Kolb, P.F. and R. Robberecht. 1996. Pinus ponderosa seedling establishment and the influence of competition with the bunchgrass, Agropyron spicatum. International Journal of Plant Sciences. 157:509-515.

Abstract Interspecific competition between Agropyron spicatum (Pursh.) Scrib. & Smith bunchgrasses and naturally established seedlings of Pinus ponderosa was examined within a pine/bunchgrass community. Canopy separation techniques were used to determine if bunchgrass culms influenced the survival of pine seedlings. In addition, two lengths of root exclusion tubes were used to determine the effects of bunchgrass root overlap on pine seedlings. The bunchgrass canopy did not significantly affect pine seedling survival. However, root competition, presumably for water, significantly decreased pine seedling survival. Exclusion of bunchgrass roots from 0.15-m and 0.30-m deep root zone of pine seedlings resulted in 40% and 80% reductions in mortality, respectively. Root exclusion also significantly delayed mortality 2-3 weeks. Pine seedlings developed taproots that reached below the zone of maximum bunchgrass root density within four weeks of germination. The pine/bunchgrass community is dominated by two species that can utilize different resource zones in the soil, thereby reducing interspecific competition except during the establishment of pine germinants. In areas with shallow soils, establishment of pine seedlings may occur successfully only if soil moisture is available in deeper soil horizons during the summer.

Key words: Pinus ponderosa - Agropyron spicatum - Interspecific competition - Root competition - Seedling survival - Roots

This project was funded by the McIntire-Stennis Cooperative Forestry Research Program through the University of Idaho, College forestry, Wildlife and Range Sciences, Moscow, Idaho. Contribution no. 795 of the Forest, Wildlife and Range Experiment Station, University of Idaho..