There are many different types of wetlands, and several often exist together, making them difficult to categorize. Complicating their identification even further, they don’t all have water year-round! To ease the process of identifying wetlands and understanding how amphibian and reptile life may be reflected in wetland habitat type, we’ve described some wetland types found in Ann Arbor.
Wooded wetlands can be either large (>5 acres) or small (<5 acres), natural or created. When large, they are also called wooded swamps or floodplain forests. When small, they are called vernal ponds. Standing water is typically present during most of the spring, but the soil surface is often dry by mid-summer. They may even be dry before the end of the spring growing season, limiting the number and variety of amphibians that are able to breed successfully in them. Wooded wetlands can be rich in amphibian life, particularly when part of a large undisturbed habitat block. Periodic drying limits predation on amphibian larvae by fish.
Wooded wetlands in Ann Arbor typically have a tree canopy of red or silver maple, willow, elm, cottonwood, or swamp white oak, with varying amounts of wetland shrubs such as dogwood and buttonbush. The ground may be covered by thick grass, or bare after the standing water dries out. When water is present, it may be covered by duckweed floating on the surface. Wooded wetlands may occur along streams or on floodplains, in flat uplands or on the edges of shallow lakes.
Open wetlands (without a tree canopy) are typically dominated by sun-loving plants and may have high diversity, with a mix of grass-like and flowering plants. They may also have mudflats, depending on the season in which they dry out. Other names for these wetlands include wet meadow, emergent marsh, scrub-shrub swamp, fen, or bog. They can have the same appearance as wetlands along lakes or rivers, but their isolation from the predatory fish common to larger water bodies may foster larger amphibian populations. Created open wetlands typically have steeper banks and deeper water than natural wetlands, and may have a narrower band of vegetation surrounding a primarily open-water center. The amphibian habitat provided by created wetlands varies.
When open wetlands have permanent standing water, they are typically called marshes and have a mix of open water and grass-like plants such as cat-tails and rushes. Wet meadows, fens, bogs and shrub swamps look like a shrubby field, except that the ground is wet during the spring. These wetlands have a mix of grasses, sedges, wildflowers and shrubs with almost no open water.
These wetlands may be highly disturbed because periodic drying has allowed them to be farmed or mined. Presence of invasive plant species is not necessarily detrimental to the breeding and foraging resources needed by amphibians and reptiles. In some cases, habitat structure can be provided by non-native plants such as reed canary grass. In other cases, invasive plants such as buckthorn and multiflora rose make amphibian movement and foraging more difficult, in addition to shading-out more beneficial plant species.
Lake and River Wetlands
These wetlands have similar size, structure and appearance to other wetlands, but may provide different amphibian and reptile habitat because of their proximity to a large body of open water. Floating-leaved plants such as water-lily may be more prominent here than in isolated wetlands, and provide habitat for turtles in addition to large amphibians such as green and bull frogs. The presence of fish greatly increases predation on amphibians, generally reducing the abundance and diversity of frogs, toads, and salamanders in these locations.