Can Relationships Between Ground-Layer Plant Cover and Biomass be Used to Follow Succession in Boreal Riparian Forests?

Abstract

The Forest Watershed and Riparian Disturbance (FORWARD) project examines the movement of water and nutrients from Canadian boreal forests before and 5 years after harvest. Plant biomass is the ideal metric for abundance, as it approximates productivity and is the basis to which other resources (e.g., nutrients) are related. However, these data are difficult and destructive to collect and therefore are not suitable for investigations of vegetation change over time. Plant cover data are easier and non-destructive to collect, but may not be proportional to the resources used by individual plants. The objectives of this study were to (1) develop allometric equations using vegetation cover for rapid and non-destructive estimates of biomass and (2) use these equations to approximate ground-layer biomass change over time, following harvest. We collected cover data from ground-layer riparian plant communities in permanent plots at buffered, cut-to-shore and control sites before and five years after harvest treatment. In addition, similar plots were established for destructive sampling of the ground-layer vegetation so that estimates of cover preceding the harvest of aboveground plant parts could be modelled according to dry weight of functional groups (i.e. dwarf shrubs, bryophytes, graminoids, ferns and forbs). Linear relationships were identified (P \u3c0.001), with slope factors depending on functional group and consequently applied to pre- and post-harvest vegetation cover data. Relative to the pre-harvest condition, no differences were detected in the control and buffer treatment in all growth forms five years after harvest. However, on average, graminoids increased by 27 g/m2 and bryophytes decreased by 73 g/m2 in the cut-to-shore treatment. Results suggest that estimating biomass, rapidly and non-destructively, from allometric equations allows for an important characteristic in boreal riparian vegetation community structure to be followed during succession