THE RELATIONSHIP BETWEEN SEASONAL-CHANGES IN RHIZOME CARBOHYDRATE RESERVES AND RECOVERY FOLLOWING DISTURBANCE IN CALAMAGROSTIS-CANADENSIS

The grass Calamagrostis canadensis (Michx.) Nutt. often forms a dense growth after logging and interferes with replanting on moist sites in northern Alberta. The objective was to determine if seasonal changes in rhizome carbohydrate reserves can provide useful predictions of the time of year when this species is most vulnerable to disturbance. Small (3 X 3 m) plots were mowed to ground level in May, June, July, or August 1988, or on all four of these dates. The lowest seasonal levels of rhizome carbohydrate reserves (10-12%) occurred early in the season (mid-May to early July). Contrary to expectations, in September 1988 the belowground carbohydrate reserves in plots mowed once during this period had increased to levels that were significantly greater (17-18%) than in unmowed control plots (15%). In plots mowed on all four dates, rhizome carbohydrate levels (11%) and biomass were significantly lower than in unmowed plots in September 1988. Despite these differences, regrowth of shoot biomass in 1989 was similar among all mowed and unmowed treatment plots. Thus rhizome carbohydrate levels were a poor predictor of shoot biomass regrowth following disturbance treatments. It is suggested that improvements in microclimate following the removal of shoot biomass and litter may have compensated for the negative effects of disturbance treatments on the plant's carbon balance.