Destruction of Understory and Overpopulation
Another reason given to justify killing deer via culling is that supposedly deer destroy the understory of the plant environment which has a negative impact on other wildlife.
This article was written by John Berhart of the Georgia Earth Alliance, an organization that has been in existence for 25 years. It addresses understory and overpopulation:
Seeds of forbs and other low-growing plants concentrate in the soil of a natural forest. The seeds sense the quality of light striking the soil above them.
If the seeds detect full-spectrum sunlight striking the forest floor, it means a disturbance has caused a light gap to develop in the overstory. Examples of natural disturbances: A canopy tree might have tipped over. Maybe there was strong wind and a blowdown. Or lightning killed a still-standing canopy tree, and its foliage is dying and being shed. Artificial disturbance examples: Game managers may have clear-cut a patch of forest (a so-called "wildlife opening"). Or, they make a large cutover with much "edge" (an uneven or wavy boundary). Or, instead of removing all overstory in an area, they decrease basal area (that is, they take out some trees and in so doing, make more area of the sky visible from the ground).
If on the other hand the buried seeds detect not a brightly sunlit forest floor above them, but infrared only, the message is DON'T GERMINATE NOW! YOU WOULDN'T SURVIVE! The seedbed is in the dense shade of layers of green leaves. Green leaves are transparent to IR and intercept the bright white light young plants require. Seeds survive by not germinating and waiting for a day when a disturbance creates a light gap, and thus an opportunity, to succeed.
Want to see open expanses of forest floor having sparse ground-level plants? Walk into the cathedral-like shade of an old forest's interior. The sparseness is not uniform. Here and there are patches of shade-tolerant herbs, ferns, and shrubs. These plants have adapted to live in low-light conditions.
Continuing your walk, you come across a glade. Wind thrown trunks of several trees lie on the ground like jackstraws. Around and among them, the ground seems to have exploded with broadleaf weedy plants, honeysuckle, and vines.
This exuberant, brushy growth happened naturally. It is what the seeds were waiting to become. It is also a salad bar of low browse that deer respond to. The seeds, and the deer, have physiological adaptations for exploiting sudden natural disturbances that happen in their habitats.
This is one of the concepts hardest for many people to understand about deer and many forest wildflower species. Where nature manages them and they aren't persecuted, their populations are never stable, but are in dynamic equilibrium with their environments. Their numbers track natural food supplies and other environmental variables (e.g., weather, fresh water, space, competitors) in smooth, natural cycles.
Why don't nature-managed, unhunted deer populations spiral "out of control"? For the same reason trees don't grow to the sky! There are no more deer or trees or other organisms that the land can support, at least, not for long. Ecologists bundle the conditions we mentioned above, plus others, such as disease, parasites, predators, into what is called Environmental Resistance.
As a given population grows, environmental resistance increases proportionately, pushing back down. This resistance is not fixed but varies with the seasons, food types, qualities and quantities, and much else.
Nature regulates wild populations. Even where hunters extirpated (made regionally extinct) the natural predators of deer, the other components of environmental resistance do the job of controlling deer numbers and density--that is, in places where humans are wise enough to stand back and not interfere.