Which Trees to Save? Industry Standards and Best Management Practices can help you make smart choices.
Is it possible?Above: code said 36” path of travel, the city (T.O.) said save the tree.
Recently a client was directed by a design review committee to “save as many trees as possible.” He came to me to ask what was possible. Fortunately there are industry standards to guide us.
The written standards and best management practices are voluntary. These are consensus standards representing scores of organizations like the USDA Forest Service, Davey Tree, ISA, ASLA and many others.
The standards and BMP’s help arborists and landscape architects decide when to hold ‘em and when to fold ‘em. Any tree can be saved given a big enough budget ($3 million for a Hong Kong Fig tree). The question isn’t what’s possible but what is feasible? What makes sense?
One of my favorite tools when deciding which trees to preserve is a 100 point evaluation guide in Fite’s BMPs. (p8) This guide helps me rate trees in eight categories that predict long-term survival or rapid decline.
General Conservation Suitability Worksheet
- Distance from Trunk to Root Cut/Fill
- Construction Tolerance by Species
- Age (Relative to typical lifespan)
- Distance from Trunk to Construction
- Soil Quality/Tolerance
- Species Desirability
This worksheet can save time by focusing your attention on the trees that are close calls. Using an electronic spreadsheet, you can quickly sort out which trees are sure to go and which are likely survivors.
General Conservation Suitability Worksheet + Plus AppraisalAbove: the potential for long-term survival compared in a spreadsheet.
By the time the arborist or landscape architect gets involved the engineer has probably already made the decisions that will determine the fate of most trees on the site. Trees growing in the footprint of proposed buildings and streets can’t be preserved in place and unless they are extremely valuable specimens, it seldom makes sense to move them.
A tree appraisal can help when deciding the feasibility of moving a tree or altering the site plan. An appraisal method like the Trunk Formula values a tree by taking into consideration all of the contributions a tree makes to a given site. If a tree is worth $200 that’s an easy decision. If a tree is worth $50,000 it deserves more scrutiny.
If the engineer or architect knew the value of the trees up front, it could help them design the site. I use AutoCAD to analyze the high value, close call trees like the cedar in the screen grab below.
Using Cad to examine is it possible?Above: CAD analysis needs an accurate survey.
Conservation Suitability Spreadsheets and CAD analysis are excellent guides to help owners, planners and designers decide what is feasible when it comes to tree preservation. But sometimes even experts can’t tell what will happen until you open the ground and see the roots.
It was feasibleAbove: five years later the sycamore is still shading the playground.