Huiquan Bi

ESTIMATING THE SELF-THINNING BOUNDARY LINE AS A DENSITY-DEPENDENT STOCHASTIC BIOMASS FRONTIER

The self-thinning rule describes a density-dependent upper boundary of stand biomass for even-aged pure plant stands in a given environment. The econometric approach of stochastic frontier production functions is adopted to estimate the self-thinning boundary line as a density-dependent stochastic biomass frontier using data from even-aged Pinus radiata stands. This method uses all the data points, but recognizes the differences in site occupancy among them. Since no subjective data selection is involved and no information contained in the data is lost, the line can be estimated without subjectivity and more efficiently than the common methods of subjective data selection. As a result, statistical inferences about the estimated self-thinning boundary line can be made objectively and more precisely. In addition, the estimates of site occupancy provide further insight into the dynamics of self-thinning stands.

Rooting density and tree size of Pinus radiata (D. Don) in response to competition from Eucalyptus obliqua (L'Herit)

Abstract Nine plots were set up in even-aged Pinus radiata plantations invaded by Eucalyptus obliqua to investigate the effect of below-ground competition from E. obliqua on P. radiata. The plots had different densities of E. obliqua. Individual trees in each plot were measured and mapped. Density contour maps of E. obliqua were made to show four different levels in the stands. Samples at three soil depths from each density level were taken to estimate the rooting density of both species. As the rooting density of E. obliqua increased, the rooting density of P. radiata decreased. This happened at all soil depths. The decrease in rooting density was closely related to the decrease in above-ground tree size of P. radiata. The results highlighted the importance of weed control in the early development of P. radiata stands.

Improving height prediction of regrowth eucalypts by incorporating the of site trees in a modified Chapman-Richards equation

Summary Height and diameter equations were developed using the Chapman-Richards function for 30 species in the regrowth forests of southeast New South Wales. These species included all commercial species of eucalypts and non-commercial small tree species of acacia and allocasuarina in the region. To improve prediction accuracy, the mean height and mean diameter of 50 largest regrowth trees/ha were incorporated in a modified Chapman-Richards function: where H and D represent total tree height in m and diameter at breast height in cm, H50 and D50 are the mean height and mean diameter of 50 largest trees/ha in m and cm respectively, a, b, c and d are parameters. Detailed evaluation of prediction accuracy through resampling showed that the incorporation lead to unbiased and more precise prediction for tree height and stem volume of most species and for stand volume of the regrowth forests. The common practice of calibrating height prediction from species-specific individual tree height-diameter equations against measured stand height can underestimate total stand volume between 3%and 5%.

Competition in mixed stands of Pinus radiata and Eucalyptus obliqua

1. Relative growth rate, mortality and stem form of individual trees in mixed stands of planted P. radiata and naturally regenerated E. obliqua over 5 years were examined in relation to their sizes and the density and leaf area index of their neighbours. 2. Relative growth rate increased with tree size and decreased with increasing neighbourhood leaf area index for both species, but it increased with increasing neighbourhood density as a result of a release from competition due to mortality in the neighbourhood. 3. Mortality affected smaller E. obliqua. The probability of death decreased with increasing tree size. 4. Height to diameter ratio, an indicator of stem form, decreased with tree size and increased with neighbourhood leaf area index for both species. 5. The growth, mortality and changes in stem form of individual trees led to changes in density-dependent stand level characteristics such as mean height to diameter ratio and size distribution patterns.

Yield equations for irregular regrowth forests of Eucalyptus fastigata on the south-east tablelands of New South Wales

Summary Old tree retention during logging results in irregular regrowth forests, for which growth and yield information are urgently required by forest managers in Australia. Using data obtained from 30 stands through random sampling in regrowth Eucalyptus fastigata forests on the south-east tablelands of New South Wales, equations were developed to determine the yield of the regrowth stands in relation to old tree density. The predicted regrowth stand volume for stands without any old trees increased from 253m3ha1 at age 20 to 623m3ha−1 at age 80 for the most productive site, from 253m3ha1 to 339m3ha−1 for the average site and from 84m3ha−1 to 206m3ha−1 for the least productive site. As old tree density increases from 0 to 100 trees ha−1 the percentage reduction in regrowth stand volume increases from 0 to 66%. As a result of past fire and logging disturbances, the old trees had a wide range of crown conditions, with many having a small and sparse crown, but not a large healthy primary crown. A clear und...