A comparison of Juniperus communis and Juniperus horizontalis habitat and selected life-history traits in northern Michigan and adjacent Canada.

Abstract

Throughout the seven week period from June 22, 1992 to August 10, 1992, I have been observing two species, Juniperus communis v. depressa (Common or Ground Juniper) and Juniperus horizontalis (Creeping Savin) growing in the northern lower and upper peninsulas of Michigan and the northern shore of Lake Superior in Ontario, Canada. Both species are gymnosperms in the family Cupressaceae. J. communis is circumpolar in Northern latitudes, while J. horizontalis is found in northern latitudes across North America. In northern Michigan and Ontario, I have observed both species growing mainly on disturbed soils in and adjacent to clearings. Both species are native in Michigan with J. communis distributed throughout the state and J. horizontalis almost entirely found on the sandy or gravelly shores and dunes of the Great Lakes. These species may grow as cohorts in similar habitats throughout the range of J. horizontalis or may also be found growing in the absence of the other. Both species occur on open, disturbed sites, with J. communis more widely distributed and in greater abundance than J. horizontalis. In this paper, I will describe my observations of the morphology, phenology, reproduction, dispersal, and habitats of J. communis and J. horizontalis, and hopefully elucidate some of the factors governing similarities and differences in their distributions and habitat within Michigan and adjacent Northern Ontario.