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Conservation Through Management...


Severely over browsed forests loose their intermediate vegetation layers including shrubs, seedling and sapling trees, and forest floor plants including wild flowers, grasses, sedges, and other low-growing plants.  In addition, the diversity of species declines in all forest layers.

Loss of seedling and sapling trees threatens the ability of forests to regenerate, trees that die or are cut are not replaced by new trees.  Forest structure is reduced to a few species of canopy trees and a ground layer of plants that deer generally do not eat such as hay-scented fern, New York fern, and a few sedges and grasses.  In some areas the ground is bare.  Loss of understory, shrub, and forest floor plants reduces all wildlife habitat.

Deer population levels, when the earliest European settlers arrived, have been estimated at 9-11 deer per forested square mile. Today levels of 30-80 deer per forested square mile are not unusual and in some urban/suburban sites such as the Delaware Valley population density is 100+ per square mile.

Simplification of forest structure and loss of biological diversity resulting from deer overabundance threatens the health and resilience of forest ecosystems.  It also diminishes the ability of our forests to carry out important ecosystem services such as air and water purification, erosion control, soil building, mineral recycling, and preservation of biological diversity.

Highly vulnerable plant species are in danger of becoming so rare that they must be classified as endangered or threatened.  At least one plant, bearberry (Arctostaphylos uva-ursi) has been lost from the state due to excessive deer browsing.  

Over browsing by deer also worsens problems with invasive exotic species of plants as deer feed preferentially on native species allowing non-native invaders to expand and prosper.  Due to the combined impact of deer over browsing and invasive species, native forest wild flowers have been replaced by stands of stiltgrass (Microstegium vimineum), garlic mustard (Alliaria petiolata), lesser celandine (Ranunculus ficaria), and Japanese honeysuckle (Lonicera japonica).  Shrub layers are dominated by non-native shrubs such as Amur honeysuckle (Lonicera maackii), Morrow's honeysuckle (Lonicera morrowii), multiflora rose (Rosa multiflora), and autumn olive (Elaeagnus umbellata).

Preservation of Pennsylvania's rich diversity of native plants and ecosystems requires that we find a way to bring deer back into balance with their environment.


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