**3.1.2 Measurements of decay of above-ground WD**

Changes of wood density in WD for early and medium decay classes on both fire-killed and harvested sites were used to estimate WD decay coefficients. We assumed that WD decay follows a single-exponential decay equation (Fahey, 1983; Busse, 1994):

$$\mathbf{y}\_t = \mathbf{y}\_0 \mathbf{:} \mathbf{e}^{\mathbf{k} \text{"t"}}$$

where yt is wood density in WD after decay of t years, y0 is initial wood density at year 0, and k is the decay coefficient. Using this equation, we estimated k values for early and medium decay classes on both fire-killed and harvested sites, which enable us to compare differences in WD decay between these two types of disturbance. No attempt was made to measure k values for advanced WD because of lack of data on years of decay in advanced WD on the study sites.

WD in the plot burned in 1961 can obviously be classified as medium and advanced decay classes after 33 years of decay, depending on the degree of contact with ground. The mean decay rate of these advanced decaying woody materials in this plot was estimated based on the above equation. This rate was assumed to be the rate for advanced decaying WD carried over from pre-disturbance forests in order to estimate the advanced WD loading in the year right after disturbances in all selected plots.
