Bare Ground Cover Research Articles

Fine spatial scale assessment of structure and configuration of vegetation cover for northern bobwhites in grazed pastures

BackgroundMonitoring forage in livestock operations is critical to sustainable rangeland management of soil and ecological processes that provide both livestock and wildlife habitat. Traditional ground-based sampling methods have been widely used and provide valuable information; however, they are time-consuming, labor-intensive, and limited in their ability to capture larger extents of the spatial and temporal dynamics of rangeland ecosystems. Drones provide a solution to collect data to larger extents than field-based methods and with higher-resolution than traditional remote sensing platforms. Our objectives were to (1) assess the accuracy of vegetation cover height in grasses using drones, (2) quantify the spatial distribution of vegetation cover height in grazed and non-grazed pastures during the dormant (fall–winter) and growing seasons (spring–summer), and (3) evaluate the spatial distribution of vegetation cover height as a proxy for northern bobwhite (Colinus virginianus) habitat in South Texas. We achieved this by very fine scale drone-derived imagery and using class level landscape metrics to assess vegetation cover height configuration.ResultsEstimated heights from drone imagery had a significant relationship with the field height measurements in September (r2 = 0.83; growing season) and February (r2 = 0.77; dormant season). Growing season pasture maintained residual landscape habitat configuration adequate for bobwhites throughout the fall and winter of 2022–2023 following grazing. Dormant season pasture had an increase in bare ground cover, and a shift from many large patches of tall herbaceous cover (40–120 cm) to few large patches of low herbaceous cover (5–30 cm) (p < 0.05).ConclusionsDrones provided high-resolution imagery that allowed us to assess the spatial and temporal changes of vertical herbaceous vegetation structure in a semi-arid rangeland subject to grazing. This study shows how drone imagery can be beneficial for wildlife conservation and management by providing insights into changes in fine-scale vegetation spatial and temporal heterogeneity from livestock grazing.

Remote sensing for rangeland conservation monitoring: Impacts of livestock removal after 15 years

Abstract Degradation from overgrazing of global arid rangelands is of significant concern for this widespread terrestrial ecosystem, and the people who rely on its sustainable use. Addressing this degradation requires a better understanding of how livestock removal and conservation management actions affect the rehabilitation of land condition. However, the dominant effect of climate and meteorological variability on arid vegetation makes isolating management‐induced change a difficult task. We present an analytically simple method for measuring relative land condition by assessing differences in remote‐sensing‐derived persistent fractional vegetation between adjacent stocked and destocked regions over time. The 22‐year observation period focusses on vegetation recovery at a long‐established sheep station after the removal of livestock and the introduction of conservation‐focussed management. The study region, in the southern Australian arid rangelands, comprises sparsely vegetated chenopod shrublands and acacia woodlands across low‐lying plains. Comparison is made to immediately surrounding stocked properties in a spatial design where climate and biogeographic variables remain consistent across the study area. We found an unequivocal relative increase in vegetation cover, and reduction of bare ground cover at the destocked property that became evident approximately 8 years after a reduction in grazing pressure. Distinctly higher persistent vegetation cover was maintained, even during periods of drought. Non‐photosynthetic vegetation cover was most indicative of long‐term change and increased by 1.1% relative to surrounding areas. Photosynthetic vegetation cover increased by 0.5%, while bare ground cover decreased by 2.1%. These cover changes, particularly in the non‐photosynthetic vegetation and bare ground components spatially coincide with the fenced boundary of the destocked property. Synthesis and applications: The ability to quantify management‐related impacts in land condition using freely available remote sensing data could support improved management by all stakeholders in these regions. The method leverages readily available satellite remote sensing data in a study design that is not dependent on large geospatial and climatic datasets that are not necessarily available in remote regions.

Multidecadal vegetation transformations of a New Mexico ponderosa pine landscape after severe fires and aerial seeding.

Wildfires and climate change increasingly are transforming vegetation composition and structure, and postfire management may have long-lasting effects on ecosystem reorganization. Postfire aerial seeding treatments are commonly used to reduce runoff and soil erosion, but little is known about how seeding treatments affect native vegetation recovery over long periods of time, particularly in type-converted forests that have been dramatically transformed by the effects of repeated, high-severity fire. In this study, we analyze and report on a rare long-term (23-year) dataset that documents vegetation dynamics following a 1996 post-fire aerial seeding treatment and a subsequent 2011 high-severity reburn in a dry conifer landscape of northern New Mexico, USA. Repeated surveys between 1997 and 2019 of 49 permanent transects were analyzed for differences in vegetation cover, richness, and diversity between seeded and unseeded areas, and to characterize the development of seeded and unseeded vegetation communities through time and across gradients of burn severity, elevation, and soil-available water capacity. Seeded plots showed no significant difference in bare ground cover during the initial years postfire relative to unseeded plots. Postfire seeding led to a clear and sustained divergence in herbaceous community composition. Seeded plots had a much higher cover of non-native graminoids, primarily Bromus inermis, a likely contaminant in the seed mix. High-severity reburning of all plots in 2011 reduced native graminoid cover by half at seeded plots compared with both prefire levels and with plots that were unseeded following the initial 1996 fire. In addition, higher fire severity was associated with increased non-native graminoid cover and reduced native graminoid cover. This study documents fire-driven ecosystem transformation from conifer forest into a shrub-and-grass-dominated system, reinforced by aerial seeding of grasses and high-severity reburning. This unique long-term dataset illustrates that post-fire seeding carries significant risks of unwanted non-native species invasions that persist through subsequent fires-thus alternative postfire management actions merit consideration to better support native ecosystem resilience given emergent climate change and increasing disturbance. This study also highlights the importance of long-term monitoring of postfire vegetation dynamics, as short-term assessments miss key elements of complex ecosystem responses to fire and postfire management actions.

Anthropogenic shrub encroachment has accelerated the degradation of desert steppe soil over the past four decades

Anthropogenic and natural shrub encroachment have similar ecological consequences on native grassland ecosystems. In fact, there is an accelerating trend toward anthropogenic shrub encroachment, as opposed to the century-long process of natural shrub encroachment. However, the soil quality during the transition of anthropogenic shrub encroachment into grasslands remains insufficiently understood. Here, we used a soil quality assessment method that utilized three datasets and two scoring methods to evaluate changes in soil quality during the anthropogenic transition from temperate desert grassland to shrubland. Our findings demonstrated that the soil quality index decreased with increasing shrub cover, from 0.49 in the desert grassland to 0.31 in the shrubland. Our final results revealed a gradual and significant decline of 36.73 % in soil quality during the transition from desert grassland to shrubland. Reduced soil moisture levels, nutrient availability, and microbial activity characterized this decline. Nearly four decades of anthropogenic shrub encroachment have exacerbated soil drought conditions while leading to a decrease in perennial herbaceous plants and an increase in bare ground cover; these factors can explain the observed decline in soil quality. These findings emphasize the importance of considering soil moisture availability and potential thresholds when implementing revegetation strategies in arid and semiarid regions.

Seasonal changes in habitat use and behavior of the threatened Pampas meadowlark Leistes defilippii

The Pampas grasslands’ biodiversity is severely threatened by habitat modification, as is the case for the Pampas meadowlark ( Leistes defilippii). Here we study the areas used by the species throughout the year in the Southern Pampas of Argentina, in association with seasonal changes in behavior, in an attempt to provide information for its effective conservation. We selected four grassland sites with livestock activities in which we studied vegetation characteristics and the abundance and behavior of the Pampas meadowlark, during breeding and non-breeding seasons. The species was absent in sites with higher bare ground cover and lower cover of &gt;30 cm vegetation, and with high proportions of forb, shrub or exotic grass species. In those areas where the Pampas meadowlark was present during the breeding season, its abundance was higher where the grassland was entirely dominated by native grasses, and abandoned another site when the grassland became dominated by introduced plant species, after the breeding period. We are the first to report the behavior of a Pampas meadowlark population throughout an entire year with its seasonal changes. Our results and description of the behavior throughout the year highlight the importance of structural heterogeneity of the grasslands, determined by a low intensity of grazing, for the breeding of the Pampas meadowlark. Also, features associated with breeding habitat can’t predict the presence of flocks during the non-breeding season, as noted in our results for vegetation structure, but vegetation composition, food availability and landscape variables could play an important role in determining which areas serve as appropriate habitat during the non-breeding season, when large flocks search the grasslands for food. A better understanding of the habitat requirements and the use of space at different scales by the Pampas meadowlark will allow the identification of the most urgent and effective measures for its conservation.

Connectivity measures across scales differentially influence dryland sediment and seed movement

Drylands makeup over 40% of the terrestrial land surface area and are highly vulnerable to degradation. The drivers of dryland degradation can lead to shifts in vegetation, such as woody plant encroachment into historic arid grasslands. Encroachment often creates connected bare plant interspaces where wind and water erosion can redistribute resources, including sediment and seeds. Dryland restoration can incorporate methods to reduce these connected pathways, thus mitigating erosion and retaining resources locally. One method to reduce connectivity is through connectivity modifier (ConMod) structures. Quantifying sediment and seeds captured in ConMod structures provides insight into resource movement on the landscape and system‐level resilience. We quantified sediment and germinable seeds captured in ConMods in relation to vegetation along a grassland‐to‐shrubland gradient, measured at multiple scales, in the Northern Chihuahuan desert, United States. We found (1) a significant but weak correlation between ConMod sediment and seed capture; (2) connectivity in the form of bare ground cover at the large and small scale correlated with sediment capture but not seed capture; and (3) sediment and seed capture were both influenced by previously implemented restoration treatments, though differentially. When investigating the capture of different seed functional groups and sizes, we found that grass seed capture increased with proximity to shrubs and that smaller seeds were both captured more frequently and more closely correlated to sediment capture. These findings have implications for the use of ConMods as restoration tools in shrub‐encroached systems.

Evaluation of methods used to improve grasslands as ring‐necked pheasant brood habitat

AbstractRing‐necked pheasant (Phasianus colchicus) demographic response is sensitive to chick survival and nest success. The establishment and management of grasslands within agricultural landscapes, often through cropland conversion programs (e.g., Conservation Reserve Program [CRP]), have positive impacts on survival and nest success. Newly established CRP and early successional habitat can provide vegetative structure selected by pheasant chicks. Ideal brood habitat provides an abundance of arthropods, an open understory promoting efficient chick movement, and a protective canopy cover. However, the natural succession of grasslands changes desired vegetative structure and challenges managers with providing adequate habitat for pheasant chicks. We investigated the efficacy of different methods of CRP management, including haying, burning, herbicide application, interseeding, and grazing, to provide adequate brood rearing habitat in cool‐ and warm‐season grasslands. We assessed chick body mass change using human‐imprinted ring‐necked pheasant chicks and investigated changes in vegetation composition and structure in relation to various habitat treatments in north‐central and north‐eastern South Dakota during mid‐June and mid‐July of 2013, 2014, and 2015. Generally, treatments that incorporated interseeding, herbicide application, or their combination had the greatest chick mass gain, reduced litter cover and depth, and increased bare ground and forb cover. Effective management for brood habitat may require more aggressive techniques than simple haying or prescribed fire techniques.

DIGITAL ELEVATION MODEL CORRECTION IN URBAN AREAS USING EXTREME GRADIENT BOOSTING, LAND COVER AND TERRAIN PARAMETERS

Abstract. The accuracy of digital elevation models (DEMs) in urban areas is influenced by numerous factors including land cover and terrain irregularities. Moreover, building artefacts in global DEMs cause artificial blocking of surface flow pathways. This compromises their quality and adequacy for hydrological and environmental modelling in urban landscapes where precise and accurate terrain information is needed. In this study, the extreme gradient boosting (XGBoost) ensemble algorithm is adopted for enhancing the accuracy of two medium-resolution 30-metre DEMs over Cape Town, South Africa: Copernicus GLO-30 and ALOS World 3D (AW3D). XGBoost is a scalable, portable and versatile gradient boosting library that can solve many environmental modelling problems. The training datasets are comprised of eleven predictor variables including elevation, urban footprints, slope, aspect, surface roughness, topographic position index, terrain ruggedness index, terrain surface texture, vector roughness measure, forest cover and bare ground cover. The target variable (elevation error) was calculated with respect to highly accurate airborne LiDAR. After training and testing, the model was applied for correcting the DEMs at two implementation sites. The corrections achieved significant accuracy gains which are competitive with other proposed methods. There was a 46–53% reduction in the root mean square error (RMSE) of Copernicus DEM, and a 72–73% reduction in the RMSE of AW3D DEM. These results showcase the potential of gradient-boosted decision trees for enhancing the quality of global DEMs, especially in urban areas.

Changes in climate, vegetation cover and vegetation composition affect runoff generation in the Gulf of Guinea Basin

AbstractAlthough considerable effort has been deployed to understand the impact of climate variability and vegetation change on runoff in major basins across Africa, such studies are scarce in the Gulf of Guinea Basin (GGB). This study combines the Budyko framework and elasticity concept along with geospatial data to fill this research gap in 44 nested sub‐basins in the GGB. Annual rainfall from 1982 to 2021 show significant decreasing and increasing trends in the northern and southern parts of the GGB, respectively. Annual potential evapotranspiration (PET) also shows significant increasing trends with higher magnitudes observed in the northern parts of the GGB. Changing trends in climate variables corroborates with shift to arid and wetter conditions in the north and south, respectively. From 2000 to 2020 vegetation cover estimated using enhanced vegetation index (EVI) shows significant increasing trends in all sub‐basins including those experiencing a decline in annual rainfall. Vegetation composition measured using vegetation continuous fields (VCFs) from 2000 to 2020 show an increase in tree canopy cover (TC), a decline in short vegetation cover and marginal changes in bare ground cover (BG). Elasticity coefficients show that a 10% increase in annual rainfall and PET may lead to a 33% increase and 24% decline in runoff, respectively. On the other hand, a 10% increase in EVI may lead to a 4% decline in runoff while a 10% increase in TC, SV and BG may reduce runoff by 4% and increase runoff by 3% and 2%, respectively. Even though changes are marginal, decomposing vegetation into different parameters using EVI and VCFs may lead to different hydrological effects on runoff which is one of the novelties of this study that may be used for implementing nature‐based solutions. The study also demonstrates that freely available geospatial data together with analytical methods are a promising approach for understanding the impact of climate variability and vegetation change on hydrology in data‐scarce regions.

Forest fire, thinning, and flood in wildland-urban interface: UAV and lidar-based estimate of natural disaster impacts

ContextWildland-urban interface (WUI) areas are facing increased forest fire risks and extreme precipitation events due to climate change, which can lead to post-fire flood events. The city of Flagstaff in northern Arizona, USA experienced WUI forest thinning, fire, and record rainfall events, which collectively contributed to large floods and damages to the urban neighborhoods and city infrastructure.ObjectivesWe demonstrate multi-temporal, high resolution image applications from an unoccupied aerial vehicle (UAV) and terrestrial lidar in estimating landscape disturbance impacts within the WUI. Changes in forest vegetation and bare ground cover in WUIs are particularly challenging to estimate with coarse-resolution satellite images due to fine-scale landscape processes and changes that often result in mixed pixels.MethodsUsing Sentinel-2 satellite images, we document forest fire impacts and burn severity. Using 2016 and 2021 UAV multispectral images and Structure-from-Motion data, we estimate post-thinning changes in forest canopy cover, patch sizes, canopy height distribution, and bare ground cover. Using repeat lidar data within a smaller area of the watershed, we quantify geomorphic effects in the WUI associated with the fire and subsequent flooding.ResultsWe document that thinning significantly reduced forest canopy cover, patch size, tree density, and mean canopy height resulting in substantially reduced active crown fire risks in the future. However, the thinning equipment ignited a forest fire, which burned the WUI at varying severity at the top of the watershed that drains into the city. Moderate-high severity burns occurred within 3 km of downtown Flagstaff threatening the WUI neighborhoods and the city. The upstream burned area then experienced 100-year and 200–500-year rainfall events, which resulted in large runoff-driven floods and sedimentation in the city.ConclusionWe demonstrate that UAV high resolution images and photogrammetry combined with terrestrial lidar data provide detailed and accurate estimates of forest thinning and post-fire flood impacts, which could not be estimated from coarser-resolution satellite images. Communities around the world may need to prepare their WUIs for catastrophic fires and increase capacity to manage sediment-laden stormwater since both fires and extreme weather events are projected to increase.

Long-term interactive impacts of the invasive shrub Lonicera maackii and white-tailed deer (Odocoileus virginianus) on a deciduous forest understory

AbstractWhite-tailed deer (Odocoileus virginianus) (hereafter, ‘deer’) and invasive plants affect forest understories, but few studies have investigated their interaction. We investigated long-term (11-yr) effects of excluding deer and removing the invasive shrub, Amur honeysuckle [Lonicera maackii (Rupr.) Herder], on plants in southwest Ohio. Deer exclusion enhanced tree seedling richness and density, but reduced annual and bare ground cover. Vine density was reduced by Lonicera, especially where deer were excluded. Seedlings of several tree species, the invasive shrub, burning bush [Euonymus alatus (Thunb.) Siebold], and the invasive vine, winter creeper [Euonymous fortunei (Turcz.) Hand.-Maz.], were indicator species of the deer exclosure by Lonicera removal treatment combination. The effect of deer on cover of native species depended on Lonicera treatment: where shrubs were removed, cover was higher where deer were excluded, but where shrubs were present, cover was higher where deer had access. We attribute these interactions to the reduced growth of, and shading by, Lonicera where deer had access and browsed this invasive shrub. Some of these effects were evident in the first 6 yr, but are now larger. Other effects were not evident in the earlier evaluation. These findings inform management of areas with high densities of deer and invasive shrubs palatable to deer. Control of only invasive shrubs will reduce native cover and not improve tree regeneration. Managing only deer will increase woody plants but reduce native cover. Management of both stressors is needed to promote tree regeneration and restoration of plant communities.

Distribution, population structure and microhabitat profile of Euphorbia bupleurifolia

Many South African succulent Euphorbia spp. are threatened by anthropogenic activities such as habitat loss and illegal harvesting. However, only a few species have been studied in sufficient detail to aid their conservation through the development of effective management plans. This study documents the distribution, abundance, and population biology of the formerly widespread Euphorbia bupleurifolia, a species endemic to the Eastern Cape and KwaZulu-Natal provinces of South Africa. Until recently, the status of wild populations of this species was largely unknown. Searches for plants in each of the 31 previously recorded localities revealed that only nine populations (29 %) still had plants in 2018, indicating a contraction of the distribution, with the species apparently now ranging from Makhanda to Port Edward. Population size and structure, flowering, microhabitat requirements and various other factors, including potential threats and disturbances, were quantified for the nine populations. Complete counts were conducted, and the diameters of plants were measured and canopy areas calculated. Population sizes varied from one (effectively extinct) to 675 plants (with a total of 1724 plants recorded across all populations). Measurements of cultivated plants at the Walter Sisulu National Botanical Garden established that the onset of reproduction can be expected for a plant with a canopy area of 2.63 cm2, and annual growth rates of 0.55±8.37 cm2 are possible. Bell-shaped size class distribution (SCD) patterns were dominant, which is attributed to an adult persistence population survival strategy. Unsustainable harvesting, inappropriate fire frequencies as well as habitat loss and degradation remain a threat to the species. Euphorbia bupleurifolia persists mostly in sites with low vegetation biomass, high bare ground cover and minimal overstorey shade. This study highlights the drastic decline of a Least Concern species, formally considered widespread (i.e. common), and provides baseline demographic data, which may be employed in future monitoring and management of the remaining populations, to improve the conservation of E. bupleurifolia. Intensified field surveys involving citizen science programmes (e.g. CREW) and subsequent uplisting of the species to a higher Red List threat category is recommended.

Tradeoffs between timber and wildlife habitat quality increase with density in longleaf pine (Pinus palustris) plantations

Longleaf pine (Pinus palustris), a historically abundant tree species in the southeastern United States, is often planted to restore the ecologically and culturally important longleaf pine ecosystem that once covered vast acreages in the southeastern United States. Government cost-share programs that support establishment of these plantations place restrictions on planting rates to promote wildlife habitat, as greater tree planting density may reduce canopy openness and herbaceous plant cover that are critical components of habitat for priority species, including gopher tortoise (Gopherus polyphemus) and Bachman’s sparrow (Peucaea aestivalis). However, there is expressed concern among some forest managers that more open grown trees in the plantations will be of inferior timber quality with more and larger horizontal branches and associated knots. We examined how density affects dynamics and tradeoffs among understory vegetation structure and composition, longleaf pine stem form (branch density and straightness), and longleaf pine survival by sampling 73 plantations of various ages (5–25 years) and planting rates (653–2445 trees per hectare (TPH)/264–990 trees per acre (TPA)) throughout the southeastern United States. We documented a relationship between planting rate and longleaf pine stand density at time of sampling (r = 0.69, p = 0.0001) and relationships between stand density and habitat and timber quality metrics. Greater stand density resulted in lower tree diameters but greater stand basal area than lower stand density. Higher planting rates led to lower branch density and lower straightness grades than lower planting rates. Canopy openness decreased with greater stand density, and bare ground cover and herbaceous cover decreased as density and stand age at time of sampling increased. Based on our results, we suggest that lower maximum planting rates are appropriate when wildlife habitat is a program objective because lower rates result in fewer tradeoffs, as reducing planting rates slows degradation of wildlife habitat when compared with higher maximum planting rates that have only mixed benefits on timber quality.

Grassland extensification enhances nest densities of ground‐nesting wild bees

Abstract Ground‐nesting wild bees provide essential pollination services in agroecosystems, but they are jeopardized by intensive agricultural management. To mitigate such negative impacts, agri‐environment schemes have been implemented. While the success of enhancing floral food resources is relatively well studied, the role of agri‐environmental schemes in providing suitable nesting habitat remains underexplored. We studied the effectiveness of meadow extensification according to the Swiss agri‐environment scheme in promoting nesting of ground‐nesting bees. Using a paired design, we quantified their nests during four rounds (March–June) in pairs of nine randomly selected extensively (i.e. no fertilizer input, postponed first mowing) and nine intensively managed meadows with similar soil properties, slope, exposure and landscape context. Nest numbers and vegetation characteristics were surveyed in areas of 250 m2. Vegetation properties were also assessed in 0.5 × 0.5 m plots around nest locations and randomly selected locations without nests within each meadow to assess their role as drivers of nesting incidence (nest presence/absence) at this plot scale. We found substantially higher nest numbers of ground‐nesting bees in extensively (mean ± SE per sampling round = 46.8 ± 14.2) compared to intensively managed meadows (0.8 ± 0.3; no nests in three of nine intensively managed meadows). Extensively managed meadows harboured nests of several dominant crop pollinator species, including aggregations of, for example, Lasioglossum malachurum contributing to high nest densities in some of them. Number of nests was negatively related to grass cover and vegetation height, which were lower in extensively compared to intensively managed meadows. Plot‐level nesting incidence increased with bare ground and moss cover, and decreased with grass cover. Synthesis and applications. Our study shows that extensively managed meadows are better nesting habitats for ground‐nesting bees than intensively managed meadows, if reduced management intensity is associated with altered vegetation characteristics such as reduced grass cover and vegetation height, and small‐scale availability of bare ground, driving these effects. This highlights that maintaining and promoting extensive management of meadows can promote ground‐nesting wild bees, including dominant crop pollinators, not only by enhancing floral resources but also by improving nesting opportunities in agroecosystems.

Hippopotamus and livestock grazing near water points: consequences for vegetation cover, plant species richness and composition in African savannas

Large mammals, such as hippopotamuses (Hippopotamus amphibius), can significantly alter the landscape, vegetation composition, and structure in savannas through their grazing habits and ecosystem engineering effects, especially around rivers. However, livestock grazing can strongly change these effects, as seen in the Kenyan Maasai Mara Ecosystem. In this region, the increasing intensity of livestock grazing along local rivers, resulting from the transition of Maasai pastoralists from a semi-nomadic lifestyle to one based on pastoral ranches near the Maasai Mara National Reserve, may alter the impact of hippo grazing on riparian vegetation. We investigated the differences in vegetation structure, plant species richness and composition between landscapes predominantly grazed by hippopotami and livestock. We studied 25 transects, each measuring 5 km and having 13 sampling plots of 10 × 10 m2 located at varying distances from rivers in the reserve (n = 16) and pastoral ranches (n = 9). We measured the height and estimated the percent cover of grasses, forbs, shrubs, and bare ground, as well as plant species composition and richness and grazing intensity. Our results show that the riverine areas were more intensely and homogeneously grazed in the pastoral ranches than in the reserve, and in the dry than in the wet season in both landscapes. In addition, grazing intensity decreased with distance from rivers in the reserve in both seasons, but only in the wet season in the pastoral ranches. The mean plant species richness was similar in both landscapes and decreased linearly with distance from rivers, but varied with grazing intensity due to differences in forb and shrub species. However, plant species composition differed significantly between the reserve and the pastoral ranches. Furthermore, species similarity indices declined with increasing distance from water. These results suggest that the effects of livestock and hippo grazing intensity on vegetation structure and spatial heterogeneity interact, and vary with landscape and season. While both hippopotamus and livestock grazing can modify riparian vegetation, livestock grazing impact on plant species composition, vegetation structure, and spatial heterogeneity appears to be more persistent, declining less rapidly with increasing distance from water. Consequently, hippo and livestock differentially impact landscape heterogeneity.

Habitat and other environmental correlates of the decline of breeding Whinchats Saxicola rubetra in the UK since the mid-1990s

ABSTRACT Capsule Declines in Whinchat Saxicola rubetra breeding abundance in the UK vary with habitat and other environmental conditions. Aims To test for associations between changes in Whinchat abundance between 1994 and 2018 and measures of habitat and environmental conditions on UK breeding sites. Methods Whinchat counts collected through a national monitoring scheme were tested at coarse 1 km2 square and finer 200 m transect scales against habitat data collected in 2017/2018, plus remotely sensed data to test for long-term change. Results At the 1 km2 square scale, mean change in Whinchat abundance was more negative where woodland occurred more frequently, and at more northerly latitudes. Rates of decline were lower where there was greater cover of Purple Moor-grass Molinia caerulea and non-bracken vegetation height was taller. At the finer 200 m transect scale, more closely resembling Whinchat territory size, rates of decline were greatest in areas dominated by human sites, woodland, and enclosed farmland, compared to unenclosed open semi-natural habitats; however, within the latter category, declines were lower in grass-dominated relative to heather-dominated habitats. Rates of decline were also lower closer to valley bottoms, with greater Bracken Pteridium aquilinum cover and at mid-elevations (300 m), and greatest where there was greater cover of bare ground and trees, and moderate cover of grasses (excluding Molinia and Lolium spp.). The strength of the finer-scale associations varied between dominant habitat types. Whinchat abundance was lower where a remotely sensed index of vegetation productivity (normalized difference vegetation index [NDVI]) was higher, and abundance change more negative where temporal increases in NDVI were greater. Conclusion Unenclosed semi-natural grassland showed the lowest rate of decline and offers the best opportunities to conserve Whinchats. Woodland expansion is likely to have a detrimental impact on breeding Whinchats. Future research should investigate how important habitat and environmental correlates influence key demographic rates affecting recruitment.

Microhabitat requirements of the uncompahgre fritillary butterfly (Boloria improba acrocnema) and climate change implications

The Uncompahgre fritillary butterfly (Boloria improba acrocnema Gall LF, Sperling FAH (1980) A new high altitude species of Boloria from southwestern Colorado (Nyphalidae), with a discussion of phenetics and hierarchical decisions. J Lepidopterists’ Soc 34:230–252 1980) was listed as federally endangered in 1991 and is considered a habitat indicator for alpine ecosystem health. They are found on patches of Salix nivalis in isolated habitats of the San Juan Mountains, Colorado, USA. Here, we estimated historical B. i. acrocnema abundance from annual distance sampling (2003–2020) at seven sub-colonies and sampled current (July 2021) measurements of herbaceous coverage, soil moisture content, and slope, aspect, and elevation at 700 sample sites. We used regression models to test the effects of these microhabitat characteristics on historical abundance. Our results show that increases in slope from 11° to 31°, individual coverage of five alpine plant species (S. nivalis, Geum rossii, Phacelia sericea, Noccaea fendleri, and Lewisia pygmaea), and soil moisture content between 0.09 m3/m3 and 0.38 m3/m3 positively influence butterfly abundance. However, increases in elevation, bare ground coverage, and presence of Salix planifolia, Aster alpinus, Antennaria media, and Androsace chamaejasme were correlated with lower abundance estimates.Implications for insect conservation Effects of climate change which decrease coverage of these alpine plant species, allow encroachment of lower elevation species, or reduce soil moisture will decrease B. i. acrocnema abundance. These results emphasize the extinction risk of B. i. acrocnema due to range limitations and prolonged drought conditions in the Western U.S. By defining additional resource requirements of B. i. acrocnema, we can model climate effects on survivorship and consider nearby microhabitats that may be habitable by this endangered species.

A regional, remote sensing-based approach to mapping land degradation in the Little Karoo, South Africa

There is growing global consensus that assessments of land degradation be conducted at regional or smaller scales. Working at this scale allows for locally relevant environmental and land use conditions to be incorporated into the assessment methodology. In this paper, a recently developed regional approach to assessing land degradation in the Hardeveld bioregion of the Succulent Karoo is applied to the Little Karoo region of this biome. The methodology uses fuzzy classification statistical techniques to combine field data with multiple Sentinel-2A and Landsat vegetation indices, as well as regionally modelled soil variables. The resultant habitat condition archetype map values show strong correlation with field observations of perennial plant and bare soil cover in 96 ground-truthed plots. The archetype map indicates that heavily degraded hotspots of high bare ground cover occur throughout the project region, although there is an overall lower average habitat condition in the western half of the Little Karoo. The mean habitat condition archetype value for the entire project area is 0.54 (standard deviation = 0.13), on a continuous scale where 0 and 1 represent the most degraded and pristine extremes, respectively. Random forest regression analysis of various environmental covariates of degradation indicates a strong relationship between habitat condition and topographic as well as rainfall variables, although the limited accuracy of modelled livestock data may obscure the negative impacts of overgrazing. The 30 m resolution habitat condition archetype map builds upon previous degradation research in the Little Karoo and has the potential to inform future conservation, restoration, and rangeland management decisions. The methodology was successfully transferred to a new region and provides an opportunity to improve reporting on the extent of land degradation across South Africa.

THE EXPLAINABILITY OF GRADIENT-BOOSTED DECISION TREES FOR DIGITAL ELEVATION MODEL (DEM) ERROR PREDICTION

Abstract. Gradient boosted decision trees (GBDTs) have repeatedly outperformed several machine learning and deep learning algorithms in competitive data science. However, the explainability of GBDT predictions especially with earth observation data is still an open issue requiring more focus by researchers. In this study, we investigate the explainability of Bayesian-optimised GBDT algorithms for modelling and prediction of the vertical error in Copernicus GLO-30 digital elevation model (DEM). Three GBDT algorithms are investigated (extreme gradient boosting - XGBoost, light boosting machine – LightGBM, and categorical boosting – CatBoost), and SHapley Additive exPlanations (SHAP) are adopted for the explainability analysis. The assessment sites are selected from urban/industrial and mountainous landscapes in Cape Town, South Africa. Training datasets are comprised of eleven predictor variables which are known influencers of elevation error: elevation, slope, aspect, surface roughness, topographic position index, terrain ruggedness index, terrain surface texture, vector roughness measure, forest cover, bare ground cover, and urban footprints. The target variable (elevation error) was calculated with respect to accurate airborne LiDAR. After model training and testing, the GBDTs were applied for predicting the elevation error at model implementation sites. The SHAP plots showed varying levels of emphasis on the parameters depending on the land cover and terrain. For example, in the urban area, the influence of vector ruggedness measure surpassed that of first-order derivatives such as slope and aspect. Thus, it is recommended that machine learning modelling procedures and workflows incorporate model explainability to ensure robust interpretation and understanding of model predictions by both technical and non-technical users.

Livestock grazing is an effective conservation tool for Californian coastal grassland ecology: An eight‐year study on vegetation dynamics

AbstractQuestionsLivestock grazing is an expanding land management tool for habitat and fuel management in California grassland ecosystems, despite mixed conclusions about its effects. Our study investigated the following questions: Does a targeted grazing regime promote grassland functioning by clearing bare ground and reducing dead litter cover? Does targeted grazing reduce grassland fuels? Does targeted grazing promote native species cover and diversity? Does targeted grazing reduce non‐native, invasive species cover and diversity? LocationThe Santa Lucia Preserve, Carmel, California, USA.MethodsMonitoring grazed and ungrazed treatment plots within 17 study sites, we surveyed the effects of a targeted grazing regime on bare ground cover, litter cover and depth, herb height, and diversity and cover of different native and non‐native species groups over an eight‐year period.ResultsOn average, grazing successfully increased bare ground (by 2.8% cover), decreased litter depth (by 3.5 cm) and cover (by 12%), and decreased herb height (by 3.9 cm). Grazed plots had greater cover of native annual forbs (+1.2% cover), while decreasing invasive Bromus diandrus (by 6.0% cover). There was no difference in either native or non‐native species diversity.ConclusionsTargeted grazing can be an appropriate tool to accomplish conservation goals, including biomass management and canopy clearing, while improving native annual forbs without risk to native species as a whole. Further steps in adaptive management must examine how the application of grazing may be altered to further promote native species and to inhibit invasive species.