The Role of Rhus Copallina in the Dynamics of the Forest‐Prairie Ecotone in North‐Central Oklahoma
1979
Petranka, James W. | McPherson, James K.
The functional role of Rhus copallina in the tension zone between forests and prairies and the mechanisms which allow clones of this species to replace climax tallgrass prairie were studied in the cross—timbers region of north—central Oklahoma. Measurements and observations indicated that bottomland forest trees were unable effectively to invade climax tallgrass prairie without the prior invasion of R. Copallina or other shrubs. Upland forest tree species, however, were frequently able to invade climax prairie, but these invasions were enhanced by the prior invasion of shrubs. The entry and growth of clones of R. copallina into climax prairie was characterized by a reduction in the density of prairie vegetation and a concomitant increase in tree seedlings, shrubs, and herbs which comprised the nearby hardwood forests. Growth ring counts of nine clones revealed an average rate of encroachment of 1.25 m/yr. The reduced fire frequencies (relative to primeval prairies) on the study area tended to favor the growth of R. copallina clones. Laboratory tests demonstrated that the rhizomes, flowers, fruits, senescent leaves, and leaf litter of R. copallina contain toxins which significantly inhibit either seed germination or seedling growth in both climax prairie and weedy test species. Lighe intensities were found to reach critically low levels in mature, well—formed clones. Seedling response in experimentally manipulated study plots further indicated that both allelopathy and competition for light significantly reduce the number of prairie seedlings underneath clones of R. copallina. Soil moisture and macronutrient content generally were higher within clones so that competition for these factors appears to be insignificant in excluding prairie species from clones.
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