Ice Storm Damage in the Urban Forest

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.

Why have an emerald ash borer plan?

Emerald ash borer (EAB) was first detected in North America in 2002 near Detroit, Michigan. Since then EAB has spread through South-Central Ontario, the north-eastern States and parts of the Mid-West. This has resulted in a 99.9% mortality of ash (Fraxinus genus) trees in these areas, to a total upwards of 100 million trees lost in woodlands and communities in the impacted areas. A further 10 billion trees are estimated to be at risk.

Due to ash species’ tolerance to a variety of poor conditions, it has been extensively planted as a street, park and yard tree. Additionally, the various ash species’ were able to capitalize on the resources made available through the loss of elm trees due to Dutch elm disease. They have, as a result, become an important canopy species throughout large parts of their range.


While the loss of elm trees in the countryside is devastating, the impact on urban trees is equally problematic. The abundance of ash trees as well as their large mature size makes these trees hazardous when in proximity to targets such as buildings and utilities. While your community may be impacted by the emerald ash borer, it is possible to plan ahead to minimize the impacts and even potentially save particularly important or valued landmark trees. The key is to have an effective emerald ash borer management plan.

The first step for any EAB management plan is to monitor the infestation status of your region in order to understand the working timeframe. The second step is to understand the size, proximity and frequency of ash in the landscape. This includes a street tree inventory as well an aerial woodlot assessment. Following the completion of the inventories, analysis and production of a detailed management plan can begin.

There are several proven methods of EAB management that minimize the long-term losses socially, culturally, environmentally and financially while mitigating the hazard posed to persons and property. To achieve these objectives it is necessary to:

  • Develop, commit to and execute an effective strategy
  • Modify existing policies
  • Assign clear responsibilities
  • Communicate and include private landowners and other stakeholders in the strategy

5022055A plan to achieve these criteria does not have to be expensive and case studies and predictive modelling both show that an effective, proactive management strategy is the only way to limit the long-term losses associated with EAB. Inaction is not an option with EAB. Additionally, this type of action aligns with multiple levels of government policy such as:

Federal Agencies

The Plant Protection Act administered by the CFIA, was enacted to “protect plant life and the agricultural and forestry sectors of the Canadian economy by preventing the importation, exportation and spread of pests and by controlling or eradicating pests in Canada” (Canada, 1990)

An Invasive Alien Species Strategy for Canada administered by the Government of Canada intends to “minimize the risk of invasive alien species to the economy, environment and society” (Government of Canada, 2004)

Provincial Agencies

The Invasive Species Strategic Plan administered by the Government of Ontario is intended to “slow, and where possible reverse, the spread of existing invasive species, and to reduce the harmful impacts of existing invasive species” (Government of Ontario, 2012)

Upper-Tier Municipal Government

Many upper-tier municipalities have adopted EAB strategies, and most Official Plans state social, cultural, environmental, and financial goals which are supported by EAB management.

For a recent distribution map of EAB positive locations please visit this link:

While the emerald ash borer will change our rural and urban landscapes, an effective strategy can minimize the risks to municipal property and control the aesthetic, cultural and environmental impacts on your community. For more information on how an emerald ash borer strategy can be valuable to your community please contact: Landon Black or Michael Wynia at 705-726-1141.