November 2025

Urban Tree Resiliency by Mitigating Below Ground Infrastructure Techniques

Dr. Andy Kaufman and Dr. Myles Ritchie

University of Hawaii

Urban forests are essential green infrastructure components in urban areas that provide environmental, ecological, social, economic, and human health benefits. In Hawaii, especially in dense urban areas like Honolulu, trees provide tremendous benefits to the approximately 9 million visitors a year and its permanent population of around 1.4 million. This project was a multi-treatment, 9-year, below ground tree infrastructure damage study that incorporated various below ground tree root mitigation techniques (Silva Cell, Root Path, Root Barrier, and three different planting pit sizes: 3’x3’, 4’x4’ & 5’x5’) in one study. Predominately, urban tree research has been done in temperate climates, which are limited to shorter growing seasons as compared to the typical growing conditions in Hawaii which enables 2-3 times more of data collection. The project was conceived by a group of professionals representing public, private, and academic urban forestry stakeholders. The study’s main goals were to quantify and qualify below ground treatments to mitigate infrastructure damage caused by tree roots; and to provide better below ground growing conditions so that urban trees can be more resilient against extreme weather events produced by climate change.

The study saw 50 trees comprised of two species (25- Rainbow Shower (Cassia x nealiae) and 25 Kou (Cordia subcordata)) selected due to their frequent use as urban trees in Hawaii. Each of the 50 trees had a concrete pad installed on their southwest facing side to simulate the effects of a sidewalk in an urban area. Each tree had their above and below ground biomass evaluated. Above ground biomass calculations included height, diameter, live crown ratio, canopy spread, health, canopy color, tree vigor, and structural quality. Below ground biomass measurements involved excavating a pit 3 feet out from the center of each trunk to a depth of 15 inches for both the treatment (concrete pad) and control (natural state) sides of the tree. An AirSpade 2000 with a 225 cfpm nozzle and 260 cfm air compressor was used to excavate each pit. The findings from this study show that the effect of root barriers on mean root depth was inconclusive, which is in line with what other research studies have shown, although there are significant trends. The variation seen in the number of “concrete damaging” roots suggests that tree roots may be impacted by tree species, barrier type, and/or soil type. This study also highlighted issues pertaining to root barriers, particularly that roots grow through, under and over the barrier and then upwards towards the surface.

Overall, the Silva Cell treatment in this study displayed the most promise to reduce infrastructure damage caused by tree roots. The root path treatment was less effective than the Silva Cell treatment, but still better than no mitigation at all. The root barrier treatment on the other hand was ineffective in containing roots in all pit sizes when viewed from outside of the quadrat area. Furthermore, smaller planting pit sizes showed greater tree vigor than the 5x5 ft pits. These larger 5x5 ft planting pits also corresponded with lower DBH values. Future research should replicate this study with the recommended methodological changes to further verify our findings.

This research study was funded in-part by TREE Fund's 2020 Asplundh - Hyland R. Johns Endowed Research Grant Program.

Excavation of a Rainbow Shower tree using an AirSpade 2000.

Roots growing along root path.

Roots growing within Silva Cell.

Lead Donors

We are deeply grateful to the following people and organizations whose accumulated contributions to TREE Fund in 2025 recently surpassed $2,500:

Paul Karpel

KASK

Danny Lippi

Vermeer Corporation

See the full list of lead donors who make our vital tree research and education work possible on our website.

Annual report

At the meeting of TREE Fund's Board on September 4, 2025, the Trustees accepted the independent financial audit for our Fiscal Year 2024, which ended on December 31, 2024. Following in-depth fieldwork and analysis, the auditors provided an "unqualified opinion," which is the desired outcome, indicating that our audited statements fairly and accurately represent TREE Fund's financial positions and internal control systems, in compliance with generally accepted accounting principles.



With this important annual step complete, we are pleased to release our Annual Report of Activities for 2024, summarizing programmatic highlights, acknowledging lead donors, and presenting a high-level overview of our balance sheet. Click here to view the Annual Report.

TREE Fund's 2025 Free Webinar Series

We are excited to continue to celebrate the 10th Anniversary of our TREE Fund Webinar series with free webinars available to the public based on research funded by TREE Fund grants. Thanks to the Alabama Cooperative Extension System for helping us again with these videos.

Mark your calendars for our next webinars!

November 4, 2025. 2:00pm CT. (Note different time from normal.)

Optimizing Tree Responses to Root Pruning in Mature Trees

Presenter: Justin Morgenroth

Click here to register for this webinar

December 9, 2025. Noon CT.

Assessing the Mechanical, Physiological, and Carbon Accounting Effects of Different Pruning Regimens

Presenter: Stella Dee

Click here to register for this webinar

See our Webinar page for more information. https://treefund.org/webinars

TREE Fund’s 1-hour webinars are free and offer 1.0 CEU credit for live broadcasts from the International Society of Arboriculture and the Society of American Foresters. Registration and information will become available on our website approximately two weeks before each webinar date.

Missed a webinar? Watch it anytime on our website. You can also subscribe to our YouTube page.

Scholarship Follow-up

Recently, we received a note from 2025 Robert Felix Memorial Scholarship awardee, Tyler Stewart of Bringham Young University (UT).

Dear TREE Fund Board of Trustees,

I would like to say thank you for the scholarship I received from your organization. Your contribution played a part in making it possible to attend a study abroad program through my program at BYU this past summer. I took two classes, Plant Health Diagnostics and Sustainable Food Crop Systems, while traveling to seven different countries in Europe. My favorites included Switzerland, France, Austria, and Liechtenstein. It was a mind opening and life changing experience. Not only was it a lot of fun, but I learned a ton! My most valuable learning experiences in college have been outside the classroom. This was definitely one of them.

I graduate from the Plant and Landscape Systems major at BYU this upcoming April. I am excited for my next adventure in life. I am currently towards growing a landscaping business upon graduation but, I am open to whatever opportunities come my way. :-)

Thank you very much for the scholarship. I am very grateful for the work your organization does!

Thanks again,

Tyler Stewart.

TREE Fund at TCI EXPO

TREE Fund will be at the TCI EXPO next week, November 6-8, in St. Louis. Stop by our booth, #2412, to say hello, learn about the most recent research funded by our grants, and meet some of our Trustees to see how you can be more involved with everything TREE Fund does. You can also pick up one of our cool, new TREE Fund stickers.

Branch Manager to Host Raffle to Benefit TREE Fund at TCI EXPO.

Heading to the TCI EXPO? Branch Manager USA is hosting a fundraiser giveaway to help raise money for TREE Fund. One winner will receive a choice of a $500 gift card towards Branch Manager equipment or a Grab Rake attachment. Raffle tickets are $20 each or two for $35. See raffle website for details. Do not need to be present at TCI EXPO to win.

President & CEO Paul Putman Visits the ISA Annual International Conference

TREE Fund President and CEO, Paul Putman, PhD, traveled to New Zealand this October to attend the ISA Annual International Conference and shares his thoughts below.

"It was an honor to represent TREE Fund at the ISA Annual International Conference in Ōtautahi Christchurch, New Zealand, where arborists from around the globe gathered to share insights, research, and innovations in tree care. From the awe-inspiring athleticism of the International Tree Climbing Championship in Hagley Park to fantastic keynotes and educational sessions to engaging conversations and closing with a leadership workshop, the team at ISA and our NZ hosts delivered a fantastic experience.

It was my first ISA international conference outside of the United States and a key takeaway was the reminder that the research supported by TREE Fund is meaningful enough that arborists and others are willing to tune in at midnight, or 6am, or during their dinner hours to learn more through our webinar series.

I’m immensely grateful for the opportunity to connect with colleagues; celebrate TREE Fund’s mission through a general session update and as part of a panel conversation; and experience the rich culture and hospitality of New Zealand. I’m especially looking forward to building upon emerging partnerships with colleagues outside of the US. More to come in 2026!"

TREE Fund

Tree Research and Education Endowment Fund

1755 Park St. Suite #200, Naperville, IL 60563

(630) 369-8300

treefund@treefund.org

www.treefund.org

TREE Fund is a 501(c)3 nonprofit whose mission is to support scientific discovery and dissemination of new knowledge in the fields of arboriculture and urban forestry.

TREE Fund earned our 2024 Candid Platinum Seal of Transparency. Check out our nonprofit profile to keep up to date with our impact. https://www.guidestar.org/profile/shared/17bf1c65-c913-4096-8695-11f0dc3fa73f.

Keep this link handy, we want to make sure you always have the information you need to support our work with trust and confidence.

TREE Fund is proud to announce that its strong financial health and ongoing accountability and transparency has earned a Three-Star Rating from Charity Navigator. This rating designates TREE Fund as an official “Give with Confidence” charity, indicating that our organization is using its donations effectively based on Charity Navigator’s criteria.