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Effect of per-capita land use changes on Holocene forest clearance and CO2 emissions
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The centerpiece of the early anthropogenic hypothesis is the claim that humans took control of greenhouse-gas trends thousands of years ago because of emissions from early agriculture (Ruddiman, 2003, 2007). A common reaction to this claim is that too few people lived thousands of years ago to have had a major effect on either land use or greenhouse-gas concentrations. Implicit in this view is the notion that per-capita land clearance has changed little for millennia, but numerous field studies have shown that early per-capita land use was large and then declined as increasing population density led to more intensive farming. Here we explore the potential impact of changing per-capita land use in recent millennia and conclude that greater clearance by early agriculturalists could have had a disproportionately large impact on CO2 emissions.
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Effect of Risk Aversion on Prioritizing Conservation Projects
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Agencies making decisions about what threat mitigation actions to take to save which species frequently face the dilemma of whether to invest in actions with high probability of success and guaranteed benefits or to choose projects with a greater risk of failure that might provide higher benefits if they succeed. The answer to this dilemma lies in the decision maker’s aversion to risk—their unwillingness to accept uncertain outcomes. Little guidance exists on how risk preferences affect conservation investment priorities. Using a prioritization approach based on cost effectiveness, we compared 2 approaches: a conservative probability threshold approach that excludes investment in projects with a risk of management failure greater than a fixed level, and a variance-discounting heuristic used in economics that explicitly accounts for risk tolerance and the probabilities of management success and failure. We applied both approaches to prioritizing projects for 700 of New Zealand’s threatened species across 8303 management actions. Both decision makers’ risk tolerance and our choice of approach to dealing with risk preferences drove the prioritization solution (i.e., the species selected for management). Use of a probability threshold minimized uncertainty, but more expensive projects were selected than with variance discounting, which maximized expected benefits by selecting the management of species with higher extinction risk and higher conservation value. Explicitly incorporating risk preferences within the decision making process reduced the number of species expected to be safe from extinction because lower risk tolerance resulted in more species being excluded from management, but the approach allowed decision makers to choose a level of acceptable risk that fit with their ability to accommodate failure. We argue for transparency in risk tolerance and recommend that decision makers accept risk in an adaptive management framework to maximize benefits and avoid potential extinctions due to inefficient allocation of limited resources.
Keywords: conservation decisionmaking,cost-effectiveness analysis, management effectiveness,Project Prioritization Protocol, risk analysis, risk tolerance, threatened species, uncertainty
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Effective Enforcement in a Conservation Area
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There are two primary approaches to wildlife conservation, the generation of economic benefits from wildlife to local communities, so that protecting wildlife is in their interest, and the enforcement of protected areas. Outside of protected areas, community- based conservation must be the cornerstone of protection (1). However, within protected areas there is debate as to whether enforcement can maintain wildlife and even whether protected areas as wildlife reserves are realistic or morally justified (2). Here, we present the history of illegal harvesting in Serengeti National Park (SNP), Tanzania; estimate the amount of antipoaching activity by park staff; and show how the level of funding for antipoaching has affected the trends in abundance of three severely affected species: African buffalo, elephant, and black rhino.
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Effects of Climatic Variability and Change on Forest Ecosystems: General Technical Report PNW-GTR-870 December 2012
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This report is a scientific assessment of the current condition and likely future condition of forest resources in the United States relative to climatic variability and change. It serves as the U.S. Forest Service forest sector technical report for the National Climate Assessment and includes descriptions of key regional issues and examples of a risk-based framework for assessing climate-change effects. By the end of the 21st century, forest ecosystems in the United States will differ from those of today as a result of changing climate. Although increases in temperature, changes in precipitation, higher atmospheric concentrations of carbon dioxide (CO2), and higher nitrogen (N) deposition may change ecosystem structure and function, the most rapidly visible and most significant short-term effects on forest ecosystems will be caused by altered disturbance regimes. For example, wildfires, insect infestations, pulses of erosion and flooding, and drought-induced tree mortality are all expected to increase during the 21st century. These direct and indirect climate-change effects are likely to cause losses of ecosystem services in some areas, but may also improve and expand ecosystem services in others. Some areas may be particularly vulnerable because current infrastructure and resource production are based on past climate and steady-state conditions. The ability of communities with resource-based economies to adapt to climate change is linked to their direct exposure to these changes, as well as to the social and institutional structures present in each environment. Human communities that have diverse economies and are resilient to change today will also be prepared for future climatic stresses.
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Effects of drought on avian community structure
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Droughts are expected to become more frequent under global climate change. Avifauna depend on precipitation for hydration, cover, and food. While there are indications that avian communities respond negatively to drought, little is known about the response of birds with differing functional and behavioural traits, what time periods and indicators of drought are most relevant, or how response varies geographically at broad spatial scales. Our goals were thus to determine (1) how avian abundance and species richness are related to drought, (2) whether community variations are more related to vegetation vigour or precipitation deviations and at what time periods relationships were strongest, (3) how response varies among avian guilds, and (4) how response varies among ecoregions with different precipitation regimes. Using mixed effect models and 1989–2005 North American Breeding Bird Survey data over the central United States, we examined the response to 10 precipitation- and greenness- based metrics by abundance and species richness of the avian community overall, and of four behavioural guilds. Drought was associated with the most negative impacts on avifauna in the semiarid Great Plains, while positive responses were observed in montane areas. Our models predict that in the plains, Neotropical migrants respond the most negatively to extreme drought, decreasing by 13.2% and 6.0% in abundance and richness, while permanent resident abundance and richness increase by 11.5% and 3.6%, respectively in montane areas. In most cases, response of abundance was greater than richness and models based on precipitation metrics spanning 32-week time periods were more supported than those covering shorter time periods and those based on greenness. While drought is but one of myriad environmental variations birds encounter, our results indicate that drought is capable of imposing sizable shifts in abundance, richness, and composition on avian communities, an important implica- tion of a more climatically variable future.
Keywords: abundance, birds, drought, Great Plains, greenness, mixed effects models, North American Breeding Bird Survey, precipitation, richness, United States
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Effects of Flow Regulation on Shallow-Water Habitat Dynamics and Floodplain Connectivity
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Our study examined the effects of flow regulation on the spatiotemporal availability of shallow habitat patches with slow current velocity (SSCV patches) and floodplain inundation in the unregulated Yellowstone River and the regulated Missouri River in Montana and North Dakota. We mapped representative sites and used hydraulic models and hydrograph data to describe the frequency and extent of floodplain inundation and the availability of SSCV habitat over time during different water years. In the Yellowstone River the distribution, location, and size of SSCV patches varied but followed an annual pattern that was tied to the snowmelt runoff hydrograph. There was less variation in patch distribution in the Missouri River, and the pattern of habitat availability was influenced by flow regulation. Regulated flows and their effects on channel mor- phology and patterns of vegetation establishment resulted in 3.0–3.5 times less area of inundated woody vegetation during normal and dry years in the Missouri River compared with the Yellow- stone River. The differences we observed in SSCV patch dynamics between rivers may have implications for fish populations and community structure through affecting the survival of early life stages. At a larger scale, the smaller area of vegetation inundated in the Missouri River suggests that nutrient cycling and the ecological benefits associated with a moving littoral zone are reduced by the altered flow and sediment regime in that river. Accurate assessments of the effects of flow alteration and successful efforts to restore riverine ecosystems will require consideration of physical and biotic processes that operate at multiple spatial and temporal scales.
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Effects of grazing on grassland soil carbon: a global review
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Soils of grasslands represent a large potential reservoir for storing CO2, but this potential likely depends on how grasslands are managed for large mammal grazing. Previous studies found both strong positive and negative grazing effects on soil organic carbon (SOC) but explanations for this variation are poorly developed. Expanding on previous reviews, we performed a multifactorial meta-analysis of grazer effects on SOC density on 47 independent experimen- tal contrasts from 17 studies. We explicitly tested hypotheses that grazer effects would shift from negative to positive with decreasing precipitation, increasing fineness of soil texture, transition from dominant grass species with C3 to C4 photosynthesis, and decreasing grazing intensity, after controlling for study duration and sampling depth. The six variables of soil texture, precipitation, grass type, grazing intensity, study duration, and sampling depth explained 85% of a large variation (`150 g m␣2 yr␣1) in grazing effects, and the best model included significant interactions between precipitation and soil texture (P = 0.002), grass type, and grazing intensity (P = 0.012), and study duration and soil sampling depth (P = 0.020). Specifically, an increase in mean annual precipitation of 600 mm resulted in a 24% decrease in grazer effect size on finer textured soils, while on sandy soils the same increase in precipitation pro- duced a 22% increase in grazer effect on SOC. Increasing grazing intensity increased SOC by 6–7% on C4-dominated and C4–C3 mixed grasslands, but decreased SOC by an average 18% in C3-dominated grasslands. We discovered these patterns despite a lack of studies in natural, wildlife-dominated ecosystems, and tropical grasslands. Our results, which suggest a future focus on why C3 vs. C4-dominated grasslands differ so strongly in their response of SOC to grazing, show that grazer effects on SOC are highly context-specific and imply that grazers in different regions might be managed differently to help mitigate greenhouse gas emissions.
Keywords: carbon sequestration, grasslands, grazing, grazing intensity, precipitation, soil organic carbon, soil texture
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Effects of irrigation on global climate during the 20th century
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Various studies have documented the effects of modern‐day irrigation on regional and global climate, but none, to date, have considered the time‐varying impact of steadily increasing irrigation rates on climate during the 20th century. We investigate the impacts of observed irrigation changes over this century with two ensemble simulations using an atmosphere general circulation model. Both ensembles are forced with transient climate forcings and observed sea surface temperatures from 1902 to 2000; one ensemble includes irrigation specified by a time‐varying data set of irrigation water withdrawals. Early in the century, irrigation is primarily localized over southern and eastern Asia, leading to significant cooling in boreal summer (June–August) over these regions. This cooling spreads and intensifies by century’s end, following the rapid expansion of irrigation over North America, Europe, and Asia. Irrigation also leads to boreal winter (December–February) warming over parts of North America and Asia in the latter part of the century, due to enhanced downward longwave fluxes from increased near‐surface humidity. Precipitation increases occur primarily downwind of the major irrigation areas, although precipitation in parts of India decreases due to a weaker summer monsoon. Irrigation begins to significantly reduce temperatures and temperature trends during boreal summer over the Northern Hemisphere midlatitudes and tropics beginning around 1950; significant increases in precipitation occur in these same latitude bands. These trends reveal the varying importance of irrigation‐climate interactions and suggest that future climate studies should account for irrigation, especially in regions with unsustainable irrigation resources.
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Effects of Management on Carbon Sequestration in Forest Biomass in Southeast Alaska
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The Tongass National Forest (Tongass) is the largest national forest and largest area of old-growth forest in the United States. Spatial geographic informa- tion system data for the Tongass were combined with forest inventory data to estimate and map total carbon stock in the Tongass; the result was 2.8±0.5PgC,or8%of the total carbon in the forests of the conterminous USA and 0.25% of the carbon in global forest vegetation and soils. Cumulative net carbon loss from the Tongass due to management of the forest for the period 1900–95 was estimated at 6.4–17.2 Tg C. Using our spatially explicit data for carbon stock and net flux, we modeled the potential effect of five management regimes on future net carbon flux. Estimates of net carbon flux were sensitive to projections of the rate of carbon accumulation in second-growth forests and to the amount of carbon left in standing biomass after harvest. Projections of net carbon flux in the Tongass range from 0.33 Tg C annual sequestration to 2.3 Tg C annual emission for the period 1995–2095. For the period 1995–2195, net flux estimates range from 0.19 Tg C annual sequestra- tion to 1.6 Tg C annual emission. If all timber harvesting in the Tongass were halted from 1995 to 2095, the economic value of the net carbon sequestered during the 100-year hiatus, assuming $20/Mg C, would be $4 to $7 million/y (1995 US dollars). If a prohibition on logging were extended to 2195, the annual economic value of the carbon sequestered would be largely unaffected ($3 to $6 million/y). The potential annual economic value of carbon sequestration with management maxi- mizing carbon storage in the Tongass is comparable to revenue from annual timber sales historically authorized for the forest.
Key words: carbon sequestration; geographic information system; climate change; forest management; Alaska.
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Effects of tree mortality caused by a bark beetle outbreak on the ant community in the San Bernardino National Forest
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Ants are used as bioindicators of the effects of disturbance on ecosystems for several reasons. First, ants are generally responsive to alteration of the biomass and diversity of the local plant community (Kalif et al., 2001) and other environmental variables (Underwood & Fisher, 2006). Second, because they occupy fixed nest locations, ants are affected by conditions on a very small scale, so that their presence and abundance are a better indicator of local conditions than are the presence or abundance of more mobile animals (Stephens & Wagner, 2006; Underwood & Fisher, 2006). Ants play important ecosystem roles and are therefore often a relevant choice for monitoring (Ho ̈lldobler & Wilson, 1990). They make up a significant percentage of the animal biomass in many ecosystems, they can be crucial to processes such as soil mixing and nutrient transport (Gentry & Stiritz, 1972), and they are important players in nutrient cycling and energy flow. Ants can also strongly influence the plant community via seed dispersal and granivory (Christian, 2001; Barrow et al., 2007). While the diversity of a given taxon is often not a reliable indicator of the diversity of other groups (Lawton et al., 1998; Bennett et al., 2009; Maleque et al., 2009; Wike et al., 2010), ant diversity is known to reflect the diversity of other invertebrates in ecosystems recovering from a disturbance in some cases (Andersen & Majer, 2004).The use of ants as bioindicators must be undertaken with caution (Underwood & Fisher, 2006). Different ant communities do not always respond to a disturbance in the same way (Arnan et al., 2009). In addition, broad measures of a bioindicator taxon, such as species richness or abundance, are potentially misleading. For instance, while it is popular to measure the species richness of bioindicator groups, the ant species richness of different habitats has been observed to respond differently to similar disturbances (Farji-Brener et al., 2002; Ratchford et al., 2005; Barrow et al., 2007), and ant species richness often does not respond at all unless disturbances are extreme (Andersen & Majer, 2004).Nonetheless, changes in the ant community can provide useful information about the responses of the ecosystem as a whole.
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