and Second Growth >
Part 1 of 2
What are they?
When talking about forests in Oregon,
a couple of terms describing forest structure often come
up: old growth and second growth. While the terms sound
like they refer to the ages of trees within a forest, in
fact they don't. The term "old growth" refers
to a forest with structural characteristics associated with
"old forests" forests largely undisturbed since
Euro-American settlement (roughly since 1850). The trees
in the forest all don't need to have been around since 1850,
but some are! Second growth refers to the second-generation
forest that grows after an old-growth forest is catastrophically
Perhaps the following discussion while
make it more clear.
When we talk about old growth,
we are referring to a forest and not just a single tree.
The tree in an old-growth stand may be old, or it may be
young. What makes old-growth forest are simply some characteristics
we expect to see in western Oregon we may see them when
the forest approaches 120-200 years in age.
An old growth, or "ancient"
forest of the Pacific Northwest has large conifer trees
that may reach several hundred years in age, but there will
also be clumps of young trees that have grown where sun
has penetrated the forest canopy. The"canopy"
is the part of a tree that contains the branches and leaves,
and in a forest it refers to the collection of tree canopies
that cover the forest floor like an umbrella.
The result of the young
and old trees, sick and healthy trees growing together,
is that the canopy is very complex, with many layers.
There are large, standing dead trees, called snags,
that poke out of the forest and provide homes for insects,
rodents, and birds, and serve as perches for birds-of-prey
like owls and eagles.
Large dead trees crisscross the forest
floor, and may lie there decaying for hundreds of years.
This downed wood provides shelter and food for many more
plants, animals, and fungi, and as it decays it acts like
a slow-release vitamin for the soils of the forest. Large
trees fall into forest streams, decaying and providing food
for insects, like the caddis and stone flies, and algae,
both of which are foods for fish. The wood in the streams
also creates pools where fish can hide and rest.