Redberry juniper-herbaceous understory interactions.

Abstract

Basal cover, density, biomass, and species richness of the understory were measured in concentric zones from the stem bases of large redberry juniper (Juniperus pinchotii Sudw.) trees to 6 m beyond their canopy edges on a shallow, rocky soil and 2 deep soils in the northern Edwards Plateau of Texas. The juniper-driven successional processes of tree dominance, debilitation of understory dominants, influx of subsidiary species, and the general reduction in diversity, density, and biomass of the herbaceous species were evident on all 3 sites. Juniper interference intensified with increasing proximity to the stem bases. Biomass and basal cover of the herbaceous understory responded to a greater extent than did density and species richness 2 years after large redberry junipers were killed with soil injections of picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid). Herbaceous biomass responses after junipers were killed indicated that the sphere of influence of large junipers was more extensive on the shallow soil than on the deep soils. Herbaceous biomass in the presence of interference by large junipers on the Kimbrough, Angelo clay loam, and Tulia loam soils was 1,300, 1,780, and 1,290 kg ha-1, respectively, compared to 2,140, 2,140, and 1,560 kg ha-1 2 years after the junipers were killed on the 3 sites, respectively. Projected herbaceous biomass when juniper populations on the sites develop into closed-canopy woodlands was 320, 880, and 270 kg ha-1 for the Kimbrough, Angelo clay loam, and Tulia loam soils, respectively.