Sunday, January 31, 2010


The benefits of trees are many. Though shade and beauty are the two we most frequently refer to, there are many others that provide very real tangible additions to our communities. For example, well placed trees can reduce energy consumption. Trees also act as giant air conditioners by "cooling" surrounding air. This is accomplished as water evaporates from the surface of leaves, much like the evaporation of water that takes place from the condenser in your air conditioner.

Wildlife habitat and screening are other benefits. The benefits mention above are all greater with larger trees. Planting new trees is important, but caring for and protecting our investment in older large trees is critical. A new awareness by the general public is beginning to unfold in recent years. Our knowledge abut how to care for trees is growing everyday. Researchers are learning more and passing that knowledge on.

One of the most aggressive areas of change in recent years has been the increased knowledge about how to protect trees during construction projects. It is no longer considered acceptable to clear large tracts of wooded areas to build homes, office buildings, and highways, without giving some consideration to tree protection strategies.

Urban foresters are now working with many developers to provide the technical expertise needed to allow construction activities and trees to co-exist on the same property. The first step is an inventory of what trees exist on the site. This can be easy on single home sites, and becomes complex on larger sites. Once the inventory is complete tree locations are plotted on a map. This gives the builder and architect an opportunity to try out several options about where to place buildings, roads, parking, utility lines, and equipment storage areas. The "footprint" of a house or building can be adjusted to minimize impact on desirable trees. The inventory will also reveal trees that should be removed because of hazardous conditions or poor health.

Tree protection plans are meant to bring trees into the planning picture, not just to save as many trees as possible. After the layout of a site plan is complete, the location of construction activities and how they will impact desirable trees becomes evident. Tree protection activities can then be prescribed. Protective fencing is recommended where root zones may be compacted. Compaction occurs when equipment drives over roots or when materials are stored over the roots. Compacted soils will deprive the tree of oxygen it needs to grow new roots. Starving a tree's feeder roots that grow near the surface is a sure way to slowly kill a tree. Using fencing to establish "tree protection zones" will keep roots healthy. To be effective, the fencing must protect the entire area under the branch spread (drip line) of the tree. Protection even beyond this area is best as roots will easily grow a vertical distance that is equal to twice the height of a tree! If any of the roots are to be cut when excavation occurs for foundations or grading, it is best to "prune" these roots before they are ripped or torn by a backhoe blade. Cutting them cleanly with root pruning equipment will allow the roots to generate tissue that covers the wound. Without this protection, root rot fungi will enter the roots and decline begins. Placement and depth of root pruning should be determined by a qualified urban forester or arborist. When fill is placed over tree roots, the result is the same as soil compaction. Existing roots are deprived of oxygen and the tree declines. If fill over roots is absolutely necessary, a system of perforated pipes can be used to feed oxygen to the roots at the original grade.

The use of retaining walls and aeration systems can greatly minimize the chances of tree decline. There are many other steps that can be taken to protect trees during construction. The steps mentioned are typically the most important, but careful review by a urban forester or arborist can help you determine which steps to take. The key is good planning and constant communication with your builder and contractors.

Many areas around the country have mandated tree protection on construction sites. Planning is now underway in St. Louis County to determine the need for a tree protection ordinance. Several communities including Kirkwood and Wildwood have introduced tree ordinances to protect our valuable assets. Just like the protection of trees, this process takes a great deal of planning and communication.

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