Old-growth forests of the Acadian Forest Region

In the absence of sufficient data from directed studies of old-growth forests in the Acadian Forest Region (AFR), we must rely on a general knowledge of forest ecology and natural succession, population biology, disturbance dynamics, and palynological evidence to understand the probable extent of old-growth, late-successional forest types before European settlement, their role in the biological diversity of Acadian forests, and the silvicultural prescriptions required to maintain a component of such old growth (OG) on the landscape. The structural features of representative Acadian old growth can be understood from the few remaining stands of such forest in the AFR and from studies in the closely related forest types of the Great Lakes – St. Lawrence Forest Region of Canada and other eastern North American temperate-zone forests. Several hundred years of land clearing for agriculture and timber harvesting has eliminated most of the old-growth forests in the Maritime provinces of Canada. Nevertheless, our limited knowledge of OG suggests that, when the average age of the dominant and co-dominant trees of the typical late-successional species associations of the AFR has reached about 150 years, such forests generally appear to have attained most of the structural features commonly associated with old-growth forests (e.g., standing and fallen, dead and dying trees in various stages of decay, a layered, multi-age canopy structure). What little OG remains is largely restricted to small, isolated stands, often associated with steep gorges that were inaccessible to harvesting or areas that were otherwise protected or avoided being harvested. Late-successional, old-growth forest types dominated by relatively shade-tolerant, long-lived species such as sugar maple (Acer saccharum Marsh.), beech (Fagus grandifolia Ehrh.), eastern hemlock (Tsuga canadensis (L.) Carr.), and red spruce (Picea rubens Sarg.) and with a significant component of eastern white pine (Pinus strobus L.) and yellow birch (Betula alleghaniensis Britt.) often represent the final stages of forest stand development. Such forests may be considered archetypical of OG in the AFR. Forests dominated by these tree species mixtures tend to regenerate naturally in forest canopy gaps left by small-scale disturbances created by fallen individual trees or small groups of trees, rather than the catastrophic, stand-replacing disturbances normally associated with boreal forests. Our objectives were (i) to describe some of the remaining old-growth forest types and their extent in the AFR, (ii) to present some perspectives on their role in biodiversity conservation, and (iii) to present a basis for developing strategies for conservation, management, and restoration. Forest-resource inventories (FRI) suggest that as little as 1–5% of present forest cover across the Maritimes is in forest older than 100 years, but our preliminary ground surveys based on this database suggest far less than that is true old-growth forest. Based on expected patterns of ecological succession, disturbance dynamics, and stand development following catastrophic natural disturbance intervals of about 1000 years, and from what the geological record tells us about forest cover before European settlement, we can project that as much as 50% of Maritime forest landscape may have been dominated by late-successional old-growth forest types over the 4000–5000 years before European settlement. Recent genetic studies suggest that these old-growth forests were probably a rich source of the genetic diversity required by these tree species to adapt to the environmental (climatic) changes that have characterized the North American continent over the past 2 million years of its glacial history. Key words: biodiversity, forest ecology, late-successional forests, natural succession, old growth, temperate zone.