Midwestern Maple-Basswood Forest

This system is primarily found in the prairie forest border region of Minnesota, Wisconsin, and Iowa, but it can range north into northern Minnesota and Wisconsin and south to central Illinois, central Missouri, and eastern Kansas. This forest system is distinguished by underlying mesic soils and the predominance of mesic deciduous species forming a moderately dense to dense canopy. Examples of this system occur on valley slopes and bottoms often with northern or eastern aspects. Soils are moderately well-drained, fertile, and medium to deep loams that have developed from glacial till or loess parent material. Acer saccharum typifies this system, with Tilia americana, Quercus rubra, and Ostrya virginiana as common associates. The dense canopy allows for a rich mixture of shrub and herbaceous species in the understory. Examples of common herbaceous species include Anemone quinquefolia, Adiantum pedatum, Arisaema triphyllum, and Sanicula spp. Spring ephemeral herbaceous species are characteristic of this system, including Aplectrum hyemale, Cardamine spp., Claytonia virginica, Dicentra cucullaria, Diplazium pycnocarpon, Erythronium americanum, Hydrastis canadensis, Phlox divaricata, and Trillium flexipes. Dynamic processes such as wind and fire can impact this system over long return cycles; however, the most immediate threats to remaining examples of this system are grazing, unsustainable logging, and conversion to agriculture.

Mesic deciduous trees form a moderately dense to dense canopy in examples of this system. Acer saccharum is the most common tree species forming the majority of the canopy and sapling layers. Common associates include Tilia americana, Quercus rubra, and Ostrya virginiana. The understory contains a rich mixture of shrub and herbaceous species such as Anemone quinquefolia, Adiantum pedatum, Arisaema triphyllum, and Sanicula spp. This system is found west and north of where Fagus grandifolia is a reliable and dominant member of the canopy.

This system is found primarily on mesic soils that are moderately well-drained and fertile. These are mostly moderate to deep loams that have developed from glacial till or loess. This system occurs near the prairie-forest border, and the closer to this border, the stronger the association this system has with natural firebreaks. These sites are typically on the east and north sides of rivers, lakes, and wetlands and topographically protected areas on valley slopes and bottoms often with northern or eastern aspects (Kucera and McDermott 1955, Grimm 1984, Moran n.d.).

Wind and fire can impact this system over long return intervals but are rare. Small-gap development and replacement due to tree death is more frequent than catastrophic fire or wind (Bray 1956, Grimm 1984). Tree canopy tends to be closed so understory plants receive little light after leaf-out in the spring. Old-growth stands may not vary greatly in species composition from mature managed forest but have different structural characteristics, including more snags, coarse woody debris, and large trees (McHale et al. 1999). This provides different habitats for wildlife and other non-plant species. This system could form large stands or be part of a large forested landscape in conjunction with other forested types, resulting in a relatively high proportion of forest interior to forest edge.

The greatest impacts on this system are due to conversion to agriculture, logging, and grazing. This system occurs on relatively fertile soils and many areas have been converted to or affected by agricultural uses. Other sites have been subject to selective or clearcut logging. Outright conversion to crops or clearcut logging destroys the affected area and has greatly reduced the range of this system. Remaining stands are also impacted by these activities on the landscape. Agricultural and urban development, road construction, and logging create gaps in formerly large blocks of forest. These serve as vectors or preferred habitat for invasive and aggressive native species, some of which thrive in the forest edge habitat but do not favor the interior of large forested stands (e.g., brown-headed cowbird (Molothrus ater)) (Howell et al. 2005)). White-tailed deer (Odocoileus virginianus) populations have increased significantly due to their preference for fragmented landscapes and elimination of top carnivores. Browse pressure at these high population levels can have significant effects on forest composition and structure (Rooney and Waller 2003).

Despite the abundance of maple-basswood forests in Wisconsin, old-growth stands are almost nonexistent. In addition, very few rich mesic hardwood forests with diverse herbaceous floras have been protected. Note that some formerly common associates are now scarce or absent (e.g., Ulmus rubra), and others may be on the brink of major declines (Fraxinus spp.).

Non-native European earthworms of the families Acanthodrilidae, Lumbricidae, and Megascloedidae can also have dramatic impacts on forest floor properties by greatly reducing organic matter (Hale et al. 2005), microbial biomass (Groffman et al. 2004), nutrient availability (Bohlen et al. 2004, Suárez et al. 2004), and fine-root biomass (Groffman et al. 2004). These physical changes in the forest floor reduce densities of tree seedlings and rare herbs (Gundale 2002) and can favor non-native invasive plants (Kourtev et al. 1999). Changes in ground layer plant community composition due to non-native earthworms are more severe in stands with high white-tailed deer densities (Wiegmann and Waller 2006).

This system ranges from northern Minnesota and Wisconsin south to eastern Kansas and Nebraska and southeast to central Illinois, Missouri, and possibly western Indiana.