Heterogeneity as the Basis for Rangeland Management

Grazing intensity alters network complexity and predator-prey relationships in the soil microbiome

Grasslands are recognized as important reservoirs of soil biodiversity. Livestock grazing is implemented as a grassland management strategy to improve soil quality and enhance plant diversity. Soil microbial communities play a pivotal role in grassland ecosystems, so it is important to examine whether grazing practices affect the soil microbiome. Previous studies on grazing have primarily focused on bacteria and fungi, overlooking an important group-protists. Protists are vital in soil microbiomes as they drive nutrient availability and trophic interactions. Determining the impact of grazing on protists and their relationships with bacterial and fungal communities is important for understanding soil microbiome dynamics in grazed ecosystems. In this study, we investigated soil bacterial, fungal, and protist communities under four grazing levels: no grazing, moderate-use grazing, full-use grazing, and heavy-use grazing. Our results showed that heavy grazing led to a greater diversity of protists with specific groups, such as Discoba and Conosa, increasing in abundance. We also found strong associations between protist and bacterial/fungal members, indicating their intricate relationships within the soil microbiome. For example, the abundance of predatory protists increased under grazing while arbuscular mycorrhizal fungi decreased. Notably, arbuscular mycorrhizae were negatively associated with predatory groups. Furthermore, we observed that microbial network complexity increased with grazing intensity, with fungal members playing an important role in the network. Overall, our study reports the impact of temporal grazing intensity on soil microbial dynamics and highlights the importance of considering protist ecology when evaluating the effects of grazing on belowground communities in grassland ecosystems.

IMPORTANCE

The significance of this study lies in its exploration of the effects of temporal grazing intensity on the dynamics of the soil microbiome, specifically focusing on the often-neglected role of protists. Our findings provide insights into the complex relationships between protists, bacteria, and fungi, emphasizing their impact on trophic interactions in the soil. Gaining a better understanding of these dynamics is essential for developing effective strategies for grassland management and conservation, underscoring the importance of incorporating protist ecology into microbiome studies in grasslands.

Assessing the contribution of nonmarket factors to the market value generated by cow-calf operations in rangelands of the western USA: A true cost accounting approach

Food system transformation requires a better understanding of the negative and positive externalities involved in food production and consumption. Although negative externalities have received substantial attention, positive externalities have been largely overlooked. True Cost Accounting (TCA) is an economic assessment aimed at accounting for externalities in food systems. The beef industry is an important part of the US food system. In the western USA, beef cattle production is a major land use and economic activity that involves direct links among the cattle, range ecosystems, range management, climate, and ranchers' decisions and welfare. We present a case study based on a TCA assessment to quantify and monetize the contribution of human, social, natural, and produced capitals, as well as farm structure, to the market value generated by cow-calf operations, a key component of the USA beef industry. We estimated an Ordinary Least Square regression model based on indicators of these capitals and of farm structure derived from publicly available data sources at the county level. From model coefficients, we estimated the marginal revenue product of these factors. Results show that nonmarket factors linked with human and social capitals support market performance by contributing to the market value of cow-calf production. These factors operate at scales above the ranch, usually remain hidden, and seldomly are considered in policy decision-making which can lead to policies that inadvertently hamper or eliminate these positive externalities.

Bird species responses to rangeland management in relation to their traits: Rio de la Plata Grasslands as a case study

Areas used for livestock production and dominated by native grasses represent a unique opportunity to reconcile biodiversity conservation and livestock production. However, limited knowledge of individual species' responses to rangeland management restricts our capacity to design grazing practices that favor endangered species and other priority birds. In this work, we applied Hierarchical Modelling of Species Communities (HMSC) to study individual species responses, as well as the influence of traits on such responses, to variables related to rangeland management using birds of the Rio de la Plata Grasslands as a case study. Based on presence-absence data collected in 454 paddocks across 46 ranches we inferred the response of 69 species considering imperfect detection. This degree of detail fills a major gap in rangeland management, as species-level responses can be used to achieve targeted conservation goals other than maximizing richness or abundance. We found that artificial pastures had an overall negative impact on many bird species, whereas the presence of tussocks had a positive effect, including all threatened species. Grassland specialists were in general sensitive to grass height and tended to respond positively to tussocks but negatively to tree cover. Controlling grass height via adjustments in stocking rate can be a useful tool to favor grassland specialists. To favor a wide range of bird species in ranches, a mosaic of short and tall native grasslands with patches of tussocks and trees is desirable. We also found that species-specific responses were modulated by their traits: small-sized birds responded positively to tussocks and tree cover while large species responded negatively to increasing grass height. Ground foragers preferred short grass while birds that scarcely use this stratum were not affected by grass height. Results on the influence of traits on bird responses are an important novelty in relation to previous work in rangelands and potentially increase our predicting capacity and model transferability across grassland regions.

Pathways of degradation in rangelands in Northern Tanzania show their loss of resistance, but potential for recovery

Semiarid rangelands are identified as at high risk of degradation due to anthropogenic pressure and climate change. Through tracking timelines of degradation we aimed to identify whether degradation results from a loss of resistance to environmental shocks, or loss of recovery, both of which are important prerequisites for restoration. Here we combined extensive field surveys with remote sensing data to explore whether long-term changes in grazing potential demonstrate loss of resistance (ability to maintain function despite pressure) or loss of recovery (ability to recover following shocks). To monitor degradation, we created a bare ground index: a measure of grazeable vegetation cover visible in satellite imagery, allowing for machine learning based image classification. We found that locations that ended up the most degraded tended to decline in condition more during years of widespread degradation but maintained their recovery potential. These results suggest that resilience in rangelands is lost through declines in resistance, rather than loss of recovery potential. We show that the long-term rate of degradation correlates negatively with rainfall and positively with human population and livestock density, and conclude that sensitive land and grazing management could enable restoration of degraded landscapes, given their retained ability to recover.

Vegetation Changes Following Large-scale Fence Removal Across a Protected Area Network Within the Kruger to Canyons Biosphere Reserve, South Africa

In the early 1990’s, reserves adjacent to Kruger National Park (KNP) removed their fences to create a continuous landscape within the Kruger to Canyons Biosphere Reserve. Understanding how these interconnected multi-management systems responded to changes in environmental factors and management regimes can help to maintain natural large-scale landscape heterogeneity and ecological resilience. Our objective was to analyze remote sensing-derived vegetation metric changes between the different management types pre- and post-fence removal. The study area included fourteen reserves and the central section of KNP. We calculated the residuals between TIMESAT-derived metrics (from AVHRR NDVI time series) and rainfall to analyze changes in vegetation from 1985 to 2006. We then compared vegetation-rainfall residuals between different management types pre- and post-fence removal using mean–variance plots, nonmetric multidimensional scaling plots, and permutational multivariate analysis of variance to statistically identify and analyze changes. All management types experienced increased greenness. Reserves that removed their fences had greater changes in vegetation post-fence removal compared to reserves that remained fenced and KNP. Our findings suggest managers may need to address landscape changes by implementing management regimes such as reducing artificial surface water to counterbalance increased grazing pressure as a result of increased animal mobility across artificially created resource gradients. Habitat connectivity within and between protected area networks can be achieved by removing fences across adjacent conservation areas thus potentially increasing ecological resilience, which is vital to effective long-term conservation.

Fire management alters the thermal landscape and provides multi-scale thermal options for a terrestrial turtle facing a changing climate

As effects of climate change intensify, there is a growing need to understand the thermal properties of landscapes and their influence on wildlife. A key thermal property of landscapes is vegetation structure and composition. Management approaches can alter vegetation and consequently the thermal landscape, potentially resulting in underappreciated consequences for wildlife thermoregulation. Consideration of spatial scale can clarify how management overlaid onto existing vegetation patterns affects thermal properties of landscapes relevant to wildlife. We examined effects of temperature, fire management, and vegetation structure on multi-scale habitat selection of an ectothermic vertebrate (the turtle Terrapene carolina triunguis) in the Great Plains of the central United States by linking time-since-fire data from 18 experimental burn plots to turtle telemetry locations and thermal and vegetation height data. Within three 60-ha experimental landscapes, each containing six 10-ha sub-blocks that are periodically burned, we found that turtles select time-since-fire gradients differently depending on maximum daily ambient temperature. At moderate temperatures, turtles selected sub-blocks with recent (<1 year) time-since-fire, but during relatively hot and cool conditions, they selected sub-blocks with later (2-3 year) time-since-fire that provided thermal buffering compared with recently burned sub-blocks. Within 10-ha sub-blocks, turtles selected locations with taller vegetation during warmer conditions that provided thermal buffering. Thermal performance curves revealed that turtle activity declined as temperatures exceeded ~24-29°C, and on "heat days" (≥29°C) 73% of turtles were inactive compared with 37% on non-heat days, emphasizing that thermal extremes may lead to opportunity costs (i.e., foregone benefits turtles could otherwise accrue if active). Our results indicate that management approaches that promote a mosaic of vegetation heights, like spatiotemporally dynamic fire, can provide thermal refuges at multiple spatial scales and thus be an actionable way to provide wildlife with multiple thermal options in the context of ongoing and future climate change.

Multidecadal effects of fire in a grassland biodiversity hotspot: Does pyrodiversity enhance plant diversity?

Native grasslands have been vastly transformed with the expansion of human activities. Applied fire regimes offer conservation-based management an opportunity to enhance remaining grassland biodiversity and secure its persistence into the future. Fire regimes have complex interactions with abiotic and biotic ecosystem components that influence environmental heterogeneity and biodiversity. We examined the pyrodiversity-biodiversity hypothesis, which suggests that more species are supported where pyrodiversity, that is, the level of environmental heterogeneity associated with different fire regimes, is greater. A mesocosm-type field experiment, maintained for 38 yr, was used to determine the response of plant diversity to 1-, 2-, 5- and 12-yr fire-return interval treatments, with early-dormant, middormant and early-growing season burns. Our sampling regime was designed to assess the influence of fire treatments and combinations thereof, over spatial scale, on plant diversity. Pyrodiversity was maximized where fire regime diversity, simulated by varying the size of patches with different fire treatments, was greatest. Species richness was predicted to be reduced at short and long extremes of fire-return interval, as suggested by the intermediate-disturbance hypothesis. The influence of fire treatments on alpha and beta diversity, and plant functional groups, were tested using multivariate and Bayesian models. Multilevel models of plant height and growth form, with fire-return interval, reflected the strong indirect influence of fire-return interval on sward structure and the plant environment. The pyrodiversity-biodiversity and intermediate-disturbance hypotheses were only partially supported and depended on the plant group and spatial scale of assessment. Although both frequent and infrequent burns made important contributions to overall species richness, richness peaked where 20-40% of the area was protected from frequent fires. The larger contribution of frequent burning to diversity was due to an interaction with scale and forb turnover over the trial area. Extremes in fire-return intervals reduced forb richness, supporting the predictions of the intermediate-disturbance hypothesis. Spring burns had a weak negative influence on forb alpha diversity, but only at small scales. For a meaningful contribution of management to plant diversity, traditional fixed biennial burns need to be supplemented with smaller patches burned with longer fire-return intervals, and extremes in fire-return intervals avoided.

Grazing Into the Anthropocene or Back to the Future?

This essay examines three central components of extensive livestock production—herd composition, grazing/pasture management, and rangeland tenure. In all of these areas, fenced, and open-range forms of migratory pastoralism face a number of shared problems. Set aside the presumption that either one of these systems is technically or institutionally more advanced than the other, and it turns out that each has lessons for the other. 1. For a variety of reasons, including climate change, we can look forward to a future world with less grass, which presents a challenge for livestock producers reliant on grass feeding livestock. With little delay and minimal scientific support, East African pastoralists are already adjusting to a new woody world by diversifying the species composition of their herds to include more browsers—camels and goats. There is a potential lesson here for commercial ranchers who have traded the stability of mixed herds for the profitability of keeping sheep or cattle alone. 2. Migratory rangeland systems distribute livestock very differently than fenced, rotational systems of livestock, and pasture management. Whereas, migratory herds exploit environmental heterogeneity, fenced ranching attempts to suppress it. Emerging archaeological evidence is demonstrating that pastoralists have amplified rangeland heterogeneity for millennia; ecological research shows that this heterogeneity sustains both plant and wildlife biodiversity at the landscape scale; and new approaches to ranch management are appropriating aspects of migratory herding for use on fenced ranches. A rapprochement between the environmental sciences, ranching, and open-range migratory pastoralism has occurred and merits wider policy recognition. 3. In contemporary Africa, indigenous tenure regimes that sustain open rangelands are eroding under pressure from market penetration and state encapsulation. At the same time in the American West, there are emerging novel land tenure instruments that replicate some of the most important functional characteristics of tenure arrangements in pastoral Africa. After many false starts, it appears that some aspects of American ranching do provide an appropriate model for the preservation of the open-range migratory systems that they were once supposed to supplant. “Development” policy needs to reflect upon this inversion of roles and its implications for accommodating diversity.

Movement-mediated community assembly and coexistence

Organismal movement is ubiquitous and facilitates important ecological mechanisms that drive community and metacommunity composition and hence biodiversity. In most existing ecological theories and models in biodiversity research, movement is represented simplistically, ignoring the behavioural basis of movement and consequently the variation in behaviour at species and individual levels. However, as human endeavours modify climate and land use, the behavioural processes of organisms in response to these changes, including movement, become critical to understanding the resulting biodiversity loss. Here, we draw together research from different subdisciplines in ecology to understand the impact of individual-level movement processes on community-level patterns in species composition and coexistence. We join the movement ecology framework with the key concepts from metacommunity theory, community assembly and modern coexistence theory using the idea of micro-macro links, where various aspects of emergent movement behaviour scale up to local and regional patterns in species mobility and mobile-link-generated patterns in abiotic and biotic environmental conditions. These in turn influence both individual movement and, at ecological timescales, mechanisms such as dispersal limitation, environmental filtering, and niche partitioning. We conclude by highlighting challenges to and promising future avenues for data generation, data analysis and complementary modelling approaches and provide a brief outlook on how a new behaviour-based view on movement becomes important in understanding the responses of communities under ongoing environmental change.

Data-driven modelling and spatial complexity supports heterogeneity-based integrative management for eliminating Simulium neavei-transmitted river blindness

Concern is emerging regarding the challenges posed by spatial complexity for modelling and managing the area-wide elimination of parasitic infections. While this has led to calls for applying heterogeneity-based approaches for addressing this complexity, questions related to spatial scale, the discovery of locally-relevant models, and its interaction with options for interrupting parasite transmission remain to be resolved. We used a data-driven modelling framework applied to infection data gathered from different monitoring sites to investigate these questions in the context of understanding the transmission dynamics and efforts to eliminate Simulium neavei- transmitted onchocerciasis, a macroparasitic disease that causes river blindness in Western Uganda and other regions of Africa. We demonstrate that our Bayesian-based data-model assimilation technique is able to discover onchocerciasis models that reflect local transmission conditions reliably. Key management variables such as infection breakpoints and required durations of drug interventions for achieving elimination varied spatially due to site-specific parameter constraining; however, this spatial effect was found to operate at the larger focus level, although intriguingly including vector control overcame this variability. These results show that data-driven modelling based on spatial datasets and model-data fusing methodologies will be critical to identifying both the scale-dependent models and heterogeneity-based options required for supporting the successful elimination of S. neavei-borne onchocerciasis.

Inter-Seasonal Time Series Imagery Enhances Classification Accuracy of Grazing Resource and Land Degradation Maps in a Savanna Ecosystem

In savannas, mapping grazing resources and indicators of land degradation is important for assessing ecosystem conditions and informing grazing and land management decisions. We investigated the effects of classifiers and used time series imagery—images acquired within and across seasons—on the accuracy of plant species maps. The study site was a grazed savanna in southern Kenya. We used Sentinel-2 multi-spectral imagery due to its high spatial (10–20 m) and temporal (five days) resolution with support vector machine (SVM) and random forest (RF) classifiers. The species mapped were important for grazing livestock and wildlife (three grass species), indicators of land degradation (one tree genus and one invasive shrub), and a fig tree species. The results show that increasing the number of images, including dry season imagery, results in improved classification accuracy regardless of the classifier (average increase in overall accuracy (OA) = 0.1632). SVM consistently outperformed RF, and the most accurate model and was SVM with a radial kernel using imagery from both wet and dry seasons (OA = 0.8217). Maps showed that seasonal grazing areas provide functionally different grazing opportunities and have different vegetation characteristics that are critical to a landscape’s ability to support large populations of both livestock and wildlife. This study highlights the potential of multi-spectral satellite imagery for species-level mapping of savannas.

Adaptive rangeland management benefits grassland birds utilizing opposing vegetation structure in the shortgrass steppe

Rangelands are temporally and spatially complex socioecological systems on which the predominant land use is livestock production. In North America, rangelands also contain approximately 80% of remaining habitat for grassland birds, a guild of species that has experienced precipitous declines since the 1970s. While livestock grazing management may benefit certain grassland bird species by generating the vegetation structure and density they prefer, these outcomes are poorly understood for avian species breeding in the shortgrass steppe. We evaluated how two grazing management systems, continuous, season-long grazing and adaptive, rest-rotational grazing, affected grassland bird abundance from 2013 to 2017 in Colorado's shortgrass steppe. We examined grazing impacts in conjunction with ecological sites, which constitute unique soil and plant communities. When grazing management was evaluated in conjunction with spatial variation in ecological sites, we found three of our five focal bird species responded to grazing management. McCown's Longspur abundance decreased in pastures rested from grazing the previous year. The effect of grazing on Horned Lark and Grasshopper Sparrow depended on ecological site: Horned Lark density was highest in pastures that were intensively grazed and Grasshopper Sparrow density was highest in pastures that were rested the previous year in the least productive ecological site. In addition, densities of all species varied across ecological sites. Our results suggest consideration of soil and vegetation characteristics can inform how adaptive management is applied on a landscape to benefit the full suite of breeding grassland birds, including species that have seemingly contrasting habitat needs. For example, a manager could target adaptive drought mitigation practices, such as resting pastures for 1 yr to generate grassbanks, in less productive soils to benefit grassland birds that prefer taller/denser vegetation structure, or could apply intensive, short-duration grazing on less productive soils to benefit species preferring shorter/sparser vegetation. A single year of intensive, short-duration grazing (i.e., one component of our rotational treatment) across the landscape, however, might not create sufficient habitat for species that prefer short/sparse vegetation in our system (e.g., McCown's Longspur). Ultimately, our study indicates how cattle production on rangelands can congruently support grassland bird populations in the shortgrass steppe.

Moderate patchiness optimizes heterogeneity, stability, and beta diversity in mesic grassland

Heterogeneous disturbance patterns are fundamental to rangeland conservation and management because heterogeneity creates patchy vegetation, broadens niche availability, increases compositional dissimilarity, and enhances temporal stability of aboveground biomass production. Pyrodiversity is a popular concept for how variability in fire as an ecological disturbance can enhance heterogeneity, but mechanistic understanding of factors that drive heterogeneity is lacking. Mesic grasslands are examples of ecosystems in which pyrodiversity is linked strongly to broad ecological processes such as trophic interactions because grazers are attracted to recently burned areas, creating a unique ecological disturbance referred to as the fire-grazing interaction, or pyric herbivory. But several questions about the application of pyric herbivory remain: What proportion of a grazed landscape must burn, or how many patches are required, to create sufficient spatial heterogeneity and reduce temporal variability? How frequently should patches burn? Does season of fire matter? To bring theory into applied practice, we studied a gradient of grazed tallgrass prairie landscapes created by different sizes, seasons, and frequencies of fire, and used analyses sensitive to nonlinear trends. The greatest spatial heterogeneity and lowest temporal variability in aboveground plant biomass, and greatest plant functional group beta diversity, occurred in landscapes with three to four patches (25%-33% of area burned) and three- to four-year fire return intervals. Beta diversity had a positive association with spatial heterogeneity and negative relationship with temporal variability. Rather than prescribing that these results constitute best management practices, we emphasize the flexibility offered by interactions between patch number and fire frequency for matching rangeland productivity and offtake to specific management goals. As we observed no differences across season of fire, we recommend future research focus on fire frequency within a moderate proportion of the landscape burned, and consider a wider seasonal burn window.

Applying a dryland degradation framework for rangelands: the case of Mongolia

Livestock-caused rangeland degradation remains a major policy concern globally and the subject of widespread scientific study. This concern persists in part because it is difficult to isolate the effects of livestock from climate and other factors that influence ecosystem conditions. Further, degradation studies seldom use multiple plant and soil indicators linked to a clear definition of and ecologically grounded framework for degradation assessment that distinguishes different levels of degradation. Here, we integrate two globally applicable rangeland degradation frameworks and apply them to a broad-scale empirical data set for the country of Mongolia. We compare our assessment results with two other recent national rangeland degradation assessments in Mongolia to gauge consistency of findings across assessments and evaluate the utility of our framework. We measured livestock-use impacts across Mongolia's major ecological zones: mountain and forest steppe, eastern steppe, steppe, and desert steppe. At 143 sites in 36 counties, we measured livestock-use and degradation indicators at increasing distances from livestock corrals in winter-grazed pastures. At each site, we measured multiple indicators linked to our degradation framework, including plant cover, standing biomass, palatability, species richness, forage quality, vegetation gaps, and soil surface characteristics. Livestock use had no effect on soils, plant species richness, or standing crop biomass in any ecological zone, but subtly affected plant cover and palatable plant abundance. Livestock effects were strongest in the steppe zone, moderate in the desert steppe, and limited in the mountain/forest and eastern steppes. Our results aligned closely with those of two other recent country-wide assessments, suggesting that our framework may have widespread application. All three assessments found that very severe and irreversible degradation is rare in Mongolia (1-18% of land area), with most rangelands slightly (33-53%) or moderately (25-40%) degraded. We conclude that very severe livestock-induced rangeland degradation is overstated in Mongolia. However, targeted rangeland restoration coupled with monitoring, adaptive management and stronger rangeland governance are needed to prevent further degradation where heavy grazing could cause irreversible change. Given the broad applicability of our degradation framework for Mongolia, we suggest it be tested for application in other temperate grasslands throughout Central Asia and North America.