Land Surveys

Historical records of vegetation conditions are useful for establishing reference conditions since Euro-American settlement. In 1785 Congress established the General Land Office and a rectangular system for surveying land. A subsequent act of 1786 provided for the subdivision of townships into one-mile square sections. With the publication of a guidebook in 1855, there was a standardized methodology for government-contracted surveyors.

The basic technique used trees at township, section, and quarter-section corners as references. Compass bearings and distances from the corner to usually either two or four trees were recorded. The common name and often the diameter of these "witness trees" or "bearing trees" also were noted, and the trees were marked with a characteristic blaze. Particularly in later years, surveyors often were instructed to provide descriptions of forest type, locations of streams and other landscape features, and the presence of major disturbances such as blow-downs.

Although bias and even fraud are inherent in some land survey data, and absolute tree density, size, and species importance values cannot be reliably calculated, these data are still of great value in characterizing vegetation at the point in time when each survey was made.

General land Office records are now held by the Bureau of Land Management (BLM). Maps, plats and written records have been transferred to microfiche and copies are available from state BLM offices.

In Arizona the address is:

BLM - Arizona State Office
222 N. Central Ave.
Phoenix, AZ 85004-2203
(602) 417-9200

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