Assessing critical habitat: Evaluating the relative contribution of habitats to population persistence

A principal challenge of species conservation is to identify the specific habitats that are essential for long-term persistence or recovery of imperiled species. However, many commonly used approaches to identify important habitats do not provide direct insight into the contribution of those habitats to population persistence. To assess how habitats contribute to overall population viability and characterize their relative importance, a spatially-explicit population viability model was used to integrate a species occurrence model with habitat quality and demographic information to simulate the population dynamics of the Ord’s kangaroo rat (Dipodomys ordii) in Alberta, Canada. Long-term productivity (births-deaths) in each patch was simulated and iterative patch removal experiments were conducted to generate estimates of the relative contribution of habitat types to overall population viability. Our results indicated that natural dune habitats are crucial for population viability, while disturbed/human-created habitats make a minor contribution to population persistence. The results also suggest that the habitats currently available to Ord’s kangaroo rats in Alberta are unlikely to support long-term persistence. Our approach was useful for identifying habitats that did not contribute to population viability. A large proportion of habitat (39%) represented sinks and their removal increased estimated population viability. The integration of population dynamics with habitat quality and occurrence data can be invaluable when assessing critical habitat, particularly in regions with variable habitat quality. Approaches that do not incorporate population dynamics may undermine conservation efforts by under- or over-estimating the value of habitats, erroneously protecting sink habitats, or failing to prioritize key source habitats.     

Management Strategies of Free-Roaming Horses in Alberta Compared with Other Jurisdictions

Management strategies of free-roaming species are subject to polarizing debates around the world. This paper provides perspectives on free-roaming horse management strategies practiced in Alberta and compares them against national management strategies used in Canada and internationally (United States and Australia) to illustrate importance of science-based and socially inclusive management schemes. Owing to their pluralistic status as an introduced and culturally significant species of western Canada, free-roaming horse populations are a contentious environmental management issue in Alberta. Some stakeholders (e.g., indigenous people, horse and animal rights advocates) believe the government aims to extirpate free-roaming horses in favor of cattle grazing. However, the Albertan government and ranchers believe it is important to conserve and manage free-roaming horse populations for all land users while minimizing adverse environmental effects in sensitive foothill and mountain grasslands and associated riparian areas in Alberta. Despite this contention, a systematic approach that is mindful of the history and cultural value of horses to society is required to properly manage this species. Best management practices from case studies were used to compare against four main concerns identified from the literature of free-roaming horse management used in Alberta. Concerns include 1) cultural heritage values, 2) free-roaming (or wild) horse designation, 3) lack of scientifically rigorous population monitoring, and 4) societal considerations. Ecological effects of free-roaming horses and human dimensions of their management are discussed. It is recommended that lessons learned from other jurisdictions be applied to free-roaming horse management in Alberta to provide a more holistic framework as the government develops a “feral horse management strategy.”     

加拿大森林经营与管理考察见闻

通过在加拿大现地20多天的森林经营与管理培训考察，对加拿大，特别是安大略省森林资源及经营管理有了较清楚了解。这些知识对提高陕西省森林经营与管理水平大有卑益。     

Evaluation of Fibre Flax (Linum usitatissimum L.) Performance under Minimal and Zero Tillage in Eastern Canada

The feasibility of producing fibre flax in minimum tillage or zero tillage (ZT) systems was investigated. The results were variable between the sites, which differed in soil type and previous cropping history. Tillage regime had no impact on fibre flax phenological development including number of days to emergence, days to flowering and days to harvest at either site. However, tillage regime had a significant effect on mean stem diameter, dry matter content and plant height at all three sampling dates at the sandy loam site, and a significant effect on mid‐season plant height at the clay site. At the sandy loam site, ZT plots had the highest populations of plants with the finest stem diameters, the lowest branching ratios, but the shortest plants by the end of the season. Overall, plant densities were greater, stem diameters thinner, and biomass production higher in the heavier soil of the clay site. These results indicate that under the growing conditions present in 1998, fibre flax can successfully be grown in minimum or ZT systems on different soil types in Eastern Canada. Moreover, the growth of fibre flax in these systems does not compromise the proportion of tall plants having thin stems and minimal branching, a critical quality parameter for fibre flax production.     

Effect of herbicides and annual weeds on the yield and seed quality of lathyrus (Lathyrus sativus L.)

Field research conducted over six location years has indicated that lathyrus (Lathyrus sativus L.) is a poor competitor with annual weed species. Failure to control annual weeds reduced lathyrus seed yields by 54–95%, depending on the weed species present and their density. Weed competition also reduced thousand-seed weight. Preplant soil-incorporated applications of trifluralin and postemergence applications of sethoxydim controlled wild oat (Avena fatua L.) and green foxtail (Setaria viridis (L.) Beav.). Trifluralin failed to control wild mustard (Sinapis arvensis L.), an important broad-leaved weed in western Canada, but this weed was controlled by both preplant soil-incorporated and postemergence applications of metribuzin. Lathyrus exhibited excellent tolerance to these herbicides, which are currently registered for use on high-acreage crops in Canada.     

Estimating the ‘critical’ distance at which adjacent land-use degrades wetland water and sediment quality

Conversion of forested lands to agriculture or urban/residential areas has been associated with declines in stream and lake water quality. Less attention has been paid to the effects of adjacent land-uses on wetland sediment and water quality and, perhaps more importantly, the spatial scales at which these effects occur. Here we address these issues by examining variation in water and sediment nutrient levels in 73 southeastern Ontario, Canada, wetlands. We modeled the relationship between water and sediment nutrient concentrations and various measures of adjacent land-use such as forest cover and road density, measured over increasing distances from the wetland edge. We found that water nitrogen and phosphorous levels were negatively correlated with forest cover at 2250 meters from the wetland edge, while sediment phosphorous levels were negatively correlated with wetland size and forest cover at 4000 meters and positively correlated with the proportion of land within 4000 meters that is itself wetland. These results suggest that the effects of adjacent land-use on wetland sediment and water quality can extend over comparatively large distances. As such, effective wetland conservation will not be achieved merely through the creation of narrow buffer zones between wetlands and more intensive land-uses. Rather, sustaining high wetland water quality will require maintaining a heterogeneous regional landscape containing relatively large areas of natural forest and wetlands.     

A multi-scaled analysis of avian response to habitat amount and fragmentation in the Canadian dry mixed-grass prairie

Previous research has suggested that ducks and songbirds may benefit from prairie landscapes that consist primarily of contiguous grasslands. However, the relative importance of landscape-level vs. local characteristics on mechanisms underlying observed patterns is unclear. We measured effects of grassland amount and fragmentation on upland and wetland songbird and duck density and nest success, and on some nest predators, across 16 landscapes in southern Alberta, Canada. We compared these landscape-level effects with local-scale responses, including distance to various edges and vegetation characteristics. We also evaluated several statistical approaches to comparing effects of habitat characteristics at multiple spatial scales. Few species were influenced by grassland amount or fragmentation. In contrast, distance to edge and local vegetation characteristics had significant effects on densities and nest success of many species. Previous studies that reported effects of landscape characteristics may have detected patterns driven by local mechanisms. As a corollary, results were very sensitive to statistical model structure; landscape level effects were much less apparent when local characteristics were included in the models.     

Vegetation Composition and Succession of Abandoned Farmland: Effects of Ecological,Historical and Spatial Factors

In North America, as well as in Europe, the mechanization and the modernization of the agricultural activities had strongly modified the agricultural landscapes. Originating from these transformations of the agricultural environment, abandoned farmlands remain poorly known environments. A holistic approach, including the analysis of ecological, historical and spatial factors, is used in order to understand the dynamics of these environments created by agricultural abandonment in southwestern Québec (Canada). The analysis of 36 abandoned farmlands in the study area reveals the existence of two ecological groups. The first ecological group is composed by abandoned farmlands originating from pasture and at the moment dominated by a spiny shrub vegetation. The second ecological group includes past cultivated field at the moment dominated by either hydric herbaceous and shrub vegetation. Abiotic ecological variables such as slope, surface stoniness, canopy opening and soil pH, as well as land-use history, and age of the abandoned farmlands, are major factors explaining the current state of abandoned farmlands. Succession vector analysis reveals a strong differentiation among abandoned farmlands as to their tree species regeneration. Possible management alternatives, such as reforestation, are proposed in order to integrate those new environments to the modern agricultural landscape.