvesting forests in an attempt to improve their resilience to future disturbances and stresses, managers initiate substantial changes in the ecosystem structure and function. Much of this activity is undertaken in the absence of information on the qualitative and quantitative differences between disturbance impacts and harvesting. To provide insight for such decisions we evaluated the ecosystem conse- quences of two major disturbance processes in New England (U.S.A.)—intense windstorms and invasive pests and pathogens—and contrasted them with impacts from preemptive and salvage harvesting. Despite dramatic physical changes in forest structure resulting from hurricane impacts and insect infestation, little disruption of biogeochemical processes or other ecosystem functions typically follows these disturbances. Indeed, the physical and organic structures produced by these disturbances are important natural features providing habitat and landscape heterogeneity that are often missing due to centuries of land use. From an ecosystem perspective there are strong arguments against preemptive and salvage logging or the attempt through silvicultural means to improve the resistance or resilience of forests to disturbance and stress. There are often valid motivations for salvage or preemptive logging including financial considerations, human safety, and a desire to shape the long-term composition and resource-production characteristics of forests. Nonetheless, there are many ecological benefits derived from leaving forests alone when they are affected or threatened by disturbances and pest and pathogen outbreaks.
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Seasonal and diel patterns in the migrations of fishes between a river and a floodplain tributary
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The population behaviours associated with the migrations of fishes in lowland river ecosystems are amongst the most poorly-understood dispersal mechanisms of temperate freshwater organisms. This study evaluated the influence of four environmental variables (light levels, river discharge, water temperature and water velocity) on the timing, intensity and direction of fish movements between the River Avon (Hampshire, England) and a small floodplain tributary, Ibsley Brook, over a 12-month period. Using canonical correspondence analysis (CCA) to identify patterns of movement (by groups of species) and the relative strengths of explanatory variables in the data, the probability of fishes migrating between the river and tributary was determined using Bayesian modelling. The intensity and direction of fish movements between the river and tributary varied temporally, both on a diel and seasonal basis, and there were species- and age-specific patterns in behaviour. Diel movements appeared to be triggered by changes in light intensity and brook water velocity, whereas seasonal movements were mostly driven by changes in river discharge and water temperature, particularly those associated with floods. This study emphasises the importance of connectivity in river systems, as fishes migrated in all conditions, but especially during rapidly- rising discharge.
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Hydrological connectivity in coastal inland systems: lessons from a Neotropical fish metacommunity
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We assessed the influence of hydrological connectivity in structuring fish communities through seasonal samplings of environmental variables and fishes in a coastal lagoon and associated pools in the Restinga de Jurubatiba National Park, Brazil. Community structure attributes such as species richness, numerical density and biomass, Shannon–Wiener diversity index and evenness were compared between periods of the lowest and highest hydrological connectivity, while the environmental gradient and fish zonation were explored through ordination techniques. The greater hydrological connectivity established in the
rainy season promoted the homogenisation of most environmental variables and fish species, which differed markedly from the arrangement observed in the dry season. Despite variation in fish species composition, community attributes showed non-significant differences between the dry and rainy seasons. The patterns of composition and numerical density in pools were strongly influenced by local factors, especially salinity, dissolved oxygen, total phosphorous concentration and water colour in the dry season, in addition to total nitrogen concentration and depth in the rainy season. Comparable to the role played by flood pulses in river-floodplain systems, the hydrological connectivity in these tropical coastal waterbodies seems to strongly influence fish community structure, and, therefore to determine regional biodiversity.
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Reconciling nature conservation and traditional farming practices: a spatially explicit framework to assess the extent of High Nature Value farmlands in the European countryside
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Agriculture constitutes a dominant land cover worldwide, and rural landscapes under extensive farming practices acknowledged due to high biodiversity levels. The High Nature Value farmland (HNVf) concept has been highlighted in the EU environmental and rural policies due to their inherent potential to help characterize and direct financial support to European landscapes where high nature and/or conservation value is dependent on the continuation of specific low-intensity farming systems.
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Regional growth decline of sugar maple (Acer saccharum) and its potential causes
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Sugar maple (Acer saccharum Marsh) has experienced poor vigor, regeneration failure, and elevated mortality across much of its range, but there has been relatively little attention to its growth rates. Based on a well-replicated dendrochronological network of range-centered populations in the Adirondack Mountains (USA), which encompassed a wide gradient of soil fertility, we observed that the majority of sugar maple trees exhibited negative growth trends in the last several decades, regardless of age, diameter, or soil fertility. Such growth patterns were unexpected, given recent warming and increased moisture availability, as well as reduced acidic deposition, which should have favored growth. Mean basal area increment was greater on base-rich soils, but these stands also experienced sharp reductions in growth. Growth sensitivity of sugar maple to temperature and precipitation was non-stationary during the last century, with overall weaker relationships than expected. Given the favorable competitive status and age structure of the Adirondack sugar maple populations sampled, evidence of widespread growth reductions raises concern over this ecologically and economically important tree. Further study will be needed to establish whether growth declines of sugar maple are occurring more widely across its range.
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Global change and conservation triage on National Wildlife Refuges
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National Wildlife Refuges (NWRs) in the United States play an important role in the adaptation of social-ecological systems to climate change, land-use change, and other global-change processes. Coastal refuges are already experiencing threats from sea-level rise and other change processes that are largely beyond their ability to influence, while at the same time facing tighter budgets and reduced staff. We engaged in workshops with NWR managers along the U.S. Atlantic coast to understand the problems they face from global-change processes and began a multidisciplinary collaboration to use decision science to help address them. We are applying a values-focused approach to base management decisions on the resource objectives of land managers, as well as those of stakeholders who may benefit from the goods and services produced by a refuge. Two insights that emerged from our workshops were a conspicuous mismatch between the scale at which management can influence outcomes and the scale of environmental processes, and the need to consider objectives related to ecosystem goods and services that traditionally have not been explicitly considered by refuges (e.g., protection from storm surge). The broadening of objectives complicates the decision-making process, but also provides opportunities for collaboration with stakeholders who may have agendas different from those of the refuge, as well as an opportunity for addressing problems across scales. From a practical perspective, we recognized the need to (1) efficiently allocate limited staff time and budgets for short-term management of existing programs and resources under the current refuge design and (2) develop long-term priorities for acquiring or protecting new land/habitat to supplement or replace the existing refuge footprint and thus sustain refuge values as the system evolves over time. Structuring the decision-making problem in this manner facilitated a better understanding of the issues of scale and suggested that a long-term solution will require a significant reassessment of objectives to better reflect the comprehensive values of refuges to society. We discuss some future considerations to integrate these two problems into a single framework by developing novel optimization approaches for dynamic problems that account for uncertainty in future conditions.
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The Montérégie Connection: linking landscapes, biodiversity, and ecosystem services to improve decision making
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To maximize specific ecosystem services (ES) such as food production, people alter landscape structure, i.e., the types of ecosystems present, their relative proportions, and their spatial arrangement across landscapes. This can have significant, and sometimes unexpected, effects on biodiversity and ES. Communities need information about how land-use activities and changes to landscape structure are likely to affect biodiversity and ES, but current scientific understanding of these effects is incomplete. The Montérégie Connection (MC) project has used the rapidly suburbanizing agricultural Montérégien landscape just east of Montreal, Québec, Canada, to investigate how current and historic landscape structure influences ES provision. Our results highlight the importance of forest connectivity and functional diversity on ES provision, and show that ES provision can vary significantly even within single land- use types in response to changes in landscape structure. Our historical analysis reveals that levels of ES provision, as well as relationships among individual ES, can change dramatically through time. We are using these results to build quantitative ES-landscape structure models to assess four future landscape scenarios for the region: Periurban Development, Demand for Energy, Whole-System Crisis, and Green Development. These scenarios integrate empirical and historical data on ES provision with local stakeholder input about global and local social and ecological drivers to explore how land-use decisions could affect ES provision and human well-being across the region to the year 2045. By integrating empirical data, quantitative models, and scenarios we have achieved the central goals of the MC project: (1) increasing understanding of the effects of landscape structure on biodiversity and ES provision, (2) effectively linking this knowledge to decision making to better manage for biodiversity and ES, and (3) creating a vision for a more sustainable social- ecological system in the region.
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Palaeodata-informed modelling of large carbon losses from recent burning of boreal forests
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Although boreal fire regimes are heterogeneous, recent trends6 and future projections7 point to increasing fire activity in response to climate warming throughout the biome. Thus, predictions8 that terrestrial C sinks of northern high latitudes will mitigate rising atmospheric CO2 may be over-optimistic.
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