Posts Tagged ‘roots’

continued from Heat, Drought and Trees, Part I 

Even our native Mexican Plum tree is not immune to the effects of heat and drought stress.

Last month’s article touched on heat damage but the subject was not covered in detail.  As with the previous article, let’s consider all trees, shrubs, groundcovers, and turf to be covered by one term:  “plants”.

Regardless of the moisture levels in the soil, extended daytime periods of 95 degrees and above slow the biological functions of plants.  This slowing phenomenon, which protects plants by reducing water loss through transpiration, is known as “self induced dormancy”.  Transpiration uses water, absorbed by the roots and transported to the upper parts of the plant, to be released into the air.  This evaporative cooling is much like the piping that emits a mist to cool the air during the State Fair.

Unfortunately, this slowing of biological function also reduces the amount of plant food (sugars, carbohydrates, and others) produced and stored by the plant.  Although fertilizers are often promoted as “plant food”, they are actually elements that are absorbed by the roots and transferred to the foliage.  The foliage, with help from the sun, produces a plant’s actual food through photosynthesis.  The resulting food is stored in the plant’s tissues.  Extended periods of heat reduce the amount of time a plant can produce and store its food.  Given our Texas weather, even a Mexican Plum can be affected.

Reducing the effects of heat

Although some of our native plants were negatively affected by the extended period of heat in 2011, native and adapted plants are best suited to survive and function quite well.  Heat tolerant landscapes contain mostly native plants that are grouped in a natural setting or environment appropriate for the plant.  Including other native companion plants as part of a planting group helps to create (or restore) a natural ecological balance.  Any plant properly placed in a healthy and balanced ecological system will better survive anything that nature can whip up.  When we isolate plants from their normal companions or when the ecology is not in balance, it is much more difficult to keep them healthy.  Grouping species typically found growing together in nature, provides a greater level of protection from heat as well as other forces of nature.

Which species of plants may be native or adaptable to an area is often debated.  However, the late plantsman, Benny J. Simpson, researched various tree species from West and South Texas that are adaptable and heat/drought tolerant.  He was a true pioneer in native plant knowledge and a research scientist at the Texas AgriLife Research and Extension Center at Dallas.  The trees he planted in test plots off Coit Road, in Far North Dallas, were only watered for the first year or two–purposely.  His research groves are open to the public and still exist today without irrigation as an example of adaptable species that can tolerate both heat and drought.  Although many of these trees are not currently available in retail nurseries, they could be if more folks ask for them in the future, wink…wink. (http://aggie-horticulture.tamu.edu/ornamentals/natives/about.html )

If a smaller plant in your yard is not heat tolerant, covering it with a shade cloth or similar material may help.  Misters that emit water vapor around smaller plants during the heat of the day can help reduce heat damage.  Plants near a white or light colored structure or a glass wall may receive more reflected sunlight, adding to the potential for heat damage.  Also, plants in areas affected by the Urban Heat Island Effect must also be able to withstand increased surrounding temperatures (www.epa.gov/heatisland/).

If it can`t stand the heat, it may not belong in our Texas kitchen. 

New home construction and remodeling around existing trees can lead to serious damage and in many cases mortality of existing trees.

There are a number of species which can only tolerate minor changes to the environment before they begin to decline in health and vigor. The Post Oak is one of these species. An above ground visible deterioration may not become evident for several years after the change has taken place. One of the biggest factors which typically goes unnoticed is that many of these trees have evolved on the site with the annual rainfall of 30 – 35 inches per year. Once we develop a site and add an irrigation system, the amount of moisture falling on the property is doubled. Existing trees, especially with root damage, will not tolerate this dramatic increase in moisture.

POST OAK (Quercus stellata)

The Post Oak is common in west Dallas county, Collin county, and Parker county. They tolerate little if any change within the environment surrounding their root zone. They tolerate additional moisture poorly as well as most landscape development. The Post Oak is commonly reported to die overnight. This is actually from many years of root deterioration. Many times this deterioration is accelerated by increased moisture. We attempt to improve the environment for redevelopment of the root system with deep root fertilization programs. This process not only provides a high quality nutrient solution to the root zone, but also aerates or adds oxygen to the root zone. Many times these programs may be designed to be very aggressive with a series of feedings during a season. Site conditions such as limited root area, soil compaction and tree condition will dictate which type of program your Arborist may design for your trees. Budget considerations are also a factor.

In most cases we are attempting to slow or stop the deterioration of the tree or trees. As frustrating as it may sound, in many cases we hope the trees look no worse next season. You must remember that many of these trees have developed their root system over the last 30 – 50 years. The development has within a matter of months eliminated a majority of the root system. It can take several years to visually see improvement. You must be patient.

Pruning to remove green or live tissue is NOT recommended. We believe that the more leaf area a tree has, the more usable food is being produced. Many times your Arborist may recommend deadwood removal ONLY.

Reducing the amount or frequency, or both, of your irrigation output will almost always be recommended. Many irrigation audits estimate that well over 75% of homeowners with automatic systems overwater.

It is difficult to tell exactly how much you should run your particular system because of all the variables to consider. However, we recommend to start at 3 times a week and 15 minutes per station. If your property has slope to it, it may be advisable to run the lower sections at a reduced time for the higher areas will be draining to those lower areas of the property.

We also recommend to avoid water-loving plant material (such as Impatiens, Caladiums, Azaleas, etc.) within the canopy area of Post Oaks, as these flowers will only tempt you to water more frequently.

We really do not feel comfortable with Post Oaks which have sustained root injury for several years after the impact or change. We have seen mature trees fail 10 and 15 years after development.

The following lists will help summarize this sensitivity of tree species common to North Texas:

Base Investigation and Clearing Root Flares Using the Air-spade_®

The Air-Spade is a handheld soil excavation tool connected to a large air-compressor. The high pressure stream of air is funneled through a small nozzle breaking dense soils apart into small particles. By using air to excavate soil, delicate roots, underground pipes, and hard surfaces are not damaged. Arborists can recommend using the Air-Spade for many reasons.

Air-Spade Uses

• Expose root flares of trees planted too deep
• Expose root flares of trees covered with fill dirt
• Expose root flares and root structure 6” to 18” below grade for base investigation
• Expose root flares for Macro-Injections
• Digging trenches without cutting roots or concrete

The root flare or root collar is the area where a tree begins to flare outward at ground level. This is a critical part of the tree where trunk tissue changes into root tissue. If this area is covered with soil and kept moist for extended periods of time, the tissue begins to breakdown. This leaves the tree vulnerable to root decay and ultimately poor health and vigor.

Base investigation is needed when an Arborist suspects deterioration of root tissue. Since roots can not be seen above the surface, the only way to confirm this suspicion is to excavate the soil and inspect the root structure.

Clearing root flares for Macro-Injections is another common use for the Air-Spade. Macro-Injection is an application method used to apply chemicals such as Alamo for Oak Wilt management. Soil and debris are removed quickly and easily without damage.

EXPECTATIONS OF AIR-SPADE WORK

1. Preparing the Soil Water the soil area around the tree one or two days prior to the Air-Spade work being done. This will soften the soil and expedite the process.
2. Clearing the Work Area The work area around the tree will need to be prepared. Prior to the movement of soil, we will remove any grass, ivy, shrubs, or flowers from around the base of the tree. This work area is typically one to two feet from the base of the tree. We do not preserve the vegetation in most cases and request you salvage any plant material you want to keep. We do not replace the vegetation removed.
3. Noisy Process Due to the high pressure air being used and the compressor needed, the process can be quite noisy.
4. Backfilling the Excavated Area When excavating a root flare, the void created can sometimes be quite deep. If the area cannot be left open, it can be filled with coarse mulch. When the area exposed is greater than eight inches deep, medium to large stone can be used backfill the area insuring greater air circulation around the base.