Forest Ecology – Part one
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Forest Ecology – Part one


Hi. This is week six,
Forest Ecology. And this is going to extend what
you learned in Forest Biology, and take what you learned also
at the Colorado State Forest Service Nursery. And hopefully put it
all together for you. So first of all, forest
ecology is the scientific study of the interrelated patterns,
the processes, the flora, the fauna, and the
ecosystems in a forest. So think about that. And what we’re
going to study today is the ecosystems, the life
cycle, ecological succession. And then in part
two, we’re going to look at biological
diversity, exotic species, and thinking globally, which is
how we manage our forests today differently than how we
did when we were just managing our backyard wood lot. So the definition
of forest ecosystem, again, it describes a
community of organisms interacting with each other
and their physical environment. So think about the tree
not growing in a vacuum, but growing in this ecosystem
that everything is related. Now the study is referred
to as forest ecology– the study of
complex interactions between the organic
and inorganic elements of a forest ecosystem. It can be anything from a small
forest to an entire watershed or landscape. So it can be from small
scale to large scale, but it’s looking at
the interrelationships. So that’s the key. We start with the
Biotic Pyramid, which is very much
review for all of you. The ecosystem
being characterized by the interdependence in
which every organism depends on every other living
and non-living thing. So on this Biotic Pyramid, we
talk about things at the bottom being smaller in size
and larger in number. So there’s millions of bacteria,
but they’re tiny microscopic. Two things that are smaller in
number, like birds and mammals, but they’re larger in size. Also, in this
particular graph, it shows you the bioaccumulation
of toxins in the food chain. So something like DDT applied to
a crop will affect the animals, and be accumulated throughout
the food chain affecting, for example, bald eagles. And how DDT made the
egg shells and produce them to be so thin that the
bald eagles would break them. And we put them on the
endangered species list to recover them, and took
DDT out of our food chain. So that’s an example
of bioaccumulation in the food chain. Also I talked about the
living and the non-living, so the living components
in the Biotic Pyramid are the producers, the
consumers, and the decomposers. Also the non-living components,
which is review from biology, is soil, climate, and water. So all six of these things
are affected in the ecosystem. So food chains
are not realistic. That’s a simple one organism
to another organism. What’s more realistic
is a food web, which is the food chains
being interconnected. So again, at the
bottom, we start with the decomposers
that are breaking down the organic matter. The producers are the plants,
which get their solar energy to be created, and
then the animals that eat the producers
are the primary consumers. And the animals that eat
the primary consumers are the secondary consumers. And the important part is
that energy is given off in each of those steps. So the transfer of energy
from one organism and in one nutritional level,
and the food web being the complex interlocking
series of food chains. So this is more realistically
what it looks like. It’s complicated and it isn’t
just a simple single chain. The nutrient cycles
are the processes that drive the dynamics, and
that is that flow of energy and the movement of
nutrients through the system. So for example, the trees
absorb the nutrients, transport the water, nutrients through
the xylem to the leaves, the leaves manufacture food
through photosynthesis, before the winter the
leaves fall, decay, and return organic
matter to the soil. So this is the flow of
energy throughout a tree. There’s also seasonal changes
due to the angle of sunlight and the rotation of
the earth’s axis, which triggers biological changes. So why do the leaves fall off? We talked about this briefly. The colder temperatures
and shorter days trigger the cells of the
base of the leaf stalk to die and form a layer of cork,
which is a barrier to water and nutrient transport. Also, what’s going on is
the chlorophyll breaks down and exposes other
leaf pigments– zanthophylls are yellow and
anthocyanins are purple– creating the change
in leaf color. The leaves no longer
produce photosynthesis. They fall, and the tree
becomes dormant until spring. So the next section
is Forest Health. I’m going to stop you here and
ask you question about food chains in a forest environment.

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