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A slow, thoughtful walk through a forest preserve
reveals a lot is going on.
First, of course, you notice the plants.
There are the trees that give the forest its distinction.
Most woodlands contain several kinds of trees.
Beneath them you'll see the younger trees and the shrubs,
the former biding their time until one of the elders falls,
signaling the race to determine which younger tree
will grow to fill that new gap in the canopy.
In the spring, that forest is filled with wildflowers,
blooming most prolifically in the early season
before the trees leaf out to shade the ground.
Looking at the leaves of all the plants,
from wildflowers to trees,
you may remark how fresh and clean and green they all look.
If you return in the fall, however, in most years,
you will notice how the leaves have become transformed.
Many have holes, gouges out of their edges,
and various other spots,
blotches and other disfiguring marks.
Some leaves, some entire plants, are missing completely.
Such changes are the work of plant-eating animals.
Most kinds of trees have an impressive list of animals
that love them -- for dinner.
At least 13 insect species and a fungus make their living
from the leaves of black or sugar maples at Meacham Grove
and Maple Grove forest preserves.
Gouges chewed out of leaf edge s usually are the work of moth
or butterfly caterpillars.
Various blotches are created by leaf miners --
insect larvae, again, often moth caterpillars --
so tiny that they fit between
the upper and lower surfaces of the leaf,
eating the thin tissues between.
Irregular, blotch-like mines under the leaf's top cuticle
are produced by one species of tiny caterpillar.
Tent-like mines on the underside of the leaf are the work
of a completely different kind of caterpillar.
Two species of minute Caloptillia moths
start out making tiny tadpole-shaped mines
in their youngest stage,
but then the caterpillars migrate out to the leaf tips
and sew these into cone-like folded enclosures,
scraping the insides for food until their development
is complete.
A fourth mine type, in the form of a zigzag line,
probably is the work of yet another moth.
Tiny dots, which may be white or black,
usually are the work of sucking insects such as lace bugs.
These stick their beaks into the leaves
and draw out tiny bits of tissue
much as a mosquito relishes the blood of a bird or mammal.
The first maple leaf consumers in the spring are tortricids,
a group of moths whose caterpillars bite through
the main veins of leaf, causing it to wilt.
The caterpillar lives within the shelter so formed,
eating part of it to support development.
A final damage type, in the form of a circular discoloration,
is more common in cool wet years
as it is the sign of a fungus colony.
With so many consumers, it may seem surprising
that we have any maple trees at all.
It turns out that these insects
are themselves tasty to other animals.
Some are larger predators like birds and mice.
Others, parasitic wasps and flies, are smaller.
Ecological research has found that the interactions
among these species are complex.
Food-web stability is helped most by consumers
that switch from one prey to another,
concentrating on the ones that are the most abundant.
So much diversity; all based on one plant species!
Multiply that by the many kinds of plants in the forest,
and you perhaps can see how the study of ecology
is so interesting to some.
Each kind of plant is the foundation of what ecologists
call a component community.
Back at Meacham Grove, the Solomon's plume,
a late spring wildflower, is host to a sawfly caterpillar
and a leaf miner.
Enchanter's nightshade, a summer-blooming annual,
is eaten by the relatively large caterpillar
of the reddish speckled dart moth,
the small inchworm caterpillar of a day-flying moth
and a leaf beetle.
Though many of these insects specialize on one kind of plant,
others are more generalists.
For example, coppery underwing caterpillars at Meacham
have been found eating leaves of red elm,
bitternut hickory, white ash, basswood and Virginia creeper.
Consumers of *** plant leaves commonly have a broader diet
than do consumers of herbaceous plants.
This is because the various *** plants
typically defend themselves
with the same class of chemical deterrents,
called tannins.
Any animal that can eat one kind of tannin-defended leaf
can eat others.
The various wildflowers each have their own
specialized chemical defense,
which forces more specialization in their consumers.
Again, all these plant eaters have their own
specialized parasites,
along with generalized vertebrate predators,
collectively forming a stable ecosystem
through population checks and balances.
What happens when these checks fail?
When, for instance, a consumer comes along
without its own limiting parasites or predators?
An example at Meacham Grove
is a plant called the trailing strawberry bush.
Its main specialist insect consumer is the colony-forming
small caterpillar of an ermine moth.
In the 1980s, trailing strawberry bush colonies
were large and common at Meacham Grove.
Then along came the ermine moths,
which in the space of a few years increased to such numbers
that the trailing strawberry bush colonies were decimated --
some wiped out entirely -- all cut back to tiny fragments.
They have not recovered to this day.
The previous example was limited to one tiny specialist insect
and its devastated host.
What do you think might happen if an extreme generalist,
capable of eating almost any of the plants,
came along without its own consumers to hold it back?
What if, in addition, this were a large animal,
capable of eating large volumes of plants?
Such, in fact, has happened.
The animal is: The white-tailed deer.
We all enjoy having deer on our preserves,
but they returned from regional extinction without the wolves,
mountain lions and other suite of predators that once held
their numbers down.
They demonstrably have threatened
the many component communities,
the plants and all the many animals they support,
from bugs to birds.
To determine the impact of the deer population
on our ecosystems, Forest Preserve District ecologists
collect vegetation data using many methods.
Small fenced areas throughout the District exclude deer
from browsing inside the fence allowing ecologists
to assess the impact deer are having on the ecosystem.
Besides collecting vegetation data,
the number of deer-vehicle collisions is also evaluated.
In addition to these measures, biologists conduct aerial counts
of deer in winter, when obscuring leaves are gone
and snow provides a backdrop against which deer stand out.
All of these data from the many preserves allow an assessment
of where deer have become so abundant
that they threaten ecological integrity.
The Forest Preserve District sends the data
to the state of Illinois,
along with a request to remove enough deer
from overpopulated preserves to bring their numbers down
to a sustainable level.
As a result of the District's efforts,
ecosystem recovery has been documented and sustained
in many preserves where active deer management has occurred.