WESTERN Rooting out problems Greg J. Monfette AVERSATILE TOOL FOR excavating around trees without harming delicate root systems an Air-Spade may well be the answer in a wide range of situations. For years, I ve worked for the City of Los Angeles, tending to the needs of approximately 700,000 trees in diverse locations. I also run a consulting business that specializes in addressing tree root/infrastructure damage. To a large extent, my work is made possible (and much easier) by the Air-Spade, a tool increasingly used by arborists to evaluate and treat root-crown disorders and a number of other applications. The Air-Spade converts highly pressurized air from a portable compressor to a directional jet stream via special nozzles fitted to the end of the device. The finely focused stream of supersonic air penetrates the soil to varying depths depending on soil conditions, crumbling or blasting away the soil particles as fast as the operator can move the tool. Tree roots, rocks and pipes are non-porous, so soil can be cleared away quickly Conventional root crown excavation. causing little or no root damage. In the hands of experienced operator exercising care and a deft touch, this device makes it possible to expose tree roots with their mycorrhizae still intact. Before the Air-Spade came along, root-crown excavations were commonly done by hand, using picks and shovels (or other specialized tools) to dig around a tree s roots to assess its health. The downside of using hand tools is that they can damage the fine, absorbing roots or nick the larger roots, which can reduce the uptake of water and nutrients from the soil or lead to decay. In addition, they can easily break underground pipes. In the hands of an arborist who fully understands tree biology and structure, this is one of the best tools available for delicate soil removal or root excavation operations. Crown excavation using Air-Spade. Developed a few years back by Concept Engineering Group of Verona, PA, the Air-Spade has been shown to be a valuable arboricultural tool. The operator, of course, needs to be aware that focusing the compressed air stream in the same location for an extended period can damage roots and dislodge mycorrhizae or damage the root cortex of thinbarked species. With careful use this is seldom a problem. Root knowledge The Air-Spade is a heavy-duty tool that connects to a high-power, towbehind air compressor equipped with a long hose similar to the system that 1
WESTERN Symptoms of Phytopthora root disease. drives a jackhammer. The tool comes with fittings and specific nozzles to achieve a range of tasks, all of which are performed by directing a triggercontrolled blast of pressurized air at a specific patch of soil. In the hands of an arborist who fully understands tree biology and structure, this is one of the best tools available for delicate soil removal or root excavation operations. When people call me, they re typically looking for someone to diagnose and manage root-crown (or root-collar) disorders. The more common pathogens causing these maladies include species of Armillaria, Phytophthora and Pythium. Phytophthora and Pythium both break down the fine, absorbing roots, reducing the tree s water and mineral uptake. This can slow growth and cause dieback or decline. Phytophthora root diseases also attack and kill areas of the bark on the root crown and the large, buttress roots, causing decline and/or death. Armillaria root disease can do the same, but typically decays the woody roots and root crown. Often the large, buttress roots and root crown are so decayed that structural support is affected. Furthermore, loss of vascular tissue in the bark and wood reduces food storage capacity and the movement of water and minerals upward and carbohydrates from the leaves. Contributing factors to these disorders include: placement of fill soil over the existing root system and against the trunk during construction; planting a tree, so that the root crown is buried; planting ornamentals including turf near the base of the tree and irrigation that keeps the trunk and/or root-crown moist. The resulting conditions favor the development of root disease pathogens or affect the health of the root crown and large roots. Consequently, soil excavation to expose the root-crown area may be needed to assess the health or extent of tissue damage or decay, and to manage the disorder. To understand why this is a problem, let s quickly review some tree biology. The root crown of a tree is at the base of the trunk where the large, buttress roots originate. Unlike the roots, the bark of the trunk and root crown are not adapted to constantly moist soil conditions. So, when the root crown is buried by fill soil, or a tree has been planted so that its root crown is below grade, root disease problems can develop. Excess moisture, whether from irrigation, poor drainage or fill soil around the root collar, favors the development of root Trench made with Air-Spade near tree to locate roots. 2 Deep planting as seen here often causes root crown decay. disease pathogens, which can invade the unhealthy bark tissue or roots stressed by poor soil aeration. When trunk and root crown tissue is kept moist or wet, gaseous exchange the movement of oxygen into the tree and carbon dioxide out of it, is inhibited. Lack of oxygen and buildup of carbon dioxide within, can affect the health and function of the phloem, which in turn increases susceptibility to soil-borne pathogens, leading to root crown lesions (cankers). This interferes with the downward movement of carbohydrate (food) to the roots, eventually leading to root dieback and reduced water uptake. If conditions remain unchanged, damage is likely to increase and the entire tree may die. In addition, the lenticels in the bark, through which gaseous exchange takes place, provide natural openings for soil-borne pathogens. Some clients create problems by planting ornamentals, requiring frequent irrigation, near a tree s base a surefire way to promote moist conditions around the root crown and large roots. Excessive shade and moist conditions at the base of a tree also invite root disorders, because the shade keeps soil moisture levels high and prevents the bark from drying.
WESTERN Note decaying bark resulting from placement of fill soil and moist conditions. Root crown exposed to allow root crown to dry. Most tree species are likely to fall victim to root-crown disorders if fill soil has been placed against the trunk, the root crown planted below grade, and/or irrigation wets the trunk and root-crown area. One of the reasons I use the Air- Spade is to remove soil from around a buried root crown to allow it to dry. This can slow or stop the progress of root disease. So when I begin soaking the soil to facilitate the excavation process, my clients often seem confused by the apparent contradiction. Moistening the soil that may be compacted makes it easier to move the soil away from the root crown and roots, while also keeping the dust level down. Still, some clients are puzzled by this, as I ve told them that too much water around the tree can cause problems. I have to explain that the shortterm introduction of even more water will make it easier for us to remedy the problem without doing any further damage to the tree. Other uses of the Air-Spade One solution to many of the problems discussed above involves removing the soil placed against the root crown, altering the irrigation system and letting the soil at the root crown dry out. The task of removing the soil is much simplified by using an Air-Spade. Over the years, I ve developed two distinct approaches to using this device. One is preventive root-crown excavation, where, if the soil appears too high, I remove whatever is necessary to expose the initial root-crown area. The other is an extensive root-crown excavation, a more invasive procedure that I use in situations requiring that I expose more of the root crown and roots to check for decay and to let the tissues dry out. This approach is used mainly when a tree is already infected with one of the soil-borne pathogens. Using a pick, shovel or other hand tools to remove the soil has the potential to damage the root system and Utility trench excavated with Air- Spade. 3 affect the health of the tree (not to mention the fact that using these tools is more labor-intensive). In many cases, the soil is highly compacted, and intense air pressure is more effective than any alternative approach. An Air-Spade also allows me to be more selective when pruning roots. After clearing away the soil, it s easy to target specific roots for directional root pruning a big step up in effectiveness from straight-line mechanical root pruning that severs all roots in its path, affecting health and sometimes, structural stability of a tree. In my practice, I use the Air Spade for other purposes, for example, I do a lot of utility trenching to identify the location and paths of gas and electric lines in preparation for major mechanical trenching. Puncturing lines is far more likely to happen when picks and shovels are used, while an Air-Spade leaves them virtually untouched. Another advantage is that the work is done more quickly when line locations are clearly defined. I m also called in on home-renovation projects involving foundation expansion. If there s a tree in the way, I use the Air-spade to locate roots, and then we can box up around them, or, sometimes, wrap them in foam, to preserve their health and integrity as the new foundation is built up over the roots instead of severing them.
WESTERN Similarly, we ve used this tool to position piers for at-grade beams. When large tree roots are present, the device can be used to find them, thereby allowing the structural contractor to make fine adjustments in locating piers. Using this process, we ve been able to preserve many fine trees on beautiful, estate properties. The cutting edge In many instances, the Air Spade or similar devices are now being used in conjunction with lawsuits to determine, for example, if a root is, or, for that matter, which root is responsible for raising a sidewalk or damaging a foundation. This may seem an obvious point, but I ve been called into cases where both public and private trees are in proximity to the damage and there s a legitimate question about which tree is causing the problem. Using the tool, we simply blow away the soil and directly identify the culprit. Insurance companies call me, too. One client, for example, submitted a claim in the belief a tree root was lifting his home s foundation. The insurance company needed proof, so we used the tool to expose the root that was causing the damage, photographed it and proved to the insurer s satisfaction that the tree was responsible. This also enabled us to save the tree. We installed an at-grade beam Example of radial mulching to improve conditions in root zone. to preserve the root and prevent it from doing any additional damage to the foundation. The Tree Spade is also useful in digging out trenches in sensitive areas. We blow away the soil to expose the roots and, as we go, can bend them out of the way of the trenching work or cut them back using target pruning. This reduces tree stress by not ripping roots out of the ground with a mechanical excavator, thereby prolonging the tree s life expectancy, and enabling us to keep trees that might otherwise have been removed. With utility trenching, we can trench and tunnel under roots a much better solution than the usual severing of roots that is involved in these installations. I ve also found the Air-Spade useful for radial and vertical trenching in instances where the grade level in the root zone has been raised or compacted. Soil compaction is widely recognized as one of the most significant stress factors affecting trees in urban environments, especially in association with development but also in well-used parks and gardens. Compacted soils have lost most of their macro-pore space that normally holds air and water, thus, resulting in reduced root respiration, poor soilwater retention and loss of beneficial root mycorrhizae. This has a dramatic influence on root health and function. With the controlled use of compressed air, it s possible to trench out radially from a tree s trunk to loosen the compacted soil. If the trenches are filled with a good soil mix, root health and function can be further improved. In addition, vertical mulching with compressed air can break through the soil horizons, improve drainage and it may improve the rooting environment around the tree. The results of such work seem to improve soil biodiversity and may influence the longevity of the trees. Soil level prior to lowering the grade and construction of the deck. Decking built around the two trees following grade lowering using the Air-Spade. 4
Case studies Many of the root problems I see are quite remarkable, and demonstrate just how easy it is to create conditions that cause serious root crown disorders. In one case, I was hired to look at two mature trees that had been planted at different times. The grade around one of the trees, a Sycamore, had been raised, and then later raised again. The second tree, a maple, was planted at a higher grade than the root crown of the first tree. Subsequently, a planter was built around both trees, and the soil level was raised within that structure. The homeowner wanted to remove the planter and restore the health of both trees. I used the Air- Spade to expose their root crowns and lower the soil to the appropriate levels around both trees. The plan was to resolve the issue entirely by building a wooden deck around the trees. This would allow for better water infiltration and soil aeration for the trees, while increasing functional space within the small yard. It also enabled me to keep the root-crown grades at different heights without creating a problem for the client in a high-traffic area. The Air-Spade made it possible for me to identify the original grades of the two trees with ease the Maple was about six inches down, and the Sycamore, about 12 inches down. In this particular case, the client also wanted to reduce the grade of the rest of the soil surrounding the Maple and the Sycamore to yield more usable area in the yard. Potholing using air pressure to dig six-inch-diameter holes from 12 to 18 inches deep along the edge of the original planter, helped me determine where the roots were in that critical span, permitting me to remove about four feet of soil all around the existing planter. At another home, my aim was to remove a planter, bring the soil level down around the root crown and then feather the soil out to create what appeared to be an intentional mound around the tree. This enhanced the landscaping in the yard and preserved the tree. Roots affecting foundation exposed by Air-Spade. In a different situation, a large trench was needed to create a root barrier along a stretch of Ficus trees that extended almost 400 feet. Here, I worked ahead of the trenching machine to expose utility lines and find large roots, enabling me to sever them properly. I ve also used the device to blow out the complex root crowns of the Ficus trees to secure their longterm health. WESTERN On yet another job, the roots of a pine tree were damaging a block wall, and the homeowner wanted to make repairs without harming the tree. I carefully removed the wall and its foundation, then blew out the soil around the foundation line to expose the root structure. This let me identify the new foundation/fence line before building a new wall safely around the roots. Although the primary use of the Air Spade is in diagnosing and treating root-crown disorders, I keep finding new applications for it. I once used it as a blower at the end of a job to do cleanup! The great thing is that anyone who already owns an air compressor and a truck to transport it is ready to go although I must add that working around tree roots should be done by qualified arborists familiar with tree biology and structure. As I see it, whether it s doing delicate work removing soil to expose roots or heavy-duty excavation, there s no better way to get these jobs done. Greg J. Monfette Neighborhood Consulting www.ncatree.com (310) 902-6581 The Air-Spade can quickly remove soil around tree roots without causing injury. 5