Michigan Forest Communities - Michigan Association of ...

ECOLOGY OF MICHIGAN FORESTS
• The melting glacier formed large
lakes, most of which drained to form
flat or undulating, silty or sandy lake
beds or lacustrine plains. Lake beds
also were exposed when the land,
relieved of the tremendous weight of
the glacier, rose along shallow shores
of the Great Lakes and the water levels
of the lakes dropped.
• In some places—especially in the
Upper Peninsula—underlying
bedrock, scraped and polished by the
glacier, was exposed.
• Long after the glacier was gone, wave
action and on-shore winds caused
sand dunes to form along the shores
of the Great Lakes and some inland
lakes.
Climate
During the millennia following the
retreat of the glacier, climate—the sum
total of sunlight, precipitation, wind,
and atmospheric deposition—has acted
upon exposed landforms, modifying
them in various ways. Glacial till has
become weathered by the action of climate
and the organisms that have
grown in it to become soil. Water erosion
and stream action have deposited
soils in downslope positions and deltas.
Wind has created dunes. Thus, the raw
spoil left by the glacier has been trans-
Table 1. Soil properties in relation to the continuum of ecological habitats.
Properties
Ecological Habitats
Xeric Dry – Mesic Wet – Hydric*
mesic
mesic
Average Very dry Somewhat Moist Very moist; Very wet
moisture during dry water may
the growing
stand in
season
spring
Drainage Excessively Very well- Well- Somewhat Very poorly
drained drained drained poorly drained or
drained undrained
Surface soil Sand to Loamy Sandy Loam to Sand to clay
textures loamy sand sand to loam to clay loam loam or organic
sandy loam loam (muck or peat)
Natural fertility Infertile Moderately Very Fertile to Moderately
infertile to fertile moderately fertile to very
fertile fertile infertile
* Hydric habitats are very complex and variable. Swamps or fens fed by flowing groundwater or surface
streams may be relatively fertile and productive, although tree growth is limited by anoxic (oxygendeficient)
conditions in the soil for all or part of the growing season. On the other extreme, the thick
peat soil of bogs and muskegs is strongly acid and saturated with stagnant water that is low in dissolved
oxygen, severely limiting tree growth. Many hydric habitats also exist between these extremes.
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