Humans have an innate love for trees. We love them for their beauty. Their structural nature—upright, spreading, weeping, columnar, contorted. Their colors—flowering, fruit-bearing, the changing of leaf color, the varieties of bark. We love them because of the way they make us feel. In fact, studies have shown that surgical patients recover more quickly when their windows provide a view of trees. We love trees for the shade they give us. Trees actually alter their environment, improving air quality, harboring wildlife and moderating the climate. Perhaps the most poignant reminder of our lasting relationship with trees is how often trees are planted in memory of a loved one or to mark a significant event.
Little wonder tree preservation gets our attention.
Tree Preservation: The Killers
The Houston area is filled with a fascinating variety of trees, from the mighty oaks and pines to the miniature ornamentals. Their chances for survival are much greater with some preservation and conservation efforts. This is offer the first part of a large scale landscape project.
Trees face three offenders when it comes to their survival during construction:
- Compaction. The main killer of trees, both during and after the construction of a home or building, is soil compaction. Soil compaction is caused by these culprits: 1) construction vehicles driving over the root zone; 2) construction materials being set down on the roots; 3) soil being piled onto the root zone, which compacts the soil and suffocates the tree by cutting off the exchange of gases in and out of the soil; and 4) continuous walking over the root system. The most common, yet overlooked, cause of compaction is foot traffic—in fact, compaction from foot traffic is the main killer of trees on a construction site. Sadly, people just don’t think it matters.
- Root damage. Root damage can come from a variety of activities, but generally it is due to digging for foundations, swimming pools, landscaping, irrigation systems, drainage systems and landscape lighting.
- Soil contamination. Soil contamination is normally due to construction materials, such as paint, turpentine, lime, cement, or acid, being left or dispensed on and near trees. Over time, these materials leach into the soil, infect it and kill the trees.
Tree Preservation: How to Lessen the Damage
There are many pro-active moves that can be made before and during construction to mitigate the damage to the existing trees on a site.
- One of the most commonsensical action items in tree preservation is to fence off the root zone to force people, trucks and materials away from the trees. Be sure to install a fence that cannot be easily taken down or breached.
- Do a deep root fertilization to the trees so that they have as much nutrition as possible during construction. It is important to start this feeding early because the feeding process takes time.
- Install a construction irrigation system to ensure tree preservation. If the existing trees had regular irrigation prior to construction, it is important to maintain that irrigation during construction. Many times, construction can go on for a year or more, so changing the irrigation—or not watering at all—can only worsen the impact of the construction process.
- Construct a path or bridge to reduce the impact of the construction. A confined path will minimize impact on the site, soil and root structure. Paths and bridges can be made of such eco-friendly materials as bark mulch, geo-grids or wood. See bridge below:
- Prune the roots to help tree preservation. If you know a tree’s roots will be cut or damaged due to the construction, yet you want the tree to remain, go ahead and trim the roots beforehand. This measure is much less stressful on the trees than having the roots ripped and torn.
- Hand-digging for utilities, electrical, plumbing and irrigation systems goes a long way in tree preservation efforts. All trenches near trees should be dug in a radial pattern to mitigate root damage. See picture of a large pipe installed under tree roots below:
- For areas that are more sensitive, compressed air can be used to blast the soil away from tree roots. This way you can see all of the roots and run your irrigation pipes, landscape lighting conduits, etc. without cutting them. See picture below of tree roots exposed with compressed air:
- For deeper trenches or for Houston’s heavy clay soils, use a hydro-vacuum to expose the roots and navigate around the tree roots without cutting them. In essence, you create tunnels in and among the root system.
- Use root barriers in tree preservation. During construction, root barriers can be installed to prevent new and existing trees from damage due to new hardscapes, swimming pools, outdoor water fountains and landscape lighting conduits.
- Once construction is completed, trees need another deep root fertilization to promote health. This treatment is especially important when you are headed into the hot months. Houston summers—all by themselves, regardless of any duress trees might be under due to construction—can be very stressful for trees.
- Aeration is another important tool in tree preservation as it promotes root growth and combats compaction.
- Inspect the trees for insect infestations, such as pine bark beetles and bores. Apply treatments as needed. Insects can kill really quickly when Houston’s weather turns hot and the trees are stressed from construction.
Tree Preservation: Why It Matters
Besides the aesthetic qualities of trees, there are some very practical reasons to put time, money and energy toward tree preservation. Energy bills are most notably affected by the presence of trees as the shade they produce helps reduce air-conditioning costs. In this ecologically-aware era in which we now live, green architects tell us that what you do on the outside of your house—like creating shade by planting trees or judiciously using the shade of existing ones—is up to seven times more effective than anything you do on the inside of your house.
Also, it’s been proven time and again that a landscaped and well-maintained yard, including trees, increases your property’s worth. “Trees are of great value to homeowners,” says Jeff Halper with Exterior Worlds. “They are more delicate than many people realize and, unfortunately, construction kills a lot of them. Since trees are such large organisms, it takes a while for them to die. So four or five years can pass before they finally do die and your builder is long gone by then.
“Another important consideration is that most upscale communities have tree replacement rules that require property owners to replace the equivalent tree size if a tree is cut down. For instance, depending on the code, if you cut down a 12-inch tree, you must replace it by using, say, three four-inch trees or two six-inch trees.”