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Forest Health: Growing Resilient Trees

What is wrong with my tree?

Many of the activities we undertake to achieve our goals and ensure the long-term sustainability of our forests, will also promote a healthy forest. There are some “sicknesses” that we can only react to, but for the most part we control the health of our forest.What does promoting a healthy forest gain you? When forests are healthy, they are better able to respond to and recover from attacks from insects and diseases. Individually, healthy trees can handle more damage from insects and diseases than trees that are stressed or otherwise sick. In fact, our trees are constantly under attack and only the healthy ones survive and flourish.

Characteristics of a healthy forest:

Many different plant species – Generally, insect and disease populations target one type or species of tree. A diversity of tree species will ensure that one insect or disease can’t wipe out all your trees. However, ensure that non-native invasive species are not part of that diversity
Not crowded – Trees become stressed when they are too crowded, and have to fight for sunlight, nutrient and water. This stress makes them more susceptible to attack by insects and diseases
Structurally complex – Structure refers to the variety of tree sizes and ages, and the presence of shrubs and ground. The greater variety (or complexity) also improves a forest’s ability to respond to attack, and supports wildlife that feed on the insects that could be attacking your trees.

Steps to keeping your forest healthy:

  1. Learn what diseases and pests are problematic for your trees and forest type
  2. Learn how to identify the cause of the trees illness
  3. Evaluate the forest as a whole
  4. Ask for professional assistance
  5. Work to promote healthy, vigorously growing trees

1. Learn which insects and diseases you need to be aware of for your forest
There are certain insects and diseases that are commonly associated with specific tree species and forest types. Most of these (99%) have only minor impacts on our trees and don’t require any specific treatment. The others are the ones to keep an eye out for and take action against once found on your property. Visit the DNR forest health website to learn more about the insects and diseases to be aware of, and see if they are a potential problem for your forest.

2. Learn how to identify the cause of the trees illness
Many times we don’t see the agent that is causing the illness in our trees, or we may only be seeing a secondary cause for the illness. The real agent may not be apparent, so you need to know how to deduce the cause from the evidence at hand. To do that, you need to be able to recognize symptoms (e.g. wilting leaves or a deformity on the trunk) and signs (e.g. tunnels in the wood or mushrooms) of the pest to the primary cause of the illness. Use the MN Extension website to match the signs and symptoms you are seeing to the appropriate insect or disease.

3. Take stock of the health conditions of your entire forest
Our forests and trees are constantly under attack by insects and diseases, so it is not uncommon to find trees infested with some kind of pest. If you have completed the first two steps in this process, then you know which pests are important to keep an eye out for and how to identify them. Now you need to put any kind of insects or diseases you find in your forest into perspective. If it just one tree that is infected with an insect or disease and the surrounding trees seem healthy, then this might not be a concern. If instead it is a group of trees that are infected or there are a number of trees scattered throughout your forest with this infection, then you may need to be concerned. At this point, it would be a good idea to get a professional opinion on your situation.

4. Professional assistance is available to help you with any pest problems
Start with your local DNR Forester, and you can find those that work in your county by visiting the DNR website. They can help to diagnose your problem and offer solutions. They may also work with regional forest health specialists within the DNR. If the problem you have is limited to a yard tree, then you need to contact your local UW-Extension office, a local arborist, or an urban forester to figure out what the problem is.
Here you can find your local UW-Extension office
Here you can find members of the Wisconsin Arborists Association

5. Tools for keeping your forest healthy
Thin your forest to keep it from getting too crowded – that means removing some of the trees so that the remaining trees have room to grow and have less competition for light, water, and soil nutrients
Don’t let your trees get too old – trees that are well beyond their normal maturity age tend to be slower growing and are more susceptible to attack from insects and diseases
Choose or favor trees that are best suited for your soil and climate – trees growing under conditions outside of their normal range will struggle to grow and be more susceptible to attack
Retain some snags and fallen logs – these will provide habitat for the predators that will eat the insects attacking your trees
Remove infested trees – if you have found that some of your trees contain particularly nasty insects and diseases, then it is a good idea to remove those from your property before the infestation spreads to your other trees

Learn how to determine if your forest needs thinning in Estimating Stocking Conditions
Learn how to thin your forest in Intermediate Cuttings in Forest Management
Learn more about snags and fallen logs as wildlife habitat in Critter Condos

Self-paced “Learn The Signs & Symptoms of Sick Trees” Lesson

In this lesson, you will learn the signs and sysmptoms of various agents that can damage your trees.

After this lesson, you will be able to:
1) describe the signs and symptoms of common damaging agents
2) be able to identify some damaging agents
3) know how to describe forest health problems to a professional

If you have questions after this lesson, please email us.
See the main page for more self-paced lessons and non-Flash versions.

Related Blog Posts

A healthy forest is a happy forest
Wildfire and your woodland

Related Publications

Gypsy Moths: Identifying and Managing Gypsy Moth Caterpillars
Forest Management Strategies to Minimize the Impact of the Gypsy Moth
Emerald Ash Borer: The Green Menace
How to Identify, Prevent, and Control Oak Wilt
10 Ways to Protect Your Woodland Property
Field Guide to Terrestrial Invasive Plants
Firewise Around Your Home
Pests of the forest section of our publications
Fire and Firewise section of our publications

Related Websites

Univ of MN Plant Diagnostics site
Firewise website
WI DNR forest health website

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