MODEL FOR CLASSIFYInG AnD MOnITORInG HACKBERRY (CELTIS OCCIDENTALIS L.)-SHRUB ECOLOGICAL TYPE In SAnD HILLS PRAIRIE ECOSYSTEM

A classification and monitoring system for the hackberry-shrub ecological type was developed based on plant succession in the Sand Hills ecosystem in northern Nebraska and southern South Dakota. Seral stages are quantitatively derived groupings of vegetation composition based on the range of variability within the current ecological type. Multivariate statistical methods determined three key variables that best assign data (sites) to one of four seral stages within the contemporary hackberry-shrub ecological type and represent one of multiple possible stable states. Basal area of hackberry (Celtis occidentalis L.), combined canopy cover values of chokecherry (Prunus virginiana L.) and wild plum (Prunus americana Marsh.), and canopy cover of western snowberry (Symphoricarpos occidentalis Hook.) were the key plant variables required for classification and moni toring to determine succession or retrogression. Four seral stages (early to late) were quantitatively identified with an accuracy of 97%. Classification involves a single sample at a site where monitoring trends require multiple seral stage assignment at the same site over time. The assigned seral stages provide resource managers with a quantitative method to evaluate their management objectives by monitoring trend. We list all coefficients required to assign data to seral stage and calculate posterior probabilities, however details of methods for monitoring protocol, seral stage classification, calculation of seral stage probabilities can be viewed at the Forest Service web site http://www.fs.fed.us/rangelands/ecology/ ecologicalclassification/index.shtml,