Using Science to Improve the BLM Wild Horse and Burro Program A Way Forward (2013) / Chapter Skim
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7 Establishing and Adjusting Appropriate Management Levels
7 Establishing and Adjusting Appropriate Management Levels
Pages 195-238
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From page 195... ...
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)
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From page 196... ...
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)
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From page 197... ...
. 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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From page 198... ...
Each of those actions takes management of free-ranging horses and burros further from the ideal of minimal management as envisioned in the original legislation, 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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From page 199... ...
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.
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From page 200... ...
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)
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From page 201... ...
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]
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From page 202... ...
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.
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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)
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. Forage Availability In a case study in Appendix 3 of the handbook, the amount of forage available for sustainable use by herbivores, or the carrying capacity of an HMA, is the accessible, palatable
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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.
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From page 206... ...
The handbook guidelines stipulate that years of above-average forage production are not to be used in calculations of forage availability -- a conservative approach that aims to reduce the need for emergency gathers. Rangeland that is not commonly used is also not included.
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From page 207... ...
Problematic Terms As discussed in the section "Major Challenges in Defining Appropriate Management Levels in Prescribed Legislation," vague definitions in the Wild Free-Roaming Horses and Burros Act and related legislation have created difficulty in implementing and assessing management strategies for free-ranging equids. The handbook does not provide any greater clarity.
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From page 208... ...
reported that definitions of overgrazing also depend on differences in theories of how ecosystems that have abundant large herbivores function without human intervention. Indicators of deterioration in rangeland health may or may not constitute evidence of overgrazing, depending on management objectives and the theory or conceptual model that the management is based on.
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From page 209... ...
, an endangered species candidate, in Wyoming. There are several possible interpretations of what constitutes a thriving natural ecological balance.
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In the Pryor Mountains, Coates and Schemnitz (1994) found partial dietary overlap year-round, and Kissel (1996)
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From page 211... ...
Challenges to Managing for a Thriving Natural Ecological Balance. Although allowing an equid ecosystem to self-regulate could be one approach to establishing a balance, it is also evident that this may not be a realistic objective in many cases, owing to human effects that are beyond the purview of BLM.
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From page 212... ...
process is generally used to establish livestock grazing, AMLs for freeranging horses and burros, and recommendations for wildlife habitat management. This process begins with an evaluation of range conditions; the evaluation assesses whether or not management and stocking levels for livestock, wild horses and/or burros, and wildlife are achieving rangeland objectives.
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From page 213... ...
The first is a focus on plant-herbivore equilibria or nonequilibria. It was once theorized that plants and herbivores would come into a natural ecological balance or equilibrium if left undisturbed.
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From page 214... ...
. The ecological dynamics of vegetation on arid rangelands are now commonly characterized by using state-and-transition models that posit that relatively stable configurations of vegetation, or "states," exist and that they may "transition" to other such states as a result of the influence of biotic or abiotic factors, such as grazing, precipitation, species invasions, fire, and seed sources (Westoby et al., 1989; Bestelmeyer et al., 2003; 0.0 0.1 0.2 0.3 0.4 0.5 Precipitation CV FIGURE 7-1 Coefficient of variation of annual rainfall in the contiguous United States.
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From page 215... ...
Over time, the outcomes of adaptive management can be used to improve the state-and-transition models. The NRCS effort to develop state-and-transition models to guide rangeland management throughout the West is a valuable opportunity to create a standardized basis for managing for desirable ecosystem states that will go a long way to maintaining a thriving natural ecological balance as mandated by the Wild Free-Roaming Horses and Burros Act as amended (see Box 7-2)
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From page 216... ...
. Although the Pryor Mountain Wild Horse Range supported 161 horses in 2003, the NRCS assess ent determined carrying capacity should be 45-142 horses on the basis of the percent of rangeland m in poor condition, the low similarities of vegetation to potential climax vegetation, a perceived downward trend in range condition, and evidence of severe erosion.
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From page 217... ...
Rangeland health was assessed by using a number of indicators "relative to soil and site stability, water shed and hydrologic function, and soil and plant community integrity" (Ricketts et al., 2004, p.
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. Monitoring and Assessing Forage Availability Once AMLs are established it is essential to determine whether forage consumption is at the predicted level.
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From page 219... ...
concluded that exclosures are nonetheless an excellent monitoring and experimental design tool that had been underused to quantify influences of free-ranging horses on vegetation and wildlife. That is particularly relevant for BLM managers of free-ranging equids because numerous exclosures have been in place for some time, and a strategically placed network of large exclosures could provide BLM with robust data for quantifying the effects of free-ranging equids among HMAs, seasons, and years of different weather.
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Which sensor is chosen depends on management objectives and expected outcomes. Several of the sensors provide specific advantages for management of free-ranging horses and burros (Table 7-2)
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NDVI of large areas for vegetation cover and predicted annual forage production. aThe IKONOS sensor is a high-resolution satellite that captures 3.2-m multispectral images and 1-m panchromatic data.
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BLM uses GIS to some extent to quantify vegetation and forage production potentials in different range sites, as delineated by NRCS or older Soil Conservation Service soil surveys. Forage production estimates for each range site have been combined or scaled up by using GIS to derive forage production.
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From page 223... ...
Spatial patterns of precipitation can be thought of as dynamic precipitation maps in the model. • Simulation of dynamic snowpack distributions across the landscape because these affect forage availability and herbivore distributions.
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From page 224... ...
Numerous relatively recent advances in ecological monitoring that can further increase confidence in results are relevant and noteworthy for the Wild Horse and Burro Program. For example, if a particular question is being addressed in terms of testing of the null hypothesis and the null hypothesis fails to be rejected (that is, no effect of a management ac tion or "treatment" was found)
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From page 225... ...
Concepts related to power can improve setting and adjusting of AMLs by providing quantification of sensitivity of a monitoring system, that is, the ability to be an early-warning system of environmental change as opposed to confirming that a system has already been dramatically altered and perhaps crossed an ecological threshold. The committee believes that the above principles could be more thoroughly integrated into the Wild Horse and Burro Program to increase the defensibility and scientific validity of management actions.
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. what constitutes rangeland health and a thriving natural ecological balance pervade such debates.
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From page 227... ...
• Improve the scientific validity of the concept of a thriving natural ecological balance. Increased Specificity and Consistency BLM should continue moving toward consistency in its protocols for setting and adjust ing AMLs; repeatability is a hallmark of ecological monitoring.
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From page 228... ...
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.
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From page 229... ...
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 grazing 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)
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From page 230... ...
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 deterioration are to be used as scientific justifications for setting AMLs, these goals need a more scientific basis and clear definition.
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From page 231... ...
Presentation at the Symposium on Free-Roaming Wild and Feral Horses at the Society for Range Management 65th Annual Meeting, Spokane, WA, January 31. Briske, D.D., S.D.
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1999. Ecosystem Modeling of the Pryor Mountain Wild Horse Range.
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From page 233... ...
1987. Slope use by cattle, feral horses, deer, and bighorn sheep.
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1996. Population Dynamics, Food Habits, Seasonal Habitat Use, and Spatial Relationships of Bighorn Sheep, Mule Deer, and Feral Horses in the Pryor Mountains, Montana/Wyoming.
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2010. Demography of the Pryor Mountain Wild Horses, 1993-2007.
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Journal of Range Management 42:266-274.
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2004. The impact of feral horses on grassland bird communities in Argentina.
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