To decay or not to decay: An accelerated field test of the validity of the Scheffer index

IRG/WP 08-20392

G M Larkin, P E Laks

The Scheffer Index was introduced in 1971 to predict the relative decay hazard of untreated wood exposed above-ground. Precipitation and temperature parameters are used in the calculation. A higher Scheffer Index value implies a greater risk of decay. An accelerated 18-month study using seven field sites with Scheffer Indices ranging from 35 to 400 and two wood types (Populus tremuloides and Pinus spp.) was used to test the validity of the Scheffer Index. Different measures of decay including visual ratings, weight loss, and mechanical strength loss show that the Scheffer Index had varied success predicting the decay hazard. Visual ratings did not correlate with historical Scheffer Indices for the field sites. Aspen ultimate compressive strength had reasonably good agreement with historical Scheffer Indices, while static bend MOE and weight loss showed limited agreement. Southern pine static bend MOE and weight loss had good correlation to historical Scheffer Indices, but the ultimate compressive strength had limited correlation. It appears that historical Scheffer Indices more accurately predicted the decay rate for Pinus spp. than Populus tremuloides in this study.

Keywords: decay rate, climate, Scheffer Index, Pinus, Populus, measures of decay

Conference: 08-11-30/12-02 Flamingo Beach, Costa Rica

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