Performance of Tsuga canadensis (L.) Carr. At the Centre and Northern Edge of its Range: A Comparison

Abstract

Populations of Tsuga canadensis (L.) Carr. (eastern hemlock) were examined in three different geographic locations, two near the species' northern range edge and one in the centre of its range, to establish whether geographic variations exist in site preference, long-term growth rates and age class structures. It was hypothesized that at the northern edge of the species' range it would preferentially occupy southern aspects, due to the warmer climatic conditions associated with these sites. It was also hypothesized that growth rates would be slower in northern areas and that age class structures would indicate a more episodic pattern of recruitment in the north. Results showed that differential site preference was exhibited in northern areas, but not to southern aspects. Instead, northerly and westerly aspects on moderate and steep slopes were preferentially occupied. An analysis of variance showed no significant differences between long-term growth rates either within or among the three populations. Examination of age and size class structures, however, did show that recruitment of stems was more continuous at the species range centre than at the northern edge of the range. It is suggested that competition and not simply climatic condi- tions may be important in limiting the range of T. canadensis in the area examined.