42 research outputs found
Observations of climate change among subsistence-oriented communities around the world
No full textThe study of climate change has been based strongly on data collected from instruments, but how local people perceive such changes remains poorly quantified. We conducted a meta-analysis of climatic changes observed by subsistence-oriented communities. Our review of 10,660 observations from 2,230 localities in 137 countries shows that increases in temperature and changes in seasonality and rainfall patterns are widespread (≈70% of localities across 122 countries). Observations of increased temperature show patterns consistent with simulated trends in surface air temperature taken from the ensemble average of CMIP5 models, for the period 1955-2005. Secondary impacts of climatic changes on both wild and domesticated plants and animals are extensive and threaten the food security of subsistence-oriented communities. Collectively, our results suggest that climate change is having profound disruptive effects at local levels and that local observations can make an important contribution to understanding the pervasiveness of climate change on ecosystems and societies
How the importance of survival estimates in estimating Whinchat population dynamics depends on the scale of migratory connectivity and site fidelity
No full textAccurate monitoring of whinchat population dynamics requires accurate estimates of breeding season survival and productivity, non-breeding survival and site fidelity (dispersal, immigration and emmigration). But monitoring of non-breeding survival between breeding seasons is confounded by the scale of site fidelity resulting in low estimates, and this will vary dependent on breeding success. Only one study (in progress) has measured true survival of whinchats on the wintering grounds (in Nigeria) where site fidelity is probably very high. Results from an ongoing geolocator tagging study also show only very large scale connectivity (at the scale of thousands of kilometres) between breeding and wintering populations. This means that annual survival rates measured at any point on the wintering ground probably average true breeding and migration survival for a large part of the breeding range, giving a representative true survival rate to use in calculating population dynamics. More importantly, if we have a measure of true average annual survival then we can calculate the proportion of adults that are dispersing and also the scale at which they disperse for breeding populations. Between winter survival rates for whinchats are the same for first year birds and adults suggesting that the ubiquitous lower survival rate of juveniles must arise between fledging and arrival at their wintering territory: therefore survival estimates for this period should be investigated. If survival immediately post-fledging or just before migration is variable then this will greatly affect local population dynamics, but once migration starts – the multiple routes and large scale connectivity - will mean populations over a large area will be affected to the same degree. If survival during first migration has declined substantially anywhere then many populations in the Palearctic will be affected. Average annual true survival for whinchats greater than about 4 months old, across much of Eastern Europe is greater than 50%: therefore it is it likely that local productivity or survival pre-migration determines an individual population’s dynamics, with the overall trajectory for the population being determined by the additive effect of first migration survival. However, further estimates of whinchat true annual survival are needed from other areas of Africa to determine if overwinter survival is always high: if not then this variation would negatively affect all Palearctic whinchat populations because of large scale connectivity, in the same way that first migration survival may do
Appendix B. A description and example using simulated data of the bivariate K-function test for dependence between two temporal point processes.
No full textA description and example using simulated data of the bivariate K-function test for dependence between two temporal point processes
Mixed-severity Fire Regimes in Dry Forests of Southern Interior British Columbia, Canada
No full textHistorical fire severity is poorly characterized for dry forests in the interior west of North America. We inferred a multicentury history of fire severity from tree rings in Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) – ponderosa pine (Pinus ponderosa Douglas ex P. Lawson & C. Lawson) forests in the southern interior of British Columbia, Canada. In 2 ha plots distributed systematically over 1105 ha, we determined the dates of fire scars, indicators of low-severity fire, from 125 trees and inferred dates of even-aged cohorts, potential indicators of high-severity fire, from establishment dates of 1270 trees. Most (76%) of the 41 plots contained fire-scarred trees with a mean plot-composite fire scar interval of 21 years (1700–1900). Most (76%) also contained one or two cohorts. At the plot scale, we inferred that the fire regime at most plots was of mixed severity through time (66%) and at the remaining plots of low (20%), high (10%), or unknown (4%) severity through time. We suggest that across our study area, the fire regime was mixed severity over the past several centuries, with low-severity fires most common and often extensive but small, high-severity disturbances also occasionally occurred. Our results present strong evidence for the importance of mixed-severity fire regimes in which low-severity fires dominate in interior Douglas-fir – ponderosa pine forests in western Canada
Fire and climate variation in western North America from fire-scar and tree-ring networks
No full textFire regimes (i.e., the pattern, frequency and intensity of fire in a region) reflect a complex interplay of bottom-up and topdown controls (Lertzman et al., 1998; Mc Kenzie et al., in press). Bottom-up controls include local variations in topographic, fuel and weather factors at the time of a burn (e.g., fuel moisture and continuity, ignition density and local wind and humidity patterns). Bottom-up regulation is manifest as fine-scale spatial and temporal heterogeneity in fire behavior and effects within landscapes subject to the same general climate. Examples include variation in fuel consumption, tree mortality and soil effects, which create complex burn severity legacies that can influence subsequent fires (Collins and Stephens, 2008; Scholl and Taylor, 2010)
OVERSTORY STRUCTURE DRIVES FINE-SCALE COUPLING OF UNDERSTORY LIGHT AND VEGETATION IN TWO TEMPERATE RAINFOREST FLOODPLAINS
No full textRiparian ecosystems – particularly floodplains – of temperate rainforest regions are productive, diverse, functionally important and socially valued, yet we lack key information about their structure and function to guide conservation and management. In two one-hectare floodplain sites in coastal British Columbia, we mapped tree locations, classified gap processes, and described understory vegetation and light transmission on a systematic grid. We used hemispheric photography and spatial interpolation to map understory light and we examined how environmental heterogeneity affects understory vegetation. Understory light levels are high (overall median 18% full sun) but vary appreciably over short distances (0.5% to 19% full sun over 14 m). Understory composition varies in relation to light transmission, indicating that overstory structure drives fine-scale spatial structure in the understory plant community. Overstory trees appear to create “shade refuges” from competition with dominant shrubs. Shrub cover increases with light and may also play a role in maintaining persistent canopy openings by slowing conifer recruitment. Despite substantial differences in age and development history, each stand exhibits fine-scale spatial coupling of understory light and vegetation. Management practices encouraging structural complexity may accelerate development of similar processes and patterns to restore floodplain function in high-density second growth stands.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author
13,000 years of fire history derived from soil charcoal in a British Columbia coastal temperate rain forest
No full textSolar Radiation Transfer Through a Subarctic Shrub Canopy
No full textMuch of the low Arctic is covered with shrubs that are partially buried by snow in winter and become exposed during melt. This study presents measurements and modeling of shortwave radiation reflection and extinction by a deciduous shrub canopy emerging from a melting snowcover in the mountains of the Yukon Territory, Canada. Shrubs shade most of the snow surface at low solar elevation angles, so only a fraction of the incoming radiation reaches the surface, but there is greater direct shortwave transmission to the surface in gaps between shrubs for higher solar elevations. A simple model is developed to incorporate the changing contributions of sun-lit gaps, shaded gaps, and shrubs to the landscape-averaged (areal) transmission and reflection of shortwave radiation. The areal transmissivity and albedo in this model are lower than in a two-stream approximation that neglects gap shading. A simple shadow parameterization is proposed for calculating shrub tundra snowmelt rates and surface energy balances in hydrological and land-surface models
