Developing a Field Indicator for Suckering Ability of Quaking Aspen

Quaking aspen is an ecologically valuable deciduous tree species in the high elevation environment typical across many parts of western North America. It is a clonal tree species which primarily depends on vegetative regeneration by root suckering after an aboveground disturbance, e.g., wildfire, removes the stems. A flush of suckers will be stimulated after a disturbance and the resulting regeneration relies on available resources from the undamaged root system for resprouting. Due to wildfire suppression efforts of the last century, many aspen stands are considered mature, overmature, or decadent and lack regeneration to replace the overstory mortality. In the absence of natural disturbance, direct management intervention in the form of prescribed burning or harvesting is needed to ensure the survival of aspen-dominated communities. In order to identify which aspen stands should be targeted for priority treatment, it is important to develop a pre-disturbance field indicator that can be used as a predictor of sucker ability. The objectives of this study were to (1) examine the relationship between individual/ general root characteristics and aboveground metrics of stand deterioration, (2) examine the relationship between individual/ general root characteristics and the number and height of suckers produced after a managed disturbance, and (3) develop a simple method for sampling roots in the field. This third objective was developed to provide foresters and land managers with assistance in making decisions on aspen regeneration capacity and also to contribute to the understanding of the future health of the stand. This study identified two root characteristics that can be used as predictive field indicators of quaking aspen sucker ability after a disturbance. Root diameter and root surface area proved to be the best predictors of regeneration density after a disturbance. All in all, the highest sucker densities were recorded on plots which contained abundant roots measuring less than 2.5 cm in diameter, indicating that most root suckers originate from small diameter roots. My results also document no relationship between carbohydrate concentration in the roots and sucker density, indicating that carbohydrate concentration cannot be used as an indicator of sucker ability. Excessive browsing of aspen regeneration by wild and domestic ungulates has become one of the primary topics of concern regarding overall aspen decline in western North America. My study points to the importance of aspen suckers rapidly growing above the herbivore browse line, so that a certain amount of leaf area can be maintained and root reserves do not become exhausted. If browsing is excessive, aspen suckers will repeatedly be hedged below the browse line or browsed down to the ground and completely eliminated