**3.1.6 Statistical analyses**

122 Sustainable Forest Management – Case Studies

oriented and to cover the variation in WD distribution. Five triangles were randomly set up in each plot. The more details on measurements and calculations were described by Wei et

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

yt = y0 **\*** e-k \* 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 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

The stump-breast height diameter table from Omule and Kozak (1989) was used to estimate DBH values from the measured stump diameters for the SOH and WTH sites. A DBH - height equation was established in adjacent uncut stands to estimate heights of stands prior to disturbances. The validated equations and biomass component ratios from Comeau and Kimmins (1989), along with estimated H and DBH were then used to estimate above- and below-ground biomass of each plot before harvesting for harvested sites. For the fire-killed sites, these biomass parameters were estimated using the decomposition model developed in this study and the biomass component ratios from Comeau and Kimmins (1989). The below-ground biomass component includes fine and

In order to quantify the amount of nutrients removed by different disturbances, samples of the different decay and size classes of CWD and WD (from two plots of each disturbance), fresh woody materials, living needles and fresh litter (from neighboring uncut stands of

Total N and P losses through harvesting were estimated from data on the biomass removed and nutrient concentrations therein. The biomass removed by harvesting was calculated from the estimated total biomass before disturbances and total WD mass left after harvesting. Total N and P losses through wildfire were estimated using assumed % loss of forest floor and foliage due to burning. Because wildfires in the study area are very variable in intensity and severity of impact, a range of severities was assumed. Based on our

above sampling plots) were collected to analyze N and P nutrient concentrations.

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

follows a single-exponential decay equation (Fahey, 1983; Busse, 1994):

al. (1997).

WD on the study sites.

coarse roots.

right after disturbances in all selected plots.

**3.1.4 Quantification of nutrient removals** 

**3.1.3 Estimates of below-ground WD** 

Homogeneity of variances and normality of distributions of data sets were checked. Data that were not homogeneous (CWD, total WD and nitrogen fixation rates) were logarithmically transformed prior to analysis. Using SYSTAT version 5.0 (Wilkinson, 1990), analyses of variance (ANOV) were performed on WD variables (e.g., above-ground CWD and total WD), nitrogen fixation rates and moisture contents (%). Where there was a significant difference, means of measured variables were compared between WTH, SOH and wildfire disturbances using the Turkey test.
