Posted: May 31, 2017

Change comes to all forests. No matter the change, some forests will survive the change with functions more or less intact; others are going to be severely impacted and lose their ability to function as they have. How do you determine your woods’ ability to survive change? How do you assess its resilience?

One of the penalties of an ecological education is that one lives alone in a world of wounds. Much of the damage inflicted on the land is quite invisible to laymen. An ecologist must either harden his shell and make believe that the consequences of science are none of his business, or he must be the doctor who sees the marks of death in a community that believes itself well and does not want to be told otherwise.

--Aldo Leopold, A Sand County Almanac

Change comes to all forests. That change may be sudden (a storm event, fire, ice damage), occur over a few years (spread of insects and diseases), or over decades (changes due to climate). No matter the change, some forests will survive the change with functions more or less intact; others are going to be severely impacted and lose their ability to function as they have. How do you determine your woods' ability to survive change? How do you assess its resilience?

With some of the more creeping change (e.g., hemlock woolly adelgid, emerald ash borer, elm yellows, Dutch elm disease), the vast majority of the public didn't notice the impacts until large numbers of trees no longer leafed out. Where there used to be forest or fencerows, now only dead trees stand. For those closely attuned to their trees, the change was apparent. Some tried to mitigate the change; others reacted to it quickly once the decline was apparent. Right now, we live in a "world of wounds."

More and more, research shared in professional publications are helping forest managers care for the woods, improve health and functionality, in the face of creeping climate change impacts. These resources are quite interesting and useful, and can help us retain health and functionality in the presence of more immediate threats. Many of these climate change publications informed this article and we'll share those resources at the end.

Resilience is the ability of a forest to, in spite of change agents, retain its identity in terms of composition (depending upon the threat type), structure, and ecological functionality. In consideration of many of the threats our woods face that can remove an entire species, at its basic premise let's work off the idea of retaining ecological functionality within a forest. So where do you start?

Start by understanding the current state of your forest, and the plant associations or communities that make it up. Depending upon the size of your property, you may have different woodland communities comprised of different species, of different ages, on different growing sites. Let's start with the characteristics of those communities.

In woodland communities, trees grow and eventually succeed one another on a site, based on their preferred and/or competitive growing conditions. This process happens as trees compete for resources and replace each other as conditions change. This process, called succession, is important to understand. Is your forest young and thick? Is your forest a little older and made up of thin poles (trees five to twelve inches in diameter) with the crowns competing with each other for light up in the canopy? Are trees starting to differentiate themselves in the competitive process - some growing larger, while others are falling behind or dying? Succession relates to the age and structure of the forest. Understanding where your forest is in the successional process will give you some idea of its ability to respond to disturbance.

Species diversity is another important characteristic to understand. Recognize that species diversity is tied to growing conditions. Each species of tree has preferred growing conditions, their physiological niche, which can be wide and include the margins where they may barely survive. Their ecological niche is more narrow and describes where they are more likely to succeed in outcompeting other species. A highly diverse forest will have more opportunities to reclaim or fill-in space if one species is lost to change. A less diverse forest has lessened opportunity to respond well.

Do you have rare communities of forest species, or sensitive sites that will be susceptible to change? Do you have sites where species are growing at an extent of their range - a refugia, or areas that create unique habitat features - vernal pools, spring seeps? What surrounds them? What tree species buffer and protect those important areas? And speaking water bodies, what about streams and rivers? Where do they fit in your forest? The importance of forests to the quality and quantity of water available to us cannot be overstated. Stewarding our forests well means that we are also stewarding the waters of the forest well.

Assess your overall forest health. Do you see declining trees? Trees whose crowns were once vibrant and full, but now look sparse? In our area, about three years ago, ash was easy to see in decline; now the majority are dead. Are there insects and diseases within the larger landscape, or upwind of you, that you should watch for? Recognize that we have cycles of pests, such as gypsy moth, and constant threats of new invaders, such as hemlock woolly adelgid, emerald ash borer, and spotted lanternfly. Asian longhorned beetle is a big threat on the horizon. It will take the awareness of alert landowners to keep that invader from becoming problematic.

Competitive and invasive plants take over the growing space from our native trees and shrubs. What lives on or adjacent to your property that will take advantage of increased light due to crown loss or tree death? What will come back if the native regeneration is outcompeted? Speaking of threats to regeneration, what are the impacts of herbivores in your woods? Do you have young trees of diverse species in your understory? Or, are they nibbled to stubs by deer? Competition and deer pressures are big threats to the next forest when the expectation is that it should be there.

Assess your connection to other areas of intact forest. How fragmented is the landscape around you? Species can migrate, with assistance from wind and seed dispersers, within a forest. If the area around you is farm fields or development, from where will threats to your forest come? To where will wildlife move?

To this point, we've focused on the trees, but what about the other parts of the forest ecosystem? Assess your soil resources as well. Forest soils have a very specific structure with a deep organic layer, under the duff layer of fallen leaves and fine woody debris, filled with macropores for water movement, and active invertebrate and vertebrate life. Are you dealing with compacted, rutted, or eroding soil? Do you have invasive earthworms in your area? Do you allow coarse woody debris (branches, tree stems, etc.) to remain on the forest floor to return its nutrients for other trees' uptake? Is anything compromising the structure and function of your forest soil?

All of the above is a lot to assess. If it sounds daunting, there are natural resources professionals who can help. Hire a consulting forester to provide you with a forest inventory of your property. The inventory should cover much of what we've just laid out for you to understand. As with all professionals, get recommendations, ask for references, and find someone who you feel comfortable working with.

Now that you've assessed your forest, what's next? Now you've got to think beyond you. What natural events have historically hit your woods - wildfires, storms, tornados, ice? What's been happening in recent past? What insects and diseases are in your area, are professionals and other landowners talking about? Keep up to date on insects and diseases. The PA DCNR Bureau of Forestry website has great resources and factsheets on the pests they're watching for. Inform yourself. Pay attention to tree species or individuals in decline - watch for increased predator activity (e.g., woodpeckers, predatory wasps). Watch for trees with leaves turning yellow - chlorotic - at the wrong time of year. Watch for early seasonal changes or brown leaves. Ask for help identifying what might be causing the problems. Again, reach out to your consulting forester, or a DCNR Bureau of Forestry Service Forester (there's one responsible for every county). Pay attention to herbivory on your trees and shrubs. Is deer pressure becoming too great or reducing the diversity of the next forest?

You can't always accurately predict the change that is coming or when it might hit. But you can plan and prepare to create and maintain resilience within your forest. What actions do you take to have the best chances for your forest to retain its functionality?

  • Monitor and plan - an inventory is a great place to start
  • Work with a professional to create an appropriate plan to increase health and diversity
  • Harvest when necessary, following best management practices, to increase age and species diversity and remove ailing trees.
  • Clean all tools, equipment, and machinery coming to your woods to reduce accidental introduction of invasive plants or pests
  • Control invasive and competitive plants using integrated pest management strategies
  • Control deer and reduce their pressure on the young trees
  • Look to the larger landscape to watch and be prepared for change
  • Remain engaged with your woods and curious about the change you see.

A resilient forest will have a high likelihood of retaining its functionality in the face of change. Unfortunately, the pressures we've introduced to our woods require us to be vigilant and helpful; if we want to keep the forest intact and functioning, we can't just let nature take its course. We must take advantage of our ecological education to prepare for change.

Shifley, Stephen R.; Moser, W. Keith, eds. 2016. Future Forests of the Northern United States. Gen. Tech. Rep. NRS-151. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station. 388 p.

Forest Stewardship Council. 2010. US Forest Management Standard with Family Forest Indicators. Updates 9/10/2012.

Horton, James, M. Langlais, T. Morton, D. Paganelli, N. Patch, and S. Wilmot. 2015. Creating and Maintaining Resilient Forests in Vermont: Adapting Forests to Climate Change. Vermont Department of Forests, Parks and Recreation.

Contact Information

Allyson Brownlee Muth, Ed.D.
  • Director, Center for Private Forests

James C. Finley Center for Private Forests


416 Forest Resources Building
University Park, PA 16802

James C. Finley Center for Private Forests


416 Forest Resources Building
University Park, PA 16802