Torre J. Hovick

Structural heterogeneity increases diversity of non-breeding grassland birds

Grassland birds have experienced greater population declines than any other guild of birds in North America, and yet we know little about habitat use and the affects of management during their non-breeding period on wintering grounds. The paucity of information on wintering grassland birds limits our ability to develop effective conservation strategies. We investigated habitat use by the winter bird community in grasslands with restored heterogeneity resulting from the interactive effects of fire and grazing. We used 500 m line transects distributed across patches (i.e., 24 months post disturbance) resulting from spring burning with growing season grazing (April-Sept) and quantified avian relative abundance, community structure, and probability of patch occupancy while accounting for imperfect detection. Grassland structure that resulted from the fire-grazing interaction created heterogeneity among patches that influenced avian habitat use during winter. Generalist birds such as the Savan...

Spatial heterogeneity increases diversity and stability in grassland bird communities

Grasslands are inherently dynamic in space and time, evolving with frequent disturbance from fire and herbivores. As a consequence of human actions, many remaining grasslands have become homogenous, which has led to reduced ecosystem function, biodiversity loss, and decreased ecological services. Previous research has shown that restoring inherent heterogeneity to grasslands can increase avian diversity, but the amount of heterogeneity (i.e., number of patches or fire return interval) and the impact on avian community stability have yet to be investigated. We used a unique landscape-level design to examine avian response to interacting fire and grazing across multiple experimental landscapes that represented a gradient of fire- and grazing-dependent heterogeneity. We used seven landscapes (430-980 ha; x = 627 ha) with varying levels of patchiness ranging from annually burned (one single patch) with spring-only fires to a four-year fire return interval with spring and summer fires (eight patches). This design created a range of heterogeneity as a result of pyric herbivory, an ecological process in which fire and grazing are allowed to interact in space and time. We found that greater heterogeneity across experimental landscapes resulted in increased avian diversity and stability over time. An index of bird community change, quantified as the sum of the range of detrended correspondence analysis axis site scores, was nearly four times greater in the most homogenous experimental landscape when compared to the most heterogeneous experimental landscape. Species responses were consistently positively associated with increased heterogeneity at the landscape scale, and within-experimental-landscape responses were most often related to litter cover, litter accumulation, and vegetation height. We conclude that increased fire- and grazig-dependent heterogeneity can result in high variability in the bird community at finer, transect scales, but increased diversity and stability at broad landscape scales. We recommend that future management efforts in rangelands focus on restored disturbance processes to increase heterogeneity and improve grassland bird conservation.

REVIEW: Evidence of negative effects of anthropogenic structures on wildlife: a review of grouse survival and behaviour

Summary Anthropogenic structures such as those associated with energy development are a major threat to wildlife as a result of direct and indirect effects on populations. Species already imperilled as a result of habitat loss and alteration also may be the most threatened by rapidly increasing energy development, and these added pressures could lead to species extinctions and further declines in biodiversity. Of particular concern are tetraonids (grouse spp.) which have life cycles that require large, intact habitats to persist. We searched the peer-reviewed literature to assess impacts of six anthropogenic structures (i.e. oil and gas, fences, wind turbines, buildings, roads and power lines) on grouse survival and displacement behaviour across four different time periods in a grouse life cycle (i.e. year around, lekking, nesting and brooding). We used 5 studies that examined a total of 23 study–structure combinations to assess displacement behaviour in grouse and found an average effect of −1·40 (95% CI: −1·50, −1·31), indicating that anthropogenic structures displace grouse. Similarly, we used 9 studies examining a total of 17 study–structure combinations to assess survival and found an average effect of −1·11 (95% CI: −1·33, −0·88), indicating a negative effect of structures on grouse survival. Oil and gas structures had the greatest negative effect on displacement behaviour (E¯ = −2·41, 95% CI: −3·28, −1·54), and of the periods of the life cycle examined, lek attendance was most affected (E¯ = −4·85, 95% CI: −6·39, −3·31). Synthesis and applications. This data-driven synthesis reveals an overall negative effect of anthropogenic structures on grouse displacement behaviour and survival. Specifically, grouse were displaced and had lower survival in the presence of oil and gas structures and the presence of roads resulted in displacement behaviour. Too few studies existed to examine the specific effects of wind turbines and fences on displacement behaviour and the impact of wind turbines, fences, buildings and power lines on survival, which emphasizes the need for research assessing the influence of these structures on wildlife. Future management should focus on limiting the amount of oil and gas and road development in areas occupied by extant grouse populations, and if unavoidable, new infrastructure should be placed at low densities away from known lekking locations as leks appear sensitive to disturbance from anthropogenic structures.

Landscapes as a moderator of thermal extremes: a case study from an imperiled grouse

The impacts of climate driven change on ecosystem processes and biodiversity are pervasive and still not fully understood. Biodiversity loss, range shifts, and phenological mismatches are all issues associated with a changing climate that are having significant impacts on individuals and ecosystems alike. Investigating and identifying effective management strategies that can conserve vulnerable species should be the focus of current and future climate change research. We investigated thermal properties of habitat for an imperiled grouse (Greater Prairie-chicken; Tympanuchus cupido) in tallgrass prairie characterized by heterogeneous fire and grazing (the fire-grazing interaction). We examined operative temperature at varying scales relevant to grouse and used historic and forecasted climate data to estimate thermal stress during nesting activities. We found that heterogeneous grasslands have high thermal variability with operative temperature ranging as much as 23°C across the landscape. Grouse exhibited strong selection for cooler thermal environments as nest sites were as much as 8°C cooler than the surrounding landscape, and fine-scale differences in thermal environments were nearly 4°C cooler than sites within 2 m of nests. Additionally, forecasted climate scenarios indicate grouse will experience 2–4 times the number of hours above thermal stress thresholds, emphasizing the need for informed conservation management. Overall, these data provide evidence that variation in grassland structure resulting from the fire-grazing interaction may be important in moderating thermal environments and highlights the complex and interactive effects of restored ecological processes on ecosystems.

Weather Constrains the Influence of Fire and Grazing on Nesting Greater Prairie-Chickens☆,☆☆

ABSTRACT Grasslands are highly imperiled as a result of widespread conversion for agriculture and alteration from human development. Remaining grasslands are susceptible to mismanagement, development and fragmentation, and variable weather associated with global climate change. Understanding the response of declining grassland species to these challenges will be important for informed conservation and management. We assessed Greater Prairie-Chicken (Tympanuchus cupido) survival and nest site selection in tallgrass prairie characterized by interacting fire and grazing disturbance and oil and gas infrastructure. We found that Greater Prairie-Chicken survival was most affected by weather variability (expressed in our models as solar radiation) while most other variables had little influence. Focal disturbance did not affect survival directly, but vegetation height, which is greatly influenced by fire and grazing processes, was positively associated with nest survival. Greater Prairie-Chickens chose nesting locations that maximized time post fire while minimizing tree cover and distance to leks. Future conservation efforts for Greater Prairie-Chickens should focus on variable fire regimens that create areas of residual biomass to increase vegetation height and potentially reduce the effects of solar radiation while decreasing woody vegetation that is avoided by nesting females. However, even the best management practices may prove to be futile in the southern Great Plains if climate change continues to create unfavorable nest survival conditions. Management that creates and maintains suitable nesting sites through the use of interacting fire and grazing should maximize the potential for high reproduction in years when local weather variables are favorable.

Temporal variability in aboveground plant biomass decreases as spatial variability increases

Ecological theory predicts that diversity decreases variability in ecosystem function. We predict that, at the landscape scale, spatial variability created by a mosaic of contrasting patches that differ in time since disturbance will decrease temporal variability in aboveground plant biomass. Using data from a multi-year study of seven grazed tallgrass prairie landscapes, each experimentally managed for one to eight patches, we show that increased spatial variability driven by spatially patchy fire and herbivory reduces temporal variability in aboveground plant biomass. This pattern is associated with statistical evidence for the portfolio effect and a positive relationship between temporal variability and functional group synchrony as predicted by metacommunity variability theory. As disturbance from fire and grazing interact to create a shifting mosaic of spatially heterogeneous patches within a landscape, temporal variability in aboveground plant biomass can be dampened. These results suggest that spatially heterogeneous disturbance regimes contribute to a portfolio of ecosystem functions provided by biodiversity, including wildlife habitat, fuel, and forage. We discuss how spatial patterns of disturbance drive variability within and among patches.

Patch-burn grazing (PBG) as a livestock management alternative for fire-prone ecosystems of North America

Many rangelands of the world are fire dependent and display a strong interaction between fire and grazing on animal behavior, productivity and ecosystem processes. The application of this fire–grazing interaction as patch-burn grazing (PBG) has recently been promoted in North America to conserve biodiversity and as an alternative for livestock management in fire-prone ecosystems to enhance forage quality and other production benefits. PBG is functionally applied by burning spatially and temporally discrete patches to allow livestock to choose where and when to graze. However, considering that the primary intent of PBG in fire-dependent ecosystems has been for the conservation of biodiversity, we synthesized the peer-reviewed literature to assess PBG as an alternative strategy for livestock management in fire-prone ecosystems. We reviewed the literature to assess PBG as an alternative livestock management approach to optimize animal production and conserve biodiversity in fire-prone ecosystems. We reviewed the results of 83 studies that focused on two main areas: (1) livestock production and inputs and (2) maintaining or improving ecosystem functioning and biodiversity to support sustainable livestock production. PBG can optimize cattle production by offsetting input costs such as supplemental feed, insecticides, herbicides, mechanical brush control, veterinary costs and cross-fencing. PBG can also maintain native herbaceous plant communities that are the resource base for cattle grazing enterprises by reducing woody plant encroachment, stimulating above- and below-ground biomass of native perennial grasses, enhancing nutrient cycling and optimizing plant diversity. PBG creates a habitat mosaic critical for many trophic levels of wildlife, particularly grassland birds, which are currently in decline. Further research is needed to clarify the potential environmental gradients defining applicability of PBG, economic outcomes of PBG, potential gastro-intestinal parasite control with PBG and other metrics of animal production. Overall, PBG is a viable management approach to improve productivity and biodiversity in fire-regulated grassland ecosystems in a manner supported by both fire and grazing disturbances. This is especially true when these communities have other organisms that depend on periodic disturbance and interaction with large animal grazing and is supported by ample empirical research.

A Hierarchical Perspective to Woody Plant Encroachment for Conservation of Prairie-Chickens

ABSTRACT Encroachment of Great Plains grasslands by fire-sensitive woody plants is a large-scale, regional process that fragments grassland landscapes. Using prairie grouse (Tympanuchus spp.) of conservation concern,we apply hierarchy theory to demonstrate how regional processes constrain lower-level processes and reduce the success of local management. For example, fire and grazingmanagementmay be locally important to conservation, but the application of fire and grazing disturbances rarely cause irreversible fragmentation of grasslands in the Great Plains. These disturbance processes cause short-term alterations in vegetation conditions that can be positive or negative, but from a long-term perspective fire maintains large tracts of continuous rangelands by limiting woody plant encroachment. Conservation efforts for prairie grouse should be focused on landscape processes that contribute to landscape fragmentation, such as increased dominance of trees or conversion to other land uses. In fact, reliance on localmanagement (e.g.,maintaining vegetation structure) to alter prairie grouse vital rates is less important to grouse population persistence given contemporary landscape level changes. Changing grass height, litter depth, or increasing the cover of forbs may impact a fewremaining prairie-chickens, but itwill not create useable space at a scale relevant to the historic conditions that existed before land conversion and fire suppression.

Dynamic Disturbance Processes Create Dynamic Lek Site Selection in a Prairie Grouse.

It is well understood that landscape processes can affect habitat selection patterns, movements, and species persistence. These selection patterns may be altered or even eliminated as a result of changes in disturbance regimes and a concomitant management focus on uniform, moderate disturbance across landscapes. To assess how restored landscape heterogeneity influences habitat selection patterns, we examined 21 years (1991, 1993–2012) of Greater Prairie-Chicken (Tympanuchus cupido) lek location data in tallgrass prairie with restored fire and grazing processes. Our study took place at The Nature Conservancy’s Tallgrass Prairie Preserve located at the southern extent of Flint Hills in northeastern Oklahoma. We specifically addressed stability of lek locations in the context of the fire-grazing interaction, and the environmental factors influencing lek locations. We found that lek locations were dynamic in a landscape with interacting fire and grazing. While previous conservation efforts have treated leks as stable with high site fidelity in static landscapes, a majority of lek locations in our study (i.e., 65%) moved by nearly one kilometer on an annual basis in this dynamic setting. Lek sites were in elevated areas with low tree cover and low road density. Additionally, lek site selection was influenced by an interaction of fire and patch edge, indicating that in recently burned patches, leks were located near patch edges. These results suggest that dynamic and interactive processes such as fire and grazing that restore heterogeneity to grasslands do influence habitat selection patterns in prairie grouse, a phenomenon that is likely to apply throughout the Greater Prairie-Chicken’s distribution when dynamic processes are restored. As conservation moves toward restoring dynamic historic disturbance patterns, it will be important that siting and planning of anthropogenic structures (e.g., wind energy, oil and gas) and management plans not view lek locations as static points, but rather as sites that shift around the landscape in response to shifting vegetation structure. Acknowledging shifting lek locations in these landscapes will help ensure conservation efforts are successful by targeting the appropriate areas for protection and management.

Predicting Greater Prairie-Chicken Lek Site Suitability to Inform Conservation Actions

The demands of a growing human population dictates that expansion of energy infrastructure, roads, and other development frequently takes place in native rangelands. Particularly, transmission lines and roads commonly divide rural landscapes and increase fragmentation. This has direct and indirect consequences on native wildlife that can be mitigated through thoughtful planning and proactive approaches to identifying areas of high conservation priority. We used nine years (2003–2011) of Greater Prairie-Chicken (Tympanuchus cupido) lek locations totaling 870 unique leks sites in Kansas and seven geographic information system (GIS) layers describing land cover, topography, and anthropogenic structures to model habitat suitability across the state. The models obtained had low omission rates (<0.18) and high area under the curve scores (AUC >0.81), indicating high model performance and reliability of predicted habitat suitability for Greater Prairie-Chickens. We found that elevation was the most influential in predicting lek locations, contributing three times more predictive power than any other variable. However, models were improved by the addition of land cover and anthropogenic features (transmission lines, roads, and oil and gas structures). Overall, our analysis provides a hierarchal understanding of Greater Prairie-Chicken habitat suitability that is broadly based on geomorphological features followed by land cover suitability. We found that when land features and vegetation cover are suitable for Greater Prairie-Chickens, fragmentation by anthropogenic sources such as roadways and transmission lines are a concern. Therefore, it is our recommendation that future human development in Kansas avoid areas that our models identified as highly suitable for Greater Prairie-Chickens and focus development on land cover types that are of lower conservation concern.