Response of Pinus taiwanensis growth to climate changes at its southern limit of Daiyun Mountain, China's Mainland Fujian Province

The Pinus taiwanensis trees of a Chinese endemic species form pure forests at infertile sites in humid subtropical China, which can aid soil reservation and ecological resiliency at such sites. Herein, we used dendrochronological methods to investigate the growth patterns and their relationship with climate by analyzing 158 cores of 79 P. taiwanensis trees at 4 sites in their southernmost distribution in China's Mainland at Daiyun Mountain in Fujian Province. Tree growths at sites with favor- able conditions generally showed an age-related growth trend, which decreased from approximately 5 mm to 0.5 mm in about a century. Trees in moderately stressed environments established high growth in their juvenile periods but were highly suscep- tible to environmental stresses such as a sharp growth decline in the 1990s. The temperature in February and the moisture in July are the major limiting factors for most of the tree growths, except for a few extremely stressed P. taiwanensis trees. The growth of the dwarf P. taiwanensis trees, with all ring diameters of the first 20 years less than 4 ram, is mainly limited by the dry climate in May. Under the potential future warming trend, drought stress can be particularly threatening to these dwarf P. taiwanensis trees, which are likely to be the germplasm resources for this species in this region.

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.

Land Consolidation with Seedling Cultivation Could Decrease Soil Microbial PLFA Diversity

The impact of land consolidation on the soil microbial PLFA diversity is of great importance for understanding the effective arable land usage,improving agricultural ecological conditions and environment.In this study,we collected the soil samples(0–20 cm)in experimental plots with 0(Z0),1(Z1a)and 4(Z4a)years of land consolidation in the forest station of Ningbo City,Zhejiang Province,southeastern China.The results were analyzed using ANOVA for randomized block design.Compared with control(Z0),the soil pH value under Z1a treatment increased by 14.6%,soil organic carbon(SOC)content decreased by 65.4%,so did the PLFA contents and relative abundance of all the microbial PLFA diversity(P<0.05),respectively.Meanwhile,for the Z1a treatment,the ratio of fungi to bacteria(F/B)significantly decreased by 35.9%(P<0.05),while the ratio of Gram-positive bacteria to Gram-negative bacteria(G+/G−)signific antly increased by 56.1%.This was strongly related to the increased soil pH values and the decrease of SOC.The Shannon index(H)and evenness index(E)of soil microbial PLFA diversity were significantly decreased after land consolidation(P<0.05).Compared to the Z1 treatment,the microbial PLFA diversity was improved slightly.Therefore,the land consolidation could significantly affect the composition of soil microbial PLFA diversity,and decrease the soil ecosystem stability.