Variability in the climate-radial growth correlation of Pinus massoniana of different diameter classes

The physiological characteristics of trees change with age,suggesting that growth-related climate signals vary over time.This study aimed to clarify the impacts of different diameter classes on the chronological characteristics of Pinus massoniana Lamb.and its response to climatic factors.Chronologies of P inus massoniana were established in small diameter(14.1 cm),middle diameter(27.3 cm),and large diameter(34.6 cm)trees according to dendrochronology.The results show that:(1)radial growth of different diameter classes had varied characteristics and climate sensitivities;(2)radial growth of small diameter trees was affected by climatic factors of the previous and the current year,while large diameter trees were mainly affected by climatic factors of the current year;and(3)precipitation and temperature were key factors that restricted the radial growth of small and large diameter trees,respectively.

Species Diversity Characteristics of a Natural Pinus taiwanensis Community with Different Diameter Classes and Forest Densities

Pinus taiwanensis is a species endemic to China.This study selected four typical plots of Pinus taiwanensis in the natural secondary forest around Macheng City,in order to reveal the characteristics of and the relationships between different diameter classes(determined based on the diameter at breast height or DBH),forest densities and species diversity,as well as the similarities of species diversity of different plots within the community.The result showed that Pinus taiwanensis was the dominant species in the community.The ratio of Pinus taiwanensis trees of diameter class IV reached a peak of 19.46%of the total followed by diameter class VII at 18.92%.The study recorded 156 species of vascular plants from 130 genera of 71 families;Pinus taiwanensis was the dominant species in the community.When the forest density was 1200 trees ha-1 with the largest average diameter of DBH=36.779±4.444 cm,the diversity(Shannon index H'=1.6716)and the evenness(Pielou index E=0.6727)of the tree layer was the highest.When the forest density reached 1525 trees ha-1 with the lowest average diameter of DBH=18.957±5.141 cm,the richness(Dma=5.4308),the diversity(H'=2.9612)and the evenness(E=0.8985)of all shrub layers climbed to the maximum.When the forest density was 1325 trees ha-1,the richness(Dma=5.8132),the diversity(H'=3.0697)and the evenness(E=0.9025)of all herb layers peaked.In terms of vertical structure,the average diversity indexes were herb layer>shrub layer>tree layer.High canopy density weakened light intensity in the community,causing a reduction in the species diversities of herbs and shrubs.The average similarity coefficient between the sample plots was 0.3356,which was at the medium dissimilarity level.External disturbances and improper management were major contributors to the low species diversity of the community.The implementation of scientific management measures is urgently needed to optimize the forest structures of Pinus taiwanensis,create a benign community environment,and promote species diversities and establish a stable forest community structure.

Vertical root distribution characters of Robinia pseudoacacia on the Loess Plateau in China

On the Loess Plateau, water is the main limiting factors for vegetation growth. Root distribution characters have special ecological meaning as it reflected the utilizations of trees to the environments. Even-aged stands ofRobinia pseudoacacia on slope lands facing south and north were selected as sampling plots for root distribution investigation. Investigatiing results showed that indicated that on all sites, root biomass decreased with depth, and the distribution depth of fine root was deeper than that of coarser root. The results of variance analysis indicated that there were great differences in root biomass among different diameter classes, and coarser root was the main sources of variance, and the root biomass, especially fine root (?<3mm) biomass on northern exposition sites was bigger than that on southern exposition sites. Analysis of the vertical root distribution parameters, root extinction coefficient, β indicated that the value of β on northern exposition was more than 0.982, while the value of β on southern exposition was less than 0.982, which indicated that the vertical root distribution depth ofRobinia pseudoacacia on southern exposition was deeper than that on southern exposition. And the distribution depth of fine roots (Φ<1mm) was deeper than that of thicker roots(Φ<3mm), which was in favor of the uptake of water and nutrients from deeper layers, helped the trees to adapt the arid environment, and promoted the growth of the upper parts of the tree. Keywords Root diameter classes - Variance analysis - Root extinction coefficient - Vertical distribution characters - Site conditions - Loess Plateau CLC number S792.27.01 Document code A Foundation Item: This research was supported by National Natural Science Foundation of China (30371150 and 40371075).Biography: LI Peng (1974-) male, post: Ph. D. in Northwest Scientific & Technological University of Agriculture and Forestry, Yangling 712100, Shaanxi Province, P. R. China. Tel: 029-82312651.Responsible editor: Chai Ruihal

Influence of Spatial Distribution on the Regeneration of <i>Piptadeniastrum africanum</i>and <i>Ocotea usambaernsis</i>in Kalikuku, Lubero, North Kivu, Democratic Republic of Congo

The aim of our study is to highlight the spatial structure of the trees and to determine its influence on the natural regeneration of the Kalikuku dense forest, with a view of its optimal conservation and enhancement. Data collection was done by measuring diameter at breast height along 10 plots of 0.5 ha in size. In analyzing these data, the Dajoz test was used to determine the horizontal spatial distribution pattern of the two most abundant tree species in the forest (Piptadeniastrum africanum and Ocotea usambarensis). The χ2 test was used to compare the frequency distribution of diameter classes for the two species tested. To estimate the difference between the number of seedlings in aggregate versus non-aggregate areas, the Wilcoxon signed-rank test was used. In addition, the equability index was used to test the preponderance of proportions between diameter classes. Finally, the natural regeneration index was evaluated.

Are models of volumetric production at the diametric distribution and total stand level mutually compatible?

The objective of this work was to compare estimates generated by a diametric distribution model and a total stand model against the pre-cut inventory.The model efficiency was also evaluated.Data were evaluated from 30 permanent sample plots in a Eucalyptus urophylla stand,comprising 24 sample plots used for model fitting,and six sample plots for validation.The volume of wood per hectare was estimated for different productive units(sites),using 7 years as the reference age.The model adjustment quality was verified by adjustment and precision statistics:the correlation between observed and predicted variables,root mean square error percentage,graphical analysis of residual distribution,and a frequency histogram for classes of relative errors and validation.Although the two-parameter Weibull probability density function adhered to the data for tree evolution in diameter classes for the reference age(7 years)in the different productivity classes,it generated imprecise estimates of the number of individuals.Consequently,it produced inaccurate volumetric production estimates.The total stand model provided reliable projections of production volumes in different productivity classes for both adjustment types,showing compatibility with the pre-cut inventory according to a Tukey test.In summary,the total stand model generated estimates that were compatible with the pre-cut inventory while the diametric distribution model did not.