Understanding why a tree died can improve management of the riparian planting and aid decision making.

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Introduction

It’s normal for buffer plantings to have at least a few trees that do not survive; however, the success of the buffer depends on preventing large numbers of losses. If you notice a dead tree, it can be helpful to identify the cause(s). Understanding why a tree died can help you make different management decisions for your buffer that will prevent additional mortality. Compare your dead tree to the photos and descriptions below to help you identify the most likely reason why the tree died. Sometimes multiple factors will play a role in the death of a plant, and you might need to address several issues in your buffer to prevent the death of other trees. The best way to prevent mortality is to match tree species selections to the site conditions and to be attentive to proper planting and maintenance techniques

Ways to be certain your tree is dead

I am assessing my tree during the growing season.
There are no leaves, buds, or signs of recent growth.
The stem is not flexible and snaps easily.
A gentle tug on the tree pulls it directly out of the ground.
Scratching the bark near the base of the tree doesn't reveal any green.

The trunk of a young tree shows a small area of bark scraped off revealing green, cambium tissue. — This small bark scrape shows green cambium tissue. The tree is alive. Photo: Kristen Koch, Penn State

Causes of Death

String Trimmer Damage:

Looks like - Slices, cuts, or tangled strips of tree tube near the ground from a string trimmer.
Why it's an issue - Damage to a tree tube doesn't necessarily kill your tree but it does make your tree more susceptible to damage from wildlife, weeds, herbicide, and future string trimming activities.
Maintenance activity - Make sure all trees are sturdy, upright, marked, and protected by some type of shelter before mowing or using any power equipment on site. Be careful to avoid hitting the shelter.

The tree tube on a young tree is pulled up and damaged near the ground. The trunk of the tree that is exposed shows severe gashes and scrapes. — String trimmers can cut through tree shelters and damage the bark of the tree. Photo: Paul Duncan, Penn State Greening the Lower Susquehanna volunteer

Animal Damage (Deer- Buck Rub):

Looks like – Rub marks, shredded bark, and gouges in tree trunks. Damage will be around 1-3 feet above the ground. Will appear during the autumn months.
Why it's an issue – Small wounds will weaken the tree and could cause the tree to become susceptible to pests or disease. Rubs that go completely around the tree will kill the tree.
Maintenance task - leave tree shelters on the tree for several seasons until the tree is large enough to withstand some buck rub. Tree trunks should be several inches in diameter before their shelter is removed.

A trunk of a young tree has a large gash and damage. — Buck rub creates a wound in the tree that can encourage pests and disease, requires energy from the tree to heal, or can even kill the tree if severe enough. Photo: Cynthia Blackwood

Animal Damage (Voles)

Looks like – Chew marks from small teeth or the tree is completely severed. Damage is most often near the ground but can occur higher up.
Why this is an issue – If caught early, the small wound might just weaken the tree. If chewing was done around the entire trunk, the tree will die.
Maintenance task - Remove vegetation from around the tree to reduce habitat for these small rodents and discourage them from visiting the tree. If you notice clumps of dried grass, fur, and other materials clumped together within the tree tube, this is likely the nest of a small rodent. While damage might not yet be done to the tree, start managing surrounding vegetation more intensely to discourage the rodents from entering the tree tubes and eventually deciding to chew on the tree.

A young seedling is shown laying on top of a tree tube. The seedling has chew marks and has been completed severed from its root system. — Voles can chew on trees up to severe inches in diameter. In some cases they will completely sever the trunk from the roots as shown. Photo: Kristen Koch, Penn State

Animal Damage (Beaver)

Looks like – A tree that is not in a tree shelter has been completely severed with evidence of large teeth marks. Normally it occurs 1-2 feet above the ground.
Maintenance Task - If there is a nearby beaver population, consider planting species that are less palatable to beaver (aspen and willows are their favorite) or plant trees that are more likely to stump sprout such as maples and oaks. Many species will stump sprout when they are young.

A mature tree is chewed several feet above ground. Chunks of the tree are laying on the ground. Other trees in the background have been chewed and completely severed. — Beaver can be beneficial residents of riparian habitat but they can also destructively chew through a mature tree. Photo: Kristen Koch, Penn State

Animal Damage (Bear and other wildlife)

Looks like – Knocked over tree tubes or evidence of claw marks.
Maintenance Task - Check on your planting often so tubes can be up-righted and re-secured.

Pests and Disease:

Looks like - Small, brown, rounded lumps on your plant's leaves and stems (Pest: Scale, large numbers of the same insect or extensively damaged leaves (Pest: Insects), or spots/blotches on leaves (Disease).
Why this is an issue - Insects and disease can put stress on trees, weakening them over time and in some cases causing mortality. Without treatment, the pest or disease can spread to other plants in your planting and surrounding forests.
Maintenance Tasks - Scouting and monitoring is the best method of preventing pest and insect damage. Diseased or infested plant materials should be removed. Identifying the pest or disease will help you determine the proper treatment and replanting protocol. The Penn State Plant Disease Clinic can help with identification.

A section of a young seedling is shown with scale. — The raised, round bumps on this tree's trunk and branches are scale, an insect pest. Photo: Jennifer Fetter, Penn State

Poor Planting Technique

Looks like – roots above the soil, planted too deep with root flare buried in the soil, sunken planting holes, or if plant can easily be pulled out of the ground and the roots are in a small ball about the size of the pot they were in before planting or the roots are bent and pointed upwards.
Why this is an issue – trees need to be planted properly for maximum soil contact, to prevent the roots from drying out or suffocating, and to prevent root girdling.
Maintenance task - It’s important to plant trees at the proper depth, right at the root collar, with root flare exposed. All roots should be oriented downward and flaring outward under the ground, for maximum soil contact. Light root pruning may be helpful, depending on the site and species.

A young seedling planted with roots above ground will very likely die because those roots will dry out and are unable to soak up moisture or nutrients. Photo: Kristen Koch, Penn State

Wrong Plant, Wrong Place

What it looks like - If you notice that certain species or that certain locations within the buffer are not thriving, this may indicate a poor species selection for that area. Some additional clues include very limited evidence of roots, large and obvious cracks in the soil surface (mud cracks, desiccation), saturated and often wet soils (soils might be gray in color), a walnut tree located near the dead tree, paved surfaces that receive winter salt application that drain to the area, yellow or mottled leaves.
Why this is an issue – each species has preferred growing conditions and certain tolerances for sunlight and shade, soil moisture, soil nutrients, walnut juglones, salt, and more. If their needs aren’t met, they will struggle to survive.
Maintenance task - you may want to test the soil and observe conditions such as sun vs shade, wind, soil moisture, adjacent walnut trees or proximity to winter deicer applications, and consider choosing species more tolerant of those specific site conditions.

Improper Herbicide Usage

What this looks like - part of the tree was growing outside of the tube. Herbicides were effectively used around the tube made obvious by nearby dead vegetation. The tree is now dead or dying.
Maintenance task - Tree tubes are much more effective than cages at preventing accidental herbicide contact. If a portion of a tree (such as a leaf, sucker, or individual branch) is accidentally sprayed while applying herbicide, you can immediately prune off the affected area and remove it to prevent greater damage to the entire tree.

Poor Weed Management

What it looks like - vines growing over shelter/tree and/or weeds growing inside the shelter
Why this is an issue - Allowing weeds to grow will result in high competition with the trees. Weeds can shade out, steal nutrients and water from, and strangle planted trees. Unmanaged weeds can also create habitat for voles, cause tubes to get knocked over from the weight of the vines, and cause other maintenance problems.
Maintenance task - Managing weeds is one of the most important maintenance tasks. Weeds can be managed using mowers, herbicide, hand-pulling, mulch, and other methods. Be very careful not to damage the tube and tree while using any of these methods. If you have not had success managing weeds, you may need to try new methods, using the lifecycle and growing conditions of the weeds to target your management approach This task is critical and cannot be ignored.

A tree tube has a tree growing straight up out of it and a weed draping out over the side of the tube. — Unmanaged weeds will grow faster than the tree stealing water, nutrients, sunlight, space, and can even strangle the tree. Photo: Sarah Xenophon, Penn State

Weather Event Damage

What it looks like – Knocked over shelter, frost heave, debris piles next to or on top of tree shelters, washed away shelter, recent flooding.
Why this is an issue – wind, flooding, freezing soils, and other weather events can cause significant damage to planted trees. Most of the time the weather event itself won’t kill the trees but the lack of maintenance to fix the issues immediately after the event will lead to the death of the trees.
Maintenance task - Plan ahead, and don’t wait until after a harmful event has occurred to create a plan. Visit your buffer as soon as possible after a damaging weather event, to ensure that trees and shelters are in place, upright and properly seated in the ground, large debris is removed, and uprooted trees are replanted.