Aspen (Populus tremuloides Michx.) stands provide a variety of ecosystem services. Throughout the western United States, aspen stands have been declining due to a decrease in widespread wildfires and an increase in browsing. 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 stems when stems are present. Clonal integration, the sharing of water, nutrients, and carbon resources, determines the number and survivorship of new individuals. Thus, restoration efforts are underway to induce suckering before entire aspen clones (including the roots) die. There are notable problems with restoration efforts, including simply providing an unlimited browse for animals, a lack of knowledge about restoration success based on age and health, and a lack of knowledge about the importance and mechanisms of clonal integration. We examined the regeneration response of aspen following fire, bark beetle infestation, thinning, and control forest plots along with the basic ecology of aspen clonal integration to elucidate best management practices. A total of 60 0.04 ha plots were established and vegetation from all strata documented. For clonal integration, we monitored both proximal and distal sap flow in roots of two aspen ramets. Data were taken for at least a week prior to a deleafing experiment. Sap flow sensors were also reversed to examine bi-directional sap flow. We hypothesized aspen regeneration would be best following more extensive disturbance. The clonal integration research was exploratory.
Results/Conclusions
As hypothesized, the strongest sucker development was observed in plots of stand-replacing fires, followed by thinning practices that also had vigorous reproduction; both treatments had over 10,000 seedlings/ha. Sites affected by the mountain pine beetle exhibited little aspen sucker growth, likely a result of high canopy cover, and sucker establishment also was poor in control forest plots; neither treatment had more than 300 seedlings/ha. Clonal integration showed a typical diel pattern to sap flow in both stems and roots; sap flow ranged from 200 to 400 g/hr in stems but reached much higher rates in roots. Contrary to expectations, deleafing showed no effect on root or stem flow. Further, sap flow was nearly entirely unidirectional from the mother to daughter ramet. The data suggest clonal integration is an important component of aspen maintenance.
