FOREST INVENTORY
				A forest inventory is often termed a “timber cruise”.  A timber cruise is an inventory of a forest stand to determine the quantity of forest products that can be derived from the stand.  In addition to timber quantity, a cruise often contains information about species composition, age, tree quality, site quality, topography, and operability for logging.  It also can include data on growth, down woody material, snags, understory vegetation, and other resources.   Click here to view or download a sample inventory report.  The report was developed by Northwest Forestry Services for one of its clients, but the names, dates, and legal descriptions have been changed. Northwest Forestry Services has cruised or examined over 800,000 acres of forestland in the Pacific Northwest.  Resources examined range from reproduction to old growth. Assignments have ranged from a few acres to tens of thousands of acres. A “typical” cruise report includes a Property Description and Timber Inventory Data as detailed below.  Some cruises contain additional information, as described under the “Other Inventory Data” heading.
				Property Description -Maps and Aerial Photographs -Location and Access -Boundary Markings -Topography -Timber Stands and Other Cover Types -Stand Ages -Operability for Timber Harvest -Legal and Physical Limitations on Timber Harvest Timber Inventory Data -Description of Methods – including cruise method (variable radius plots, fixed      area plots, etc.), sampling intensity, log lengths (minimum, maximum, and      preferred lengths by species and sort), minimum scaling diameter, minimum      merchantable log, and minimum merchantable tree -Per Acre and Average Tree Data – including species composition, average      diameter, basal area, number of trees, number of logs, and cubic and board      foot volumes -Log Quality Data – including breakdown of volume by species, log sort, and log      grade -Sampling Error of the Volume Estimate Other Inventory Data -Description of Methods -Estimated Growth by Timber Stand and Species -Weight and Volume of Down Woody Debris -Number of Pieces of Down Woody Debris -Number and Size of Snags -Coverage of Understory Vegetation by Type of Vegetation (shrub, herb,      grass) or by Species -Other Resources as Requested
		Key Points to Consider in Interpreting Cruise Data Cruise results are always estimates, not precise figures.  Only a sample of trees on a property is measured.  Measuring every tree would be too time consuming and expensive. Even if every tree were measured, the results would be an estimate, because the cruiser cannot see all defects within a tree.  The cruiser estimates defect based on training and experience. The sampling error estimate in the cruise report is a measure of the precision of the volume estimate.  For cruises conducted for sale or acquisition purposes, sampling error target is a standard error of 5% to 7%.  That is, based on sampling error alone, the probability that true volume is within one standard error of cruise volume is 68 percent.  It is 95 percent that the true value is within two standard errors of cruise volume, and 99 percent that it is within three.  For cruises conducted for management planning purposes, the standard error may be 10% to 15%. Usually, the biggest factor affecting price of the cruise is sampling intensity. Obviously, the more sample plots that are installed, the more expensive is the cruise.  On the other hand, more sample plots result in a lower sampling error and consequently, a more precise volume estimate.   The volume estimate can vary depending on cruise methods.  For example, board foot volume is higher when logs are cruised in 32-foot lengths than when they are cruised in 40-foot lengths.  Preferred length depends on the requirements of the log market.
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