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.
A problem that has always existed in self‐thinning studies is the lack of objectivity in determining which data points to include when fitting the maximum biomass‐density line. This paper demonstrates a more objective method of selecting data points using data from 12 even‐aged Pinus radiata stands undergoing self‐thinning. The method involves the division of a cluster of data points into a specified number of intervals. From each interval, that point having the maximum stand biomass is selected to contribute to the fitting process. This process is repeated a specified number of times using an increasing number of intervals. Each time an estimate of the line is obtained. From these estimates, one can be chosen to represent the maximum biomass‐density line. The method may also be useful in other areas involving the definition of a boundary condition.
Pinusradiata may exhibit moderate to severe stem deformity (Toorour syndrome) when planted on ex-pasture sites in southern Australia. However, the deformity does not occur on ex-eucalypt forest sites unless N fertilizer is applied. While the symptoms of Toorour syndrome are visually similar to those induced by Cu deficiency, the syndrome is associated with high foliar Cu concentrations (and concentrations of Mn and Zn). Furthermore, although Cu-deficient trees typically exhibit lower stem lignin concentrations than nondeformed trees, there is no apparent reduction in the stem lignin concentrations of trees exhibiting Toorour syndrome. Unlike Cu deficiency, the syndrome is not alleviated by Cu fertilizer applications. From comparisons of soil chemical properties between ex-pasture (deformed) and ex-eucalypt (nondeformed) sites, across a range of soil types and lithologies, it is concluded that (i) the syndrome is associated with previous land use rather than soil type or lithology, (ii) the syndrome is associated with the high fertility of ex-pasture soils, in particular, high NO3-N production, relative nitrification, and Mn availability, and (iii) it is unlikely that the syndrome is a consequence of single trace element or other element deficiencies.
A replacement series experiment was carried out to determine the competitive aggressiveness of three
species, P. radiata, E. regnans and A. melanonylon towards each other at seedling stage. Seedlings of
the three species were grown at an overall density of six plants per pot for each species combination,
providing all combinations of two species from 0:6 to 6:O. In addition, seedlings were grown in pure
stands from one plant to six plants per pot for the three species. The relative crowding coefficient, the
relative yield total, the relative effects of intra- and inter-specific competition on the yield of each
species were the four indices calculated. Acacia melanoxylon was the most aggressive species,
followed by P. radiata then E. regnans. In comparison with their corresponding monoculture,
A. melanonylon in mixtures showed the smallest decrease in shoot/root ratio, whilst P. radiata had a
greater decrease and E. regnans showed the greatest reduction. The average relative yield total of
E. regnans and A. melanoxylon was close to 1 for both shoots and roots, indicating an almost complete
overlap in resource use between the two native species. The relative yield total of P. radiata and
E. regnans was 1.27 for shoots and 1.48 for roots, suggesting a possible difference in resource use between
them. The results of this experiment provide a valuable qualitative insight into the relative magnitudes of
the effects of inter- and intra-specific competition between the seedlings of the three species.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.