PARENT SESSION
Poster Session #53: Plant Competition.
Thursday, August 8. Presentation from 8:00 AM to 9:30 AM. Exhibit Hall B & C, TCC

Changes in understory composition with silvicultural treatments - implications on competitive interactions with conifer regeneration.

Bonnet, Veronique^*,1, Schoettle, Anna², Shepperd, Wayne², Hazlett, Donald³, ¹ Matcom at the Rocky Mountain Research Station, Fort Collins, CO² Rocky Mountain Research Station, Fort Collins, CO³ P.O. Box 345, Pierce, CO

ABSTRACT- Understory composition and characteristics can affect the regeneration success of ponderosa pine. This analysis was designed to assess the effects of silvicultural methods on understory composition that may impact seedling regeneration via interspecific competition. The study is located in central Colorado and is a replicated 2x2 factorial of two overstory treatments (sheltered-wood and seed-tree) and two forest floor treatments (soil scarification and non-scarification). The treatments were installed in 1980. The effects of the treatments on the continual ponderosa pine seedling recruitment and understory vegetation characteristics were still evident in 1996. The total cover of the understory vegetation was affected only by the overstory treatment, yet the cover by the different growth-forms was differentially affected by both overstory and forest floor treatments. Scarification favored grasses and forbs and reduced the cover by sedges. The more open overstory of the seed-tree treatment again favored grasses and also increased cover by sedges. In the open habitat, cover by forbs was increased only when the forest floor was also disturbed by scarification. Ponderosa pine seedling survival, even for new germinents, was significantly greater in the plots receiving forest floor scarification. These results demonstrate that the effects of a one-time scarification treatment are still evident in the understory dynamics even after 16 years. These results suggest multiple possibilities of interspecific competition between understory vegetation and ponderosa pine seedlings.

KEY WORDS: Pinus ponderosa, regeneration, understory , competition