The conservation value of urban riparian areas for landbirds during spring migration: Land cover, scale, and vegetation effects

Urbanization changes bird community structure during the breeding season but little is known about its effects on migrating birds. We examined patterns of habitat use by birds at the local and landscape level during 2002 spring migration at 71 riparian plots along an urban gradient in Cincinnati, Ohio, USA. Using linear regression, we examined variation in relative density, species richness, and evenness of four migratory guilds associated with natural land covers and building area at four scales (50, 100, 250, 500 m radial buffers). We also examined the influence of local vegetation using multiple regression models. As building area increased, riparian forests tended to be narrower and have fewer native trees and shrubs. In general, native birds were positively associated with tree cover (within 250-500 m of stream) and native vegetation, and negatively with building area (within 250 m); exotic species responded inversely to these measures. Short-distance migrants and permanent residents displayed the weakest responses to landscape and vegetation measures. Neotropical migrants responded strongest to landscape and vegetation measures and were positively correlated with areas of wide riparian forests and less development (>250 m). Resident Neotropical migrants increased with wider riparian forests (>500 m) without buildings, while en-route migrants utilized areas having a wide buffer of tree cover (250-500 m) regardless of buildings; both were positively associated with native vegetation composition and mature trees. Consequently, developed areas incorporating high native tree cover are important for conserving Neotropical migrants during stopover.     

Exploring Ground Vegetation Change for Different Deposition Scenarios and Methods for Estimating Critical Loads for Biodiversity Using the ForSAFE-VEG Model in Switzerland and Sweden

The ForSAFE-VEG model was used to investigate the impacts of climate change and air pollution scenarios on soil chemistry and ground vegetations composition. In particular, the model involves a ground vegetation model incorporating plant changes to ambient site conditions in terms of climate and chemistry, but the model also incorporate competition between the different plant groups. The model was validated against observed values and reproduced observations of tree growth, soil chemistry, and ground vegetation compositions to satisfaction. The results show that the ground vegetation reacts strongly to changes in air pollution, in particular nitrogen as well as to climate change with major shifts in plant composition. A procedure for estimating critical loads for nitrogen, using ground vegetation biodiversity as criterion, was tested and the method seems operable. It suggests that if we want to protect the present biodiversity of the ground vegetation, this will face significant difficulties because of permanent climate change that induced changes in the ecosystem. We conclude that the reference state for ground vegetation biodiversity is rather to be sought for in the future, hopefully using models, than in the past or present.     

Do frugivorous birds assist rainforest succession in weed dominated oldfield regrowth of subtropical Australia?

Exotic plants often form the first woody vegetation that grows on abandoned farmland. If this vegetation attracts vertebrate frugivores which disperse the seeds of native plants, then native plants may recruit to such oldfield sites. However, there is debate about the extent to which exotic vegetation assists or suppresses the regeneration of native plants, and about its effects on faunal biodiversity. These issues were investigated in subtropical eastern Australia, where rainforests were cleared for agriculture in the 19th century, and where regrowth dominated by camphor laurel (Cinnamomum camphora, an exotic, fleshy-fruited tree) has become common on former agricultural land. The study assessed the assemblages of frugivorous birds, and the recruitment of rainforest plants, at 24 patches of camphor laurel regrowth. The patches were used by nearly all frugivorous birds associated with subtropical rainforest. Many of these birds (16 of 34 species) are considered to have a medium to high potential to disperse the seeds of rainforest plants, and eight of these were abundant and widespread in regrowth patches. Of 208 recorded plant species, 181 were native to local rainforest. The ratio of native to exotic species was higher amongst tree recruits than adult trees, both for numbers of species and individuals. Among native tree recruits, 79% of 75 species, and 93% of 1928 individuals, were potentially dispersed by birds. These recruits included many late-successional species, and there were relatively more individuals of late-successional, bird-dispersed native species amongst recruits than adult trees. The species richness, but not the abundance, of both frugivorous birds and of bird-dispersed rainforest trees decreased with distance from major rainforest remnants. Camphor laurel regrowth provides habitat for rainforest birds and creates conditions suitable for the regeneration of native rainforest plants on abandoned farmland. Careful management of regrowth dominated by fleshy-fruited exotic invasive trees can provide an opportunity for broadscale reforestation in extensively-cleared landscapes.     

Urban drainage systems: An undervalued habitat for aquatic macroinvertebrates

Knowledge about the ecology of urban water systems is very scarce. We assessed the conservation value of urban drainage systems in lowland areas and compared these with similar watercourses in rural areas. A total of 36 water bodies in urban areas were selected to investigate the macroinvertebrate biodiversity in relation to environmental variables. Multivariate analysis of aquatic macroinvertebrate assemblages was used to distinguish urban water types and to link these types to key environmental variables. Several biodiversity indices for urban water systems were compared with those for other drainage systems in The Netherlands. Four types of macroinvertebrate assemblages were distinguished in the urban water systems, differing in environmental conditions and values of ecological indicators. The variation in macroinvertebrate assemblages was significantly explained by nitrate, pH, grain size (sediment composition), transparency, nymphaeid and submerged vegetation. Urban drainage systems can sustain a macroinvertebrate biodiversity comparable to that of drainage systems in rural areas (ditches and canals) and (semi)natural watercourses (lotic waters such as small streams and rivulets) and can even be a habitat for red list species. To optimize biodiversity values, urban water management should aim at lowering nutrient levels, stimulating vegetation (diversity of habitat structure) and increasing transparency, which are key factors for macroinvertebrate diversity. We show the potential conservation benefits of water systems in urban areas, but further studies are needed to investigate the optimal design of cities to include biodiversity as an integrated part of the urban environment, thereby sustaining a higher biodiversity in an increasingly urbanizing world.     

Effects of anthropogenic land use on forest birds and butterflies in Subic Bay, Philippines

Despite the loss of 83% of native forests in the Philippines, little is known on the effects of this massive habitat loss and degradation on its forest biotas. This is a cause for concern because of the threat posed to the country’s large number of endemic taxa. To investigate the impacts of anthropogenic disturbance, forest birds and butterflies were surveyed in closed and open canopy forests, as well as suburban, rural and urban areas within the Subic Bay Watershed Reserve and Olongapo City in western Luzon. Measures of forest species richness and population densities for both taxa were similar in the two forest types, but showed different patterns in the other habitats. Indirect gradient analysis showed that forest bird species were positively correlated with vegetation variables (i.e., canopy cover, tree density, height to inversion and ground cover), while forest butterflies were not strongly correlated to any of the measured habitat variables. Community composition of birds in forests was distinct from those in modified habitats, while butterfly communities were more similar. A simulation showed that canopy cover of 60% or higher was required by 24 of the 26 bird species that were sensitive to canopy loss. Endemicity and nesting strata were the significant predictors of vulnerability to habitat disturbance for birds, while endemicity and larval hostplant specificity were significant for butterflies. Both taxa were negatively affected by anthropogenic disturbance but may respond to different components in the habitat (i.e., structure and resources), and thus cannot be used as surrogates of each other. Conservation of forests with contiguous canopy cover should be prioritized, and more ecological research is needed to improve the knowledge on the effects of disturbance on Philippine biodiversity.     

Impacts of coffee agroforestry management on tropical bee communities

Though it is undoubted that tropical bees are influenced by habitat composition, few studies have investigated the relative importance of both local and landscape-level habitat parameters in supporting large and diverse bee communities. The conservation of native bee communities within agroforestry landscapes is particularly urgent given the importance of pollination services within these systems. In this study, we examined tropical bee communities within a largely deforested shade coffee-growing region in Chiapas, Mexico. We used regression tree modeling to examine the response of bee functional groups to local and landscape-level habitat management. Our models revealed that the most predictive factors for bee abundance and species richness were the number of tree species, the number of tree species in flower, and the canopy cover of the local agroforestry landscape. Solitary bees were most abundant in habitats with high canopy cover, while social bees were most abundant in habitats with greater tree species richness. Cavity-nesting and wood-nesting bee abundance was positively affected by the amount of canopy cover in the farm, while ground-nesting bees were most abundant in habitats with a large number of tree species in flower. Our results demonstrate that across bee sociality groups, nesting guilds, and tribes, the most critical factor impacting native bee communities was within-farm local vegetation management. These results reveal the important role that agroforestry managers can have on biodiversity conservation, and the potential contribution they can make by creating resource-rich agricultural matrices. Specifically, our findings highlight the importance of diverse overstory tree management in supporting native bee communities within tropical agroforestry systems.     

How do butterflies define ecosystems? A comparison of ecological regionalization schemes

Ecological regionalizations, such as ecoregions or environmental clusters, are often used as coarse filters for conservation. To be effective biodiversity surrogates, regionalizations should contain distinct species assemblages. This condition is not frequently evaluated and regionalizations are rarely assessed comparatively. We used a national dataset of Canadian butterfly collections to evaluate four regionalizations (ecoregions, land cover and productivity regime classifications, and a spatial grid) at two thematic resolutions using analysis of similarity (ANOSIM) and species indicator values. Overall, the spatially constrained schemes (ecoregions and grids) best captured patterns of butterfly community composition and species affinities, indicating that butterfly communities are strongly structured by space at the continent scale. In contrast, when comparing regions only within spatial or environmental neighbourhoods (i.e., comparing between regions that are adjacent along geographic or environmental gradients), all regionalizations performed similarly. Adjacency in environmental space is thus as important as physical adjacency at determining community dissimilarity. Productivity regimes and land cover will be useful biodiversity surrogates when considered in conjunction with space or within a spatially constrained area. This finding was confirmed with two ecoregional case studies (of the Algonquin-Lake Nipissing and Thompson–Okanagan Plateau ecoregions), which also revealed that the relative performance of regionalizations depends upon the context of the study area. We conclude that including species data can improve the efficiency of environmental surrogates for systematic conservation planning.     

Native vegetation cover thresholds associated with species responses

We examined data on bird and reptile assemblages in a plantation landscape in southern New South Wales, south-eastern Australia, for evidence of threshold responses to the amount of native eucalypt vegetation in circular areas of 2000 and/or 1000 m around field survey sites. These circular areas contained varying proportions of native Eucalyptus and exotic radiata pine Pinus radiata forest thereby providing a basis for examining potential threshold effects in relation to the area of native vegetation cover. For bird species richness or the probability of detection of individual bird species we found no empirical evidence of a threshold response to the area of native vegetation cover, or any other potential explanatory variables. All relationships were characterised by considerable variability in the response data. “Broken-stick” relationships which involved sudden change points did not fit the response data better than smooth relationships obtained from generalised additive or linear models. As with birds, there was no evidence that a threshold model between lizard richness and the amount of native vegetation within 1000 m described the relationship any better than a smooth, continuous or other type of relationship. Several related factors may explain our results. An important one is that species-specific responses to landscape conditions mean that marked thresholds will not be seen for an aggregate measure like species richness at a given value for a given landscape variable. Another is that factors other than the amount of native vegetation may significantly influence underlying patterns of species occurrence. This highlights a need to be aware of the potential effects of various ecological processes, even when a substantial amount of native vegetation cover remains.Our findings do not rule out the possibility of the existence of threshold relationships. However, irrespective of the choice of measure of predictor variable (e.g., the amount of native vegetation cover), it will often be difficult to detect and estimate threshold responses due to high inherent variability - a characteristic of the vast majority of ecological datasets. Furthermore, even if it is possible to estimate functional (threshold) forms and although they might be useful from an explanatory perspective, in most instances they are likely to be of limited value in a predictive sense. This calls into question the practical significance of the threshold concept.     

Altered vegetation structure and composition linked to fire frequency and plant invasion in a biodiverse woodland

Relationships between fire history, vegetation structure and composition, and invasion by introduced plant species have received limited attention in Australian woodlands. A study in a Mediterranean, fire adapted urban Banksia woodland remnant in the biodiversity hotspot of southwest Australia investigated: (1) Have significant changes occurred in the woodland tree canopy between 1963 and 2000? (2) Do correlations exist between fire frequency and canopy cover? (3) If there is a difference in the vegetation composition of Banksia woodland invaded by the South African Ehrharta calycina (PCe) and Pelargonium capitatum (PCp) compared to largely intact remnants (GC)? and (4) Do correlations exist between vegetation condition, composition, fire frequency and invasion? Aerial photography, processed in a Geographical Information System, was used to establish fire history and changes in canopy cover over time (1963–2000). PCe and PCp sites experienced the greatest number of fires, with a net reduction in canopy cover in all areas experiencing four or more fires (60% of all woodlands). Frequent fire corresponded with a decline in native cover, richness and diversity, a shift from native to introduced species, changes in the relative importance of fire response categories, and loss of native resprouting shrub cover. Life forms of introduced species, which included no trees, shrubs and perennial sedges, contrasted strongly with those of native species, which had poor representation of annual and perennial grasses. Clear ecological and conservation consequences due to the loss of species diversity, changes in fire ecology and invasion have occurred in the Banksia woodlands. This study provides an understanding of the invasion process, enhancing conservation knowledge to improve the adaptive management of the key threatening process of invasion in biodiverse communities.     

Urbanization and riparian forest woody communities: Diversity, composition, and structure within a metropolitan landscape

Understanding how urban land-use structure contributes to the abundance and diversity of riparian woody species can inform management and conservation efforts. Yet, previous studies have focused on broad-scale (e.g., urban to exurban) land-use types and have not examined more local-scale changes in land use (e.g., the variation within “urban”), which could be important in urban areas. In this paper we examine how local-scale characteristics or fine-scale urban heterogeneity affect(s) the diversity, composition, and structure of temperate woody riparian vegetation communities in the highly urbanized area of Cincinnati, Ohio, USA. We use an information-theoretic approach to compare vegetation models and canonical correspondence analyses to compare species responses to urban variables. We found that urban riparian areas can harbor a high diversity of native canopy and shrub species (38 and 41, respectively); however, native and exotic woody plant species responded differently to urbanization. Exotic canopy species increased with the level of urbanization while native canopy and understory species declined. Understory species diversity displayed a greater response to urbanization than did canopy diversity, suggesting temporal lags in canopy response to disturbances associated with present and recent land-use changes. Certain native and exotic woody species represent ecological indicators of different levels of urbanization. Native species characteristic of pre-European settlement conditions were restricted to the wide riparian forests with little urban encroachment. Several native early-successional species appear tolerant to urbanization. Two exotic species, the tree Ailanthus altissima and the shrub Lonicera maackii, were the most abundant and ubiquitous woody species and appear to exploit urban disturbances. These exotic species invasions have the potential to modify forest composition and ecological function of urban riparian systems. In addition, altered hydrology may be a contributing factor as canopy and understory stem density of high-moisture-requiring species decreased with an increase in impervious surface and grass cover and with proximity to roads and railroads. In the face of urbanization, maintaining wide riparian forests and limiting building, road and railroad development within these areas may help reduce the invasion of exotic species and benefit hydrological function in temperate riparian areas.     

Changes of the functional diversity of soil microbial community during the colonization of abandoned grassland by a forest

The impact of secondary succession of grassland communities towards a Norway spruce forest on soil microbial community was studied on a belt transect established in the Pol’ana Mts., Central Europe. Data on understory vegetation, light availability, soil properties and microbial activity were collected on 147 plots distributed over regular grid. Moreover, distributions of functional groups of microorganisms were assessed using BIOLOG analysis on a subset of 27 plots. Mantel partial correlations between microbial community indicators and environmental variables showed that microbial activity generally decreased with increasing tree density and size, whereas it increased with increasing radiation at the soil surface, soil temperature, and cover and diversity of understory vegetation. Functional richness and diversity of microorganisms were positively correlated with solar radiation, but also with plant species richness and diversity. Abundance of several functional groups correlated closely with succession-related variables. Redundance analysis of microbial data provided slightly different outcomes. Forward selection yielded only two environmental variables significantly influencing the composition of the microbial community: tree influence potential and organic carbon content. Abundances of several functional microbial groups correlated with tree influence, documenting that microbial community changes are at least partially driven by the colonization of grassland by trees. Nevertheless, the relative importance of abiotic environment change and plant community succession on microbial community dynamics remains unresolved.     

Scattered trees in rural landscapes: foraging habitat for insectivorous bats in south-eastern Australia

Scattered trees and small patches of vegetation among farmland are typical of rural landscapes throughout the world, often comprising a significant proportion of remaining habitats for native fauna. Insectivorous bats can use such isolated resources owing to the high mobility of most species, but little is known of the relationship between bats and tree density, or of the impact of incremental loss of trees in the landscape. Bats were surveyed at 30 sites in south-eastern Australia, in five habitat categories representing a range of tree densities from remnant woodland blocks (>35 trees/ha) to sparsely scattered trees (<1 tree/ha), and open paddocks devoid of trees. Sampling was undertaken by using harp traps and ultrasonic bat detectors. The abundance of potential arthropod prey was assessed by using light traps. Eleven species of insectivorous bats were recorded and bats were widespread in all habitat categories; all species were recorded around scattered trees. Overall activity, as revealed by detectors, did not differ significantly between the four treed categories, but in open paddocks there was a lower level of activity and a different community composition. However, a regression model revealed a significant quadratic relationship between activity of bats and tree density, with highest activity at 20-30 trees/ha. All species were recorded in open paddocks, but for eight of the ten species this represented <7% of their total activity recorded across all habitat categories. For six species, significant positive correlations were found between activity levels and the abundance of potential arthropod prey. In contrast to bat detectors, trapping results showed a significant difference in overall abundance of bats between wooded habitats, with decreased abundance as tree density declined. This study highlights the value of scattered trees as foraging habitat for bats, and emphasizes that, in rural land mosaics, such small and isolated habitat components have value for the conservation of biodiversity, and require greater recognition and protection.     

Are higher taxa adequate surrogates for species-level assemblage patterns and species richness in stream organisms?

We examined the utility of using genera and families as surrogates of species-level assemblage patterns. We assessed cross-taxonomic level congruence, as well as taxonomic structure-environment and taxon richness-environment relationships in stream macroinvertebrate and diatom data surveyed across Finland. A number of interesting and important findings emerged from our analyses. For both macroinvertebrates and diatoms, species richness was strongly correlated with genus and family richness, and similarities in assemblage structure between species-, genus- and family-level matrices were also significant and relatively strong. For macroinvertebrates, the key environmental variables for assemblage structure and taxon richness remained the same irrespective of taxonomic level. For diatoms, however, the environmental variables related to variation in diatom taxon richness varied between taxonomic data sets, while determinants of assemblage structure remained largely the same. For macroinvertebrates, relatively similar amounts of variation in assemblage structure and taxon richness for species-, genus-, and family-level data were accounted for by the environmental variables, shared environmental and spatial variables, spatial variables, and total variation explained. By contrast, for diatoms, these components of variability differed somewhat between taxonomic levels. Our results suggest that, for macroinvertebrates, even family-level data could be used in rapid biodiversity assessments, where the objective is to examine biodiversity patterns and rank sites according to their conservation value in our study region. Families might also perform well in this task in other regions that are characterized by low faunal species diversity, but the situation is likely to be different for regions with higher species diversity. Although weaker than the relationships in macroinvertebrate data, species-level data for diatoms also showed rather similar patterns to genus- and family-level data. However, due to the low number of diatom families, it is likely that families do not provide enough variability in biodiversity patterns. Thus, for diatoms, genus-level data could perhaps be more efficient than family-level data in correlating with species-level data and portraying assemblage patterns for conservation purposes.     

What makes an effective restoration planting for woodland birds?

Large-scale vegetation clearing accompanying agricultural development has been a major driver of biodiversity loss. Efforts to reverse this problem have often included revegetation, but the value of revegetated areas for biodiversity is poorly known. We addressed aspects of this knowledge gap using a case study in south-eastern Australia. We quantified relationships between bird species richness and the probability of detection for eight individual bird species and: (i) the context of a planting, i.e. the types of the vegetation cover in the neighborhood of a planting, (ii) the configuration of a planting, i.e. the location and geometry of a planting, and, (iii) the content of planting, i.e. the vegetation features of a planting.The presence and nature of the effects of these explanatory variables varied with each of our response variables. A combination of context, configuration and content variables were needed to explain the variability in species richness and the presence of individual species. Context effects were highly significant, particularly the amount of planted and remnant native vegetation surrounding plantings. We speculate that when the area surrounding a planting was potentially suitable, recognition of planting “patch” boundaries disappeared and, correspondingly, configuration effects such as planting size were limited. Our results suggest that maximizing the value of planted areas for bird biota requires consideration not only of the features of the vegetation within a planting, but also where a planting is placed.     

The abundance of hollow-bearing trees in urban dry sclerophyll forest and the effect of wind on hollow development

Anthropogenic change, particularly in urban landscapes, has resulted in the fragmentation of indigenous vegetation into often small isolated ‘remnants’. The persistence of arboreal fauna in small urban remnants in part depends on the distribution and abundance of habitat resources within the remnant. We surveyed 44 small (<2.5 ha) eucalypt remnants located within the south-eastern suburbs of metropolitan Melbourne to ascertain the abundance of hollow-bearing trees, an important ecological resource. The probability of a live or dead tree containing a hollow was investigated in relation to site variables that influenced exposure to wind, a factor thought to increase the propensity of hollow formation in eucalypt trees. A total of 2678 live and 224 dead eucalypt trees were surveyed, of which 350 live (12%) and 70 dead (31%) trees were hollow-bearing. The probability of a tree being hollow-bearing was strongly positively associated with the diameter of the tree, however, past management practices have lead to a paucity of large (>80 cm DBH) trees in small urban remnants. We found that variables that measured exposure to wind were correlated with the chance that a live tree will be hollow-bearing while reducing the chance that a dead tree will be hollow-bearing. Although highly variable, the number of hollow-bearing trees contained within small urban remnants (mean of 5.8 ha⁻¹) fell well below that contained in areas of un-logged non-urban forest. Our results indicated that large numbers of hollow-bearing tree are unlikely to be recruited into urban remnants for a significant time-span and as such there is an increased importance placed on maintaining the current inventory of hollow-bearing trees for the maintenance of biodiversity in urban areas.     

GIS-models work well, but are not enough: Habitat preferences of Lanius collurio at multiple levels and conservation implications

Species conservation largely depends on knowledge of habitat needs of target species. GIS-models are increasingly used to assess habitat preferences and distribution of target species, but their accuracy is constrained by availability of digital data layers. We developed a two-steps approach aiming at showing pros and cons of landscape (GIS)- and site-level habitat models, identifying key habitat factors for conservation of a threatened bird species, the red-backed shrike Lanius collurio. A spatially explicit GIS-model was generated using landscape variables, and a second model at site level was developed using fine-scale variables measured on the ground. The GIS-based model was then extrapolated to the entire region to obtain a map of distribution of suitable habitats. Positive associations between shrike occurrence and both hedgerow length and partial shrub cover were detected at both scales. Shrikes were also positively associated with grassland cover at landscape level and with partial cover of untilled herbaceous vegetation at the finer scale, and negatively affected by lucerne cover. The GIS-model led to an affordable map of predicted habitat suitability which should help conservationists to focus on different local priorities, but was unable to identify effects of untilled and lucerne cover. Site-level model gave fine details for habitat management, but its application elsewhere requires ground-measurements of factors. Combining the multiscale models could indicate more urgent actions at large scales (e.g. maintaining suitable habitats, or improving connectivity among isolated patches) and draw a detailed figure of the most suitable habitat for the species. Shrike occurrence was associated with a higher number of shrub and tree species: the indicator value of the species should ensure general benefits for biodiversity from dedicated management.     

ANNUAL SOIL MOISTURE REGIMES IN THE ROOTING ZONE ACROSS THE PRAIRIE-FOREST BOUNDARY OF SOUTH-WEST ALBERTA

Vegetation cover is shown to play a major role in determining the soil moisture content in the Front Range of the Rocky Mountains near Calgary. Thus lodge-pole pine abstracts more moisture from the soil both in summer and winter than aspen, while least moisture loss is experienced on bare soil. Clearly vegetation cover must be kept constant when comparing two soils. Additional important variables are aspect and parent material. It was also found that permanent (IS bar) wilting-point, as commonly used, bears little relation to the permanent wilting-point of even the more moisture-loving native trees studied. They all do not wilt until a much lower moisture content is reached.     

Buffelgrass (Pennisetum ciliare) land conversion and productivity in the plains of Sonora, Mexico

Bufflelgrass (Pennisetum ciliare syn. Cenchrus ciliaris) is an African grass that has been widely introduced in subtropical arid regions of the world to improve rangelands for cattle production. However, it can have a negative effect on the diversity of native plant communities. Buffelgrass was introduced to Sonora, Mexico in the 1970s as a means to bolster the cattle industry. “Desmonte,” the process by which native desert vegetation is removed in preparation for buffelgrass seeding, alters the land surface such that buffelgrass plots are easily detectable from aerial and Landsat satellite images. We estimated the extent of conversion to buffelgrass in a 1,850,000 ha area centered on Hermosillo, from MSS and TM images from 1973, 1983, 1990 and 2000. We then compared the relative above-ground productivity of buffelgrass to native vegetation using Normalized Difference Vegetation Index values (NDVI) from Landsat and Moderate Resolution Imaging Spectrometer (MODIS) satellite sensor systems. Buffelgrass pastures have increased from just 7700 ha in 1973 to over 140,000 ha in 2000. Buffelgrass pastures now cover 8% of the land surface in the study area. Buffelgrass pastures have lower net primary productivity, estimated by MODIS NDVI values, than unconverted desert land. The desmonte process removes trees and shrubs, while the buffelgrass plantings are often sparse, leading to an apparent net loss in net primary production from land conversion. We recommend that the desmonte process be discontinued until its efficacy and safety for native ecosystems can be established, and that a comprehensive plan for preserving biodiversity while accomodating economic development be established for this region of the Sonoran Desert in Mexico.     

The conservation value for mammals of reserves in the western Australian wheatbelt

Twenty-three reserves in the Western Australian wheatbelt were examined in an attempt to assess their conservation value for native mammals, excluding bats. Multiple regression analysis on log transformed data showed that 72% of the observed variation in mammal species richness between reserves was accounted for by reserve size. The addition of the other reserve variables examined did not increase significantly this explained variation, although significant correlations existed with most variables. Estimates suggest that a minimum reserve area of about 40,000 ha is required to conserve that part of the regional assemblage of mammals in southern and western Australia likely to persist in the face of moderate disturbances by man and his agencies. Reserves should have large areas of major vegetation formations and maximise the number of regional vegetation associations. Nature reserves as small as 30 ha are valuable sanctuaries for certain species of native mammals.Comparison with mammal faunas isolated on islands by Quaternary glacioeustatic sea-level rise shows that in relation to area, wheatbelt reserves are richer in species, but the slopes of the regressions are similar, particularly for those islands that are little disturbed by man and introduced predators. We suggest that most of the species of mammals surviving in the wheatbelt are suited to existing within patches of vegetation, such as nature reserves, because they are adapted to surviving within the natural archipelago of soil and vegetation types which characterise the wheatbelt and southwestern Western Australia. We suggest that the species of mammals that have become extinct in the wheatbelt are those that are unable to cope with alteration in environmental patchiness caused by changes in the pattern of fires resulting from European occupation.     

Soil and climate are better than biotic land cover for predicting home-range habitat selection by endangered burrowing owls across the Canadian Prairies

Statistical models that describe species-environmental relationships are important components within many wildlife conservation strategies. These models are typically developed from studies conducted on small geographic scales (hundreds of square kilometres), representing a relatively small range in environmental conditions. Such local models from local studies are often then extrapolated to predict the suitability of other unsampled regions. The value of many models would be increased by considering larger-scale processes that might be structuring spatial patterns across species distributions. We examined home-range habitat selection by burrowing owls throughout the mixed prairie grassland region of western Canada (180,000 km²) to determine whether owl selection for biotic factors changes along abiotic gradients. Specifically, we classified 37 explanatory variables into five categories (geography, grassland fragmentation, land-use, soil, and climate), created models for each set of variables, and evaluated the predictive ability of each model. We then examined interaction effects to determine if the relationship between land cover variables and the probability of owl home-range selection varied within large-scale abiotic criteria. Our results showed that soil and climate produce the most predictive models of burrowing owl home-range selection and create unique environmental conditions for owls which are independent of land cover at this scale. This study provides new insight into burrowing owl habitat requirements, and strengthens the case for considering large-scale abiotic gradients when prioritizing areas for species conservation.