The production of lumber using chainsaws in Guyana

SUMMARY

The structure, conduct and performance, and the environmental impacts of the chainsaw lumber production sector in Guyana are investigated. Chainsaws are a highly mobile lumber technology that is used to rip or produce lumber within the forest. Chainsaw lumbering operations have become the dominant lumber producer for the domestic market. Production costs are only 53% of wholesale lumber prices. On a ms basis, chainsaw operations' net profit is 80% of the gross price paid for logs at sawmills and more than twice the profit of firms engaged in the harvesting and transportation of logs to sawmills. Sawmills recognize this cost advantage and are increasingly using chainsaws in the production of lumber.

The handling and transportation of chainsawn lumber within the forest is environmentally less damaging than log production. The log recovery rate is 10–15% for chainsaw operations, as compared to the sawmill average of 40–45%. Log residue from chainsaw operations is left within the forest which promotes faster forest regrowth, while that at sawmills is wasted. Chainsaw operations harvest immature trees, engage in the harvesting of selective species, over-harvest trees per unit area of land, and engage in frequent reentry of the forest. Because of these practices, the chainsaw lumber sector is not environmentally sustainable and will require regulation. Policies that follow a non-market solution will be required in regulation.     

扁刺栲在两种类型林分中的生长过程分析

通过对扁刺栲—华木荷林区针阔混交林、次生阔叶林的群落调查以及扁刺栲的树干解析．研究结果表明：(1)扁刺栲在针阔混交林与次生阔叶林中,胸径快速生长期分别在a8～12和a10～14之间,生长高峰值分别出现在a10和a12,最大值分别为1．07cm和0．85cm．(2)扁刺栲在针阔混交林与次生阔叶林中,树高快速生长期分别在a6～10和a10～14之间,生长高峰值分别出现在a8和a10,最大值分别为0．55m和0．56m．(3)在针阔混交林中,16a生扁刺栲单株材积达0．0134m^3,而在次生阔叶林中只有0．0103m^3．在分析不同林分中扁刺栲生长差异及其原因的基础上,建议对次生阔叶林经营应采用动态管理．     

云阳森林公园游客规模灰色预测

本文用灰色系统理论中的GM(1,1)模型预测了云阳森林公园的游客规模,提供了一种有价值的旅游景点游客数量预测方法.     

城郊森林区对城区环境生态影响

城郊森林区正成为城市生态绿地系统的重要组成部分，本文选定常熟市及近郊的虞山国家森林公园作为实验区，根据主要环境影响因子的测试结果，分析探讨城郊森林区对城市区域的生态影响及作用机制，表明森林群落是优于其它下垫面类型的多层，多效，可持续利用的城区环境生物净化器。     

小流域森林生态系统土壤发生与元素地球化学特性

本文研究了广东五华县牛角塘综合治理试验区几种典型森林生态系统土壤的物质迁移、肥力特性及元素迁移与富集传性，结果表明，生态类型的差异不仅会影响到土壤的肥力状况，同时由于水土流失等因素的影响，还会造成土壤机械组成、元素迁移富集特点以及其它发生学特性的差异，林地、半林地及光山地之间在这些方面也存在着明显的差异性．     

长白山暗针叶林建群种竞争关系的研究

根据野外调查数据,利用Hegyi单木竞争指数模型,定量地研究了长白山暗针叶内主要建群种（以鱼鳞云杉为例）的种内、种间竞争关系,结果表明：暗针叶林中鱼鳞云杉种内竞争强度随着林木径级的增大而迅速减小,也就是说,在暗叶叶林内,鱼鳞云杉种群由于自然调节的作用,随着林木径级的增大,林木因自然稀疏过程导致部分个体死亡,加大了株间距离,因此对光、温、水等生态条件及资源的竞争强度降低,暗针叶林内鱼鳞云杉种内种间竞争强度的顺序为：鱼鳞云杉－鱼鳞云杉＞鱼鳞云杉－臭冷杉＞鱼鳞云杉－红松＞鱼鳞云杉－长白落叶松＞鱼鳞云杉－岳桦＞鱼鳞云杉－杂木,鱼鳞云杉种内种间竞争强度可用幂函数关系CI＝AD－B（其中CI为竞争强度：D为对象木胸径;A、B为参数）表示,并可模拟和预测鱼鳞云杉种内种间竞争强度,从预测结果中发现：当鱼鳞云杉胸径达到35cm后,竞争强度变得小,且变化幅度不大,说明此时该生态系统已基本上达到稳定状态,这可为暗叶林的经营管理提供依据,即在鱼鳞云杉胸径达到35cm之间辅以必要的人工管理措施,以期使得该生态系统尽快达到稳定状态,图2表4参10     

亚热带常绿阔叶林和杉木林皆伐后林地土壤肥力的变化

研究了皆伐对亚热带常绿阔叶林和杉木林林地土壤（δ0-20cm)肥力的影响。结果表明：皆伐后林地土壤生生物数量增加，土壤酶活性增强，增强的幅度以水解酶活性为大，但随着时间的推移，微生物数量和酶活性均下降；土壤有机质，全氮，全磷含量下降，速效养分虽有较大幅度的增加，但随着时间的推移也呈下降趋势；土壤交换性能得到了一定程度的改善，土壤物理性质变差。表5参10     

森林生态系统中土壤呼吸研究进展

土壤呼吸是土壤微生物活性和土壤肥力的一个重要指标，是土壤碳流通的一个重要过程，也是陆地生态系统碳循环的一个关键部分，对研究全球变化有非常重要影响。文章综述了森林生态系统土壤呼吸的各种测量方法，比较了静态气室法和动态气室法的优缺点，认为动态红外气体分析法是最可靠的方法之一；探讨了影响土壤呼吸速率的各种因素，指出在各生物和非生物因素中，温度对土壤呼吸的影响最大；最后提出了土壤呼吸研究过程中存在的一些问题及今后的发展方向。     

Effects of Harvest of Nontimber Forest Products and Ecological Differences between Sites on the Demography of African Mahogany

Abstract: The demographic impacts of harvesting nontimber forest products (NTFP) have been increasingly studied because of reports of potentially unsustainable harvest. Nevertheless, our understanding of how plant demographic response to harvest is altered by variation in ecological conditions, which is critical for developing realistic sustainable‐use plans, is limited. We built matrix population models to test whether and how variation in ecological conditions affects population responses to harvest. In particular, we examined the effect of bark and foliage harvest on the demography of populations of African mahogany (Khaya senegalensis) in two contrasting ecological regions of Benin, West Africa. K. senegalensis bark and foliage harvest significantly reduced its stochastic population growth rates, but ecological differences between regions had a greater effect on population growth rates than did harvest. The effect of harvest on population growth rates (Δλ) was slightly stronger in the moist than in the drier region. Life‐table response experiments revealed that the mechanism by which harvesting reduced λ differed between ecological regions. Lowered stasis (persistence) of larger life stages lead to a reduction in λ in the drier region, whereas lowered growth of all life stages lowered λ in moist region. Potential strategies to increase population growth rates should include decreasing the proportion of individuals harvested, promoting harvester‐owned plantations of African mahogany, and increasing survival and growth by promoting no‐fire zones in gallery forests. Our results show how population responses to harvest of NTFP may be altered by ecological differences across sites and emphasize the importance of monitoring populations over the climatic range in which they occur to develop more realistic recommendations for conservation.     

Modelling spatial and temporal variability in a zero-inflated variable: The case of stone pine (Pinus pinea L.) cone production

Modelling masting habit, i.e. the spatial synchronized annual variability in fruit production, is a huge task due to two main circumstances: (1) the identification of main ecological factors controlling fruiting processes, and (2) the common departure of fruit data series from the main basic statistical assumptions of normality and independence. Stone pine (Pinus pinea L.) is one of the main species in the Mediterranean basin that is able to grow under hard limiting conditions (sandy soils and extreme continental climate), and typically defined as a masting species. Considering the high economical value associated with edible nut production, the masting habit of stone pine has been a main concern for the forest management of the species. In the present work we have used annual fruit data series from 740 stone pine trees measured during a 13 years period (1996-2008) in order: (a) to verify our main hypothesis pointing out to the existence of a weather control of the fruiting process in limiting environments, rather than resource depletion or endogenous inherent cycles; (b) to identify those site factors, stand attributes and climate events affecting specific traits involved in fruiting process; and (c) to construct a model for predicting spatial and temporal patterns of variability in stone pine cone production at different spatial extents as region, stand and tree. Given the nature of the data, the model has been formulated as zero-inflated log-normal, incorporating random components to carry out with the observed lack of independence. This model attains efficiencies close to 70-80% in predicting temporal and spatial variability at regional scale. Though efficiencies are reduced according to the spatial extent of the model, it leads to unbiased estimates and efficiencies over 35-50% when predicting annual yields at tree or stand scale, respectively. In this sense, the proposed model is a main tool for facilitating decision making in some management aspects such as the quantification of total amount of cones annually supplied to nut industry, design of cone harvest programs or the optimal application of seedling felling.