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Door Peninsula

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About the Door Peninsula

The Door Peninsula is a region in Wisconsin located between the main portion of Lake Michigan and Green Bay; although it is mostly a peninsula, it also includes several islands, up through Washington and Rock Islands.

This region is flat on a large-scale but has highly variable local topography, including glacial features such as gently rolling hills that originated as ground moraine, drumlin fields, and numerous features of lake origin, including sand dunes, former lake terraces and abandoned beach ridges. There are some steep bluffs along the lake and bay, but the coastline is flatter in other places. The region is underlain mainly by dolomite, which is covered in shallow, calcium-rich glacial till, but there is also extensive sand along the lakeshores. Soils here tend to bed loamy and calcium-rich, ideal for Western Agriculture, but there is some diversity, with some excessively-drained sands on beach ridges and dunes, as well as poorly-drained sands, especially where thin layers of sand are underlain by clay or bedrock.

There are a number of lakes of various sizes, many of which are surrounded by wetlands and broad bottomlands, and there are also some slow-moving rivers and streams; the rivers tend to be broad and straight where they flow over bedrock closer to their source, and downstream they shift to being heavily meandering but steeper-banked where they flow into the sandier lake sediments.

Although the climate is towards the cold end of a humid continental climate, the presence of water on both sides moderates the climate and extends the growing season to as long as 160 in the warmer parts of this region. The freezing of the lake is inconsistent from year to year. Green bay always eventually freezes along the whole length of this peninsula, and in some years Lake Michigan completely freezes over, but in other years, the center of the lake remains thawed. Furthermore, in some years, even when the lake does not completely freeze, extensive ice forms, often miles out, along the shoreline. But in the warmest years, the water remains thawed even close to shore. This phenomenon has multiple effects: the side on green bay is markedly less moderate in temperature than the Lake Michigan shoreline, but the winter lows on the green bay side are more consistently low, whereas along Lake Michigan, the degree of moderation afforded by the lake differs considerably from year to year.

Regardless of any variation, the lake-moderated climate combined with the diversity of soils and topography makes this region unusually high in plant biodiversity for a region so far north.

Prior to European settlement, this region had extensive areas of northern white-cedar (Thuja occidentalis) swamps in the bottomlands near the shoreline. The better-drained beach ridges supported a mix of eastern white pine (Pinus strobus) and eastern hemlock (Tsuga canadensis). On broader but low upland sites that were more mesic, the richest sites sometimes had some growth of northern hardwood forest, with primarily sugar maple (Acer saccharum) and American beech (Fagus grandifolia). Although northern white-cedar was dominant throughout, swamps here also supported tamarack (Larix laricina), balsam fir (Abies balsamea), red maple (Acer rubrum), paper birch (Betula papyrifera), black ash (Fraxinus nigra), black spruce (Picea mariana), Eastern hemlock, quaking aspen (Populus tremuloides), and balsam poplar (Populus balsamifera). In low depressions along the lake plain with poorly-drained, acidic sands, black spruce and tamarack were dominant.

Along Lake Michigan, some of the drier ridges supported mostly white pine and red pine (Pinus resinosa), with some white spruce (Picea glauca), balsam fir, and hardwoods. The wetter swales along Lake Michigan supported marshes or sedge meadows. Floodplain forests were dominated by silver maple (Acer saccharinum) and butternut (Juglans cinerea). Upland areas of ground moraine mostly supported northern hardwood forest of beech and maple.

Nowadays, much of this region has been cleared for agriculture. Very little forest remains in the interior of the peninsula, although there are considerable wetlands and swampy areas remaining along the shoreline, in the floodplains of streams, and around some of the lakes.

The region has been artificially dissected by a canal at Sturgeon Bay, the largest city of the region.

This region is bordered to the south by the Lake Michigan Lacustrine Clay Plain. To the north, it is surrounded by water, but if you view the island chain as a continuation of this region it is bordered to the north by the Menominee-Drummond Lakeshore of Michigan's upper peninsula; that region has a similar geology but is distinguished by its colder climate and its connection on land only to other colder regions, whereas this region is connected by land to warmer, more southerly regions.