Vegetation composition structure and soils monitoring at Grant-Kohrs Ranch National Historic Site: 2009 annual data report

Shorrock, Donna; Ashton, Isabel; Britten, Michael; Burke, Jennifer; Pillmore, David; Schweiger, E.

The Rocky Mountain Network has identified the condition of vegetation composition, structure, and soils (VCSS) in terrestrial systems as one of its high priority vital signs. Using this protocol, we monitor the status and trend in grassland, shrubland, and woodland ecosystems as they are affected by natural and anthropogenic disturbance over time. Grant-Kohrs Ranch National Historic Site (GRKO), a small, accessible park established to preserve and demonstrate historic ranching life, is characterized by grasslands and perfect for implementing a three-year VCSS pilot study beginning in 2006. 2009 is the first year of sampling post-pilot and the data are summarized here.The VCSS protocol uses a probability survey design allowing us to estimate measures of vegetation composition and structure along with multiple soil parameters across the entire park. Sample frames used within the design were derived from a Natural Resources Conservation Service (NRCS) GIS layer of Soil Survey Geographic Database (SSURGO) soil types. To refine this sample frame, we removed sensitive sites (e.g., cultural resources), developed park infrastructure, wetlands, and areas with greater than 50% tree cover. We are exploring possible post-hoc allocation of sites to park defined internal management zones that prioritize different resources. In 2009, crews sampled eight sites at GRKO, revisiting one of these sites, which contributes to ongoing estimates of within-season variation. The sites fell into four internal management zones: upland pasture, pasture/hayfield, riparian area/woodland, and railroad bed and barrow pit/wetland. At each site, we used a variety of cover estimation techniques in plots and along transects. Additionally, we collected frequency data, landscape context (disturbance) data, soil cores for laboratory analyses, and performed soil aggregate stability tests. Crews found 104 vascular plant species at GRKO monitoring sites, 30 of which are non-native. Almost half of the 10 most abundant species are exotic; at least two of these species are harvested for hay. Overall community diversity proved to be lower than expected for similar community types in western Montana and markedly lower when looking strictly at the native component. The most abundant species documented at the sites included native grasses such as bluebunch wheatgrass (Pseudoroegneria spicata) and needle and thread grass (Hesperostipa comata). Equally common were exotic grasses, namely smooth brome (Bromus inermis), quack grass (Elymus repens), and Kentucky bluegrass (Poa pratensis). Spiny phlox (Phlox hoodii), was the only abundant perennial forb recorded.Crews noted and recorded both anthropogenic and natural disturbance using two different indices, a modified version of the Human Disturbance Index (HDI) developed by the Colorado Natural Heritage Program and the Natural Disturbance Index, which is modeled after standard qualitative, categorical disturbance indices such as HDI and the California Rapid Assessment Method for Wetlands. These indices provide contextual information about the history of the landscape and aid interpretation of ecological variables. The scale for both indices ranges from 0-100 with lower scores indicating less impact from disturbance. Human disturbance scores at GRKO were moderate, ranging from 28 to 58, while natural disturbance scores were lower, ranging from 3-35. In preliminary work, we found no first order relationships among these coarse measures of disturbance and vegetation or soil characteristics. Survey design-based VCSS monitoring will continue at GRKO in future years. When enough plots have been sampled, we will conduct design-based estimates of core vegetation and soil parameters and model-based trend analyses.

Vegetation composition structure and soils monitoring at Grant-Kohrs Ranch National Historic Site: 2009 annual data report

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