Thursday, April 30, 2009

Root Crowns

Most people never get to see what a tree looks like underground. Today we did some root crown excavations so I took a few pictures. This first one shows clearly what can go wrong and why we sometimes excavate.

The tree is about 10 inches in diameter and the width of the hole is about two feet. We blew out the top six inches or so of soil to get a look at the primary trunk flares. When soil gets added around the base of a tree, it loses some of the deepest roots that no longer get enough air and/or water. It responds by sending new roots upward toward the surface. Sometimes a small root crosses over a flare and chokes it off like a noose. The dark line across the center flare in this picture is such a girdling root. We cut it at either end to relieve the pressure, but left it in the groove that had formed around it so as not to damage the bark underneath.

Another problem with added soil is that it traps moisture against the stem of the tree. Roots are well equipped to keep out water they don't want, but stems and branches are not. Trapping moist soil against the bark can lead to decay, disease, or insect infestation. The second picture shows a tree that was about 4 inches too deep. In this case, it wasn't from raising the grade of the lawn, but rather it is a recent transplant that was buried too deep. It may have been the fault of the installer, but just as likely could have been that way in the container. Nurseries tend to add a little soil to the top of the root ball each time they repot, so often container-grown trees are several inches deep before they are ever purchased. The next shot is from the other side of the same tree. You can see a dark line where the soil was before we started at the bottom of the gray bark . The hole is a little deeper than it needs to be because we like to inspect thoroughly for problems when we have the opportunity. When all is finished, we will fill the deepest parts of the hole, leaving the arching trunk flares exposed.The last one shows a tree that has been excavated and had the soil aerated to about 10 feet from the trunk. There are bits of grass still poking through, but it has been pretty dried out and may not survive if we left it like this. The final step is to spread compost over the soil, then top it all off with a three-inch layer of wood chips as mulch. That combination will choke out almost all of the remaining grass. Any stragglers that poke through will be easily pulled out. By creating this buffer between tree and lawn, we avoid weedeater damage and make more water and nutrients available to the tree (grass is a very good competitor).

I'm often asked how far out a tree should be mulched. I always say, some is better than none, and more is better than less. In a forest, there would be little or no grass and everything would be mulch. The closer we can get to that ideal, the better off our trees will be. For more information about mulching, visit the ISA consumer site.

Tuesday, April 21, 2009

Leaf Rollers


In Austin, it's oak leaf roller season. Every year, live oaks are visited by these small, green caterpillars. Some years, it seems like a plague. This year, I have not seen many yet, but there may still be time.

Most people notice these things when they start dangling from the trees. They will hang by a single strand of web, similar to a spider's web. For those of us who find tiny, green worms really creepy, this can be a very difficult time. Walking to the car or mailbox means dodging worms and webs left and right. Often, after I've been working among them, I feel something tickle me hours later and absentmindedly squash one of the caterpillars onto my fingers. It's not very pleasant, but really it's no big deal for the trees in most cases.

Today I didn't see any caterpillars, but I did see the signs they were around. These photos show how the moth gets its name. On the right is a healthy branch next to one with all the leaves affected. Below is a closeup of some affected leaves. If you pry open those curled leaves, you will find inside either a larva or the remains of a cocoon that one made.

We usually get a few calls every year asking what to do about these critters. In the heavy years, we tend to get a lot of calls. But, except in severe cases, there really isn't much cause for action. The caterpillars eat some of the leaves, and some people get really creeped out, but things quickly run their course and the problem solves itself. The birds feast during heavy years, leading to light infestation the following year.

If a tree is so covered that it seems likely to suffer from the leaf damage, treatment would be the same as for any worm or caterpillar. I recommend spraying with Bt (Bacillus thuringiensis), which is deadly to larvae but pretty harmless otherwise. It still is wise to take care with Bt, since it does not discriminate between nasty larvae and caterpillars of desirable, pollinating moths and butterflies. Stronger pesticides are available, of course, but they would be overdoing things in this case. The Bt will do the job, and if it misses a few, they will be gone soon regardless.

Tuesday, April 14, 2009

Pecans

The State Tree of Texas, Pecan (Carya illinoensis) trees are among the largest in our area. They make nice shade trees in addition to providing an edible nut. The natives tend to have small, bitter nuts that are mostly scavenged by wildlife. But planting the right cultivar will yield bushels of the things every couple of years once the tree is established.

As an arborist, I have mixed feelings about these trees. Of course, I love a big, nice tree, but working on them is a real challenge. First, their bark comes off in flaky plates. These plates are notorious for grabbing lines and not letting go. To ascend a tall tree, most climbers throw a sack of shot on a light cord through a nice crotch. When the bag comes back down, the climber ties on a rope pulls it into the crotch, then climbs it into the tree. Pecans often thwart this process. The small cord gets caught under a flake of bark and the bag won't drop. It sometimes takes several good throws before one finally returns to the ground.

Once the rope is in, the real work begins. Pecans are brittle trees that tend to sprawl out in every direction. They get really heavy with nuts in the fall. The older ones have often had at least one "tree trimmmer" strip them out at some point, so there is little interior growth and not much branch taper. What this all adds up to is, they often overreach and break large limbs. When a good arborist is at work, almost every Pecan job will include some crown reduction.

Crown reduction is more than just taking out weight, though it often gets called weight reduction. Taking a heavy branch from the inside of the canopy will not help much. If you imagine holding a dumbell, it's a lot easier to hold it close to your body than at arm's length. The same principle applies in trees. Removing interior growth does very little to reduce strain on weak limbs while contributing to weak taper development and exposing the entire crown to more wind stress. A proper crown reduction is better thought of as sail reduction. By shortening the longest limbs, we reduce the surface area that is hit by strong winds. This is the relief the tree really needs.

So, the climber has to get to the ends of branches. That's in a tree known to break easily. Often, it's a tree that has broken already in the past, so there is not always a nice, central tie-in point to allow for easy movement through the tree. The branches tend to be widely spaced, so the climbing is more difficult than in trees where it is possible to step from branch to branch like in a jungle gym. Once there, a climber has to cut branches and drop them 75 feet or more. In a suburban lawn, that's a big opportunity to break something; most branches have to be held until they can be tossed to a safe area.

These are things that get a real climber going. Some climbers are in it for the trees; some are in it for the money (such as it is). But, a few of us do it for the thrills. Pecans are for us. As much as I might complain, I really enjoy doing something that few people can. I get great views and, usually, nice breezes. These early spring jobs don't provide much shade, but in the summertime, I have shelter from the sun, as well. In late October and early November, pruning a pecan means all the nuts you can eat and a bag or two to take home for pie or pralines. And, since they like to grow near lakes and rivers, sometimes we get to see interesting birds and other wildlife.These crested something-or-others (the client told me what they were, but I'm a tree guy, not a birder) hung out all day near our last pecan job. There was also a red-tailed hawk in the area. I enjoyed watching and hearing it on and off for a few days.

I've been sitting on these photos a few weeks now--if anyone is actually following this blog, they may have noticed my long absence (sorry, I got down after that HEB mess). Today, the trees above are probably either covered in catkins, or fully leafed out, or both. I missed out on the shade on this job, but my sunburn is healed and I enjoyed the wide open skies while I was working.



UPDATE: If you've been wondering about the trees I reported on last time, I have learned more. I sent photos to the City Arborist, and he told me there will be penalties for the damage done. Austin has an ordinance requiring a certain number of trees per 'x' parking spaces. Even though the parking lot has been there for decades, they still have to comply with the ordinance. It is only slightly more consolation than before, since the trees are irrevocably damaged, but I hope the penalties will send a message to the property manager that this kind of shoddy work will not be tolerated. As much as I might like to see them paying top dollar for premium work, I will be satisfied knowing that at least they will be motivated to find a reasonably qualified company for future tree work.

Incidentally, the guys did go back to paint their wounds. They painted oaks, elms, and sweetgums. They managed to skip the sycamores. They painted everything they could reach from the ground (more or less) but didn't get the upper canopies. All things considered, this is not a big concern to me. But it's one more piece of evidence that these guys do not know what they are doing.