Introduction

The purpose of my blog is to share with you what I have learned based on my experience as a practicing forester in California and Washington and as the general contractor in our former homestead in Mendocino County, California and our current homestead in Kittitas County, WA. As a forester, for more than a decade, I have practiced forestry within the context of a strong land ethic that endeavors to balance economic return with the beauty, clean water, clean air, wildlife habitat, recreation and carbon storage offered by well managed forests. As home and property owners, my family and I challenge ourselves to make our footprint smaller, through conservation, sourcing quality materials from well managed sources as close to home as possible and use of alternative technologies within a budget. Thank you for visiting my blog and I hope that the information provided will help you as a steward of the forest and in the place that you call home.

March 26, 2006

A Snapshot in Time

By Thembi Borras

It is a rare practice to measure every tree to assess the quality and quantity of the forest. Instead, a sample is taken, called a timber cruise. The intensity of a timber cruise and the data collected is a function of why it is being done, a smaller sample is usually taken for forest management decision making and a larger sample is usually taken to determine value for a sale or purchase. The intensity of the cruise often ranges from 5% to 20%.

For example, the Jones family owns 200 acres of homogenous forestland; from which most of the timber was removed in the 1950's and which they now want to put into active management. The landowner and forester agree a 10% cruise is appropriate for forest management decision making including preparation of a long term management plan. The forester uses 1/5 acre fixed radius plot sampling, twenty acres is the sample size which equates to 100 plots. The radius of a fifth acre circular plot or the distance from plot center to plot edge is 52.7' horizontal distance. All merchantable trees in each plot are measured for height and diameter. Additional data collected includes basal area (a measure of stand density), the length of the radial increment of the last 10 years (a means to ascertain growth rate), the number, height and diameter of snags and number of seedlings, saplings and poles. Back in the office the forester converts the field measurements and reports the results to the landowner. Following is a cross section of the results. The Jones Family Forest supports 15,000 bf/acre of which 10,000 bf/acre is redwood and 5,000 bf/acre is Douglas-fir, 50% of the volume is in trees with diameters 18"-24", the average growth rate is 4.5%, the conifer basal area is 175 square feet, the forest stand is well-stocked with young trees and the number of snags greater than 16" is one per acre.

The Jones family now has a snapshot in time quantifying and qualifying their forest stand. During the course of time they may have the property recruised. The data from which can be compared to this original baseline. Future cruises will also help them determine if they are meeting their management objectives.

A portion of this production was gleaned from the California Forestry
Handbook by T. F. Arvola, 1978.

March 19, 2006

Determining Tree and Log Volume

By Thembi Borras

Given the tree diameter at breast height (dbh) and the tree height to a merchantable top, there are tools available to help you estimate the volume in a standing tree. Volume tables are one such tool. Volume tables are, in part, specific to species and log rule. Log rules are ways to estimate the number of boards a milled tree will yield. The log rule used regionally is Scribner Decimal C. Volume is most commonly reported in board feet for trees that will be made into lumber. A board foot is 12" wide by 12" long by 1" thick. These are familiar units to anyone who buys lumber.

The volume of a tree may be measured several times before it is made into lumber. When I mark a tree to be cut, I record the dbh and height in logs to a merchantable top. In the local species specific volume table developed by Peter Joos that I use, logs are defined as 16' long and the merchantable top diameter is defined as 6". For example, a 26" dbh redwood with (5) 16' logs to a 6" top is reported in the table to have 620 board feet. As a general rule, height to a 6" top is usually about 30' less than the total height, but can vary greatly depending on the form of the tree. This tally of tree volume helps the landowner, logger and forester plan.

The tree, once it has been cut and bucked into logs, may be measured again by the faller. Henceforth each log is considered individually. The volume of each log is determined by measuring the small end diameter inside the bark and the length of the log. Given these inputs a different volume table is used to estimate the board foot volume. For example, a log 24" in diameter and 20' long with trim has a gross volume of 500 board feet. After the log is skidded, loaded and trucked to the mill, people called scalers will make the same measurements, but will reduce the gross volume of the log by the defect that they identify in it. The resulting figure is called the net volume. Commonly, the landowner is paid by the mill based on the net volume scaled at the mill.

March 12, 2006

Measuring Tree Diameter and Height

By Thembi Borras

Trees are in part valued on their volume. To determine the volume of a tree the diameter and the height of the tree must be measured.

A flexible measuring tape can be used to measure the diameter. The diameter of a tree is measured at breast height, which is defined as 4.5 feet above the ground on the uphill side of the tree. The circumference of the tree is what you will measure by wrapping the tape around it, making sure there are no kinks in the tape and the tape does not sag. To convert the circumference at breast height to the diameter at breast height (dbh), divide by 3.14. For example if the circumference is 82", dividing by 3.14 will yield a result of 26", therefore the dbh of the tree is 26".

A measuring tape and two sticks of equal length can be used to measure the height of a tree. Find the center point on one of the sticks, hold the other stick perpendicular to it, effectively making the letter "T". Step away from the tree until you can see the top and bottom. Put the base of the "T" between your eyes, then walk away or toward the tree until the top and bottom of the stick line up with the top and bottom of the tree. Make a mark on the ground, the distance between your mark and the tree is the total height of the tree, if you are on flat ground. If you are on sloped ground, the slope distance will need to be converted to horizontal distance.

These are exercises for interested persons that do not have the tools of the forestry trade available to them. Foresters use diameter tapes, biltmore sticks and relaskops to measure diameter and height, or their eye to discern diameter and height more efficiently.