Speaker: Dr. Ryan Klein, Assistant Professor of Arboriculture, University of Florida Moderator: Dr. Bodie Pennisi, Horticulturist, University of Georgia Duration: 51:30
Bodie Pennisi: Thank you, Richie. Good afternoon, everyone, and welcome to the Getting the Best of Pests Green Industry Series for 2026. I hope everyone is keeping warm, and we have a great lineup of speakers for today's webinar. Our first speaker is Dr. Ryan Klein, who is an assistant professor of arboriculture at the University of Florida. He has 12 years of experience in the tree care industry and the nursery industry. His research focuses on tree risk assessment, arboricultural best management practices, and the impacts of natural disasters on urban tree populations. Ryan, the floor is yours.
Ryan Klein: Thank you for the introduction, Dr. Pennisi, and thanks for the housekeeping, Rich.
So today, we're going to be talking about some general best management practices related to newly planted trees as they're maturing in the landscape, and just some things we should be aware of — whether we're homeowners, whether we work for a municipality, we have our own business, whatever. Just some best practices to hopefully ensure that we're maximizing the benefits that our urban trees are providing, minimizing some of the management inputs, and then setting trees up for long-term survival in the landscape.
Here's a picture from Savannah, Georgia. I love to use this in my slides — just a great urban canopy, a nice little pocket park within the city. You got some nice mature live oaks there providing lots of shade. And if we do the right things throughout the life of the tree, we can have situations like this. Obviously, we're up against things like development and mismanagement, but it is possible.
Some of the things we're going to cover: urban trees and some of the adversity they face, whether it be natural occurrences or manmade adversity, because at the end of the day, a lot of the issues that trees face are due to human inputs. We're going to look at designing sites and how that can impact survival long-term. And then we're going to touch on some best practices that we can implement from the time that we're planting the tree to the time that the tree is potentially ready to be removed. And then at the very end, depending on how long I ramble on, I'll touch on some of the research that I'm currently working on that kind of falls into the bucket of best practices.
So I assume most people on this call have some semblance of an understanding of the benefits that trees provide. Anything from environmental benefits, economic, curb appeal, societal functions — we might want to gather under a tree for a picnic or something like that. Failures of urban trees can pose significant consequences to public health and safety, property damage, disrupting utilities, things like that. The biggest thing to keep in mind is that the risk of injury or death as a result of some sort of tree failure is extremely low. In the US, it's about 35 people a year die from some random tree failure, compared to a lot of other things that we actively participate in. It's a very low likelihood that something's going to happen. That's not to say when I was riding my bike around campus today when those trees were whipping in the wind, I wasn't keeping my eye on some of those branch unions as I went under them.
So I'm going to use Florida here just to kind of point out a general trend across the country. This was part of a project that came out probably about five or six years ago now. Essentially, they were looking at the current state of Florida based off of 2010 data and then looking to see what it would project out as far as population increases and use of natural resources. What they found was that by 2070, basically a third of the state is going to be developed and the population is essentially going to double. So currently we're around 22 million and we're going to get up to almost 40 million in the next 45 years or so.
Areas where they're already very densely populated are going to see population increases. So we're going to start building up a lot of those areas — the major cities, coastal areas, places people really want to move to because we have a lot of people moving to the state. But then also you're going to see sprawl into some of the less densely populated areas, maybe in the center of the state, due to cheaper land and more available space because we're already pretty congested on the coastal areas and within the cities. The project was proposing planned development to where we could have more compact development, less sprawl, less stress on some of these natural resources. But it all comes down to being strategic when we're designing our urban areas for future growth.
So that in conjunction with things like climate change, natural disasters, and things like that — the Intergovernmental Panel on Climate Change was predicting somewhere between a 2.7 to 3.6 degree increase in global surface temperatures by the end of the century. I think it was last summer or the summer before, we've already surpassed that threshold. Along with that, an increased frequency and intensity of natural disasters: droughts, fires, extreme wind events, pest outbreaks. I mean, who here hasn't seen at least a couple of those in the news every year for the past four or five years? So maybe there's something to that.
This can also pose significant risks to urban forest canopy cover. So aside from developers coming in and taking out large swaths of trees, forested areas, heritage trees, and things like that, we also have these natural events that are impacting canopy cover and the benefits we receive from trees. In the Southeast, which would also impact Georgia, we're seeing warmer minimum temperatures and less precipitation.
I don't know if anybody out there has seen this — it's from Davey and the Arbor Day Foundation — but it's a future plant hardiness zone map. I pulled up the best-case scenario here, and essentially it goes through since 1980 and shows how hardiness zones are shifting. This was Athens, Georgia — not all cities are listed on the interactive map, but fortunately they did have one for Athens. From about 1980, the hardiness zone was 7B. When you get to about 2010 to currently, it's 8A, and then it goes to 8B by the end of the century.
So along with that, just being strategic as a manager of trees and landscapes — how does that change the species palette that we're able to plant in areas? Now that it's getting warmer, there might be some species that were maybe better suited for the southern part of the state or potentially even northern Florida that didn't grow in your area before, and they may now be suitable candidates for planting. The other thing I will say, because we've done a research trial on this: it's not necessarily the warm temperatures that seem to be the issue as far as what you can plant where. It's actually those minimum cold temperatures. So you still have to keep in mind minimum cold tolerance when you're assisting some of the migration of species that maybe weren't commonly planted in your area previously.
Another site you can reference to see what's potentially going to happen in the future — this is out of University of Maryland's Center for Environmental Studies. They have this map where you can plug in your city and they tell you what your city is going to be like in the future. Athens, Georgia, in 60 years is projected to be similar to Kaplan, Louisiana. So your climate conditions are going to be similar to that, which means tropical and subtropical grasslands, savannas, and shrublands. When I've done this before for other cities, every once in a while it'll pull one up from a different country. I was trying to think — it might've been Fort Lauderdale not too long ago I did this for, and they said it was going to be like somewhere over in Saudi Arabia. So depending where you're at in the country, by the end of the century, or in this case 60 years, your climates might change pretty drastically, which again could affect your plant palette.
The other thing that we have to compete with in a lot of areas here in the Southeast, especially those closest to the coast, are some of the impacts of disasters — specifically hurricanes and the tornadoes that pop up from that. We have this high concentration of urban development along these coastlines. Some of it's planned. Some of it's maybe planned less well. We also have these landscapes that have been designed, preserved natural ecosystems, things like that. A lot of these areas are susceptible to these extreme wind events — especially landscapes and maybe structures, not always depending on when they were built, but they can sustain considerable damage.
One thing to keep in mind here when we're talking about risk and likelihood of failure of trees is that even trees that are deemed to be structurally sound, low-risk trees — if you have a category two or higher hit your area, all bets are off of whether or not that structurally sound tree is still going to survive. Just keep that in mind. And a lot of that has to play into the site design as well. It's not just the tree structure.
As far as hurricane season goes, typically June 1st to the end of November is the hurricane season. The peak season is mid-August to late October, when you get those waters in the Atlantic and the Gulf that warm up enough to get those tropical waves. Fortunately for me, more storms hit the state of Florida than any other. I say that jokingly, but I always tell people when I'm giving talks and meeting people for work purposes that I hope their city has a tree inventory before the hurricane hits. And then I hope they're the next one to be hit. I say that jokingly because we don't have that front-end data about what trees are there, what condition those trees are in, and all that stuff. Once the storm hits, it's not as meaningful to just say, "Hey, that tree failed, this tree failed." A lot of times people go in and say all of this species failed or a lot of this species failed. Yeah, but there were management inputs. There was quality of trees when they were planted, their site conditions. There's a lot of other variables that if we have that front-end data, it makes the aftermath a little bit more meaningful from a research perspective.
When we're looking at the 10 most expensive hurricanes in the US, six of the top 10 have happened since 2017. I know last year was a lull in hurricane season — I don't think we had any major storms hit Florida. But the way things are trending over the past 10 years or so, it does seem like there's an increased frequency and intensity. So just something to be mindful of when we're planting these trees out there and being strategic and making sure we have high-quality trees.
There's lots of other stressors in the urban environment unrelated to natural disasters. We got poor soil quality, compacted soil, urban heat islands that can cause drought-like conditions, lack of management, improper management, all these different things, construction damage. Basically the past research on the topic has found that we have an increased mortality rate in these urban areas due to a lot of these variables. So these urban trees have a shorter life expectancy, typically, than trees in rural areas.
You'll find certain trees are going to do better in these urban sites because they can tolerate a lot more adversity. But what we need to be cautious of is that we don't over-plant a lot of these species and develop some sort of monoculture, because then when the next emerald ash borer or Dutch elm disease or oak wilt or whatever comes into your community, you might lose a substantial portion of your canopy.
Unfortunately, though — and we found this when we were doing one of my PhD student's studies where we were trying to introduce underutilized species — the growers are not growing them. So sourcing some of these underutilized trees can be problematic, especially if you're looking for certain sizes and certain numbers of trees. If you're wanting to do a large planting effort, you might be able to find a half dozen of an underutilized species, but you might not be able to find 40 or 50 of them. And maybe they're one gallon rather than 45 gallons. So just some other things to consider if you're trying to diversify your urban forest.
Big thing is right tree, right place. And hopefully everybody's heard this ad nauseam, but I hate to say it — we're still not doing it. As the larger green industry community, we need to determine what's going to be the best fit for the site that we have a planting space for. Yeah, maybe we want that large live oak that could potentially provide shade, assuming it gets to maturity. But at the end of the day, maybe that's not the right tree for a three-foot-wide planting strip.
There's a balance there. You want to make sure we're minimizing the management inputs. And if you're planting the wrong species in a certain site, it might increase those exponentially. There's lots of online information. You can lean on local knowledge. You can also go out there and do a site evaluation. There's lots of interactive sites online where you can do site evaluations. I'll talk about a project I was involved in a little bit later to determine right tree, right place.
The other thing is you obviously want to plant something that you have an interest in — it's got some desired characteristics, something like that. But the goal here is to maximize tree benefits, minimize those inputs and potential risks to public health and safety. When you have trees that have low survival rates, at the end of the day, you're losing those long-term benefits. So you want to start with that high-quality nursery stock and then proactive maintenance from there.
I've seen a couple of studies over the years where typically trees are not paying some sort of net benefits until around 25 years. So if we're constantly in a cycle of replacing trees every 15 to 20 years, we're basically just paying out the labor, the cost to maintain, materials, and everything else that goes into it, but we're not really receiving any of those net benefits.
I mentioned desired species traits. There's a ton out there — maybe function, you want shade or drought tolerance, mature size, you want something that is going to grow within the space rather than outgrow it. Maybe you want something that is specifically excurrent or decurrent because of the site and there needs to be some sort of clearance or visibility. Ornamental traits — showy flowers, leaf color, maybe you want something that's got strong wood associated with it so it's going to be more resilient in storms. Something that's adapted to urban environments, things related to future climates and stuff like that.
So I mentioned site evaluation. When you're conducting the evaluation, you want to identify any site characteristics that could adversely impact growth, establishment, and survival at the site. Above ground, some of the things to consider are environmental factors like available sunlight, exposure to wind, nearby trees that could shade it out and adversely affect the way the tree's structure develops. And then some urban factors such as proximity to utility lines, buildings that are nearby, signs that might be blocked to where the tree is then needing to be improperly pruned later to get some sort of clearance for visibility.
Then some of those below-ground site attributes — things like soil quality, compaction, drainage — all things that could affect establishment and survival. Are there any potential site modifications that can be made? Is it possible to move lights or wires? Probably not. A lot of municipalities are going to underground utilities on new developments. Those can also be just as problematic as above-ground utilities — they limit the planting space. Are there soil amendments that can be applied, or can you improve the drainage by regrading the site or something like that? And then finally, any sort of maintenance post-planting. So irrigation — is it even possible to irrigate at this site? Pruning — how frequently is somebody going to get out there and structurally prune the tree throughout the first decade or so the tree is in the landscape? Any fertilization or pest control needs.
We see a lot of this, unfortunately — small planting spaces. You got your little islands, your peninsulas, your planting strips. The planting strips, best case scenario, are going to allow those roots to extend out both directions toward neighboring trees. The one on the left there, that little small planting island — they should have just paved over the whole parking lot. That tree's not going to survive. A lot of wasted time, money, loss of potential future benefits when we don't start with some planning or design that can prevent situations like this. Sometimes there's stuff in code that will prevent it at the municipal level. If you do have only a small space that you can plant in, plant a species that's not going to get large. Don't try to plant that large growing shade tree.
Here's an ideal situation. Roots can grow two to three times wider than the crown of the tree on a decurrent tree. Fine roots can be found well beyond the canopy or the drip line. So when we have these small planting spaces, it's very confined. You get deflected roots and potentially wind throw. The roots are going to help anchor the tree under high winds, so we want them to spread out as far as they possibly can.
This is what we see more times than not in practice. You got a shade tree planted under the utility lines in a small planting strip next to light poles and signs. And you got curbing and sidewalks surrounding it to where roots are being deflected. This is not a good place for this tree to be planted. Maybe the utilities came after and the tree just happened to get butchered because they needed to run the lines. My guess is they probably planted the tree — maybe it was a homeowner, maybe it wasn't a municipality. Either way, we need to avoid situations like this.
We set ourselves up for failures when we plant in these small spaces. Unless we design a site that promotes future growth, we have a lot of these issues. It's going to limit the wind resistance of trees. Structure plays into it too, sure. But designing sites to promote future survivability and in this case wind resistance is going to be in our best interest as far as getting those long-term benefits. You can see there in the top left image, those roots were kind of confined between the sidewalk and the curb. They weren't able to get out. Large trees, the loading from the wind hit it — see the same in the bottom there. And then the trees failed.
Again, it's about matching the species to the site. The other thing to keep in mind here — it's not always just the wind speed. It's usually a combination of the wind speed and then saturated soils. So you'll get root slippage in the soils, and then these trees come down when we have some sort of loading applied to it.
Another issue that we see with limited space — again, it's poor design that doesn't account for growth at maturity. The image on the left there, that looks great. You got a four-inch tree and that four-foot-wide planting strip looks like it fits right. But as the tree grows, it's going to outgrow that space, becomes a liability over time. You can see in that picture there on the right, there's a lifting sidewalk. Lawsuits occur because of situations like this. They come in, they replace the sidewalk. They end up cutting — in this case, you're going to cut off part of the trunk flare in order to get the forms in there to replace the sidewalk. Destabilizes the tree. Not ideal.
Mature trees are going to have this zone of rapid taper where the buttress roots are going to transition to these ropey laterals. Essentially this can extend four feet past the visible trunk flare. So we want to have enough open space that's going to allow for the trunk flare and some of these ropey laterals. It's going to make sure that the tree is more stable and prevent some of these failures.
There's been some research on this that looks at trunk flare diameter in relation to DBH. What they found is that there's this relationship where as trunk flare diameter increases, so does DBH. So planting recommendations have developed to avoid some of these sidewalk conflicts. Essentially you want to take trunk flare diameter plus four foot on each side, and that should be the size of the space for the tree at maturity.
Another study looked at this perspective in relation to the street trees in Tampa, Florida. This was done by Dr. Koeser down here at University of Florida. What he found was that for a mature live oak of 69 inches, you basically needed a 16-foot-wide planting strip. Laurel oak at about 54 inches, you needed 14 foot. And crape myrtles — an eight-inch crape myrtle, you still need a three-foot planting strip. I see crape myrtles basically planted in cracks sometimes. They're alive, but we can do better, I think, is the message there.
Again, this is what we get when we don't allow for enough space for that trunk flare and those ropey laterals to establish and stabilize the tree. Wasted money, loss of benefits, cost to clean up — it can perpetuate negative stereotypes of trees associated with risk, because public perception is big when we're talking about some of these urban plantings.
It's better for us to design these sites and the tree plantings prior. Unfortunately, that's not always the case. Sometimes we're planting in whatever space we have available just to try and increase canopy cover and things like that. But if we do have the ability to plan on the front end, things like structural soils, suspended sidewalks, Silva Cells — they're going to allow for more root growth and allow for more support for the tree to stabilize itself. Surface materials aren't going to get damaged in the process because the roots are going to stay below it. We can do better with some of these creative design solutions to increase the lifespans of the trees and then reduce some of those infrastructure conflicts.
The picture in the bottom center there, that's from Austin, Texas. They do a really good job of these suspended sidewalks. As the trunk increases in diameter, they just cut the hole around it bigger. But the actual soil level is probably about a foot or so below that suspended sidewalk. So just something that can be done. The problem usually with these creative design solutions, unfortunately, is they cost a lot more than just planting the tree in the existing hole. And not always is there the know-how in every community by the contractors doing the work to install some of this stuff. So I think we're still far enough out from seeing this across the board at all of our cities, but it is an option.
Tree spacing — another thing here. Trees planted further apart are going to develop larger, low-growing limbs. When we go to get vertical clearance, that means we end up making large pruning cuts. There's a higher likelihood that we're going to introduce decay then into the main stem, due to these urban trees having access to sunlight on all sides — that's how these large low-growing limbs develop, along with other defects.
Maybe if we plant trees a little bit closer together, kind of like the European model, the management inputs will be a little bit less or more spaced out. Maybe we're not making as large of cuts. It's going to give that closed canopy aesthetic a lot sooner. And then also, if you think of a forested area versus a tree standing alone in a park without any protection from itself, you're going to get a little bit of help from the neighboring trees to dampen the effects of the wind and potentially prevent them from failing in a future storm.
Here's some examples of trees planted individually, in a strip. The images to the right there are more of that natural planting. Obviously, the bottom one there is a wooded area, but the top right one, you got trees kind of closely planted together to where they can buffer one another.
If you're interested in failure profiles, there was a study from 2007 by Duryea and company, and they assessed the damage of about nine or ten hurricanes in the Florida area. One was from Puerto Rico. And then they put together a survey that basically asked all these green industry professionals their perspectives of failure — basically whether or not species had a high likelihood of failure. They ranked them from high, medium, to low based off of these observations from previous hurricanes. And then they came up with a list of about 76 species — some tropical, some subtropical, some coastal plains — but essentially ranked them as far as how good they were under extreme wind events. So if you're interested in that, Duryea et al., 2007.
Another document that came out in 2023 — it was a FEMA document by Koeser and Salisbury and a couple other folks. Basically, they did something similar, but their list pulled from tons of previous literature that maybe mentioned two or three species, maybe it mentioned 40. They compiled all this information together into one document and they had 281 species and they ranked them from lowest to highest as far as wind resistance. So you can just type in "Koeser FEMA hurricane wind resistant trees" and it should pop up on Google.
Another thing — and I don't believe Georgia has it; if they do, I apologize, I missed it — but there's maybe four or five states throughout the US that have some grading system for nursery stock. Florida has the nursery grading standards. Essentially, it just basically goes through four different grades of a tree from the highest quality being Florida Fancy to the lowest quality being Cull, which essentially means you put it on the burn pile.
A lot of municipal codes have adopted the grading system and recommend at least a Florida Number One or higher. That's the second highest level. Essentially the grading system identifies different defects that could have some structural issues down the road, whether it be a large codominant stem up in the top half of the canopy, or whether it be a circling or girdling root down in the root system that could potentially lead to either a failure in the canopy or destabilizing the tree down the road. I actually have a master's student who's wrapping up a project on the grades and standards, quality of nursery stock, stuff like that, that hopefully we'll have published by the summer.
Just some considerations — if you're a homeowner looking for a tree, whether you go to a nursery or a box store or wherever you're sourcing your plant material, or if you own a business and you're ordering trees, or your municipality and trees are being delivered to a development and you need to inspect them. Things to consider: production method, size, planting, root ball dimensions, root defects, trunk and branch structure — all these different things to be cognizant of to ensure a high-quality tree before we even determine right tree, right place, site conditions, aftercare, and all that. First step is the quality of the tree.
When we are looking at site conditions, right tree, right place — I mentioned there's some online sites. I worked on a site called Florida Trees. It was formerly developed by Dr. Gilman back in the '90s. The site went offline probably five years ago. I was able to get a grant to bring it back online. Essentially it goes through proper plant selection for hardiness zones 8 through 11, and it goes through site attributes above and below ground, all those things we talked about, tree characteristics, and then it's going to kick out a list of suitable species for the site.
In order for this site to function, there's this big thing that I liken to a spider web, but it has all these questions and rules and all these things that go into it in order to ensure that the species list it kicks out are going to be suitable for your site conditions. So you can go through this question-answer process. I kind of think of it as — if anybody remembers those books, I was a kid in the late '80s, early '90s. They were the "choose your own adventure" books you'd read and then it would tell you to go to page 39 — "Oh, you fell off a cliff, start over," whatever. It's kind of like that situation, except with identifying trees for your planting space.
If you want to do the more involved process — because the process where you go through and answer the questions, which we call the expert system, could be about 30 to 35 questions to get through it. If you want to go the maybe more basic one where you just check a whole bunch of boxes that are relevant to your site, you can do that as well.
All this information stems from about 1,100 tree species fact sheets. I don't know if anybody's familiar with the EDIS fact sheets from the University of Florida, but all that information is then piped into the tree selector. Actually, the tree selector is what generated those fact sheets in the first place about 20 years ago. And then now I help to update them and keep them relevant when any of the information changes.
Here's an example of what one of those species fact sheets looks like — it's got everything on there from general information about the tree, hardiness zone, uses, attributes like foliage, flowers, pest issues, management, all that good stuff. The site contains lots of different educational materials outside of even the selector. So you got the fact sheets, there's a site analysis form on there, links to other websites, a tree ID function. A lot of this stuff is going to be specific to the Southeast — hardiness zones 8 through 11 — but it touches on urban conditions and whether trees are suitable. The website's very easy to use; we have it as mobile friendly now. But it gets at that right tree, right place.
We just got a grant from the dean's office here at the university and my college to do some stuff that is potentially going to add to this, hopefully in the next couple of years, as well as do some other AI-related projects. But this is one component of that. So hopefully we're going to add to this here shortly.
The other thing is, from a best practices standpoint, ensuring that we're following proper planting procedures. This is the ISA's Best Management Practices for Tree Planting. Essentially, following this is going to ensure that your planting is hopefully successful, assuming you have high-quality nursery stock, assuming you planted the tree in the right place, all those good things.
I mentioned right tree, right place — this can impact the survivability of the tree long-term. One of the first things to consider is what type of plant material are you planting? Are you wanting something bare root and small? These are going to be field grown, dug without soil, typically. B&B — these are harvested from the field, the ball spaded out, wrapped in burlap. These are going to be larger trees usually. It's important to consider things like timing the dig, timing the planting. And then container-grown trees — these are very common down here in the Southeast. Plastic containers, larger trees are going to be in wooden boxes. The biggest thing is making sure that the container is an appropriate size for the above-ground portion of the tree, and then also when you take the containers off the tree, make sure you're addressing any sort of root defects. I'll touch on that here in a second.
Planting — you want to make sure there's adequate drainage. You don't want the hole filling up and water just sitting in there creating some sort of anaerobic conditions, so you might have to improve the drainage — whether it be adding a drainage tile, whatever, depends on the soil type.
The width of the hole — if you have high-quality soil, you really only need to dig it about the same size as the root ball. If you got poor-quality soil, you might want to dig it twice the size of the root ball. That's going to allow the roots to establish into the surrounding landscape a little bit quicker.
As far as depth, you want to plant the root ball a couple inches above grade, whether it be container grown or field dug. The ball's going to settle over time, especially with container-grown trees due to the substrate being different than the native soil. So just plant it a little bit high. And the other thing is, you want to make sure that if you have any excess soil that's on top of the trunk flare, that needs to be removed away. Otherwise, circling and girdling roots can occur.
You can see here in the left image, that's the trunk flare. You want that to be at or slightly above soil grade. And then same with the image on the right there — you can see that there's that excess soil that needs to be removed, cut that circling root at planting, and that'll help the tree down the road not have any stability issues or health issues because it's getting girdled by the root.
Here's just a complete mess — you can see on the left there, you got circling roots, diving roots, kinked roots, overlapping roots, just the whole slew of things. So when we pull that container off, this is something we need to be aware of.
You can get imprints from containers. So if a grower leaves it in the container too long, you can see there on the left — circling roots. If I was to guess from this image, that's probably a three-gallon, five-gallon container. It was planted up into maybe a 30 or 45 at some point, but those root defects from being left in that container were not addressed prior to upping it to a larger container, and they're always going to be there — they're just going to keep growing larger. Same with the one on the bottom right there — there were some girdling roots because there was soil piled up on the trunk flare, and they don't go away unless we mitigate them.
What you have is trees that, if you have a girdling root, could die four or five years out. You pull the soil back, the mulch back, and you see that the tree's getting choked out. So again, these are things we want to address at planting.
As far as soil goes, some people like to add amendments and stuff like that. If the tree's not going to survive in the soil at the site, the existing landscape soil, it's probably not the right tree for the right place. We're doing some work right now with biochar, compost amendments, combinations of those. Hopefully we'll have that published in the summer as well.
Another thing just to be cognizant of — certain soil types, especially more heavily clayed soils, glazing, drying, things like that from digging in the ground. If this does happen, just kind of break it up with the rake or shovel. Any synthetic materials — synthetic burlap, plastic twine, anything like that — make sure you remove it because just like those circling roots, it can girdle the trunk of the tree and cause it to die prematurely.
When we do have root defects due to trees staying in a container for too long, it's real easy just to take a very sharp spade, a handsaw, something like that, and just trim the outside of the root ball — take off a couple inches on the outside and on the bottom. Be good to go. It's going to capture most of those defects enough to at least get the majority of those roots out in the surrounding landscape. Alternatively, you can do radial slices. One thing with that, though, is you might catch a defect at a point where it's still continuing to grow in a circle. It's going to put on growth and then continue that process. So shaving is a little bit better from what we found with some of our research, and some other researchers have found something similar. But slicing is better than doing nothing.
When you are ready to plant — making sure the hole's an adequate size, stabilizing the tree, backfilling, not compacting the soil. You can lightly tamp it, breaking up any clumps, things like that. Creating a soil ring around the root ball so then when it does rain or you irrigate, that moisture stays over top of the root ball. And then don't place any additional soil on the trunk flare after you've already taken it off. Make sure that it's planted high and all that excess soil is off.
Same goes with mulch. We don't want to pile it on too thick — two to three inches of some organic mulch, six- to eight-foot diameter ring around the tree. It's going to help prevent any sort of mechanical injury, keep the weeds down, keep soil temperatures a little bit lower. And this is especially important when we have high temperatures and little rain. But don't pile it up on the trunk. Again, volcano mulching can also result in root defects as they break down in the soil.
Should have minimal pruning at planting, assuming you start with a high-quality tree. But if you do need to make a snip here or there, now's the time to do it because you don't know when you might be back. If you're the person planting, maybe it's never. If you're the homeowner, obviously you could make some snips over time.
So on the left here, this is a high-quality tree. You got a nice dominant central leader. The one on the right, you got lots of codominant stems competing from low in the canopy. This is a recipe for potential failures in the future. The way I like to think of it with structural pruning is we're constantly chasing those defects up higher in the canopy. The single stem is going to be more resilient when we have some sort of storm.
It's about identifying that dominant leader, also identifying the lowest branches in the permanent canopy. At some point, urban trees — we need to get clearance, whether it be for the lawnmower, sidewalks, passing vehicles, things like that — spacing out scaffolding branches and reducing competition with that central leader.
It could be as easy as making a couple of small half-inch cuts, and that'll set the tree up for a decent structure for the next two to three years. And then also eliminating things like clusters. When you do that, you're going to promote better connections with the branch tissue.
Here's just an example — could be as simple as three or four cuts in order to achieve the objective of reducing some of that competition, spacing branches, things like that. We're talking about vertical clearance — again, identifying what the permanent canopy is. When you're planting a 45-gallon tree, odds are all of the branches on that tree are temporary. Knowing that as a tree manager, maybe we reduce some of them over time. We remove them kind of systematically every couple of years. Just things like that where we don't have those large, low-growing limbs that end up resulting in a large pruning wound later.
The tree on the left — several years there without pruning, it's just going to keep growing. It was on the right there at planting, and you'll see those defects, those small codominant stems that were on the right are now large codominant stems on the left. And like I said, it could be as easy as just making one cut. You cut the codominant stem and the tree's set up for a couple more years before you need to address it.
Here were some trees we structurally pruned for one of my master's students' projects. And you can see the big takeaway here is it doesn't have to be a massive pile of debris. So this was a year and a half after planting. Pile of debris there is relatively small. The dynamic between the size of the debris pile and whether or not a person feels like they got value is kind of upside down. A lot of times I talk to people and they say, "Hey, there wasn't a massive pile out in my yard after the arborist came and did his work." Well, that doesn't necessarily mean that the tree wasn't properly pruned. A lot of times, a smaller pile is proper pruning, and that massive pile — they over-pruned it or took larger cuts than they needed to, or took too much off in the wrong locations. Another example — small pile, handful of cuts made to bring that back to a good structure.
At planting, if you do need to have any support systems — staking, guying, bracing — just don't forget to remove those after, because it could girdle the tree and be problematic down the road. Same goes with guards, wraps, things like that. There are several examples of this online. You can type in "planting diagram," but it just basically goes through all the things we've talked about to ensure that you've properly planted the tree.
The other thing is during the establishment period, water is usually the most limiting factor. Water stress can kill trees or prevent it from establishing. So just making sure that the trees are getting irrigated properly, avoiding compacted soils. You don't want to drive over the root zone in the area where you just planted a tree. It could inhibit development.
There's some guidance, at least with grades and standards. I know there's some other recommendations that are more state specific, but for the Southeast here, depending on where you're located in the state, it gives recommendations for how much irrigation throughout the establishment period, how long the establishment period is based off of your location, things like that. So just looking into different guidance on that to ensure that the tree properly establishes.
Maintenance — aside from watering, fertilization, antitranspirants if needed, pest, disease, pruning — all those things we need to consider.
When we're talking about mature trees — we just talked about newly planted trees. Mature trees, hopefully the structure's already in good shape. A lot of times you show up to a tree and it's a nightmare. Not much you can do with mature trees other than manage loading. So loading to reduce failure. A lot of times with mature trees, maybe a little bit of structure, but it's mostly clearance, appearance, risk reduction.
When a tree is mature, it's mostly heartwood at that point, where when it's younger, it's mostly sapwood, dynamic, and can respond to adversity. But when we're talking about large trees, we really want to avoid those large pruning cuts. Throughout the life of the tree, you got the growth phase, the maintenance phase, the death phase when there's natural retrenchment or we're helping to make the canopies more compact to reduce failures.
Most of the work that we're doing on mature trees is going to be on that exterior of the canopy. We don't want to be making those large cuts. So out there, four to five inches, maybe three would be where we're making some of those cuts. We want to eliminate any defects. Here's a bark inclusion that failed. You can see there's no connective tissue in that center picture there where that black area is. It was just two stems rubbing up against each other. This could have been taken care of when the tree was a lot younger just by making some smaller cuts, pushing growth up into the other side of the tree.
Here's a great example — I think this was over in Amsterdam — where nice dominant leader, they're very proactive with their structural pruning.
Similar to planting, following the BMPs, ANSI A300 pruning standards is going to be your best friend as far as guidance there. Also down in Florida, we have a prescription pruning qualification. I'm one of the instructors for it — it's a two-and-a-half-day course. We go through things like conditions of concern, objectives, pruning branches, limitations. It's all about making sure that the person that's prescribing the work and the person that is doing the work are on the same page. And then when the person that sold the work shows up, looks at the tree, the pruning was done as they envisioned it. So it's a common language that can be used to make sure that proper pruning is achieved.
Lots of different factors we talked about here that can impact the success and survivability of urban trees, from the quality of nursery stock, site conditions, aftercare — big thing is that right tree, right place. We can, on the front end with planning, creative design solutions, all that stuff, make sites that are more conducive for future growth. We also want to factor in the management aspect — proactive maintenance, not just when there's a failure, not just when that hurricane's a week out and, "Hey, I need to prune my tree." Being proactive is in the best interest of the tree.
So I have two minutes here, and I'm just going to say a couple quick things on the current research. This is that study on the grades and standards. Just one thing to point out — root defects were all over the place. We randomly selected seven growers throughout the state of Florida that had 15-gallon live oaks, common species, common size that the homeowner can take home. But what you notice here is the size of these trees was all over the place. We had trees as tall as almost 14 feet, as short as just under five feet. For grades and standards, I think it's about seven to eight feet as common for a 15-gallon tree, inch-and-a-half caliper, and these ranged anywhere from under an inch up to three inches. And you can see the root defects were prevalent.
Here's some of the other stuff we're working on — biochar, how spacing impacts management, got multiple irrigation studies right now. We're doing some large tree moving studies, pruning studies, survival performance — tons of different things.
So sorry I took it to the final minute, but thank you for your time. I don't want to interrupt with the other speaker, but if you do have any questions, please send them my way in email. Happy to answer them.
Bodie Pennisi: Thank you, Ryan. Yes, that was lots of really, really excellent information. We have a comment that came in really early, and I just want to share and read so you can see it. Norma: "Thank you so much for covering the planting of trees in sidewalk areas. I've been complaining about this for years. Hopefully, the architects will stop calling for them in areas that are too small to accommodate them." And I think we all can agree that this is a perpetual problem that we're seeing across — it almost doesn't matter where you are, you're seeing these kind of problems.
Ryan Klein: Yeah, and unfortunately, just to that point — the University of Florida, and I know a couple other universities, do not require my class or any urban forestry, dendrology, anything like that for their curriculum. So it's kind of unfortunate that certain fields are out there doing tree-related designs and they might not have had that background.
Bodie Pennisi: Totally agree with you. Coming from UF and from the Environmental Horticulture department, you guys have a whole lot more focused things that you can offer to your students, and at UGA we're the Department of Horticulture so our students don't really have that kind of specialization. It's kind of disappointing to hear that even at your place you don't have that kind of way to get them to take some required courses.
Ryan Klein: Well, and just so you know, because I saw you came from Environmental Horticulture — we are no more as of the first of the year. I'm in forestry now.
Bodie Pennisi: I wasn't going to say it! Well, makes sense. We're really looking forward to your research. I have been reading some of it in the past few years, and it sounds like a good reason to call you again and get you to share some more — especially about the biochar. That's one area that I think has a lot of potential.
Ryan Klein: Yeah, and that study will finish here in the next month, and then the deliverables will be the next couple of months. So I should have a talk by summer.
Bodie Pennisi: Great. All right, well, we'll put you down. Appreciate it. I don't see any other questions, so thank you again so much. And we're off for the first break.
Ryan Klein: Take care.
Bodie Pennisi: Thank you.
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