Evaluation of sampling methods for the estimation of structural indices in forest stands

The paper is about the accurate (i.e. unbiased and precise) and efficient estimation of structural indices in forest stands. We present SIAFOR, a computer programme for the calculation of four nearest-neighbour indices, which describe the spatial arrangement of tree positions, the distribution pattern of species, and the size differentiation between trees. The study uses SIAFOR as a sampling simulator in eight completely stem-mapped forest stands of varying area and structural complexity. We statistically evaluate two sample types (distance and plot sampling), comparing sampling error, bias and minimum sample size for index estimation. We introduce the concepts of measurement expansion factor (MEF) and design expansion factor (DEF) for the technical evaluation of sample type efficiency (optimal sample type). Results indicate that sampling error can reach high levels and that minimum sample sizes for index estimation often amply exceed the limit of 20% of tree density or 20 trees per species per hectare, that we set as the highest feasible sample size in normal situations. We found clear feasibility limits (in terms of minimal tree densities and reachable accuracy levels) for the estimation of all investigated indices. Generally, equal or higher sample sizes are needed for plot sampling than for distance sampling to reach equal accuracy levels. Nevertheless, plot sampling resulted more efficient for the estimation of tree size differentiation at low to medium accuracy levels. For all other investigated indices distance sampling resulted more efficient than plot sampling. Minimum sample size increases with accuracy and is negatively correlated with tree density. At a given accuracy level minimum sample size is highest for the estimation of relative mingling and lowest for tree size differentiation; furthermore it is generally lower in large stands than in small ones. Because of the consistency of our conclusions in all of the investigated stands, we think they apply in most stands of similar area (between 1 and 10 ha) and species diversity (not more than four species).     

基于《施工企业安全生产评价标准》的水利水电施工工程项目重大危险源评价

水利水电施工工程项目重大危险源不同于其他危险化学品等行业重大危险源的评价.施工工程项目的安全性和可靠性既取决于施工工程各单元的危险性,还与施工现场安全管理和施工企业安全生产能力有关.目前,我国尚缺乏水利水电施工工程项目重大危险源的评价标准,为了研究水利水电施工工程项目重大危险源的评价,采用作业条件危险性分析方法,对施工工程的危险性进行评价,然后根据行业标准《施工企业安全生产评价标准》( JGJ/T 77-2010)的取值方法和权重标准对施工企业安全生产综合能力进行评价,使用企业安全生产综合能力评价因子作为管理抵消因子,最终确定施工工程重大危险源.结合某水利水电工程项目的实际,进行了应用分析,结果表明,该方法能比较准确、客观地描述施工类工程项目的重大危险源评价.     

Effects of early management of Pinus massoniana plantation target trees on soil physicochemical properties and plant diversity北大核心CSCD

In order to provide a theoretical reference for the early management of target trees in the low mountain region of eastern Sichuan, and a theoretical basis for the sustainable management of masson pine (Pinus massoniana) plantations, we chose three different kinds of densities (100 target trees per hectare, 150 target trees per hectare, and 200 target trees per hectare) in a 33-year-old masson pine plantation in the low mountain region of eastern Sichuan. We investigated the change patterns of soil physicochemical properties and plant diversity during the early stage of the management of the target trees. The results showed that compared to the control (CK), the early stage of management of P. massoniana plantation target trees dramatically improved the soil physical properties, the pH value, contents of organic matter, and total phosphorus (P < 0.05); however, the available phosphorus and the available nitrogen varied slightly (P > 0.05). Compared to the control (CK), significant (P < 0.05) differences in the richness index were observed between shrubs and herbs (P < 0.05), and in the shrub layer, the dominant position was replaced by others. Simpson, Shannon, and Pielou indexes of shrubs showed no significant difference in the study (P > 0.05). On the contrary, Simpson, Shannon, and Pielou i ndexes of herbs were significantly lower than those for CK (P < 0.05). There were significant correlations between plant species diversity and soil physicochemical properties such as soil pH, contents of total phosphorus, and the available nitrogen. The early stage of management of P. massoniana plantation target trees significantly improved the plant diversity and soil physicochemical properties. Among all the three different treatments, the density of 150 target trees per hectare had the best effect on the soil physicochemical properties and plant diversity. © 2018 Science Press. All rights reserved.     

Microecosystem Analysis of the Structure and Functions of Forest Biogeocenoses

The microecosystem approach and an adequate system of quantitative methods have been used to study the relationship between the chorologic changes in the structure and functions of edificator tree stand and other components of the pine (Pinus sylvestris L.) forest cenoecosystems of the Transural and Northern Turgai regions. Significant correlations of the density of pine undergrowth with the litter thickness; of its growth with root competition, stand closeness, and, to a lower degree, photosynthetically active radiation (PAR); and of the numbers of small mammals and groups of soil mesofauna with herbaceous phytomass have been found. The possibility of the synthesis of population-ecological, synecological, and biogeocenological methods has been demonstrated.     

HYDROLOGY OF A DRAINED FORESTED POCOSIN WATERSHED1

ABSTRACT: In order to assess the effects. of silvicultural and drainage practices on water quality it is necessary to understand their impacts on hydrology. The hydrology of a 340 ha artificially drained forested watershed in eastern North Carolina was studied for a five-year period (1988–92). Effects of soils, beds and changes in vegetation on water table depth, evapotranspiration (ET) and drainage outflows were analyzed. Total annual outflows from the watershed varied from 29 percent of the rainfall during the driest year (1990) when mostly mature trees were present to as much as 53 percent during a year of normal rainfall (1992) after about a third of the trees were harvested. Annual ET from the watershed, calculated as the difference between annual rainfall and outflow, varied from 76 percent of the calculated potential ET for a dry year to as much as 99 percent for a wet year. Average estimated ET was 58 percent of rainfall for the five-year period. Flow rates per unit area were consistently higher from a smaller harvested block (Block B - 82 ha) of the watershed than from the watershed as a whole. This is likely due to time lags, as drainage water flows through the ditch-canal network in the watershed, and to timber harvesting of the smaller gaged block.     

桉树人工林生态系统养分循环与平衡研究Ⅴ.桉树林间种山毛豆对土壤肥力与林木生长的作用

桉树人工林间种山毛豆对提高土壤肥力和促进林木生长有极其显著的作用。间种5年后，林地表层土壤有机质和全量养分N、P、K的质量分数，分别为18．21kg／hm^2、0．85kg/hm^2、0．43kg／hm^2、1．30kg/hm^2，而对照林地分别为13．70kg/hm^2、0.56kghm^2、0．34kg/hm^2、1．10kg/hm^2；林地土壤有效养分含量显著提高；土壤结构和土壤水分物理性质显著改善；桉树生长量显著增加，刚果W5桉平均株高增长16％，平均胸径增长22％，单位面积的木材蓄积量增加59％。     

施肥对落叶松人工林植物养分及生理特性的影响

以东北林业大学帽儿山实验林场的14年生落叶松人工幼龄林为研究对象，对白浆化的暗棕壤林地进行了施肥试验。采用完全随机排列的方法，在林分内设置了9个施肥处理和1个无肥对照。在生长旺盛期测定了叶片和根系的全N和全P质量分数以及光合速率、呼吸速率、叶绿素质量分数等指标。结果表明，单施520kg/hm^2尿素，在提高全N、全P质量分数的同时，还能促进根系对磷素的吸收和利用，增加光合速率和叶绿素质量分数；单施314kg／hm^2磷酸二铵，能加快根系对养分的转移速度，提高光合系数(光合速率／呼吸速率)，且是这些施肥处理中效果最好的施肥水平，这说明此林龄的落叶松林容易缺磷，应适量多施磷肥；处理436kg／hm^2尿素 236kg／hm^2磷酸二铵 133kg／hm^2氯化钾，由于K肥的混入，加快了根系对N、P的转移，使叶片中的质量分数增加，有利于光合作用的进行。因此，合理的施肥措施，不仅能提高落叶松人工林叶片与根系的养分质量分数，还能提高叶片的光合能力。对于此幼龄林，少N多P或N、P、K混合施肥效果最佳。     

桉树人工林生态系统养分循环和平衡研究Ⅲ. 桉树人工林生态系统的养分平衡

在当地现行的生产技术规程和营林措施的条件下，刚果W5桉树人工林生态系统中，N和K的收支帐为亏损，P、Ca、Mg为盈余。在一个轮伐期内，每公顷养分质量的收入中，N为327．13kg／hm^2，P为110．48kg／hm^2，K为206．13kg／hm^2。，Ca为679．53kg／hm^2，Mg为173．72kg／hm^2；每公顷养分质量的支出中，N为366．59kg／hm^2，P为35_3lkg／hm^2，K为212．22kg／hm^2，Ca为452．77kg／hm^2，Mg为79．52kg／hm^2。但这仅仅是一种表观数字。桉树人工林生态系统养分不平衡的主要原因，是桉树凋落物和采伐剩余物不能回归土壤，以及严重的水土流失。解决问题的关键是转变思想认识，制定有效的措施，使桉树凋落物和采伐剩余物回归土壤，同时在桉树行间间种豆科绿肥牧草。     

桉树人工林地土壤肥力灰色关联分析

根据桉树人工林地土壤营养元素含量及土壤酶活性变化,利用灰色关联分析方法评价了桉树人工林地的土壤肥力,列出了以土壤营养元素含量及土壤酶为指标的土壤肥力水平排列顺序.文章认为,以土壤酶活性作为桉树林地土壤肥力的评价指标时,还需对它们的适宜范围作进一步探讨.     

桉树人工林生态系统养分循环与平衡研究Ⅰ. 桉树人工林生态系统的养分贮存

采用田间试验和定位方法，在标准样地中研究养分的输入、输出和贮存。桉树人工林生态系统的养分贮存，包括土壤、桉树林分和凋落物三者贮存的养分。在田间试验的基础上，获得了大量的分析数据。论述了刚果W5桉树人工林生态系统土壤养分的贮存量、林分的养分贮存量和凋落物层的养分贮存量以及上述分系统内大、中量元素的含量比例。土壤养分的贮存量，全量养分以K最多，其次为N、P；有效养分贮存量大小的顺序为N，K，Ca，P，Mg，Mn，Zn，Cu，B。桉树林分的总养分贮存量，是逐年增加的，但以第2年的增量最大；各元素贮量大小，则每年不同。凋落物层的养分贮存量，总体上逐年增长，但以第4年最多；各元素贮存量大小的顺序为N，Ca，Mg，K，P。这些结果，对于指导桉树施肥，有重要的参考价值。