Webinar Date: January 15, 2026 Speaker: Dr. Ryan Klein, Assistant Professor of Arboriculture, University of Florida Moderator: Dr. Bodie Pennisi, Horticulturist, University of Georgia Duration: 51:30 Series: Getting the Best of Pests — Green & Commercial CEU Categories: Pending assignment
Dr. Ryan Klein, assistant professor of arboriculture at the University of Florida with 12 years of industry experience, presented a comprehensive overview of best management practices for establishing and maintaining urban trees throughout their lifespan. His presentation addressed the full arc of urban tree care, from nursery stock selection through mature tree management, with emphasis on proactive planning and site design.
Klein opened by contextualizing the challenges facing urban forests, citing Florida population projections showing the state doubling to nearly 40 million by 2070 and a third of its land area becoming developed. He connected this development pressure to climate change data, noting that hardiness zones for Athens, Georgia have already shifted from 7B to 8A and are projected to reach 8B by the end of the century, which has direct implications for species selection. He also discussed hurricane impacts on urban canopy, referencing the Duryea et al. (2007) study ranking 76 species by wind resistance and a 2023 FEMA document by Koeser and Salisbury covering 281 species.
A central theme was "right tree, right place," with Klein stressing that trees generally do not provide net benefits until approximately 25 years after planting, making species-site matching critical to avoid costly replacement cycles. He introduced the Florida Trees website, an online tool with over 1,100 species fact sheets that guides users through site evaluation to identify suitable species for hardiness zones 8 through 11.
Klein devoted substantial time to planting site design, explaining that mature live oaks with a 69-inch DBH require approximately 16-foot-wide planting strips to accommodate trunk flare and lateral root development, based on research by Dr. Andrew Koeser. He highlighted creative design solutions including structural soils, suspended sidewalks, and Silva Cells that accommodate root growth while preventing infrastructure conflicts.
The presentation covered planting procedures in detail, including proper planting depth, root defect correction through root ball shaving rather than radial slicing, appropriate mulching practices of two to three inches in a six- to eight-foot ring, and the importance of structural pruning to establish a dominant central leader. Klein concluded with a brief overview of his current research, including studies on nursery grading standards, biochar soil amendments, tree spacing, irrigation, large tree moving, and pruning.
0:00 Introduction and Speaker Bio 1:09 Urban Tree Best Management Practices Overview 4:04 Population Growth and Development Pressures 5:44 Climate Change and Shifting Hardiness Zones 9:36 Hurricane Impacts on Urban Forests 12:47 Urban Stressors and Reduced Tree Lifespan 14:24 Right Tree, Right Place 17:04 Site Evaluation for Tree Planting 20:00 Small Planting Spaces and Common Mistakes 22:37 Trunk Flare Research and Planting Strip Width 25:39 Tree Spacing and Wind Resistance 28:37 Nursery Stock Grading Standards 30:33 Florida Trees Online Species Selection Tool 34:00 Planting Procedures and Root Ball Preparation 37:58 Root Defects, Soil Amendments, and Mulching 41:03 Structural Pruning Principles 45:18 Managing Mature Trees 48:04 Current Research at University of Florida 49:13 Audience Discussion and Closing
Q: Why is "right tree, right place" so important from an economic standpoint? A: According to Dr. Klein, urban trees typically do not provide net benefits until approximately 25 years after planting. If trees are constantly being replaced every 15 to 20 years due to poor species-site matching, communities are paying out labor, materials, and maintenance costs without ever receiving the long-term environmental and economic returns those trees could provide.
Q: How are hardiness zones expected to shift in the Southeast over the coming decades? A: Klein referenced data from Davey and the Arbor Day Foundation showing that Athens, Georgia has already shifted from hardiness zone 7B (around 1980) to 8A currently. Projections indicate it could reach 8B by the end of the century. He also cited a University of Maryland tool predicting that Athens' climate in 60 years will resemble Kaplan, Louisiana. He cautioned that while this expands the potential species palette, minimum cold temperatures remain the critical limiting factor for planting decisions.
Q: How wide should a planting strip be for a large shade tree like a live oak? A: Research by Dr. Andrew Koeser at the University of Florida found that a mature live oak with a 69-inch DBH requires approximately a 16-foot-wide planting strip to accommodate the trunk flare and lateral root development. Laurel oaks at 54 inches DBH need about 14 feet, and even an 8-inch crape myrtle still needs a 3-foot strip. The general formula is trunk flare diameter plus four feet on each side.
Q: What are the main root defects to look for when purchasing container-grown trees? A: Klein identified circling roots, diving roots, kinked roots, and overlapping roots as common defects in container-grown nursery stock. These often result from trees being left in containers too long, creating root imprints from the container walls. If not corrected at planting, these defects persist and grow larger over time. Girdling roots in particular can choke the tree and cause death four to five years after planting.
Q: What is the preferred method for correcting root defects at planting? A: Klein recommended root ball shaving over radial slicing. Using a sharp spade or handsaw, removing a couple of inches from the outside and bottom of the root ball captures most defects and redirects root growth outward into the surrounding landscape. While radial slicing is better than doing nothing, it may cut a circling root at a point where it continues growing in a circle, perpetuating the defect.
Q: Why might closer tree spacing be beneficial in urban plantings? A: Klein explained that trees planted further apart develop larger, low-growing limbs due to sunlight access on all sides. Removing these later requires large pruning cuts that can introduce decay into the main stem. Planting trees closer together, similar to the European model, can reduce the size of required pruning cuts, achieve a closed canopy aesthetic sooner, and provide a wind-buffering effect where neighboring trees help dampen wind forces and reduce the likelihood of failure during storms.
Q: What is the Florida nursery grading standards system, and why does it matter? A: Florida has a nursery grading system that classifies trees into four grades from the highest quality, Florida Fancy, down to Cull, which essentially means the tree should be discarded. Many municipal codes have adopted the system and require at least a Florida Number One grade or higher for plantings. The grading system identifies structural defects such as large codominant stems or circling and girdling roots that could lead to failures or stability problems down the road.
Q: What are the key mulching guidelines for newly planted trees? A: Klein recommended applying two to three inches of organic mulch in a six- to eight-foot diameter ring around the tree. This helps prevent mechanical injury from mowers, suppresses weeds, and moderates soil temperatures. However, he cautioned against volcano mulching — piling mulch up against the trunk — because as the mulch breaks down into soil, it can promote root defects similar to those caused by burying the trunk flare.
Q: What role does site design play in tree wind resistance during hurricanes? A: Klein emphasized that even structurally sound trees can fail in category two or higher hurricanes, especially when wind combines with saturated soils that cause root slippage. Trees confined in small planting spaces between sidewalks and curbs have restricted root systems that cannot provide adequate anchoring. Designing sites with sufficient rooting space and using creative solutions like structural soils and suspended sidewalks can significantly improve tree stability during extreme wind events.
Q: What is the Florida Trees website and how can it help with species selection? A: Florida Trees is an online tool originally developed by Dr. Gilman at the University of Florida in the 1990s and recently brought back online by Dr. Klein through a grant. It covers hardiness zones 8 through 11 and contains over 1,100 species fact sheets. Users can go through either a detailed expert system of about 30 to 35 questions about their site conditions or a simpler checklist, and the tool generates a list of species suitable for their specific planting site.
Q: How should structural pruning be approached on young trees versus mature trees? A: For young trees, Klein described structural pruning as "chasing defects up higher in the canopy" by maintaining a dominant central leader, spacing scaffolding branches, and reducing codominant stems with small cuts. He noted that a few half-inch cuts can set a young tree up for two to three years. For mature trees, however, the approach shifts to managing loading on the exterior of the canopy with small cuts at three to five inches, since mature trees are mostly heartwood and cannot respond to large pruning wounds the way younger sapwood-dominant trees can.
Getting the Best of Pests (GTBOP) is a continuing education webinar series hosted by the University of Georgia Center for Urban Agriculture. The Green Industry Series targets commercial and private pesticide applicators in the ornamental, turf, and landscape industries.
For more information about the GTBOP program, visit the UGA Center for Urban Agriculture website.
Processed for UGA Center for Urban Agriculture / GTBOP Archives