Life of a Maple Part 2: Soil and Roots

A moist maple forest with rich soil.

A Sugar Maple seed doesn't get to choose where and what type of soil it gets to land on.  Typically, where the seed lands is a result of wind direction and strength at the time it falls.  Where ever the seed germinates and begins to grow is where it will spend the rest of its life.  The unfortunate majority will die long before reaching a foot in height.  Often, predators such as deer and squirrels, find the young seedling far to appetizing to pass it by.  Many seedlings will also unfortunately find themselves in soil that is less than ideal.  As far as deciduous forest trees go, the Sugar Maple is quite picky, much like Goldilocks.  The soil can't be too wet or the roots will suffocate as they drown in the water soaked soil.   Neither can the soil be too dry or the roots will dehydrate.  Nor can the soil have too much clay or too much sand.  They soil has to be just right. Even when the soil has just the right texture (meaning the right amounts of clay and sand) and the right amount of water, the soil might not be good enough.  The soil also has to have high levels of nutrients.  Soils with low nitrogen or calcium may prevent healthy growth and longevity of maples.  Even then, maples seem to prefer very deep soils deposited by glaciers over any other type of soil.  The maple is very picky...

The reason the maple is so very picky is because of its roots.  Just like branches of deciduous trees shed their leaves annually, larger roots also shed tiny roots annually and with dry weather.  Maples produce an abundance of these fine roots at very shallow depths, right where the nutrients are highest.  It has been estimated that 60 percent of annual productivity of maples is actually contained within these roots.  This is quite amazing when you consider the great density of leaves maple trees produce annually.  The fact that so much of the tree is in-fact these very sensitive tiny roots makes the whole tree very sensitive to whatever happens on or in the most shallow layers of soil.  Trampling by foot traffic, vehicles, or cattle can damage these roots as well as cause the soil to dry out, killing the roots and potentially killing the whole tree.  If fire burns across the ground, the surface soil will be significantly dried out also potentially killing the roots.  The heat of the fire can also kill the roots very easily.  Pollution, such as acid rain, can change the chemistry of the soil, also killing fine roots and damaging the overall tree.

Fortunately, the maple tree does have some adaptations that help make it at least a little less sensitive to changes in the surface soil.  For one, the overall root system of maples is capable of hydraulically redistributing moisture from deep within the soil to more shallow soils.  The thick shade of maples also helps to prevent evaporation of moisture from the soil.  Also, the fact that maples transpire, or "exhale", large amounts of water vapor while photosynthesizing helps cool the environment and increase humidity.  Fallen leaves are very absorbent and are a very effective mulch that help hold moisture in the soil.  All of this helps moisture to be retained within the soil where it can be utilized by the tree and prevents moisture from evaporating into the environment.  All around, the maple works to keep its environment as moist as possible.

Sugar Maple tree in fall.