The ecological continuity of 28 northern hardwoods, spruce–fir (Picea–Abies), eastern hemlock (Tsuga canadensis L. Carrière), and eastern white-cedar (Thuja occidentalis L.), stands in the Canadian Maritimes has been assessed and the sites ranked among 77 stands in the Acadian Forest Ecoregion using an index of ecological continuity based on the total number of calicioid lichens and fungi collected at each site. Distinguished by their tiny (1–2 mm tall) stipitate apothecia, the calicioid lichens and fungi are a natural unit of investigation, with most species dependent on the occurrence of mature forests containing trees of different ages and varied light and temperature regimes. Given that the diversity of microhabitats can be expected to increase over time in an ageing forest and that the calicioid lichens and fungi can be found growing in more of these microhabitats than any other group of species, it is the presence or absence of these species that provides the evidence whether a forest that looks old really is old and has been little disturbed over a long period of time. Among the stands under investigation in the Maritimes, the wilderness areas at French River, Panuke Lake, Margaree River, North River, and Sugarloaf Mountain in Nova Scotia, the Little Tobique cedar stand at Mount Carleton Provincial Park in New Brunswick, and the Townshend Woodlot Natural Area on Prince Edward Island have been assessed as ancient forest sites based on of the presence of more than 15 calicioid species. Described here as the oldest of the old growth, an ancient forest is defined as a fourth category of forest succession following pioneer, seral, and young old-growth forests. Nine young old-growth forests have also been identified in the Acadian Forest Ecoregion of the Canadian Maritimes, as have several seral and pioneer-stage stands. For those stands assigned calicioid index scores of 10 or less, these values are considered accurate reflections of the much modified or secondary nature of these communities as recorded in site descriptions. For those stands that have been modified by the effects of pollution or the spruce budworm, an assessment using an index of ecological continuity is considered as much a measure of ecological integrity as it is of continuity. Key words: calicoid lichens, old-growth forests, biomonitors, lichens, biodiversity, Canadian Maritimes
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