Physical properties of dead and downed round-wood fuels in the boreal forests of western and northern Canada

The quantity of dead and downed woody fuels in forests is commonly estimate d using the line intersect method of sampling. Determination of the mass of wood per unit area for each size class requires values for the mean specif ic gravity, piece tilt angle and piece diameter. We present these values fo r dead and downed round-wood materials less than 7 cm in diameter based on surveys of slash and naturally fallen materials in six boreal forest region s of western and northern Canada and for eight common species in these regi ons. There was considerable variation in the three variables: mean specific gravity ranged from 0.34 to 0.65 Mg m(-3), tilt ranged from 5 degrees to 3 3 degrees, and mean squared diameter ranged from 31% below to 71% above the value at class mid-point. Values of each were strongly related to size cla ss, species, fuel type and to region. We conclude that values derived from other study areas or species can give substantial inaccuracies in estimatin g dead and downed round-wood fuel loads if applied to sites within the stud y region, although ultimate accuracy obtainable will be more influenced by the length of sampling line. The three variables are combined into a single factor so that fuel loads can be simply calculated by multiplying this fac tor by the number of intersects per metre of transect.