The influence of dormant brush sprays on forest succession in Western Oregon

Abstract

This study was designed to learn the effect a specific herbicide practice on plant communities. Data were obtained from brushfields that had been aerially sprayed with 2,4-D (2,4 dichiorophenoxyacetic acid) and/or 2,4,5-T (2,4,5 trichlorophenoxyacetic acid). Qualitative data on species composition, cover percent, height, response to herbicide and site description were collected. Quantitative data dealing with frequency, density, and dispersion were also collected. These data were analyzed to determine the influence of dormant treatments involving these herbicides on the distribution and vegetational pattern of the forbs and herbs, as well as the woody plants. The developmental stage of the vegetation greatly influenced its response to the applied chemical. That is, an increase in ,density and height of the brush cover was accompanied by increased interception of the herbicide by the taller brush species and, generally, a decrease in the effect of the herbicide on low-growing vegetation. Therefore, the time elapsed between clearcutting and chemical treatment was a dominant factor in the effect of the herbicide on the various vegetative strata. The data assembled imply that the seral development on an area such as that sampled can be controlled in part by the aerial application of herbicides. The collection and subsequent statistical analysis of the quantitative data reveals that phytotoxic chemicals introduced into a rather balanced ecosystem cause a significant adjustment within the plant population. Certain seres may be extended and/or various resistant species may fill environmental niches which might otherwise be occupied by species sensitive to herbicidal treatments. A slope comparison study was incorporated into the basic plan of the research problem, but from the data- collected and analyzed it was impossible to determine conclusively whether reaction of vegetation on the southeast slopes to chemical treatment differed significantly from that of vegetation on the northwest slopes. Substantial differences between the flora on the two opposing aspects prevail, but evidence was not conclusive that herbicides were responsible for this difference.