Case Study: Ecological Integrity of Grasslands in the Apache Highlands Ecoregion

Transcription

1 Standard 9: Screen all target/biodiversity element occurrences for viability or ecological integrity. Case Study: Ecological Integrity of Grasslands in the Apache Highlands Ecoregion Summarized from: Marshall, R.M et al. (2004) and Gori, D.F., and C.A.F. Enquist (2003) Purpose and region of analysis The Apache Highlands Ecoregional Assessment team conducted a detailed assessment of the ecological integrity of grasslands throughout the ecoregion in order to identify the best remaining examples of native and restorable grasslands. This ecoregion occurs in Arizona, New Mexico and Mexico and is a landscape of grasslands, deserts and mountain ranges. Grasslands are of particular importance because of the threats of development, constant grazing, invasive species and loss of fire regime. Criteria/Methods The ecological integrity of ecosystem targets can be evaluated via various measures of the size, condition and landscape context of a particular occurrence of that target. The Apache Highlands team chose to give special attention to assessing the integrity of grassland systems in the region. The ecoregion was assessed for changes in grassland composition and structure as well as the current and historical extent and distribution of grassland types. They used an expert-based approach for this assessment, receiving input from 24 range management specialists from government agencies, academic institutions and non-governmental organizations. This method was selected over the more conventional approach which relies on the use of remotely sensed data. Cost, time and technical problems associated with image processing and model development led to the decision to use an expert based method over the more conventional approach. Expert input was solicited, mapped and ground-truthed with extensive field reconnaissance and quantitative vegetation sampling at random sampling points. Expert input was ascertained through a mapping exercise. Experts were given 1:100,000, 1:150,000, or 1:250,000 digital raster graph (DRG) maps overlain with the GAP vegetation associations for Arizona or New Mexico. Experts then delineated polygons that represented current and former grasslands and each polygon was classified into one of six grassland condition types (figure 1). Occasionally, when an area was heterogeneous, a synthetic type was assigned, such as A&B or A&D. Additionally, experts were asked to identify potential grasslands (both current and former) that would require field reconnaissance to confirm. Field reconnaissance

2 focused on locations identified by experts as being type A, B (see definitions below), or of unknown type since it was not possible to visit all grassland locations. Details about field methodologies can be found in Gori and Enquist (2003). Further information on the process can be found in Schussman and Gori. (2004) and Marshall et al. (2004). The location and extent of six grassland condition types were identified: A) native grassland with low shrub cover, B) shrub-encroached non-native grassland with restoration potential using prescribed fire, C) sacaton riparian grassland, D) non-native grassland with low shrub cover, E) shrub-encroached non-native grassland, and F) former grassland that has undergone a type conversion to shrubland. For the portion of the ecoregion in Mexico, less data and fewer experts were available. As a result, Landsat TM satellite images were used to conduct a mix of supervised and unsupervised classification to identify grasslands. Available experts assisted the classification process though many areas were classified as unknown. Two separate accuracy assessments were conducted. Results report 76-88% accuracy of grassland condition classifications. Figure 1: Grassland classification for the Apache Highlands Ecoregion (Southeast corner). The entire state of Arizona was also classified.

3 Products/Outcomes The team had data on the historical and current extent of grassland, the size and condition of remaining grasslands and ownership of areas containing grasslands. These data together allowed the team to answer questions such as: What proportions of grasslands still occur as high quality grasslands? Where are these grasslands? What type of ownership are they under? Where are areas in need of the most immediate restoration actions? etc. Answers to these questions assisted in the identification of priority areas for conservation and restoration. When it came time to set goals for the conservation of targets in the Apache Highlands Ecoregion, the team was able to set more explicit quantitative goals for grassland targets than for any other species or system targets. The data was available to create a rudimentary species/area curve to determine the percentage of grasslands necessary to maintain 90% of the native species diversity in grassland systems. This goal was distributed among the 6 grassland condition types where the all of the grasslands in the best condition would be protected and the remaining percentage would be distributed among the lower condition classes.

4 Tools ArcView 3.2 GIS 1:100,000, 1:150,000, or 1:250,000 digital raster graph (DRG) maps GAP vegetation associations for Arizona or New Mexico (Arizona Gap Project 1998; Thompson et al. 1996). 1:200,000 BLM land cover/land ownership maps Landsat TM images GAP protection status (Weinstein 2002) and land ownership (ALRIS 1998) spatial data sets References ALRIS Program Arizona Land Resources Information System, Arizona State Land Department. Arizona Gap Program U.S. Geological Survey/Cooperative Park Studies Unit/ University of Arizona, Tucson, AZ. Gori, D.F., and C.A.F. Enquist An Assessment of the Spatial Extent and Condition of Grasslands in Central and Southern Arizona, Southwestern New Mexico and Northern Mexico. Prepared by The Nature Conservancy, Arizona Chapter. 28 pp. Available on line at: Marshall, R. M., D. Turner, et al. (2004). An Ecological Analysis of Conservation Priorities in the Apache Highlands Ecoregion, The Nature Conservancy of Arizona, Instituto del Medio Ambiente y el Desarrollo Sustentable del Estado de Sonora, agency and institutional partners: 152 pp. Available on line at: Poiani, K. A., B. D. Richter, et al. (2000). Biodiversity conservation at multiple scales: Functional sites, landscapes, and networks. Bioscience 50(2): Schussman, H., and D. F. Gori An Ecological Assessment of the Bureau of Land Management's Current Fire Management Practices: Materials and Recommendations for Future Fire Planning. The Nature Conservancy, Arizona Chapter. 86 pp. Available on line at: Thompson, B.C., P.J. Crist, J.S. Prior-Magee, R.A. Deitner, D.L. Garber, and M.A. Hughes Gap analysis of biological diversity conservation in New Mexico using geographic information systems. Final Gap Analysis Report, U.S. Dept. of Interior, New Mexico Cooperative Fish and Wildlife Research Unit, Las Cruces, NM.

5 Weinstein, S Gap analysis of land stewardship in the Apache Highlands Ecoregion. Report to The Nature Conservancy, Tucson, AZ.