Ryan F. Limb

Conservation of Pattern and Process: Developing an Alternative Paradigm of Rangeland Management

Abstract This article examines the question of how well the rangeland management profession has served conservation of patterns and processes that support multiple ecosystem services. We examine the paradigms under which rangeland management operates and argue that our profession developed under the utilitarian paradigm with the primary goals of sustainable forage for livestock production. While optimization of multiple rangeland products and services has always been a consideration, a comprehensive set of principles have not be been developed to advance this concept. We argue that fire and grazing, often viewed as mere tools used for production goals, should rather be viewed as essential ecosystem processes. Rangeland management continues to operate under the utilitarian paradigm appropriate to societal values of the 20th century and by and large has failed to provide management guidance to reverse degradation of several highly valued ecosystem services. We support this argument with evidence that biodiversity has declined on rangelands in the past half century and that much of this decline is due to management goals that favor a narrow suite of species. The full suite of ecosystem services valued by society will only benefit by management for heterogeneity, which implies that there is no one goal for management and that landscape-level planning is crucial. Explicitly incorporating heterogeneity into state-and-transition models is an important advancement not yet achieved by our profession. We present new principles for rangeland management formed on the basis of conservation of pattern and process. While recognizing that many rangelands have significant deviations from historic plant communities and disturbance regimes, we suggest that management for conservation of pattern and process should focus on fire and grazing to the extent possible to promote a shifting mosaic across large landscapes that include patches that are highly variable in the amount of disturbance rather than the current goal of uniform moderate disturbance. Resumen Este artículo examina la pregunta de que tan bien los profesionales en manejo de pastizales han aplicado los patrones y procesos en la conservación de los servicios multiples que proveen los ecosistemas. Examinamos los paradigmas bajo los cuales opera el manejo de pastizales y discutimos el desarrollo de nuestra profesión bajo el paradigma utilitario con el principal objetivo de sustentabilidad forrajera para la producción de ganado. Mientras que la optimización de los múltiples productos y servicios de los pastizales han sido consideradas un paquete completo de principios no ha sido desarrollado para avanzar en este concepto. Discutimos que el fuego y el pastoreo a veces son vistos como simples herramientas usadas para objetivos de producción cuando deberían ser vistas como partes esenciales de los procesos del ecosistema. El manejo de pastizales continúa operando bajo el paradigma utilitario típico de los valores sociales del siglo XX y por mucho ha fallado en proveer directrices de manejo para revertir la degradación de varios servicios valiosos de los ecosistemas. Apoyamos este argumento con evidencia de que la biodiversidad ha decaído en los pastizales en la mitad del siglo pasado y mucho de esta disminución se debe a los objetivos de manejo que favorecen a un reducido número de especies. El juego completo de servicios valuados por la sociedad solo beneficiara con el manejo por heterogeneidad el cual implica que no hay un objetivo para el manejo y que la planeación a nivel paisaje es crucial. Incorporando de manera explícita modelos de estado y transición es un avance importante que no ha sido logrado por nuestra profesión. Presentamos nuevos principios para el manejo de pastizales desarrollados en base a procesos y patrones de conservación. Mientras reconozcamos que muchos pastizales tienen desviaciones significativas de históricas comunidades de plantas y regímenes de disturbio, sugerimos que el manejo por conservación de patrones y procesos deberá enfocarse en fuego y pastoreo en medida de lo posible para promover el cambio en un mosaico a través de grandes paisajes que incluyen parches que son altamente variables en la magnitud de disturbio en lugar de objetivos actuales de disturbio uniforme y moderado.

Pyric–Herbivory and Cattle Performance in Grassland Ecosystems

Abstract Achieving economically optimum livestock production on rangelands can conflict with conservation strategies that require lower stocking rate to maintain wildlife habitat. Combining the spatial and temporal interaction of fire and grazing (pyric–herbivory) is a conservation-based approach to management that increases rangeland biodiversity by creating heterogeneous vegetation structure and composition. However, livestock production under pyric–herbivory has not been reported. In both mixed-grass prairie and tallgrass prairie, we compared livestock production in pastures with traditional fire and grazing management (continuous grazing, with periodic fire on tallgrass prairie and without fire on mixed-grass prairie) and conservation-based management (pyric–herbivory applied through patch burning) at a moderate stocking rate. Stocker cattle weight gain, calf weight gain, and cow body condition score did not differ (P > 0.05) between traditional and conservation-based management at the tallgrass prairie site for the duration of the 8-yr study. At the mixed-grass prairie site, stocker cattle gain did not differ in the first 4 yr, but stocker cattle gained more (P ≤ 0.05) on conservation-based management and remained 27% greater for the duration of the 11-yr study. Moreover, variation among years in cattle performance was less on pastures under conservation management. Traditional management in mixed-grass prairie did not include fire, the process that likely was associated with increased stocker cattle performance under conservation management. We conclude that pyric–herbivory is a conservation-based rangeland management strategy that returns fire to the landscape without reduced stocking rate, deferment, or rest.

Tallgrass Prairie Plant Community Dynamics Along a Canopy Cover Gradient of Eastern Redcedar (Juniperus virginiana L.)

Abstract North American grasslands make up less than 75% of their historic pre-European settlement area, and they continue to be converted to woodlands by woody plant encroachment. Conversion of grassland to woodland alters nutrient cycling, water use, and light penetration, which drives herbaceous plant community dynamics. Because studies examining this relationship among Juniperus species are limited largely to individual trees, we designed a study to examine the relationship between stand-level canopy cover of eastern redcedar (Juniperus virginiana L.) and the herbaceous plant community. We documented herbaceous plant species composition, abundance, and biomass within a North American tallgrass prairie invaded by eastern redcedar in which canopy cover of eastern redcedar ranged from 0% to 80%. Herbaceous species richness declined as a function of increased canopy cover of eastern redcedar and subsequent loss of open space, but this decrease in species richness closely followed a species–area model. Moreover, composition of C3 and C4 grasses and forbs did not change with increasing canopy cover. Herbaceous biomass, which declined with increasing canopy cover, varied most within those plots with intermediate canopy cover. While we found that species richness and biomass declined as canopy cover increased, the decline followed a species–area relationship and was without abrupt change typical of ecological thresholds. We recommend additional research with removal of eastern redcedar trees over a range of canopy cover to assess restoration potential along the encroachment gradient.

Growing-Season Disturbance in Tallgrass Prairie: Evaluating Fire and Grazing on Schizachyrium scoparium

Abstract Historically, fire occurred throughout the year in the Great Plains, but current fire prescriptions are generally limited to the dormant season because of concerns for potential damage to fire-sensitive herbaceous plant species deemed economically and ecologically important. We coupled a field-based study and a controlled greenhouse study to quantify the effects of fire season and herbivory on plant species composition, along with survival and productivity of little bluestem (Schizachyrium scoparium [Michx.] Nash). We investigated the effects of both dormant and growing-season fire interacting spatially with grazing on plant community composition in a 10-yr field study. We also examined the influence of both growing-season fire and clipping on survival and aboveground and belowground production of potted little bluestem plants at multiple ages in a controlled greenhouse experiment. Plants were grown to 6 wk, 10 wk, or 18 wk, then either burned or clipped, followed by as many as two successive clipping events. Plant community composition and canopy cover of little bluestem were unaffected by season-of-burning in the field study. Survival of individual little bluestem seedlings in the greenhouse study was dependent primarily on plant age, with nearly 100% survival among all burning and clipping treatments at 18 wk old. Burning or clipping once did not decrease survival compared to seedlings that were not burned or not clipped, and burning followed by clipping did not decrease survival over multiple clipping events among 6-wk-, 10-wk-, or 18-wk-old plants. Both aboveground regrowth and belowground biomass increased with burning, but clipping reduced regrowth. Based on both field and greenhouse experiments, we conclude that little bluestem is well adapted to growing-season disturbance. Moreover, little bluestem responds more positively to growing-season fire than to clipping. Our results provide no evidence that little bluestem should be deferred from grazing after burning as part of a rangeland management strategy.

Experimental tree removal in tallgrass prairie: variable responses of flora and fauna along a woody cover gradient

Woody plant encroachment is a worldwide phenomenon in grassland and savanna systems whose consequence is often the development of an alternate woodland state. Theoretically, an alternate state may be associated with changes in system state variables (e.g., species composition) or abiotic parameter shifts (e.g., nutrient availability). When state-variable changes are cumulative, such as in woody plant encroachment, the probability of parameter shifts increases as system feedbacks intensify over time. Using a Before-After Control-Impact (BACI) design, we studied eight pairs of grassland sites undergoing various levels of eastern redcedar (Juniperus virginiana) encroachment to determine whether responses of flora and fauna to experimental redcedar removal differed according to the level of pretreatment redcedar cover. In the first year after removal, herbaceous plant species diversity and evenness, woody plant evenness, and invertebrate family richness increased linearly with pretreatment redcedar cover, whereas increases in small-mammal diversity and evenness were described by logarithmic trends. In contrast, increases in woody plant diversity and total biomass of terrestrial invertebrates were accentuated at levels of higher pretreatment cover. Tree removal also shifted small-mammal species composition toward a more grassland-associated assemblage. During the second year postremoval, increases in herbaceous plant diversity followed a polynomial trend, but increases in most other metrics did not vary along the pretreatment cover gradient. These changes were accompanied by extremely high growing-season precipitation, which may have homogenized floral and faunal responses to removal. Our results demonstrate that tree removal increases important community metrics among grassland flora and fauna within two years, with some responses to removal being strongly influenced by the stage of initial encroachment and modulated by climatic variability. Our results underscore the importance of decisive management for reversing the effects of woody plant encroachment in imperiled grassland ecosystems.

Heterogeneity of Thermal Extremes: Driven by Disturbance or Inherent in the Landscape

Ecologists are beginning to recognize the effect of heterogeneity on structure and function in arid and semiarid ecosystems. Additionally, the influences of temperature on ecosystems are widely documented, but landscape temperature patterns and relationships with vegetation are rarely reported in ecological studies. To better understand the importance of temperature patterns to the conservation and restoration of native ecosystems, we designed an experiment to investigate relationships among soil surface temperature, landscape heterogeneity, and grazing intensity. Grazing intensity did influence the vegetation structure and composition. Heavy treatments had the greatest bare ground and the least vertical structure. Ungrazed treatments had the most litter and live grass cover. However, average temperatures among the three grazing treatments were not different and ranged less than 2°C during midday summer periods. The temperature difference between riparian and upland landscapes within grazing treatments was 21°C. Landscape position (riparian vs. upland) did have a significant influence on soil surface temperature and produced a variation in temperature 11 times greater than grazing intensities. Thermal heterogeneity did not differ among grazing treatments. Lower soil surface temperatures (associated with riparian areas) may provide a critical thermal refuge for many animals in arid and semiarid ecosystems on hot summer days, when air temperatures can exceed 37°C. Riparian zones, specifically riparian vegetation, are an important component in ecosystem management.

Synthesis Paper: Assessment of Research on Rangeland Fire as a Management Practice☆

ABSTRACT Rangelands are fire-dependent ecosystems severely altered through direct fire suppression and fuels management. The removal of fire is a dominant cause of ecological sites moving across thresholds with the majority of North American rangelands currently showingmoderate or high departure from reference conditions. Recognizing the need to restore fire on rangelands and incorporate prescribed fire into management plans, the Natural Resource Conservation Service initiated the Conservation Effects Assessment Project (CEAP) to evaluate the validity current practices through peer-reviewed scientific literature. We updated the CEAP review and broadened the discussion of prescribed fire as a global management practice. We reviewed and summarized prescribed fire literature available through Web of Science using search terms in the title. The majority of literature (40%) evaluated plant responses to fire with fire behavior and management (29%), wildlife and arthropods (12%), soils (11%), and air quality (4%) evaluated less frequently. Generally, fire effects on plants are neutral to positive and the majority of negative responses lasted less than 2 years. Similarly, soil responses were recovered within 2 yr after burning. However, most studies did not report how long treatments were in place (62%) or the size of experimental units (52%). The experimental literature supporting prescribed burning is in need of greater managerial relevance that can be obtained by directly addressing spatial scale, temporal scale, and interaction with other disturbances, including drought and grazing. Reliance on information from single fires applied on small plots tracked for a relatively short time interval greatly constrains inferences and application to ecosystem management and information should be applied with caution. Therefore, conservation purposes need to incorporate temporal dynamics to the extent that this information is available. The complex interaction of scientific knowledge, social concerns, and variable policies across regions are major limitations to the successful and critical restoration of fire regimes.

Plant Community Response Following Removal of Juniperus virginiana from Tallgrass Prairie: Testing for Restoration Limitations

Abstract Woody plant encroachment in natural grasslands is a widely documented global phenomenon that alters ecosystem dynamics by altering historic vegetation composition and suppressing herbaceous productivity. Abundant woody plants often suppress native plants sufficiently to establish successional thresholds difficult to reverse without species augmentation. Juniper (Juniperus virginiana L.) is expanding in North American tallgrass prairie, but it is currently unknown if encroachment creates successional restrictions that limit restoration potential. We selected 16 50×50-m sites with juniper canopy cover ranging from zero to approximately 75% in tallgrass prairie near Stillwater, Oklahoma, USA. Juniper trees were removed from 7 of the sites along the gradient of juniper canopy cover. Canopy cover of plant species and herbaceous plant productivity were estimated at each site 1 year before and 1, 2, and 5 years after tree removal. Before trees were removed, plant species richness and productivity declined as juniper canopy cover increased, and plant community composition dissimilarity of reference sites increased as juniper canopy cover increased. These relationships remained consistent on all non-removal sites throughout the study. The first year after juniper removal, species richness increased on all removal sites compared to intact sites and productivity on removal sites increased two years after removal. Plant community dissimilarity between reference sites and juniper removal sites remained relatively high (30–60%) the first two years after tree removal on all removal sites, but dissimilarity was about 22% 5 years after juniper removal. Within 5 years, removal sites were comparable to reference plant communities. Grassland restoration frequently requires species manipulation and additional seeding, particularly when overcoming successional limitations. Juniper encroachment into tallgrass prairie alters plant community species composition and productivity. However, in our study, juniper associated succession limitations were not apparent, and complete autogenic restoration was achieved within 5 years without seeding or species manipulation.

Altered Herbivore Distribution Associated With Focal Disturbance

Abstract Natural disturbances historically created structurally diverse patterns across the landscape, and large herbivores concentrated herbivory in areas where disturbance decreased standing senesced biomass that acted as a grazing deterrent through decreased palatability and overall forage quality. However, following European settlement, many natural large-scale disturbance regimes that influence vegetation and herbivore grazing selection were altered or removed and replaced with fine-scale anthropogenic disturbances. It is unclear how fine-scale focal disturbance and alteration of vegetation structure influences livestock distribution and grazing. Therefore we used a tracked vehicle as a disturbance agent in a mesic mixed-grass prairie to assess the influence of focal anthropogenic disturbance on livestock distribution and grazing. Track vehicle disturbance decreased the height of vegetation (P < 0.05) but did not alter plant species composition (P > 0.05). Cattle fecal pat density was greater (P ≤ 0.05) in locations with track vehicle disturbance. Little bluestem tiller height was shorter (P ≤ 0.05) in tracked locations than nontracked locations in grazed treatments, but was not different in nongrazed locations the first growing season following disturbance. Fecal pat density and tiller height were not different (P > 0.05) between tracked and nontracked locations following the second growing season. Therefore, we concluded that fine-scale focal anthropogenic disturbance alters herbivore distribution and defoliation and can maintain structural heterogeneity, but the effect is ephemeral and does not create long-lasting grazing lawns.

Fine and Coarse-Scale Patterns of Vegetation Diversity on Reclaimed Surface Mine-land Over a 40-Year Chronosequence

Rangelands are described as heterogeneous, due to patterning in species assemblages and productivity that arise from species dispersal and interactions with environmental gradients and disturbances across multiple scales. The objectives of rangeland reclamation are typically vegetation establishment, plant community productivity, and soil stability. However, while fine-scale diversity is often promoted through species-rich seed mixes, landscape heterogeneity and coarse-scale diversity are largely overlooked. Our objectives were to evaluate fine and coarse-scale vegetation patterns across a 40-year reclamation chronosequence on reclaimed surface coalmine lands. We hypothesized that both α-diversity and β-diversity would increase and community patch size and species dissimilarity to reference sites would decrease on independent sites over 40 years. Plant communities were surveyed on 19 post-coalmine reclaimed sites and four intact native reference sites in central North Dakota mixed-grass prairie. Our results showed no differences in α or β-diversity and plant community patch size over the 40-year chronosequence. However, both α-diversity and β-diversity on reclaimed sites was similar to reference sites. Native species establishment was limited due to the presence of non-native species such as Kentucky bluegrass (Poa pratensis) on both the reclaimed and reference sites. Species composition was different between reclaimed and reference sites and community dissimilarity increased on reclaimed sites over the 40-year chronosequence. Plant communities resulting from reclamation followed non-equilibrium succession, even with consistent seeds mixes established across all reclaimed years. This suggests post-reclamation management strategies influence species composition outcomes and land management strategies applied uniformly may not increase landscape-level diversity.