Population ecology of Pinus pungens in pine-oak forests of southwestern Virginia

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Virginia Polytechnic Institute and State University

I studied aspects of the population ecology of table mountain pine, Pinus pungens, in pine-oak forests on Brush Mountain, Montgomery County, Virginia. The objective of this study was to examine the age structure and recruitment dynamics of P. pungens, a fire-adapted conifer, and to determine whether P. pungens populations would persist in the absence of fire. The age distributions of P. pungens on the Brush Mountain study sites were bimodal, with peaks in seedling and canopy age classes and a major trough in the sapling and understory age classes. Age and diameter of P. pungens understory and canopy trees were positively related, but diameter was a poor predictor of age. The sparse representation of P. pungens in the seedling, sapling, and understory strata of the Brush Mountain sites strongly indicates that under current disturbance regimes, maintenance of P. pungens populations is unlikely. The prevalence of oak advance regeneration ard other gap-exploiting woody species such as ard Sassafras albidum and Nyssa sylvatica suggests that gap replacement processes would favor these species and not P. pungens

Recruitment of P. pungens was not limited by seedfall from serotinous cones or from seed predation by animals. Seedfall occurred throughout the year at low levels and was concentrated in the spring and summer months. The unavailability of seedling habitat strongly limited recruitment of P. pungens seedlings. Litter depth and type were important determinants of P. pungens seedling habitat; seedlings occurred almost exclusively in shallow pine litter. There was little overlap between the distributions of habitat variables for seedlings and random points in the forest, indicating that suitable seedling habitat was rare. Summer drought and substrate were important factors influencing the establishment and survivorship of seedlings.

Greenhouse studies were conducted to determine the influence of leaf litter and water regime on early establishment of P. Pungens. Emergence of seedlings was consistently highest in pine litter and lowest in hardwood litter at all water regimes and in litter-free treatments at low watering intervals. Survival of seedlings was enhanced by litter at low water regimes. Significant litter/water interactions indicated that the effects of litter and water regime were not independent; litter significantly decreased the loss of soil moisture from experimental treatments. Evidence suggests that depression of P. pungens seedling emergence in hardwood litter was due to physical-mechanical effects.