Wood strength loss as a measure of decomposition in northern forest mineral soil

Wood stake weight loss has been used as an index of wood decomposition in mineral soil, but it may not give a reliable estimate in cold boreal forests where decomposition is very slow. Various wood stake strength tests have been used as surrogates of weight loss, but little is known on which test would give the best estimate of decomposition over a variety of soil temperature conditions. Our study showed that radial compression strength (RCS) was a better indicator of wood strength change in southern pine (Pinus spp.) and aspen (Populus tremuloides Michx.) than surface hardness or longitudinal shear. The suitability of using the RCS to measure wood decomposition in boreal mineral soils was tested in six Scots pine (Pinus sylvestris L.) plantations along a North–South gradient from Finland to Poland. After 3 years RCS losses ranged from 20% in northern Finland to 94% in central Poland, compared to dry weight losses of 3% and 65%. RCS was a sensitive indicator of initial wood decomposition, and could be used in soils where decomposition is limited by low temperature, lack of water or oxygen, or where a rapid estimate of wood decomposition is wanted.