The coarse-root dynamics of ramets of Populus tremuloides (aspen) were investigated with respect to persistence of the original root connections (roots of parent trees from which the ramets originated), the time of establishment of new roots at the base of the stem and the fate of the communal root system after death of individual trees, Parts of the root systems of three declining stands of aspen ramets were hydraulically excavated. From each stand, sections of all structural roots were collected at the base of live and dead trees and were analysed using dendrochronology techniques. Parent roots were identified in the root system of every tree. The trees initiated new structural roots shortly after suckering. Live roots were often connected to the stump of dead and decayed trees. Grafting was common, especially at or near the stumps. Death of trees along the parent roots over time did not seem to favour the entry of significant decay. Nor promote breakage of the original root connections. Instead of becoming independent of the parent root system the ramets incorporated the parent roots into their own root systems, remaining interconnected.

In north-central Alberta, 12 plots (9 m²) were hydraulically excavated in young trembling aspen (Populus tremuloides Michx.) stands (5-10 years old) of different sucker density to quantify the effects of sucker density on the parental root system, on the formation of new roots and on the growth of suckers. All roots were collected and divided into live and dead parental roots and new root categories. Size and age of parent roots at the time of suckering were determined. Total biomass ranged from 1 to 18 t/ha of live roots. Living root biomass was proportional to stand density and leaf area index (LAI). Low-density stands had a higher proportion of dead roots. Suckers in plots with more parental root biomass/sucker had greater height growth. Root/shoot ratios ranged from 0.46 to 3.52 but were not correlated with stand densities. Stands with larger basal area of suckers and greater mean parent root diameter produced more biomass of new roots. This research suggests that young sucker-origin aspen stands support a large underground biomass and that high sucker densities and LAI are required to prevent loss of parental root biomass. ©2001 NRC Canada

Trembling aspen (Populus tremuloides Michx.) and white spruce (Picea glauca (Moench) Voss) seedlings were grown at uniform air temperatures but different soil temperatures (5, 15, and 25 degreesC), and gas-exchange and growth characteristics were examined during active growth and early dormancy. At 5 degreesC, Populus tremuloides had no root growth and limited growth in leaf area and shoot mass compared with the large increases in leaf and shoot mass at 25 degreesC. In contrast, Picea glauca had some root growth at 5 degreesC and moderate growth of roots at 15 and 25 degreesC; however, there were no differences in aboveground mass at the different soil temperatures. Net assimilation and stomatal conductance in Populus tremuloides were reduced with decreasing soil temperatures, while in Picea glauca soil temperatures did not affect these gas-exchange variables. In both species, root mass was higher in the dormant period than during the growing period, while root volume remained constant. Generally, the growth variables of Populus tremuloides were more suppressed by cold soils than in Picea glauca. Root total nonstructural carbohydrates (TNC) decreased between the active growth and dormancy period by nearly 50% in Populus tremuloides, while there was no change in TNC in Picea glauca. Results suggest a more conservative use of TNC reserves in Picea glauca combined with a tolerance to cold soil temperatures compared with Populus tremuloides. ©2001 NRC Canada