Assisted revegetation trials in degraded salt-marshes.
Abstract
At coastal sites adjacent to the Hudson Bay lowlands, intensive foraging by increasing numbers of lesser snow geese Anser caerulescens caerulescens has converted salt-marsh swards to hypersaline mudflats largely devoid of vegetation. Assisted revegetation trials were undertaken in order to determine the ability of plants to establish in degraded salt-marsh sediments. Soil plugs of the former dominant graminoids, Puccinellia phryganodes and Carex subspathacea, were transplanted into plots of hypersaline bare soil. Some plots were treated with fertilizer and peat mulch to determine if ameliorations enhance plant growth. Transplants of P. phryganodes established in degraded sediments, but those treated with fertilizer and peat showed significantly higher growth than those in bare soil after two growing seasons. The ratio of the mean basal area of plants in treated plots compared with bare plots was between 1.7 and 4.0:1 at different sites. Transplants of C. subspathacea did not establish readily in degraded sediments and no growth enhancement was observed with soil amendments. Growth rate and mortality of plants both varied between sites and years, reflecting variation in the frequency of hot, dry weather from late June to early August of each year, and the salinity and water content of soils during that period. The potential for revegetation of mudflats is discussed in the context of the soil degradation processes. Fine-grain variation in soil conditions presents a major challenge for the restoration of plant assemblages in these coastal marshes. The extent of soil degradation and of vegetation loss makes it unlikely that unassisted revegetation will occur at some sites, even in the absence of goose foraging, without erosion of consolidated sediments and the establishment of plant assemblages in fresh unconsolidated sediments.