Stand level pine response to occupancy of woody shrub and herbaceous vegetation

The relationship between age-5 pine height and vegetation cover was estimat ed for loblolly pine (Pinus taeda L.) and slash pine (Pinus elliottii Engel m.) stands using regression analysis. This paper utilizes results from four locations of a vegetation control study that included herbicide treatments to control woody shrub and herbaceous vegetation. Age-5 average dominant h eight was predicted from first-year herbaceous cover, untreated first-year shrub cover, and fifth-year shrub cover. Dominant height increased 0.5 m fo r each decrease of about 30% in either first year herbaceous cover, untreat ed first-year shrub cover, or year-5 shrub cover. Lack of vegetation contro l on beds where vegetation was allowed to recolonize before planting reduce d dominant height an additional 0.5 m. A competition index was constructed that estimates the difference between "potential" and actual age-5 pine hei ght. Stand-level models were developed to link age-5 pine height and occupa ncy of competing vegetation to quadratic mean DBH, specific DBH percentiles , and stand basal area. The effects of interspecific competition on stand b asal area and diameter percentiles could be accounted for through the effec ts of competing vegetation on dominant height except for treatments that di d not control woody shrubs.