Establishing the value of a salt marsh as a potential benchmark: vegetation surveys and paleoecological analyses as assessment tools

Abstract

Identifying tidal salt marshes as priority sites for conservation or restoration remains a challenge, as several sites are so severely degraded that allocating financial resources for their protection would be questionable. The decision-making process could nevertheless be facilitated by comparing species assemblages and the dynamics and (or) ecological functions of a site with an ecological benchmark, i.e., a tidal marsh that remains free from anthropogenic disturbances. We used plant surveys and plant macrofossil and pollen analyses for evaluating the benchmark potential of the Pointe-aux-Épinettes marsh, a protected salt marsh of the St. Lawrence River estuary (Canada) and one of the last salt marshes that could potentially be a benchmark along the estuary. Historical evidence indicated that the forests surrounding the marsh were converted into agricultural lands circa 1850. Nevertheless, this land-use change had little impact on the marsh. The long-term impacts of trampling and grazing by livestock on the vegetation were negligible. Macrofossil analyses indicated that the plant assemblages were dynamic, but past and current vegetation assemblages are representative of those characterizing an undisturbed salt marsh, with a very high proportion of native wetland species. In a context where truly undisturbed salt marshes are extremely rare ecosystems, our study indicates that the Pointe-aux-Épinettes plant assemblages could be used as benchmarks against which the condition of the vegetation of other salt marshes in northeastern North America could be evaluated.