Phil Graeve masters defense
Thursday, March 22, 2012, 02:00 PM
Natural Resources, Room 100

Controls on pinyon and juniper seedling establishment in the Uncompahgre Plateau, Western Colorado

Extreme climate events have the potential to cause sudden shifts in ecological communities. In this study I investigated the direct and indirect effects of climate on Colorado pinyon (Pinus edulis) and Utah juniper (Juniperus osteosperma) communities on the Uncompahgre Plateau in western Colorado. I described extreme loss of pinyon overstory basal area for pinyon but found no such changes in juniper overstory related to a severe drought from 2000-2004. I determined age structure of pinyon seedlings, and tested for the effects of current year and antecedent year climate on seedling establishment. Finally, I described microhabitat preferences (substrate microhabitat and overstory canopy) for pinyon and juniper seedlings and assessed whether suitable microhabitats may have changed as a consequence of overstory die-off. No annual patterns related to climate were found with pinyon establishment, and pinyon establishment appears to be relatively constant for the past 30 years. Each species exhibited distinct preferences for certain substrate microhabitats, especially different types of litter. Pinyon seedlings avoided bare soil microhabitats. Both pinyon and juniper seedlings avoided open overstory microhabitat, and pinyon preferred juniper overstory microhabitat. This study indicates that episodic overstory mortality events and continuous pinyon establishment characterize pinyon community dynamics on the Uncompahgre Plateau, at least within the 30 year time frame investigated in this study. Juniper seedlings are less abundant but likely more resilient to climate-induced changes in microhabitat structure. In contrast, pinyon establishment and survival in the overstory canopy may be reduced due to direct and indirect effects of climate, especially if predictions of increased drought frequency and severity are true.

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Event Contact: Jeri Morgan can be reached at (970) 491-4373

Sponsored by the Graduate Degree Program in Ecology.