Why Maintain Trees?
|By Helen M. Stone|
If a tree falls in a forest and there is no one there to hear it, does that mean it needed maintenance? Probably not. Unless it was one of Mother Nature?s early culls, the tree probably reached a ripe old age before its demise.
If a tree dies in an urban setting, does that mean it needed maintenance? Probably so ? but the right kind. In spite of the fact that our urban trees are lashed to stakes, irrigated to a point where the soil resembles soup and ?trimmed? on a regular basis, the sad fact is that city trees have short lives. Where a tree in the forest might live 100 years or more, when you plant it on a city street, it?s usually dead by the time it reaches a decade.
So does that mean that trees shouldn?t be maintained? Definitely not! Urban trees need maintenance through all phases of their lives. However, in our eagerness to provide proper growing conditions, we often end up interfering with the tree?s biological processes. Or, if we don?t provide maintenance, the tree dies a slow death as it struggles to survive.
Trees generally need the most care as they get established. If they are pruned and irrigated correctly when young, maintenance requirements will be greatly reduced in the future.
Let?s assume that we have
There are volumes of information on any of the above topics. In fact, if those factors are not met, the most sophisticated maintenance techniques will end up as an exercise in futility. However, for the purpose of this article, we will take for granted that all these requirements have been met.
Probably the most important aspect of follow-up maintenance is irrigation. Plainly put, roots will not grow into dry soil. On the other hand, soil that is constantly saturated will result in anaerobic conditions, which simply means that there is no oxygen. Roots require both water and oxygen for life, so the proper balance must be met.
While irrigation during establishment and beyond is a given in drier climates, studies by Dr. Edward Gilman at the University of Florida showed that even in climates with regular rainfall, supplemental irrigation meant not only quicker establishment, but also better overall tree structure. Trees without irrigation tended to develop weak branches and were prone to cracks in the bark later in their life.
Consider that a nursery tree in a container can be irrigated as much as three times a day. The rootball is almost constantly at an optimal state of moisture, since soil drainage is usually excellent. Thus, frequent, light irrigation is necessary for the best rate of establishment. Be sure to keep the rootball evenly moist, but also irrigate beyond the rootball so that roots can grow into the surrounding soil. Keep in mind that if the soil dries out completely, minute root hairs and so-called ?feeder roots? can die completely.
You could lose almost an entire year?s root growth if you under-irrigate the first summer,? Gilman cautions.
This does not mean that the tree should be submerged in ?soil soup.? If a tree is planted in a sidewalk cutout, irrigating properly becomes a huge challenge. Monitor conditions carefully. Use a soil probe to see just how wet the soil gets and to what depth. Check frequently to see just how long it takes for the soil to begin to dry out. You want to irrigate before it gets completely dried out, but infrequently enough to allow oxygen to remain in the soil.
Pruning to train young trees is also crucial to their long-term success. If you establish a strong foundation for future growth, maintenance will be greatly reduced. After all, a healthy tree requires much less maintenance than one that is struggling. Pruning a young tree is easy; it can generally be done from the ground or using a short ladder and will only require a good pair of hand pruners. At most, you might need loppers or a hand saw.
Dr. Larry Costello, University of California Cooperative Extension Environmental Horticulture Advisor, San Francisco?San Mateo counties, has devised a five-step pruning program to train young trees.
First, inspect the tree and remove dead, diseased and unwanted branches. Next, identify and establish a central leader. Trees that have two leaders develop ?codominant stems? and ?included bark.? This will inevitably lead to the tree splitting in half at some point in its life. It is critical to develop the central leader early on. If codominant stems are allowed to develop, removal later on can leave large wounds and compromise the structural integrity of the tree.
Identify the lowest permanent branch, depending on the use. For example, street trees should be pruned so the lowest branch on the sidewalk side is at eight feet and the lowest branch on the street side is at 14 feet from the ground. Strong attachments should also be preserved and weak attachments should be removed.
Identify scaffold branches above the lowest prominent branch. Select strong attachments and check radial spacing and vertical spacing. You need to visualize how large the branches will be when they are mature.
Look at branches below the lowest permanent branch and remove them at an early age. You can leave them during the first years of a tree?s life to protect the trunk, but take them off before they reach an inch or so in diameter. (Note: A video, ?Training Young Trees for Structure and Form,? is available through the University of California Agriculture and Natural Resources publications catalog. For more information, visit http://anrcatalog. ucdavis.edu/.)
Establishing a sturdy structure is generally best done over the course of a couple of years, especially removal of lower branches. If you can do nothing else, though, be sure to establish a central leader. And don?t forget to remove any stakes! Tree stakes should always be removed after the first year or so.
Proper fertilization is probably the next important maintenance concern. The need for nutrients will vary, depending on the soil type. The only way to truly customize a fertilization program is with a soil test. This will tell you the nutrient content of the soil, the pH and, if necessary, the salt content. Knowing this, you can determine which nutrients the tree needs.
However, like most plants, nitrogen is probably the major nutrient that is needed for growth. Many other nutrients are already present in the soil. If a tree is grown
in or near a turf area, though, it probably gets enough nitrogen if the turf is fertilized regularly.
Fertilizers can be applied in the early spring before the tree puts on its major growth flush. Some arborists also recommend an early fall application, as many trees experience major root growth during autumn. Newly planted trees should receive small amounts of quick release nitrogen (about .1 (1/10) lb per 100 sq. ft.) or twice that amount for slow-release N. Broadcast and water in.
If a tree has a thriving root system due to proper irrigation in its early years, plus a strong branch structure because of good training and pruning, it will be much easier to maintain later on. However, it will still need some maintenance to do its best.
Once established, the second phase of a tree?s life begins. This is a growth phase. Depending on the species and location, trees can double in size during a single growing season. If you are ?inheriting? a tree during this phase, it?s still not too late to perform corrective pruning. Follow the basic steps for tree establishment listed above. Keep in mind, though, that you shouldn?t remove more than one-third of the total canopy ? less than one-quarter is even better. In this phase, the tree can still recover from major branch removal if it is in good overall health.
Don?t take this to mean th at you should be topping the tree. Topping ? removing large branches and leaving big stubs ? is never recommended. If the tree is ?too big,? remove it now and plant something else that fits the space. Topping can make the tree a liability for life.
Your fertilization rate should increase to .2-.4 (2/10-4/10) lb. N per 100 sq. ft. Soil pH can often affect the uptake of many micronutrients, but iron is usually the biggest problem. Intervenal chlorosis (yellowing between the veins of the leaves) usually means an iron deficiency, but only a soil test can tell you for sure. Iron can be applied on the soil surface. For faster results, foliar sprays can be used. Trees may also be injected with iron and other micronutrients.
Irrigation should be adjusted now so that the tree receives more water less frequently. A tree?s roots absorb the most water directly beyond the tree?s dripline. Therefore, drip emitters that are near the trunk can be eliminated at this time. Although ?infrequent, deep irrigation? may be the usual recommendation, keep in mind that almost all of a tree?s roots are in the top two feet of the soil?s surface and the majority of the roots are in the top foot. Use your soil probe to see how deep the water goes.
In the third phase of a tree?s life ? maturity ? maintenance can actually decrease, especially if the tree has been well cared for in its youth. Irrigation can be adjusted once again for less frequency and longer duration. Fertilization rates can be cut back to .1-.2 lb. per 100 sq. ft.
Pruning should be kept to a minimum. Remove only dead or dying branches. If there are hazardous or crossing large branches due to neglect or injury, they can be carefully removed. However, the tree will need to be monitored carefully.
Mature trees can often suffer symptoms from soil compaction. In this case, drilling or trenching and adding organic matter (be careful to work around major roots) can often improve the tree?s health.
Cabling and bracing trees with structural problems was a popular option that is gradually falling out of favor because of liability concerns. Proper cabling and bracing can save branches and result in years of additional life. But should the tree fail, the arborist who performed the job can be held responsible for any resulting damage to people or property.
The final phase of a tree?s life is senescence ? a nice way to say old age, decline and death. Many times, senescent trees are magnificent, beloved specimens. Hard decisions must be made as to safety and liability.
Basically, when the liabilities outweigh the advantages, it?s time for the final maintenance option ? removal. However, we are then given the opportunity to select, plant and maintain a new tree that will offer shade and beauty for generations to come.