Friday, July 29, 2011

Eastern deciduous forest dry uplands

A late successional mature dry Eastern Deciduous Forest composed primarily of White Oaks.

The third type of Eastern Deciduous Forest is the dry, or xeric, forest.  These forests are often on hills adjacent to rivers and have sandy dry soils.  Standing on one of these hills, which can be quite large, you might be surprised to know that millenniums ago the hill was actually in the river!  That is, the sandy sediments in and along the river were blown on shore forming sand dunes.  These sandy wind deposited soils, called loess, stabilized when vegetation was established and eventually formed prairies or forests similar to what we see today in the Midwest.  So many millenniums ago the sandy hills that line rivers simply wouldn't have been there.  They would have instead been sandy sediments along the riverbed awaiting winds to blow them away and deposit them as dunes that would eventually turn into hills.  This is not always the case for xeric woodlands but is very often the case.

A loess hill Tall Grass Prairie, Oak Savanna near Cedar Rapids.  This Loess hill is adjacent to the Cedar River floodplain.  It has extremely sandy soil which once resided in the Cedar River until it was blown away and deposited as this hill.  The Red and Bur Oak trees in this savanna are adapted to prairie fires, the dry soil conditions, and are therefore important early successional trees in this type of environment.  A savannah, in the absence of fire, is a type of early successional forest.
One way you can identify loess deposits is to look for sandy soils, especially on hills, that are adjacent to rivers.  The sandy soils are course or gritty feeling and typically light in color, indicating low organic content.  Also, the absence of rocks and bedrock may indicate loess.  These sandy soils drain water rapidly and are warmer, therefore making them dry.  All plants that colonize these areas therefore must be well adapted to dry Midwestern conditions.  While nothing compared to desert conditions, some desert species such as yuccas and prickly pear cacti can on occasion be found here.  And being grasses generally favor drier conditions than trees, prairies often favor these sandy sites.  Red, Bur, and White Oak trees are also well adapted to these dry conditions and will often colonize these areas forming savannas, which is an early successional stage of xeric forests.  These oak species are well adapted to prairie fires, therefore allowing them to survive surrounded by prairie.  Sumac and Red Cedar are also important colonizing or early succession forest species, but these can only grow in the absence of fire.  Oaks and Cedars are very long lived and tough trees.  Cedars have the remarkable ability to grow just about anywhere including out of cracks in rocks.  Typically early successional trees do not survive into later more mature forests but both Oaks and Cedars can survive hundreds of years, seeing a forest from first establishment all the way through late successional maturity.
Oak, Hickory, and Ironwood xeric forest near Cedar Rapids, Iowa.
Typically, once Oaks are established more shade tolerant trees will start to colonize the area.  Hickory trees are one of the more common large trees that come along later in xeric forests.  Ironwood are a common understory tree with dogwoods as a common shrub layer.  With all the acorns and Hickory nuts within these forests they are popular places for squirrels, deer, and turkey.  There are also a lot of fruits present in the dry forests.  Wild Black Cherries seem to have a preference for these sandy soils.  Tree diversity is less in xeric forests when compared to mesic forests and as a result there is less bird diversity, but birds and other animals are abundant none-the-less.  As for bird watching though I typically stick to more mesic forests, but for admiring majestic Oaks and Hickory trees that are hundreds of years old I'll go for the xeric forests.
Old mature White, Red, and Bur Oaks growing in a dry deciduous forest.

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