How rare is too rare to harvest?: Management challenges posed by timber species occurring at low densities in the Brazilian Amazon

Tropical forests are characterized by diverse assemblages of plant and animal species compared to temperate forests. Corollary to this general rule is that most tree species, whether valued for timber or not, occur at low densities (<1 adult tree ha⁻¹) or may be locally rare. In the Brazilian Amazon, many of the most highly valued timber species occur at extremely low densities yet are intensively harvested with little regard for impacts on population structures and dynamics. These include big-leaf mahogany (Swietenia macrophylla), ipê (Tabebuia serratifolia and Tabebuia impetiginosa), jatobá (Hymenaea courbaril), and freijó cinza (Cordia goeldiana). Brazilian forest regulations prohibit harvests of species that meet the legal definition of rare – fewer than three trees per 100 ha – but treat all species populations exceeding this density threshold equally. In this paper we simulate logging impacts on a group of timber species occurring at low densities that are widely distributed across eastern and southern Amazonia, based on field data collected at four research sites since 1997, asking: under current Brazilian forest legislation, what are the prospects for second harvests on 30-year cutting cycles given observed population structures, growth, and mortality rates? Ecologically ‘rare’ species constitute majorities in commercial species assemblages in all but one of the seven large-scale inventories we analyzed from sites spanning the Amazon (range 49–100% of total commercial species). Although densities of only six of 37 study species populations met the Brazilian legal definition of a rare species, timber stocks of five of the six timber species declined substantially at all sites between first and second harvests in simulations based on legally allowable harvest intensities. Reducing species-level harvest intensity by increasing minimum felling diameters or increasing seed tree retention levels improved prospects for second harvests of those populations with a relatively high proportion of submerchantable stems, but did not dramatically improve projections for populations with relatively flat diameter distributions. We argue that restrictions on logging very low-density timber tree populations, such as the current Brazilian standard, provide inadequate minimum protection for vulnerable species. Population declines, even if reduced-impact logging (RIL) is eventually adopted uniformly, can be anticipated for a large pool of high-value timber species unless harvest intensities are adapted to timber species population ecology, and silvicultural treatments are adopted to remedy poor natural stocking in logged stands.     

Vertebrate population responses to reduced-impact logging in a neotropical forest

Vertebrate population densities were quantified in lowland central Guyana using line-transect censuses at three forest sites subjected to reduced-impact logging (RIL), and three adjacent unlogged sites. We censused a range of forest vertebrate species including large canopy-dwelling and terrestrial birds, three primates, one rodent and one tortoise. Two 4 km transects at each site were repeatedly surveyed during the wet season of 2008 to derive population density estimates on the basis of a cumulative survey effort of 416 km. RIL had ended within 16 months, and sites had been subjected to a mean extraction rate of 3.9 m³ ha⁻¹, equivalent to only 1.1 trees ha⁻¹. Three of the 15 vertebrate species examined here exhibited significantly different abundances at forest RIL sites, two of which were negative. Large frugivores such as primates were less abundant in sites subject to RIL, whereas smaller frugivores, granivores, folivores and insectivores were more common in logged sites. We are unable to reliably distinguish between responses of different taxonomic groups, since robust abundance metrics could only be estimated for four mammal species. Despite this, species traits including dietary guild, body mass, home range size and vertical stratification of forest use are used to explain varying responses. Our findings suggest that responsible reduced-impact logging practices in neotropical forests can be considered as a relatively benign form of forest management that can coexist with the requirements of both local economies and biodiversity conservation. However, our study sites experienced comparably low extraction rates, and detrimental effects such as hunting were low. Our results therefore provide an opportunity to scrutinise the effects of best practice logging systems, though do not necessarily represent typical circumstances across tropical forests.     

Beyond reduced-impact logging: Silvicultural treatments to increase growth rates of tropical trees

Use of reduced-impact logging (RIL) techniques has repeatedly been shown to reduce damage caused by logging. Unfortunately, these techniques do not necessarily ameliorate the low growth rates of many commercial species or otherwise assure recovery of the initial volume harvested during the next cutting cycle. In this study, we analyze the effect of logging and application of additional silvicultural treatments (liana cutting and girdling of competing trees) on the growth rates on trees in general and on of future crop trees (FCTs) of 24 commercial timber species. The study was carried out in a moist tropical forest in Bolivia, where we monitored twelve 27-ha plots for 4 years. Plots received one of four treatments in which logging intensity and silvicultural treatments were varied: control (no logging); normal (reduced-impact) logging; normal logging and low-intensity silviculture; and, increased logging intensity and high-intensity silviculture. Tree growth rates increased with intensity of logging and silvicultural treatments. The growth rates of FCTs of commercial species were 50–60% higher in plots that received silvicultural treatments than in the normal logging and control plots. Responses to silvicultural treatments varied among functional groups. The largest increase in growth rates was observed in FCTs belonging to the partially shade-tolerant and the shade-tolerant groups. These results indicate that silvicultural treatments, in addition to the use of RIL techniques, are more likely to result in a higher percentage of timber volume being recovered after the first cutting cycle than RIL alone.     

The compatibility of timber and non-timber forest product extraction and management

We discuss the extent of compatibility of timber and non-timber forest product (NTFP) extraction in two neotropical localities from biophysical, social, and institutional perspectives: the community concession forests of the Petén, Guatemala, and extractivist communities in northern Bolivia. In both localities, timber is harvested via reduced-impact logging (RIL) practices. In Guatemala, the main NTFP extracted is foliage from the understory xate palm (Chamaedorea spp.); in northern Bolivia, the fruits of the Brazil nut tree (Bertholletia excelsa). The Guatemalan case suggests a relatively high degree of compatibility due to low timber harvesting intensities, coupled with temporal, spatial, and social segregation of xate extraction in a well-defined land tenure system. In northern Bolivia, forest management regulations pay little attention to NTFPs and land tenure issues and related conflict complicate efforts to limit timber harvesting impacts on Brazil nut trees. The introduction of timber management plans overlain on customary property rights systems in which the extraction of Brazil nut is organized could undercut its management system. The two case studies suggest that specific legislative, education, and project interventions may help to promote the compatibility of timber and NTFP extraction and management. These include formal training of foresters on NTFP ecology and management while taking into account the perspectives of multiple stakeholders in the design of management plans. Tropical forest users, research managers, and policy makers will also better understand the need for integrated management of timber and NTFPs, if the trade-offs and potential economic benefits from NTFP extraction are clarified.     

Reduced-impact logging: Challenges and opportunities

Over the past two decades, sets of timber harvesting guidelines designed to mitigate the deleterious environmental impacts of tree felling, yarding, and hauling have become known as “reduced-impact logging” (RIL) techniques. Although none of the components of RIL are new, concerns about destructive logging practices and worker safety in the tropics stimulated this recent proliferation of semi-coordinated research and training activities related to timber harvesting. Studies in Southeast Asia, Africa, and South and Central America have clearly documented that the undesired impacts of selective logging on residual stands and soils can be substantially reduced through implementation of a series of recommended logging practices by crews that are appropriately trained, supervised, and compensated. Whether reducing the deleterious impacts of logging also reduces profits seems to depend on site conditions (e.g., terrain, soil trafficability, and riparian areas), whether the profits from illegal activities are included in the baseline, and the perspective from which the economic calculations are made. A standardized approach for calculating logging costs using RILSIM software is advocated to facilitate comparisons and to allow uncoupling RIL practices to evaluate their individual financial costs and benefits. Further complicating the matter is that while there are elements common to all RIL guidelines (e.g., directional felling), other components vary (e.g., slope limits of 17–40° with ground-based yarding). While use of RIL techniques may be considered as a prerequisite for sustaining timber yields (STY), in particular, and sustainable forest management (SFM), in general, RIL should not be confounded with STY and SFM. This confusion is particularly problematic in forests managed for light-demanding species that benefit from both canopy opening and mineral soil exposure as well as where harvesting intensities are high and controlled primarily by minimum diameter cutting limits. These qualifications notwithstanding, since logging is the most intensive of silvicultural treatments in most tropical forests managed for timber, some aspects of RIL are critical (e.g., protection of water courses) whether forests are managed for STY, SFM, or even replacement by agricultural crops.     

大熊猫主食竹产地土壤重金属评价

通过对大熊猫主食竹产地华蓥山岩溶区土壤重金属元素As、Cd、Cr、Hg、Pb和Cu的调查分析,采用单因子污染指数法、综合污染指数法和相关性分析法对当地的土壤重金属环境质量进行了评价.结果表明,研究区6种重金属的单因子污染指数均小于0.7,综合污染指数也均小于0.7.土壤重金属中Hg与pH值、As之间存在显著正相关作用,...     

不同遮荫强度对几种苗木生长的影响

以黄金榕、花斑垂叶榕、乳斑榕的苗木为试验材料,来探讨不同遮荫强度苗木生长、水份利用及苗木生长环境的影响,试验表明：一层遮荫网处理的苗木比无遮荫网和二层遮荫网处理的苗木在株高、冠幅、根径以及叶片数目等方面均增长较快,苗木的地下部分、叶和茎含水量均较低。无遮荫处理利用较多水分,以及土壤温度在14：00点左右的时间明显高于所有的遮荫处理。     

木瓜榕和对叶榕上昆虫群落结构

在西双版纳热带雨林中的木瓜榕和对叶榕两个种群内共采集昆虫标本20088号,其中访问木瓜榕的昆虫有8目21科33属,共40种,在对叶榕上采集到37种昆虫,隶属于7目21科32属。两种榕树的昆虫群落组成特点表现为：害虫种类多,种类达群落总种数的94．6％－97．0％,但个体数量少,主要是鳞翅目、鞘翅目及同翅目等类群的昆虫;许多昆虫既喜食榕果又可危害叶片,部分种类仅取食叶片和蛀干;这些类群中在隐头花果内外活动的昆虫种类最多,达54％,数量上占到93．1％－94．3％。益虫种类少,则个体数量多,尤其是传粉榕小蜂和群数量占绝对优势（86．4％－90．2％）,它的成功传粉影响着榕树群落的构建和稳定。     

榕属植物在福建省园林中的应用

榕属植物具有生性强健、形态优美、遮荫效果好、耐修剪、寿命长等优点 ,是优良的园林绿化树种 ,在福建省园林中应用广泛。文中介绍了榕属植物在福建省园林中的应用类型 ,列出了福建省园林中应用的主要榕属植物 ,并指出应用中应注意的问题     

爱玉子与薜荔比较分析研究

爱玉子与薜荔为同属不同种的藤本植物,两者虽有相似之处,但也存在许多较大的区别。通过收集有关资料和研究,着重介绍爱玉子与薜荔在形态特征、隐花果特性、天然分布以及商品品质等方面的不同之处,以供有关学者和拟引种爱玉子的投资者参考。     

森林采伐限额管理制度创新设计——可流转交易的采伐指标银行体系

回顾我国森林采伐限额制度存在的问题与不足,提出在指标可流转前提下建立采伐指标银行体系,并进行了采伐指标配给和流转环节等设计。针对采伐指标的配给、价格的生成、储蓄、借贷、还贷等各环节可能出现的问题提出了对策建议。旨在以市场实现采伐指标的最优化配置,从而优化森林资源消耗结构,提高社会各界经营林业的积极性和实现森林资源的可持续增长。     

峨眉山和神农架地区森林环境与野生大熊猫栖息地特征的比较

本文通过自然地理环境、竹类分布特征以及植被中植物区系的属分布区类型的比较,分析了现今野生大熊猫（Ailuropoda melanoleuca）分布区域与原有大熊猫分布的峨眉山以及大熊猫早已绝迹的神农架自然保护区的差异.结果表明：峨眉山属于大熊猫分布区域,而神农架的地理经度超出了大熊猫分布区域,其它环境因子与野生大熊猫分布地区无显著性差异（p＞0.05）;竹子种类也分布有大熊猫喜食的中小径竹;同时植物区系的属分布区类型之间没有明显的差异,森林植被的垂直分布格局极为相似.因此,造成大熊猫现在在峨眉山和神农架地区没有自然分布可能是历史上社会经济的不断发展和人为干扰程度的增加等综合作用的结果.     

云南普洱市小叶榕主要害虫的生物学特性及防治

调查记录了云南普洱市小叶榕的5种害虫,并分述其危害特点、生物学特性及其有效的防治措施。     

笔管榕榕果发育的初步研究

对温州市区笔管榕榕果的形成时期、着生部位、结果数量、发育温度、生长特性和果实结构进行了初步研究,对进一步开发笔管榕资源提出了建议.     

榕属树种的扦插生根试验

对黄叶榕,花叶垂叶榕,垂叶榕和黄叶垂叶榕４年榕属树种进行扦插生根试验,结果表明;扦插所用的材料,处理的方法和扦插时间不同,其平均生根率也不同。这４个树种的扦插最好在秋季进行,选用经黄化处理的当年生半木质化枝条作插穗,其基部蘸生根粉后扦插,可提高生根率,缩短生根时间。     

小叶铺地榕泥炭穴盘覆膜扦插繁殖技术

小叶铺地榕是一种新开发的优良园林地被植物,具有良好的市场前景。经5年多的研究开发,总结出适合小叶铺地榕规模繁殖的泥炭穴盘覆膜扦插技术,文章详细介绍了该技术的应用效果和操作细节,为小叶铺地榕的推广应用提供了可靠的技术参考。     

基于森林健康理念的采伐作业技术措施

论述在我国实施森林健康项目的意义及森林健康理念在生态采伐中的应用,包括采伐方式、采伐强度、采伐木确定、伐木和集材技术、伐区清理、更新方式等方面的内容.认为森林健康项目的实施涉及到林权所有人的切身利益,在制定作业设计时要增加公众参与,广泛听取不同利益主体的意见.