Minimum Soil Volumes for Trees Part 1: Lessons Learned from Municipalities

Trees need an adequate volume of rootable, oxygen-rich soil to thrive, and minimum soil volume policies are a powerful tool for arborists and other advocates to leverage better growing conditions for trees, especially in urban areas.

In preparation for Peter MacDonagh’s presentation at the 2012 ISA conference in Portland, OR, “Leveraging Healthy Urban Forests with Minimum Soil Volume Policies,” we did an informal survey of cities with minimum soil volume standards to shed light on how these policies came to be, what resistance had to be overcome to enact these policies, how that resistance was overcome, as well as strengths and weaknesses of the policies.

We wanted to learn as much as we could from those on the forefront of setting minimum soil volume policy, and our hope is that what we learned, and what we’re sharing here, can help people who are just beginning to consider this solution in their own cities and towns.

To start, we knew of 18 municipalities that had minimum soil volume policies for trees, so we sent out 18 surveys. Filling out our survey was a bigger time commitment than just filling out multiple choice questions, so many thanks to the 8 people who responded! We  asked the following open-ended questions to allow participants to share their unique experiences:

  1. What are your agency/organization’s standards, codes, or recommendations regarding minimum soil volumes for trees? Please specify which of these are required vs. recommended.
  2. What specific obstacles were encountered in establishing your minimum soil volume requirements?
  3. How were those obstacles overcome?
  4. Who had to be involved in order for it to make it through the approval process?
  5. What year were your minimum soil volume standards enacted?
  6. How long did the process of setting soil volume standards take, from beginning to end?
  7. What prompted the development of your soil volume standard?
  8. What have you learned since these standards were enacted?
  9. What has worked well?
  10. What would you do differently?

Some of the highlights of the answers we received were:

  • The most common obstacles encountered in establishing minimum soil volume standards were cost and conflicts with utilities.
  • By far the most common answer to the question “How were those obstacles overcome?” was through education.
  • Many different parties had to be involved for soil volume standards to make it through the approvals process. Answers to the question “Who had to be involved in order for it to make it through the approval process?” included Planning, Engineering, City Council, Public Works, Environmental and Maintenance staff, Economic Development, City Attorney, City Manager, Building and Planning, Developers and Chamber of Commerce, Residents who care about trees, Urban Design town staff, Street Transportation LA’s, Operations, Corporate Communications, Development Services, Fire, Consultants
  • Answers to the question, “What would you do differently?” included:
  1. Have more standard details and design guidelines to give to developers
  2. Education
  3. More effective communication with other municipalities
  4. Push harder
  • Standards of all the municipalities that responded have been enacted fairly recently. The oldest standard was enacted in 2007/2008; many were only enacted in the past 2 years.
  • The process of setting soil volume standards takes time. Answers to the question “How long did the process of setting soil volume standards take, from beginning to end?” ranged from 6 months to 5 years.

Part II: Research Versus Implementation

Image: edoration

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