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Impervious surface thresholds to select planting sites

Steve Frank1 & Adam Dale2

1North Carolina State University1, University of Florida2

 

The amount of impervious surface cover within a 25m radius around a tree or planting site can predict gloomy scale abundance and red maple condition. But how much is too much? Long story short, trees surrounded by 0-32% impervious surface tend to be in good or excellent condition with few scales. Trees surrounded by 33-62% impervious surface tended to be in fair condition with more scales. Trees surrounded by more than 62% impervious surface cover were in poor condition with severe scale infestations.

So now we have impervious surface thresholds but how do you measure impervious surface cover? We developed the ‘Pace to Plant’ technique to quantify the amount of impervious surface surrounding a tree or planting site in five steps.

 

Step 1. Stand at the planting site and identify the closest impervious surface edge. In this picture it is the curb right of the tree. Take 25 steps at 45o to the nearest impervious edge, counting the steps that land on impervious surface (white footsteps in figure).

 

Step 2. Turn 90o from the initial transect. Take 25 more steps counting those that fall onto impervious surface.

 

Step 3. Take 25 more steps, 90o to the previous transect, counting the steps that fall onto impervious surface.

 

Step 4. Take 25 more steps, 90o to the previous starting point, counting those that fall onto impervious surface. This is the final leg, making an ‘X’ through the planting site and totaling 100 steps taken.

 

Step 5. The total number of steps that fall onto impervious surface equals the percentage of the surrounding ground area that is impervious to water. Using the impervious surface thresholds, this percentage can guide tree selection decisions. In the figure, 66/100 white footsteps landed on impervious surface, meaning that 66% of the area within the circle is impervious. This is not a good planting site for red maples.

 

            Impervious surface thresholds and the ‘Pace to Plant’ technique are one approach to inform where to plant red maples and to predict which established red maples may require extra care.

 

Get the full story: Dale, AG, Youngsteadt, E and Frank, SD. 2016. Forecasting the ffects of heat and pests on urban trees: Impervious surface thresholds and the ‘Pace to Plant’ technique. Arboriculture & Urban Forestry.

 

Detailed extension material: http://ecoipm.org/pace-to-plant/