Home » Forest handbook

ABNEY LEVEL -Hand-held clinometer used to measure slope in percent.

ACRE - An area of land measuring about 43,560 square feet. A square 1-acre plot measures about 209 feet by 209 feet; a circular acre has a radius of 117.75 feet.

ADMINISTRATIVE UNIT - The basic geographic management area within a Forest Service Region, Station, or Area.

BACKCUT -Final cut in felling a tree. Made on the opposite side of the direction of fall.

BACKFIRE -Blaze set in front of an advancing forest fire in an effort to check the wildfire by cutting off its fuel supply.
-Controlled fire set into the wind.

CALIPER -Instrument for determining tree and log diameters by measuring their rectangular projection on a straight graduated
rule via two arms at right angles to (and one of them sliding along) the rule itself.
-The optical caliper determines upper, out-of-reach tree diameters through an optical system incorporating two parallel lines of
sight separated by a variable baseline.

CALKS (caulks) -Short, hobnail-like spikes in the soles and heels of boots, designed to give secure footing while walking on
logs. Also known as corks.