Anoka Ecosystems:
Oak Woodland
Oak Woodlands occur throughout the Anoka Sandplain on dry and mesic sites and between forest-woodland ecosystems and prairie ecosystems. In terms of species composition and physical structure, Oak Woodlands are between Oak Savanna and Oak Forest. These woodlands are quite variable, due to history of fire and cutting, soil type and nutrient availability, and the landform on which they occur. However, typically these ecosystems have very open canopies and large open spaces with oak trees growing in patches. Oak Woodlands require that more than 30% of the tree cover be oak, but otherwise this ecosystem is diverse.
Though oaks must comprise a minimum of 30% tree cover, aspens may comprise up to the other 70% of the tree cover. However, the subcanopy may also include species such as American hazelnut. Similar to dry oak forests, oak woodlands often have a dense shrub layer composed of a variety of species including blackberries, raspberries, gooseberries, quaking aspen, hazelnuts, dogwoods, chokecherries and prickly ashes.
Despite not being differentiated from Oak Savannas by early surveyors, it is thought that Oak Woodlands were once the dominant community across the Anoka sandplain. Today, however, these communities are sparsely located throughout the county. Being dependant on fire for ecosystem maintenance, historically small trees and shrubs could not establish. However, As farms and towns expanded throughout the county, woodlands in the region were utilized as pasture and farmland. Disturbed sites quickly developed into scrubby Oak Forests overgrown with smaller trees and shrubs and today may contain prickly ash and other invasives that becomes very thick. There are some efforts being made to restore the few Oak Woodlands that are left in Anoka County.
Sources:
"Minnesota Land Cover Classification System: User Manual." Version 5.3 Minnesota Department of Natural Resources, Central Region, 2004.
"Minnesota's Native Vegetation: A Key to Natural Communities" Version 1.5 Minnesota Department of Natural Resources, Natural Heritage Program, 1993.
Wovcha, D, B. Delaney, G. Nordquist. Minnesota's St. Croix River Valley and Anoka Sandplain: A Guide to Native Habitats Minneapolis: University of Minnesota, 1995.
