Drought Stress and Spiraling Decline of Trees

Matthew Scott, sales arborist at Davey's Raleigh office, discusses drought stress and the steps you can take to help your plants during drought season. 

In this episode we cover:  

• Drought stress in North Carolina (:38)
• How to identify drought stress on trees (1:06)
• Solutions for drought stress (2:53)
• Can you use these solutions on existing trees? (3:36)
• Watering larger trees (4:36)
• How mulch helps trees during drought stress (6:15)
• Drought history in North Carolina (7:17)
• The long-term impact of droughts (8:35)
• How droughts affect dogwoods (9:37)
• What is the spiral of decline? (10:40)
• How weather impacts planting (13:03)
• What to plant during a drought (14:40)
• Tree risk assessment and drought stress (16:18)
• How Matthew got his start in the tree industry (17:57) 

To find your local Davey office, check out our find a local office page to search by zip code.  

To learn more about how you can help your plants during a drought, read our blogs, How to Keep Your Landscape Resilient During Seasonal Summer Drought and How To Pick The Right Trees For Drought-Prone Landscapes.

Connect with Davey Tree on social media:
Twitter: @DaveyTree
Facebook: @DaveyTree
Instagram: @daveytree
YouTube: The Davey Tree Expert Company
LinkedIn: The Davey Tree Expert Company 

Connect with Doug Oster at www.dougoster.com. 

Have topics you'd like us to cover on the podcast? Email us at podcasts@davey.com. We want to hear from you!  

Transcript

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Doug Oster: Welcome to the Davey Tree Expert Company's podcast, Talking Trees. I'm your host, Doug Oster. Each week, our expert arborists share advice on seasonal tree care, how to make your trees thrive, arborists' favorite trees, and much more. Tune in every Thursday to learn more, because here at the Talking Trees podcast, we know trees are the answer. This week, I'm joined by Matt Scott. He's a sales arborist in Raleigh, North Carolina, for the Davey Tree Expert Company. Matt, welcome so much to the show.

Matt Scott: Hi, Doug. Great to be here. I appreciate you having me on.

Doug: I love it when an arborist comes up with the topics, and so we've got a whole list of cool stuff you want to talk about. Right off the bat, it's drought. Drought stress in particular and that's been a problem in North Carolina, right?

Matt: Yes, it's something we've really been seeing a lot of recently and I'd say the last three years, we've gotten into some pretty good droughts. It's been hard on the trees and it's something that we're starting to see a lot of negative effects from.

Doug: When you're looking up at a tree, how do you know it's drought stressed? Of course, you probably know because there's been no rain.

Matt: Right. You keep an eye on that or how much rain we've been having, and you start to see it across different tree species. If a lot of the different species are showing the same symptoms, that's a good hint that it's something abiotic. With drought in particular, the tree's first defense on that is closing up its stroma and slowing down transpiration a little bit, and slowing down how much water it's losing, which may not be an obvious effect looking at the tree. The first thing you might pick up on when you look at a tree that's drought stressed, is wilting in the leaves. It's actually a defense mechanism in plants to try to reduce some of the water loss that it would have from those leaf surfaces.

Initially that wilting can be reversed, in that if the tree or the plant gets water, those leaves will plump back up and flush back out. In some plants, like in corn, that can happen even within the same day. It might be wilty and stressed in the middle of the day, and they get some water in the afternoon, and then the leaves come back to life. It will reach a certain point where you get to permanent wilt, and with that, you get a buildup of abscisic acid, and you'll actually see leaves start to drop prematurely. Wilting leaves would be an early sign of drought stress, and then a lot of leaves dropping out of the canopy would be the further, or it's been drought for a little while on that tree.

Doug: My guess is the solution is water, water, water, right?

Matt: Yes, water, water, water. It's important. Even mature trees need water, and there's two ways you can look at the equation. Either you need to prevent some of the water loss, which is what the tree is doing through wilting or closing those stoma, or you can add more water to the system. Watering the trees is important, but also better soils will tend to hold on to water through periods of drought, particularly soils that have more organic matter, so adding things like humates and organic matter to the soil can help bridge the gap in between times with less water.

Doug: Can you do that with an existing tree? Can you make those improvements?

Matt: Yes, absolutely. Mature trees will tend to weather drought stress a little better. They have more stored energy in them. Younger trees, particularly new plantings, will have more obvious signs, or they'll show symptoms from a lack of water sooner. Where we are now, the mature trees are starting to show signs, too, because we've had this repeated years of drought. It is something you can do to any established tree. Water in the root zone, and then we use a liquid humate product, which would add organic matter and help with the soil but also incorporating things in the soil, like a compost or mulching the trees on the top a couple inches would help as well.

Doug: For a big tree, how do I know how much water to put on it so that it does recover?

Matt: It can be a considerable amount of water. Ideally for watering, you want to go, if anything, a little more on the infrequent side, but really drench the root area. The best thing to do would be to get a little core and measure, or take a core at a couple spots around the root zone, to make sure that when you're watering, it's getting beneath the top inch of soil, which can take a good amount of water to do. Especially if there's turf grass on top of it, because that turf's going to take away some of the water as well. You really want to drench the area. I'd say to the point where you want to see it start to pool just on the surface. Not a consistent pool, but that tells you that top layer is saturated.

When that happens, it's enough water that's going to start infiltrating to the absorbing roots of the tree. Most of the roots that are going to absorb water in the tree are in that top two foot of soil. If you drench it and go with a little less frequently but heavier watering, the tree's not going to develop all of its roots in that top layer. It's going to have absorbing roots throughout that layer of those top couple feet, which benefits you because in times where there's less water in the root zone, there may be some lower down in that profile and not just in that top couple inches of soil.

Doug: We talk about mulch a lot on this program, and I'm not even going to mention the V word. Volcano.

Matt: Sure, yes. That's [inaudible 00:06:27] common, yes.

Doug: Yes, we all hate it. We know. I talk about it almost every other week. In the case of a tree that doesn't have the soil that it really needs, you're adding humates. Certainly using a layer of compost as a mulch with maybe some bark mulch and not too thick is eventually going to help that tree, right, as it decomposes?

Matt: Yes, absolutely. A triple-shredded leaf mulch or bark mulch or something like that. A good mulch will decompose and start to help that. As long as it's not piled up against the trunk. If you talk about every week, maybe I'm preaching to the choir, but not volcano-ing, not against the trunk. You want to see the root flare, all of those things that everybody else must be hitting on, too.

Doug: Oh, yes. You have to talk about it though, Matt, just because it's such a maddening thing. Everywhere I go, I'm speaking about gardening. I see it and just like you, I try to educate people. Not standing on a soapbox, but just explaining the science of like, "This is bad. I know you might like the way it looks, but this is bad." During this period, how long have you guys been in this, like, prolonged drought?

Matt: I'd say during the summer for the last three years, we've gotten into these conditions. This spring, we had a month or two where we were getting pretty consistent rain, which helps out a lot. As things were leafing out this spring, they looked pretty good, but even within the last month or so, we really start to see that tail off. In some of that, we have a lot of pine and a lot of things that are a little bit more adapted, at least in our natural forest. In the landscape, you're seeing things from all over that maybe see those symptoms a little more.

Doug: I don't think there's anything worse for a plant professional than a long drought, whether you're a gardener or a tree expert. Drought is a tough thing to deal with. There's only so much water to go around if you've got a lot of trees. There's sort of a-- I don't know if the right word is sadness, but there's a sort of like, "Oh, boy, I wish it would rain."

Matt: Yes, right. I've given that advice to clients before, to water their trees, and they'll talk about restrictions that they have on watering the landscape. It's a tough problem to crack. It takes quite a while watering something with the hose to replace even an inch of rain, which can happen fairly quickly. There's really no replacement for Mother Nature and rain in that regard.

Doug: Yes, I know. In the landscape, it's like you're keeping the stuff alive, but you're not giving it what Mother Nature would give it. That leads me right to dogwoods. Dogwoods was on your list. Drought and dogwoods, boy, those two things do not go together, especially if they're not sited in the right place.

Matt: Right. I seem to see a lot. It depends on the property and if I'm walking through the woods, you catch dogwoods. They're always understory plantings or they might be near openings. When we see them planted in the landscape, they can do all right for a couple of years if they're planted out in the middle of the front lawn as a specimen planting. Then when you get into a situation like a drought or after a few years in that not ideal location, then you really start to see the leaf drop, the dead limbs, and a spiral of decline with the other diseases and things that they get too.

Doug: Let's talk about that spiral of decline because I have a shrub here, it had been here. I inherited it 20-some years ago and my Davey arborist came and I said, "Oh boy, this thing, it's just-" He goes, "Yes, it's a combination of two pests and getting old," and took his knife and poked around the bottom. He goes, "You got some rot here." He goes, "Trim it back, just take most of this off." It's not just one thing that can affect a tree or shrub, right?

Matt: Right, and it ties well into drought because oftentimes it's something like that, a nutrient deficiency or a drought, or a weather event or water logging, that starts this spiral of decline. Any given plant has certain things that it's going to be predisposed to, or things that it likes or doesn't like. Having too much light might be something that predisposes the dogwood to other problems. Take any given plant, might have its specific things, but then you're going to have these inciting factors beyond that, that further compound it. In a dogwood that's planted in an unideal location, it's got a little bit too much light.

Now we're into a drought year, so it's going to be declining even more. Now it's in this stressed, weakened state. That's when you're going to start to see things like the dogwood anthracnose or maybe some borers come in. Usually those kind of disease and insect issues are further to the bottom of the spiral, where the real thing that's creating the negative health of the plants are those bigger factors. When we're walking onto a property or like with your shrub that had some insect issues and some other things, it's important that we want to address those conditions. Also we're just going to be in this cycle of always addressing the insect or the disease issue, unless we address some of those predisposing factors or the inciting factors, like the nutrient deficiencies, or like the drought that got it to that stressed point to begin with.

Doug: Has the weather changed what you're planting or the way that you're planting?

Matt: I would say it's always a factor and more so within a site, I would say, than anything else. There's microclimates even within the larger area that we're having. Choosing it for the specific site is important. I would say choosing plants that are more drought tolerant is a good idea in general, since we've been having these consecutive years of drought. It's not a coincidence that you see pines throughout North Carolina, because they are a little bit better adapted for less water and drought conditions.

The needles themselves are an adaptation to conserve water. There's a little bit more volume per surface area in a needle compared to a leaf. There's also the stoma on there are sunken down a little bit, so in times of high wind and dry conditions, you don't get that quite zapping out of the water like you do across a leaf surface.

Doug: I know it's dependent on the site. Again, we always talk about right tree, right place. What's some stuff that you're planting or what's some things that you like to plant when you find the right spot? Maybe off the beaten path or maybe that might be better for people when we're dealing with drought?

Matt: I'd say we check specific plant characteristics, but pines would be good. Things that have a little bit of a waxy leaf coating are generally a little better too, so like a ligustrum or camellia around here. If you feel the leaf, it has that extra layer of cuticle and that can help prevent the leaves from drying out. On the other side of that, if you think about like a hydrangea leaf, that's just very easily dried out. It's more supple than the little bit hardier plants. Things like the ligustrum, or around here, elaeagnus does great, but I don't know if I'd want it growing too close to my house. It tends to take over, but it's a good idea for a planting for a hedge or that sort of thing, that would be pretty tolerant for these conditions.

Doug: When you say camellia, you break my heart because we cannot grow them up in Pittsburgh. We're just a little bit too far north. Maybe as things change here, and they are changing, something's different in the climate. Maybe we'll be able to grow them, but every time I travel to a little bit of a warmer climate and I see camellias, they are just stunningly beautiful. To me, they don't look tough, but they must be a really tough plant, right?

Matt: Yes. I like them. They flower at a unusual time too. In a garden, having that interest earlier in the season, I think is a really good quality.

Doug: When we're talking drought stress, we're talking spiral declines of trees. Let's talk a little bit about when you get on site with tree risk assessment, as trees do start to decline.

Matt: Yes, tree risk assessment. There's a formalized process that the ISA uses and essentially what it is, it's combining the likelihood that a tree or a part of a tree might fail, with the consequences of what might happen if it does fail. We're doing a version of this most times when we go onto a property or we're giving advice to clients. We're looking for factors in the trees, things like cracks, cavities, heaving. Those would be very obvious signs of an increased likelihood of failure in the tree. Then you're assessing if it failed at that part, what's it going to hit?

I give this advice to people all the time, if they have a big natural area on the back of their property, they might have 50 trees back there, they're all going to have deadwood in them. You don't want to go walking through there in a storm, but it's not necessarily a risk and a hazard if it's not going to strike anything when it falls. On the flip side of that, if that tree has a couple of dead branches and it's right next to the house, that standard is going to be a lot higher for what we need to do. Maybe pruning those out or doing something to mitigate some of that risk of failure.

Doug: Makes good sense. Before I let you go, I want to ask you a few questions about your job. How did you get into this and why is it right for you?

Matt: I've been in the tree care industry since 2016, which to me doesn't sound like that long ago, but I guess that's eight years. I've been doing it a little while now. I'm an outdoors guy. I like hiking and backpacking. I'm a plant guy in general too. I have a bachelor's in biology, but I found myself taking a lot of plant bio ecology type classes. To me, what's really interesting about plants is just the complexity that's maybe not there on the surface level, or if you don't really know what's going on there. Plants have to defend themselves against getting eaten, but they can't move, so they have to develop some sort of defense. That's where you find spikes or chemical defenses in some of the amazing plant compounds that you get.

That's just one example of a complexity that you find when you get more and more into this. The drought stress that we were talking about, just the processes that are there. It's not just tree or background or that sort of thing. Then when I go for those hikes or that backpacking, I find that it doesn't look like woods or forest anymore. It looks like maple tree and pine tree and oak tree and, oh, look at what's going on with this one. There's a lot to look at. There's a rich environment there that I really enjoy.

Doug: Man, I'm going to leave it right there. That is good stuff. Thanks for joining us and thanks for all the great information. I really enjoyed talking to you today.

Matt: Thanks, Doug. I enjoyed it as well. I appreciate you having me on.

Doug: Matt, we hope you all get some good spring, summer rains down there this season. Now tune in every Thursday to the Talking Trees podcast from the Davey Tree Expert Company. I'm your host, Doug Oster. Do me a big favor, subscribe to the podcast so you'll never miss one of these shows. If you've got an idea for an episode, maybe a comment, send us an email to podcasts@davey.com. That's P-O-D-C-A-S-T-S at D-A-V-E-Y.com. As always, we like to remind you on the Talking Trees podcast, trees are the answer.

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