Date of this Version
Rolfsmeier, Steven B. December 1989. Species Richness Gradients of Oak Forest Plants Along the Missouri River in Nebraska and Iowa. Nebraska Game and Parks Commission. 99 pp.
The upland deciduous forests of the Missouri River valley contain many plants typical of forests to the east of this area, which are assumed to have migrated northward and westward along the river in postglacial times. Previous workers have reported a gradient of decreasing species richness upstream among woody species, which is suggested to be the result of climatic gradients and differential dispersal capabilities of the immigrant species. Floristic work on all vascular species in eight woodland sites along the Nebraska-Iowa border quantifies the presence of similar gradients for herbaceous species, but of differing degrees. These studies also reveal the presence of northern and western forest elements upstream, which may have entered the valley from the west. Disjunct species distributions and comparisons of climatic and floristic gradients suggest that the distributions of species parallel precipitation and temperature gradients, but may not all be under climatic control.