Succession of Pinyon-Juniper Communities After Mechanical Disturbance in Southcentral New Mexico

Abstract

Principal component analysis (PCA) was used to interpret secondary succession of pinyon-juniper stands after cabling or bulldozing. Soil types were used to separate 93 sample units into 3 groupings. A PCA was run on 2 of the groupings. Groups of sample units were defined as community types for each ordination. Stepwise discriminant analysis using environmental variables was used to assist in delineation of community types. Species that contributed the most to the first 3 principal components were compared among community types for each ordination using an analysis of variance and a comparison of the least squares means. Grasses on the deeper soils usually increased after cabling, but after 25 years they had declined to near pretreatment levels. Wavyleaf oak (Quercus undulata Torr.) increased after cabling, and on the older cablings it had reached higher cover values than on the other community types. Pinyon and juniper response appeared to be dependent on density and size of trees before cabling. If the stand was near climax before cabling, pinyons rapidly became dominant on the site. If it was seral, there would be more junipers, but their slow growth and the time they require for maturation required more time before they dominated the site. The successional pattern following cabling on relatively deep soils is similar to what was found after fire, but it occurs faster. Cover of grasses and shrubs increased more on rock-free soils compared to sites treated similarly but with rock. The ordinations indicated that succession in pinyon-juniper communities is directional and leads towards climax with a decrease in variability among sites.