Drought tolerance of trees in Southeast Texas

In 2011, we are experiencing the worse drought ever recorded in Texas. In The Woodlands, our forest is our most important asset that cannot be immediately replaced. We need to protect this asset.

Trees often reach deep into the soil to find moisture but some have shallower roots than others. The questions  "Are my trees dying?" and "How can I prevent my trees form dying?" have been raised by many of my readers and friends. Although I have written one other article on this subject, this year is different and we need to address the issue as it is. Here are the answers and some references to put you in the know. I have asked the same questions, so I share my findings and observations. Personally, I have trouble with pines, Magnolias and some hardwoods. I will list trees by name below and give you drought and water tolerance information. A very important thing to remember in the summer - there are trees which hibernate as a defensive mechanism. Unless you are sure the tree is dead, do not remove it until next Spring when it does not bud and produce leaves. If you know the name of the tree, you can use this as a  reference (and other internet sites) to see if it is hibernating, and then rid yourself of it if it is dead. Or you can consult with an arborist.

A tree will have a water content of 200% normally. In a bad drought, it will fall to 100% with the tree living. A large tree needs a lot of water to reach normalcy after it has declined to the severe drought level. At an extreme level, many will die for thirst. You can't allow a tree to reach that stage, because it likely will not recuperate.⁴

First, do water your trees!! Use a drip irrigation technique or an injection technique. I use a drip irrigation hose and a hand-held nozzle sprayer.  I also use a rotating sprayer if there are plants near the tree that also need to be watered. A friend of mine suggested going to a home supply store and getting a bunch of inexpensive buckets. Put a couple of holes in each one and fill with water to drip irrigate several trees at once. He uses this method for small fruit trees. You can use a triangular placement method. For trees I simply cannot live without, I lay  the hose around the tree in a helical configuration extended to the drip line.  Drip irrigate under low water pressure for one hour. I can see the water dripping, but it is not dripping fast. In 100 degree heat, without any rain, I will do this every 10 days to two weeks. For trees that can stand drought more such as pines, every three weeks. The Texas Forestry Service recommends watering each tree every 10 days 1-4 inches.¹ The volume depends on the type of tree. If the roots are shallow and the ground is porous, 1-2 inches is about what I would use for the frequency I recommend.  Both the frequency and volume are dependent on the soil, species and weather. Always water in the evening to the early morning to match the hydration cycle of a tree. ⁴  If a tree has a low drought  tolerance, you need to pay close attention to it under heat stress and make sure you water the tree in advance of stressing it to the point of wilting. Watering is preventative medicine, not a cure. A nice little article I found searching via Google was in the Lufkin newspaper. ³

Here is a list of the trees I researched. I have most of them in my yard. I have adjusted some of the wording  to include local observations.
+ Bald Cypress: drought tolerant. Defense is to simply shed its leaves and hibernate. Small ones will eventually die if the dry period is for a long time. Tree is beautiful if kept watered. If no access to water, the tree will appear dead by leaves turning a dark brown.
+ Blackjack Oak - drought resistant - self defense is to hibernate and come back next Spring. Leaves turn brown and tree looks dead, but is not. Disease can kill the trees during this hibernation.
 + Bur Oak - very drought tolerant

+ Chinese Tallow: very drought resistant. Tree is hard to kill and invasive. These trees do not belong here. Please do not plant them. Instead, remove them from our ecosystems.
+ Crepe Myrtle - very drought tolerant. Excellent for cul-de-sac island.
+ Dogwood: low drought tolerance. Needs its water once a week.
+ Live Oak  - very drought tolerant. Also salt resistant. A Texas survivor. Tree likes its water and will grow much more rapidly when adequately watered.

+ Loblolly Pine: drought tolerant but highly intolerant under an attack by beetles and very vulnerable when small. Doesn't wilt, just dies. Hose configuration helical but from the trunk, not from the drip line.

+ Long Leaf Pine: very drought tolerant when large, vulnerable when small. Use same helical arrangement as Loblolly. Also highly vulnerable to insect damage and disease when under drought stress.

+ Magnolia: drought resistant - is susceptible to leaf browning and even death if no water at all
+ Mulberry: drought tolerant
+ Pecan: drought tolerant - needs water in fruit bearing months. Does best near and with water.
+ Redbud: drought tolerant, its leaves wilt easily but tree recovers at night
+ River Birch: drought tolerant - a strong survivor
+ Sawtooth Oak - drought resistant - will defoliate in self-defense against drought. Looks dead but is not.
+ Shumard Oak - very drought tolerant
+ Southern Red Oak: drought tolerant. Evidence indicates increased mortality in drought years
+ Sweetgum: low drought tolerance - watch closely for stress
+ Sycamore: drought tolerant
+ Texas Persimmon: extremely drought resistant. Survives when many others fail but also vulnerable to insect attacks.
+ Water Oak: low drought tolerance. Name says it all.
+ Wax Myrtle: drought resistant - definitely has its limits. Entire branches will die without water
+ White Oak:  very drought tolerant - may lose some limbs in drought
+ Willow Oak: drought tolerant. Does best where there is water.
+ Winged Elm: very drought resistant.Sheds leaves under duress
+ Yaupon: extremely drought resistant. Probably the most tolerant of all native trees. Lack of water affects berry production

+ There are many more trees to catalog. Generalizations are made such as "pecan" that is not necessarily true for all species. Breeding for drought tolerance is possible and in the case of food-bearing trees, is often the case. We are also likely to find exceptions to native species. I find articles through Google Search for the tree name and "drought", I can find the needed information on many trees. If you would like any additional name included, please let me know, and I will be glad to research and document the findings.

¹ Effects of Drought on Trees - Texas Forestry Service
² Tree and Shrub Irrigation during a drought - Texas AgriLife Extension Service
³ Native Plants - watering trees in a drought, Lufkin Daily News
⁴ Drought Damage to Trees - Warnell School of Forest Resources,University of Georgia

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

How to water trees during a drought in Southeast Texas

This article applies to any drought-stricken area including Southeast Texas, especially The Woodlands Texas. Anyone who knows me, knows I love trees. It is time to be concerned about this year's drought. This year could be a record breaker! That is, this could go down as the worse year in history for a summer dry spell. La Nina is the key. When will it go away? Next hurricane? Regardless of the answer, we need to water our trees now. Two months have passed without significant rainfall.

Any tree planted within the last two years must be watered now. My suggestion is to water a small tree thoroughly every two weeks. Trees that have been planted more than two years ago may need attention now also. They can be watered every three weeks. Very large trees can generally get away without water for four weeks but be careful. One formula for application volume is 10 gallons per inch diameter of tree trunk. The temperature is so high now (100+ degrees) that all plants need more frequent watering than they normally require. To water trees, it is advantageous to understand where the roots are located, the physical nature of the roots and water delivery process to the leaves.

How do leaves get water?
A tree's primary source of water is an area from the surface to about a foot and a half deep, located around the tree. To understand what the root system looks like, simply look at the tree and picture the tree limbs as roots which are usually a mirror image of the tree limbs. The length of the roots will be longer than it corresponding limb and will extend beyond the drip line of the leaves. Now think of the leaves as fine roots needing to find water. The tap root will penetrate much further, but the shallower roots are its source of life and are the key to the tree's health. 90%+ of the roots of a tree are within the first foot of soil! In broadleafed trees, water is delivered to the leaves of the tree from the roots by a physical process called transpiration which leverages a basic physics process called capillary pressure. A pressure that counteracts gravity pull is produced by the capillary walls consisting of cells especially made to move water and nutrients from the soil to the leaves. In the leaves, during the day, the stomata under the leaves constrict to preserve water. But as inevitable evaporation occurs in the heat, water must be replaced by the capillary pressure pushing the water into the tree leaves, keeping a pressure in the capillaries. Without water in the root system, the capillary pressure can fail, causing the tree to die. The first sign of lack of pressure in the capillary system is the wilting of the leaves, next a browning, and then a total failure of the capillary system. A pine tree is different. It moves water from live cell to live cell, using a pass-the-baton type process. It is much slower than the capillary process, so pine trees die easier when the water dries up. By the time the leaves turn color on a pine tree, it is too late to recover. Pine and Cypress trees react to a shortage of water in the heat by shedding many of its leaves, thereby reducing its consumption and thirst.

How to water your trees

So as the soil dries, the process of moving water up the trunk of the tree to the limbs is diminished, stressing a tree in its ability to cope with drought. The tree needs your help. A small tree can get by with watering every 2-4 weeks. I use a two gallon bucket. One bucketful for a seedling, two bucketfuls for a 3 foot tree and three bucketfuls for a 10 foot tree. One recommendation is to provide a tree with 10 gallons per caliper (diameter) inch. To do this effectively, you must have the base of the tree mulched as an shallow upside down bowl structure so that the water is held within the irrigation area intended. Get the water to the area on the ground that mirrors the ends of the branches. This is where the ends of the roots occur below the ground. The base of the tree needs to be mulched to conserve evaporation from the ground. The larger the tree and the older age of a tree makes the process more difficult. A large tree needs considerably more water and it must be delivered slowly. A drip hose wrapped in concentric circles around the tree will soak the ground. That is the best way to make sure water reaches one full foot below the surface. It may be more advantageous to use a needle approach however for the large trees, where the water is delivered directly to the roots a foot underground. A water measurement device to one foot deep is handy for you to know if you have reached the depth intended. One can also purchase watering devices for trees at any tree nursery, but they are not required.

Conserving water and being a good neighbor

When the time comes to water trees, we almost always are under a water alert from our water utility for watering lawns. We are either asked to voluntarily conserve water or required to water the lawn only on prescribed days in order to maintain water pressure to homes and have emergency water in case of fire. Drip watering devices do not utilize a lot of water and therefore are not a threat to the water pressure if used with low pressure. However, it is wise to monitor the consumption of your watering process by taking a water meter reading before and after you have watered a tree, so that you understand how much water you are using and what the delivery rate is. If the usage is more than about 10 gallons per hour, you should not be drip watering on days that your home is not allowed to water the lawn.

Watering your lawn is not the way to deliver water to your trees, unless they are seedlings and even that is insufficient for seedlings. If you water your lawn and do not water your trees, the root system will die at normal feeder root depths and only live on the very surface. High wind can then blow your tree down much easier! One inch of water on a lawn is a significant watering but will not reach very deep for a tree's use. Remember Hurricane Ike!

Take care of your trees. They take decades to grow back. The loss of deep roots has proven to be a significant risk to homes and fences in high winds. I recommend reading the references below for additional information.

Additional Resources

¹ Architecture of a tree
² Caring for Trees During Drought

Yellow Yellow everywhere! Woodlands Pine Pollen and Allergies

Take a deep breath or not? What damage can all this stuff do to a house or automobile? Each Spring we see a great deal of evidence that the pines are blooming. On top of that, we have other trees pollinating at the same time. Do our air conditioners filter the stuff out in the house? I suppose I am not the only person to ask these questions. We see this stuff on top of water, on our cars, all over everything!

As it turns out, the Pine Tree emits a pollen that is extraordinarily large and heavy, covered with a substance that makes it less of a threat to humans with allergies than the other tree pollens. Those pollens we can't see are typically worse for those who have allergies. Pine pollen is colorful but aggravating as a dust and probably not a risk to us. It's yellow color comes from it's sulfate content, as one might expect. Logically, we reason that if everything is covered in a yellow substance and that substance is pine pollen, we would be putting the material in our lungs also. That would be true, but not in the volume we might expect by what we observe. Once the material falls, it is unlikely to be inhaled, although it is being blown about on the ground. It is just too heavy to be effectively lifted back up to our nostrils. The pollen is 50-90 micro-meters in diameter, 2-3 times the size of the pollens which tend to stimulate our histamine reactions, which we commonly know as an "allergy". Each pollen grain has a very small amount of allergen, so the combination of an abundance of the grains in the air, the specific allergen itself and personal reactivity to the allergen, all combine to form individual allergic reactions.¹ Saying all of this, there are disagreements as to how well the wind lifts and propels the pine pollen. It is said that pollen travels hundreds of miles in some cases. In our case,I would tend to say that almost all of it rests nearby the source.
Would it be surprising to find out that the pollen is actually considered a healthy product to consume? Yep, all that yellow powder is considered by some as healthy stuff to eat. It is purported to be a remedy for all sorts of things. Personally, I would not say it is or isn't a remedy or treatment for such conditions as osteoporosis or chronic arthritis or Fibromyalgia, or regulates the immune or cardiology systems. There are probably some of you out there who has an opinion on the health aspect of consuming honey made from pine pollen or the use of a pollen extract supplement. If so, please leave us your comment.

In regard to an automobile, the only advice I could come up with is to make sure you rinse the car first and not scrub the auto with the pollen present. It is abrasive material. Running or strenuous work outside? Just common sense. I would take certain precautions to not inhale much air during the time when the pines are pollinating, mostly because of the other allergens in the air at the same time, not specifically because of the pine pollen itself, unless tests have found you to be allergic to the pine pollen. If you are allergic to pollens, you should pay attention to the count by weather forecasters.

When we look at the blooms on the trees, what do we see at this time of year? Something very elegant for both the female and male parts of a tree! The male cones are where the pollen is disseminated and combined with the female cone, is how the tree propigates.

References

¹Sampter's Immunologic Diseases

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