Understory-overstory relationships in ponderosa pine forests, Black Hills, South Dakota

Abstract

Understory-overstory relationships were examined over 7 different growing stock levels (GSLs) of 2 size classes (saplings, 8-10 cm d.b.h. and poles, 15-18 cm d.b.h.) of ponderosa pine (Pinus ponderosa) in the Black Hills, South Dakota. Generally, production of graminoids, forbs, and shrubs was similar between sapling and pole stands. Trends among GSLs were also similar between these tree size classes. Graminoids and forbs were most abundant in clearcuts and the 5 m2/ha basal area. Intermediate amounts were produced at GSLs of 14-23 m2/ha and lowest in unthinned stands which had basal areas ranging from 27-33 m2/ha and 37-40 m2/ha in sapling and pole stands, respectively. Total understory production followed the same trends. Shrubs, however, appeared to produce most at intermediate stocking levels but were variable. Graminoid and forb production were best estimated by the model logY=a+bX. Relationships for total production were better described by Y=a+bX. However, variability of shrub production precluded selection of a single model; the best model varied between tree size classes. Standard errors of the estimate indicate that reasonably good predictive models can be developed for pole and sapling stands considered separately or combined. When years were combined, however, SEs increased markedly, indicating less reliable models.