NORTHWEST FORESTRY SERVICES HAS INVENTORIED OVER one MILLION ACRES OF FORESTLAND. properties range from a few acres to 30,000 acres or larger. inventories have been conducted for both private and public owners.
INFORMATION PROVIDED IN An inventory REPORT - A forest inventory generally is compiled by performing a timber cruise. in A timber cruise, a forest stand is measured to determine the quantity and quality of forest products that can be derived from it. In addition to timber quantity and quality, a cruise often contains information about species composition, age, tree health, site quality, topography, and operability for logging. It also can include data on growth, down woody material, snags, understory vegetation, and other resources. Items included in an inventory report are listed below:
Description of Methods - each report includes a description of the cruise methods. it describes the type of sampling method (variable radius plots, fixed area plots, percentage cruise, etc.), sampling intensity, minimum, maximum, and preferred log lengths by species and sort, minimum scaling diameter, minimum merchantable log size, and minimum merchantable tree size.
Per Acre and Average Tree Data - For each sample tree, species, diameter, height, defect, form, and other data are recorded. these data are used to compute species composition and average diameter, number of trees, number of logs, and cubic and board foot volumes by species.
Log Quality Data - During the timber cruise, each tree is divided into logs. quality and defect are recorded for each log. The data are used to breakdown stand volume by species, log sort, and log grade.
Sampling Error of the Volume Estimate - estimated sampling error is computed for each inventory. see discussion under "key points to consider below."
Description of Property - other items included in most inventory reports include the following:
- Maps and Aerial Photographs
- description of Location and Access
- notes regarding any Boundary Markings that were found during the cruise
- Topography as it relates to logging operability
- descriptions of Timber Stands and Other Cover Types, including stand ages, species composition, tree stocking, past history, and any other important stand characteristics
- site quality for growing trees, usually expressed as a site index
- legal and physical constraints on timber harvest
Other Inventory Data - Depending on the project, the following types of data may be included in the inventory:
- Estimated Growth by Timber Stand and Species
- Weight, Volume , and number of pieces of Down Woody Debris
- Number and Size of Snags
- Coverage of Understory Vegetation by species or Type of Vegetation (e.g., shrub, herb, grass)
- Other Resources as Requested
KEY POINTS TO CONSIDER - Cruise results always are estimates, not precise figures. on all but the very smallest properties, Only a sample of trees is measured. Measuring every tree would be too time consuming and expensive. Even if every tree were measured, the results still would be an estimate, because the cruiser cannot see defects inside of a tree. The cruiser estimates the amount of defect inside a tree 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 as high as 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 specifications. 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 log lengths depend on the requirements of the log market.