Heterogeneity In Vegetation Structure Research Articles

The LTAR Grazing Land Common Experiment at the Central Plains Experimental Range: Collaborative adaptive rangeland management.

Semiarid rangelands throughout the western Great Plains support livestock production and many other ecosystem services. The degree to which adaptive multi-paddock (AMP) grazing management approaches can help achieve desired ecosystem services remains unclear. At the Central Plains Experimental Range in northeastern Colorado, a management-science partnership with a diverse stakeholder group is comparing collaborative adaptive rangeland management (CARM), designed to incorporate AMP principles, to traditional rangeland management (TRM), consisting of season-long grazing during the growing season. Each treatment was implemented on a set of 10, 130-ha pastures paired by soils, topography, and plant communities to evaluate how CARM affects vegetation (composition and production), livestock production (steer weight gain), and wildlife habitat (vegetation structure for grassland birds). For the first 5 years of the experiment, CARM cattle were managed as a single herd using AMP grazing with planned year-long rest in 20% of the pastures. Relative to TRM, CARM enhanced heterogeneity in vegetation structure across the landscape, benefiting two grassland bird species. However, this came at the cost of 12%-16% lower steer weight gains in CARM versus TRM and declining populations of a third bird species of conservation concern in both treatments. Here we discuss how increased understanding of ecological and social processes during the experiment's first 5 years led to changes in the CARM treatment and management objectives during the next 5 years. We also discuss how innovations in remote sensing, environmental sensors, ecosystem modeling, social learning, and economic analyses are being integrated into and supported by the CARM experiment.

Hybrid inversion of radiative transfer models based on topographically corrected Landsat surface reflectance improves leaf area index and aboveground biomass retrievals of grassland on the hilly Loess Plateau

ABSTRACT Accurate monitoring of the leaf area index (LAI) and aboveground biomass (AGB) using remote sensing at a fine scale is crucial for understanding the spatial heterogeneity of vegetation structure in mountainous ecosystems. Understanding discrepancies in various retrieval strategies considering topographic effects or not is necessary to improve LAI and AGB estimations over mountainous areas. In this study, the performances of the look-up table method (LUT) using radiative transfer model (RTM), machine learning algorithms (MLAs), and hybrid RTM integrating RTM and MLAs based on Landsat surface reflectance (SR) before and after topographic correction were compared and analyzed. The results show that topographic correction improves the accuracies of retrieval methods involving RTM more significantly than the MLAs, meanwhile, it reduces the performance variability of different MLAs. Based on the topographically corrected Landsat SR, the random forest (RF) combined with RTM improves the retrieval accuracy of RTM-based LUT by 7.7% for LAI and 13.8% for AGB, and reduces the simulation error of MLA by 15.1% for LAI and 20.1% for AGB. Compared with available remote sensing products, the hybrid RTM based on Landsat SR with topographic correction has better feasibility to capture LAI and AGB variation at 30 m scale over mountainous areas.

Meta-analysis shows that wild large herbivores shape ecosystem properties and promote spatial heterogeneity.

Megafauna (animals ≥45 kg) have probably shaped the Earth's terrestrial ecosystems for millions of years with pronounced impacts on biogeochemistry, vegetation, ecological communities and evolutionary processes. However, a quantitative global synthesis on the generality of megafauna effects on ecosystems is lacking. Here we conducted a meta-analysis of 297 studies and 5,990 individual observations across six continents to determine how wild herbivorous megafauna influence ecosystem structure, ecological processes and spatial heterogeneity, and whether these impacts depend on body size and environmental factors. Despite large variability in megafauna effects, we show that megafauna significantly alter soil nutrient availability, promote open vegetation structure and reduce the abundance of smaller animals. Other responses (14 out of 26), including, for example, soil carbon, were not significantly affected. Further, megafauna significantly increase ecosystem heterogeneity by affecting spatial heterogeneity in vegetation structure and the abundance and diversity of smaller animals. Given that spatial heterogeneity is considered an important driver of biodiversity across taxonomic groups and scales, these results support the hypothesis that megafauna may promote biodiversity at large scales. Megafauna declined precipitously in diversity and abundance since the late Pleistocene, and our results indicate that their restoration would substantially influence Earth's terrestrial ecosystems.

Structural effects of reedbed grazing and its cessation on reed-nesting songbird densities

Reedbeds are crucial breeding habitats for vulnerable songbird species. Irrespective of their protection status, these habitats may be threatened by organic matter accumulation, progressively leading to structural homogenization and habitat succession towards woodland. Managers prevent excessive litter build-up with various interventions opening-up the reedbeds, such as grazing, which may be detrimental or suitable for some reed bird species. We assessed the effects of extensive grazing by horses and its cessation in the medium and long terms on reedbed structure, and the consequences on reed-nesting songbird densities in Estagnol Nature Reserve, a protected wetland near the French Mediterranean coast. We compared reedbed structural features between grazed, newly ungrazed and old-ungrazed plots. During nine years, we censused four songbird species in spring and collected water level data in the same survey plots. Grazing reduced reedbed extent, rejuvenated the vegetation with more short green stems on a thinner litter, and produced higher structural heterogeneity and discontinuity compared to long-lasting non grazing. Newly ungrazed plot showed intermediate effects. All surveyed songbird total densities were similar among plots while species numbers and densities differed. Grazed reedbed was more attractive to Moustached Warblers (Acrocephalus melanopogon) and Great Reed Warblers (Acrocephalus arundinaceus), likely due to the large edges and the high vegetation structural heterogeneity. However, Moustached Warblers were more negatively affected by higher water level in grazed reedbed, presumably because flooding prevents litter foraging. The newly ungrazed reedbed was not preferred by any species. All warbler species were found under low density in the old-ungrazed reedbed, where Reed Buntings (Emberiza schoeniclus) were exclusively found. Food availability related to thick litter layer may explain this predilection. Common Reed Warblers (Acrocephalus scirpaceus) were found everywhere in similar densities. We conclude that reedbed management by extensive horse grazing and also its long-term cessation may benefit several songbird species. Within a context of wetland degradation and disappearance, both management strategies are useful to establish and maintain suitable habitats for reed-nesting songbird communities.

3D-гидродинамическое моделирование потоков СО2 и CH4 в приземном слое атмосферы (На примере лесного участка «Рошни-Чу»)

Introduction: The aim of this study is to evaluate the spatial variability of carbon dioxide (CO2) and methane (CH4) fluxes at the reference site "Roshni-Chu" of the carbon measurement megasites of the Chechen Republic using modeling experiments with in-situ measurements and remote sensing data. Methods and materials: Measurements of carbon dioxide (CO2) and methane (CH4) fluxes at the soil surface at the "Roshni Chu" forest site in the mountainous forest region of the Chechen Republic were conducted using a dynamic closed chamber connected to a portable gas analyzer G4301 (Picarro, USA). Leaf photosynthesis and respiration parameters of the main edificators and sub-edificators of premontane broadleaf forests were measured using the portable photosynthetic system LI-6800 (LI-COR, USA). Landsat 8 data were used to produce digital maps of surface topography and Nor-malized Difference Vegetation Index (NDVI). A 3D process-based atmospheric transfer model was chosen to describe the spatial variability of carbon dioxide and methane fluxes within the atmospheric boundary layer. The model is based on a one-and-a-half closure scheme for the Navier-Stokes and continuity equations, solved using Reynolds averaging and the Bussiness conjecture. Results: It was shown that a three-dimensional (3D) mathematical transfer models based on the solution of the equations of thermo-hydrodynamics are among the most effective methods for estimating vertical and horizontal fluxes of greenhouse gases in the atmosphere, taking into account the heterogeneous vegetation structure and surface topography. Based on the modeling results, maps of spatial distribution of turbulent exchange coefficient and horizontal wind speed at 5 m height, and maps of spatial distribution of CO2 and CH4 methane fluxes at 5, 25 and 50 m height were created. It was revealed that the "Roshni-Chu" forest area serves as a CO2 sink from the atmosphere under warm sunny weather in summer. The greatest uptake is detected near the local elevations. The fluxes of CH4 are almost negative, the lowest values of CH4 uptake are connected with uneven topography and are observed in small depressions between the hills. Conclusions: Based on the study of the wind field and the greenhouse gas fluxes at the carbon experimental site "Roshni-Chu" in the Chechen Republic, a significant spatial heterogeneity of the vertical CO2 and CH4 fluxes was revealed. The model approach, together with field measurements and remote sensing data, can be very effective for assessing the spatial heterogeneity of greenhouse gas fluxes at sites with non-uniform topography and vegetation. The method of modeling the spatial distribution of CO2 and CH4 fluxes within the atmospheric boundary layer can be used in different forest regions of the North Caucasus to describe the regional greenhouse gas balance.

Effects of long‐term fixed fire regimes on African savanna vegetation biomass, vertical structure and tree stem density

Abstract Fire plays an integral role in shaping the vegetation structure of savanna ecosystems. However, the effects of fire regime characteristics, such as frequency and season of burn, on savanna vegetation structure, biomass and tree abundance across landscape types are largely unknown. We used high‐resolution airborne light detection and ranging (LiDAR) to investigate the long‐term effects of fire manipulation on savanna vegetation in Kruger National Park, South Africa. We analysed the effects of fire exclusion and experimental burns every 1, 2, 3, 4 and 6 years and during different seasons on aboveground biomass (AGB), tree stem densities and vegetation vertical height profiles across a rainfall gradient and on contrasting geologies. Across savanna types, and especially in drier savannas, fire season was more influential for constraining AGB than fire frequency. Plots experiencing fires during the late‐ and mid‐dry season had 44.50% and 43.60%, respectively, lower AGB relative to unburnt plots than wet‐season fires. However, in mesic savannas, fire frequency interacted with fire season to influence AGB: plots subjected to high frequency, dry‐season fires had 55.35% lower AGB than unburnt plots, whereas plots burnt in the wet season at lower frequencies had lower AGB (24.40% lower than unburnt plots) than plots subjected to high frequency, wet‐season fires (13.74% lower AGB than unburnt plots). Fire regimes had variable effects on tree densities, and effects varied with the savanna type. Woody vertical vegetation profiles showed the largest differences in response to dry‐season fires, with the greatest divergence in vegetation height classes <5 m. Synthesis and applications. Understanding the influence of fire regimes on vegetation structure has important implications for the management of savanna heterogeneity and for predicting trajectories of change in savanna vegetation as fire regimes vary with climate change. We show that the magnitude of the effect of fire on woody vegetation structure varies with savanna context. Our results suggest that heterogeneous vegetation structure can be achieved by applying fires in the dry season in mesic savannas, whereas in dry savannas, variation in fire regimes is less consequential for constraining biomass accumulation and altering vegetation structure.

Patch-burn grazing provides resources for upland-nesting ducks

Contemporary rangeland management has expanded from a focus on forage and livestock production to multi-use management practices that include concepts like biodiversity and natural disturbance regimes. Patch-burn grazing (PBG) has been promoted as a multi-use land management practice that can restore vegetation structural heterogeneity and subsequently increase diversity of higher trophic levels, such as grassland birds. However, little is known about how the diverse assemblage of upland-nesting ducks responds to disturbances like interacting fire and grazing within a PBG framework. PBG divides a pasture into equal proportions (i.e., patches) and burns an individual patch annually to reduce residual vegetation and attract livestock grazing. Upland-nesting ducks are generally thought to require dense vegetation structure associated with areas of low disturbance for nesting. However, prescribed fire and grazing are essential for the conservation and management of grasslands. PBG may negatively affect ducks in recently burned patches, but may also support ducks through the provisioning of greater structure in patches with greater year(s) since fire (YSF) and could be a viable management strategy to meet grassland and duck conservation objectives. To assess the compatibility of PBG with duck conservation, we estimated nest site selection and survival of duck nests on private lands managed with PBG in the unglaciated plains and prairie pothole region of North Dakota, USA. We located 478 duck nests of four species: 230 Blue-winged Teal (<em>Spatula discors</em>), 72 Gadwall (<em>Mareca strepera</em>), 71 Mallard (<em>Anas platyrhynchos</em>), and 105 Northern Pintail (<em>A. acuta</em>). Blue-winged Teal, Gadwall, and Mallard selected for ≥ 2 YSF and avoided ≤ 1 YSF patches. Northern Pintail selected for 1 YSF and 2 YSF patches. Year(s) since fire affected survival differently for Blue-winged Teal and Gadwall, indicating the importance of variable structure resulting from disturbance regimes. Additionally, nest survival decreased as litter accumulation increased for Blue-winged Teal and Gadwall. Our findings indicate that PBG created nesting areas for ducks in later YSF patches. However, we found contrasting effects of survival in selected patches for certain species. High selection but low survival was limited to a single patch and does not necessarily limit duck nesting activity with adjacent patches having high selection and survival. Additional management strategies may be required to ensure > 1 YSF patch consists of vegetation characteristics that will attract duck nesting activity. Given our results, it appears that variable structure resulting from PBG is in line with conservation objectives, and given the need for multi-objective management, this may be a good choice for land managers interested in game and non-game conservation goals.

Embracing inherent and imposed sources of heterogeneity in rangeland bird management

AbstractRangeland simplification is a global threat to biodiversity. Historically, rangelands exhibited varied vegetation structure, which provided a diverse wildlife habitat. Vegetation heterogeneity resulted from interactions between topoedaphic (inherent heterogeneity) and disturbance factors (imposed heterogeneity). Until recently, these interactive sources of heterogeneity have been ignored in rangeland management and study. Under an emerging paradigm that embraces heterogeneity, contributions of disturbance and topoedaphic conditions to rangeland biodiversity remain largely unknown. Using the avian community, we assessed the effects of wetland area, ecological site, and topographic roughness (inherent heterogeneity) and four grazing strategies (imposed heterogeneity; patch‐burn grazing with one or two seasons of fire, season‐long grazing, and modified twice‐over rotational grazing with variably stocked paddocks) on vegetation structure, avian diversity, avian community composition, and avian densities. The interaction between inherent and imposed heterogeneity influenced avian community composition but not species‐specific densities. The effects of management on vegetation structural heterogeneity varied over years, though patch‐burn management generated heterogeneity and temporal stability in vegetation structure compared to season‐long grazing and modified twice‐over rotational grazing. Patch‐burn and season‐long grazing pastures had higher diversity than modified twice‐over rotational grazing. Community composition was sensitive to ecological site, topographic roughness, and wetland area, suggesting that both the fire‐grazing interaction and inherent heterogeneity maintain biodiversity. Out of our six grassland obligate focal bird species, two responded to inherent heterogeneity, while three were most sensitive to imposed heterogeneity. One species, western meadowlark (Sturnella neglecta), did not respond to either source of heterogeneity, potentially indicating responsiveness to factors outside our study, such as annual precipitation or heterogeneity at fine scales. Our results indicate that both inherent and imposed heterogeneity are important in shaping grassland bird abundance, diversity, and community composition and that conserving rangeland biodiversity in the future will require managing for greater imposed heterogeneity while embracing existing landscape variability.

Habitat associations of dryland avian communities during an extended dry period

AbstractThe influence of resource availability on ecosystem function varies spatially and temporally, among and within ecosystems. Dramatic shifts in moisture‐driven resources can drive bottom‐up effects on animal behaviours and distributions. Further, complexity arises when landscapes are influenced by large mammalian grazers and predator‐induced trophic cascades, such as those mediated by the dingo (Canis familiaris (Dingo)) in the eastern arid Strzelecki Desert in Australia. During the driest two‐year period on record for this region, we investigated the persistence of avian communities associated with structurally distinct dunes and swale habitats, and across two different land management regimes (pastoral land with livestock and dingoes, and Sturt National Park managed for conservation without these animals). We grouped all birds into dietary functional groups to infer patterns of habitat use associated with available resources. We also compared incidental observations of the ‘winter’ bird community in part of the study region between the extended dry period of 2018/2019 and wet period of 2020/2021. Despite habitat partitioning, the avian community did not differ between land management regimes except in species richness during the dry period, likely driven by the low numbers of birds present during the surveys. Incidental observations indicated that insectivorous and omnivorous species dominated the bird community in the dry period, with granivorous species forming a greater proportion of the bird community during wet times. Birds with completely or partially insectivorous diets dominated avian species composition on surveys in the dry period, but there were distinct structural vegetation associations among functional groups, indicating that heterogeneity in vegetation structure was likely important for the conservation of refuges, which enable the persistence of avifauna during extended dry periods. Distinct habitat type, structure and available resources shaped avian communities in this landscape, during the extremely resource‐limited extended dry period, with implications for conservation and management, particularly given the increasing drying effects of climate change.

Synergetic Roles of Mangrove Vegetation on Sediment Accretion in Coastal Mangrove Plantations in Central Thailand

Mangrove plantations can potentially restore the vegetation structures protecting coastal areas. In Avicennia alba plantations in central Thailand, we investigated the vegetation structures (trees, seedlings, pneumatophores, and belowground roots), sedimentation rates, and elevation changes over one year across the shore. The results showed a heterogeneous vegetation structure with an increasing tree basal area (BA) and seedling density towards the interior. The pneumatophore quantitative characteristics decreased towards the interior in association with the topographic gradient and inundation period. The sedimentation rates, which were greater in the plantation than on the mudflat, showed a negative correlation with the height, total surface area, and total volume of the pneumatophores. This indicates that the pneumatophores facilitated the transportation of fine sediments into the interior. Our results suggest that an optimal complexity of the aboveground vegetation structure might enhance the sedimentation rates. According to the gradient of tree BA and seedling density, the fine root density increased towards the interior. The monthly elevation changes in the plantation showed less fluctuation than those on the mudflat. The net elevation changes indicated sediment accretion within the plantation and erosion on the mudflat. Our results demonstrate the synergetic roles of mangrove plantations in which the aboveground structures facilitate sediment redeposition and the belowground roots stabilize sediment accretion in coastal areas.

Radar and multispectral remote sensing data accurately estimate vegetation vertical structure diversity as a fire resilience indicator

AbstractThe structural complexity of plant communities contributes to maintaining the ecosystem functioning in fire‐prone landscapes and plays a crucial role in driving ecological resilience to fire. The objective of this study was to evaluate the resilience to fire off several plant communities with reference to the temporal evolution of their vertical structural diversity (VSD) estimated from the data fusion of C‐band synthetic aperture radar (SAR) backscatter (Sentinel‐1) and multispectral remote sensing reflectance (Sentinel‐2) in a burned landscape of the western Mediterranean Basin. We estimated VSD in the field 1 and 2 years after fire using Shannon's index as a measure of vertical heterogeneity in vegetation structure from the vegetation cover in several strata, both in burned and unburned control plots. Random forest (RF) was used to model VSD in the control (analogous to prefire scenario) and burned plots (1 year after fire) using as predictors (i) Sentinel‐1 VV and VH backscatter coefficients and (ii) surface reflectance of Sentinel‐2 bands. The transferability of the RF model from 1 to 2 years after wildfire was also evaluated. We generated VSD prediction maps across the study site for the prefire scenario and 1 to 4 years postfire. RF models accurately explained VSD in unburned control plots (R2 = 87.68; RMSE = 0.16) and burned plots 1 year after fire (R2 = 80.48; RMSE = 0.13). RF model transferability only involved a reduction in the VSD predictive capacity from 0.13 to 0.20 in terms of RMSE. The VSD of each plant community 4 years after the fire disturbance was significantly lower than in the prefire scenario. Plant communities dominated by resprouter species featured significantly higher VSD recovery values than communities dominated by facultative or obligate seeders. Our results support the applicability of SAR and multispectral data fusion for monitoring VSD as a generalizable resilience indicator in fire‐prone landscapes.

Heterogeneity-Based Management Restores Diversity and Alters Vegetation Structure without Decreasing Invasive Grasses in Working Mixed-Grass Prairie

Non-native plants can reduce grassland biodiversity, degrade wildlife habitat, and threaten rural livelihoods. Management can be costly, and the successful eradication of undesirable species does not guarantee the restoration of ecosystem service delivery. An alternative to the eradication of invasive species in rangelands is to target the restoration of diversity and heterogeneous plant structure, which have direct links to ecosystem function. In this study, we evaluate patch-burn grazing (PBG) with one and two fires per year and variably stocked rotational grazing in Poa pratensis- and Bromus inermis-invaded grasslands using traditional (cover) and process-based (diversity and vegetation structural heterogeneity) frameworks in central North Dakota, USA. Within 3–4 years of initiating management, we found little evidence of decreased Poa pratensis and Bromus inermis cover compared to continuous grazing (Poa pratensis F3,12 = 0.662, p = 0.59; Bromus inermis F3,12 = 0.13, p = 0.13). However, beta diversity increased over time in all treatments compared to continuous grazing (tPBG1 = 2.71, tPBG2 = 3.45, tRotational = 3.72), and variably stocked rotational treatments had greater increases in spatial heterogeneity in litter depth and vegetation structure than continuously grazed pastures (tvisual obstruction= 2.42, p = 0.03; tlitter depth = 2.59, p = 0.02) over the same time period. Alternative frameworks that promote grassland diversity and heterogeneity support the restoration of ecological services and processes in invaded grasslands.

Taxonomic and community composition of epigeal arthropods in monoculture and mixed tree species plantations in a deciduous forest of Ghana

Tropical forests provide several ecosystem services and functions and support approximately two-thirds of the world’s biodiversity but are seriously threatened by deforestation. Approaches to counteract this menace have revolved around afforestation with several or a single tree species. We thus investigated how plantation forests with either a single or several tree species influenced arthropod taxonomic and community composition using pitfall traps to sample selected groups of epigeal arthropods (Araneae, Coleoptera, Orthoptera and Hymenoptera) and with environmental variables assessed simultaneously. Our results revealed 54 taxonomic groups with significantly higher taxonomic richness, activity density, and diversity in the mixed stands than in the monoculture stands. The significant differences in community composition were mainly driven by families including Lycosidae, Formicidae, Staphylinidae, Scotylidae, Hydrophilidae, Gryllidae and Scarabaeidae and were explained by distinct habitat characteristics (canopy openness, litter depth, deadwood volume, and tree height). While the diverse tree communities and heterogeneous vegetation structure offered food and habitat resources for diverse arthropod groups, the allelopathic nature coupled with homogenous stand characteristics of the Tectona grandis stands in the monoculture suppressed the growth of understorey vegetation that could otherwise serve as food and habitat resources for arthropods, which might have led to limited activities and diversity of arthropods in the monoculture plantation stands. The findings thus highlight the need to promote mixed tree plantations in degraded tropical areas, especially when restoring biodiversity is the prime management focus.

The influence of contrasting fire management practice on bush encroachment: Lessons from Bwabwata National Park, Namibia

AbstractQuestionsBush encroachment, (i.e. disproportionate woody vegetation increase at the cost of grassland) has negative impacts for biodiversity conservation and tourism by homogenising habitat structure and decreasing grazing and game‐viewing. While herbivory, rainfall, and CO2 all influence changes in woody vegetation cover, fire has the best potential for vegetation management. Changes in fire management can either encourage or suppress bush encroachment and a better understanding of how changes in fire regime affect vegetation structure is needed. Therefore, this study addressed three questions: (a) how has woody cover changed over two decades (1999–2019); (b) what is the role of land use, rainfall, and fire in influencing woody cover change; and (c) what are the management implications?LocationBwabwata National Park (BNP), Namibia.MethodsThe study used a novel combination of repeat ground photography and satellite‐based remote‐sensing products to explore the change in woody vegetation in relation to rainfall, land use, and fire seasonality.ResultsWoody vegetation has increased by 13% since 1999 in BNP. Change in vegetation structure differed in the east and west of the park. Early‐season burns in the east of the park were associated with an increase in trees over 3 m tall consisting primarily of Dialium englerianum, Terminalia sericea and Burkea africana. Repetitive late dry‐season fires in the west of the park were associated with an increase in shrubs under 3 m dominated by Baphia massaiensis and Terminalia sericea.ConclusionsBoth early‐ and late‐season fires are of value in management of bush encroachment. Early dry‐season fires appear to reduce the rate of bush encroachment and contribute to maintaining a heterogeneous vegetation structure. This fire management strategy reduces wildfire risk, conserves biodiversity, and promotes tourism and is, therefore, recommended for the park.

Feature-dependent group structures and hierarchical songbird-habitat relationships in a managed forest landscape

We examined the importance of local habitat features on forest songbird distributions using a feature-dependent group framework that organizes species in relation to variable importance of species-habitat relationships. Habitat features included vegetation structure, floristics, and environmental (i.e., topography) classes. We also examined evidence for hierarchical habitat selection by assessing feature positioning within the ensemble structural models, Random Forests. From the 44 species examined, we distinguished 14 groups, comprising two to eight species per group, and examined variation in habitat importance across the groups. Overall, floristic species turnover, shrub density, canopy height, and tree basal area were among the most important features. On average, however, no specific feature class was more important than the others across the entire collection of species. Instead, we interpreted group partitioning to occur primarily by species differentiating among specific forest types, such as bottomland riparian or oak-dominated (Quercus spp.) stands, and species responding to structural variation across successional gradients. The positioning of habitat features within individual tree models showed that for those species among specific forest types, floristics features were selected first in the models followed by environmental features. Whereas when vegetation structural features were most important, structural features were typically selected first followed by floristics. The large variability in responses likely reflects the large heterogeneity in vegetation structure and composition present in our Central Hardwood, USA, forest landscape. In such cases, avian community assembly processes incorporated the primary moisture (mesic-xeric tree species) and successional (open- to closed-canopy) vegetative gradients of these forestlands, which underscores the importance of maintaining vegetation heterogeneity under accelerating environmental change. By including diverse suites of habitat types, we demonstrate how these features vary in their importance across songbird assemblages in a diverse forestland and identify key habitat features in the conservation of these bird communities.

Using Very-High-Resolution Multispectral Classification to Estimate Savanna Fractional Vegetation Components

Characterizing compositional and structural aspects of vegetation is critical to effectively assessing land function. When priorities are placed on ecological integrity, remotely sensed estimates of fractional vegetation components (FVCs) are useful for measuring landscape-level habitat structure and function. In this study, we address whether FVC estimates, stratified by dominant vegetation type, vary with different classification approaches applied to very-high-resolution small unoccupied aerial system (UAS)-derived imagery. Using Parrot Sequoia imagery, flown on a DJI Mavic Pro micro-quadcopter, we compare pixel- and segment-based random forest classifiers alongside a vegetation height-threshold model for characterizing the FVC in a southern African dryland savanna. Results show differences in agreement between each classification method, with the most disagreement in shrub-dominated sites. When compared to vegetation classes chosen by visual identification, the pixel-based random forest classifier had the highest overall agreement and was the only classifier not to differ significantly from the hand-delineated FVC estimation. However, when separating out woody biomass components of tree and shrub, the vegetation height-threshold performed better than both random-forest approaches. These findings underscore the utility and challenges represented by very-high-resolution multispectral UAS-derived data (~10 cm ground resolution) and their uses to estimate FVC. Semi-automated approaches statistically differ from by-hand estimation in most cases; however, we present insights for approaches that are applicable across varying vegetation types and structural conditions. Importantly, characterization of savanna land function cannot rely only on a “greenness” measure but also requires a structural vegetation component. Underscoring these insights is that the spatial heterogeneity of vegetation structure on the landscape broadly informs land management, from land allocation, wildlife habitat use, natural resource collection, and as an indicator of overall ecosystem function.

Cattle grazing in CRP grasslands during the nesting season: effects on avian abundance and diversity

AbstractThe Conservation Reserve Program (CRP) is a primary tool for restoring grassland in the United States, in part as wildlife habitat, which has benefited declining grassland bird populations. Among potential mid‐contract management practices used to maintain early‐successional CRP grasslands, cattle grazing had been prohibited and is currently disincentivized during the primary nesting season for birds (much of the growing season), despite the important role that large herbivores historically played in structuring grassland ecosystems. Conservative grazing of CRP grasslands could increase spatial heterogeneity in vegetation structure and plant diversity, potentially supporting higher densities of some grassland bird species and higher bird diversity. Our objective was to determine the effect of experimental cattle grazing on species‐specific relative abundance and occupancy, species diversity, and community dissimilarity of grassland birds on CRP grasslands across the longitudinal extent of Kansas, USA (a 63.5‐cm precipitation gradient) during the 2017–2019 avian breeding seasons. Fifty‐three of 108 fields were grazed by cattle during the growing seasons of 2017 and 2018 and all fields were rested from grazing in 2019. For all analyses, we examined separate model sets for semiarid western versus more mesic eastern Kansas. Using data from line transect surveys, we modeled relative abundances of 5 songbird species: grasshopper sparrow (Ammodramus savannarum), dickcissel (Spiza americana), eastern meadowlark (Sturnella magna), western meadowlark (Sturnella neglecta), and brown‐headed cowbird (Molothrus ater). Grazing had delayed yet positive effects on abundances of grasshopper sparrow in western Kansas, and eastern meadowlark in eastern Kansas, but negative effects on dickcissel abundance in western Kansas and especially on burned fields in eastern Kansas. Somewhat counterintuitively, brown‐headed cowbirds in western Kansas were more abundant on ungrazed versus grazed fields in the years after grazing began. In addition, we modeled multi‐season occupancy of 3 gamebird species (ring‐necked pheasant [Phasianus colcicus], northern bobwhite [Colinus virginianus], mourning dove [Zenaida macroura]) and Henslow's sparrow (Centronyx henslowii); grazing did not affect occupancy of these species. In eastern Kansas, species diversity was highest in grazed, unburned fields. In western Kansas, bird communities in grazed and ungrazed fields were dissimilar, as determined from multivariate analysis. Though regionally variable, conservative stocking of cattle on CRP grasslands during the nesting season as a mid‐contract management tool might increase bird species diversity by restructuring habitat that accommodates a greater variety of species and decreasing abundances of species associated with taller, denser stands of vegetation.

Ecological Disturbance Through Patch‐Burn Grazing Influences Lesser Prairie‐Chicken Space Use

ABSTRACTAcross portions of the western Great Plains in North America, natural fire has been removed from grassland ecosystems, decreasing vegetation heterogeneity and allowing woody encroachment. The loss of fire has implications for grassland species requiring diverse vegetation patches and structure or patches that have limited occurrence in the absence of fire. The lesser prairie‐chicken (Tympanuchus pallidicinctus) is a declining species of prairie‐grouse that requires heterogeneous grasslands throughout its life history and fire has been removed from much of its occupied range. Patch‐burn grazing is a management strategy that re‐establishes the fire‐grazing interaction to a grassland system, increasing heterogeneity in vegetation structure and composition. We evaluated the effects of patch‐burn grazing on lesser prairie‐chicken space use, habitat features, and vegetation selection during a 4‐year field study from 2014–2017. Female lesser prairie‐chickens selected 1‐ and 2‐year post‐fire patches during the lekking season, ≥4‐year post‐fire patches during the nesting season, and year‐of‐fire and 1‐year post‐fire patches during post‐nesting and nonbreeding seasons. Vegetation selection during the lekking season was not similar to available vegetation in selected patches, suggesting that lesser prairie‐chickens cue in on other factors during the lekking season. During the nesting season, females selected nest sites with greater visual obstruction, which was available in ≥4‐year post‐fire patches; during the post‐nesting season, females selected sites with 15–25% bare ground, which was available in the year‐of‐fire, 1‐year post‐fire, and 2‐year post‐fire patches; and during the nonbreeding season they selected sites with lower visual obstruction, available in the year‐of‐fire and 1‐year post‐fire patches. Because lesser prairie‐chickens selected all available time‐since‐fire patches during their life history, patch‐burn grazing may be a viable management tool to restore and maintain lesser prairie‐chicken habitat on the landscape. © 2021 The Wildlife Society.

Identifying fine‐scale habitat preferences of threatened butterflies using airborne laser scanning

AbstractAimLight Detection And Ranging (LiDAR) is a promising remote sensing technique for ecological applications because it can quantify vegetation structure at high resolution over broad spatial extents. Using country‐wide airborne laser scanning (ALS) data, we test to what extent fine‐scale LiDAR metrics capturing low vegetation, medium‐to‐high vegetation and landscape‐scale habitat structures can explain the habitat preferences of threatened butterflies at a national extent.LocationThe Netherlands.MethodsWe applied a machine‐learning (random forest) algorithm to build species distribution models (SDMs) for grassland and woodland butterflies in wet and dry habitats using various LiDAR metrics and butterfly presence–absence data collected by a national butterfly monitoring scheme. The LiDAR metrics captured vertical vegetation complexity (e.g., height and vegetation density of different strata) and horizontal heterogeneity (e.g., vegetation roughness, microtopography, vegetation openness and woodland edge extent). We assessed the relative variable importance and interpreted response curves of each LiDAR metric for explaining butterfly occurrences.ResultsAll SDMs showed a good to excellent fit, with woodland butterfly SDMs performing slightly better than those of grassland butterflies. Grassland butterfly occurrences were best explained by landscape‐scale habitat structures (e.g., open patches, microtopography) and vegetation height. Woodland butterfly occurrences were mainly determined by vegetation density of medium‐to‐high vegetation, open patches and woodland edge extent. The importance of metrics generally differed between wet and dry habitats for both grassland and woodland species.Main conclusionsVertical variability and horizontal heterogeneity of vegetation structure are key determinants of butterfly species distributions, even in low‐stature habitats such as grasslands, dunes and heathlands. The information content of low vegetation LiDAR metrics could further be improved with country‐wide leaf‐on ALS data or surveys from drones and terrestrial laser scanners at specific sites. LiDAR thus offers great potential for predictive habitat distribution modelling and other studies on ecological niches and invertebrate–habitat relationships.

Using Grazing to Manage Herbaceous Structure for a Heterogeneity‐Dependent Bird

ABSTRACTGrazing management recommendations often sacrifice the intrinsic heterogeneity of grasslands by prescribing uniform grazing distributions through smaller pastures, increased stocking densities, and reduced grazing periods. The lack of patch‐burn grazing in semi‐arid landscapes of the western Great Plains in North America requires alternative grazing management strategies to create and maintain heterogeneity of habitat structure (e.g., animal unit distribution, pasture configuration), but knowledge of their effects on grassland fauna is limited. The lesser prairie‐chicken (Tympanuchus pallidicinctus), an imperiled, grassland‐obligate, native to the southern Great Plains, is an excellent candidate for investigating effects of heterogeneity‐based grazing management strategies because it requires diverse microhabitats among life‐history stages in a semi‐arid landscape. We evaluated influences of heterogeneity‐based grazing management strategies on vegetation structure, habitat selection, and nest and adult survival of lesser prairie‐chickens in western Kansas, USA. We captured and monitored 116 female lesser prairie‐chickens marked with very high frequency (VHF) or global positioning system (GPS) transmitters and collected landscape‐scale vegetation and grazing data during 2013–2015. Vegetation structure heterogeneity increased at stocking densities ≤0.26 animal units/ha, where use by nonbreeding female lesser prairie‐chickens also increased. Probability of use for nonbreeding lesser prairie‐chickens peaked at values of cattle forage use values near 37% and steadily decreased with use ≥40%. Probability of use was positively affected by increasing pasture area. A quadratic relationship existed between growing season deferment and probability of use. We found that 70% of nests were located in grazing units in which grazing pressure was &lt;0.8 animal unit months/ha. Daily nest survival was negatively correlated with grazing pressure. We found no relationship between adult survival and grazing management strategies. Conservation in grasslands expressing flora community composition appropriate for lesser prairie‐chickens can maintain appropriate habitat structure heterogeneity through the use of low to moderate stocking densities (&lt;0.26 animal units/ha), greater pasture areas, and site‐appropriate deferment periods. Alternative grazing management strategies (e.g., rest‐rotation, season‐long rest) may be appropriate in grasslands requiring greater heterogeneity or during intensive drought. Grazing management favoring habitat heterogeneity instead of uniform grazing distributions will likely be more conducive for preserving lesser prairie‐chicken populations and grassland biodiversity. © 2021 The Wildlife Society.