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Hazard trees

Hazard trees are trees that can be dangerous because of the possibility of them falling over or breaking and dropping large branches to the ground. Most trees are considered hazard trees if they are dead and over an area where there are people or property. Some trees are more hazardous than others though, even when they are alive, because of the type of soil they grow in or because they are easily attacked by fungus or insects.

Defects commonly seen on trees native to Wisconsin forests


Species Life expectancy (years) Defects
Ash (black) 200-300 Weak unions. Uprooting (black ash is most abundant in moist locations and along low banks of streams where uprooting is more likely to occur).
Ash (green and white) 100-120 Weak unions. Dead branches in the upper and outer crown.
Aspen (big-toothed and quaking) 60-90 Extensive decay from canker-rot Phellinus tremulae. Stem breakage due to infection by hypoxylon and other cankers. Rapid decay.1
Basswood 150-200 Weak unions from both branch unions and stump sprouts.
Birch (white and yellow)
White: 70-110
Yellow: 150-250
Extensive decay from canker-rot Inonotus obliquus. Stem breakage due to the presence of nectria canker. Rapid decay.1
Box Elder 70-100 Weak unions.
Butternut 60-75 Branch breakage due to the presence of butternut canker.
Cherry (black) 120-150 Dead branches throughout crown.
Cottonwood (eastern) 70-120 Dead branches throughout crown. Rapid decay.1
Fir (balsam)
70-100 Uprooting or lower stem breakage may occur as a result of root rot or decay of the root collar region. Balsam fir frequently has a shallow root system. Rapid decay.1
Maple (red and sugar)
Red: 80-140
Sugar: 150-250
Weak unions. Dead branches. Stem breakage due to the presence of eutypella and nectria cankers. Cracks.
Oak (black and northern pin)
Black: 150-200 Extensive decay from canker-rot Phellinus everhartii. Weak unions. Cracks. Dead branches in lower crown from natural branch mortality and upper crown from several factors causing dieback. Dead trees may be common due to oak wilt and two-lined chestnut borer.
Oak (red) 400 Dead branches (see black oak). Dead trees (see black oak).
Oak (white) 300 Extensive decay (see black oak). Dead branches (see black oak).
Pine (jack)
60-100 Extensive decay from canker-rot Phellinus pini. Rapid decay.1
Pine (white)
200-300 Extensive decay from canker-rot Phellinus pini. Dead branches in lower crown due to natural branch mortality. Dead tops due to presence of white pine blister rust canker.
Spruce (white and black)
White: 100-200
Black: 150-200
Uprooting – particularly true on wet sites; spruces tend to be shallow rooted.

1 Rapid decay denotes species that are likely to decay quickly if in a state of decline from numerous other initiating factors.

Last revised: Thursday July 30 2015