Aspen (Populus tremuloides Michx.) stands provide a variety of ecosystem services, including watershed protection, wildlife habitat, pulp, landscape diversity, and recreation. Throughout the western United States, aspen stands have been declining over the past 100-150 years (Gallant et al. 2003), due to a decrease in widespread wildfires and an increase in grazing, domestic and natural (especially elk). Natural pathological rotation for aspen stands is approximately 115 years, so many of the ramets (clones of the same individually propagated from underground stems, i.e., rhizomes) that developed from the previous disturbance regime are gone or senescing. Because the main regeneration strategy of aspen is by suckering from the parent root system (i.e., clonal or vegetative reproduction), disturbances can only increase aspen stands when they are still present. Clonal integration, the sharing of water, nutrients, and carbon resources, determines the number and survivorship of new individuals (Stuefer et al. 2002). Thus, restoration efforts are underway to induce suckering before the entire aspen clone (including the roots) dies. There are notable problems with restoration efforts, including simply providing an unlimited browse for animals, a lack of knowledge about restoration success, and a lack of knowledge about the importance of clonal integration; the latter two likely closely linked. Land stewards are left to make their best guess on how to spend their limited funds toward restoration strategies.
            Clonal integration has become a central tenet of vegetation ecology. In The Ecology and Evolution of Clonal Plants (de Kroon & Groenendael 1997), researchers demonstrate “how elementary processes at the level of the individual, the population and the community are influenced by clonal growth." Investigations of clonal plants have elucidated the importance of vegetative propagation in plant-herbivore interactions, variance in population gene pools, responses to disturbances, controls of biodiversity, and evolution of semelparity. However, most of this research has occurred overseas (especially Europe and China) and using herbaceous plants, leaving a gap in our knowledge regarding woody clonal integration and if knowledge of herbaceous plants can be transferred to woody plants. The proposed research thus has both an applied and basic research component. I propose to examine the efficacy of various restoration strategies, along with documenting the mechanistic and physiological ability, through an analysis of clonal integration, of aspen stands to sucker sprout.

Objectives and Hypotheses
The first objective of this research is to compare aspen regeneration following three methods of anthropogenic management for aspen stands in the Rocky Mountains, control (no manipulation), thinning pine, and thinning pine and prescribed burning, and one method of natural disturbance, recent pine death following insect outbreak. I hypothesize that the greatest amount of disturbance (thinning and burning) will lead to the greatest re-growth of aspen due to its life history characteristics (i.e., pioneer species adaptations). I further hypothesize that pine loss due to insect mortality will render greater aspen regeneration than anthropogenic thinning alone.
            The second objective to this research is to determine the extent of clonal integration within aspen stands, and relate that integration to success of suckering. We hypothesize that integration is required for suckering success and that the greater the exchange, the greater the growth and survival of suckers.

 


 

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