马尾松人工林不同经营方式短期经济效益分析

  目的  明晰3种不同经营方式在不同规格径材出材量和经济效益方面的差异，为营林项目经济可行性和森林可持续发展提供参考。  方法  以中国林业科学研究院热带林业实验中心马尾松人工林为研究对象，选取近自然化改造、常规经营（轮伐期经营）和无经营活动3种经营方式下林分持续10年（2008—2018年）的观测数据，采用现金流和重置成本法分别计算大、中、小径材的木材价值和补植阔叶树种的苗木价值，通过财务静态、动态经济指标和敏感性分析法来评价3种经营方式的经济可行性与风险承受能力，综合比较3种经营方式的经济效益。  结果  （1）3种经营方式下马尾松材种结构动态变化存在明显不同:10年间，近自然化改造林分大径材出材量由1.22 m3增长至56.85 m3、中径材出材量由23.34 m3增长至79.57 m3、小径材出材量由69.79 m3减少至68.76 m3；常规经营林分大径材出材量由0.29 m3增长至38.97 m3、中径材出材量由22.51 m3增长至90.89 m3、小径材出材量由80.69 m3减少至78.83 m3；对照林分大径材出材量由0.25 m3增长至27.97 m3、中径材出材量由20.95 m3增长至93.69 m3、小径材出材量由189.39 m3减少至181.98 m3。（2）10年间，近自然化改造林分、常规经营林分和对照林分的净利润动态均呈单调递增趋势，投资利润率动态分别为单调递增、先增高再降低和单调递减趋势。在第10年，近自然化改造林分、常规经营林分和对照林的净现值分别为594、265、193，净利润分别为87 384.96、85 745.21和71 935.09元/hm2，投资利润率分别为8.02 %、7.92 %和5.95 %。10年间，近自然改造方式中冠下补植阔叶树种的苗木价值持续增加，苗木收益在营林总收益中的占比（W值）呈增高、降低、增高、降低的波浪动态，在第4 ~ 6年，大叶栎、灰木莲等乡土速生树种达到中、小径材标准，W值降低至11.26 %，在第8 ~ 10年，随着红锥、格木、香梓楠等珍贵树种达到小径材标准，W值再次降至11.93 %。  结论  3种经营方式的马尾松人工林都为经济可行性投资。近自然化改造初期营林成本较高，但更有利于培育大径材、促进乡土珍贵和速生树种资源后续的开发和利用，满足不同市场的需求；轮伐期经营倾向于单一树种的抚育经营，追求速生丰产和相对集约化管理；无经营措施林分大径材比例低，天然更新稀少，不利于森林资源的可持续利用。 

Short-term economic benefit analysis under different management modes of Pinus massoniana plantation

  Objective  This paper aims to clarify the differences in the yield and economic benefits of three different management modes in varied specifications of diameter timber, as well as to provide reference for the economic feasibility of forest management projects and forest sustainable development.  Method  Taking the Pinus massoniana plantation in the Experimental Center of Tropical Forestry, Chinese Academy of Forestry Sciences as the research object, the observation data of the stand for 10 years (2008?2018) under the three management modes of near-natural transformation, conventional management (rotation operation) and control sample plot were selected. The wood values of large, medium and small diameter timber and the seedling value of replanted broadleaved trees were calculated by cash flow and replacement cost method, respectively. Dynamic economic indicators and sensitivity analysis method were used to evaluate the economic feasibility and risk tolerance of the three management modes, and the economic benefits of three management modes were comprehensively compared.  Result  There were obvious differences in the dynamic changes of wood structure of P. massoniana under the three management modes. From the 2nd to 10th year, the yield of large diameter timber increased from 1.22 to 56.85 m3, the yield of medium diameter timber increased from 23.34 to 79.57 m3, and the yield of small diameter timber decreased from 69.79 to 68.76 m3. In the mode of rotation management, yield of large diameter timber increased from 0.29 to 38.97 m3, the yield of medium diameter timber increased from 22.51 to 90.89 m3, the yield of small diameter timber decreased from 80.69 to 78.83 m3. In the mode of control management, the yield of large diameter timber increased from 0.25 to 27.97 m3, the yield of medium diameter timber increased from 20.95 to 93.69 m3, and the yield of small diameter timber decreased from 189.39 to 181.98 m3. During the past 10 years, the net profit (NP) under the three management modes of the near-naturalized transformed stand, the rotation management stand and the control all showed monotonous increasing trend, and the return on investment (ROI) of the three management modes showed a monotonous increasing trend, first increasing and then decreasing trend according to the above sequence. In the 10th year, the net present value of the near-naturalized transformed stand, the conventional management stand and the control were 594, 265, 193, respectively, the NP was 87 384.96, 85 745.21 and 71 935.09 CNY/ha, and the ROI was 8.02%, 7.92% and 5.95%, respectively. In the past 10 years, the seedling value of broadleaved tree species replanted under the crown continued to increase under the near-natural transformation mode, and the proportion of seedling value to stand economic income (W value) presented the trend of increasing-decreasing-increasing-decreasing. In the 4th?6th year, the fast-growing native tree species such as Quercus griffithii and Manglietia conifera reached the standard of medium and small diameter timber, and the W value decreased to 11.26%. In the 8th?10th year, as the Castanopsis hystrix, Erythrophleum fordii, Michelia hedyosperma and other precious tree species reached the standard of small diameter timber, the W value decreased again to 11.93%.  Conclusion  The P. massoniana plantation under three management modes are economically feasible investments. The initial cost of near-natural transformation is higher, but it is more conducive to cultivating large diameter timber, promoting the subsequent development and utilization of native precious and fast-growing species resources, and meeting the needs of different markets; the conventional management (rotation operation) tends to single tree species nurturing management, pursuing fast-growing and abundant production and relatively intensive management; the proportion of large diameter timber in the stand without management measures is lower, and natural regeneration is scarce, which is not conducive to the sustainable use of forest resources.