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The Variation of Stand Structure with Age and Its Hydrological Effects of Larch Plantation in Liupan Mountains

  • Corresponding author: YU Peng-tao, yupt@caf.ac.cn
  • Received Date: 2022-04-28
    Accepted Date: 2022-05-12
  • Objective To study the change of stand structure with age and its hydrological influence, and provide a theoretical basis for forest vegetation construction and management in the semi-arid area, Liupan Mountains. Method The main plantation type -- Larix principis-rupprechtii (Larch) plantation was selected in Diediediegou small watershed in the semi-arid area, Liupan Mountains. Based on daily meteorological data from 1993—2002, both the coupled stand structure model and BROOK90, an ecohydrological model were applied to simulate the variation of stand structures (average tree height, diameter at breast height (DBH), canopy density and leaf area index (LAI)) with plantation age, and then its effects on each water balance component (interception, transpiration, soil evaporation and runoff) were obtained. Result The Larch plantation could be divided into rapid growth period (5~15 years old), slow growth period (15~40 years old) and stable period (over 40 years old) with the increase of age. During the rapid growth period, the average tree height, average DBH, canopy density and canopy LAI increased rapidly with the increase of age, with an average annual growth rate of 0.48 m·a−1, 0.54 cm·a−1, 0.03 and 0.19, respectively. During the slow growth period, the average stand tree height, DBH and canopy density increased slowly, while the LAI increased first and then decreased. But during the stable period, the stand structures did not change significantly. In the fast growth period, the average annual interception and transpiration increased rapidly with the increase of age, and the rate was 1.91 and 24.13 mm·a−1, respectively. Meanwhile, the average annual soil evaporation and water yield decreased rapidly with the increase of age, and the decrease rate was 10.58 and 14.88 mm·a−1, respectively. In the slow growth period, the change of average annual transpiration, soil evaporation and runoff with age slowed down, and tended to be stable when the age was 30 years. The average annual change rates were 0.62, −0.75 and −0.76 mm·a−1, respectively. Conclusion In the semi-arid area of Liupan Mountains, the stand structure of Larch plantations changes continuously when the stand age is less than 30 years, especially less than 15 years, which significantly affectes the eco-hydrological function. And when the stand age is over 30 years old, the stand structure is stable and the water balance components tend to be stable too, which indicates that it is no longer necessary to consider the influence of stand age in the integrated forest-water management.
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  • [1]

    Wang Y H, Yu P T, Feger K H, et al. Annual runoff and evapotranspiration of forestlands and nonforestlands in selected basins of the Loess Plateau of China[J]. Ecohydrology, 2011, 4: 277-287. doi: 10.1002/eco.215
    [2]

    Yu P T, Wang Y H, Wu X, et al. Water yield reduction due to forestation in arid mountainous regions, northwest China[J]. International Journal of Sediment Research, 2010, 25(4): 423-430. doi: 10.1016/S1001-6279(11)60009-7
    [3]

    Xu L H, Wang Y H, Yu P T, et al. Hydrological impacts of afforestation: a case study based on simulation of TOPOG in the small watershed of caogou in Liupan Mountains, China[J]. Journal of Resources and Ecology, 2010, 1(3): 202-210.
    [4] 龚固堂, 黎燕琼, 朱志芳, 等. 川中丘陵区人工柏木防护林适宜林分结构及水文效应[J]. 生态学报, 2012, 32(3):923-930.

    [5]

    Dietz J, Hölscher D, Leuschner C, et al. Rainfall partitioning in relation to forest structure in differently managed montane forest stands in Central Sulawesi, Indonesia[J]. Forest Ecology and Management, 2006, 237(1): 170-178.
    [6] 曹向文, 赵洋毅, 段 旭, 等. 磨盘山华山松人工林林冠截留和产流特征及其影响因子[J]. 西南林业大学学报(自然科学), 2017, 37(6):105-112.

    [7] 肖 洋, 张淑兰, 张海军, 等. 小兴安岭红松林冠层截留降雪特征及模拟[J]. 林业科学, 2021, 57(7):11-19. doi: 10.11707/j.1001-7488.20210702

    [8] 吕 刚, 王 磊, 张 卓, 等. 辽西低山丘陵区不同年龄荆条冠层截留降雨模拟实验研究[J]. 生态学报, 2019, 39(17):6372-6380.

    [9]

    Brauman K. A, Freyberg D L, Daily G C. Forest structure influences on rainfall partitioning and cloud interception: A comparison of native forest sites in Kona, Hawai'i[J]. Agricultural and Forest Meteorology, 2010, 150(2): 265-275. doi: 10.1016/j.agrformet.2009.11.011
    [10]

    Liu Z B, Wang Y H, Tian A, et al. Modeling the Response of Daily Evapotranspiration and its Components of a Larch Plantation to the Variation of Weather, Soil Moisture, and Canopy Leaf Area Index[J]. Journal of Geophysical Research:Atmospheres, 2018, 123: 7354-7374.
    [11]

    Yang B, Lee D K, Heo H K, et al. The effects of tree characteristics on rainfall interception in urban areas[J]. Landscape and Ecological Engineering, 2019, 15(3): 289-296. doi: 10.1007/s11355-019-00383-w
    [12] 王 磊, 孙长忠, 周 彬. 北京九龙山不同结构侧柏人工纯林降水的再分配[J]. 林业科学研究, 2016, 29(5):752-758. doi: 10.3969/j.issn.1001-1498.2016.05.018

    [13] 刘泽彬, 王彦辉, 田 奥, 等. 六盘山半湿润区坡面华北落叶松林冠层截留的时空变化及空间尺度效应[J]. 水土保持学报, 2017, 31(5):231-239. doi: 10.13870/j.cnki.stbcxb.2017.05.036

    [14]

    He Z B, Yang J J, Du J, et al. Spatial variability of canopy interception in a spruce forest of the semiarid mountain regions of China[J]. Agricultural and Forest Meteorology, 2014, 188(15): 58-63.
    [15] 王贺年, 余新晓, 赵 阳, 等. 北京山区4种优势林分生态用水实验研究[J]. 水土保持通报, 2012, 32(4):62-64 + 70. doi: 10.13961/j.cnki.stbctb.2012.04.062

    [16]

    Giambelluca T W, Scholz F G, Bucci S J, et al. Evapotranspiration and energy balance of Brazilian savannas with contrasting tree density[J]. Agricultural and Forest Meteorology, 2009, 149(8): 1365-1376. doi: 10.1016/j.agrformet.2009.03.006
    [17]

    Iida S, Tanaka T, Sugita M. Change of evapotranspiration components due to the succession from Japanese red pine to evergreen oak[J]. Journal of Hydrology, 2006, 326(1): 166-180.
    [18] 魏 曦, 梁文俊, 毕华兴, 等. 晋西黄土区油松林分结构与水土保持功能的多因子复合关系[J]. 林业科学研究, 2020, 33(3):39-47. doi: 10.13275/j.cnki.lykxyj.2020.03.005

    [19] 尤海舟, 孙浩伦, 王立方, 等. 不同间伐强度蒙古栎次生林产流、产沙特征分析[J]. 中南林业科技大学学报, 2020, 40(3):105-110. doi: 10.14067/j.cnki.1673-923x.2020.03.013

    [20] 黄柳菁, 林 欣, 刘兴诏, 等. 广东不同林龄乔木生物量及物种多样性与叶面积指数的关系[J]. 西南林业大学学报(自然科学), 2017, 37(6):91-98.

    [21] 崔宁洁, 张丹桔, 刘 洋, 等. 不同林龄马尾松人工林林下植物多样性与土壤理化性质[J]. 生态学杂志, 2014, 33(10):2610-2617. doi: 10.13292/j.1000-4890.2014.0221

    [22] 付晓燕, 江大勇, 郭万军, 等. 林龄、密度对华北落叶松人工林下生物多样性的影响[J]. 河北林果研究, 2009, 24(1):33-37. doi: 10.3969/j.issn.1007-4961.2009.01.008

    [23]

    Matthieu B, Steeve P, David P. Hydraulic limitations in dominant trees as a contributing mechanism to the age-related growth decline of boreal forest stands[J]. Forest Ecology and Management, 2018, 427(11): 135-142.
    [24] 王小兰, 陈甲瑞, 杨小林, 等. 尼洋河流域高山松次生林林分因子与林龄的相关性[J]. 西北农林科技大学学报(自然科学版), 2019, 47(11):16-24. doi: 10.13207/j.cnki.jnwafu.2019.11.003

    [25] 韩新生. 六盘山半干旱区三种典型植被的结构变化及其多功能影响[D]. 北京: 中国林业科学研究院, 2020, 93-110.

    [26]

    Brooks R H, Corey A T. Hydraulic properties of porous media[J]. Colorado State University Hydrology Paper, 1964, 3: 1-27.
    [27]

    Federer C A. BROOK 90: a simulation model for evaporation, soil water, and streamflow[EB/OL]. (2021-04-09)[2022-05-06]. http://www.ecoshift.net/brook/brook90.htm.
    [28] 张二亮, 宫 宇, 陈永军, 等. 华北落叶松生长规律初探[J]. 河北林果研究, 2015, 30(1):30-32.

    [29] 刘 菲, 黄荣林, 江珊鸿, 等. 江南油杉人工林生长规律研究[J]. 中南林业科技大学学报, 2020, 40(3):39-52. doi: 10.14067/j.cnki.1673-923x.2020.03.006

    [30]

    Ahmad B, Wang Y H, Hao J, et al. Optimizing stand structure for trade-offs between overstory timber production and understory plant diversity: A case-study of a larch plantation in northwest China[J]. Land Degradation and Development, 2018, 29(9): 2998-3008. doi: 10.1002/ldr.3070
    [31] 田 奥. 六盘山半湿润区华北落叶松人工林的多种功能时空变化与优化管理[D].北京: 中国林业科学研究院, 2019, 40-55.

    [32] 牛 赟, 成彩霞, 赵维俊, 等. 祁连山大野口流域青海云杉林水文特征与生态因子关系研究[J]. 中南林业科技大学学报, 2017, 37(1):62-68. doi: 10.14067/j.cnki.1673-923x.2017.01.012

    [33] 董玲玲, 康峰峰, 韩海荣, 等. 辽河源3种林分降雨再分配特征及其影响因素[J]. 水土保持学报, 2018, 32(4):145-150.

    [34] 赵文玥, 吉喜斌. 干旱区稀疏树木冠层降雨截留蒸发的研究进展与展望[J]. 地球科学进展, 2021, 36(8):862-879. doi: 10.11867/j.issn.1001-8166.2021.001

    [35]

    Yu P T, Wang Y H, Du A P, et al. The effect of site conditions on flow after forestation in a dryland region of China[J]. Agricultural and Forest Meteorology, 2013, 178-179: 66-74. doi: 10.1016/j.agrformet.2013.02.007
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The Variation of Stand Structure with Age and Its Hydrological Effects of Larch Plantation in Liupan Mountains

    Corresponding author: YU Peng-tao, yupt@caf.ac.cn
  • Ecology and Nature Conservation Institute, Chinese Academy of Forestry, Beijing 100091, China

Abstract:  Objective To study the change of stand structure with age and its hydrological influence, and provide a theoretical basis for forest vegetation construction and management in the semi-arid area, Liupan Mountains. Method The main plantation type -- Larix principis-rupprechtii (Larch) plantation was selected in Diediediegou small watershed in the semi-arid area, Liupan Mountains. Based on daily meteorological data from 1993—2002, both the coupled stand structure model and BROOK90, an ecohydrological model were applied to simulate the variation of stand structures (average tree height, diameter at breast height (DBH), canopy density and leaf area index (LAI)) with plantation age, and then its effects on each water balance component (interception, transpiration, soil evaporation and runoff) were obtained. Result The Larch plantation could be divided into rapid growth period (5~15 years old), slow growth period (15~40 years old) and stable period (over 40 years old) with the increase of age. During the rapid growth period, the average tree height, average DBH, canopy density and canopy LAI increased rapidly with the increase of age, with an average annual growth rate of 0.48 m·a−1, 0.54 cm·a−1, 0.03 and 0.19, respectively. During the slow growth period, the average stand tree height, DBH and canopy density increased slowly, while the LAI increased first and then decreased. But during the stable period, the stand structures did not change significantly. In the fast growth period, the average annual interception and transpiration increased rapidly with the increase of age, and the rate was 1.91 and 24.13 mm·a−1, respectively. Meanwhile, the average annual soil evaporation and water yield decreased rapidly with the increase of age, and the decrease rate was 10.58 and 14.88 mm·a−1, respectively. In the slow growth period, the change of average annual transpiration, soil evaporation and runoff with age slowed down, and tended to be stable when the age was 30 years. The average annual change rates were 0.62, −0.75 and −0.76 mm·a−1, respectively. Conclusion In the semi-arid area of Liupan Mountains, the stand structure of Larch plantations changes continuously when the stand age is less than 30 years, especially less than 15 years, which significantly affectes the eco-hydrological function. And when the stand age is over 30 years old, the stand structure is stable and the water balance components tend to be stable too, which indicates that it is no longer necessary to consider the influence of stand age in the integrated forest-water management.

  • 宁夏六盘山作为我国西北半干旱地区植被建设的关键区,自上世纪80年代后期就开始了长期的造林活动。虽然造林后植被覆盖有了明显提高,但是也造成了径流的显著减少,且这种径流减少在我国半干旱区更明显,可达到50%以上[1-3]。要协调林水之间这个矛盾,需要厘清造林对水文功能的影响,尤其是植被结构的改变如何影响水文功能。

    研究表明,林分结构会影响森林的生态水文功能[4]。林冠的截留再分配过程受树高、胸径、LAI等林分特征[5-7]和降水量、降水强度等因素[6,8-9]的影响,其中,降水量和林冠LAI是主要影响因子[10-11]。王磊等[12]对华北石质山区不同郁闭度的侧柏人工林的研究发现,随着郁闭度的增加,林冠截留量逐渐增大。此外,林冠结构不仅影响冠层截留,也会影响到林分的蒸散[13-14],而且林分的类型和结构也与蒸散及其组成分量有密切的关系[15-16],如Iida等[17]研究同一地区不同时期的红松林,发现各蒸散分量随林分结构的改变而发生明显的变化。林分结构也会直接或间接地影响到产流量,如魏曦等[18]在晋西黄土区油松人工林的量化研究发现,产流量受林分结构的影响较大,总影响系数为0.986;尤海舟等[19]研究冀北山地的蒙古栎天然次生林的产流量,发现除降水外,郁闭度、冠幅、枯落物厚度等因素都会影响产流量,且郁闭度的影响比冠幅大。

    上述研究多是通过对森林进行对比研究得到的,直接比较了不同林分结构下的水文影响。然而,林分结构随林龄在不断变化,这包括林冠层、林下层及土壤层等一系列的林分结构指标[20-22]和树高、胸径等的变化[23-24]。由于这些林分结构指标随林龄的变化,森林的水文功能也在不断变化,然而,有关人工林随林龄所发生的结构变化和其水文影响却由于森林的寿命较长,常常几十年,甚至更长,难以连续同步观测其结构和其水文功能在整个生命过程中的变化,但这对预测和管理林水关系又是十分必要的;作为管理者,如果在造林之前就能了解和预测森林结构和水文功能随林龄的变化,那么造林等森林管理行为将会更加有效和有的放矢。因此,通过生态水文模型等方法,模拟森林的结构随林龄的变化和该变化所带来的水文影响就显得十分必要。

    叠叠沟小流域是六盘山典型的半干旱区,而华北落叶松(Larix principis-rupprechtii Mayr.)是该流域的主要造林树种,也是目前主要的人工林类型。在该区域现有的林水关系研究中,多是研究某一个时段或近几年的变化,不能反映人工林的结构随林龄的变化所带来的水文影响。因此本研究以叠叠沟小流域的华北落叶松人工林为研究对象,应用前人构建的该小流域华北落叶松人工林的林分结构耦合模型和生态水文模型BROOK90,模拟植被结构(平均树高、胸径、郁闭度、LAI)随林龄的变化及其对各水分平衡分量(截留量、蒸腾量、土壤蒸发量、产流量)的影响,旨在为六盘山半干旱区的植被建设和经营管理提供理论依据。

    • 叠叠沟小流域(106°4′~106°9′ E,35°54′~35°58′ N),是六盘山西北部一个具有代表性的小流域,海拔1 973~2 615 m,为典型的半干旱大陆性季风气候,年平均气温5.9 ℃,年均降水量445 mm,其中80%集中在6—10月的雨季。土壤类型以黄土和灰褐土为主,且土壤厚度变化大,从上坡的20 cm到坡脚的2 m以上不等。

      在叠叠沟小流域下游的阴坡坡脚处,设置了一个30 m × 30 m的固定样地(表1)。样地植被为1982年种植的华北落叶松林,林下没有灌木生长,主要是草本,如蒿属植物(Artemisia spp.)等。土壤为砂壤土,且土壤较厚,大于1 m。2018年,林分密度为1 300 株·hm−2,平均胸径为12.1 cm,平均树高为11.5 m,林分冠层LAI约为4.3,林冠郁闭度0.8,草本覆盖度约0.8。本研究BROOK90模型的率定和检验均以此样地的实测数据进行。

      经度
      Longitude
      (°E)
      纬度
      Latitude
      (°N)
      海拔
      Elevation/
      m
      坡向
      Aspect/°
      坡度
      Slope/°
      坡位
      Slope
      position
      平均胸径
      Mean DBH/
      cm
      平均树高
      Mean tree
      height/m
      LAI郁闭度
      Canopy
      density
      林分密度
      Stand
      Density/
      (tree·hm−2
      土壤厚度
      Soil
      Thickness/
      cm
      106.14735.9722 0503301112.111.54.30.81 300>200

      Table 1.  Basis information of the fixed Larch plantation plot

    2.   研究方法
    • 本研究引用韩新生基于叠叠沟小流域实地调查的华北落叶松林的基本林分结构特征(树高、胸径、郁闭度、LAI)所构建的林分结构多因子耦合模型[25],模型中的函数关系如表2所示。本研究中植被结构的变化为该模型的计算结果。

      林分结构指标   
      Stand structure index   
      模型表达式
      Model expression
      R2
      平均树高
      Average tree height (H)
      $H=33\times \left[1-\mathrm{e}\mathrm{x}\mathrm{p}\left(-0.027 6\times {age}^{1.41}\right)\right]\times \mathrm{e}\mathrm{x}\mathrm{p}\left(-4.24\times {10}^{-29}\times {den}^{7.27}\right)\times$
      $ \mathrm{e}\mathrm{x}\mathrm{p}\left(-1.13\times {10}^{-8}\times {sa}^{3.56}\right)\times\left[1-\mathrm{e}\mathrm{x}\mathrm{p}\left(-0.142\times {sth}^{0.201}\right)\right] $
      0.804
      平均胸径
      Mean diameter at breast height (DBH)
      $DBH=110\times \left[1-\mathrm{exp}\left(-0.0206\times {age}^{1.38}\right)\right]\times \mathrm{exp}\left(-0.00015\times {den}^{0.969}\right)\times$
      $ \mathrm{e}\mathrm{x}\mathrm{p}\left(-5.93\times {10}^{-5}\times {sa}^{1.62}\right)\times \left[1-\mathrm{e}\mathrm{x}\mathrm{p}\left(-0.101\times {sth}^{0.969}\right)\right] $
      0.716
      郁闭度
      Canopy density (CD)
      $ CD=[1-\mathrm{exp}\left(-0.0151\times \left({den}^{0.684}\right)\right] \times [1-\mathrm{e}\mathrm{x}\mathrm{p}(-0.0446\times {age}^{1.16}]\times$
      $ \mathrm{e}\mathrm{x}\mathrm{p}\left(-3.16\times {10}^{-10}\times {sa}^{4.36}\right)\times[1-\mathrm{e}\mathrm{x}\mathrm{p}(-0.0365\times {sth}^{0.914})] $
      0.736
      叶面积指数
      Leaf area index (LAI)
      $ LAI=5.5\times \left[1-\mathrm{e}\mathrm{x}\mathrm{p}\left(-0.584\times {den}^{0.26}\right)\right] \times \left\{{array}{c}1.1\times {\left[1-\mathrm{e}\mathrm{x}\mathrm{p}\left(-0.0756\times age\right)\right]}^{1.75}\\ -0.55\times {\left[1-\mathrm{e}\mathrm{x}\mathrm{p}\left(-0.0878\times age\right)\right]}^{17.1}{array}\right\}\times $
      $ \mathrm{e}\mathrm{x}\mathrm{p}\left(-5.22\times {10}^{-15}\times {sa}^{6.74}\right)\times\left[1-\mathrm{e}\mathrm{x}\mathrm{p}\left(-0.0529\times {sth}^{0.769}\right)\right] $
      0.846
      注:模型表达式中的“age、den、sa、sth”分别表示“林龄、林分密度、坡向、土壤厚度”。
        Note: "age, den, sa, sth" in the model expression represent "stand age, stand density, slope aspect, soil thickness" respectively.

      Table 2.  Expressions for the coupled model of the stand structure

    • BROOK 90模型是确定的、基于过程的集总式生态水文模型,它不考虑水平方向上流域或者其他模拟对象的差异和相邻区域间横向的水分交换,只在垂直方向上详细刻画水分的运动与传输。该模型在一个点尺度上或在一个小而均匀的流域内,在一天的时间步长上估计水文循环中降水-蒸发-径流部分的陆地阶段。

      BROOK90通过叶面积指数和植被冠层截留容量的函数计算截留量,利用改进的Penman-Monteith方法——Shuttleworth-Wallace方程计算蒸腾和蒸发,根据Brooks和Corey改进的方法定义土壤-水分特征[26]。通过Darcy–Richards方程模拟土壤中的水分运动[27]

    • 主要地形、土壤参数(如纬度、坡度、土壤厚度、石砾含量、田间持水量)和植被参数(如树高、LAI、郁闭度、根生物量及其垂直分布)由华北落叶松人工林固定样地实测所得(表1),无法直接测量得到的参数(如植被最大导水率、快速径流系数QFPAR和QFFC)通过固定样地实测的土壤含水量进行校准得到(表3)。其余参数由于对华北落叶松人工林的水文变化不敏感,根据BROOK 90模型手册设为默认值。

      最大叶片导度
      GLMAX/(cm·s−1
      植被最大导水率
      MXKPL/(mm·d−1·mpa−1
      土壤含水量大于田间持水量时的
      快速径流系数
      QFPAR
      田间持水量时的快速
      径流系数
      QFFC
      入渗系数
      INFEXP
      2120.350.30.1

      Table 3.  The values of parameters calibrated by BROOK90 at Diediegou

      利用华北落叶松人工林样地2018年的实测土壤含水量数据进行模型率定,2019年的土壤含水量数据验证模型。在模型率定和检验期间,用2018年和2019年叠叠沟的气象数据驱动模型。采用Nash-Sutcliffe效率系数(E)、绝对误差(A)和相对误差(B)来评价模型率定和检验的精度。计算公式如下:

      式中:$ {MW}_{i} $为实测土壤含水量,$ {SW}_{i} $为模型模拟土壤含水量,$ {MW}_{av} $为整个模拟期间实测土壤含水量的平均值,$ n $为实测次数。

    • 为了厘清林龄对林分结构和各水分平衡分量的影响,以华北落叶松人工林固定样地为例,制定了包含不同林龄的情景。在该情景中,坡向为22.5°,林分密度为1 300 株·hm−2,土壤厚度为100 cm,设置了12种林龄情景,其中,林龄的变化范围为5~60 a,每5 a为一个时间步长。

    • 先用林分结构耦合模型计算得到每个林龄情景下的森林结构参数,如树高、胸径、郁闭度和LAI等,再将上述结构参数代入到BROOK90模型中,模拟每个情景下的水文过程。所有的模拟均基于1993—2002年固原气象站的日气象数据进行,然后再基于每日的水文过程得到年尺度上的截留量、蒸腾量、土壤蒸发量等各水分平衡分量。

    3.   结果与分析
    • 图1表明,在华北落叶松人工林固定样地内,BROOK90模型模拟的土壤含水量与实测土壤含水量的变化趋势和峰值基本一致。率定期间(2018-06-10—2018-10-27)和检验期间(2019-05-28—2019-11-01)的Nash-Sutcliffe效率系数分别为0.72和0.69。样地各土层土壤水分的模拟相对误差均不超过15%,绝对误差均小于5%(表4)。

      Figure 1.  The value of measured and simulated soil moisture in 0~60 cm of larch plantation plot in the calibration and validation period

      土层
      Soil layer/cm
      率定
      Calibration
      检验
      Validation
      天数
      Number of
      days
      平均绝对误差(A
      Mean absolute
      errors/%
      平均相对误差(B
      Mean relative
      errors/%
      天数
      Number of days
      平均绝对误差(A
      Mean absolute
      errors/%
      平均相对误差(B
      Mean relative
      errors/%
      0~10342.016.40302.247.36
      10~20342.006.72303.7314.94
      20~40341.976.49302.809.72
      40~60341.635.30302.568.76

      Table 4.  Errors of simulated soil moisture in different soil layers in relation to measured values in the larch plantation plot.

    • 基于林分结构耦合模型模拟结果表明,本华北落叶松人工林的林分平均树高和郁闭度随林龄的变化均表现为林龄5~15 a时随林龄的增加快速增大,之后增速变缓,在35 a之后,平均树高随林龄的增加不再发生明显变化,而林分郁闭度则比平均树高晚5 a达到稳定;平均胸径在林龄5~20 a时随林龄的增加而快速增大,在林龄45 a之后达到稳定;冠层LAI随林龄的变化趋势为,在林龄5~20 a时随林龄的增加快速增大,之后增速渐缓,在林龄30 a达到最大值,之后逐渐减小,在林龄60 a后稳定在最大值的约3/4处(图2)。在快速生长期(林龄5~15 a),林分平均胸径的增长速率最快,为0.54 cm·a−1;其次是平均树高,为0.48 m·a−1;冠层LAI和郁闭度的增长速率较慢,年均增长率分别为0.19和0.03。在林龄5~60 a时,林分平均树高、平均胸径、郁闭度和冠层LAI的变化范围分别为2.3~10.0 m、2.3~13.3 cm、0.20~0.80、0.65~3.40。

      Figure 2.  Variation of stand structure with age in the fixed larch plot

    • 林分结构的变化会改变水文过程和各水分平衡分量。因此,年均截留量随林龄的变化表现为林龄5~20 a时随林龄的增加快速增大,之后增速变缓,在林龄30 a达到最大,之后随林龄的增加而略减小,在林龄60 a之后趋于稳定。年均蒸腾量随林龄的变化表现为林龄5~10 a时随林龄的增加而快速增大,在10~25 a时增速变缓,25 a之后不再随林龄增加发生明显变化。与年均蒸腾量相反,年均土壤蒸发量和产流量随林龄的变化均表现为在林龄5~10 a时随林龄的增加而快速减小,林龄10 a之后,减速变缓,在林龄30 a之后达到稳定(图3)。在快速增长期,年均截留量、蒸腾量、土壤蒸发量和产流量的变化速率分别为1.91、24.13 、−10.58、−14.88 mm·a−1;在缓慢增长期,年均蒸腾量、土壤蒸发量和产流量的变化速率分别为0.62、−0.75、−0.76 mm·a−1。在林龄5~60 a时,年截留量、年蒸腾量、年土壤蒸发量和年产流量的变化范围分别约为2.5~36.5、65.0~316.5、23.5~140.0、33.5~195.0 mm;达到稳定后,分别占年均降水量(410 mm)的8.5%、77.2%、5.7%、和8.2%。

      Figure 3.  Variation of annual water balance components with age in the fixed larch plot

    4.   讨论
    • 华北落叶松人工林平均树高与胸径随林龄的变化过程符合林木生长的”S”型曲线,但两者的生长过程不同步,这与前人研究其他地区的华北落叶松林的结果大致相同[28];且在其他树种上也有相似结果,如刘菲等[29]发现油松人工林树高快速生长期比胸径早2 a。林分郁闭度随林龄的动态变化研究报道较少,本研究中,郁闭度随林龄增加不断增大,最终趋于稳定。在本研究区,林龄5~15 a之前,郁闭度随林龄增加而快速增大,但也有研究发现,在半湿润区,华北落叶松人工林的郁闭度在林龄20~30 a时随林龄增加而快速增大[30];平均树高和胸径随林龄的变化趋势基本一致,在林龄30 a以前快速增长,比本研究区多延续了15 a [31],这可能与本研究区的半干旱气候有关,干旱导致快速生长阶段提前结束。

    • 本研究发现,在快速生长阶段(林龄5~15 a),年截留量和年蒸腾量的年均增加量分别为1.9 mm·a−1和24.0 mm·a−1,占森林稳定阶段年截留量和年蒸腾量的5.5%和7.5%;年土壤蒸发量和年产流量的年均减少量分别为10.6 mm·a−1和15.0 mm·a−1,占森林稳定阶段年土壤蒸发量和年产流量的45.3%和44.8%。在缓慢生长期(林龄15~40 a),年截留量、年蒸腾量、年土壤蒸发量和年产流量在林龄15~30 a间的平均增加(减少)量分别为0.99、0.62、0.75、0.76 mm·a−1,并在林龄30 a左右达到最大(最小)值,且保持基本稳定。由此可知,林龄大于30 a后,可不考虑林龄对本研究区华北落叶松人工林水文功能的影响;在林龄小于30 a时,尤其是小于15 a时,各水分平衡分量明显变化,此时林龄对水文功能的影响必须加以考虑,即在半干旱区华北落叶松人工林的管理和建设过程中,考虑中龄林,尤其是幼龄林对水文功能的影响时必须考虑林龄的影响。

      研究表明,森林的水文影响是由森林结构和降水特征共同影响的[32],如森林的冠层截留量和截留率随林外降水量显著变化[33],且与冠层结构密切相关[33-34],坡向、坡度和土壤厚度等也对森林的水文功能有显著影响[35]。本研究虽未考虑降水等气象因子的波动以及气候变化带来的水文影响,仅关注在气候不变、立地条件相同的情况下,森林因为年龄变化引起的结构变化,从而产生的水文影响,但是仍然建议在林业管理中,在考虑林龄的影响时,进一步考虑气候变化和立地条件的作用。

    5.   结论
    • 华北落叶松林的生长可分为快速生长期(林龄5~15 a)、缓慢生长期(林龄15~40 a)和稳定期(林龄40 a之后)。在快速生长期,林分平均树高、平均胸径、郁闭度和冠层LAI均随林龄的增加而快速增大;在缓慢生长期,林分平均树高、平均胸径和郁闭度呈缓慢增大趋势,而冠层LAI则呈先增大后减小的趋势;在稳定期,林分结构变化不明显。

      在快速生长期,年均截留量随林龄增加快速增大,年均蒸腾量、土壤蒸发量、产流量随林龄增加先快速增大(减小),在林龄10 a后增速(减速)变缓。在缓慢生长期,年均蒸腾量、土壤蒸发量和产流量随林龄的变化减慢,并在林龄30 a左右就趋于稳定。

      因此,在生态水文研究和林水综合管理中,在林龄小于30 a时必须考虑林龄的影响,当林龄大于30 a时,不必再考虑林龄的影响。

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