The genotypes of 21 clones of 18 Populus × canadensis Moench cultivars ('Baden 431', 'Blanc du Poitou', 'Canada Blanc', 'DN44', 'Dorskamp 925', 'Eugenei', 'Gelrica', 'Grandis', 'Heidemij', 'I-55/56', 'I-132/56', 'I-262', 'Jacometti', 'Ostia', 'Regenerata', 'Robusta', 'Steckby', and 'Zurich 03/3') were determined for 31 allozyme loci coding for 9 enzyme systems in root tips. Horizontal starch gel electrophoresis was used to assay the enzymes. All clones had allozyme gene and allele contribution from both P. deltoides Marsh, and P. nigra L. The interclonal allozyme variability was controlled by nine loci. 'Canada Blanc' and 'Ostia' shared the same 31-locus genotypes, whereas each of the remaining 19 clones, including 3 clones of 'Robusta' and 2 clones of 'Jacometti', had unique multilocus genotypes. On average, unique genotypes differed from each other at 3.59 loci. Principal-component analysis of the clonal genotypes at 9 variable loci indicated 4 loci (Idh-2, Idh-3, Mdh-4, and Idh-1) to be the most discriminating among the clones. The first two principal components accounted for 48% of the total variance in the nine loci. Clones on the principal component analysis ordination (principal components 1 and 2) were separated into 3 groups; 14 belonged to one group and 5 to a second group. 'Blanc du Poitou' was widely separated from all others. 'Canada Blanc' and 'Steckby' showed the highest genetic interrelationships. Three 'Robusta' clones and two 'Jacometti' clones were in the same group., The interrelationships among the clones based on allozyme genotypes were in general agreement with their speculated origin and (or) morphology.Key words: Populus × canadensis, allozymes, multilocus genotypes, clone–cultivar identification, clone relationships.

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The technique of random amplified polymorphic DNA (RAPD) fingerprinting was used to differentiate species and identify clones of 15 poplar and 15 willow clones (ramets of three poplar clones were also included to verify the stability of the results). Four random DNA primers (Deca-11, Chl-1, Chl-4 and Chl-10) and an M13 universal primer were used to determine DNA polymorphism among the clones. Based on the DNA banding pattern obtained with the four DNA primers by polymerase chain reaction (PCR) amplification we conclude that RAPD fingerprinting with properly selected primers can be used for clonal and species differentiation of poplar and willow. The technique is simple, accurate and inexpensive.

Isoenzyme studies were conducted on root tips of 200 Populustremuloides clones selected from eight geographic regions (populations) along north–south and east–west transects in Ontario. Starch gel electrophoresis was used to assay crude enzyme extracts from young root rips of rooted suckers obtained from the clones sampled. A total of 15 isozyme loci coding for eight different enzyme systems were resolved. The mean of total gene diversity was 0.252. An average of 79% of the loci were polymorphic in any one population, with an average of 2.7 alleles per locus. More than 90% of the genetic variability could be attributed to within-population differentiation. A deficiency of observed heterozygotes was calculated for all populations studied. The fixation index averaged 0.462. The genetic distance estimates among populations had an overall mean of 0.103. There was no correlation between genetic and geographic distances. Results of this study suggest this species in its Ontario range is genetically variable and moderately differentiated.

Biomass production and quality in seedlings and coppices of Salixamygdaloides Anderss., S. eriocephala Michx., S. exigua Nutt., and S. lucida Muhl. were investigated in a full-sib family test. Between 65 and 77% of the variation in plant biomass was due to species, while less than 5% was due to families. Approximately 39% of the variation in moisture content and 37% of the variation in specific gravity was due to species differences, while only 3 and 14%, respectively, was due to families. Salixeriocephala produced the highest yields, with an average 1-year coppice production of almost 1 kg/plant (dry matter) and had the lowest moisture content and highest specific gravity of the four species. There was a strong positive correlation between seedling and coppice productivity for all species, with S. eriocephala and S. lucida producing the most vigorous regrowth from coppice.

Fast-growing willows are cultivated as coppice in short rotation biomass plantations. The production and sustainability of the system is based on the ability of trees to resprout after repeated harvesting. The large variation in coppicing ability is due to plant genotypic differences in structure and physiology as well as environmental factors. Morphological and structural prerequisites for resprouting were compared in two shrubby willows with high coppicing ability, S. viminalis and S. eriocephala, and one treeformed species, S. amygdaloides, with low coppicing ability. The initiation and development of buds and the resprouting pattern of coppiced stools were compared. All buds were axillary in origin and showed the same principal structure consisting of one main shoot primordium and two lateral primordia. In S. viminalis and S. eriocephala the lateral buds contained several leaf primordia and sprouted shortly after the main bud. In S. amygdaloides further development of lateral buds was inhibited after formation of two budscales, and leaf primordia were not formed until the buds were forced to sprout. The number of sprouts developing after coppicing were correlated to the structure and number of buds and their position on the stools. Selfthinning rate was high and many shoots originating from lateral buds died. Most buds were located above ground on the remaining basal portions of harvested stems. No adventitious buds were found on the stools. Significantly different bud differentiation pattern and frequent sylleptic sprouting resulted in lower coppice response in S. amygdaloides compared to S. viminalis and S. eriocephala.

The low profitability of agriculture, the greenhouse effect, acidification, the energy supply, ground water pollution, waste disposal and depopulation of the countryside are some of the problems in urgent need of solution not only in Sweden but in many other western countries. Naturally, there is no single solution to all these complex problems. However, by establishing plantations of fast-growing deciduous tree species on abandoned or surplus arable land it is possible to address many of these problems in a positive way. More than 15 years of research and development within the National Swedish Energy Forestry Program (NSEFP) have resulted in a new agricultural crop with a high potential for sound ecological and economic outcome. The further utilization of biomass plantations for environmental clean-up programmes and waste cycling is now developing on a regional and local basis. As a complement to pure energy plantations, mixed forest stands are discussed as multipurpose production systems for wood chips, short fiber and veneer. Key words: alternative crops, biomass plantations, energy crops, energy forestry, Salix, short-rotation forestry