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Tree care standards and guidelines

The American National Standards Institute (ANSI) A300 Standards for Tree Care Operations represents the tree care industry's consensus on tree care practices. The standards can be used to prepare tree care contract specifications. The A300 standard consists of seven parts:

Part 1 - Pruning
Part 2 - Fertilization
Part 3 - Supplemental Support Systems (includes Cabling, Bracing, Guying, and Propping)
Part 4 - Lightning Protection Systems
Part 5 - Management of Trees and Shrubs During Site Planning, Site Development, and Construction
Part 6 - Transplanting
Part 7 - Integrated Vegetation Management (IVM) [management of vegetation in electic utility corridors]

These tree care operations standards may be purchased directly through industry and professional associations such as the International Society of Arboriculture (ISA) and the Tree Care Industry Association (TCIA). A separate set of safety standards, ANSI Z133.1, covers safe arboricultural working practices.

The ISA has developed Best Management Practices (BMP) guides as how-to companion documents for the ANSI A300 standards. These BMPs provide more details about how the standards are applied.

These national standards and BMPs have the advantage of being widely accepted throughout the industry. However, being consensus documents that are national in scope, they may not account for local conditions and issues as well as a locally-adopted standard would. Furthermore, because the documents are copyrighted, they cannot be duplicated for local use and distribution. In practice, larger organizations adopt their own standards and guidelines that are based on these national standards (for example, City and County of San Francisco's Tree Pruning Standards and Guide). They can then distribute these standards as necessary. Cooperative Extension programs, state and federal agencies, and other organizations have also produced various tree care standards and BMP guidelines. These are widely available for access and dissemination.

Pruning standards and guidelines

Many different documents and websites discuss proper pruning methods for mature trees. In addition to the ANSI A300 Part 1 standards and ISA BMP Guidelines noted above, the USDA Forest Service has an online website and downloadable PDF document that covers most of the basic concepts of pruning (How to Prune - Publication NA-FR-01-95).

Pruning required to training young trees is discussed at the ISA website and the Urban Tree Foundation website.

Guideline specifications for nursery tree quality

Root and top defects in commercial nursery stock can be the cause of poor establishment in new tree plantings. Worse yet, defects such as girdling roots and poorly structured tops can lead to serious problems many years down the road.

The Guideline Specifications for Nursery Tree Quality are a standard set of specifications for container-gorwn tree nursery stock. By adhering to these specifications, tree buyers can be assured of obtaining high quality nursery stock that is free of many common defects and problems. The guidelines were produced by a committee of municipal arborists, urban foresters, U.C. Cooperative Extension horticultural advisors, landscape architects, non-profit tree groups, horicultural consultants, and others.

Tree protection in construction sites

Part 5 of the ANSI A300 standard (Management of Trees and Shrubs During Site Planning, Site Development, and Construction) and the corresponding ISA BMP publication provide standards for tree protection in areas undergoing construction activities. Many other sources, including local planning departments, have developed standards and guidelines designed to protect trees during construction and development. Locally adopted standards may be preferable to more generic national guidelines if they properly account for local soil conditions, tree species, climate, and other important factors.

The main shortcoming of many existing guidlines is that they are not based on actual data showing how well trees of varying species, sizes, and conditions survive after varying levels of root disturbance and loss. Although trees can survive over the short term with varying levels of root loss and damage, significant root damage can reduce tree vigor, resulting in premature decline and death. Many tree protection standards are based the maximum amount of root destruction that a tree will tolerate over the short term. Protection activities are commonly limited to the "critical root zone". A preferable standard would be based on a no effect level - the amount of disturbance that is unlikely to have a noticiable long-term impact on the tree. This requires that a large percentage of the total root zone be protected, typically including many of the roots located beyond the tree's dripline.