Timber Inventory Growth and Yield Data

(Last Revised 10/18/2002)

A timber inventory determines the volume of standing timber on the ownership. The process of obtaining inventory data involves field data collection ("sampling") using accepted statistical methods. MRC uses a sampling process known as 'stratified random sampling'. Every stand in MRC's ownership has been assigned a vegetation type by analysis of aerial photos. For purposes of obtaining a reliable inventory estimate, all vegetation types are sampled in every planning watershed. The intensity to which each planning watershed is sampled is statistically determined. Our goal is to obtain an estimate for each planning watershed of the net conifer volume to within 10 percent of the mean at the 90 percent confidence level.

Inventory foresters collect information throughout the year so that the inventory is continuously updated. Data collected in the field include tree diameter, height, crown size, condition, small trees ("regeneration"), downed logs, brush, canopy cover, slope, aspect, and other information as encountered such as nests and watercourses.

Growth data is obtained by re-measuring permanent plots at regular intervals. This information is incorporated into MRC's growth model which is based on CRYPTOS, the redwood-region growth model produced by UC Berkeley. For our use, we have calibrated CRYPTOS to reflect the growth rates that have been measured on MRC lands. This model produces reliable growth and yield projections based on current inventory data.