Document: DUN-3-38-17

Causes of Juniperus ashei seedling growth suppression.

MCKINLEY, D.* and O.W.VAN AUKEN

University of Texas at San Antonio, TX ¹

Abstract:
Juniperus ashei density has increased in many grasslands by encroachment. Formerly, Juniperus ashei was apparently restricted to canyons, ridges and areas with shallow soils, which because of their relative isolation, were protected from fire. It is postulated that overgrazing and fire prevention has allowed Juniperus ashei to flourish in regions that historically were grasslands or savannas. Overgrazing has led to the reduction of light fluffy fuel consisting mainly of grasses, which is essential for fire. Fire is necessary for the continued maintenance of grassland communities, without which woody plant encroachment is possible. The replacement dynamics of these woodlands are not understood. Adult Juniperus ashei tree produces a zone of inhibition below the canopy that suppresses the growth of Juniperus ashei seedlings. Juniperus ashei seedlings below the adult Juniperus ashei canopy have a lower mortality, but they also have lower growth rates than canopy edge seedlings that have a higher mortality and also a higher growth rate. When adult Juniperus ashei trees are killed by either natural or anthropogenic causes, seedlings below the former canopy may grow rapidly to replace the former parent tree. A factorial field experiment was set up on the southern Edwards Plateau of Texas to determine the possible cause of seedling growth suppression. Intraspecific competition from the adult trees including light, water and nutrient availability were manipulated by canopy alterations, with additions of water, nutrients and artificial shade. Initial results suggest that there are several factors that influence this phenomenon. The factor that seems to have the most important contribution to Juniperus ashei seedling growth is light with water availability being secondary. Nutrient levels are important, but mostly influence the continued growth of this species.

Keywords: Juniperus ashei

This abstract is being presented at: 10:30 AM in session:
Poster Session #12: Disturbance Ecology.