Resilient Forests Initiative - Managing Deer Impacts

Hungry white-tailed deer can eat much of the vegetation in a forest that is within their reach.

Keeping white-tailed deer in balance with forest ecosystems is critical to managing resilient forests.

Deer love living on the edge, and people love giving an edge - not purposefully, necessarily, to deer. The places where a yard, field, or farm meets the forest are referred to in ecologist parlance as “edge habitat”, and the countryside of the eastern US is awash with this ecological zone that deer so often thrive in. Add to that the absence of “top line” predators (wolves and mountain lions), conditions have conspired to allow the deer population to explode over the past several decades.

Too Many Deer

A healthy forest needs to have enough tree seedlings and saplings to regenerate the forest canopy after a disturbance. Analysis of NPS Inventory and Monitoring (I&M) and other long-term datasets makes it clear that many eastern national parks lack adequate tree regeneration due to decades of over browsing by white-tailed deer. Most of their preferred foods, logically, are native plant and tree species that they have evolved with over the millennia. This higher “deer herbivory” pressure on mostly native plants helps many non-native invasive species flourish in high deer-density areas.

Deer numbers have dramatically increased in the Eastern US.

NPS image

As deer apply more pressure to native species, they free up space and other resources that invasive species are poised to take advantage of. With no deer management, parks are at-risk of losing their forests which are unable to replace themselves after disturbances such as microbursts, insect infestations, or ice storms. Deer-dominated forest ecosystems tend to shift towards thickets of invasive shrubs as canopy trees decline from disturbances or age.

Forest health monitoring by I&M Networks provides information on the status of park forest regeneration. Tracking intensity of deer browse impacts and the number and species of seedlings and saplings can predict whether a park’s forest is capable of regenerating after disturbances. As the map below shows, many eastern park’s forest regeneration is in either Imminent Failure or Probable Failure, meaning that park forests will eventually shift to shrub thickets over time without management intervention. First and foremost, managing deer will be essential for tree seedlings and saplings to begin to recover.

Through collaboration within Region 1, parks can establish and implement deer management programs by building on the lessons learned at their neighboring parks. National park units, such as Catoctin Mountain Park and Rock Creek Park, that manage deer have seen positive trends in tree regeneration.

As deer populations in these parks have declined, seedling numbers have concurrently increased. While increases in seedlings are a positive change, they don’t guarantee future regeneration outright. It takes many years for these small and vulnerable seedlings to grow into large, resilient saplings on their quest to reach the canopy, and they face many threats to their survival along the way.

The below image comparison shows the early success of forest regeneration in Rock Creek Park since the implementation of a deer management plan.

Left image
Very little regeneration of trees and plants occurred on the forest floor before deer management began in Rock Creek Park.
Credit: NPS image

Right image
Forest regeneration has recovered dramatically since an on-going deer management plan was implemented.
Credit: NPS image

Keeping white-tailed deer in balance with forest ecosystems is critical to managing resilient forests.

In the video below, see how Eastern national parks have had successes maintaining healthy forests through deer management and other tools.

Duration:

5 minutes, 54 seconds

How forest monitoring in eastern national parks helped reveal issues with long-term forest sustainability, and the successes parks have had in addressing the issue at Gettysburg National Military Park, Rock Creek Park, and Catoctin Mountain Park.

For more information

Explore this Case Studies in Deer Management StoryMap

Contact NPS Wildlife Biologist/T&E Coordinator Sheila Colwell for further details on regional deer management.