PARENT SESSION
Oral Session #52: Plant Ecology: Light and Carbon Allocation.
Presiding: T. Day
Wednesday, August 7. 8:00 AM to 11:30 AM. Gila Meeting Room, TCC.

Abiotic and biotic factors influencing Juniperus ashei (Cupressaceae) juvenile plant growth.

McKinley, Duncan^*,1, VanAuken, Oscar¹, ¹ University of Texas at San Antonio, San Antonio

ABSTRACT- Juniperus ashei is an evergreen, small shrub or tree that is widely distributed on the Edwards Plateau of central Texas. Recently, the density of J. ashei has increased in many grasslands by encroachment. How the abiotic and biotic factors influences this encroachment and their effects on the replacement dynamics of this species in existing woodlands is poorly understood. A factorial (3x2x2x2) field experiment was set to investigate the influence of the adult tree(s), light levels, water and nutrient availability on J. ashei juvenile plant growth. Relative growth rates of basal diameter, height and number of seedling branches were used as response variables in a four-way multivariate analysis of covariance, which used canopy, light, water and nutrient treatments as independent variables. Covariables included surface light levels, soil depth and cover of other species at each seedling position. The pattern of J. ashei seedling growth in the field experiment can best be explained by a significant three-way interaction between the canopy, shade and water treatments (P = 0.04, F = 2.21). Evidence from this study suggests that the replacement dynamics of J. ashei are strongly influenced by the adult trees, with light and water availability being the primary constraining factors. Nutrients appear to be important in J. ashei seedling growth, but not a primary limiting factor. Furthered growth and replacement of the adult trees appears to be limited by interactions of these constraining factors.

KEY WORDS: Juniperus ashei, Cupressaceae