Anoka Ecosystems:
Dry Oak Forest
Dry oak forests are common throughout the Anoka Sandplain. This forest type is characterized by an open canopy of multi-stemmed, 50 to 60 foot oak hybrids with a denser network of lower branches. In these forests, the subcanopy is more dense than the canopy, with patchy shrub and ground layers of vegetation. In most cases, these forests are relatively young, and were once either oak savannas, which were predominantly grasses with intermittent oaks, or woodlands, which typically had 25-60% tree cover.
Northern pin oaks, white oaks and bur oaks dominate the drier stands of oak forest. However, the canopy of this ecosystem may also include species such as black cherry, paper birch, quaking aspen, or big-toothed aspen. The subcanopy may often include red maple, as well as bitternut, though not on the Anoka sandplain, and oaks, which occur along forest edges. The lower, denser shrub layer is most often American hazelnut, though blackberry, gray dogwood, chokecherry and Juneberry are also common shrubs in dry stands. The ground layer often has a variety of forest herbs, such as bracken fern, sweet cicely, pog-peanut, blueberry, and shoots of Virginia creeper. The oaks have a poor regeneration rate in undisturbed stands, and disturbance often introduces a ground cover of Pennsylvania sedge and a dense subcanopy of prickly ash, common blackberry, and red raspberry, as well as exotic species including common buckthorn and Tartarian honeysuckle.
These dry oak forests are often very young and have gradually converted from savannas and woodlands, often due to the absence of fire. This absence, due to human development and strict controls, has allowed small tree and shrub regeneration, which has then allowed an influx of invasive species. This regeneration can also succeed because of a fairly open canopy, which results in a denser middle layer. In addition, mature trees on nutrient-poor sandy soils are typically shorter and smaller in diameter than those found in the more nutrient rich mesic stands.
Sources:
"Minnesota's Native Vegetation: A Key to Natural Communities"
Version 1.5 Minnesota Department of Natural Resources, Natural Heritage
Program, 1993.
Wovcha, D, Delaney, B, Nordquist, G. Minnesota's St. Croix River Valley and Anoka Sandplain: A Guide to Native Habitats Minneapolis: University of Minnesota, 1995.
