Lessons Learned from a Decade of Forest Health Monitoring in NETN

white ash
Forests in NETN parks support older and more complex features than surrounding lands, but still have a ways to go to achieve full forest function.

NPS photo.

By NETN Ecologist Kate Miller.

As NETN’s Plant Ecologist, I have spent that past 10 years monitoring forest health in national parks across the eastern U.S. Forest conditions for Network parks vary from site to site, but a general rule of thumb is that more northerly parks tend to be in better condition and suffer less from regional stressors. The overall good news for all parks is that they preserve areas of older forest habitat that are of regional significance, consistently housing more coarse woody debris, higher densities of large trees, and higher proportions of late successional forest than surrounding forest lands. That said, our study plots indicate that these parks have lower levels of coarse woody debris and snags (standing dead trees) than needed to support the full range of wildlife dependent on these features. As park forests continue to develop, we expect them to become even more important sites of older forest habitat.

The bad news is that forests in NETN parks are threatened or already under attack by a number of serious stressors, including invasive plant species, deer overabundance, exotic forest pests, and climate change to name a few. Issues of deer overabundance and invasive species, which tend to go hand-in-hand, are most extreme in New Jersey’s Morristown NHP. As indicated by lack of seedlings, saplings, and even small trees. Tree regeneration has failed to reach the canopy for many years - possibly decades - in park forests. When natural canopy disturbances do occur (blow downs, etc.), there aren’t enough sub-canopy trees to fill in the gaps, and the canopy may become sparser over time. While less extreme than in Morristown, we also see considerable impacts from high deer levels in New York’s Roosevelt-Vanderbilt NHS and Saratoga NHP, as well as Connecticut’s Weir Farm NHS. Not coincidentally, invasive species are also abundant in these parks. Exotic shrub thickets, which thrive both in high deer densities and in disturbed soils (e.g., historically plowed fields), are causing problems throughout NETN parks, including in Morristown NHP, Minute-Man NHP (Massachusetts), and Saratoga NHP. Invasive species and deer are less abundant in NETN’s more northern parks, including Acadia NP (Maine), Marsh-Billings-Rockefeller NHP (Vermont), and Saint-Gaudens NHS (New Hampshire), and we encourage managers to try their best keep it that way!

Deer fawn
Deer overabundance can have an exacerbating affect on problems brought about by climate change.

Vicki Gibson

An Uncertain Climate

While we are unsure exactly how climate change will impact forests in NETN parks, we are certain that impacts will happen, if they are not already happening. In the short-term (years to decades), reducing non-climate stressors in parks, such as invasive plant species and exotic forest pests, is one of the best management actions park managers can take to ensure that forests are resilient for responding and adapting to a changing climate. In the long-term, climate change adaptation will be necessary, and managers should be starting the process of planning for climate change adaptation now. Beyond reduction of non-climate stressors, my primary recommendation to park managers in the short-term is to take a largely hands-off approach to forest management. In other words, park managers should allow forests to develop under natural processes, such as succession and natural disturbance, and should only intervene when natural processes are disrupted by a stressor, such as overabundance of deer. In Marsh-Billings-Rockefeller NHP, where sustainable timber harvesting is embedded in park management objectives, we recommend managers find ways to maintain or increase tree species diversity and complex forest structure through their forestry operations. Given that selective forestry can reduce tree species diversity and forest structure, managing forests to counteract this trend could be a challenge for the park.

I encourage land managers, from small private landowners to land management agencies, to take a similar hands-off approach, particularly if their land is not managed for timber production. Over the years, I have observed many a well-intentioned landowner who, through trying to be a good land steward, takes actions that impair rather than improve ecosystem health. Many of these mistakes relate to the misconception that forests need to be “cleaned up” to be healthy. My main objective in writing this article is to dispel this myth, and to proclaim that healthy forests are messy! I also offer the following guidelines that I abide by on my own property, and that I hope are useful for others.

Six Simple Guidelines

  • Dead wood is good wood. While they may look messy to an untrained eye, dead and dying trees are important features of a healthy forest. As stated by Franklin et al. (1987), “At the time a tree dies, it has only partially fulfilled its potential ecological function”. Dead standing (snags) and down wood provide crucial habitat for many species of birds, small mammals, amphibians, insects, mosses, and fungi. Down wood also provides important habitat for tree seedlings to germinate. The tip-up mounds created by downed trees provide additional regeneration sites for tree seedlings, and are important habitat for small mammals and ground-nesting birds. In fact, the Winter Wren, whose exuberant and melodious trills are one of the first songs of spring, is a species that specializes in nesting in the root-wads of downed trees. Where possible, leave dying trees and dead wood to persist in the forest.
  • Encourage native species. Invasive species are a major threat to the health of our northern forests. Refraining from planting non-native species, and removing invasive species that are already present are some of the best ways to ensure a healthy forest. Personally, I have been battling a stand of oriental bittersweet for the last 5 years on my property. There are a number of excellent websites that provide useful information on how to identify and manage invasive plants, including the Invasive Plant Atlas of New England (https://www.eddmaps.org/ipane/), the New York Invasive Species Information (http://www.nyis.info/), and the New Jersey Invasive Species Strike Team (http://www.njisst.org/).
  • Keep the good bugs happy and the bad bugs away. Insect pollinators are critical to a functioning ecosystem, vital to farmers, and are extremely vulnerable to pesticides. Following organic gardening practices and planting a diversity of native flowering plants is a good and proven way to keeping pollinators happy. More information on pollinator conservation can be found here: http://www.xerces.org/pollinators-northeast-region/. Exotic forest pests, which pose a big threat to several very common species in the northeast, are primarily spread by the movement of firewood. For more information about specific forest pests and how to slow their spread, check out the U.S. Forest Service Northern Research Station’s Invasive Species website (http://www.nrs.fs.fed.us/disturbance/invasive_species/). Many states also have informative websites specific to pests in their state.
  • Protect the soil. Healthy soils are important for ensuring healthy forests. Earthworms, which are not native to the northeastern US, may be good for the garden, but are not good for northern forests. Leaf litter, which supplies nutrients to plants and buffers the underlying soil from desiccation, can be quickly consumed by earthworms. Many beloved understory plants, including trout lily and trilliums, are dependent on a thick layer of leaf litter, and can quickly decline after earthworm introduction. Seedlings of common tree species, including sugar maple and northern red oak, are also sensitive to earthworms. Earthworms are often used as fishing bait, and may also come in compost, mulching, or other nursery material. To avoid further spread of earthworms in the northeast, unused bait should go in the trash, not in the woods. Also avoid dumping excess mulching or compost containing worms in the forest. For more information, check out the Great Lakes Worm Watch program’s website (http://www.nrri.umn.edu/worms/).
  • Maintain forest buffers. Forests can slow the movement and improve the quality of water flowing into streams, ponds and wetlands. Forested buffers also provide shade for streams, which improves habitat for cold-water fish species like brook trout. Forest buffers are important for many species of amphibians that breed in aquatic habitats, but spend most of the year in upland habitats. Maintaining forest buffers adjacent to streams, ponds and wetlands can go a long way in protecting aquatic ecosystems and the species dependent on these habitats.
  • Above all else, just let it be. Doing nothing is a perfectly acceptable approach to managing forests where timber production is not the primary objective, and where stressors are not impeding natural processes. Nature typically does not require human intervention to be a healthy functioning ecosystem. Allowing natural processes, such as disturbances and dying trees, to occur without human interference is good practice for northeastern forests.

Following the above guidelines will promote forest health across the northeast, and I encourage interested readers to check out the links provided to learn more about sound land stewardship. For more information on the Network park forests, visit NETN’s website (go.nps.gov/netn), which houses numerous 2-page resource briefs, annual technical reports, and detailed monitoring protocols for the programs we are currently implementing. We also have a Facebook page where we post updates from field crews and announce public events.

Last updated: February 21, 2018