Heterogeneity In Vegetation Structure Research Articles

Online appendix 1:Spatial refuges buffer landscapes against homogenisation and degradation by large herbivore populations and facilitate vegetation heterogeneity

Environmental heterogeneity across savanna landscapes, including different seasonal resources at different distances to water, may play a critical role in maintaining the size and diversity of wildlife populations and the sustainability of their resource base. We investigated whether extensive landscapes with functionally diverse seasonal resources and large waterless regions can mediate the effect of herbivory on plant composition, structure and diversity. Vegetation composition, structure and richness in two different vegetation types (mopane and sandveld woodland) at three distance zones (0 km – 5 km, 10 km – 15 km and > 20 km) from the permanent water of the Okavango Delta and Linyanti Swamps were surveyed. We modelled vegetation response of the most abundant species to herbivory in relation to distance from permanent water, and included fire frequency as a covariate. Trees favoured by elephants during the dry season occurred typically as immature, pollarded populations within 5 km of permanent water sources while mature tall populations of these species were found far from water (> 10 km – 15 km). Similarly, short high-quality grazing grasses were higher in abundance within 5 km of permanent water, whereas taller high-quality perennial grasses peaked in abundance beyond 20 km from permanent water. Trends in herbaceous richness with distance from water were contingent upon vegetation type, while tree richness did not change with distance from water. Spatial refuges in waterless regions of landscapes facilitate the creation of heterogeneity of vegetation structure, composition and richness by large herds of mammalian herbivores. Therefore, the extension of herbivore dry season foraging range, for example, by the creation of artificial water points (AWP) in backcountry woodlands, could seriously undermine the resilience of landscapes to herbivory by reducing the availability of spatial refuges. Consequently, it reduces the resilience of herbivore and predator populations that depend on these spatial refuges. We strongly advise that future scientific work, and management and policy actions should be focused on the identification and sustaining of these spatial refuges in wildlife areas.Conservation implications: Management and policy actions should be focused on the identification and sustainability of spatial refuges in wildlife areas. Too many AWP in backcountry woodlands could undermine the resilience of landscapes to herbivory by reducing the proportion of landscapes beyond 15 km from permanent water.

Interacting effects of fire severity, time since fire and topography on vegetation structure after wildfire

Fire is an important disturbance in forest ecosystems globally. Many of the effects of fire on forest processes are mediated through effects on vegetation structure. Understanding how fire properties, fire regimes and environmental variation interact to affect structure is required in the face of predictions of increasing size and severity of fires – “megafires”. Here, we investigated the influence of topographic position, fire severity, and time since last fire on vegetation structure in foothill eucalypt forests, two years after a large wildfire in south-eastern Australia. We found that forest gullies had significantly greater structural complexity than forest slopes; but that fire severity and time since last fire influenced the structure of vegetation in gullies and slopes in similar ways. Two years after wildfire, severely burnt gullies and slopes (tree crowns scorched or consumed) had a reduced canopy cover, but a denser cover of eucalypt saplings up to 4m tall, than gullies and slopes that had not been burnt. Compared with severe fire, understorey fire had much less influence on the structure of vegetation, with a significant effect only on slopes. There was little effect of the time since last fire prior to 2009 (≤3years vs. ≥20years) on subsequent vegetation structure after wildfire in either gullies or slopes. Finally, we found that fire did not homogenise the structure of gullies and slopes: vegetation structure in paired gullies and slopes did not become more similar following understorey or severe fire. Two years after a large wildfire, heterogeneity in the structural complexity of forest vegetation was evident at both the site and landscape scale. At the landscape scale, fire-induced heterogeneity in vegetation structure, arising from spatial variation in fire severity, provides habitat structures of differing quality for plants and animals. At a finer scale, the rapid return of distinct vegetation structure between adjacent gullies and slopes is important for the persistence of species that depend on a complex vegetation structure or require fine-scale heterogeneity in vegetation.

Disturbance ecology of Tasmanian highland grassland — an overview and implications for conservation management

Active manipulation of disturbances such as fire and grazing is often necessary to maintain or enhance biodiversity values in grasslands. However in many instances information is lacking on the disturbance regimes most likely to achieve conservation aims. This paper provides an overview of the effects of fire and grazing in Tasmanian highland grasslands, and the implications of these for conservation management of this vegetation. In Tasmania, highland grassland is defined as occurring above 600 m above sea level. The vegetation is typically dominated by species of Poa. Highland grassland is grazed by a suite of native herbivores and has a history of stock grazing, which continues at some sites of high biodiversity value. There is evidence that Indigenous Tasmanians regularly burnt highland grasslands and that Indigenous burning was instrumental in maintaining grassland at sites that otherwise would be forest. For highland grasslands below 1000 m asl, a reduction in the biomass of dominant grasses through disturbance is necessary in order to maintain plant species diversity. The use of periodic fire, together with native grazing, is likely to be beneficial in this regard. The combination of fire and grazing is also likely to prevent woody plant invasion and maintain vegetation structural heterogeneity. The near ubiquity of native grazing species means there is no ecological imperative for stock grazing. Low productivity of grasslands occurring above 1000 m means that competitive exclusion of interstitial species by grasses is unlikely and therefore active application of disturbance as a management tool will rarely, if ever be necessary. Disturbance management should be accompanied by a well-designed monitoring program and regular review of the management strategy

Habitat selection by breeding WhinchatsSaxicola rubetraat territory and landscape scales

We determined breeding season habitat preferences for a declining migrant grassland bird, the WhinchatSaxicola rubetra,using intensive, territory‐scale habitat and invertebrate data, and independently gathered landscape‐scale field survey and remotely sensed habitat data to determine whether the same habitat relationships were evident at both spatial scales. At the territory scale, low‐elevation and a heterogeneous vegetation structure with a high density of perches and tussocks were the dominant features of occupied habitats. The landscape‐scale model successfully predicted areas where breeding Whinchats were more likely to occur, and similar and consistent relationships with habitat features occurred at both spatial scales. However, plant species richness and topographic slope elicited different responses at different spatial scales, with steeper slopes and high plant species richness favoured at the landscape scale, whereas at the territory scale, low plant species richness was preferred and slope did not determine settlement. These differences reflect differences in the way the data were measured and extrapolated. This study identifies important attributes of lowland grassland habitats and landscapes for a stable population of breeding Whinchats, and the analysis shows the good predictive ability of remotely sensed data to model this species' distribution at larger spatial extents. Our findings provide methods for assessing habitat availability for this declining species and for managing habitats and landscapes to provide these essential elements.

Grassland structural heterogeneity in a savanna is driven more by productivity differences than by consumption differences between lawn and bunch grasses.

Savanna grasslands are characterized by high spatial heterogeneity in vegetation structure, aboveground biomass and nutritional quality, with high quality short-grass grazing lawns forming mosaics with patches of tall bunch grasses of lower quality. This heterogeneity can arise because of local differences in consumption, because of differences in productivity, or because both processes enforce each other (more production and consumption). However, the relative importance of both processes in maintaining mosaics of lawn and bunch grassland types has not been measured. Also their interplay been not been assessed across landscape gradients. In a South African savanna, we, therefore, measured the seasonal changes in primary production, nutritional quality and herbivore consumption (amount and percentage) of grazing lawns and adjacent bunch grass patches across a rainfall gradient. We found both higher amounts of primary production and, to a smaller extent, consumption for bunch grass patches. In addition, for bunch grasses primary production increased towards higher rainfall while foliar nitrogen concentrations decreased. Foliar nitrogen concentrations of lawn grasses decreased much less with increasing rainfall. Consequently, large herbivores targeted the biomass produced on grazing lawns with on average 75 % of the produced biomass consumed. We conclude that heterogeneity in vegetation structure in this savanna ecosystem is better explained by small-scale differences in productivity between lawn and bunch grass vegetation types than by local differences in consumption rates. Nevertheless, the high nutritional quality of grazing lawns is highly attractive and, therefore, important for the maintenance of the heterogeneity in species composition (i.e. grazing lawn maintenance).Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-016-3698-y) contains supplementary material, which is available to authorized users.

The Effects of Patch-Burn Grazing on Vegetation Structural Heterogeneity in the Northern Tallgrass Prairie of South Dakota

Patch-burn grazing was developed as a grazing system to increase vegetation structural heterogeneity in managed grasslands of the central Great Plains. To evaluate this system in northern tallgrass prairie, we compared the structural response of vegetation following patch-burn grazing to that of continuous season-long grazing at two sites in eastern South Dakota. We established two pastures at each site and randomly assigned one pasture at each site to a patch-burn grazing treatment and the other to a continuous season-long grazing treatment. We allotted cow-calf pairs to each pasture during the summers of 2007 through 2009. We burned one patch of the patch-burn grazing pastures each spring for three years, leaving one patch not burned at the end of the study. We measured foliar cover of major plant functional groups, litter cover, and visual obstruction at the end of each grazing season and measured forage quality three times during the final summer. Ordination of principal component patch means showed greater vegetation structural heterogeneity for patch-burn grazing than season-long continuous grazing each year. Our results suggest that patch-burn grazing is a strategy that has potential to increase vegetation structural heterogeneity in northern tallgrass prairies and should be tested at other northern locations.

Effects of water level and grassland management on alpha and beta diversity of birds in restored wetlands

Summary Nearly 60% of European wetlands have been lost to drainage or to the cessation of grassland management. Large amounts of resources are put into wetland restoration with the aim to recover biodiversity. However, few studies have simultaneously evaluated effects of management, wetness and flooding dynamics on biodiversity of restored wetlands such as seasonally flooded wet grasslands. We inventoried bird communities over 4 years at 137 sites (each 3·1 ha) within five restored wet grassland areas in Sweden to investigate whether species richness and occurrence of 12 common wet grassland species were related to (i) local conditions such as management (grazing, mowing and unmanaged areas), basic wetness and spring flooding dynamics. Further, we investigated whether (ii) the composition of the adjacent landscape (20 ha) related to local bird diversity and (iii) species turnover (i.e. beta diversity) differed between sites characterized by their basic wetness, degree of flooding and predominant management regime. Local species richness was positively linked to degree of flooding and basic wetness of grasslands but not to type of grassland management. Species richness tended also to be negatively linked to proportion of forest at the landscape scale. Although variable, the same results were also true concerning the probability of the occurrence of a single species at the local scale. Species turnover between sites, and thus total species richness, was distinctly higher in (i) grazed as compared to mowed grasslands except in dry non‐flooded grasslands and (ii) flooded as compared to non‐flooded sites. Similar patterns held for the subset of 12 red‐listed species. We suggest that the high beta diversity in grazed and flooded grasslands is driven by the heterogeneous vegetation structure, resulting in good conditions for foraging and nesting for several wet grassland bird species. Synthesis and applications. The selection of wetlands for conserving wet grassland birds should prioritize temporary flooded grasslands of moderate wetness, preferably far from forest edges. Restoration and management of wet grasslands should include water level management, removal of shrubs and trees, and low‐intensity grazing, whereas mowing could be used in non‐flooded grasslands of low basic wetness.

Impacts of fire and grazing management on South Africa’s moist highland grasslands: A case study of the Steenkampsberg Plateau, Mpumalanga, South Africa

Background: Grasslands are heavily utilised for livestock agriculture and the resultant degradation through mismanagement contributes to an estimated 60% of this biome being permanently transformed. This study focused on the impact of fire and grazing in moist highland grasslands.Objectives: To determine the contribution of burning frequency and grazing intensity combined (for domestic livestock and indigenous ungulates) on vegetation structure heterogeneity and species diversity.Methods: Eight study sites under different management regimes were sampled over two summers. Vegetation structure characteristics and diversity data were collected monthly within multiple replicates in each study site. A disc pasture meter was used to assess standing biomass. Differences in vegetation structure characteristics, plant community composition and plant species assemblage structure across sites were statistically analysed using analyses of variance, indicator species analyses, multidimensional scaling ordinations and two-way cluster analyses.Results: The combination of heavy grazing and annual burning leads to a distinct plant community dominated by disturbance specialist species. Selective grazing by indigenous herbivores promotes a community of unpalatable species. This study illustrates that fenced indigenous herbivores, even at moderate stocking densities, have a greater detrimental impact on plant diversity and structure than do domestic livestock.Conclusion: Intensive grazing and burning have a detrimental impact on plant species diversity and structure. This also affects resultant palatability for grazing livestock and fenced game. To promote both grazing quality and ecological integrity we recommend a minimum sustainable ‘fodder capacity’ or standing phytomass of 5000 kg per large-animal unit per hectare for domestic livestock in moist highland grasslands.

Description of vegetation and soil properties in sagebrush steppe following pipeline burial, reclamation, and recovery time

Sagebrush (Artemisia tridentata Nutt.) steppe displays a high degree of heterogeneity in vegetation structure and in the spatial distribution of soil properties. Sagebrush steppe in south central Wyoming, USA, is experiencing a multitude of surface disturbances that involve vegetation removal and soil mixing. We hypothesized that drastic disturbance associated with pipeline burial would result in homogenization of above- and below-ground properties and that soil variability would be higher in areas with longer recovery time. We established a spatially explicit sampling design (<15m scale) on neighboring reclaimed pipelines of different ages (1, 5, 36, and 55years), and two adjacent undisturbed areas. We used descriptive statistics and Bayesian geostatistical models to quantify and compare the plant community and soil properties (soil moisture, organic carbon concentration, total microbial abundance, and electrical conductivity) across plots. Disturbance initially resulted in uniform cover of weedy plant species; older plots had uniform cover of grasses. Shrub and forb cover was highest in the 55year old plot, but lower than the undisturbed reference areas. Soil properties in the youngest plots had increased soil moisture and salinity and decreased microbial abundance; these differences were less apparent in the older treatments. Disturbance did not result in universal homogenization of soil properties, and variability did not necessarily increase with recovery age for all properties. At the scale sampled, vegetation and soil properties did not display strong spatial correlation structures. Vegetation and soil properties in the 55year old plot were most similar to the undisturbed sagebrush steppe, indicating greatest degree of recovery, compared with younger recovery ages.

The future of grazing research

The future of grazing research

Impacts of Contrasting Alfalfa Production Systems on the Drivers of Carabid Beetle (Coleoptera: Carabidae) Community Dynamics.

Growing concerns about the environmental consequences of chemically based pest control strategies have precipitated a call for the development of integrated, ecologically based pest management programs. Carabid or ground beetles (Coleoptera:Carabidae) are an important group of natural enemies of common agricultural pests such as aphids, slugs, and other beetles. Alfalfa (Medicago sativa L.) is one of the most common forage crop species in the semi-arid western United States. In 2011, Montana alone produced 4.0 × 10(6 )Mg of alfalfa on 8.1 × 10(5 )ha for gross revenue in excess of US$4.3 × 10(8), making it the third largest crop by revenue. We conducted our study over the 2012 and 2013 growing seasons. Each year, our study consisted of three sites each with adjacent systems of monoculture alfalfa, alfalfa nurse cropped with hay barley, and an uncultivated refuge consisting of a variety of forbs and grasses. Carabid community structure differed and strong temporal shifts were detected during both 2012 and 2013. Multivariate fuzzy set ordination suggests that variation in canopy height among the three vegetation systems was primarily responsible for the differences observed in carabid community structure. Land managers may be able to enhance carabid species richness and total abundance by creating a heterogeneous vegetation structure, and nurse cropping in particular may be effective strategy to achieve this goal.

Greater prairie‐chicken brood‐site selection and survival in the Nebraska sandhills

ABSTRACTThe greater prairie‐chicken (Tympanuchus cupido pinnatus) is a grassland bird species of conservation concern, although the region of the Nebraska Sandhills has the largest and most stable population in North America. The Sandhills region is semiarid and dominated by privately owned rangeland; vegetation in the region is typically less dense than the tall grass ecosystem. Most management recommendations for the greater prairie‐chicken are based on work in tall grass prairies, so our goal was to estimate the responses of brood‐site selection and survival to the unique vegetation characteristics of the Sandhills region. We studied prairie‐chickens on private rangelands in Rock and Brown Counties from 2009 to 2011. We radio‐marked 139 females and monitored females with broods from May through July using pickup‐mounted and handheld telemetry systems. We used discrete choice models to assess micro‐scale habitat selection within used pastures. Specifically, we investigated the effect of local heterogeneity of vegetation structure and composition on site selection. The contiguous grasslands of the Sandhills contain variation in soils, slope, and proximity to water table, so we also assessed selection of these ecological sites (the equivalent of land‐use categories in fragmented landscapes) for brood‐rearing within the broad landscape (macro‐scale). Last, we assessed variation in brood survival in response to weather and vegetation structure and composition. Prairie‐chicken females with broods selected sands ecological sites (upland, rolling hills sites) that had thicker vegetation with higher visual obstruction reading (VOR; = 7.7 cm, SE = 0.4), more variable VOR ( = 20.1, ±2.1), and greater litter depth ( = 0.07 cm, ±0.01) than at coupled random locations (VOR: = 6.6 cm, ±0.1; variance VOR: = 15.6, ±0.8; litter depth: = 0.05 cm, ±0.01). The selection function for brood sites peaked for sites with approximately 10 cm VOR, which was significantly less than the range of 20–30 cm of visual obstruction suggested for management of tallgrass prairies. In fact, only 5.0% of random sites and 5.4% of sites used by hens with broods had VOR &gt;20 cm. However, VOR and litter depth did not explain variability in brood survival, and we found considerable uncertainty in our analysis of daily survival. Models with forb cover were ranked highest in the survival analyses (combined ωAIC c = 0.63), which provided some support for a positive effect of forb cover on brood survival (βforb cover = 0.327, SE = 0.337). We suggest that land managers in the Sandhills region provide brooding habitat in grazed, upland ecological sites that is characterized by minimal bare ground, a consistent distribution of litter, a forb component, and VOR levels of 4–11 cm in pastures in the vicinity of leks. © 2015 The Wildlife Society.

The cascading impacts of livestock grazing in upland ecosystems: a 10‐year experiment

Livestock grazing is a major driver of land‐use change, causing significant biodiversity loss globally. Although the short‐term effects of livestock grazing on individual species are well studied, a mechanistic understanding of the long‐term, cascading impacts is lacking. We manipulated livestock densities using a unique, replicated upland experiment over a 10‐year period and found significant effects of grazing treatment on plant and arthropod biomass; the number of Anthus pratensis breeding bird territories; the amplitude of Microtus agrestis population cycles and the activity of a top predator, Vulpes vulpes. Lower plant biomass as a result of higher stocking densities led to cascades across trophic levels, with fewer arthropods and small mammals, the latter affecting predator activity. Breeding bird territories were a function of arthropod abundance and vegetation structure heterogeneity. Our results provide a novel food‐web analysis in a grazing experiment to provide a mechanistic understanding of how food‐webs in upland ecosystems respond to long‐term livestock grazing pressure, with consequences for management.

Fearscapes: Mapping Functional Properties of Cover for Prey with Terrestrial LiDAR

Heterogeneous vegetation structure can create a variable landscape of predation risk—a fearscape—that influences the use and selection of habitat by animals. Mapping the functional properties of vegetation that influence predation risk (e.g., concealment and visibility) across landscapes can be challenging. Traditional ground-based measures of predation risk are location specific and limited in spatial resolution. We demonstrate the benefits of terrestrial laser scanning (TLS) to map the properties of vegetation structure that shape fearscapes. We used TLS data to estimate the concealment of prey from multiple vantage points, representing predator sightlines, as well as the visibility of potential predators from the locations of prey. TLS provides a comprehensive data set that allows an exploration of how habitat changes may affect prey and predators. Together with other remotely sensed imagery, TLS could facilitate the scaling up of fearscape analyses to promote the management and restoration of landscapes.

Black wildebeest seek shade less and use solar orientation behavior more than do blue wildebeest

Many ungulates, including wildebeest, seek shade and orient their bodies relative to incoming solar radiation in order to reduce environmental heat loads. Blue (Connochaetes taurinus) and black wildebeest (Connochaetes gnou), which co-exist artificially in some reserves in South Africa, are thought to adopt different thermoregulatory behaviors to mitigate high environmental heat loads. However, whether or not blue and black wildebeest use different behaviors to reduce heat loads in regions where they co-occur has never previously been examined. We compared the shade seeking and solar orientation behavior of free-ranging blue and black wildebeest in summer at three locations in South Africa where both species co-occur. We found that blue wildebeest exhibited more shade seeking behavior than did black wildebeest at all times of day, at all study sites. Black wildebeest remained in the sun but were more likely than blue wildebeest to orient their bodies parallel to the sun at all study sites, a behavior which reduces the amount of surface area exposed to incoming radiation. Black wildebeest were most likely to employ parallel solar orientation during the hottest times of the day when the sun was not directly overhead (i.e., solar noon ± 1 hour). We thus demonstrate that co-occurring blue and black wildebeest use different thermoregulatory behaviors to reduce high heat loads. It is possible that the lack of shade in the historical distribution of black wildebeest led to selective pressure for reliance on solar orientation. Differences in thermoregulatory behavior can affect species-specific heat loads, habitat use, body mass, fitness and grazing activity. Such differences may also allow blue and black wildebeest to inhabit separate microclimates within the same habitat, provided there is sufficient heterogeneity in vegetation structure, potentially facilitating reproductive isolation.

The impact of grazing management on Orthoptera abundance varies over the season in Mediterranean steppe-like grassland

As semi-natural grassland has a high level of biological diversity, understanding the effects of grazing and its variation over time is important in order to identify sustainable grazing practices. We measured temporal variation in Orthoptera abundance and spatial vegetation structure during seasonal grazing in an extensive sheep-farming system. We studied five grazed pasture areas (pre-grazing and post-grazing) and two adjacent ungrazed grasslands. We recorded the total abundance of Orthoptera and described the vegetation structure of 175 replicate plots (25 per pasture/grassland) during six field sampling sessions. We demonstrated that the impact of grazing on Orthoptera abundance is species-specific and greatly varies over the grazing season. The decrease of phytovolume is significant after 4–7 weeks of sheep grazing. Total Orthoptera abundance was higher in pre-grazed plots than in ungrazed plots, and higher in ungrazed plots than in post-grazed plots. These differences were particularly high during the peak of adult abundance. No difference in species richness was observed between grazing intensities. Total Orthoptera abundance positively correlated to phytovolume only when grazing pressure was high. However, the relationship between abundance and phytovolume differed between species. Extensive grazing by sheep tends to homogenize spatial vegetation structure and to temporarily reduce total Orthoptera abundance at pasture scale. However, rotational grazing allows spatial and temporal heterogeneity in vegetation structure to be maintained at farm scale, heterogeneity that is beneficial for Orthoptera. In contrast, absence of grazing has a negative impact on Orthoptera abundance as it favours the accumulation of litter, which is detrimental for a high proportion of xerothermophilic Orthoptera associated with bare ground and short vegetation.

Effects of large herbivores on grassland arthropod diversity.

Both arthropods and large grazing herbivores are important components and drivers of biodiversity in grassland ecosystems, but a synthesis of how arthropod diversity is affected by large herbivores has been largely missing. To fill this gap, we conducted a literature search, which yielded 141 studies on this topic of which 24 simultaneously investigated plant and arthropod diversity. Using the data from these 24 studies, we compared the responses of plant and arthropod diversity to an increase in grazing intensity. This quantitative assessment showed no overall significant effect of increasing grazing intensity on plant diversity, while arthropod diversity was generally negatively affected. To understand these negative effects, we explored the mechanisms by which large herbivores affect arthropod communities: direct effects, changes in vegetation structure, changes in plant community composition, changes in soil conditions, and cascading effects within the arthropod interaction web. We identify three main factors determining the effects of large herbivores on arthropod diversity: (i) unintentional predation and increased disturbance, (ii) decreases in total resource abundance for arthropods (biomass) and (iii) changes in plant diversity, vegetation structure and abiotic conditions. In general, heterogeneity in vegetation structure and abiotic conditions increases at intermediate grazing intensity, but declines at both low and high grazing intensity. We conclude that large herbivores can only increase arthropod diversity if they cause an increase in (a)biotic heterogeneity, and then only if this increase is large enough to compensate for the loss of total resource abundance and the increased mortality rate. This is expected to occur only at low herbivore densities or with spatio-temporal variation in herbivore densities. As we demonstrate that arthropod diversity is often more negatively affected by grazing than plant diversity, we strongly recommend considering the specific requirements of arthropods when applying grazing management and to include arthropods in monitoring schemes. Conservation strategies aiming at maximizing heterogeneity, including regulation of herbivore densities (through human interventions or top-down control), maintenance of different types of management in close proximity and rotational grazing regimes, are the most promising options to conserve arthropod diversity.

Rangeland Health Assessment: A Useful Tool for Linking Range Management and Grassland Bird Conservation?

Large-scale loss and degradation of North American native prairie coupled with sharp declines in grassland bird populations call for a clear understanding of the effects of livestock production on bird habitat selection. Grassland birds typically select breeding habitat based on a suite of structural and community vegetation features shaped by grazing. Rangeland health indices are a tool for assessing grassland structure and community composition that may offer biologists and range managers common language to achieve grassland bird recovery goals. We used point-count surveys, vegetation measures, and indices of rangeland health to examine bird-habitat relationships on native grassland in southwestern Saskatchewan for 10 grassland bird species. We used an information theoretic approach to compare the support of three hypotheses explaining variation in bird abundance as a function of local vegetation characteristics: bird abundance is best explained by 1) vegetation structure, 2) vegetation structure heterogeneity, or 3) plant community. Vegetation structure variables were present in top-ranking models (i.e., models within four Akaike information criterion units of top model) for eight species and solely comprised top-ranking models for Baird’s sparrow (Ammodramus bairdii), chestnut-collared longspur (Calcarius ornatus), horned lark (Eremophila alpestris), McCown’s longspur (Rhynchophanes mccownii), and savannah sparrow (Passerculus sandwichensis). Structural heterogeneity variables were present in top-ranked models for grasshopper sparrow (Ammodramus savannarum), horned lark (Eremophila alpestris), and western meadowlark (Sturnella neglecta). Plant composition variables solely comprised top-ranking models for clay-colored sparrow (Spizella pallida) and were present in top-ranked models for grasshopper sparrow and vesper sparrow (Pooecetes gramineus). Our results indicate that vegetation structure variables, namely litter mass, vegetation volume, and bare ground cover, best explain variation in bird abundance. Although the rangeland health index received little support as a predictor of bird abundance, vegetation structure components of the index could be used to communicate grazing management guidelines that maintain grassland bird habitat.

Improved methods for measuring forest landscape structure: LiDAR complements field-based habitat assessment

Conservation and monitoring of forest biodiversity requires reliable information about forest structure and composition at multiple spatial scales. However, detailed data about forest habitat characteristics across large areas are often incomplete due to difficulties associated with field sampling methods. To overcome this limitation we employed a nationally available light detection and ranging (LiDAR) remote sensing dataset to develop variables describing forest landscape structure across a large environmental gradient in Switzerland. Using a model species indicative of structurally rich mountain forests (hazel grouse Bonasa bonasia), we tested the potential of such variables to predict species occurrence and evaluated the additional benefit of LiDAR data when used in combination with traditional, sample plot-based field variables. We calibrated boosted regression trees (BRT) models for both variable sets separately and in combination, and compared the models’ accuracies. While both field-based and LiDAR models performed well, combining the two data sources improved the accuracy of the species’ habitat model. The variables retained from the two datasets held different types of information: field variables mostly quantified food resources and cover in the field and shrub layer, LiDAR variables characterized heterogeneity of vegetation structure which correlated with field variables describing the understory and ground vegetation. When combined with data on forest vegetation composition from field surveys, LiDAR provides valuable complementary information for encompassing species niches more comprehensively. Thus, LiDAR bridges the gap between precise, locally restricted field-data and coarse digital land cover information by reliably identifying habitat structure and quality across large areas.

Vegetation composition and structure influences bird species community assemblages in the highland agricultural landscape of Nyandarua, Kenya

We examined the effects of vegetation composition and structure on bird species diversity and richness of foraging guilds in the highland agricultural landscape of Nyandarua, Kenya. Bird point counts and vegetation surveys were undertaken during four sampling periods. Linear mixed models were used to examine the effects of vegetation variables on bird species diversity and richness of respective foraging guilds, and logistic generalised linear models used to examine vegetation effects on the presence/absence of the 17 most common bird species. Bird species diversity increased with increasing density of woody plant species and vegetation structural heterogeneity. Two gradients of increasing vegetation structural heterogeneity were most important in influencing bird community composition and had positive effects on species diversity and the presence of most of the species assessed: (1) increasing closed cover due to woody plant density, which also had positive effects on species richness of frugivores and nectarivores, but negative effects on carnivores, and (2) increasing fallow and cultivation versus decreasing grassland/pasture cover, which also had a positive effect on species richness of granivores and omnivores. This study reaffirms the need to maintain a structurally rich agricultural landscape for it to support agrobiodiversity.