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Departments » UW Extension » Urban Horticulture & Natural Resources
General Information

Welcome to Brown County UW-Extension's

Urban Horticulture
Natural Resources Pro


Article of the Week
(Originally published in the Green Bay Press-Gazette on June 18, 2017)

Why Trees Fail During a Storm
Removing damaged trees, broken branches, and debris after stormy weather is a tedious task and can be expensive. Oftentimes, examining the damaged trees can provide a better understanding on the cause of its failure. Three common factors for a tree’s failure during severe weather are weak branch unions, decayed wood, and root problems.

Weak branch union:

When examining a tree, look beyond the canopy’s foliage health and asses its entire architecture form and the union of the branch to its main/lateral stem. A mature leaning tree (40 degrees or more) can be a major cause of concern, as it creates a structural imbalance in its architecture and is likely to fail. These trees should be removed from the property before the next major storm occurs.

Branching structure of a tree is largely determined by the tree’s natural growth habit. A tree with good branch unions can resist windstorms and has the ability to withstand snow loads. A strong branch union to its main or lateral stem is characterized by a broad branch angle (‘U’ shaped union) and has an upturned branch bark ridge (a strip of raised bark between the branch and main stem union). A weak branch union occurs when a branch and stem (or co-dominant stems) grow closely together where the bark is formed inside a tightly narrow union (‘V’ shaped union) and is termed as “included bark”. As the trunk and the branch grow, the narrow union between them becomes weaker and is more prone to failure. Nearly one-fourth of urban trees that fail during a windstorm are due to a weak branch union. Corrective pruning at its young stage can prevent weak unions. Lindens, silver maple, boxelder, Freeman maple, red maple, Callery pear, hackberry, and willow are well known to develop poor branching structure.

Decayed wood:

When a tree is wounded (lawn mower/vehicle damage to the bark, improper tree pruning, vandalism), decay-causing fungi penetrates into the internal wood and destroys the tissues. This weakens the structural stability of the tree over a period of time and causes the tree’s failure. Common signs and symptoms of decayed wood are hollow holes, rotten wood, mushrooms, conks, bulges, and large cracks. If more than 40 percent of the tree trunk or its branches show an indication of decay, then the risk of the tree’s failure is high.

Root problems:

Heavy rain accompanied by high winds can uproot and topple large, mature trees and is referred to as wind-throw effect. But have you wondered why certain trees are uprooted whereas a neighboring tree seems to be fine? Certain tree species (willows, poplars, cottonwood, Norway maple) have shallow root systems that are naturally vulnerable to wind-throw effect. When the ground becomes soft and saturated with moisture from heavy rain, the succeeding wind can easily lift the shallow roots and blow down the tree. Other factors that can contribute to wind-throw effects are construction damage to its main root system, and confining the root spread by trenching or installing landscape edging materials deep into the soil.

Identifying these common tree defects and addressing the issues can ensure your property safety associated with trees and can prolong a tree’s life span. Tree health and risk assessment are best done by a certified arborist and should be done on a routine basis. To find a list of certified arborists, visit

V-shaped branch union leads to included bark formation, causing poor branch union.

U-shaped branch union indicates a strong branch union.

Internal decay leads to collapse of the tree during windstorm. Hollow wood, mushroom and conk growth on the bark, and oozing sap are indicators for internal decay issues.

For horticulture-related questions and advice, contact Brown County UW-Extension’s Horticulture Help Desk at 920-391-4615 or


2017 All-America Selection Vegetable Winners
After extensive plant field trials across the country, All-America Selections (AAS) announces the best performing vegetable winners for this year. These winners are selected based on their trial garden performance in North America for fruit quality, yield, pest and disease resistance, and overall growth. You can find the seed sources of these
award winning varieties at Click here to learn more about this topic.


Horticulture Help Desk Services
We offer free consultations on lawn care advice, insect and disease diagnosis, and plant and insect identification. We also address tree and shrub problems as well as help you select the plants that are best suited to your needs and site. Soil tests and advanced diagnosis services are available for a fee.

Bring your live or digital specimen to the Horticulture Help Desk:

210 Museum Place, Green Bay, WI 54303
Hort Help Desk Phone: 920-391-4615

The UW-Extension Office is open Monday through Friday from 8 AM to 4:30 PM.
If a horticulture staff member is not available when you call or visit, messages and samples can be left with UW-Extension reception, and a staff member will contact you.

We are here to serve you by connecting the University system, Master Gardener volunteers, and you - Northeast Wisconsin residents - to help things grow.

Contact:  Vijai Pandian - Horticulture Educator
Phone: 920-391-4611
Fax: 920-391-4617
Click here to email
Mailing Address:  Brown County UW-Extension
210 Museum Pl
Green Bay, WI 54303
Hours:  Monday - Friday, 8 AM - 4:30 PM
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