An Ecological Study of Kalmia latifolia (L.) in the Maryland Piedmont

Abstract

Mountain laurel, Kalmia latifolia (L.), is a major component of eastern deciduous forests. It is associated with upland and dry sites but the environmental conditions that limit its range are poorly understood. This experiment determined the effects of light and moisture on the growth, reproduction. and characteristics of a population of K la4folia in the Piedmont region of Maryland. Soil moisture did not vary substantially within the stand or across the stand boundaries. Where differences occurred, stand density and plant stem diameter were significantly affected by moisture (r²= 0. 253 and 0.265, respectively). Within the stand there was generally uniform soil moisture and light affected plant growth and population dynamics. Stand density, basal area, percent of stems that were living, and individual plant growth and reproduction increased as canopy cover decreased; suggesting that light was a critical factor regulating K. latifolia success. Plant stem diameters were greater at the summit (4.03 cm) than at the hill shoulder (2.48 cm) where canopy cover was less. However, plant density was higher at the hill shoulder (74.6 stems/100m²) than at the summit (17.4 stems/100 m²) and the footslope (18.5 stems/100 m²). Larger individual sizes were likely due to longer-lived plants but lower stand density suggested significant population thinning had occurred at the summit due to higher canopy cover. 'the denser shoulder area population was associated with openings from rock outcroppings and treefall that reduced canopy cover. The highest canopy cover at the footslope and toeslope impacted growth, and reproduction. The hillslope topography and the overstory structure (canopy cover) in combination with sun blocking from the opposing hillsides appeared to reduce sunlight at lower slope elevations. The stand at the footslope had a significantly lower percentage of living plant stems (45%) than the summit, shoulder, and backslope positions (>72%). Reproduction also was less at the footslope (0.2 flowers and 0 fruit per plant) than at the shoulder position (7.3 flowers and 6.3 fruit per plant). While both soil moisture and light impact the growth of the stand, previous site history is also an important factor. In the study area, the rocky soil and steepness of the slope may have limited forestry and agricultural use facilitating survival of a native mountain laurel population.