PARENT SESSION
Poster Session #71: Plant Ecology: Physiology and Function.
Friday, August 9. Presentation from 8:00 AM to 9:30 AM. Exhibit Hall B & C, TCC

The effects of pinyon pine mortality on understory plant communities.

Foley, Anna^*,1, Gehring, Catherine¹, ¹ Northern Arizona University, Flagstaff, AZ

ABSTRACT- Ecotonal shifts may occur in the southwestern US as a result of the increased intensity and frequency of drought predicted by many global climate change models. For example, areas of northern Arizona experienced substantial adult pinyon pine (Pinus edulis) mortality following recent droughts, resulting in juniper-dominated woodlands. It is important to determine the effect that mortality of dominant species, such as pinyon, will have on associated plant communities. We compared the plant communities under the canopy of living and dead pinyons and adjacent open areas. Ordination analysis revealed significant differences in plant species composition among the three areas. Total vegetation cover and species richness were greatest under the dead pinyons compared to the live pinyon understory and the open areas. Biomass was also significantly higher under dead pinyons than live pinyons. The understory plant communities of live and dead pinyons were dominated by forbs while the open areas were dominated by grasses. Finally, the understory plant community of dead pinyons had higher occupation by annual plant species than open areas. The increased biomass and plant community differences associated with dead pinyons could be due to factors such as increased light, soil moisture and nutrients, or changes in AM fungal inoculum, factors that are currently being measured. We conclude that the mortality of pinyons due to increased drought stress results in a unique plant community dominated by herbaceous forbs.

KEY WORDS: ecotone, dominant tree mortality, understory plant community