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Comparing ESDs to habitat characteristics

Written by Rachel Mealor and Jeff Beck

By UW Extension Range Specialist Rachel Mealor and Jeff Beck, UW Wildlife Habitat Restoration Ecology

Jeff Beck, assistant professor in the Department of Renewable Resources at the University of Wyoming, recently co-authored an article evaluating the comparability of Ecological Site Descriptions (ESDs) and habitat characteristics that influence Greater Sage grouse.

The greater sage grouse is a species that has recently received a lot of attention, so this comparability study is timely. The article begins with outlining what an Ecological Site Description (ESD) is and brings to light the limitations of their use in interpreting wildlife habitat values. Considering that limitation, the over-arching goal of the research was to look at ESD information and evaluate whether current ESD data collected for management purposes could be used to refine models for sage grouse nest occurrence and success.

Nest occurrence is a location where a female sage grouse nested, whereas a successful nest is a nest where at least one egg in the clutch hatched. More specifically, three questions were asked: 1) Are ESDs useful in predicting sage grouse nest site occurrence and success as a univariate explanatory variable? 2) Can ESD information refine predictions of local-scale nest site occurrence and success models? 3) Can ESD information refine landscape-scale nest site occurrence models by serving as a surrogate for local scale information that cannot be mapped in a geographic information system (GIS)?
Their study location was in the Powder River Basin and included parts of Johnson County. The site was dominated by Wyoming big sagebrush with an understory of native and non-native grasses. Various methods were used to evaluate each of the three questions with existing sage grouse data collected from radio-telemetry, prior analyses and Natural Resources Conservation Service (NRCS) ESDs.

The authors concluded that ESD information was not an effective predictor of grouse nest site occurrence or success without other local- or landscape-scale habitat information (question 1, above). They also determined that ESD information did not refine predictions of local-scale habitat models of nest site occurrence or success (question 2), but there was some level of uncertainty involved. For the final question, clear evidence was found to suggest that ESD information, as collected by the NRCS, does not refine landscape-scale habitat selection models by serving as a surrogate for local scale information that cannot be currently mapped in a GIS.

From this research, one could conclude that there is some uncertainty in the effectiveness of current ESD information as a basis for making sage grouse management decisions. However, it should be noted that the study design was opportunistic in the sense that an existing data set on sage grouse locations was used when they overlapped with NRCS ESD information and may not have considered the full use of ESD information.

In closing, the authors provide ways in which they feel ESDs could be improved from a wildlife habitat, specifically sage grouse, perspective. They suggest including structural measures that are known to influence nest occurrence and nest success for field measures regarding sage-grouse management using ESDs.

One aspect currently lacking in ESD classifications is the adequate description of sagebrush occurrence, which is known to be an important component for sage-grouse. Although the percent composition and production of plants is described in ESD data, there is no measurement of vegetative height, canopy cover and other structural measures such as visual obstruction. Another idea discussed was to incorporate sage grouse habitat ecology into a sage grouse preference table, which could increase the use of ESDs. Further information on specific forb, grass and shrub species that are of benefit to sage grouse could help guide resource managers in determining sage grouse index scores for sites that could support grouse. They suggest there might be use in developing preference tables for each plant species to evaluate their suitability as habitat or a food source for grouse throughout various life stages. Overall, this study demonstrates that ESD databases would need to be refined to include relevant habitat measurements before they could be used to accurately predict sage grouse nest occurrence and success.    

So, does this mean that ESDs should not be utilized? Absolutely not! However, this study illustrates the current limitations of ESDs. Ecological Site Descriptions have not yet progressed to their full potential and they are not an all-encompassing land management tool. ESDs display some shortcomings when it comes to interpreting and evaluating wildlife habitat values. However, ESDs can be a very useful tool in establishing a general idea of percent composition and production of plants. There is a lot of useful information contained in them, however, like all tools, there are limitations involved.
Gaining a clear understanding of the tool and how to best apply it is just as important as having the tool. One would not use a saw to drive a nail, as there are limitations to its usefulness for that particular situation. There are other ways to determine sage grouse habitat characteristics; however ESDs in their current state may not have all the information necessary to make specific land management decisions. This paper does, however, suggest information that would be useful to refine current ESDs to make them more applicable for sage grouse habitat inventory and management.