树干径流模型

以红松代表针叶树,栎树代表阔叶树,通过模拟实验研究树干径流过程,根据实验结果从机理上构造了模型。树干径流模型为一个方程组用“辗转迭代法”求出了数值解。该方程组基本上揭示了树干径流的规律,从实验与模拟结果对比分析中得到了佐证。     

树干径流单因子模拟实验分析

树干径流是发生在森林生态系统中的重要水文现象之一。已往,有关这方面的观测研究工作并不少见,但主要侧重于野外实际观测。由于影响因素错综复杂,单因子对干流影响的分析得不出比较满意的结果。     

林冠分配降雨过程的模拟实验分析

实验发现,降雨通过林冠的穿透过程线、树干径流过程线与电感电容电阻串联电路暂态过程线极为相似。由此启发,用此电路暂态方程拟合穿透降雨与树干径流过程并求出了解析解。进而,根据余项法求出截留强度表达式。此举拓宽了森林水文学理论研究思路。     

树干径流对梭梭"肥岛"和"盐岛"效应的作用机制

为探明荒漠灌木个体周围土壤养分和盐分的空间分布及其成因,以荒漠灌木梭梭(Haloxylon ammodendron Bge.)为研究对象,对其周围土壤pH值,电导率,有机碳,全氮和有效磷的空间异质性以及树干径流的化学性质进行了研究。结果表明:树干周围出现显著的"肥岛"效应,且土壤有机碳,全氮和有效磷的"肥岛"作用范围发生在距主根大约20—40 cm以内。土壤pH值和电导率在主根周围25 cm以内的值却显著低于外围,而在离主根25 cm处出现了"盐岛",即在梭梭主根中心形成了一种高养分、低盐和低pH值的环境。树干径流和自然降雨化学性质的对比研究表明:除pH值和CO23-外,树干径流中其他化学离子的含量均显著高于自然降雨中的含量,说明这种高养分、低盐分的环境是由树干径流引起的,也就是树干径流带给土壤养分的同时将盐分带走。     

米槠常绿阔叶次生林和杉木人工林穿透雨和树干径流可溶性有机质浓度和质量的比较

以中亚热带米槠常绿阔叶次生林和杉木人工林为研究对象,定位观测了穿透雨和树干径流中可溶性有机质(DOM)浓度的变化,分析了DOM腐殖化程度和芳香性特征.结果表明: 研究区米槠次生林穿透雨可溶性有机碳(DOC)浓度的变化幅度明显高于杉木人工林,且前者DOC浓度显著高于后者,相比大气降水DOC浓度,分别增加了7.2和3.2倍.杉木人工林树干径流DOC浓度约为米槠次生林的2.5倍,且两种林分树干径流DOC浓度均呈现旱季高于雨季的趋势.相关分析结果显示:米槠次生林和杉木人工林树干径流DOC浓度均与其相应的水量呈极显著负相关.米槠次生林穿透雨DOM腐殖化程度和芳香性均显著高于杉木人工林;相反,杉木人工林树干径流DOM腐殖化程度和芳香性均显著高于米槠次生林.说明米槠次生林穿透雨中DOM结构较复杂且具有较多的芳香族化合物,而杉木人工林树干径流中DOM结构复杂于米槠次生林.米槠次生林和杉木人工林穿透雨和树干径流的DOM数量和质量具有明显差异,对土壤有机碳的积累可能产生重要影响.     

模拟氮沉降对东北地区兴安落叶松树干呼吸的影响

2011年的5月至2012年的12月,对兴安落叶松(Larix gmelinii)人工林进行了模拟氮沉降实验,设置了4个氮沉降水平处理,分别为:对照(0 g N m-2a-1)、低氮(5 g N m-2a-1)、中氮(5 g N m-2a-1)和高氮(15 g N m-2a-1),每个处理设置3个重复样地。所施氮肥为NH4NO3,以溶液方式在生长季内每月喷施1次。采用红外气体分析法于2012年4月底—10月份,每隔15d左右测定1次树干呼吸,共测定12次。结果表明:各个氮处理下的树干呼吸速率基本与树干温度的变化一致,均呈单峰型季节变化模式,其中7月底最高、10月底最低。氮处理均提高了落叶松的树干呼吸速率,且随着氮输入水平的增加,平均树干呼吸速率呈现逐渐增强的趋势。生长季内,对照、低氮、中氮、和高氮处理条件下的树干表面释放的CO2通量分别为67.3、72.5、78.9 g C/m2和86.5 g C/m2。树干温度与树干呼吸速率存在显著的指数函数关系,而且温度敏感性(Q10)随着氮输入的逐渐升高亦随之增强,对照、低氮、中氮、和高氮处理下的Q10值分别为1.67、1.80、2.01和2.54。另外,伴随氮输入的逐渐增加,树干的氮含量也逐渐升高,树干氮含量与树干呼吸速率之间也具有一定的相关性,能够解释树干呼吸变化的38.3%。     

树干径流过程的动态响应模型

本文用实验测试法测量了干流过程。结果表明,干流过程曲线与R-L-C电路瞬态响应过程(包括输入、输出曲线)极为相似。据此,可用R-L-C电路瞬态响应过程曲线拟合干流过程,求出解析解。在计算机上调试参数,讨论其水文学意义,定性分析参数与影响干流因子的关系,取得了满意的结果。     

矮牡丹的树干解析

通过矮牡丹的树干解析,得出了以下结论：矮牡丹的地径的增长速度、株高的增长速度在植株生长３─９年时最快,以后逐渐变慢;株高生长的成熟龄为６─１２年,在植株生长９年以后,几个标本的生长速度都明显降低;在材积的增长过程中,１６年株龄的标本仍然没有达到成熟龄,连年生长曲线和平均生长曲线没有交点,表明矮牡丹的生长仍然处于旺盛阶段;立地条件对植株的生长也有着较大的影响,在立地条件较好的区域,植株明显生长比较快,而在立地条件较差的区域生长也差。     

树干自然温度梯度变化对热扩散法测算树干液流速率的影响

为了揭示树干自然温度梯度的变化规律及其对树干液流速率测算结果的影响,于2007年5月至10月利用改进的SF-L型热扩散式树液流测定装置,对北京低山区生长的油松和侧柏的树干自然温度梯度、加热温差和气象、土壤水分因子进行了连日同步监测。结果表明:(1)树干自然温度梯度对加热针温差的影响,侧柏大于油松。(2)树干自然温度梯度对液流速率计算结果的影响具有显著的统计意义(P0.01),平均误差大于30%,误差峰值出现在太阳高度角较小的时候。(3)影响树干自然温度梯度最重要的环境因子是光照强度,其次是空气温度。上述结果说明,树干自然温度梯度对热扩散法测定的液流速率的影响不可忽视,研究树木耗水机制时应予以充分考虑。光照强度和空气温度是影响树干自然温度梯度最重要的两个因子,但其影响机制仍需进一步研究。     

气候与土地利用变化下宁夏清水河流域径流模拟

气候和土地利用变化是影响水资源变化最直接的因素。应用SWAT模型对干旱半干旱区小流域宁夏清水河流域径流进行多情景模拟预测,以历史气候要素变化趋势和CA-Markov模型分别设置未来气候和土地利用变化情景,以决定系数R2和Nash-Sutcliffe模型效率系数Ens(Nash-Sutcliffe efficiency coefficient)来衡量模拟值与实测值之间的拟合度,并评价模型在清水河流域的适用性。结果表明,韩府湾站在校准期和验证期的R~2分别为0.80和0.71,Ens分别为0.77和0.69,泉眼山站在校准期和验证期的R2分别为0.66和0.63,Ens分别为0.62和0.56,表明构建的SWAT模型可以用于清水河流域的径流模拟。对未来气候和土地利用变化情景下径流的模拟结果显示,径流变化主要由降水变化主导,降水减少和气温升高的综合作用对流域径流变化影响最为显著;由于耕地和建设用地的增加,未来3种土地利用情景下流域径流量将均会呈现明显增加变化。与2010年相比,到2020年,自然增长情景流域径流将增加17.04%,林地保护情景径流将增加14.44%,规划情景径流将增加13.98%;综合降水、气温和土地利用的结合变化情景显示,未来流域径流将会有不同程度的下降,规划情景和气候变化的结合情景的径流下降最为明显,而有意增大林地和加强生态保护的林地保护情景对减缓流域径流下降具有一定作用。在气候变化的大背景下,根据水资源利用管理目标,可通过调整流域管理措施,特别是土地利用变化和改善区域小气候来减缓气候变化对流域水资源的负面效果,以此来改善流域径流和生态环境状况。     

Infanticide and fertility among Eskimos: A computer simulation

Until recently, certain Eskimo groups were reported to practice female infanticide in the belief that the time spent suckling a girl would delay the mother's next opportunity to bear a son, males being preferred to females because of their future role as providers in a hunting economy. From sex ratios in census data, rates of female infanticide of up to 66% for some groups have been inferred, leading some ethnographers to conclude that these groups were headed for extinction. Eskimo beliefs regarding the effects of infanticide on fertility, however, are in accord with the results of research on the relation of fertility and lactation: The cessation of lactation following infanticide would significantly shortern the expected interval until the next birth. Given this fact and available field data regarding the parameters of Eskimo population growth, the present computer simulation indicates that Eskimo populations could sustain a rate of 30% female infanticide and still survive. Higher reported rates are explained as the combined result of female infanticide plus the tendency of ethnographers to overestimate to overestimate the ages of juvenile females relative to juvenile males.     

Evaluation of marker-assisted selection through computer simulation

Computer simulation was used to evaluate responses to marker-assisted selection (MAS) and to compare MAS responses with those typical of phenotypic recurrent selection (PRS) in an allogamous annual crop species such as maize (Zea mays L.). Relative to PRS, MAS produced rapid responses early in the selection process; however, the rate of these responses diminished greatly within three to five cycles. The gains from MAS ranged from 44.7 to 99.5% of the maximum potential, depending on the genetic model considered. Linkage distance between markers and quantitative trait loci (QTLs) was the factor which most limited the responses from MAS. When averaged across all models considered, flanking QTLs within two marker loci produced 38% more gain than did selection based on single markers if markers were loosely-linked to a QTL (20% recombination). Flanking markers were much less advantageous when markers were closely-linked to a QTL (5% recombination), producing an advantage over single markers of only 11%. Markers were most effective in fully exploiting the genetic potential when fewer QTLs controlled the trait. Large QTL numbers exacerbated the problem of marker-QTL recombination by requiring more generations for fixation. In annual crop species, MAS may offer a primary advantage of enabling two selection cycles per year versus the 2 years per cycle required by most PRS schemes for the evaluation of testcross progeny. MAS thus appears to allow very rapid gains for the first 2–3 years of recurrent selection, after which time conventional methods might replace MAS to achieve further responses.Publication number 19, 330 of the Minnesota Agricultural Experiment Station     

Contact pressure models for spiral phyllotaxis and their computer simulation

We present a simple, biologically motivated model for the creation of phyllotactical patterns in capitula and their computer simulation. An in-depth investigation of Ridley's contact pressure model is performed and a refinement of contact pressure between primordia on the basis of local centroidal Voronoi relaxation is presented. Using this method in combination with Hofmeisters rule for placing new primordia creates stable patterns with Fibonacci spirals of high degree for a large range of initial conditions.     

Analysis and computer simulation of accretion patterns in bacterial cultures

Patterned growth of bacteria created by interactions between the cells and moving gradients of nutrients and chemical buffers is observed frequently in laboratory experiments on agar pour plates. This has been investigated by several microbiologists and mathematicians usually focusing on some hysteretic mechanism, such as dependence of cell uptake kinetics on pH. We show here that a simpler mechanism, one based on cell torpor, can explain patterned growth. In particular, we suppose that the cell population comprises two subpopulations —one actively growing and the other inactive. Cells can switch between the two populations depending on the quality of their environment (nutrient availability, pH, etc.) We formulate here a model of this system, derive and analyze numerical schemes for solving it, and present several computer simulations of the system that illustrate various patterns formed. These compare favorably with observed experiments.     

On investigating the statistical properties of the populous path algorithm by computer simulation

Summary Goodman et al.'s (1974) populous path algorithm for estimating hidden mutational change in protein evolution is designed to be used as an adjunct to the maximum parsimony method. When the algorithm is so used, the augmented maximum parsimony distances, far from being overestimates, are underestimates of the actual number of nucleotide substitutions which occur in Tateno and Nei's (1978) computer simulation by the Poisson process model, even when the simulation is carried out at two and a half times the sequence density. Although underestimates, our evidence shows that they are nevertheless more accurate than estimates obtained by a Poisson correction. In the maximum parsimony reconstruction, there is a bias towards overrepresenting the number of shared nucleotide identities between adjacent ancestral and descendant nodal sequences with the bias being stronger in those portions of the evolutionary tree sparser in sequence data. Because of this particular property of maximum parsimony reconstructed sequences, the conclusions of Tateno and Nei concerning the statistical properties of the populous path algorithm are invalid. We conclude that estimates of protein evolutionary rates by the maximum parsimony - populous path approach will become more accurate rather than less as larger numbers of closely related species are included in the analysis.     

Growth and refuge location in continuous,modular organisms: experimental and computer simulation studies

Summary Guilds of crustose bryozoans exhibited a range of growth outlines, varying from circular to elongate, and the stones on which they grew contained a range of refuge types, varying in size from a few mm² to a few hundred cm². These refuges, if encountered by the growing colonies of competitively subordinate species such as Electra pilosa L., enabled the latter to avoid competitive exclusion due to overgrowth mortality. Computer simulations suggested that, although modular organisms which are elongate are, in general, more likely to encounter spatial refuges than those with a different shape through vegetative growth, shape is less important than the size of the organisms themselves or the size and density of the spatial refuges. Moreover significant interactions between these 4 variables showed that they should be considered together and not in isolation from one another. Examples are given of variable growth forms in continuous, modular organisms from different taxa, including plants, and the importance of these predictive studies to refuge location by modular organisms is discussed.     

Episodic stemflow inputs of magnesium and potassium to a tropical forest floor during heavy rainfall events

Summary Stemflow inputs of magnesium and potassium were measured from 57 canopy trees representing eight species under heavy rainfall conditions in two tropical forest sites in northeast Queensland, Australia. In the premontane tropical moist forest site on the Atherton Tableland, the stemflow input per unit trunk basal area of 51 canopy trees was found to be 0.46 g m^-2 of Mg²⁺ and 4.22 g m^-2 of K⁺ for an average wet season rainday of 99 mm. In the wetter montane tropical rainforest site on Mount Bellenden Ker, the stemflow input per unit trunk basal area of six canopy trees was 5.55 g m^-2 of Mg²⁺ and 9.12 g m^-2 of K⁺ for a wet season rainday of 38 mm. These stemflow inputs from single raindays are greater than the mean annual rainfall input and are almost of the same order of magnitude as the mean annual throughfall input of these cations to areas equal to the trunk basal area from which the stemflow was collected. Stemflow cation fluxes of this magnitude are mainly attributable to the funnelling of large quantities of rainwater down the trunks of these canopy trees by their thoroughly wetted, upwardly inclined branches.