Grazing Capacity Analysis, Work in Progress, Using GIS to determining the amount of grazing on public lands consistent with rangeland health standards and guidelines.

James Catlin, Wild Utah Project

Abstract

Livestock grazing on Bureay of Land Management (BLM) lands has a long history in the West. For more than half a century, BLM has managed the number of livestock that graze on public lands for sustained yield. This policy has evolved today to manage grazing in deference to the needs of ecological health. Range monitoring and analysis has also changed over the years and, in the process, BLM has collected decades of range data.

In the past decades, GIS has emerged in BLM to play a major role in land use planning and management. But surprisingly, BLM generally has not used GIS to analyze the amount of livestock grazing that is consistent with BLM's standards for rangeland health.

In recent decades, the Natural Resources Conservation Service is creating soil maps using GIS. These maps create polygons which represent categories of soil each with a specific potential natural plant community. Using current field data and these soil maps, we suggest that GIS has the ability to assess the amount of forage that might be expected in an allotment.

Based on the ecological needs of a specific area and recent field forage surveys, our analysis will estimate what part of that forage amount might be available for livestock and still retain vegetation required to meet the needs for plant community health and wildlife requirements.

To demonstrate our GIS forage capacity analysis, we will apply our method to a case study for an allotment in the Grand Staircase-Escalante National Monument. Our grazing capacity analysis method is still evolving but we expect that such a GIS analysis tool will be important to land managers, to those who graze livestock, and to others in the conservation community.

The resulting analysis produced forage values and related livestock numbers that are less than those now permitted in the allotment. If correct, these results would indicate that current levels of grazing use might correlate with declines in rangeland health.

Introduction

This study proposes a method of using GIS with information on soils, plants, livestock use, and ecological needs to estimate the amount of livestock grazing that can occur and the habitat still maintain its health and productivity. The work reported here is a study still underway and we expect to see changes in the methods described here as our studies continue.

Land managers normally allocate livestock use for rangelands in terms of their number and the duration of grazing for a specific grazing allotment. The grazing allotment is the spatial unit used by the Forest Service and the Bureau of Land Management (BLM), and allotments vary greatly in size. Land managers determine the amount of grazing that can be allowed ba sed on the forage capacity of the allotment. Grazing capacity refers to the number of livestock and the duration of grazing that can occur in a sustained manner for a given allotment (Galt 2000).

Grazing on federal lands has been for a long time seen as economially and socially important in the western United States. Grazing management practices and analysis methods describe in the next section in this paper have evolved under the principle of sustained forage productivity. Even when plant production is sustained, ecological degradation of rangelands often still occurs. Recognizing this a decade ago, the BLM and the Forest Service adopted rangeland health standards designed to restore and maintain the health of ecosystems.

To implement these rangeland standards, a number of inventory procedures and management guidelines have been developed by Federal agencies. While progress has been made in assessing the health of upland range and stream communities, the BLM has not updated its method of calculating range capacity. Still missing from the BLM's range management tools is an analysis tool that determines the amount of livestock that can be allowed and the rangeland still meet the rangeland health standards. This paper presents our work to develop such a tool.

The next section of this paper summarizes past BLM forage capacity assessments and describes potential ecological factors to be considered in forage capacity analysis. If you think of the rangeland forage as an endowment fund, then the amount that you withdraw from the endowment (amount of forage consumed by grazing) is dependent on the interest rate (annual growth largely dependent on the amount of precipitation) of the capital asset (the plant community). To ensure that the capital base of the endowment does not decline over time, the amount withdrawn (grazed by cattle) is the annual production minus that necessary to renew the endowment (meet the ecological needs of the area.)

A number of considerations guide the selection of the percent of the annual plant community production that could be allocated to livestock after ecological considerations are met.

We have research underway on this topic that, unfortunately, is not yet available to guide this paper's analysis. In the interim, this analysis will use a range of proportions of forage that might be available for livestock based on an cursory review of the scientific literature. These are 50%, 25% and 10% of the annual palatable forage production to be allocated for livestock.

Next, this paper applies the percentages just described to a data table derived by spatial analysis of forage production. The Upper Hackberry Grazing Allotment provides an example that describes how this method could be applied using GIS. Soil maps were acquired from the BLM along with the soil map unit site descriptions. We augmented this data with field data we have collected on the current amount of annual forage produced. Our team clipped and weighed a number of sample points to representative the amount of current forage produced today in each soil map unit.

BLM range management and stocking levels

Grazing stocking numbers have not always been determined by a range capacity analysis. Early livestock numbers assigned to grazing allotments were developed over a half century ago. In many cases, the number of livestock that were allowed to graze were the result of regional social processes that relied on personal experience and subjective data from field trips as part of a politically negotiated settlement.

Over the decades, adjustments, usually reductions, were made to the numbers of livestock largely without the benefit of a capacity analysis. Decades of monitoring of BLM allotments has captured some but not all ecological data as far back as the late sixties. Commonly on BLM lands, changes in the quantity and timing of grazing were made as adjustments based on utilization and trend monitoring.

Around 1980, the BLM began a more rigorous inventory and analysis called SVIM for Soil Vegetation Inventory Method. SVIM lead to the development of soil maps and estimates of the available forage for each soil unit. Forage capacity for an allotment assumed that half of the herbaceous and grassy species were available for livestock. This method relied on a number of assumptions that proven to be problematic. The focus of the capacity analysis was on the total sustained forage. As a result, this method did not consider key ecological factors such as plant community composition, excessive grazing use in key habitat such as riparian areas, soil nutrient cycle maintenance, and nongame wildlife needs. In spite of these short comings, SVIM proved to be a major step forward in range management.

BLM's SVIM analysis suggested that BLM may be required to reduce the number of livestock on a large number of allotments. For political reasons, most of these recommended changes did not occur and BLM halted the use of SVIM in making stocking decisions. The Director of the Bureau of Land Management at that time issued instructions that required BLM to have five years of monitoring data before it could make reductions in the amount of allowed livestock use. This effectively halted the use of SVIM to assist in making grazing decisions. To this day, BLM rarely involves grazing capacity analysis in making grazing decisions.

This may change as BLM implements rangeland health standards developed about a decade ago. BLM developed standards and guidelines for each state that are consistent with a national policy of managing grazing in deference to the health of ecosystems. Ecosystem health is linked to the productivity of the land and its ability to service local communities on a sustained basis (National Research Council 1994). The loss of biodiversity through the loss of native species has long term implications to the health of watersheds and the ability of the land to provide forage in the most efficient manner. The importance of a full suite of native wildlife and plants in the health of ecosystems has been firmly established by the scientific community. (Soulé and Terborgh 1999) Rangeland standards that restore and maintain ecosystems provide the resilience and diversity that ensures, in most cases, the best productivity of the land.

Measuring the composition, structure, and ecological processes for a specific habitat in an ecosystem is beyond anyone's resources at this time. As a practical necessity, we are required to use indicators to monitor ecosystem health. Total annual production in plant biomass and soil litter, for example, can be sampled while energy flow and soil nutrient generation are impractical to measure. In assessing the amount of forage that can be removed from an allotment, ecological considerations include soil nutrient recycling, plant community structure, its composition and productivity, wildlife habitat needs, requirements for habitat resiliency, to name a few.

As generally practiced by BLM, current monitoring focuses on key species that represent the most productive perennial grass leaving unmonitored species most at risk. In the past, BLM commonly recommends stocking levels that consume 50% of the annual production of grasses and forbs. This 50% represents a commonly used proportion found in many allotment management plans, grazing environmental impact statements, and agency technical maps. The assumption made is that this level of consumption is adequate for wildlife and sustained production of forage. Many have questioned this assumption (Holechek 1998). More recently, stocking levels based on 25% for than annual forage have been suggested for the semiarid south west(Gaft).

Research now underway will hopefully either validate these percent plant community consumption levels or perhaps lead to yet another number. For the analysis presented here, we will repeat our capacity analysis for three values, 50%, 25%, and 10% of the forage available to livestock.

25% represents more current recommended use found in a some of the range management literature(Galt et. al. 2000). This study also uses 10% to reflect the level of forage use that might apply in cases of serious ecological stress such as the need to restore degraded rangelands or respond to a serious drought.

The Natural Resources Conservation Service (NRCS) provides key spatial data for use in this capacity analysis. NRCS soil surveys have developed maps of polygons called soil map units. Each soil map unit represents generally small areas that possess common soil characteristics, climate, and composition of its plant community. A grazing allotment usually is divided into a number of discrete soil map units. The description for a soil map unit includes an estimated amount of forage that is produced for that specific soil unit type. This annual forage production estimate lists the pounds per acre of forage that a healthy and fully productive potential natural plant community would produce for a specific soil map unit.

While the resolution of the maps is not suitable for a site specific project such as the construction of a bridge, this resolution is adequate for grazing allotment and other larger scale analysis. The objective of (soil) mapping is not to delineate pure taxonomic classes but rather to separate the landscape into segments that have similar use and management requirements (SCS 1991).

Soil mapping involves collecting samples, laboratory analysis, engineering tests, climate measurements, plant community inventories, and assembling production data. Plant community productivity are estimates based on field experience, plot experiments, and production records. Each soil map unit has a description that includes the total annual plant production measured in dry weights of pounds per acre. Three production categories (favorable, normal, and unfavorable) represent the expected annual production of the potential natural plant community. Favorable conditions reflect years where precipitation is more that two inches above normal. Normal conditions reflect plant growth resulting from average annual precipitation. Unfavorable conditions reflect droughts where where annual rainfall is less than two inches below average. The forage production expected from the potential natural plant community is described in a range that reflects different amounts of annual precipitation.

This plant productivity provided by the Natural Resources Conservation Service represents the total annual production of grasses, forbs, shrubs, and trees for a specific soil map unit. The site description includes the percent production that can be attributed to each of these categories of the plant community (SCS 1993) . While livestock sometimes browse on shrubs, we did not include the annual production of shrubs in the available forage. Livestock generally browse measurable amounts of shrubs only after grasses and forbs have been grazed more that 50%.

Many of the past soil surveys is now available over the internet. Digital soil data can be found on the Web on the National Map Unit Interpretation Records (MUIR) database www.statlab.iastate.edu/soils/muir/, and in the Soil Survey Geographic (SSURGO), www.ftw.nrcs.usda.gov/ssur_data.html.

GIS Use in Livestock Capacity Analysis

The GIS data needed for this analysis includes a map of the grazing allotment boundaries, a soil map delineating soil map units. Tabular data that relates specific soil map units to forage production for the potential natural plant community are then related to the appropriate soil map unit.

In this analysis, I also incorporated data taken from field clipping surveys we conducted in the demonstration allotment. These clipping surveys more accurately reflect the annual growth found today for grasses and forbs for each the soil map. Our analysis provides a comparison of the grazing capacity of the potential plant community with the current productivity as represented by our clipping surveys.

To calculate the forage available to livestock, I removed those areas that BLM had identified as unsuitable for livestock grazing. These areas are typically cliffs and areas too remote from water sources for livestock. GIS was used to clip the soil map coverage leaving only those soil map units that BLM identified as suitable for livestock.

We also removed soil map units where annual palatable forage is so low that the land can not support livestock grazing. BLM's 1980 grazing EIS includes a criterion that establishes such a minimal necessary plant productivity amount (BLM 1980. BLM classified areas as unsuitable if they produced palatable perennial forage less than 17 lb per acre per year. Our clipping survey identified a number of areas that were unsuitable under this criterion.

Demonstration Allotment, Upper Hackberry Allotment

We chose the Upper Hackberry allotment to demonstrate how GIS might be used with soil map unit data to assess this allotment's range capacity. We chose this area in part because BLM has consistently reported that the grazing permit holder has been "doing a good job of managing their allotment" (BLM 1995) and also because this area represents habitat found widely in this region. This allotment is part of a regional grazing planning effort and, for this reason, more recent digital data ares available. Lastly we chose this allotment based on size. By choosing an allotment of more modest size, twenty thousand acres, we were able to conduct field surveys of plant productivity.

This allotment, inside the Grand Staircase-Escalante National Monument, is located a few miles south of Kodachrome Basin State Park and ten miles east of Bryce Canyon National Park. The area is dominated by sandy soils, pinyon juniper forests, sagebrush plateaus, sandstone escapements, badland hills, and entrenched perennial streams on the allotment borders. Based on fifty years of rain gage data, the average precipitation for this area is11 inches a year.

Today, most rangelands today produce forage at substantially lower yields than predicted by the Natural Resources Conservation Service. BLM's grazing records support this point. In the Upper Hackberry Allotment example, the upland loam (basin big sagebrush) soil map unit is predicted to produce between 1250 to 750 lbs of annual plant growth per acre per year for the potential native community with an average precipitation year and a dry precipitation year. The composition of this potential plant community for this soil map unit expects that 35% of the plant production would be from shrubs and the rest from forbs and grasses. In this analysis, we did not include shrubs in the forage base for livestock. So the predicted potential native community production for the upland loam soil map unit for a potential native plant community would be 600 lbs per acre of grasses and forbs in an average year and 500 lbs per acre in a dry year.

This analysis occurred during an prolonged drought and, for this reason, this analysis used the unfavorable values for plant productivity in this analysis.

Thanks to BLM's recent land use plan and upcoming grazing EIS for this area, BLM was able to supply a number of coverages that aided this analysis. These coverages used in this analysis include site writeup area maps which described soil map units, grazing allotment boundaries, rangeland health assessment sites, and range project sites.

While most of the coverages provided the information we needed, some modifications were needed. We had to create a map of those lands BLM had identified as unsuitable for grazing based on a paper map in an allotment management plan. BLM's soil map did not inventory state and private, some of which are found inside the Upper Hackberry Allotment. Using geo-referenced aerial photos, we edited the soil map unit coverage to include similar polygons for what were at one time state lands. Based on soil map unit descriptions, we added plant community productivity estimates to the appropriate soil map unit in the table for the coverage.

The annual plant productivity described for the average year for soil map unit relates to the range condition of an area. Range condition is assessed by comparing the deviation of the composition (percent of each species) against the potential native plant community. These are then broken into four classes: 76-100% Excellent (potential natural community), 51-75% Good (Late seral), 26-50% Fair (mid seral), and 0-25% Poor (early seral).

Based on recent plant community composition transects, I was able to assess current range condition. The Upper Hackberry Allotment's plant community is only 23% of the potential native community and thus has a range condition class of poor. This range condition rating justifies a prescription for very light grazing in order to restore more rapidly the productivity of this allotment. This rating also includes the current productivity of seeded areas as compared with expected productivity.

Analysis and Discussion

The calculations on the table associated with the soil map produced a number of animal units months of grazing that the Upper Hackberry Allotment could support, Table 2.

Table 2

The current grazing use reported by the permittee shows an use of 408 AUMs over the past five years. Since the grazing period is 7.5 months, this number equates to 54 head of livestock on the range for seven and a half months.

Based on current forage production, our analysis found that this allotment has 451 AUMs if 50% of the palatable forage is allocated to livestock. A 50% level of the annual forage for livestock is consistent with past tradition of range management.

The 50% forage use by livestock over the long term has caused problems. Several factors show that this allotment has forage production roughly one tenth of that expected for similar habitat in excellent condition. Our clipping study also sampled similar soil map units in a long ungrazed near by state park. Several decades of nongrazing has nearly doubled the productivity of this state park's forage. While the state park is not fully recovered, it shows a significantly higher productivity.

If the analysis allocates 25% of the palatable forage to livestock, then only 226 AUMs are supported in the Upper Hackberry Allotment. This amounts to 30 head of livestock for the 7.5 month grazing season. The 25% level is recommended for the semiarid west reflecting the need to leave a margin grazing use to allow plant productivity to increase and increase resiliency of the plant community to annual precipitation changes. In the Upper Hackberry Allotment, each AUM requires 68 acres of suitable rangeland. Note that an additional 33% of this allotment is unsuitable for grazing reflecting the conditions found in many allotments in this region.

Additional BLM monitoring shows problems in this allotment. The long term trend monitoring focuses on Indian rice grass and an exotic planted perennial grass, crested wheat grass. This allotment's trend studies for Indian rice grass shows that the percent of plant cover for this grass is about one tenth of that expected for similar potential natural plant communities. In addition to this, BLM's riparian health assessments have found that the riparian areas in this allotment are functioning at risk or not meeting the rangeland health standard. Lastly, the seedings BLM established in the sixties and eighties are producing forage at about one eighth of that expected by BLM in the description of the range treatment. This information indicates that the current level of grazing over time has contributed to a net long term loss in productivity of the land.

While allocating a fraction of forage to livestock is remains unclear if the 25% level for livestock is low enough for a significantly degraded area. 25% may best suited for semi arid rangelands in good or excellent condition. If so, then a further reduction may be warranted. The combination of a drought, the need for a prolonged period to regenerate the soil nutrient base, continued heavy use in unprotected riparian areas, and the need for recovery of the plant community composition may support even a lower level of grazing. The 10% level indicates that this allotment could only provide 90 AUMs. At this level of use, only 12 livestock would spend 7.5 months on the range.

Conclusions

The widespread adaption of GIS by land managers aids making key management decisions. This paper demonstrates one potential use, estimating the amount of livestock grazing that can be allowed and still have the rangelands meet rangeland health standards.

The results shown on Table 2 will be further reviewed as our research continues. Research on the amount of the plant community needed for regeneration, litter, soil nutrients, wildlife habitat and other ecological needs to be better understood. As our studies for the Southwest rangelands progresses, our research hopes to better define these forage percentages that can be assigned for livestock taking into account land managers rangeland health standards. Stay tuned and we will report more about this next year.

Citations:

Galt, Dee, Francisco Molinar, Joe Navarro, Jamus Joseph, and Jerry Holecheck. 2000. Grazing capacity and stocking rate. Rangelands. December

Holechek, Jerry, Rex Pieper, Carlton Herbel. 1998. Range management: principles and practices. Prentice Hall, New Jersey

Natural Research Council, Committee on Rangeland Classification. 1994. Rangeland Heath,

New methods to classify, inventory, and monitor rangelands. National Academy Press. Washington D.C.

Soulé, Michael, John Terborgh. 1999. Continental Conservation, Scientific foundations of regional reserve networks. Island Press, Washington, D.C.

United States Department of the Interior (USDI). 1966. The third wave, conservation yearbook no. 3. U.S. Government Printing Office. 1966-O-229-165 p 91.

United States Department of Agriculture, Soil Conservation Service. 1991. Soil survey of Canyonlands area, Utah. p 5.

United States Department of Agriculture, Soil Conservation Service (SCS). 1993. Range site description (for soil map units), Section II-E. unpublished documents.

United States Department of the Interior, Bureau of Land Management (BLM). 1995. Upper Hackberry Allotment summary, September 13, 1995, unpublished report.

United States Department of the Interior, Bureau of Land Management (BLM). 1980. Kanab/Escalante grazing management environmental impact statement. Appendix 9.

Author Information:

James Catlin, Wild Utah Project, 68 S. Main Street, Suite 400, Salt Lake City, Utah 84101. (801) 328-3550 wup@xmission.com