one of the basic assumptions of the mixed-mating model is that the pollen pool of a population is homogeneous. however mounting evidence would suggest that a homogeneous pollen pool is not the norm in populations of forest tree species. such a phenomenon may have major implications upon the mating systems and genetic structure of forest tree species. the present study was conducted in order to develop a better understanding of the nature and implications of pollen pool heterogeneity in natural populations of black spruce. four natural stands of black spruce within 100 kilometers of thunder bay, ontario were studied using isozyme markers from eight polymorphic loci. the stands studied represent the two basic ecological conditions under which black spruce is found, i.e. upland and lowland stands. both log-likelihood g tests and multiple group discriminant analysis indicated the presence of heterogeneous pollen pools for all four sites. however, as indicated by the canonical for the first discriminant function of each site, the separation power of data from three of the four sites was quite small (r2 of 0.063 to 0.127) . only for raith 2 was the seperation power strong (r2 of 0.379). overall the heterogeneity tended to be random in nature. due to the apparent random nature of the heterogeneity it was not possible to associate the examined site characteristics with the relative degree of pollen pool heterogeneity observed in the four sites. possible agents which may have produced a heterogeneous pollen pool are considered as are potential implications of this phenomenon on the genetics of black spruce.