Distribution of Viola blanda in relation to within-habitat variation in canopy openness, soil phosphorus, and magnesium'

Abstract

GRIFTH, C. (School of Biological Sciences, University of Kentucky, Lexington, KY 40506). Distribution of Viola blanda in relation to within-habitat variation in canopy openness, soil phosphorus, and magnesium. Bull. Torrey Bot. Club 123: 281-285. 1996.-Abiotic resources in a deciduous forest often are patchily distributed, with different microsites having different resource levels. If plant growth and reproduction depends on access to these resources, then plants may occupy only the richer microsites within a habitat. In order to determine if the presence of individual ramets of Viola blanda Willd. (Violaceae) are correlated with microsite resource levels, I measured soil chemistry (pH, total N, P, K, Ca, Mg) and canopy openness at 100 random points and the nearest 100 points with V. blanda along a 600 m transect in the Cumberland Plateau in eastern Kentucky. A quadratic discriminant function in combination with a cross-validation method found that resource levels correctly classified 77.5% of the violet points and 55.2% of the random points. Wilcoxon signed-rank tests indicated that phosphorus concentrations and tree canopy openness were significantly higher at the violet points than at the random points. However, the random points had higher magnesium levels. Several mechanisms may explain this pattern, including differences in pollinator activity as a result of light levels, myrmecochory, clonal growth, or higher growth rates on microsites with higher resource levels.