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A Study On The Growth Of Larix Principis-rupprechtii And The Influence Of Water Condition In The Small Watershed Of Diediegou On The North Side Of Liupan Mountains

Posted on:2008-08-15Degree:DoctorType:Dissertation
Country:ChinaCandidate:W GuanFull Text:PDF
GTID:1103360215986753Subject:Ecology
Abstract/Summary:PDF Full Text Request
In this paper the growth and water use regularities were studied for Larix principis-rupprechtii which is one of the main plantation tree species on north side of the LiupanMountains. And the effects of main environment factors on growth were analyzed. The growthcharacteristics under water limited conditions were illuminated in detail. This study is helpfulto understand the interrelation between plantation growth and water condition in the semiaridarea, and to promote the development of theories and techniques of the restoration offorest/vegetation in semiarid area. The research conclusions could offer scientific guidance forthe harmonious and integrated management of forest and water. The main conclusions were asfollows:1. Variation regularities of stem diameter of Larix principis-rupprechtii within growingseasonThe tree stem diameter showed daily and seasonal variation, this variation is composed of2 components: the really growth and the expanding/shrinkage caused by water content changein stem. The daily stem diameter variation is mainly caused by the water content of stem, andis influenced by the weather condition (especially weather type and solar radiation). In sunnydays, the daily variation process of stem diameter could be divided into 3 phases: expansion,increment and contraction. In cloudy days, the expansion phase was significant at night, whilethe contraction phase in day time was weakened. In rainy day, because of the absorption ofbark, the stem diameter increased continuously until the rain stopped. When the precipitation ishigher than 5 mm, it could cause a diameter change bigger than the value of normal days. Theseasonal variation of stem diameter was mainly determined and presented the true stem growth.According to the seasonal pattern of diameter growth which decreases gradually within thetotal growth period, it can be divided into 3 growth phases, i.e. the rapid growth phase (Mayand June), slow growth phase (July and August) and basically none growth phase (Septemberand October). The corresponding averaged daily diameter variation range of 12 different-sizedsample trees were 38.1μm, 9.2μm and -3.9μm, respectively. The negative growth in theperiod of Sep~Oct can be interpreted by the decreasing water content of stem. The averagedstem diameter growth of 12 sample trees during the observation period (May 1 to Oct. 28 in2006) was 2419.3μm.2. The effects on stem diameter variation/growth by environmental factorsThe effects of tree growth and spacial characters: In the rapid growth phase, all tree growth characters (including DBH, tree height, canopy diameter, canopy thickness etc.) weresignificantly correlated with stem diameter variation. And the influences of DBH and canopycharacters were more significant than tree height. Among the tree spacial characters (includingsize ratio, size differentiation, spacial distance and competition index etc.), only competitionindex had a significant and negative correlation with diameter variation. In slow growth phase,all tree growth characters were significant related with stem diameter growth, and the canopydiameter and tree height were more important. The spacial distance was the only significantfactor in all spacial charaters. In the basically none growth phase, no significant effect wasobserved for all the tree characters on stem diameter change.The effect of soil water potential: There was no significant correlation between stemdiameter variation and soil water potential, if the time scale used was smaller than one day.However, the correlation gradually became significant, if the time scale increased to day, 3days and 10 days, especially for the soil layer of 40~100 cm. But it was significant only for thesoil layer of 60~80 cm, if the time scale was increased to month. Based on the our studies, itcan be concluded that 3~10 days should be the suitable time scale unit for research the effect ofsoil water potential on stem diameter variation.The effective soil layers and their seasonal change: Because of the water limitation, theeffective soil layer influencing stem diameter variation had an obvious seasonal change. Basedon the correlativity analysis between the daily stem variation and water used in different soillayers, it showed that: 1) In May, the soil water potential was higher, the value of 1 m soil layerwas -182.1 KPa, the effective soil layer was located at 0~40 cm; 2) In Jun, soil water conditionget worse, and the averaged soil water potential of 1 m soil layer was -323.9 KPa, so theeffective layer was moved down to the layer of 80~100 cm; 3) In July, although the soil waterpotential reduced to -515.3 KPa, the effective soil layer rose to the layer of 40~60 cm, this canbe an integrated result of upper soil recharge by infiltrated rainwater and the enhanced surfacesoil evaporation; 4) In August, the soil water condition was further improved since increasedrainfall, the averaged soil water potential was -438.2 KPa, it is hard to see any soil layerplaying more important role, or it can be said that the total soil layer of 1 m is effective. 5) InSeptember, because of the precipitation accumulation, the soil water potential rose to -320.5KPa in 1 m layer, and -49.9 KPa in the layer of 0~40 cm, the layer of 0~40 cm became theeffective layer. 6) In October, the stem diameter growth stopped, or in fact shrinked followingdecreasing soil and air wetness, therefore no correlation relation between soil water potentialand stem diameter growth was observed.The effect of meteorological factors: 1) The daily effects: There were significant effectson the daily stem diameter variation only in May and June for the solar radiation and air temperature, with a time lag of 1~5 days. The effect of precipitation and relative air moisture issignificant throughout the whole growth period, without a time lag. The air saturation vaporpressure deficit had significant correlation with the stem diameter change, with a time lag of1~5 days, however, this correlation is lower than that of relative air humidity. Wind speed didnot show an obvious effect on stem diameter growth. 2) The monthly effect: The order of thefactors according to their influence from high to low was solar radiation>air water potential>relative air humidity>maximum wind speed>air saturation vapor pressure deficit>averagewind speed, and there were no obvious effect for the monthly air temperature, soil temperature,and precipitation. In summary, water condition factors, especially the relative air humidity,were the most important limiting factors for stem growth in whole growth period, while thesolar radiation and air temperature were important only in the early part of growth period. Theinfluence of meteorological factors was also depended on the dominance degree of individualtrees; the growth of predominant trees was more sensitive to air temperature change. However,the correlativity between stem diameter growth and water condition factors (relative airhumidity, precipitation, etc.) did not show any difference between trees with markedlydifference of growth characters. So it could be concluded that water condition factors play animportant effect on stem diameter growth.3. Characters of sap flow of Larix principis-rupprechtii and the influencing factorsThe sap flow velocity (SFV) possesses both daily and seasonal variation. In sunny days,the daytime process of SFV was a single-peak curve, and there was a weak SFV of around 0.1cm/min during night times. In cloudy days, the peak time of SFV was lagged about 2 hourscompared with that of sunny days, and the value was more or less lowered. In rain times, SFVwas dropped down to the night level, but it was recovered soon to the lever of correspondingweather condition after the rain stopped. For typical sunny days, the averaged peak value ofSFV of 9 sample trees was 0.510, 0.412 and 0.219 cm/min for the three stem diameter growthphases respectively; the corresponding daily averages were 0.152, 0.120 and 0.105 cm/minrespectively. The average of accumulated sap flow of 9 sample trees for the three stemdiameter growth phases were 773.38, 688.90 and 479.71 L respectively.The effects of tree growth characters and spacial characters: There was no significanteffect on SFV for all the characters. But all the tree growth characters had significant effect onsap flow flux, because the tree growth characters are directly related with stem diameter whichis linearly related with the sap wood area. For example, the averaged daily sap flux was 13.845L/d for the tree with a DBH of 17.7 cm; while that was 5.294 L/d for a tree with DBH of 5.7cm. Considering the effect of stem diameter will greatly improve the fitness and increase theprecision of the simulation of the accumulated sap flow flux of stem. The effect of soil water: In the period from May to August, SFV was more significantrelated with the soil water potential of some soil layers within the main root zone (0~40 cm),this means that the soil water condition in root zone have a limiting influence on thetranspiration of trees. However, there was no significant correlation between SFV and soilwater potential of any soil layer, and the correlation decreased further in October, indicatingthat no more water-limitation or limiting soil layer existed after the soil water condition wasimproved in the period after rainfall-season.The effect of meteorological factors: In the period of May to September, solar radiationhad very significant effect on SFV, as the dominant influencing factor. Air temperature wasobviously and negatively related with SFV only in May. The effect of soil temperature was lesssignificant than that of air temperature. There was a significant negative correlation betweenrelative air humidity and SFV. During the rain process, the instantaneous SFV would markedlydecreased to a very low level; But for the days with intermittent rainfall, the daily average SFVwas positively related with the precipitation amount, this could be the response to the increasedsoil wetness caused by rainfall infiltration. A positive correlation was observed between theSFV and air water potential as well as air saturation vapor pressure deficit, but it was notsignificant in June and August. There was no significant effect of wind speed on SFV.Based on a simulation of SFV, the influence range to SFV by soil water potential of layer0~100 cm, daily solar radiation, daily air temperature was calculated, they are 1.876, 0.055,and 0.048 cm/min respectively, showing that soil water condition is the most important factorcontrolling tree transpiration.Simulation of SFV and the accumulated sap flow (SFC): A regression equation (R=0.832)was established for relating daily SFV with daily solar radiation, soil water potential of 1 mlayer, and air temperature. The regression coefficients in this equation were further describedas functions of tree growth characters and spacial characters (DBH, canopy diameter, canopythickness, spacial distance and competition index). And this SFV regression equation wasfurther developed to an equation describing SFC in growing season (R=0.826). In addition,another SFC equation was built by using DBH and time as independent variables with R valueof 0.859.4. The simulation of stem diameter growth (variation)Daily stem diameter variation: 1) the daily solar radiation was used as independentvariable to get the regression equation (R=0.905) of daily stem diameter variation. And theregression coefficients in this equation were described as functions of DBH and canopydiameter. 2) The daily relative air moisture was used as independent variable to get theregression equation (R=0.881) of daily diameter variation, and the regression coefficients were the function of DBH and size differentiation. 3) Different main influencing factors were chosenfor getting the regression equations of daily stem diameter variation in each of the 3 growthphases of stem diameter. (a) In the rapid growth phase, the independent variables were dailyrelative air humidity, daily air temperature, daily wind speed and daily saturation vaporpressure deficit, and regression coefficients were functions of DBH and canopy diameter. Thevalue of R was 0.813. (b) In slow growth phase, the daily precipitation, relative air humidityand air water potential were chosen as independent variable of the regression equation, and theregression coefficients were the functions of DBH, canopy diameter and spacial distance, withR of 0.830. (c) In the basically none growth phase, the regression equation of had theindependent variables of daily precipitation, water potential of 1 m soil layer, and dailymaximum wind speed. The coefficiencies were the functions of DBH, canopy diameter andspacial distance, and the value of was 0.801.Simulation of the accumulated diameter growth: 1) The regression equation of theaccumulated diameter growth was established with the independent variable of time, thecoefficients were the functions of DBH and canopy diameter, with R of 0.937. 2) Theaccumulated solar radiation as independent variable of the equation was developed, and thecoefficients were the functions of DBH, canopy diameter and size differentiation, with R of0.857. 3) The relation between accumulated air temperature and accumulated diameter growthwas regressed; the coefficiencies were the functions of DBH and canopy diameter, with R of0.892. 4) After jointing the equations of accumulated diameter growth change of the 3 growthphases, we got an equation of the accumulated diameter growth for the whole growing season,and its R value was 0.888. 5) The accumulated transpiration was used as the independentvariable of the regression equation of the accumulated diameter growth, and the equationcoefficiencies were the functions of DBH, with R of 0.849.5. The growth in successive years of Larix principis-rupprechtii and effect by relatedfactorsThe height and diameter growth in successive years: According to the growth rate, theheight growth of Larix principis-rupprechtii of our sampled young trees could be divided intoslow growth period (first 5 years after planting) and rapid growth period (5~20 years afterplanting). The average height growth rate of trees was 0.34 m/a in slow growth period and 0.54m/a in rapid growth period for the plot of down-slope. For the first 10 years after planting, theheight growth rate was slowest (0.272 m/a) for the plot on the upper-slope, fastest (0.538 m/a)for the plot on the middle-slope, and with a middling rate of 0.423 m/a for the plot on thedown-slope. The growth rate of ground diameter of stem (15 cm above ground) in successiveyears was also faster for the plot on the middle-slope, with the annual average of 1.2 cm/a, middling in the plot on the upper-slope (<1.0 cm/a), and slowest for the plot on thedown-slope (<0.4 cm/a).Factors influencing the height growth in successive years: The analysis of height growthof trees growing at the same site and with same ages showed that the height growth wasinfluenced by the characters of both growth characters and spacial characters of trees. Theinfluence of different factors on the annual average of height growth of 20-years-aged treeswas ordered as competition index>DBH>canopy thickness; while other factors showed noobvious influence. The height growth of trees with the same age but growing on different siteswas positively related with soil thickness, and influenced by forest density. Within themeteorological factors, the precipitation of last year had the most important effect on the heightgrowth of current year. The averaged air temperature of last 12 months before growth periodwas positively related with the height growth. However, other meteorological factors had nosignificant effect on height growth of trees.Factors influencing tree stem diameter growth in successive years: 1) the diameter growthof trees was limited by the forest density. The stand with moderate density and canopy closurehad a better micro-environment which is favorable for a fast diameter growth, such as the treesin the plot on middle-slope. A lower forest density led to an unfavorable micro-environment inforest stand, and caused a slower diameter growth, such as the trees in the plot on theupper-slope. A too high density would restrain the diameter growth, such as the trees in the ploton the down-slope. 2) The diameter growth of trees was influenced by the soil thickness, forexample, the stand on the upper-slope with a soil thickness of less than 30 cm, its lower abilityto retain and supply water restrained the diameter growth. 3) The factors of DBH, tree height,canopy diameter and canopy thickness were positively related with the diameter growth oftrees. 4) The meteorological factors before growing season was poorly related to the diametergrowth, while it is mainly influenced by the meteorological factors representing waterconditions in the growing period of the same year.
Keywords/Search Tags:Liupan Mountains, Larix principis-rupprechtii, stem diameter growth, sap flow velocity, environmental factors
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