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Apr.  2023
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Analysis on the Effect of Close-to-nature Transformation of Pinus massoniana Pure Forest Plantation

  • Corresponding author: LU Yuan-chang, YLu@caf.ac.cn
  • Received Date: 2022-09-22
    Accepted Date: 2022-10-20
  • Objective To provide the reference basis for decision-making for the close-to-natural management of plantations, the changes of forest quality and the development of tree species were analyzed after the close-to-natural transformation of Pinus massoniana. Method In 2007, 20 experimental plots for close-to-natural transformation of Pinus massoniana single species plantation were set up in the Tropical Forestry Experimental Center of Chinese Academy of Forestry in Pingxiang County, Guangxi , including16 operational plots and 4 control plots. In 2007, the first comprehensive survey was done to obtain basic data, and the implementation of selective cutting for target tree management was carried out in the winter of the same year. In the spring of 2008, trees of six broad-leaved species were planted in the stand. In 2016, the second felling for target tree tending was implemented. After 2007, the re- survey of the sample plot was carried out every 2 years, and a total of 7-phase monitoring data were obtained. Statistical calculation was made for the important value index (IVI), average diameter at breast height and pure growth of standing volume based on the monitoring data, and the effect of close-to-natural transformation of Pinus massoniana single species plantation towards multi-species mixed forest was analyzed and evaluated based on tree species composition, stand structure, stand growth, soil and microorganisms development in forest. Result After 13 years of close-to-natural transformation of Pinus massoniana pure plantation, the stand gradually transited to the structure of uneven-aged multi-species mixed forest. The IVI of the 6 tree species enriching planted under the forest were in the top 10 of IVI series, and the natural regeneration of Styrax tonkinensis and Vernicia fordii species appeared in the stand. The distribution of diameter at breast height of Pinus massoniana transformed forest was enlarged from 5 cm to 55 cm, showing the rapid development trend of mixed uneven-aged forest under the promotion of management measures. However, the untreated control stands still showed diameter class distribution of single species even-aged stand. The growth of the transformed stand was significantly higher than that of the control stand, and the growth of the stand was mainly concentrated in the trees with larger diameter, which improved the economic value of forest woods. In addition, the soil microbial content and soil physical and chemical properties of the transformed stand were significantly improved than those of the control stand. Conclusion Adjusting tree species composition is the most important management measure in Close-to-natural transformation of forest. Enlarging the distribution range of diameter class structure is the basic target of close-to-natural transformation of conifer even-aged plantation. Close-to-natural transformation increases significantly the forest growth, promotes the development of soil micro-organisms and improves the quality of forest ecosystem.
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    [25] 曾 冀. 广西大青山杉木马尾松人工林近自然化改造试验研究[D]. 北京: 中国林业科学研究院, 2017.

    [26] 明安刚. 南亚热带针叶人工林近自然化改造过程中群落结构与碳动态研究[D]. 北京: 中国林业科学研究院, 2017.

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Analysis on the Effect of Close-to-nature Transformation of Pinus massoniana Pure Forest Plantation

    Corresponding author: LU Yuan-chang, YLu@caf.ac.cn
  • 1. Research Institute of Forest Resource Information Techniques, Chinese Academy of Forestry, Beijing 100091, China
  • 2. Beijing Forestry University, Beijing 100083, China
  • 3. Tropical Forestry Research Center, Chinese Academy of Forestry, Pingxiang 532600, Guangxi, China
  • 4. Research Center of Forest Management Engineering, National Forestry and Grassland Administration of China, Beijing 10009, China1

Abstract:  Objective To provide the reference basis for decision-making for the close-to-natural management of plantations, the changes of forest quality and the development of tree species were analyzed after the close-to-natural transformation of Pinus massoniana. Method In 2007, 20 experimental plots for close-to-natural transformation of Pinus massoniana single species plantation were set up in the Tropical Forestry Experimental Center of Chinese Academy of Forestry in Pingxiang County, Guangxi , including16 operational plots and 4 control plots. In 2007, the first comprehensive survey was done to obtain basic data, and the implementation of selective cutting for target tree management was carried out in the winter of the same year. In the spring of 2008, trees of six broad-leaved species were planted in the stand. In 2016, the second felling for target tree tending was implemented. After 2007, the re- survey of the sample plot was carried out every 2 years, and a total of 7-phase monitoring data were obtained. Statistical calculation was made for the important value index (IVI), average diameter at breast height and pure growth of standing volume based on the monitoring data, and the effect of close-to-natural transformation of Pinus massoniana single species plantation towards multi-species mixed forest was analyzed and evaluated based on tree species composition, stand structure, stand growth, soil and microorganisms development in forest. Result After 13 years of close-to-natural transformation of Pinus massoniana pure plantation, the stand gradually transited to the structure of uneven-aged multi-species mixed forest. The IVI of the 6 tree species enriching planted under the forest were in the top 10 of IVI series, and the natural regeneration of Styrax tonkinensis and Vernicia fordii species appeared in the stand. The distribution of diameter at breast height of Pinus massoniana transformed forest was enlarged from 5 cm to 55 cm, showing the rapid development trend of mixed uneven-aged forest under the promotion of management measures. However, the untreated control stands still showed diameter class distribution of single species even-aged stand. The growth of the transformed stand was significantly higher than that of the control stand, and the growth of the stand was mainly concentrated in the trees with larger diameter, which improved the economic value of forest woods. In addition, the soil microbial content and soil physical and chemical properties of the transformed stand were significantly improved than those of the control stand. Conclusion Adjusting tree species composition is the most important management measure in Close-to-natural transformation of forest. Enlarging the distribution range of diameter class structure is the basic target of close-to-natural transformation of conifer even-aged plantation. Close-to-natural transformation increases significantly the forest growth, promotes the development of soil micro-organisms and improves the quality of forest ecosystem.

  • 稳定的森林生态系统具有较高的树种多样性水平、丰富的林分结构、较高的生长活力和物质生产能力,是多功能森林经营追求的基本目标[1-3]。我国有大面积的人工针叶纯林,存在树种单一、结构简单、生长退化、稳定性差等问题。近自然改造是将这些人工纯林导向稳定森林生态系统的有效途径。近几年来,一些学者展开了对马尾松(Pinus massoniana Lamb.)人工纯林近自然化的研究。罗应华等[4]对马尾松人工林近自然化改造对植物自然更新及物种多样性的影响进行了探讨;何友均等[5]使用马尾松和杉木(Cunninghamia lanceolata (Lamb.) Hook.)人工纯林早期改造数据,研究了马尾松和杉木人工针叶纯林近自然改造早期对群落特征和土壤性质的影响;明安刚等[6]研究了近自然化改造对马尾松和杉木人工林生物量及其分配的影响;李婷婷[7]根据马尾松近自然化改造的两期数据,对比了近自然化改造对森林结构、树种组成及生长量的影响;范歌[8]对马尾松-大叶栎(Quercus griffithii Hook. f. et Thoms. ex Miquel)异龄复层混交林生长及生态功能进行了研究;张可欣等[9]对马尾松3种不同经营方式所产生的经济效益进行了对比。从现有的研究来看,研究所使用的数据观测周期不够长,或研究只关注了近自然化改造对针叶纯林的某一方面的影响,缺乏对胸径30 cm以后林分生长动态和森林生态系统整体特征变化的综合分析。本研究以中国林科院热带林业实验中心马尾松人工林近自然化改造为例,提出马尾松人工纯林近自然化改造的技术要点,基于改造作业林分和对照林分在2007到2020年的13 a内的观测数据,对森林的树种组成和多样性、林分结构和稳定性、林木生长与收获等方面的状态和变化做了分析,提出近自然化改造的森林生长动态和经营改造效果。这些结果可为我国人工针叶纯林的近自然化改造和混交林经营提供参考依据。

    • 试验地位于广西凭祥中国林科院热带林业实验中心伏波实验场,21°57′47″~22°19′27″ N、106°39′50″~106°59′30″ E,海拔130.0~1 045.9 m,属南亚热带季风气候,日照充足,雨量充沛,干湿季明显,年均气温20.5~21.7 ℃,年均降水量1 200~1 500 mm,年蒸发量1 261~1 388 mm,日最大降水量为206.5 mm。土壤为花岗岩发育而成的砖红壤,土层厚度 > 80 cm[10-11]

      热带林业实验中心植被和树种资源丰富,现已查明共有211科926属2 000余种,主要树种有马尾松、杉木、湿地松(Pinus elliottii Engelmann)、加勒比松(Pinus caribaea Morelet)、红锥(Castanopsis hystrix A. DC.)、西桦(Betula alnoides Hamilt.)、米老排(Mytilaria laosensis Lec.)、云南石梓(Gmelina arborea Roxb.)、八角(Illicium verum Hook. f.)、格木(Erythrophleum fordii Oliv.)、大叶栎(Quercus griffithii Hook. f. et Thoms. )等[11]

    2.   材料与方法
    • 试验林总面积为24 hm2,造林时间为1993年,造林密度2 500株·hm−2,造林后连续3 a管护抚育,于2000年执行透光伐抚育,设计抚育间伐强度25%。于2004年第1次疏伐抚育,抚育疏伐强度35%,抚育后林分密度为1 220株·hm−2;于2007年(林龄14 a时)设计实施近自然化改造,林分发育阶段处于竞争生长阶段。

    • 试验设计的科学假设是通过单株目标树抚育经营提高优势木的生长效果;通过补植多个树种来增加林分结构的复杂性,形成针阔混交林生态系统的基本结构,以发挥针阔树种间的竞争优势和生态互补性价值;通过优势个体、树种组成和林分结构的经营促进实现加速土壤发育、提高林分生长量和改进森林生态环境服务功能的整体目标。经营设计的要点是上层以目标树为中心的单株木生长抚育和下层6个阔叶树种补植为特征的综合抚育。补植树种包括红锥 + 香梓楠、大叶栎 + 格木、灰木莲 + 铁力木及6个阔叶树种的4种组合模式,每种组合实施0.067~0.133 hm2的补植,树种均采用1:1带状混交,株行距4.5 m × 3.0 m,4种不同组合的补植最终形成块状混交的林分空间格局。具体的技术设计可参考陆元昌等[12-13]和谢阳生等[14]研究的相关内容。2007年设计的试验林区域立地情况基本一致,监测样地分4组,每组4个作业样地和1个对照样地,每个样地面积为400 m2(20 m × 20 m),样地之间保持20 m以上距离。分别设计了马尾松-速生阔叶树镶嵌式林下补植、马尾松-红锥或马尾松-格木珍贵硬阔叶树林下补植等用材主导的多功能混交林经营类型及相应的森林作业法。

    • 纯林近自然改造的示范林于2007年实施目标树作业法的第一次抚育间伐作业,蓄积采伐强度为35%,采伐后马尾松保留375~450株·hm−2;2008年春季进行了林下补植,补植密度750株·hm−2,苗木类型为1年生容器苗。2009年执行第一次样地复测,之后每间隔1 a进行1次复测。补植后的2008—2009年间,针对阔叶幼树进行侧方割灌除草;2016年执行第二次促进目标树生长的干扰树间伐,强度为林分总蓄积的25%,同时也间伐了部分长势旺盛并影响马尾松生长的大叶栎。之后对林下天然更新做了识别、标记和侧方割灌处理,对马尾松和补植阔叶树的目标树进行了修枝作业。

    • 2007年首次作业时设置作业观测样地4组共16个,设置对照样地4组共4个,每个样地面积为400 m2,开展了作业前后调查。从2007年后,每2年执行1次复测调查和样品分析。调查内容包括地上部分乔木、灌草、地表凋落物和微生物层、土壤根系层的核心指标。乔木的指标有树木位置、胸径、树高、枝下高、冠幅、林层位置、干材质量、生活力、损伤以及林下幼苗更新等;灌草包括灌草种类、株数等指标;凋落物层的指标包括凋落物量、凋落叶碳氮比等;土壤和微生物层的指标包括孔隙度、土壤pH值等土壤理化性质指标。本研究主要使用林分复测获得每木调查的基础数据作为结构和生长动态分析的基础数据,评价的内容主要包括树种组成和多样性、森林结构和稳定性、林木生长与收获等3个方面。

    • 采用重要值指数(IVI)来表述林分树种组成结构。重要值是相对多度、相对显著度以及相对频度三者之和,以其表示该种在群落中的优势程度[15]。计算公式如下[1]

      其中,相对频度(%)=100 × 某个种的频度/所有种的总频度;相对显著度(%)=100 × 某个种的胸高断面积/所有种的胸高断面积之和;相对多度(%)=100 × 某个种的株数/所有种的总株数。

    • 采用净生长量[16]计算林分生长动态变化,其计算公式如下:

      其中,Z为林分净生长量,Vb为期末林分蓄积量,Va为期初林分蓄积量。

    3.   结果与分析
    • 表1是马尾松纯林近自然化改造13 a作业林分与对照林分乔木树种的变化情况。作业林分中马尾松是上层的保留树种,其重要值指数(IVI)值最大,为43.475; 人工补植的6个主要树种IVI值分别排在第2~6及第8位。大叶栎、灰木莲的IVI值较高,反应了其速生性和较强的林下竞争生长特性;作为高价值珍贵阔叶树种的红锥、格木IVI值分别为9.592和9.147,分别排在第3和第5位,表现出良好的林下竞争生长特性,这个结果对后续补植培育树种的选择是非常有价值的;铁力木13 a来在林下一直表现为生长缓慢和缺乏活力,尽管对其作为林下存活生长的特征还不能定论,但是在有其他选择的情况下不建议用其作为马尾松纯林混交化的补植树种。而作为天然更新出现,并生长进入起测径阶的树种目前有香梓楠、安息香、黄毛榕、假番石榴等,是由于抚育性采伐对林分空间结构的干扰带来的积极效果。从对照林分的情况来看,经过13 a的生长,马尾松IVI值为90.291,仍占绝对优势地位,其他有一些零星的乔木和灌木分布。

      序号
      No.
      作业林分 Operational forest对照林分 Control stand
      主要树种
      Dominant species
      IVI耐荫性
      Shade
      resistance
      速生性
      Fast-growing
      珍贵性
      Preciousness
      树种
      Species
      IVI
      1. 马尾松 Pinus massoniana 43.475 4 1 n 马尾松 Pinus massoniana 90.291
      2. 大叶栎 Quercus griffithii 11.662 3 1 n 三叉苦 Evodia lepta 1.301
      3. 红锥 Castanopsis hystrix 9.592 2 2 p 星毛鸭脚木* Schefflera minutistellata 1.034
      4. 灰木莲 Manglietia glauca 9.465 3 2 p 牛屎木 Alnus cremastogyme 0.668
      5. 格木 Erythrophleum fordii 9.147 2 2 h 假番石榴 Psidium sp. 0.660
      6. 香梓楠 Michelia hedyosperma 4.543 3 2 p 白背桐 Mallotus paniculatus 0.653
      7. 安息香* Styrax tonkinensis 3.151 2~3 1 p 华润楠 Machilus chinensis 0.361
      8. 铁力木 Mesua ferrea 1.834 2 3 h 安息香* Styrax tonkinensis 0.346
      9. 黄毛榕* Ficus esquiroliana 1.228 1~2 2 n 火力楠 Michelia macclurei 0.336
      10. 假番石榴 Psidium sp . 1.006 1 2 n 算盘子 Glochidion puberum 0.331
      11. 华润楠 Machilus chinensis 0.876 2 1 n 漆树* Toxicodendron verniciflum 0.328
      12. 星毛鸭脚木* Schefflera minutistellata 0.664 1 3 n 野牡丹 Melastoma candidum 0.325
      13. 杉木 Cunninghamia lanceolata 0.415 3 2 n 油桐 Vernicia fordii 0.325
      14. 白锥 Castanopsis faberi 0.217 2 2 p 其他 Others 3.041
      15. 油桐 Vernicia fordii 0.203 3~4 2 n
      16. 火力楠 Michelia macclurei 0.198 2 2 p
      17. 牛屎木 Alnus cremastogyme 0.196 2 1 n
      18. 枫香 Liquidambar formosana 0.194 2~4 1 n
      19. 苹果榕 Ficus oligodon 0.110 1 1 n
      20. 潺槁树 Litsea glutinosa 0.107 3 3 p
      21. 山油麻 Trema cannabina 0.099 1 1 n
      22. 毛黄肉楠 Actinodaphne pilosa 0.098 1 1 n
      23. 五月茶 Antidesma bunius 0.098 1 1 n
      24. 水东哥 Saurauia tristyla 0.098 1 1 n
      25. 漆树* Toxicodendron verniciflum 0.097 3 3 p
      26. 海南蒲桃 Syzygium hainanense 0.097 3 2 p
      27. 白背桐 Mallotus paniculatus 0.096 3~4 2 n
      28. 其他 Others 0.910 1 1 n
        *:作业林分中天然更新生长进入起测径阶(5 cm)的乔木树种。
        *: The natural regeneration of the operating forest stands into the arbor species of the scale (5 cm)
        耐荫性:1-耐荫 2-早期耐荫 3-喜阳 4-强阳 Shade tolerance: 1 - shade resistance 2 - early shade tolerance 3 -heliophilous 4 - strong heliophil  速生性:1-速生2-中生3-慢生 Fast growth: 1 - fast growth, 2 - medium growth, 3 - slow growthw growth
        珍贵性:h-高价值珍贵 p-珍贵 n-非珍贵 Preciousness: h - high value precious p - precious n - non precious

      Table 1.  Changes of tree species in working stand and control stand within 13 years

    • 图1表明,伏波分场的马尾松纯林在2007年近自然化改造作业后,部分林木生长迅速,径级和蓄积结构均有显著的变化。马尾松林分在改造前(13 a前)所有林木集中分布在胸径10~25 cm范围内,呈典型的单一树种单一林层的马尾松人工纯林结构(图1a为2007年作业处理前的林分径级结构图);经过近自然经营处理13 a后,作业林分中的林木从5 cm起测径阶开始到55 cm径阶范围内均有林木分布(图1c),呈现出经营措施促进下快速形成混交异龄林格局的发展动态;而未作处理的对照林分通过13 a生长,林木径级分布有所扩展,但最大径级只到45 cm,比经营处理的林木少了10 cm,依然呈同龄纯林的径级格局(图1b)。可见优势木抚育和林下补植经营作业显著地增加了林木生长速度并由此提高了林分结构丰富度。此外,图1同样展示出随着林分径级的增大,径级内的林木株数减少,但径级蓄积量提高。

      Figure 1.  Distribution of the number and accumulation of forest trees in the 13-year period of close-to-nature transformation of Pinus massoniana forest

    • 表2可以看出,改造林分和对照林分蓄积生长量的明显特征,首先是经营作业林分的生长量达到19.72 m3·a−1·hm−2水平,比对照林分16.58 m3·a−1·hm−2,每hm2每年多了3.14 m3;其次,较大径阶的林木对全林生长的贡献也显著高于中小径阶,作业样地中大于30 cm径阶的林木为227株,仅占全部株数的22.66%,蓄积生长量10.94 m3·a−1·hm−2,占全林的55.48%,活立木蓄积量为211.98 m3·hm−2,占全林的70.96%。可见胸径30 cm后的少数大径级林木的生长对全林生长量和蓄积量的贡献率非常显著;中径级林木,例如15~20 cm径阶单株木对全林生长量的贡献率仅为0.12%;而45~50 cm径阶的单木生长量对全林生长量的贡献率为0.46%,达到前者的近4倍;50~55 cm径阶的生长量为0.35 m3·a−1·hm−2,占全林生长量的1.77%,单株木对全林生长量的贡献率达到0.59%。

      径级
      Diameter
      改造作业后2020年混交林
      Mixed forest in 2020 after renovation work
      未作业对照2020年马尾松纯林
      Unemployed control Pinus massoniana forest in 2020
      株数/
      (株·hm−2
      Number of trees
      断面积/
      (m2·hm−2
      Basal area
      蓄积/
      (m3·hm−2
      Volume
      生长量/
      (m3·a−1·hm−2
      Growth
      株数/
      (株·hm−2
      Number of trees
      断面积/
      (m2·hm−2
      Basal area
      蓄积/
      (m3·hm−2
      Volume
      生长量/
      (m3·a−1·hm−2
      Growth
      < 51700.160.440.08550.060.160.02
      5~102241.105.440.87630.251.050.37
      10~152082.4416.552.06310.422.730.13
      15~20721.6714.031.721634.0730.140.50
      20~25341.3712.661.0233113.27104.612.64
      25~30674.1237.623.0330617.98148.727.03
      30~351068.6778.094.45947.4563.932.89
      35~40859.3984.644.03444.6941.681.83
      40~45273.5832.771.57192.5523.231.17
      45~5061.059.820.5400.000.000.00
      50~5530.696.660.3500.000.000.00
      小计 Subtotal1 00234.24298.7219.721 10650.74416.2516.58
      间伐量 Cutting volume173.860
      合计 Total472.58416.25

      Table 2.  Comparison of structure and growth of near-natural mixed transformation and control stands of Pinus massoniana forest

      表3所示,作业林分在获得结构稳定性、活力改善及生长量增加的同时,以活立木间伐量表示的直接收益是2007年为104.1 m3·hm−2,2016年为69.76 m3·hm−2,10年间的总抚育间伐收获量为173.86 m3·hm−2;按70%出材率、 950元·m−3的马尾松木材平均市场价格、 150元·m−3的抚育作业成本和15%综合管理税务费用等主要经济指标计算,在扣除所有成本后,作业林分通过抚育性采伐获得的纯收益为7 600元·a−1·hm−2。而对照样地由于没有抚育间伐,因此该项没有收益。当然,经济收益与市场价格、税收管理政策和劳动力成本等多变因素有关,所以7 600元·a−1·hm−2的纯收益是一个动态的数据,但是每年获得17.39 m3·hm−2的活立木收获量是可靠而稳定的,且是在林分水平上满足了收获量小于生长量(19.72 m3·a−1·hm−2)的可持续经营基本原则。

      径阶
      Diameter
      2007作业前
      Before the 2007 operation
      2007间伐量
      2007 cutting volume
      2016间伐量
      2016 cutting volume
      2020年混交林状态
      State of mixed forest in 2020
      株数/
      (株·hm−2
      Number of
      trees
      蓄积/
      ( m3·hm−2
      Volume
      株数/
      (株·hm−2
      Number of
      trees
      蓄积/
      (m3·hm−2
      Volume
      株数/
      (株·hm−2
      Number of
      trees
      蓄积/
      (m3·hm−2
      Volume
      株数/
      (株·hm−2
      Number of
      trees
      蓄积/
      (m3·hm−2
      Volume
      生长量/
      (m3·a−1·hm−2
      Amount of
      growth
      < 51700.440.08
      5~102245.440.87
      10~1526024.4325023.4920816.552.06
      15~20925145.1457580.617214.031.72
      20~2515038.8412540.473412.661.02
      25~307529.296737.623.03
      30~3510678.094.45
      35~408584.644.03
      40~452732.771.57
      45~5069.820.54
      50~5536.660.35
      合计 Total1 335208.41825104.120069.761 002298.7219.72

      Table 3.  Dynamic table of thinning and accumulation growth of Pinus massoniana near naturalized transformation forest in13 years

    4.   结论
    • 本研究基于2007—2020年13 a的观测数据,从树种组成结构与多样性、林分结构与稳定性、林分生长与收获等方面探讨了马尾松纯林近自然化改造的经营效果,得到以下主要结论:

      1)人工促进树种多样性、调整树种组成是针叶纯林近自然化改造最关键的经营措施。树种多样性与林分生产力呈现正相关[17-18],多个树种构成的森林也对应着多样化的内部关系和复杂的森林功能和产出[19-21]。本案例可见,由于红锥、大叶栎等6个补植树种的进入,马尾松人工林在13 a后基本形成了针阔混交异龄林的格局,树种构成的变化成为后续其他森林生态系统结构和功能发展的基础。多功能森林经营通过林下人工补植混交树种,提高树种丰富度,促进先锋树种林分向亚顶级或顶级树种林分的过渡,使单一功能的人工针叶纯林向多功能针阔混交复层异龄林发展。

      2)扩大径级结构分布范围是针叶纯林近自然化改造的基本指标。丰富的林分结构是稳定的森林生态系统的最基本的质量指标,而林木胸径大小和分布格局是最基本的林分结构内容[22-24]。快速改善林分空间结构的有效手段一方面是促进目标树向大径级生长,另一方面是补植乡土树种及保护促进天然更新幼苗幼树。经过处理的林分上下层林木与对照林分相比生长速度更快,13 a间从5 cm起测径阶到55 cm径阶范围内均有林木分布,呈现出在经营措施的促进下快速形成混交异龄林的基本格局。

      3)林分中数量比例占少数的大径级林木是森林蓄积量的主要贡献者。本研究的作业林分中,胸径30 cm以下的林木占全林总株数的77.35%,其蓄积量占全林蓄积的29.04%;胸径30 cm以上的林木株数占全林株数的22.65%,但生长量和蓄积量却占全林的55.48%和70.96%。也就是说,随着胸径大于30 cm的大径级林木出现和生长,森林的生长量和蓄积才开始快速提高,森林中少数优势林木个体是构成森林蓄积量和生长量的主体部分,是森林多种功能的主要承载对象。让少数优势林木个体快速生长的目标树经营技术是当前我国森林经营中值得推广的关键技术。

      4)近自然化改造显著提高了森林的生长活力和物质生产功能。作业林分的蓄积生长量到达19.72 m3·a−1·hm−2,与纯林对照比较,生长量提高了3.14 m3·a−1·hm−2,单株林木的生长量比对照林中提高3倍以上,使得森林的物质产出能力进一步提高,在“林分水平上满足收获量小于生长量”之可持续经营基本原则的条件下,每年可获得17.39 m3·hm−2的活立木收获量,折合纯收益为7 600元·a−1·hm−2

      5)近自然化改造改善了森林土壤。近自然化改造不仅使地上部分森林的生长和结构得到了改善,同时对地表及地下部分也有积极的影响。从曾冀、明安刚[25-26]在相同样地上获取的土壤数据分析表明,马尾松近自然化改造后,大量阔叶树落叶分解和光照水分等综合环境因素改善,使林下微生物种群和数量增加,凋落物层的细菌、真菌和丛枝菌根真菌的生物量在全年水平上显著高于未改造的纯林。微生物种群增加并促进土壤养分发育加速,土壤理化性质发生显著变化,马尾松细根生物量显著增加。

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