7

Establishing and Adjusting Appropriate Management Levels

The Wild Free-Roaming Horses and Burros Act of 1971 (P.L. 92-195), as amended by the Public Rangelands Improvement Act of 1978 (P.L. 95-514), requires the Bureau of Land Management (BLM) to “determine appropriate management levels for wild free-roaming horses and burros on [designated] public lands.” The legislation makes BLM responsible for deciding how these appropriate management levels (AMLs) of free-ranging horses and burros should be achieved within the agency’s multiple-use mandate, including consideration for wildlife, livestock, wilderness, and recreation. BLM is also directed to manage for a thriving natural ecological balance, to prevent deterioration of the range, and to use minimal management for free-ranging horses and burros.

An AML has been interpreted by BLM as being a population size with upper and lower bounds for each individual Herd Management Area (HMA). Options listed in the legislation for keeping horses and burros within set population levels include removal of animals from the range, destruction of animals,1 sterilization, and natural controls on population levels, although the legislation does not limit BLM to these actions or specify acceptable types of sterilization or natural controls. Much of the controversy surrounding the management of free-ranging horses and burros focuses on the appropriate limit, if any, for the numbers of these animals on the range and how to keep free-ranging equid populations within a prescribed limit. From submitted public comments and statements made by members of the public at information-gathering meetings, it was clear to the committee that stakeholders vary in their opinions about how AMLs are established and what constitutes an AML. Because AMLs are a focal point of controversy, how they are established, monitored, and adjusted should be transparent to stakeholders and supported by scientific information.

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1 The destruction of healthy, unadoptable free-ranging horses and burros has been restricted by a moratorium instituted by the director of BLM since 1982 and by the annual congressional appropriations bill for the Department of the Interior since 1988.



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7 Establishing and Adjusting Appropriate Management Levels T he Wild Free-Roaming Horses and Burros Act of 1971 (P.L. 92-195), as amended by the Public Rangelands Improvement Act of 1978 (P.L. 95-514), requires the Bureau of Land Management (BLM) to “determine appropriate management levels for wild free-roaming horses and burros on [designated] public lands.” The legislation makes BLM responsible for deciding how these appropriate management levels (AMLs) of free-ranging horses and burros should be achieved within the agency’s multiple-use mandate, includ- ing consideration for wildlife, livestock, wilderness, and recreation. BLM is also directed to manage for a thriving natural ecological balance, to prevent deterioration of the range, and to use minimal management for free-ranging horses and burros. An AML has been interpreted by BLM as being a population size with upper and lower bounds for each individual Herd Management Area (HMA). Options listed in the legisla- tion for keeping horses and burros within set population levels include removal of animals from the range, destruction of animals,1 sterilization, and natural controls on population levels, although the legislation does not limit BLM to these actions or specify acceptable types of sterilization or natural controls. Much of the controversy surrounding the manage- ment of free-ranging horses and burros focuses on the appropriate limit, if any, for the num- bers of these animals on the range and how to keep free-ranging equid populations within a prescribed limit. From submitted public comments and statements made by members of the public at information-gathering meetings, it was clear to the committee that stake­ olders h vary in their opinions about how AMLs are established and what constitutes an AML. Because AMLs are a focal point of controversy, how they are established, monitored, and adjusted should be transparent to stakeholders and supported by scientific information. 1  The destruction of healthy, unadoptable free-ranging horses and burros has been restricted by a moratorium instituted by the director of BLM since 1982 and by the annual congressional appropriations bill for the Depart- ment of the Interior since 1988. 195

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196 USING SCIENCE TO IMPROVE THE BLM WILD HORSE AND BURRO PROGRAM The committee was asked to • Evaluate BLM’s approach to establishing or adjusting AMLs as described in the Wild Horses and Burros Management Handbook (BLM, 2010). • Determine, on the basis of scientific and technical considerations, whether there are other approaches to establishing or adjusting AMLs that BLM should consider. • Suggest how BLM might improve its ability to validate AMLs. To accomplish its assignment, the committee first investigated the basis of the Wild Horses and Burros Management Handbook approach to setting AMLs. The investigation included gaining an understanding of legislative definitions and interpretations that BLM has used to develop its AML policies. The committee then evaluated BLM’s approach to setting AMLs as described in the handbook. Finally, the committee explored alternative, improved approaches that BLM could consider in setting and validating AMLs. Scientific methods can be used to assess the condition of rangeland and its ability to sustain foraging and browsing animals. However, decisions regarding what kinds of animals should occupy the land, how many species should be in an area, how the land should be used, and what the balance of different uses of the land should be are questions of policy, not science. The committee’s task in this chapter is to explore the science behind the establishment and adjustment of appropriate management levels. THE HISTORY OF APPROPRIATE MANAGEMENT LEVELS The Wild Horses and Burros Management Handbook was written in response to a critique by the Government Accountability Office (GAO) stating that, as of 2008, BLM had not provided formal guidance to its field offices on how AMLs should be established and that there was a lack of consistency in setting AMLs in the agency (GAO, 2008). The following summarizes the legislative context for establishing and adjusting AMLs. It then draws conclusions about the challenges inherent in establishing and adjusting AMLs on the basis of the committee’s review of the legislation. The Legislative Setting for Establishment of Appropriate Management Levels The Public Rangelands Improvement Act of 1978 amended the 1971 act to state that information from rangeland inventory and monitoring, land-use planning, and court- ordered environmental impact statements should be used to determine whether horses are exceeding AMLs. The 1978 Code of Federal Regulations (CFR) asserted that BLM should as- certain the optimum number of free-ranging equids supported by an area and that enough forage should be allocated to horses and burros to maintain them at that number in healthy conditions while considering an area’s soil and watershed conditions, wildlife, environ- mental quality, and domestic livestock (43 CFR §4730.3 [1978]). The concept of defining AMLs by the optimum number of horses that maintains a thriving natural ecological bal- ance and avoids deterioration of the range was reaffirmed in Dahl v. Clark, 600 F. Supp 585, 592 (1984) and by the Department of the Interior’s Interior Board of Land Appeals (IBLA) (Animal Protection Institute of America, 109 IBLA 112, 119 [1989]). Under its enabling legislation, the 1976 Federal Land Policy and Management Act (P.L 94-579), BLM is required to manage public lands under the principles of multiple use and sustained yield. The agency’s objectives are

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ESTABLISHING AND ADJUSTING APPROPRIATE MANAGEMENT LEVELS 197 1) to periodically and systematically inventory public lands and their resources and their present and future use projected through land-use planning processes; 2) to manage public lands on the basis of multiple use and sustained yield; 3) to manage public lands in a manner that will protect the quality of scientific, scenic, historical, ecological, environmental, air and atmospheric, water resource, and archaeological values; 4) where appropriate, to preserve and protect certain public lands in their natural condition; 5) to provide food and habitat for fish and wildlife and domestic animals; 6) to provide for outdoor recreation and human occupancy and use; and 7) to manage, maintain and improve the condition of the public rangelands so that they become as productive as feasible for all rangeland values in accor- dance with management objectives and the land use planning process. (BLM, 2001, p. I-1) Those objectives originate with the Taylor Grazing Act of 1934 (P.L. 73-482), as amended and supplemented by the Federal Land Policy and Management Act of 1976, and the Public Rangelands Improvement Act of 1978. In addition, managers of free-ranging horses and burros must also be mindful of or necessarily follow (depending on the particular law) the guidance in the Wilderness Act of 1964 (P.L. 88-577), the National Historic Preservation Act of 1966 (P.L. 89-665), the Clean Water Act of 1972 (P.L. 92-500), the Endangered Species Act of 1973 (P.L. 93-205), the Forest and Rangeland Renewable Resources Planning Act of 1974 (P.L. 93-378), and others. Managers of free-ranging horses and burros must balance a litany of complex and even conflicting considerations when setting and maintaining AMLs in the context of those laws. A Senate conference report that accompanied the Wild Free- Roaming Horses and Burros Act states  The principal goal of this legislation is to provide for the protection of the animals from man and not the single use management of areas for the benefit of wild free-roaming horses and burros. It is the intent of the committee that the wild free-roaming horses and burros be specifically incorporated as a component of the multiple-use plans governing the use of the public lands. (U.S. Congress, 1971, p. 3) Historically, BLM efforts to identify the appropriate number of free-ranging equids that should inhabit each HMA have been challenging and controversial, even after the term ­ ptimum was replaced in the CFR with the charge to “consider the appropriate manage- o ment level for the herd, the habitat requirements of the animals, [and] the relationships with other uses of the public and adjacent private lands” while continuing to manage free-ranging horses and burros on designated HMAs (43 CFR §4710.3-1 [1986]). Previous reviews of BLM’s setting of AMLs consistently reported that established AMLs were not based on thorough assessments of range conditions. The U.S. District Court for the District of ­ evada, IBLA, and GAO all noted that AMLs of many HMAs in the 1970s and some N in the 1980s were based on administrative decisions rather than information about the carrying capacity of the range (Dahl v. Clark, 1984; 109 IBLA 119; GAO, 1990). The agency acknowledged in its 2003 strategic plan (updated in 2005) that diverse methods had been used to establish AMLs (BLM, 2003, revised 2005). In general, more consistent data collec- tion has also been recommended for grazing management (Veblen et al., 2011). Even though AML determination has been harmonized to derive from an agency-wide land-use planning process, diversity is still an issue because each state office conducts habitat assessment in its own way (BLM, 2003, revised 2005). In addition to a critique that formal guidance on setting AMLs had not been given to field offices, the 2008 GAO report noted that, as late as 2002, AMLs had not been set for two-thirds of HMAs. 

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198 USING SCIENCE TO IMPROVE THE BLM WILD HORSE AND BURRO PROGRAM Major Challenges in Defining Appropriate Management Levels in Prescribed Legislation The committee identified three overarching challenges that permeate any consideration of how to set or adjust AMLs. These challenges stem from the historical and legislative background of AMLs and the institutional and environmental context of BLM in consider- ing the setting and adjustment of AMLs. First, although biological and physical measurements are used to estimate the capacity of rangelands to support free-ranging horses and burros, the allocation of forage among multiple users is a policy decision. Second, the legislation includes requirements that seem contradictory. As reviewed in Chapter 1, the 1971 act (as amended) calls for horses and burros to be managed “as an integral part of the natural system of the public lands” and that “all management activities shall be at the minimal feasible level” but also requires the protection of a thriving natural ecological balance, which encompasses other species—especially threatened, endangered, and sensitive species—and avoidance of range deterioration caused by overpopulation. As a result, horses and burros are limited to specified areas, populations are controlled, and herds are largely protected from starvation and drought. Thus, the stipulations for their management are different from those for wildlife, which can be hunted or left to self- regulate naturally, and for livestock, which can be removed from the range by their owners at BLM request. Equids have been able to inhabit western rangelands for hundreds of years without human intervention despite weather, predation, and disease. On most HMAs, horse popu- lations have demonstrated an ability to reproduce at a rate sufficient to sustain themselves and, in most cases, to increase in abundance. However, their reproductive success may cause them to migrate or disperse in search of more resources or to have undesirable effects on soils and vegetation, both of which can bring them into conflict with other land uses. Population processes involved in food limitation, climatically driven variations in food and water, fire, predation, or natural barriers that limit access to additional food can, in some circumstances, effectively operate to regulate populations without human intervention (see Chapter 3). However, allowing horses or burros to self-regulate by permitting them to starve or to suffer from disease outbreaks is unacceptable to a large portion of the public (see section “Consequences and Indicators of Self-Limitation” in Chapter 3) and herbivory- induced changes in soils and vegetation may be unacceptable to some. Restricting horses and burros to designated HMAs can interfere with processes involved in self-regulation when dispersal or migratory movements are disrupted, when key resource areas are made unavailable (see Chapter 3), or when natural predators are lacking (see section “Effects of Predation” in Chapter 3). Management interventions may become necessary as surrogates for self-regulation processes. Interventions likely involve removals because hunting, eutha- nasia, and sale for slaughter are not currently acceptable options. Setting AMLs in light of conflicting mandates leads to expensive and controversial approaches to management of rangeland herbivores, including gathering and removing horses and burros, fertility control, manipulation of genetic attributes, adoption, and feed- ing or pasturing horses. Each of those actions takes management of free-ranging horses and burros further from the ideal of minimal management as envisioned in the original legisla- tion, regardless of how they represent attempts to work within the institutional and legal framework that shapes and constrains the protections for free-ranging horses and burros. Third, although the legislation calls for setting AMLs to maintain a thriving natural ecological balance and to prevent rangeland deterioration, these terms are uninformed by

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ESTABLISHING AND ADJUSTING APPROPRIATE MANAGEMENT LEVELS 199 science and open to multiple interpretations; precise definitions would improve the ability to use them as goals for management. For example, the concept of a thriving natural eco- logical balance does not provide guidance for determining how to allocate forage and other resources among multiple uses, which ecosystem components should be included and monitored in the “balance,” or when a system is considered to be out of balance. It brings up arguments over whether such a balance exists in nature or is even possible. Avoiding rangeland deterioration and setting of land health standards may be seen as a problem of developing specific ecological measurements and standards or as a matter of arriving at a consensus about how rangelands should be maintained. A standard, broadly agreed-on definition of rangeland deterioration and how to measure it has proved an elusive goal for decades. EVALUATION OF THE HANDBOOK APPROACH The BLM Wild Horses and Burros Management Handbook was written to respond to GAO’s criticism that BLM had not provided guidance to its field offices on how AMLs should be established. To understand how AMLs were set without a specific protocol, the commit- tee surveyed 40 HMAs (Box 7-1). Beever and Aldridge (2011) provided a comprehensive review of criteria used by BLM managers to establish AMLs. The handbook seeks to rectify the lack of guidelines for setting AMLs by making recom- mendations for their establishment and adjustment in several sections. Most specifically, Appendix 3 of the handbook defines AMLs and provides guidelines for setting them. AML decisions determine the number of WH&B [wild horses and burros] to be managed within an HMA or complex of HMAs. AML is expressed as a population range with an u ­ pper and lower limit. The AML upper limit is the number of WH&B which results in a TNEB [thriving natural ecological balance] and avoids a deterioration of the range. The AML lower limit is normally set at a number that allows the population to grow to the ­upper limit over a 4-5 year period, without any interim gathers to remove excess wild horses and burros. (BLM, 2010, p. 67) Table E-1 in Appendix E shows the upper limit set for HMAs as of May 2012. The hand- book states that an AML should be evaluated or re-evaluated “when review of resource monitoring and population inventory data indicates the AML may no longer be appropri- ate” (BLM, 2010, p. 18). Reasons that may warrant a re-evaluation include changes in the environment; newly federally protected threatened, endangered, or sensitive species; and other relevant data. The handbook prescribes processes for the decision-making aspects of setting and ad- justing AMLs. Chapter 2 of the handbook, on land-use planning, suggests that the pro- cess of setting and adjusting AMLs should take place as part of comprehensive planning, should be based on monitoring and evaluation, and should follow required decision-­making procedures. AML may be adjusted (either up or down) through the site-specific environmental analysis and decision process required by the National Environmental Policy Act of 1970 (NEPA) (P.L. 91-190). An analysis under NEPA is also required to establish a population range (up- per and lower limit) for AMLs initially established as a single number. Development of a LUP [land-use plan] amendment or revision is not generally required. (BLM, 2010, p. 10) The handbook states that an LUP should provide a process for adjusting AMLs once they are established. The process varies from one LUP area to another. If an LUP does not

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200 USING SCIENCE TO IMPROVE THE BLM WILD HORSE AND BURRO PROGRAM BOX 7-1 Reasons Given by Managers for Setting and Adjusting Appropriate Management Levels The committee recognized that, by and large, AMLs for individual HMAs had been set before the publi- cation of the handbook in June 2010 and that little time had passed for adjustments to be made between the publication and when the committee’s survey questions (Appendix D) were distributed to 40 HMAs in January 2012. The committee wanted to gain an understanding of how AMLs had been established and adjusted before publication of the handbook. The 40 HMAs in the survey were the same as those sampled for population-estimate and survey-method information (Appendix E, Table E-3). Survey respondents reported considerable variation at the HMA level in the approaches used for as- sessment and monitoring on HMAs. Establishment of HMAs generally occurred through consultation with state departments of fish and game for habitat and wildlife assessment, as called for in the legislation; use of state or regional BLM standards for rangeland (or public land) health as the “Standards for Land Health” stipulated as a goal in the handbook (BLM, 2010, p. 59); and reliance on the number of horses and cattle on the range at the time of HMA establishment to determine a goal for population levels, and in some cases to establish a ratio of number of horses to number of cattle as a framework for adjusting numbers. The committee asked BLM managers who had been surveyed how they allocated forage among horses, cattle, and wildlife. Only a few fully addressed the question, and their responses were diverse. Use at the time of AML establishment was the most common answer, along with use of the original numbers at the time of the establishment of the HMA, the number specified in accordance with a resource manage- ment plan, the outcome of a land-use planning process, or a combination of the three. For example, in one HMA, the allocation between free-ranging horses and livestock was based on the original AMLs in the resource management plan, maintaining the original ratio of forage use for livestock and horses so that livestock and horses were reduced at the same rate. In this HMA, forage allocations were not increased because all the areas were stocked at or above carrying capacity. In another state, managers reported that in consultation with their department of fish and wildlife, the biologists at BLM made forage allocations to the native and exotic ungulates. Often, the forage allocated for existing livestock grazing privileges in an HMA was subtracted from total forage availability to determine the amount available to wildlife and horses. Participating districts reported that measures of range condition and trend, upland utilization (amount of forage grazed, also termed “actual use” away from water), noxious weeds, and other types of rangeland and vegetation monitoring were considered relevant to adjusting and setting AMLs. One district used “negatively impacted vegetation functionality” as part of the justification to adjust an AML. Such consider- ations were frequent among reasons listed by managers for resetting or reaffirming AMLs. No data were provided on the metrics used to make the decisions, although some managers referred to other reports and multiple-use directives that were used in arriving at decisions. Monitoring of range and animal conditions; threatened, endangered, and sensitive species; and habitat was also conducted as part of setting, maintain- ing, or adjusting AMLs according to the survey. Most respondents to the committee’s survey reported that rangeland-monitoring studies (upland utilization, upland and riparian trend, and noxious-weeds monitor- ing) were being used to assess and evaluate forage availability in HMAs.a On one HMA in another state, the AML was set after an intensive 5-year monitoring program. Data that were used included actual use, range condition and trends, utilization, precipitation, range sites, observa- tions, and frequency of concentration areas for free-ranging horses. To change the AML again, the district provide a process for adjusting AMLs, it may need to be revised or amended so that AML adjustments can be made. In the committee’s view, the setting of an AML within a NEPA planning process when allocating resources among uses is in concert with the recognition that tradeoffs and v ­ alues are parts of management decisions. The NEPA process provides for public com- ment and review and increases public participation in environmental decisions although ­ the relationship is consultative rather than collaborative, tends to be bureaucratic, and

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ESTABLISHING AND ADJUSTING APPROPRIATE MANAGEMENT LEVELS 201 reported that it would need to conduct a similar monitoring program that would include re-examining the entire HMA and potentially reallocating forage for all animals. One district reported that in the 1975 HMA planning process, forage-production calculations from 1952 were used to estimate how many animals could be supported on BLM-managed land in the HMA. That carrying capacity was revised in 1975 because of rangeland seedings conducted in the HMA in 1974. BLM then identified the forage allocated to existing livestock grazing privileges in the HMA and subtracted that amount to calculate forage available to horses and wildlife. The state department of fish and wildlife was consulted to determine the forage required by wildlife. Forage allocations to livestock, wildlife, and free-ranging horses were made commensurate with the available forage within a reasonable distance from water and in consultation with the state wildlife agency. Managers in one state reported limiting forage use to 55 percent of production. No details were pro- vided as to how annual plant production was determined. The committee received the most comprehensive response to the question of allowable use from man- agers who used forage production maps from 1958 to estimate total forage production and determined the forage available on the basis of 50-percent utilization rate. The biologists reported currently using monitoring studies to assess and evaluate forage allocations in the HMAs. Because horses are on the range year-round but cattle are not, temporal separation has been used to distinguish horse and cattle effects on water holes and other features. Surveyed managers of districts in California, Oregon, and Wyoming cited effects on watersheds and riparian areas, riparian utilization, riparian trend, and insufficient or unreliable water as causes for adjustment. “Timing and duration of flow” was also provided as a reason for changing AMLs. Managers of the 40 surveyed HMAs reported that AMLs often had been adjusted or reaffirmed since 1971. For example, on one HMA, AMLs were changed 13 times from 1979 to 2007. Reasons for the changes were related either to four essential habitat components (forage, water, cover, and space) or to the political process. Examples of reasons included emergency gathers after extensive wildland fire, free- ranging horse distribution data, absence or inadequacy of winter range available for horses, climate and weather, and change in space available to free-ranging equids (for example, because of land closures, land trades, land-use planning efforts, boundary discrepancies, or a “checkerboard” jurisdictional pattern adjoining HMAs). Responders also cited splitting current herds into smaller groups, adverse effects of horses on cultural resources, improving vegetation conditions, enhancing wildlife habitat, and updating manage- ment plans as reasons for adjusting AMLs. a  “All Bureau of Land Management grazing allotments are periodically evaluated to assess rangeland health and evalu- ate the trend in rangeland condition and the influence grazing management has on the multiple rangeland resources associated with these allotments. [As an example, one district] employs two methods of evaluating grazing allotments. The first strategy involves a one-time field assessment by an Interdisciplinary Team composed of various BLM resource specialists. This team completes an assessment based on observations of vegetation and soil conditions. The second, and most commonly used strategy, involves a formal allotment evaluation process. During this process, an interdisciplinary team composed of various resource specialists evaluates resource conditions and creates management recommenda- tions for the allotment. The end product of this process is an allotment evaluation document which summarizes resource conditions and trend and makes recommendations for future grazing management and range improvements on the allotment. Typically allotment evaluations occur every five to 10 years depending on the resource concerns for a given allotment.” (Sharp, no date, p. 1) does not foster deliberation (Hourdequin et al., 2012). In any case, the decision-making process should be clearly distinguished from the data-gathering and analysis that pro- vide the information used in decision-making. The committee’s focus is on the scientific analysis that feeds into decisions that ultimately must reflect social values, compromise, and economic realities. A multitiered analysis process is stipulated by the handbook for establishing and adjust­ ing AMLs. Tier One instructs managers of free-ranging horses and burros to “determine

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202 USING SCIENCE TO IMPROVE THE BLM WILD HORSE AND BURRO PROGRAM whether the four essential habitat components (forage, water, cover, and space) are present in sufficient amounts to sustain healthy [wild horse and burro] populations and healthy rangelands over the long-term” (BLM, 2010, p. 67). Assessing the amount of sustainable forage available for the animals’ use is required by Tier Two. Tier Three concerns the genetic health of populations. Tiers One and Two are germane to this chapter; issues pertaining to Tier Three are discussed in Chapter 5. The Tier One evaluation as described in the handbook for four habitat factors—forage, water, cover, and space—determines whether the features necessary to support horse and burro basic needs are present. It considers water, forage, space, and cover as limiting fac- tors and requires evaluation of whether they are sufficient. Because of the inherent climatic variability of typical rangelands, the handbook recommends evaluating rangelands under conditions when they are likely to be low in forage production. Tier Two considers forage availability and quantity in detail. This section first reviews the handbook’s approach to water, cover, and space and then discusses its approach to forage. Forage availability is described in greater detail because it must be measured and used as a primary method for determining the number of herbivores that the range will support in Tier Two of the handbook-prescribed analysis. The section concludes with a review of problems related to terms and consistency in the handbook. Water In keeping with its approach of using limiting factors to evaluate habitat suitability for horses and burros, the handbook instructs managers that the amount of available water is to be calculated on the basis of the driest part of the year (BLM, 2010). However, the hand- book does not expand beyond the limiting-factors concept and provides little information about the importance of water in sustaining populations or about specific protocols for water monitoring and assessment. Water quantity and availability are to be assessed, but the handbook does not discuss poor water quality (such as nutrient content, sediment load, and water temperature). One BLM district reported in the committee’s survey that in its 1975 HMA plan process, water was identified as a limiting factor for summer use in drought years; as a result, forage allocations to livestock, wildlife, and free-ranging horses were then made with specific attention to water supplies and carrying capacity. One concern of the committee would be the age of the data because water supplies, developments, and land use have often changed and are subject to further alterations because of climate change. Another concern would be the possibility of conflict arising from competition between BLM and state agencies with responsibilities for water management. For example, the Nevada Division of Environmental Protection is responsible for water-quality standards and moni- toring in the state. To prevent overlapping or competitive efforts, cooperative interaction between that office and BLM would be valuable. Although riparian condition has been used as one of a suite of criteria to justify removal of free-ranging equids, the handbook provides relatively little specificity on the criteria to use in such decisions. Areas near water should be considered foci of concentration for horses and burros and monitored accordingly. Analyses of habitat use by free-ranging horses in sagebrush (Artemisia spp.) communities reported that horses seek riparian habitats (Crane et al., 1997). Free-ranging horses typically range farther from water sources than domestic cattle but need more water than forage alone can provide in most seasons and locations. Free-ranging horses can travel to water every 3 days to twice a day, and numerous factors affect their drinking frequency, for example, ambient temperature, succulence of existing

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ESTABLISHING AND ADJUSTING APPROPRIATE MANAGEMENT LEVELS 203 vegetation, wind speeds, and activity levels (Pellegrini, 1971; Meeker, 1979; Greyling et al., 2007). Horses’ use of water can affect water sources that influence vegetation, soils, and other species, so amounts and effects of current use should also be considered in evaluating water as a habitat component (Greyling et al., 2007). Use of areas near streams can increase runoff (Dyring, 1990b; Rogers, 1994), break down streambanks (Dyring, 1990a), reduce water quality (Nimmo and Miller, 2007), cause vegetation trampling, alterations in stream flow, and downstream siltation (Rogers, 1991), and accelerate gully erosion (Berman et al., 1988). Boggy habitats also can be altered by free-ranging horses (Dyring, 1990b; Rogers, 1991; Clemann, 2002). Similarly, soils, vegetation, and small mammals in and adjacent to springs can be markedly affected by free-ranging equids even when livestock have been absent for extended periods (Beever and Brussard, 2000). There is evidence of interaction between forage characteristics and riparian-area use; the characteristics of forage may be affected by concentrated animal use near water. In the Sheldon National Wildlife Refuge in Nevada, 3 years of exclusion of free-ranging horses from grazing in riparian zones led to a 40-percent increase in cover of plant litter compared to bare ground and a 30-percent decrease in extent of bare ground, whereas these metrics remained generally constant in the paired riparian plots that continued to be grazed by horses (Boyd et al., 2012). In the nonexclosed areas, estimates of use from September to October based on standing biomass varied from negligible to nearly 100 percent (Boyd et al. 2012). In contrast, Greyling et al. (2007), studying areas of heavy use around a waterhole in Namibia, reported that the “expected degradation gradient radiating out from the water troughs due to over-utilization by the horses was not found. Neither vegetation species composition, density, nor standing biomass measured at various distances from the troughs confirmed a degradation gradient.” Methods of measuring riparian condition are available. Proper functioning condition is a monitoring tool developed by BLM to assess the physical functioning of riparian and wetland areas (BLM, 1998). It provides a consistent approach that takes into consideration hydrology, vegetation, and soil-landform attributes and encourages a team approach which includes wildlife, hydrology, and plant-science expertise. This method is qualitative by design and thus lacks rigorous quantitative analysis and statistical inference. However, it can provide a framework for identifying sites where water impairments have occurred and where improved management of water resources is required. Measures of water quality (such as temperature, salinity, nutrients, dissolved oxygen, and sediment) or hydrogeo­ morphology (such as groundwater discharge, active floodplain, sinuosity, and width and depth ratio) do not appear to be actively used by BLM and might serve as indicators for modifying management decisions related to free-ranging horses and burros (BLM, 1998). Soil conditions—such as storing moisture, allowing infiltration, stabilizing vegetation, and balanced release of water—and preventing rill or sheet erosion by water-caused or wind- caused dust are also possible indicators. A new synthesis of literature pertaining to ripar- ian management practices (George et al., 2011) may provide insights on how to manage free-ranging horses in riparian areas. Further, a standard range-improvement action for mitigating damage to riparian areas involves fencing sensitive areas and providing troughs at locations away from natural waters. Given the extensive diversion, piping, and regula- tion of springs already in place across the western United States, additional use of troughs should be balanced against consideration for native fauna dependent on natural flows.

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204 USING SCIENCE TO IMPROVE THE BLM WILD HORSE AND BURRO PROGRAM Cover and Space Vegetation provides cover for free-ranging equids. For example, trees provide shade that allows equids to avoid direct insolation during the hottest times of the day, a rubbing surface that they can use to scratch topical irritations, visual concealment from predators, and forage (Pellegrini, 1971; Hanley, 1982). In the second paragraph of Chapter 3 of the handbook, an emphasis is placed on evaluating habitat suitability on the basis of access to “forage, water, or thermal or hiding cover.” The implication is that without access to those resources, horse removals may be necessary. Many models suggest that contemporary climate change may alter the distribution of trees and the balance of deciduous versus ever­ reen trees in parts of the domains of HMAs (Fuhlendorf et al., 1996, 2012; Tausch, g 1999). The direct effects to horses of such changes are unknown. Before considering horse r ­ emovals when cover and space are inadequate, where it does not cause conflict with other uses, managers may also consider increasing habitat availability by establishing greater connectivity between key habitats (through removing barriers and creating corridors for travel, habitat improvement, providing water at key points, land acquisition, or other methods). It is not clear from the handbook (BLM, 2010) what is meant by space, and there does not seem to be a good definition or way of measuring it in the scientific literature. The analysis of adequate “space” in the handbook apparently is derived largely from whether the horses and burros will stay in the habitat. For example, the handbook states that the animals “require sufficient space to allow the herd to move freely between water and forage within seasonal habitats” (BLM, 2010, p. 13). The need to adjust AMLs because of changes in the area available to equids was cited several times by surveyed managers—such changes as land closures, land trades, LUP efforts, boundary discrepancies, or a “checkerboard” jurisdictional pattern adjoining or within HMAs. To be more specific, the discussion in the handbook should emphasize the spatial movements of free-ranging horses and burros relative to water, cover, and forage. Other aspects that might be considered include the influence of sunshine, shade, the viewshed, predator escape routes, and slope position (e.g., leeward for shelter from weather and windy gaps for insect avoidance). There is a direct relationship between space and access to spatially heterogeneous resources (such as those listed) in landscapes where horses and burros may be (Coughenour, 1991, 2008). Those resources are often dispersed patchily. As a result, the four key habitat components (forage, water, cover, and space) and other resources are naturally heterogeneous in distribution and availability and should be evalu- ated on the basis of their spatial and temporal variability. Because horses and burros, like most ungulates (Hobbs, 1996), use landscapes hetero- geneously, assessment ideally would occur at multiple spatial resolutions. In particular, free-ranging equids will use some portions of the landscape often (especially when equid densities are high) and use other parts rarely or never (e.g., areas more than 15 km from water sources, slopes of more than 50 percent [Ganskopp and Vavra, 1987], and areas domi- nated by large boulders or monoliths). Multiple-resolution assessment could be especially valuable in situations in which dynamics at one spatial resolution can influence dynamics at other spatial resolutions (cross-scale dynamics; Allen, 2007). Forage Availability In a case study in Appendix 3 of the handbook, the amount of forage available for sus- tainable use by herbivores, or the carrying capacity of an HMA, is the accessible, palatable

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ESTABLISHING AND ADJUSTING APPROPRIATE MANAGEMENT LEVELS 205 biomass that grows on the site annually, modified by an allowable use factor (AU). An AU is the percentage of annual production that can be grazed without causing plants to decline in production and growth. Typical AUs are between 25 and 60 percent, meaning that 25 to 60 percent of the annual forage growth can safely be allocated to grazing; that is, it is available forage. However, AUs are often adjusted for local conditions, as it is in the case study, and for season of grazing; AUs are higher in dormant than in growing seasons. AUs are based on data about the effects of specific percentages of “use” on plant species and communities that are rarely available. Studies of the response of specific species and plant communities to herbivory and how the species and communities are influenced by season of grazing, the amount and frequency of herbivory, and varied growing conditions have been numerous but by no means comprehensive (e.g., Hanley, 1982; Paige and Whitham, 1987; Paige, 1992; Belsky et al., 1993; Hawkes and Sullivan, 2001). In fact, it is usually dif- ficult to determine exactly how even widely used AUs were derived. The handbook’s case study details the use of at least 3 years of grazing utilization and use mapping data with annual population estimates of horses to determine weighted uti- lization data, potential carrying capacity, and a proposed carrying capacity. It is not clear where the AU for plant species is acquired. In the case study, it appears that all the available forage will be allocated to horses and that only horse data are used, although at the end it is shown that the results can be converted for other herbivores (BLM, 2010). The explana- tion of how to calculate the weighted average forage utilization is relatively clear, but it is not clear how annually adjusted population estimates of horses, expressed in animal unit months (AUMs), are acquired. An AUM is a standardized unit of forage consumed per “animal unit” each month. Knowledge of annual herd population sizes for at least 3 years is critical for the prescribed method in that they are the basis for establishing annual forage availability, the most common habitat factor used for establishing AMLs. Use of utilization and use mapping data to infer forage production levels is a pragmatic approach that takes multiple factors into account, including “background” consumption by all users of forage, areas of concentration, and site-specific production limitations. Ideally, however, direct forage-production data should also be used to determine forage availability. Measuring how much forage is consumed by what species (horses and burros versus livestock versus wildlife) would be helpful in determining how many animals can be supported relative to forage supply, although the committee acknowledges that this can be difficult. The methods for assessing utilization are not described in the manual; however, examination of various BLM reports indicated that utilization was simply visu- ally estimated. This method is prone to inaccuracy and is generally not well validated. More direct measures of utilization could be made through the use of grazing exclosures, particularly movable exclosures. Issues related to determining horse population size are detailed in Chapter 2. Another complication is that a substantial part of the diet of horses may not be herba- ceous plants, such as grass, and the case study includes only herbaceous growth to calculate forage availability. A fair amount of research on diets of free-ranging horses of the western United States that occurred in the 1970s and 1980s confirmed that horses are typically grazers (that is, most of the food that they consume is grasses and graminoids) but that the proportions of individual food items and even of plant life forms consumed vary markedly annually, among seasons, by location, and among individuals, including variation by age, sex, and reproductive state and history (Hansen, 1976; Hubbard and Hansen, 1976; Hansen et al., 1977; Olsen and Hansen, 1977; Krysl et al., 1984; McInnis and Vavra, 1987). That is due in part to the fact that the nutritive value of plant species can vary markedly among seasons and years (Miraglia et al., 2008). Utilization of browse should be identified and

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228 USING SCIENCE TO IMPROVE THE BLM WILD HORSE AND BURRO PROGRAM could be used to map and overlay total and percentage utilization by the different spe- cies in the landscape. The committee believes that BLM should continue to develop the AIM strategy and to participate in development of state-and-transition models for western rangelands with NRCS. As is the case with all large herbivores, free-ranging horses and burros not only use the environment but change it, and these effects need to be considered in assessment of AMLs. Effects of trampling and concentrated use on soils, insects, small mammals, and plants should be monitored in addition to forage consumption. Given BLM’s multiple- use mandate, it may want to consider wider monitoring of one or more aspects of eco- logical condition and function that are not tied solely to equid health. Metrics related to such aspects should reflect the effects of processes that large-bodied herbivores impose on ­ecosystems—namely, patch creation, redistribution of nutrients via selective herbivory and later urination and defecation, compaction of upper soil horizons, and rubbing and tram- pling of vegetation. Although it can be challenging to measure ecological function ­ irectly, d there are numerous methods and techniques for indexing ecological services, such as loss of soil by wind or water erosion; riparian-channel function; clean water; and physical struc- ture of vegetation for perching, resting, or escape cover. Explicit attention to a reasonable subset of ecological services and ecosystem components is a good idea fiscally because con- serving the potential of landscapes to remain resilient and to resist degradation may make expensive remediation, rehabilitation, or emergency recovery efforts unnecessary. Native threatened, endangered, and sensitive species require focused conservation attention. Such attention provides BLM with a mosaic of conservation elements that reflect ­ iverse dis- d turbance regimes, including parts of the landscape with no nonnative herbivores. Many disturbance-sensitive species seem likely to become increasingly rare, especially in the arid and semiarid landscapes of western North America that are being affected by invasive plants, climate change, and uncharacteristic fire regimes. Water quality needs to be considered in addition to water supply in looking at avail- ability for multiple species. Numerous methods have been developed to perform such monitoring, including ones that involve robust statistical designs, have been used specifi- cally for grazing systems, and have been used by many local, state, and federal agencies that have diverse stakeholders (Beever and Pyke, 2004; Herrick et al., 2005a,b; Thoma et al., 2009). Consultation and collaboration with state and federal agencies charged with water quality responsibilities are necessary. BLM should use a strategically placed network of large, long-term exclosures to quan- tify the long-term effects of free-ranging equids, livestock, and wildlife among HMAs, seasons, and years of different weather. The Challenge of Minimal Management The way that AMLs are established and adjusted ensures that population growth rate is maximized (see Chapters 2 and 3). The density-dependent and environmental constraints that would reduce population growth rate and keep a natural population in check are pre- cluded by management removals to avoid range deterioration. In a self-regulating, food- limited system, a lack of adequate food eventually suppresses the population if predation does not (see Chapter 3), and this sometimes results in effects on vegetation, soils, and other species. Removals to prevent those effects also prevent self-regulation of the horse population and in fact may allow it to reach its maximum potential growth rate. Therefore, there is a need to predict and state explicitly the population-level outcomes of managing

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ESTABLISHING AND ADJUSTING APPROPRIATE MANAGEMENT LEVELS 229 for vegetation conditions that may be expected in a sustainable but differently functioning ecosystem that includes large herbivores. A program of continuing, ad infinitum removals may not be economically sustainable or socially acceptable. However, letting horses become food-limited, having many horses in poor condition, and having horses die of starvation on the range are not acceptable to a sizable proportion of the public. The use of more benign methods to control population growth rate (such as contraception) may reduce (but perhaps not minimize) the level of management intervention while avoiding the unacceptable outcome of food limitation. Various fertility-control mechanisms are described in Chapter 4 with their consequences for population processes (see Chapters 3, 4, and 6) and genetic processes (see Chapter 5). A scientific approach is needed to identify objectively the constraints on horse and burro populations and their effects on the expression of natural processes under minimal management. The ecosystem might look different and function differently in the presence of more minimally managed equid populations from how it does with no or markedly reduced populations, but it may nevertheless be sustainable over time. Such a scientific approach would provide a more solid justification of management interventions. For ex- ample, the anticipated effects of different equid densities on vegetation and rangeland ecosystem functioning should have a scientific basis. Likewise there should be a basis for assertions that barriers to dispersal or barriers to access to critical habitats preclude natural processes; and the assertions should be explicitly described and justified for a specific HMA on the basis of an understanding of how ecosystems would function with large herbivores and minimal management. Ideally, from a research standpoint, such questions would be addressed in a replicated spatial mosaic in which some herds or areas would be allowed to self-regulate and others would be managed as they are currently being managed. Allocation versus Assessment Transparent processes for allocation should be developed, such as participatory adap- tive approaches. Participatory approaches are discussed in Chapter 8. Managing for Unpredictability The committee examined traditional pastoral systems adapted to arid ecosystems. BLM is charged with using “minimal” management for free-ranging horses and burros, so exten- sive pastoral systems adapted to arid rangelands that use little or no supplemental feeding, energy, and physical infrastructure might offer some insight into how to manage free- ranging equids. Traditional pastoral systems emphasize mobility, flexibility, and reserves (Oba et al., 2000). Mobility is the movement of animals from one area to another on scales from the local to across biomes; flexibility is being able to adjust boundaries, herd sizes and components, and timing and patterns of mobility. Reserves are areas that are grazed only during extreme events. The origins of those practices owe much to the natural movements and behaviors of free-ranging herds. Can BLM use this information in developing strategies for coping with the unpredictability of arid rangeland environments? How much and within what kinds of bounds in nonequilibrium environments graz- ing influences vegetation trajectories is debatable; however, it is indisputable that there is great unpredictability in forage production and that grazing management cannot reduce it (Vetter, 2005). BLM’s system of calculating forage availability without including years of high production attempts to adjust for this unpredictability by removing high-productivity years from the calculation; however, there will always be extreme events in nonequilibrium

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230 USING SCIENCE TO IMPROVE THE BLM WILD HORSE AND BURRO PROGRAM conditions. Even with a conservative approach, an important lesson from traditional pas- toral systems is that the extreme events need to be planned for and that flexibility in num- bers, timing, and boundaries is important. From the theoretical developments in rangeland ecological dynamics, it is also known that some sites will be permanently altered by unpre- dictable events. There will be a constant need for adaptation, so an adaptive-management process for setting and adjusting AMLs should be explored. In addition to intensive monitoring of grazing utilization, rangeland ecological condi- tion and trend, actual use and climate data, using NRCS ecological site descriptions and associated state-and-transition models for horse-occupied habitat would not only help to standardize ecological information agency-wide, but it would build on substantial previ- ous work and facilitate use of the already existing National Resource Inventory database. That would provide value to the consistent investment by BLM that is needed at this time. Ecological site descriptions are land-classification systems that identify and stratify lands on the basis of soil-, climate-, and herbivory-influenced ecological potential and ecosystem dynamics. State-and-transition models are included in individual ecological site descriptions that characterize thresholds, community phases within states, and irreversible transitions that degrade ecological processes and lead to alternative states (Stringham et al., 2003). In fact, BLM has already recognized the need to develop such models for BLM lands in its 2011 AIM monitoring strategy. Conceptual ecological models based on science and other expert input are being developed to provide a common language that addresses ecosystem sustainability, a means of identifying indicators of key ecosystem attributes, and a basis for resource decisions predicated on maintaining or restoring ecosystem capacities. Managing for a Thriving Natural Ecological Balance and to Prevent Rangeland Deterioration If maintaining a thriving natural ecological balance and preventing rangeland deterio- ration are to be used as scientific justifications for setting AMLs, these goals need a more scientific basis and clear definition. Recently developed concepts that might be of use in helping to set and adjust AMLs include those of ecological sustainability (Smith et al., 1995; Turner et al., 2003; Weltz and Dunn, 2003; Mitchell, 2010) and ecosystem resilience (Carpenter et al., 2001; Walker et al., 2006; Briske et al., 2008). As those concepts are devel- oped and tested scientifically, adopting a sustainability or resilience framework would be a marked advancement, and it would be more likely that such a framework would have a credible scientific basis. REFERENCES Allen, C. 2007. Interactions across spatial scales among forest dieback, fire and erosion in northern New Mexico landscapes. Ecosystems 10:797-808. Archer, S. and F.E. Smeins. 1991. Ecosystem-level processes. Pp. 109-139 in Grazing Management: An Ecological Perspective, R.K. Heitschmidt and J.W. Stuth, eds. Portland, OR: Timber Press. Austin, M.P. 1985. Models for analysis of species response to environmental gradients. Pp. 10-11 in Theory and Models in Vegetation Science: Abstracts, R. Leemans, I.C. Prentice, and E. Van Der Maarel, eds. Stockholm: Almqvist & Wiksell International. Beever, E.A. and C.L. Aldridge. 2011. Influences of free-roaming equids on sagebrush ecosystems, with a focus on Greater Sage-Grouse. Pp. 273-290 in Greater Sage-Grouse: Ecology and Conservation of a Landscape Species and Its Habitats, S.T. Knick and J.W. Connelly, eds. Berkeley: University of California Press. Beever, E.A. and P.F. Brussard. 2000. Examining ecological consequences of feral horse grazing using exclosures. Western North American Naturalist 60:236-254.

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ESTABLISHING AND ADJUSTING APPROPRIATE MANAGEMENT LEVELS 231 Beever, E.A. and P.F. Brussard. 2004. Community- and landscape-level responses of reptiles and small mammals to feral-horse grazing in the Great Basin. Journal of Arid Environments 59:271-297. Beever, E.A. and J.E. Herrick. 2006. Effects of feral horses in Great Basin landscapes on soils and ants: Direct and indirect mechanisms. Journal of Arid Environments 66:96-112. Beever, E.A. and D.A. Pyke. 2004. Integrated Monitoring of Hydrogeomorphic, Vegetative, and Edaphic Condi- tions in Riparian Ecosystems of Great Basin National Park, Nevada. U.S. Geological Survey, Scientific Inves- tigations Report 2004-5185. Reston, VA: U.S. Geological Survey. Beever, E.A., R.J. Tausch, and P.F. Brussard. 2003. Characterizing grazing disturbance in semiarid ecosystems across broad scales, using diverse indices. Ecological Applications 13:119-136. Beever, E.A., R.J. Tausch, and W.E. Thogmartin. 2008. 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