Woody Plant Communities of the Iowa Loess Hills: Expansion From 1855 to 2000, Extant Composition, and Ecological Succession.

The Loess Hills of western Iowa are a unique geologic landform historically covered by scattered bur oaks in a matrix of mixed-grass prairie. Since European settlement, however, woody plant encroachment has altered the ecosystem and presently endangers the last substantial prairies remnants in Iowa. Aerial photographs from 2000 and General Land Office field survey notes from the 1850s documented an increase in woody Plant cover from 7% in 1855 to 25% in 2000 for three centuries in the Loess Hills region of western Iowa. Woody Plant species composition along a lowland-ridge-top coenocline on both north and south aspects in centrally located Monona County, Iowa, was evaluated to quantify extant vegetation and to serve as a base for future comparison. Ridge-tops were dominated my smooth sumac (Rhus glabra), eastern red cedar (Juniperus virginiana), and rough-leaved dogwood (Cornus frummondii) with middle slopes dominated by bur oak (Quercus macrocarpa), ironwood (Ostrya viginiana), green ash (Fraxinus pennsylvanica), or hackberry (Celtis occidentalis). Lower slopes were dominated by American linden (Tilia americana) with an understory of ironwood, although green ash and hackberry were also represented. Assuming woody plants expand upslope, these communities infer a sere for the study stite succeeding from eastern red cedar to bur oak-ironwood to hackberry-ironwood communities on hilltops and slopes with species such as American linden, green ash, or hackberry dominating lower slopes. Overall, this study indicated that, in the absence of active management, woody communities of some type can ultimately be expected to replace both the prairie remnants of the Iowa Loess Hills and the extant bur oak-dominated forest