the relative efficiencies of using different methods to detect genetic variation in cold hardiness were evaluated, and the adaptive variation among aspen provenances was further studied. this thesis is organized as three parts. the first part is a comparison of chlorophyll fluorescence, electrical conductivity and cambium visual scoring to detect genetic variation in cold hardiness of twelve aspen provenances from northwestern ontario. comparison of results indicated that rank of provenances in cold hardiness by three methods was similar, but ec is more sensitive to detect variation level among populations. all methods can be a good indicator of adaptive variation, although the adaptive mechanism each method detected may be different. the second part is to evaluate adaptive variation in cold hardiness among 20 aspen provenances from northwestern ontario using electrical conductivity. significant variation among provenances was detected, and the variance expressed among provenances was higher than 70%. principal component analysis summarized 14 variables into three principal components representing different phases of development. pc-1 mainly represented cold hardiness development after late september, while pc-2 and pc-3 mainly explained the cold hardiness in early-mid september. multiple regression analysis of each pc against modeled climatic variables unique to each seed source indicated that growing season length and precipitation in august were the best predictors of pc-1, while temperatures were always the best predictors of pc-2. the third part of this thesis is to further evaluate the genetic variation of 34 provenances of trembling aspen and three hybrids, and the results were compared with those by cambium visual scoring (cvs). provenance effects were significant, and the correlations between chlorophyll fluorescence and cambium visual scoring were significant.