With the general consensus being that ice storm occurrence is increasing as an unwelcome benefit of climate change, a significant risk is posed to the value of urban forests. Significant costs are typically associated with the clean-up and removal of trees as well as the incidental damage to property. These costs are evident in mainstream media because they are easily quantified.
Environmental and social costs are more difficult to assess, but even a cursory analysis demonstrates that they dwarf the typical valuation. Toronto’s urban forest has been valued at $7 billion and estimated to return $80 million in environmental benefits (Alexander & McDonald, 2014). This translates to a $125/household valuation (Alexander & McDonald, 2014). This valuation suggests returns of $1.35-$3.20 per dollar invested in annual maintenance (Alexander & McDonald, 2014). Beyond this are the numerous mental and physical health associations with the urban forest estimated into the billions. The urban forest thereby represents a significant investment in the city itself and the negative effects of ice storms are a significant threat.
In recognition of this threat there are certain species that preform better in ice storms. Research shows that there is no correlation between specific gravity, modulus of rupture or modulus of elasticity in the prediction of ice storm damage (Hauer et. al., 1993). The most effective determinant of damage is branch coarseness. Trees with fewer, larger branches (high volume to surface area) fared much better than finely branched species (Hauer et. al., 1993). Additionally, excurrent trees preformed better that decurent trees (Hauer et. al., 1993).
Of course ice storm susceptibility is only one consideration in the management of and urban forest but research is emerging that will help understand the risks faced.
Table One: Ice Storm susceptibility/resilience by species (Hauer et. al., 1993)
|Susceptible Common Street Trees
(Worst to Best)
|Resistant Common Street Trees
(Best to Worst)
|Ulmus pumila (Siberian elm)||Gymnocladus dioicus (Kentucky coffeetree)|
|Gleditsia triacanthos (honey-locust)||Tilia tomentosa (silver linden)|
|Pyrus calleryana ‘Bradford’ (Bradford pear)||Thuja occidentalis (eastern white-cedar)|
|Celtis occidentalis (common hackberry)||Quercus bicolor (swamp white oak)|
|Quercus palustris (pin oak)||Ginkgo biloba (ginkgo)|
|Plantanus occidentalis (sycamore)||Quercus rubra (red oak)|
|Fraxinus pennsylvanica (green ash)||Quercus alba (white oak)|
|Liriodendron tulipifera (tulip-tree)||Tilia cordata (little-leaf linden)|
|Fraxinus americana (white ash)||Liquidambar styraciflua American sweetgum)|
|Acer saccharinum (silver maple)||Acer rubrum (red maple)|
Alexander, C., McDonald, C. (2014) Urban Forests: The Value of Trees in the City of Toronto. Toronto: TD Economics.
Hauer, R., Wang, W., Dawson, J., (1993) Ice Storm Damage to Urban Trees. Journal of Arboriculture. 19(4) pp 1-15.