Dendroecological analysis of the population dynamics of an old-growth forest on cliff-faces of the Niagara Escarpment, Canada

1 We examined temporal fluctuations in age structure and population dynamics in an ancient forest of Thuja occidentalis on cliff-faces of the Niagara Escarpment, Canada. Living stem density was 1003 stems ha(-1) and total numbers of dead stems and living trees on the cliff and in the talus were consistent along the length of the cliff-face, and similar to other old-growth forests. 2 The extreme longevity of T. occidentalis and the presence of persistent coarse woody debris provided a rare opportunity to reconstruct the palaeodemography of this forest, to determine whether the stable uneven-aged structure is indicative of a forest population free of disturbance and existing in a steady-state condition. 3 The forest had maintained a stable uneven-aged structure or reverse-J age structure with no evidence of disturbance for the 12 reconstructed years between 1770 and the present. There had been a net population reduction since 1770, with mortality rates exceeding recruitment rates over the last 140 years. While recruitment rates had varied, there had been continuous recruitment and survival of seedlings over this time. 4 Synchronous radial growth releases occurred in over 20% of the dated trees during 11 years between 1450 and 1992. Synchronous radial growth suppression occurred during three other years. 5 Cliffs and other rock outcrop ecosystems may, as a class of habitat types, represent systems that are locally constant, even when their neighbouring communities experience large-scale disturbance.