Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Wildland Resources

Committee Chair(s)

Karen E Mock


Karen E Mock


James N. Long


Zhao Ma


Douglas J. Shinneman


Aspen forests and woodlands are widespread across the western United States and are a primary component of many ecosystems in the west. Aspen is a clonal species, with reproduction occurring both by root sprouting (suckering) and seeding. Traditionally, western aspen forests were thought to consist almost entirely of large clones established several thousands of years ago, with seeding events being rare and ecologically negligible. Although clones in the western US can grow to be many acres, recent studies have demonstrated a far greater proportion of small clones than had been previously thought to exist. In this study I wanted to answer some important questions about how local conditions may lead to the recent establishment of these small clones, how clones interact with one another in genetically diverse stands, and how individual clones cope with environmental pressures over time.

In the first portion of my study, I used genetic tools to identify clones across Cedar Mountain, Utah (~10 miles southeast of Cedar City) and found areas of high and low clonal diversity (a greater number of individual clones in a stand would lead to higher clonal diversity). Areas of high clonal diversity occurred in areas where fires have been more frequent over recent time, suggesting that fire may play a role in preparing landscapes for aspen seedlings to germinate and become established.

In another portion of the Cedar Mountain study I showed at how adjacent aspen clones interact with one another. In particular I determined how frequently clones seemed to be spreading into adjacent clones (versus having stable boundaries). I found that approximately a quarter of the clones seemed to be spreading into surrounding clones, and three-quarters of the clones displayed more stationary behavior. These findings suggest that the process of clonal displacement and replacement within stands may be quite slow but does occur.

The third portion of my thesis addressed ecological tradeoffs that might occur in aspen. Aspen leaves are consumed by many species of insects, and must cope with this pressure over their lifetimes. Alternative ways of coping with herbivory include resisting attacks by producing defense chemicals to reduce attacks or growing new tissues vigorously following herbivory. Previous greenhouse studies have shown that aspen experiences tradeoffs between resistance (defense chemistry) and resilience (growth following attack) in experimental settings, and I wanted to determine if these tradeoffs were also present in mature, naturally-occurring aspen forests. I did detect a tradeoff between a particularly effective group of defense chemicals and growth, and the tradeoff varied among individual aspen clones. I also found that individual clones differed with respect to the concentration of all defense chemicals and also with respect to growth.

The findings of this study may help influence management decisions when objectives are to promote aspen stand resilience and persistence over time. Forest managers can create conditions favorable to seedling establishment and the promote establishment of new clones which will likely increase the chances for some clones to tolerate changing conditions over time. The establishment and maintenance of clonal diversity should also provide forest resilience, both in terms of ecosystem function and adaptation to changing conditions.