Nitrogen-fixation dynamics in a cut-and-carry silvopastoral system in the subhumid conditions of Guadeloupe, French Antilles

This paper summarizes several studies on N recycling in a tropical silvopastoral system for assessing the ability of the system to increase soil fertility and insure sustainability. We analyzed the N₂ fixation pattern of the woody legume component (Gliricidia sepium), estimated the recycling rate of the fixed N in the soil, and measured N outputs in tree pruning and cut grass (Dichanthium aristatum). With this information, we estimated the N balance of the silvopastoral system at the plot scale. The studies were conducted in an 11-year-old silvopastoral plot established by planting G. sepium cuttings at 0.3 m × 2 m spacing in natural grassland. The plot was managed as a cut-and-carry system where all the tree pruning residues (every 2-4 months) and cut grass (every 40-50 days) were removed and animals were excluded. No N fertilizer was applied. Dinitrogen fixation, as estimated by the ¹⁵N natural abundance method, ranged from 60-90% of the total N in aboveground tree biomass depending on season. On average, 76% of the N exports from the plot in tree pruning (194 kg [N] ha^–1 yr^–1) originated from N₂ fixation. Grass production averaged 13 Mg ha^–1 yr^–1 and N export in cut grass was 195 kg [N] ha^–1 yr^–1. The total N fixed by G. sepium, as estimated from the tree and grass N exports and the increase in soil N content, was about 555 kg [N] ha^–1 yr^–1. Carbon sequestration averaged 1.9 Mg [C] ha^–1 yr^–1 and soil organic N in the 0-0.2 m layer increased at a rate of 166 kg [N] ha^–1 yr^–1, corresponding to 30% of N₂ fixation by the tree. Nitrogen released in nodule turnover (10 kg [N] ha^–1 yr^–1) and litter decomposition (40 kg [N] ha^–1 yr^–1) contributed slightly to this increase, and most of the recycled N came from the turnover or the activity of other below-ground tree biomass than nodules. This revised version was published online in June 2006 with corrections to the Cover Date.     

长白山过伐林区云冷杉针阔混交林林分结构的研究

如何经营过伐林，使其保持好的林分结构，是林分生态系统在经营情况下正向演替和产生较高效益的关键问题之一。本文以金沟岭林场的云冷杉针阔混交林为研究对象，分析了在用捡查法经营情况下的林分连续14a的结构状况及变化，认为十几年的检查法经营实验，调整和改善了林分的径阶和蓄积结构，林分生态系统保持稳定并逐步提高。     

橡胶树风灾保险处理实践与改进

简要描述了热带风暴"天鹅"对海南农垦橡胶树造成的灾害,分析了风灾保险的处理过程和发现的问题,探讨保险条款释义和实务操作等环节上的改进,以期完善海南橡胶树风灾保险工作。     

An inventory of Guadua (Guadua angustifolia) bamboo in the Coffee Region of Colombia

Management of renewable natural resources and the corresponding policy formulation should be founded on reliable data and information. This refers both to information on the resource itself and to information on the market situation. In this paper, we present methodology and major results of an inventory of the Guadua resources, in a study area of about 1 million ha within the Coffee Region of Colombia. This inventory produced for the first time sample-based statistical estimations of the Guadua area and growing stock. In the study area, land cover of Guadua patches was estimated to be 3.9% or about 40,000 ha (minimum patch area 0.3 ha). This is higher than figures published earlier. Estimation for mean number of standing culms (including shoots and dry culms) per hectare was 6,940 with a mean diameter at breast height of 10.8 cm, apparent commercial volume of 654 m3/ha, commercial wood volume of 304 m3/ha, oven-dry biomass of 311 ton/ha, and total carbon stock of 156 ton/ha. While the low-intensity sampling approach worked well and may serve as an example for similar studies, we identified a number of issues for further research, particularly in what refers to as the basic mensurational models for Guadua volume and biomass estimation from inventories.     

Survival of tanoak (Lithocarpus densiflorus) and Pacific madrone (Arbutus menziesii) seedlings in forests of southwestern Oregon

Survival of tanoak (Lithocarpus densiflorus) and Pacific madrone (Arbutus menziesii) seedlings was studied in order to interpret succession in conifer hardwood forests and to determine ways to suppress establishment of these species. Seed protected from rodents and birds, and unprotected seed was sown in clearcuts and in conifer stands 40 to 200+ years old. Second-year survival rates of tanoak seedlings were high (50–70%) in exposed clearcuts and conifer stands. Seed predators appear to be of prime importance in limiting tanoak establishment. Survival rates of Pacific madrone seedlings on the same sites as the tanoak were low (0–8%), and many factors caused mortality. Seedlings of both species grew slowly; after 3 years, average tanoak height was only 6.0 to 14.0 cm, average madrone height 2.0 to 6.0 cm.     

广东江门地区雷林1号桉的自然更新与扩散

调查了雷林1号桉单株的扩散情况及雷林1号桉林缘在广东江门地区主要植被类型(杉木人工林、红花荷人工林和灌木丛)中的扩散情况,采用小样方法调查了雷林1号桉林下乡土乔木树种的自然更新情况.调查发现:15年生雷林1号桉单株在45°扇形样地单向扩散的最大距离为17.82 m,扩散苗最多22株,平均树高4.72 m;雷林1号桉不能扩散进入20年生杉木人工林,可以扩散进入红花荷幼林,但实生苗数量很少,还可以扩散进入地被物较少的灌木丛,且更新苗数量较多.分析表明:雷林1号桉在引种栽培地能自然更新;雷林1号桉种子落地接触土壤、光照充足是其更新的主要条件;有5种乡土树种能在雷林1号桉林下自然更新且正常生长,因此,目前雷林1号桉对乡土树种的自然更新没有影响.     

甘肃盐池湾自然保护区动物物种多样性现状及保护对策

甘肃盐池湾自然保护区属野生动物类型自然保护区，区内有脊椎动物22目48科135种。其中鱼类5种，两栖类1种，爬行类2种，鸟类96种，兽类31种。含国家Ⅰ级保护动物10种，Ⅱ级保护动物24种。是国家重点保护野生动物的集中分布区之一，尤其是高原有蹄类，占我国北方列入保护名录有蹄类（16种）的56．3％。     

澳大利亚、新西兰天然林保护管理对我国的启示

文章介绍了澳大利亚和新西兰两国的天然林经营保护方面的基本情况和做法,提出进一步完善我国正在实施的天然林保护工程政策和管理机制,如制定符合国际林业发展趋势和我国国情的天然林资源保护政策;大力发展人工林,提高林产品产量进而促进天然林保护;加强国际合作,提高我国天然林可持续经营能力等。     

河北零叶蝉的研究

河北零叶蝉系一新种，是吸食柿树叶片汁液的害虫。分布河北、安徽。此虫在河北西部山区１年发生２代或３代，以卵在柿树当年生小枝皮层内越冬。在大发生地区，可用４０％氧化乐果喷冠、涂干或干基钻孔挂瓶输药进行化学防治。天敌有日本高姬蝽、红点平盲蝽、紫斑突额盲蝽、碎斑平盲蝽等。     

天然林择伐经营技术的应用研究

按照森林可持续经营的原则，从天然林生态保护角度出发，以福建省永安市为例。利用森林分类经营方法对天然林经营进行科学分类，提出天然林因林因地实行合理的择伐方式是实现天然林可持续发展的有效途径，为天然林择伐经营的具体实施提供科学依据。