Assessing ecosystem health using the ecological site framework in the absence of ecological site descriptions

Background/Question/Methods

Changes in climate interacting with natural and anthropogenic disturbances will alter the resilience and resistance of ecosystems. Managing for sustainable ecosystem services requires knowledge of ecosystem change through time. Long term monitoring is essential to tracking ecosystem change and the establishment of baseline information on current conditions is the first step. Extensive sampling of ecosystems on the Manti-La Sal National Forest in southeast Utah was conducted to quantify current conditions and their spatial variability. Vegetation sampling and soil pedon descriptions were conducted on 148 spatially balanced randomly selected plots. The study area encompasses 1300-km² of plateaus, canyons, and mountains, with elevation ranging from 1710 to 3463 m and is divided into 15 grazing allotments; other major land uses include logging and recreation. The structure of our study follows the premise of the Ecological Site concept by classifying the landscape based on potential vegetation, soil type, climate, and geomorphic setting. However, our study area does not have suitable Ecological Site Descriptions (ESDs) for evaluating the sampled plots. Previous studies have used hierarchical clustering methods to examine potential States-and-Transitions within described Ecological Sites. This study proposes multivariate techniques to identify and describe potential Ecological Sites as well as potential states within them.

Results/Conclusions

Preliminary cluster analyses and ordinations show strong groupings based on geomorphic setting and soil properties that are accurately described by vegetation data using indicator species analyses; that is, we identify potential Ecological Sites. Additionally, strong sub-grouping is also evident within groups that have enough samples, suggesting an ability to discriminate potential states within a potential Ecological Site. Further examination of the variability within the groups suggests it will be possible to evaluate the range of topographic, climatic, soil, and vegetation properties within each group.  Using these statistical methods combined with a literature review of the studied ecosystems, one can assemble post hoc ESDs including State-and-Transition Models that can be used to classify and evaluate sites that do not have published ESDs. The proposed methods are not meant to replace existing ESDs. They are proposed with the intent of allowing land managers and researchers to use data collected in areas that are not described by ESDs consistently with those that are.