Dirac Twidwell

Ecosystem services lost to oil and gas in North America

Net primary production reduced in crop and rangelands Advanced technologies in oil and gas extraction coupled with energy demand have encouraged an average of 50,000 new wells per year throughout central North America since 2000. Although similar to past trends (see the graph, this page), the space and infrastructure required for horizontal drilling and high-volume hydraulic fracturing are transforming millions of hectares of the Great Plains into industrialized landscapes, with drilling projected to continue (1, 2). Although this development brings economic benefits (3) and expectations of energy security, policy and regulation give little attention to trade-offs in the form of lost or degraded ecosystem services (4). It is the scale of this transformation that is important, as accumulating land degradation can result in continental impacts that are undetectable when focusing on any single region (5). With the impact of this transformation on natural systems and ecosystem services yet to be quantified at broad extents, decisions are being made with few data at hand (see the graph, this page).

The rising Great Plains fire campaign: citizens' response to woody plant encroachment

Despite years of accumulating scientific evidence that fire is critical for maintaining the structure and function of grassland ecosystems in the US Great Plains, fire has not been restored as a fundamental grassland process across broad landscapes. The result has been widespread juniper encroachment and the degradation of the multiple valuable ecosystem services provided by grasslands. Here, we review the social–ecological causes and consequences of the transformation of grasslands to juniper woodlands and synthesize the recent emergence of prescribed burn cooperatives, an extensive societal movement by private citizens to restore fire to the Great Plains biome. We discuss how burn cooperatives have helped citizens overcome dominant social constraints that limit the application of prescribed fire to improve management of encroaching woody plants in grasslands. These constraints include the generally held assumptions and political impositions that all fires should be eliminated when wildfire danger increases.

Refining thresholds in coupled fire-vegetation models to improve management of encroaching woody plants in grasslands

Summary 1. Restoration priorities are typically established without quantitative information on how to overcome the thresholds that preclude successful restoration of desirable ecosystem properties and services. We seek to demonstrate that quantifying ecological thresholds and incorporating them into management-oriented frameworks provide a more comprehensive perspective on how the threshold concept can be applied to achieve restoration goals. 2. As an example, restoration actions have been largely unsuccessful when based on prevailing ecological knowledge of fire-based thresholds in nonresprouting Juniperus woodland. We build on previous threshold-based research and link well-established models from applied fire physics with a widely applied ecological positive feedback model of woody plant encroachment to introduce a more comprehensive understanding of the mechanism influencing fire intensity and juniper mortality. 3. Our coupling of physical and ecological fire models revealed a critical knowledge gap, a lack of a quantitative estimate on the critical surface fire intensity required to cause mortality of Juniperus ashei trees, which limits the linking of scientific knowledge from these two disciplines. 4. To quantify the relationship between fire intensity and J. ashei mortality, we input data from a previous experiment into Byram’s fireline intensity model. This critical surface fire intensity–mortality threshold was estimated to be Is > 160 kJ m � 1 s � 1 . This value establishes a specific threshold that managers should target when attempting to use restoration to collapse J. ashei woodlands. 5. Synthesis and applications. For scientific information associated with the threshold concept to be useful to practitioners, specific information is needed that demonstrates how to use restoration activities to overcome thresholds and collapse the current, degraded state in favour of a more desired ecological state. With this in mind, we present a broadly applicable decision support model within a state and transition framework that identifies the ecological states where the surface fire intensity–mortality threshold is most likely to meet restoration objectives and provides examples of how fuel properties that drive fire intensity should be targeted in restoration to surpass this threshold.

National-scale assessment of ecological content in the world's largest land management framework

Meeting the diverse sustainability targets of modern society has led to the development of national-level management frameworks meant to guide resource management actions and conservation funding decisions. In U.S. rangelands, state-and-transition models have been developed within the Ecological Site Description (ESD) Database as an application of alternative state theory and to move the discipline toward a more dynamic platform for resource management. After 15 years of development, and with government-mandated collaboration among federal agencies, these models are set to become one of the worlds largest guiding frameworks for terrestrial ecosystem management. Yet, ESD state-and-transition models are being marketed for broad-scale application without a national-level critique evaluating their strengths and limitations. In this article, we conduct a national assessment of ESDs with a central focus on evaluating the specific details of ESD state-and-transition models. Importantly, we are not evaluating the conceptual underpinnings of the state-and-transition management framework, but rather its application. Specifically, we (1) quantify and summarize the information presented in ESD state-and-transition models; (2) determine whether ESDs fully meet U.S. Congresss goal of a nationally consistent system for defining, mapping, and interpreting ecological sites; (3) identify limitations and logical holes in ESD predictions; and (4) evaluate whether conservation funding priorities are consistent with output from ESDs. Our evaluation reveals multiple shortcomings in the application of the state-and-transition model concept within ESDs, primarily that they are highly subjective, inconsistent in design and application, focus on a single historical climax community, and overuse grazing as a driver of both ecological degradation and restoration. Considering that many of these limitations have been a consistent criticism of rangeland assessment procedures throughout the history of the discipline, state-and-transition models within ESDs will require major reconstruction beyond the current plans for revision if they are to meet societys demand for more effective management and utilization of rangeland resources. While ESDs were developed to link science and management in rangeland ecology, our assessment suggests well-intentioned management frameworks built upon expert opinion and qualitative inputs will not effectively shift ecosystem management from long-held practices rooted in community climax theory to modern scientific perspectives based on alternative state theory.

Quantifying spatial resilience

1. Anthropogenic stressors affect the ecosystems upon which humanity relies. In some cases when resilience is exceeded, relatively small linear changes in stressors can cause relatively abrupt and nonlinear changes in ecosystems. 2. Ecological regime shifts occur when resilience is exceeded and ecosystems enter a new local equilibrium that differs in its structure and function from the previous state. Ecological resilience, the amount of disturbance that a system can withstand before it shifts into an alternative stability domain, is an important framework for understanding and managing ecological systems subject to collapse and reorganization. 3. Recently, interest in the influence of spatial characteristics of landscapes on resilience has increased. Understanding how spatial structure and variation in relevant variables in landscapes affects resilience to disturbance will assist with resilience quantification, and with local and regional management. 4. Synthesis and applications. We review the history and current status of spatial resilience in the research literature, expand upon existing literature to develop a more operational definition of spatial resilience, introduce additional elements of a spatial analytical approach to understanding resilience, present a framework for resilience operationalization and provide an overview of critical knowledge and technology gaps that should be addressed for the advancement of spatial resilience theory and its applications to management and conservation.

Surface Fuel Sampling Strategies: Linking Fuel Measurements and Fire Effects

Abstract We assessed the effectiveness of different sampling strategies in linking fine fuel load and crown scorch of ashe (Juniperus ashei) and redberry juniper (J. pinchotii) for prescribed fires conducted in wet and dry periods of the growing season on the Edwards Plateau, Texas, USA. Our aim was to determine if spatial and temporal variation in crown scorch was best predicted by estimates of fuel load sampled with spatially explicit, multiscale sampling strategies or with traditional, simple random sampling of fuel load. We found that multiscale sampling of fuel load underneath and adjacent to juniper crowns was more effective than simple random sampling in predicting crown scorch for the 14 fires conducted in the wet period and the five conducted in the dry period. The type of sampling strategy employed was critical in relating fuel load to crown scorch during the wet period. Percent crown volume scorched ranged from 0% to 100% in these conditions. In contrast, the type of sampling strategy was less important in the dry period when crown scorch was >90% for all juniper trees. We use these findings to illustrate how a multiscale sampling design can increase prediction power, thereby improving our ability to provide resource professionals with critical values to target in management. Using such a strategy in this study revealed that fine fuel loading of 2 670 kg · ha–1 were needed to scorch juniper trees 100% for the conditions present in the wet period, whereas only 1 280 kg · ha–1 were needed in the dry period. To provide managers with this type of information, we suggest that researchers shift from simple, random sampling of fuels to alternate sampling designs where randomization is maintained in the designation of treatments or selection of observations (i.e., individual juniper trees) but where fuel is systematically sampled at the location of the observation of interest.

Plant Invasions or Fire Policy: Which Has Altered Fire Behavior More in Tallgrass Prairie?

Human behavior has rapidly evolved from fire-promoting to aggressively attempting to minimize its magnitude and variability. This global shift in human behavior has contributed to the adoption of strict policies that govern the purposeful and planned use of fire in ecosystem science and management. However, it remains unclear the extent to which modern-day prescribed fire policies are altering the potential magnitude and variation of fire behavior in scientific investigations and ecosystem management. Here, we modeled the theoretical historical range of variability (ROV) in fire behavior for the tallgrass prairie ecosystem of North America. We then compared sensitivities in the magnitude and variation in the historical ROV in fire behavior as a result of (1) policies governing prescribed fire and (2) woody and herbaceous plant invasions. Although considerably more attention has focused on changes in fire behavior as a result of biological invasions, our model demonstrates that contemporary fire management policies can meet or surpass these effects. Policies governing prescribed fire management in tallgrass prairie reduced the magnitude and variability of surface fire behavior more than tall fescue invasion and rivaled reductions in fire behavior from decades of Juniperus encroachment. Consequently, fire and its potential as a driver of ecosystem dynamics has been simplified in the study and management of this system, which may be contributing to misleading conclusions on the potential responses of many highly researched environmental priorities. We emphasize the need to study changes in fire dynamics as a function of both social and ecological drivers, in an effort to advance our basic understanding of the role of fire in nature and its potential usefulness in ecosystem management.

Prescribed Extreme Fire Effects on Richness and Invasion in Coastal Prairie

Abstract Widely-held, untested assumptions in many prairies are that high-intensity fires conducted during droughts will decrease native herbaceous species richness and lead to rapid invasions by alien species. We compared native and exotic herbaceous species richness and aboveground herbaceous biomass one year following the application of high-intensity growing-season fires in Texas coastal prairie. Fires were conducted in June 2008, when precipitation was 96% below the long-term monthly average, at the end of a severe 5-mo drought, resulting in high fire intensities within treatment units. Native forb species richness was greater in burned than unburned areas. In contrast, species richness of native grasses, exotic forbs, and the frequency of King Ranch (KR) bluestem [Bothriochloa ischaemum (L.) Keng.] did not significantly differ between burned and unburned treatments. The potential to use prescribed extreme fire to maintain native herbaceous species richness while not increasing KR bluestem provides preliminary evidence that growing season fires conducted during droughts can be a viable management strategy in coastal prairies. Nomenclature: King Ranch bluestem, Bothriochloa ischaemum (L.) Keng. Management Implications: King Ranch (KR) bluestem is an invasive C4 grass introduced from Europe and Asia that has led to declines in the richness of plant, avian, and arthropod species in prairie ecosystems. Managers in Texas Gulf coastal prairies are concerned that using fire to manage woody plant encroachment will trigger rapid invasion by KR bluestem and decrease native herbaceous species richness. The objective of this study was to compare the rapid responses of native and exotic herbaceous species in burned and unburned treatments in a huisache–mesquite-invaded coastal tallgrass prairie. In this study, prescribed fires were conducted in the growing season with special permission during a county-mandated burn ban initiated by a severe, prolonged drought that caused considerable grass curing and the potential for high fire intensities (referred to as prescribed extreme fire). Our results counter previously unsubstantiated assumptions in coastal tallgrass prairies and show that prescribed extreme fire increased native forb species richness while maintaining the richness of native grasses, and not increasing King Ranch bluestem significantly. Because other research has shown burning in the dormant season is more likely to facilitate rapid invasion by KR bluestem, prescribed extreme fires in the growing season might be more effective at maintaining herbaceous species richness in coastal prairies prone to KR bluestem invasion.

Shrubland resilience varies across soil types: implications for operationalizing resilience in ecological restoration.

In ecosystems with alternative stable states, restoration success can be thought of as overcoming the resilience of an undesirable state to promote an alternative state that yields greater ecosystem services. Since greater resilience of undesirable states translates into reduced restoration potential, quantifying differences in resilience can enhance restoration planning. In the context of shrub-encroached rangeland restoration, shrubland resilience is the capacity of a woody vegetated state to absorb management interventions designed to produce a more desirable grass-dominated state, and remain within its current regime. Therefore, differences in the resilience of a state can be quantified in a relative sense by measuring whether a state switches to an alternate state following perturbation or remains in its current stability domain. Here we designed an experimental manipulation to assess the contribution of soils to differences in the relative resilience of a shrub-invaded state. In this large-scale experiment, we repeated perturbations across a gradient of soil textures to inform restoration practitioners of differences in the relative resilience of shrubland occurring on different soil types to common rangeland restoration practices. On each soil type, we compared the relative ability of the shrubland state to withstand chemical and mechanical brush control treatments, commonly employed in this study region, to untreated controls. While the shrubland community composition did not differ prior to the study, its capacity to absorb and recover from brush removal treatments depended on soil type. Shrubland resilience to chemical and mechanical brush removal was highest on coarse soils. On these soils, brush removal temporarily restored grassland dominance, but woody plants quickly regained pretreatment levels of dominance. However, shrublands on fine soils did not recover following treatments, continuing to be grass-dominated for the duration of the study. This study highlights a simple approach for prioritizing restoration actions by mapping the locations of different soil attributes that support shrub-dominated states with differing levels of resilience to brush control. This experimental approach provides a basis for operationalizing resilience in restoration and prioritizing management actions across a range of environmental conditions, which is critical given the economic constraints associated with broad-scale mechanical and chemical interventions for rangeland restoration.

Heterogeneity as the Basis for Rangeland Management

Rangeland management, like most disciplines of natural resource management, has been characterized by human efforts to reduce variability and increase predictability in natural systems (steady-state management often applied through a command-and-control paradigm). Examples of applications of traditional command and control in natural resource management include wildfire suppression, fences to control large ungulate movements, predator elimination programs, and watershed engineering for flood control and irrigation. Recently, a robust theoretical foundation has been developed that focuses on our understanding of the importance of variability in nature. This understanding is built upon the concept of heterogeneity, which originated from influential calls to consider spatial and temporal scaling in ecological research. Understanding rangeland ecosystems from a resilience perspective where we recognize that these systems are highly variable in space and time cannot be achieved without a focus on heterogeneity across multiple scales. We highlight the broad importance of heterogeneity to rangelands and focus more specifically on (1) animal populations and production, (2) fire behavior and management, and (3) biodiversity and ecosystem function. Rangelands are complex, dynamic, and depend on the variability that humans often attempt to control to ensure long-term productivity and ecosystem health. We present an ecological perspective that targets variation in rangeland properties—including multiple ecosystem services—as an alternative to the myopic focus on maximizing agricultural output, which may expose managers to greater risk. Globally, rangeland science indicates that heterogeneity and diversity increase stability in ecosystem properties from fine to broad spatial scales and through time.