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6. Time lag effects and rainfall redistribution traits of the canopy of natural secondaryPinus tabulaeformison precipitation in the Qinling Mountains, China

Author

王得祥 Wang Dexiang, 陈书军 Chen Shujun, 陈存根 Chen Cungen, 邹伯才 Zou Bocai, 侯琳 Hou Lin, and 张硕新 Zhang Shuoxin

Subjects
Hydrology, Canopy, Stemflow, Ecology, Agroforestry, Forest ecology, Environmental science, Canopy interception, Precipitation, Vegetation, Interception, Throughfall, Ecology, Evolution, Behavior and Systematics
Abstract

The interception of precipitation by vegetation and subsequent evaporation during and after rain events is an important component of the hydrological budget of forest ecosystems,particularly for forests in ecologically and hydrologically sensitive regions such as Qinling National Forest.This forest was incorporated into the State Natural Forest Protection Project and is managed solely for soil and water conservation.The Qinling Mountains are a major mountain range in China and are the major headwater source for one of the three routes of the South-to-North Water Transfer Project.The evergreen Pinus tabulaeformis is the dominant canopy species at elevations from 1400 to 1700 m.Extensive studies have been conducted to examine the canopy interception,throughfall and stemflow in P.tabulaeformis forest ecosystems across China,mostly in juvenile(≤30 years) or middle-aged(31—50 years) plantations.However,information on rainfall partitioning in natural forests,especially near-mature stands(51—60 years),is lacking,which impedes our understanding of the hydrological ecosystem services in this region.The objective of this study was to understand rainfall partitioning characteristics and lag effects in the Qinling natural secondary P.tabulaeformis forest.Fifty-five-year-old stands of P.tabulaeformis in Ningshan,Shaanxi,were chosen and the precipitation,canopy interception,throughfall and stemflow were measured from 2006 to 2008(recorded in 5—10 months of each year).One-hundred times complete measurement data were analyzed.Total precipitation was 1576.4 mm.Rainfall was partitioned as follows: 62.4% throughfall,4.4% stemflow and 33.2% interception by the tree canopy.The redistribution of precipitation by the canopy was more closely related to the rainfall classes.In a single rainfall event,the higher the rainfall class,the greater the stemflow and throughfall rate and the lower the interception rate.The relationships between throughfall(TF),stemflow(SF),crown interception(I) and total rainfall(P) were described significantly by linear,quadratic and power functions,respectively(TF = 0.6548P-0.4937,R2 = 0.9596;SF=-0.2796 + 0.0452P + 0.0005P2,R2 = 0.8179;I = 0.5958P0.8175,R2 = 0.8064).Under similar rainfall conditions,the higher the rainfall intensity,the shorter the time to saturate the canopy.The timing of throughfall,stemflow and rainfall events after precipitation were not synchronous,and lag periods ranged from(78.5±8.8) min to(16.0±0.0) min and from(111.0 ± 33.0) min to(41.2 ± 0.0) min following precipitation for throughfall and stemflow,respectively.The time lag shortened gradually as rainfall class increased.After precipitation had ceased,especially,when the rainfall is greater than 10.0 mm,the termination of throughfall also lagged from(3.2±2.6) min to(12.0±0.0) min.However,with regard to stemflow prior to termination of rainfall,the smaller the rainfall class,the earlier termination occurred from(-58.3±21.5) min to(-9.8±0.0) min.

Published
2012

7. Genetic consequences of fragmentation in “arbor vitae,” eastern white cedar (Thuja occidentalisL.), toward the northern limit of its distribution range

Author

Xu, Huaitong, Tremblay, Francine, Bergeron, Yves, Paul, Véronique, Chen, Cungen, Xu, Huaitong, Tremblay, Francine, Bergeron, Yves, Paul, Véronique, and Chen, Cungen

Abstract

We tested the hypothesis that marginal fragmented populations of eastern white cedar (EWC) are genetically isolated due to reduced pollen and gene flow. In accordance with the central-marginal model, we predicted a decrease in population genetic diversity and an increase in differentiation along the latitudinal gradient from the boreal mixed-wood to northern coniferous forest. A total of 24 eastern white cedar populations were sampled along the north-south latitudinal gradient for microsatellite genotyping analysis. Positive Fis values and heterozygote deficiency were observed in populations from the marginal (Fis = 0.244; PHW = 0.0042) and discontinuous zones (Fis = 0.166; PHW = 0.0042). However, populations from the continuous zone were in HW equilibrium (Fis = -0.007; PHW = 0.3625). There were no significant latitudinal effects on gene diversity (Hs), allelic richness (AR), or population differentiation (Fst). Bayesian and NJT (neighbor-joining tree) analyses demonstrated the presence of a population structure that was partly consistent with the geographic origins of the populations. The impact of population fragmentation on the genetic structure of EWC is to create a positive inbreeding coefficient, which was two to three times higher on average than that of a population from the continuous zone. This result indicated a higher occurrence of selfing within fragmented EWC populations coupled with a higher degree of gene exchange among nearneighbor relatives, thereby leading to significant inbreeding. Increased population isolation was apparently not correlated with a detectable effect on genetic diversity. Overall, the fragmented populations of EWC appear well-buffered against effects of inbreeding on genetic erosion.

Published
2012
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11. Genetic consequences of fragmentation in "arbor vitae," eastern white cedar (Thuja occidentalis L.), toward the northern limit of its distribution range.

Author

Xu H, Tremblay F, Bergeron Y, Paul V, and Chen C

Abstract

We tested the hypothesis that marginal fragmented populations of eastern white cedar (EWC) are genetically isolated due to reduced pollen and gene flow. In accordance with the central-marginal model, we predicted a decrease in population genetic diversity and an increase in differentiation along the latitudinal gradient from the boreal mixed-wood to northern coniferous forest. A total of 24 eastern white cedar populations were sampled along the north-south latitudinal gradient for microsatellite genotyping analysis. Positive F(is) values and heterozygote deficiency were observed in populations from the marginal (F(is) = 0.244; P(HW) = 0.0042) and discontinuous zones (F(is) = 0.166; P(HW) = 0.0042). However, populations from the continuous zone were in HW equilibrium (F(is) = -0.007; P(HW) = 0.3625). There were no significant latitudinal effects on gene diversity (H(s)), allelic richness (AR), or population differentiation (F(st)). Bayesian and NJT (neighbor-joining tree) analyses demonstrated the presence of a population structure that was partly consistent with the geographic origins of the populations. The impact of population fragmentation on the genetic structure of EWC is to create a positive inbreeding coefficient, which was two to three times higher on average than that of a population from the continuous zone. This result indicated a higher occurrence of selfing within fragmented EWC populations coupled with a higher degree of gene exchange among near-neighbor relatives, thereby leading to significant inbreeding. Increased population isolation was apparently not correlated with a detectable effect on genetic diversity. Overall, the fragmented populations of EWC appear well-buffered against effects of inbreeding on genetic erosion.

Published
2012
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