. The Canadian field-naturalist. 60 m 0) <D 50 — 40 30 1825-f ire n=138 I I I I ^^Ftll^l 1941 -fire n=150. Figure 3. Age structures for the three sampled Pimis strobus stands, S17 (top), S18 (middle), and S19 (bottom). Arrows indicate fire years. Discussion Successful Eastern White Pine regeneration has followed after the respective fires in all three stands. A comparable postfire age-distribution was found for Red Pine also at its northern limit in the same area (Bergeron and Gagnon 1987), a pattern which is indicative of broadly stable populations at the land- scape level (Parker 1986; En
. The Canadian field-naturalist. 60 m 0) <D 50 — 40 30 1825-f ire n=138 I I I I ^^Ftll^l 1941 -fire n=150. Figure 3. Age structures for the three sampled Pimis strobus stands, S17 (top), S18 (middle), and S19 (bottom). Arrows indicate fire years. Discussion Successful Eastern White Pine regeneration has followed after the respective fires in all three stands. A comparable postfire age-distribution was found for Red Pine also at its northern limit in the same area (Bergeron and Gagnon 1987), a pattern which is indicative of broadly stable populations at the land- scape level (Parker 1986; Engelmark et al. 1994). The pattern of postfire recruitment is also reported for Jack Pine (Desponts and Payette 1992) and Pitch Pine (Meilleur et al. 1997) at their northern limits. This supports our idea that climate is not solely con- trolling the northern distribution limits of these pines. Further, the multi-aged Eastern White Pine distri- bution found in this study is congruent with results presented by Holla and Knowles (1988) at the Eastern White Pine limit in Ontario, corroborating that a continual recruitment is possible even without recent fire disturbance (>230yr in this study), pro- vided that small-scale gaps suitable for regeneration (, wind-throws or open xeric outcrops) are avail- able in the landscape (Quinby 1991). Germination is regarded to be most successful on bare soil or thin organic layers. In addition, many seed trees form the uppermost canopy and as Eastern White Pine has a relatively large seed production (Powells 1965), seeds disseminate easily. Accordingly, in this study regeneration was successful within existing stands. But maybe the relative lack of dry habitats suitable for regeneration (, rock outcrops) in the land- scape of the Northern Clay Belt (cf. Clayden and Bouchard 1983), is partly limiting further Eastern White Pine expansion under present climate and dis- turbance regimes. This is, in part, contradicted by the greater nort
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