by Reynold Conger

Created on: November 17, 2011

We tend to think older is better, but often do not define what we mean by better.

There are those ecologists who put great importance on biodiversity.  Thus it is understandable they may assume mature forests are better and thus more bio diverse because of their age.  This assumption appears very reasonable to those who think of a forest as a static ecosystem.

Forests are ecosystems, but they are not static.  While changes may take decades or centuries, all forests are changing even if only replacing dying trees with new growth.

Forests pass through a series of stages as they age.  Every now and then a catastrophe destroys a forest.  That may be a forest fire, disease, volcanic eruption or a human activity such as agriculture.  For example, If an efficient farmer clears land and grows crops, most of the forest species are eliminated from a large piece of land.  If the farmer eventually abandons the farm, as happened in Northern Wisconsin at the end of the 19th century, the vacant fields will revert back to forest.  What we have to understand is that the new forest is not the same as the one the farmer cleared.

The first plants to return to bare land are the pioneering species.  They may not even be trees.  Pioneering species include grasses, berry bushes and fast growing trees such as aspen and birch.  These pioneering species share the following properties.  Most of them can thrive on poor soil.  They do not tolerate being shaded by other plants.  They are relatively short lived plants that mature, die and rot within a short time.  There are few aspen trees that are older than 60 years old.  Aspens over 30 years often have core rot.  Pioneering species generally have good propagation strategies through wind blown seeds and/or by sprouting roots.  These pioneering species quickly take hold because they need a minimum to survive.  As the forest of pioneering species ages, the tree species and larger bushes tend to displace the grasses and lower bushes.

The leaf litter of the pioneering species produce a rich layer of forest top soil.  Trees also shade large areas of the ground.

Intermediate species, generally pines and spruce, Require a rich soil for the seedlings.  Most intermediate species do better with only partial sunlight.  Thus as a forest of pioneering species matures, the intermediate species have an advantage.  Slowly over time, the intermediate

• 1
• 2
• Next Page >>