Southern Forests: a Journal of Forest Science

The purpose of this study was to compare Beta, Gamma, Johnson’s SB and Weibull functions fitted by different methods for describing the horizontal structure of Khaya ivorensis (African mahogany) plantations in Brazil. The database comprised 128 plots from six plantations at varying ages. The function fits were compared using the Kolmogoroff–Smirnoff test, mean bias and mean absolute error for the number of trees and basal area per hectare per diameter class. Johnson’s S_B outperformed the other functions, although all functions provided an adequate fit. The best methods were method of moments and maximum likelihood fitted using 25% of the minimum observed diameter as the location parameter for the Johnson’s S_B function. The errors were greater in diameter classes with higher frequencies. Location and scale parameters were highly correlated with mean diameter and age for the Weibull and Johnson’s S_B functions, respectively, which is convenient for diameter prediction. Gamma’s scale parameter had medium correlation with age. Beta’s parameters had low correlation with stand attributes assessed.

Radial variations in wood properties, cell morphologies and cell proportions were investigated for nine 4-year-old Neolamarckia cadamba trees planted in a community forest in East Java, Indonesia. The relationships between stem diameter and wood properties, cell morphologies or cell proportions were determined to ascertain the effects of stem diameter on these properties. In the radial variations, almost all of the wood properties, cell morphologies and cell proportion in N. cadamba were changed at around 4 to 6 cm distance from the pith, except for fibre diameter, and the proportion of fibre and axial parenchyma. For trees with larger stem diameter, the vessel diameter was also found to increase. In addition, the ray parenchyma and cell wall proportions in trees with larger stem diameter were lower than those in trees with smaller stem diameter. However, the wood properties obtained from the larger stem diameter trees did not always show lower values. The wood properties in N. cadamba were correlated to fibre wall thickness and vessel diameter.

In a water-scarce country such as South Africa, timber and fibre production often stands in conflict with catchment water yields. The optimal provision of both is sought. Forest hydrological experiments improve our understanding of the soil–plant–atmosphere continuum and facilitate the development of rapid estimation techniques through extrapolation. To quantify and characterise the influence of local environmental conditions on single-tree water use, whole-tree daily sap flow for three indigenous afrotemperate tree species (Podocarpus latifolius, Ilex mitis and Ocotea bullata) and one introduced and intensively managed tree species (Pinus radiata) was measured. Hourly sap flux, soil water content and weather data were collected for a year in an indigenous forest and a plantation stand in the southern Cape afrotemperate region. Correlation analyses for whole-tree daily sap flow and environmental variables related to water and energy availability were done. Cross-validation was then employed to test combinations of non-covarying independent parameters for the prediction of whole-tree sap flow responses to environmental variables. Generalised linear models were developed for each species. For the Pinus radiata plantation species, separate models were developed for tree specimens in the subdominant, average and dominant diameter classes. The dominant diameter class model had the best R² value of 0.80 (p < 0.00). For the indigenous tree specimens, the Ilex mitis model had the highest R² (0.65, p < 0.00). Validation of the models with independent data indicated positive and significant Pearson correlation coefficients for the observed versus predicted daily sap flow values, with the dominant diameter Pinus radiata specimens showing the highest correlation value (r = 0.91, p < 0.00), whereas those for the indigenous species were r = 0.63, p < 0.00; r = 0.78, p < 0.00; and r = 0.66, p < 0.00 for Podocarpus latifolius, Ilex mitis and Ocotea bullata, respectively. The results indicate that variable-specific linear models can be employed to estimate whole-tree sap flow and water use as a function of environmental factors with an acceptable degree of accuracy for both introduced and indigenous tree species.