Hardwood Trees after the Drought

Some parts of Texas remain under an extreme drought, but here in Southeast Texas, we in The Woodlands Texas are only "dry". After several years of low rainfalls and extreme summer heat, our trees have been severely stressed. Under stress, the trees are vulnerable to disease. One such disease that takes advantage of this opportunity is a fungus called  Hypoxylon canker¹. I had three trees alive with this disease for 14 years in my yard. In the 14th year, we had our severe 2011 drought, which killed all three trees. One hardwood, a Sweetgum, was killed from the disease 5 years ago. One killed in 2011 was a Red Oak (probably from Oak Wilt disease) and another was a Sweetgum. Now in 2012 another Sweetgum has died. All these hardwoods first lost top branches and decay set in at the top, gradually killing from the top down. After the trees die, the condition continues in the wood and behind the bark, revealing itself with obvious signs as in the photo below. Treating this condition is very difficult. Preventing the disease from continual advancement is accomplished by plenty of water. So extreme drought accompanied by extreme heat, creates just the right conditions to cause this fungal disease to thrive.

Note the black condition inside the bark 

Bark falling off the tree about a year later after the kill

The Texas Forestry Service predicts a loss between 100 million and 500 million trees in Texas from the 2011 drought². That is a lot of trees! The impact from disease remains unknown. We will experience that this year and beyond! Certainly I am an example of the consequences of the drought on our hardwoods.

¹ Hypoxylon Canker and Oaks, East Texas Gardening
² Texas Forestry Service - Second phase of Drought Assessment

One more summer gone, many tree years gone, Winter's Respite

There remain a number of trees to cut down after the terrible loss we had this past year with beetles in our pines. Based on what I saw, the 1000+ trees that had to be removed from public areas along roads, paths, parks and medians, most of the trees were older than 10 years. Many were 30+ years old. Let's just say conservatively, they were each ten years old on the average. That would present us with a 10000-year tree-year growth loss. I could not say what number of tree years we have in our forest, but it is a very very large number, so the percentage of loss remains fairly low. Yet intuitively, none of us can rest peacefully with the results. The primary reason we must not just write this off is the mere fact that there is a forecast for ensuing years of continuing and even worse drought. Then too, we lost a large number of trees in 2008 to the hurricane. The combined two events raise our alarm to a higher level than the norm.

How are we going to deal with rain shortages, water conservation and preserving our trees at the same time? We must put some financial resources into our future. If this year is only a taste of the future, we should be doing something about it and not just let nature take its own natural course. The one valued commodity that we have, unique from other communities, is our large trees. Without them, we are just another large subdivision on the outskirts of Houston - waterway or not, parks or not, nice homes or not. Nothing really matters except our trees.

Woodlands Pine Trees - we are losing the battle. Now Pine Bark Beetles!

Pine bark Beetles are having a field day, because our pines are weak from the 2009 Texas drought. As you travel about in The Woodlands and Southeast Texas forests, you will see dying or dead trees. A dying tree is turning brown, typically from the bottom limbs towards the top, whereas a completely dead tree has no green leaves at all. The water delivery system has been cut off. Sometimes one, sometimes several trees are dead in a "stand" of trees. One business I visited just today had a problem with this insect. Someone from the Association had already been there to advise the business to remove the infected trees as quickly as possible. That business planned to cut them down this evening. I inspected the trees and discussed the issue with the manager. One tree dead, one adjacent tree dying and two more infected. In that these beetle attacks are classic, by the book, I believe they will lose all four trees. They have already received a guide on what species of trees are recommended to replace those they are losing. These beetles are slowly killing our mature trees and those not so mature. Since it takes decades for a tree to reach 50 feet in height, we are losing what we prize as our trademark - the pine forest trees. It is happening to all species but the Loblolly tends to be more adaptive to the beetle than the Shortleaf or Longleaf. It is not difficult to identify a tree that has been infected. On my street alone, we have lost three large pines this year to the beetle. I have seen three other pines lost in our neighborhood and several others in the park nearby.

This Woodlands tree to the right, infested with these insects, appears to have the pox. A bubbly mass of sap and a bit of the drilled out cambium layer shields ants and other intruders, like woodpeckers from the tunnels built for their eggs and subsequent larvae. The result is a nice tube cavity suitable for eggs to develop and which can be expanded by the young as they mature. This insect deprives a tree from water when many of the insects attack simultaneously. Since the beetle can explore, attack and finish their reproduction cycle in a matter of a few days, they accomplish  complete tree destruction by their numbers and can carry on their attack to a full stand of trees in one summer. Their life cycle is very interesting. One beetle will serve as an "explorer". He finds a tree, bores into it and when he is able to reach the inner layer, he excretes a chemical that attracts other beetles. Hundreds can be drawn to one tree and they can collectively kill the tree to make a nice habitat for their offspring. The eggs hatch under the bark in the incubation tube and the cambium under the bark serves as food for the hatched larvae. The larva then changes into a pupa.

This ugly little thing is a live larva, found under the bark and beneath the inner bark layer of an infected tree here in The Woodlands. If you recall your biology, you know the pupa of a beetle is equivalent to the worm stage of a butterfly. The larva stage of the beetle is equivalent to the worm stage of a butterfly. Instead of eating leaves, this beetle eats the cambium or the live part of the tree trunk, the part that creates the outer ring of wood and the inner bark.

This is the area of the tree from which the pupa was extracted. You can see the bark (outer layer), the cambium (orange second layer which has living cells) and the wood (light brown inner layer). The cambium is the food for the larvae and pupae.

This is the adult, courtesy of  the University of Georgia Bugwood Network.

A stand of infected trees (or perhaps better stated "trees under attack)", is on the Woodlands Parkway. Two trees are dead and two adjacent trees are now under attack. Since it takes about 8 days to kill a tree, this will be completed in only one more week. Then others will get infected unless these are removed now.

Some interesting facts about the beetle: they do not die off in the winter. They tend to attack the same tree several times over, but their lifecycle is slower than it\ is in the summer. The insect is active all year long. Adults will lay eggs and leave their eggs host to attack another tree, but they will also reemerge and lay eggs in a tree previously attacked, even using the same tube. They lay about 30 eggs per mating sequence. They do have enemies - the woodpecker, mites,  and two types of beetles. I am reasonably sure I saw a Checkered Beetle on a tree infested with the Pine Bark Beetle.

When inspecting trees, one will find another visual hint of an infection, the running of sap such as you see on the right. Inside the bark, there are probably pupae causing the flow of sap to flow out of the tree instead of up water moving up the tree.

You might also see this - the powdery cuttings of the inner bark or outer cambium.

How does one treat this problem? Unfortunately, the remedy is very difficult. Generally, in forest management, the trees are cut down and isolated from others in a stand.  They can be allowed to stay or burned.. At a residence or park, there may be insecticide remedies or natural predator remedies but the insect attacks are so quick and  thorough, there may not be enough time to react. Prevention measures against a flying insect is not very promising. At the time of writing this article, I have not ascertained the best approach, although I would prefer to take the natural predator avenue. This is the next step in my study. I believe it is best to get this concise information to readers in order to educate what might be happening in their piece if the forest.

On September 26th, I visited a booth of the Forest Forest Service. We discussed this problem and the following is from my learning there. The forest service is currently inundated with concerns from all over the state. A prolonged drought weakens our pines to the extent that they become not only vulnerable to the beetles but are significantly at risk of death. This year has been a very bad year for the IPS Bark Beetle. This species attacks the weak trees and does it in stands or groups close together, unlike the Souther Pine Beetle and turpentine beetle, which attack healthy trees and takes out one at a time here and there, not typically in stands. A tree infected with the engraver beetles will often have three IPS species in it. The six-spined calligraphus is the largest at 5mm and attacks the large diameter portion of the tree - trunk and limbs. The eastern five-spined grandicollis is the mid sized at 4mm and attacks the smaller branches in the mid part of the tree. The smallest at 3mm is the southern avulsus which attacks the small branches, typically at the top or the furthest from the root system, in recent growth parts of a tree.  One species at the base, one in the center and another in the top. Our trees in The Woodlands are susceptible, because they typically grow in shallow soils with a clay layer beneath it, making the soil not give up the water that the tree needs in a drought.  Typically the IPS Beetle, also called the "engraver", is 3-5 mm in length. The other beetle now active in the forest is the black turpentine beetle, a lover of fresh pine sap and thereby the name. They however are typically found in stumps and injured trees usually associated with logging but in our case, with the injuries from hurricane Ike.²  
It is important to note that a home owner could have a healthy tree and three days later the tree could be dying from these beetles. The engraver beetles act fast and in mass!

Although we are not going into treatment in this article, the advice was - give the tree masses amount of water as soon as it sees the problem. A lot of water will also help your trees through very stressful times in a prolonged drought. Another piece of advice is to keep the areas around a pine tree free from fresh cuttings. Do not cut your trees and place the cuttings under the tree. Remove fallen live branches from pines, thereby removing the attractive material that initially brings the beetle under your tree.

Every year we have this issue with beetles but this one is particularly tough because of the hurricane and the drought. We typically see cycles of infestations. Expect the southern pine bark beetle to emerge in big numbers in a few years. They typically follow a major infestation of the engraver beetles about five years afterward.  The last really bad infestation of that beetle was in 1985 when 15000 infestations were reported (note that this was the number of event reported, not the number of trees - one infestation might cover 100 acres or more).  

What has happened is that hurricane Ike produced a lot of material on the ground that the beetle could feed on and that attracts it. In the Spring, the material was available but as the summer drought unfolded, the beetles needed to get their nutrition from the live trees. Once an explorer finds a vulnerable tree, he chemically calls the others and bingo! There is an infestation attracting all species of the engraver beetle and possibly other species as well. Thanks to the representatives from the forest service for their valued input to this article.

References
1. Bark Beetles of Concern to the Southern U.S. by the University of Georgia Bugwood Network
² Southern Pine Beetle or Pine Engraver or IPS Beetle, a brochure by the Texas Forest Service