Root Pruning Saves Trees!

I worked for Friends of the Urban Forest (FUF ) from 1999 to early 2008. During that time it was not uncommon for street trees to reach a certain age, 5 to 7 years, and then just blow over in the wind. The tree was too big and heavy to be supported by stakes, but the roots had never developed because of root defects, caused by nursery containers early in life. Every winter storm generated hundreds of calls for downed trees and many could not be saved. 

This root wrapping around the trunk began circling in a long-ago nursery container. If it is not removed soon, it will cause problems for the tree.

Around 2000 we began inspecting nursery stock and rejecting trees with really problematic roots. Around 2002 we began root pruning 18-month and 3 year trees at maintenance visits to correct circling roots found within the top few inches. In late 2007, we began extensive root pruning at planting as recommended by Dr. Ed Gilman and Brian Kempf. 


4 years later, this recent article, written by my successor, notes how the new planting method has improved tree rooting and reduced emergency “downed tree” calls. The data is there, so inspect and root prune your young trees.  Who wants to lose their tree 5 years after planting?

Tree Care Chronicles

Root pruning saves trees

by Heather Ellison, Tree Care Manager

Rainy and windy days used to keep me busy taking calls about downed trees and dispatching volunteer Emergency Tree Care crews.  Today, such days cause far fewer problems.  We have Ed Gilman at the University of Florida to thank!

Arborists once thought that when planting container-grown trees, we should massage the root ball, pulling away the outer circling roots and removing the root mass on the bottom. Root defects such as circling or kinked roots deep in the root ball were largely left untouched. Over time the problem roots would fail to grow out—leaving the trees unstable and vulnerable in storms—or they would impair the flow of water and nutrients to the tree, weakening it and making it more susceptible to pests and diseases.

Professor Gilman and Brian Kempf, director of the Urban Tree Foundation, showed that when tree roots are pruned, aggressively if necessary, the trees usually establish much faster, are far more stable and produce more feeder roots than un-pruned trees.  We have increasingly embraced this practice, and now it is the rule rather than the exception.

The results have been astounding.  Our trees are often firmly rooted six months after planting, and our emergency calls for fallen trees have dropped dramatically. 

For more info about Professor Gilman and his research projects, visit http://bit.ly/edgilman.  For more info on container-grown trees and root establishment, see http://bit.ly/containertrees.

Municipalities That Are Doing More for Trees

In the day-to-day, we can become so focused on what isn’t working with the way we design and plant street trees that it can be difficult to focus on the people and places that are actually doing right by them. It’s just so much easier than trying to move the needle.

To that end, I want to recognize the envelope-pushers — those municipalities that are rethinking the vital role trees play in the health of our planet and population and creating rules and recommendations to support them. They take action every day by promoting policies and projects that set trees up for long-term success and environmentally meaningful contribution.

Along with my colleagues, I've identified the following communities for their ambitious policies that are redefining requirements for green utilities, specifically for trees, soil and stormwater management:

• Toronto’s Green Development Standard – Perhaps the most ambitious initiative we’ve yet seen, the City of Toronto calls for street trees to get a minimum of 15 m3 (529 ft 3)of high quality soil per tree if in a shared planter, and a minimum volume of 30 m3 (1,059 ft3) of soil per tree if in a single planter.

• Baltimore Waterfront Healthy Harbor Initiative – This initiative sets an example for increasing the tree canopy as a way to preserve the environment and manage stormwater. Using permeable paving, landscaping, rain gardens, and green roofs, it asks for sites to filter more than 50 percent of stormwater runoff from areas and install at least 1,500 cubic feet of soil for tree pits using structural soils or suspended pavement for any new impervious surfaces or retrofit/redevelopment projects.

• University of Florida (IFAS Extension) – The project created an Urban Design for a Wind Resistant Urban Forest. Planners increased the soil and depth requirements to allow trees to mature and live longer using the following guidelines (soil area based on mature tree size, 3’ deep or greater):
  Small (shorter than 30’) = 10’x10’x3’ = 300 ft3
  Medium (Less than 50’ height or spread) = 20’x20’x3’ = 1,200 ft3
  Large (Greater than 50’ height or spread) = 30’x30’x3’ = 2,700 ft3

• West Virginia Department of Environmental Protection – The community created a municipal handbook to manage wet weather through specific green infrastructure and made the following soil recommendations:
  Large tree = 970 ft3
  Medium tree = 750 ft3
  Small tree = 500 ft3

• Athens-Clarke County, Georgia – The community created best management practices for community tree planting and soil volume minimums:
  Small Canopy: 100 square feet x 2’ deep = 200 ft3
  Medium Canopy: 225 square feet x 2’ deep = 450 ft3
  Large Canopy: 400 square feet x 2’ deep = 800 ft3

• State of Minnesota Sustainable Building Guidelines (MSBG) – Where trees are planted in hard surfaces, the community uses a structural soil media mix of minimum soil volume of 500 cubic feet (cf) per tree. If soil volumes cannot be met it is recommended that trees be planted in minimum 8′ wide by approximately 3′ deep trenches so that soil volumes are shared between trees.

• Charlotte, North Carolina & Mecklenburg County – Planners amended the planting area requirements and recommendations for commercial development to increase the absolute minimum soil volume and planting area to 274 square feet per tree. The minimum width of the planting area is 8’ at the trunk of the tree.

• British Columbia (Canada) 7^th Edition BC Landscape Standard - Recommended minimum soil volume per tree of 6m³ (212ft³), and more is better.

• Markham, Ontario “Trees for Tomorrow: Streetscape Manual”  – These design guidelines make the following soil volume recommendations:
  Large stature tree in boulevard = 30 cubic meters/1,059 cubic feet (if single) or 15 cubic meters/530 cubic feet (if shared) of root space
  Medium stature tree in boulevard = 23 cubic meters/812 cubic feet of root space
  Small stature tree = 15 cubic meters/530 cubic feet root space
  Minimum soil volume for tree planting in a parking lot island is 15 cubic meters/530 cubic feet.

• Aspen, Colorado & Pitkin County – The community amended its structural soils specifications so that soil area is now based on a targeted mature tree size, requiring 30 inches or more depth and a correcsponding increase in soil volume.
  Soil area based on mature tree size, 30” deep or greater
  Small (shorter than 30’) = 10’x10’x2.5’ = 250 ft3
  Medium (Less than 50’ height or spread) = 20’x20’x2.5’ = 1,000 ft3
  Large (Greater than 50’ height or spread) = 30’x30’x2.5’ = 2,250 ft3

• Chicago Landscape Ordinance – The city amended planting standards and now requires parkway trees to have a minimum depth of three feet of soil. Planting areas require a minimum of 24 square feet of surface area with no dimension less than three feet.

• Denver Parks and Recreation Forestry Department – The city’s “Street Tree Plan Review Checklist” sets a soil volume minimum of 750 cubic feet of soil per tree and states that, “5’ x 5’ pit areas shall no longer be accepted, must use trenches, root paths, break out zones, structural cells, or other un-compacted soil technology.”

• Emeryville, California - The community requires minimum rootable soil volumes for new trees planted in the public right of way by private developers. The minimum is based on the size of the tree at maturity: 600 cubic feet for a small tree, 900 for a medium tree and 1200 for a large tree.

• Alexandria, Virginia – The city’s Landscape Guidelines specify that street trees be provided with a minimum of 300 cubic feet of soil per tree and recommends that one tree be present for every ten spaces in parking areas.

Are any of these perfect? Probably not. Certainly there are things I would change about almost all of them. Still, setting soil volume minimums for street trees tacitly enforces the message that business as usual as far as tree planting is concerned isn’t good enough. We need to rethink how we plan for our urban forests and the role of green infrastructure in the built environment. The new game in town is high performance urban forestry.

Are you involved with making soil volume recommendations for trees? Hopefully you can use some of this information to help persuade your co-workers and clients of this important effort.

Should your city or town be on this list, or do you know of any others that we missed? I want to hear about your goals for growing healthy trees in your community. Please email me at RethinkTrees@deeproot.com.

This post was originally published on Green Infrastructure for Your Community.

A Year on Cherry Street...early spring (February)

I take care of a garden in San Francisco that belongs to my mother's cousins. Their mom, my great-aunt Marcy, was a tiny lady with a huge spirit. She went to UC Berkeley in the 1920s and was one of the founding members of Planned Parenthood. I was lucky enough to stay at this house with Aunt Marcy in 1994 and get to know her more. She loved this garden and did something in it every day even into her 90s. Here she is studying the central bed which is now dominated by a large lilac shrub.

The paving stones are actually recycled broken-up concrete. This was installed in the mid-20th century sometime. You have to watch your step or you'll trip over one. Marcy's son John tells me there used to be a mobile chicken coop back there in about the 1940s-50s. He built it with no bottom and moved it around the yard every few days so the poop would fertilize the soil. I'm not sure if that was before or after the paving stones went in. It's clear that my family had a "green" sensibility long before it became fashionable...

Every season, something different is in bloom. Knowing Aunt Marcy, I'm sure she planned it that way. However, many of the plants are naturalized - they spread to places they were not planted - by seed, (foxglove), underground runners (strawberry) or multiplying bulbs (Spanish bluebell). So every year flowers and plants pop up in unpredictable places. I sometimes help this along by shaking seeds or transplanting bulbs into locations that seem to need it, but truth is the garden doesn't need my help in this regard.

Here's what's blooming in February:

Pink-flowering current (Ribes sanguineum) Planted after Aunt Marcy's time. This shrub had to be dug up and replanted when a large tree came out next to it a few years ago. I'm happy to say it has recovered with a vengeance!

Camellia and azalea on the right (probably planted by Aunt Marcy), small geraniums on the left.

Mystery bulb - anyone know what it is? It doesn't spread, but the one plant comes back nicely every year.

An elderly fuschia...I tend not to remove plants unless they are completely dead or causing a problem...

A hidden hellebore treasure - I have to keep the surrounding foliage pruned out of the way so this baby is not totally overrun.

Registered Consulting Arborist! and why you should care...

Yeah, I'm so, like, an RCA now. What? Well, I just completed the Registered Consulting Arborist (RCA) requirements put together by the American Society of Consulting Arborists (ASCA) Never heard of it? You're not alone. It's an achievement, but it's hard to brag about without some explanation. Come on, let me tell you, it'll just take a minute....

An arborist is a tree specialist. A Certified Arborist has passed a 200-question exam on a wide range of topics including soils, tree biology, climbing and safety. It's the entry-level certification in our industry. If you want a tree pruned, removed or planted, a Certified Arborist is often your best bet.

A consulting arborist applies their knowledge and experience to complex tree issues including protecting trees during construction, assessing hazard trees and legal cases. We give advice, usually in writing. In addition to understanding trees, we have to be good technical writers. We have to be clear, concise, logical, interesting and knowledgable....sure, no problem.

I passed the Certified Arborist exam in 2000. Being a Certified Arborist doesn't give you all the skills necessary to be a consultant, so going through the RCA requirements helped a lot. Here's what I had to do:

1. Have a certain amount of education and experience to even apply in the first place.
   
2. Attend and graduate an intensive 3-4 day seminar called the Consulting Academy. Here we talk about report writing, consulting ethics, running a consulting business, etc. We also have to pass an exam and write 2 sample reports that are graded. A passing grade for the reports is a 75.
   
3. After graduating the Academy, you could stop there. Many consultants do. But if you want to go on to become an RCA, you have to write 2 more reports for grading.

This whole process took me about 2 years after graduating the Academy. Some people take less time. Some people never get around to it. There's no time limit, therefore no deadline to finish the additional reports.

Why did I do it? I write a lot of arborist reports at work and wanted to take advantage of the learning opportunity. A course in technical writing could have been helpful, but I wouldn't have learned as much about the consulting business that way.

 Many of my arborist colleagues say things like, "When I get too old to do all this physical work, I want to be a consultant." But you can't make the switch that easily. Climbing, pruning and running a tree service business don't prepare you for writing technical reports and all the paperwork that consultants have to deal with. So if you want to be a consultant, start learning while you're still young. Go to the Consulting Academy. If you have the opportunity to work for an experienced consultant, do so.

And if you are hiring an arborist, be aware what kind of an arborist you need to hire. Ask them about their qualifications. Many situations requiring an arborist report specify that it must be written by a Certified Arborist. But an RCA or a Consulting Academy graduate is more likely to produce a well-written, easy-to-read report with high-quality information. On the other hand, the RCA program didn't teach me anything about taking out that big dead oak tree in your yard,

Well, thanks for celebrating with me. One day everyone will know what an RCA is. I guess it's up to us RCAs to raise our own profile. Maybe you can help...