Density-dependent mortality and the latitudinal gradient in species diversity

Ecologists have long postulated that density-dependent mortality maintains high tree diversity in the tropics. If species experience greater mortality when abundant, then more rare species can persist. Agents of density-dependent mortality (such as host-specific predators, and pathogens) may be more prevalent or have stronger effects in tropical forests, because they are not limited by climatic factors. If so, decreasing density-dependent mortality with increasing latitude could partially explain the observed latitudinal gradient in tree diversity. This hypothesis has never been tested with latitudinal data. Here we show that several temperate tree species experience density-dependent mortality between seed dispersal and seedling establishment. The proportion of species affected is equivalent to that in tropical forests, failing to support the hypothesis that this mechanism is more prevalent at tropical latitudes. We further show that density-dependent mortality is misinterpreted in previous studies. Our results and evidence from other studies suggest that density-dependent mortality is important in many forests. Thus, unless the strength of density-dependent mortality varies with latitude, this mechanism is not likely to explain the high diversity of tropical forests.     

Drought sensitivity shapes species distribution patterns in tropical forests

Although patterns of tree species distributions along environmental gradients have been amply documented in tropical forests, mechanisms causing these patterns are seldom known. Efforts to evaluate proposed mechanisms have been hampered by a lack of comparative data on species' reactions to relevant axes of environmental variation. Here we show that differential drought sensitivity shapes plant distributions in tropical forests at both regional and local scales. Our analyses are based on experimental field assessments of drought sensitivity of 48 species of trees and shrubs, and on their local and regional distributions within a network of 122 inventory sites spanning a rainfall gradient across the Isthmus of Panama. Our results suggest that niche differentiation with respect to soil water availability is a direct determinant of both local- and regional-scale distributions of tropical trees. Changes in soil moisture availability caused by global climate change and forest fragmentation are therefore likely to alter tropical species distributions, community composition and diversity.     

木榄母树下2种红树植物幼苗生长特征研究

在广西北仑河口珍珠港内进行木榄母树下栽植木榄（Bruguiera gymnorrhiza)和红海榄（Rhizophora stylosa)幼苗试验。选取3棵母树,分别以每棵母树为中心,在东、西、南、北方向上,离母树5．0m距离内按每0．5m栽植2条胚轴。以1月、4月、7月、10月为冬、春、夏、秋季代表月,测定母树下幼苗的实生高、基径、叶数及分枝等生长指标。结果表明：木榄的平均成活率随时间的推移呈下降趋势,栽植1年后的成活率为67．0％,2年后的平均保存率为48．9％,夏季的成活率较春季的高3．7％;红海榄幼苗成活率总的呈下降趋势,造林1年后成活率为58．3％,2年后的保存率为42．0％。木榄母树下3．0m－5．0m和3．5m－4．5m的中离分别为木榄幼苗和红海榄幼苗的适宜生长范围。2种幼苗生长的季节动态均表现为主茎生长高峰期在夏季,基径生长高峰期在秋季。红海榄苗前3年的生长量和生长速度均高于木榄苗,在苗期生物量构成中红海榄分配给叶的份额逐年增加,木榄分配给叶的份额则逐年减少。     

Increasing dominance of large lianas in Amazonian forests

Ecological orthodoxy suggests that old-growth forests should be close to dynamic equilibrium, but this view has been challenged by recent findings that neotropical forests are accumulating carbon and biomass, possibly in response to the increasing atmospheric concentrations of carbon dioxide. However, it is unclear whether the recent increase in tree biomass has been accompanied by a shift in community composition. Such changes could reduce or enhance the carbon storage potential of old-growth forests in the long term. Here we show that non-fragmented Amazon forests are experiencing a concerted increase in the density, basal area and mean size of woody climbing plants (lianas). Over the last two decades of the twentieth century the dominance of large lianas relative to trees has increased by 1.7-4.6% a year. Lianas enhance tree mortality and suppress tree growth, so their rapid increase implies that the tropical terrestrial carbon sink may shut down sooner than current models suggest. Predictions of future tropical carbon fluxes will need to account for the changing composition and dynamics of supposedly undisturbed forests.     

浙江天童受损常绿阔叶林实验生态学研究(Ⅳ):土壤种子库在受损常绿阔叶林恢复初期中的作用

模拟了常绿阔叶林的4种不同受损程度(间伐大树,清理下木,清除地上植被以及植被和表土完全破坏),于2003年10月在天童国家森林公园内各设置1个受损样方.通过分析土壤种子库萌发格局、种类组成及其与受损样地第一年恢复物种的相似性,探明土壤种子库在受损常绿阔叶林恢复初期中的作用.结果表明,(1)在16个0.5 m×0.5 m的取样面积上,土壤种子库共萌发出995株幼苗,密度为248.75粒/m~2,分属21科27属28种,其中乔木7种,灌木8种,藤本4种,草本9种.(2)土壤种子库对4种干扰方式的样地物种恢复贡献率为:Ⅰ号(0.467)Ⅳ号(0.389)Ⅱ号(0.368)Ⅲ号(0).(3)檫木(Sassafra tzumu)、拟赤杨(Alniphyllum fortunei)、大青(Clerodendrum cyrtophyllum)和山鸡椒(Litsea cubeba)等先锋种可通过土壤种子库大量更新;米槠(Castanopsis carlesii)和石栎(Lithocarpus glaber)等虽具有种子库,但数量少;而南酸枣(Choerospondias axilliaris)和香樟(Cinnamomum camphora)等种子不能通过土壤种子库实现更新.研究表明土壤种子库对天童地区受损常绿阔叶林的恢复作用比较有限.     

The limits to tree height

Trees grow tall where resources are abundant, stresses are minor, and competition for light places a premium on height growth. The height to which trees can grow and the biophysical determinants of maximum height are poorly understood. Some models predict heights of up to 120 m in the absence of mechanical damage, but there are historical accounts of taller trees. Current hypotheses of height limitation focus on increasing water transport constraints in taller trees and the resulting reductions in leaf photosynthesis. We studied redwoods (Sequoia sempervirens), including the tallest known tree on Earth (112.7 m), in wet temperate forests of northern California. Our regression analyses of height gradients in leaf functional characteristics estimate a maximum tree height of 122-130 m barring mechanical damage, similar to the tallest recorded trees of the past. As trees grow taller, increasing leaf water stress due to gravity and path length resistance may ultimately limit leaf expansion and photosynthesis for further height growth, even with ample soil moisture.     

毛白杨扦插育苗技术研究

毛白杨由于根原始体的数量较少及生长抑制物质的存在,造成了硬枝扦插育苗成活率很低.实验采用扦插育苗的方法,系统研究了提高毛白杨成活率的因素.结果表明,树干基部萌生条、种条基部插穗、插穗粗度为1.2 ～2.0cm、长度为10～ 14cm、土壤温度为18 ～ 30℃、土壤含水量为80％ - 90％时,能够显著提高毛白杨扦插的成活率;适宜浓度的萘乙酸、吲哚乙酸、赤霉素及生根粉处理均能够极显著提高毛白杨育苗成活率.     

苗木稳态营养加载技术研究进展

苗木稳态营养加载技术目前已成为欧洲和北美苗木施肥的主要技术,广泛运用于栎属、云杉属、松属等欧美地区主要造林树种。我国于1988年利用稳态营养加载技术对兰考泡桐、刺槐、杉木、湿地松等树种的苗木进行了初步经营,21世纪以来该方面研究基本处于停滞状态。笔者从稳态营养加载技术的理念、稳态营养加载参数确定技术、稳态营养加载在容器苗应用、稳态营养加载与树种敏感性、稳态营养加载与秋季施肥、缓释肥、菌根及苗木质量等方面,对国际上近30年的相关研究成果进行综述,并结合当今研究热点,对该领域研究前景进行了展望。     

南靖和溪南亚热带雨林林隙内树种更新初步研究

通过对南靖南亚热带雨林中林隙和非林隙林分的研究调查，初步分析了主要树种在林隙内外的数量特征、树种在林隙内的空间分布与数量和生长状况的关系。由于受光照条件和林隙边缘植物的影响，决定林隙区域内土壤种子库种子萌发、幼苗生长、发育，植物种群数量分布等特征，最终影响到森林的更新。     

北碚榕试管苗优质苗木的培育

以北碚榕试管苗为材料,炼苗后采用可降解的无纺布育苗袋育苗,研究不同育苗基质(品氏营养土、蛭石、珍珠岩、林下腐殖土的不同体积混合物)、不同叶面追肥(0.5%～2%尿素、NPK复合肥和Hoagland营养液)对苗木生长和移栽成活率的影响.结果表明,最佳育苗基质为品氏营养土,试管苗移栽30d后株高增加1.90cm,叶片增加2.75枚,移栽成活率为96.29%;最适叶面追肥为1%尿素,喷施30d后(1次/3d),株高增加1.94cm,叶片增加3.2枚,移栽成活率达100%;株高7～9cm(叶龄5～8枚)的苗木,移栽田间30d后,株高增加1.4cm,叶片增加3.4枚,移栽存活率达96.25%,长势良好.     

湖南省莽山的植被

<正> 湖南宜章县莽山林区位于湖南南端,与广东乳阳林区毗邻,地处北纬24°54′48″-25°03′,东经112°43′-113°00＇,总面积约2万公顷。山深林茂,人烟稀少,是我国东南部基本上属原生型常绿阔叶林及中山针阔混交林最大面积的保存地。常绿阔叶林(Laurisilva,下简称为常绿林)在全世界以中国面积最大,而中国东南部又以南岭山脉最盛。莽山石坑崆海拔1,922米,是南岭一高峰。森林苍郁,树种复杂,植被区系与生态在学术研究上具有典型意义。 本文主要是根据1964、1965及1979年的调查总结而成。计采集植物标本1800余号,并对1万米~2样地乔木(胸径>3厘米)作每木测定,分层分级统计。森林样方为10 × 10米,每个工作单位取5-20个样方,计500-2000米~2。由于乔木组成复杂,故采用curtis的重要值指数(Importance Index Value-I.V.I,即相对密度De％+相对频度F％+相对显著度Do％=300 ~[1,14,15])来表示各种树种在群落中的优势地位。     

Lianas as structural parasites: A re-evaluation

Lianas are a principal physiognomic component of tropical and subtropical forests and are typically considered to be parasites of trees. In contrast, the substantial contribution of lianas to rainforest leaf litter production (up to 40%) suggests that they play important roles in nutrient cycles and may benefit their host trees. Lianas contribute disproportionately to total forest litter production at least partially because lianas invest relatively little in support structures and proportionately much more to leaf production when compared with trees. In contrast to tree leaves, liana leaves are higher in nutrient concentrations, relatively short-lived, and decompose more rapidly. In addition, the special life form of lianas allows them to grow vertically and horizontally in the forest and relocate nutrients, mainly towards their host trees, through the production of leaf litter. Consequently, lianas may contribute substantially to the high rainforest productivity, and the roles they play in liana/tree associations and rainforest dynamics needs to be re-evaluated.     

绒毛白蜡引种试验研究

从美国原产地引进的绒毛白蜡种子，在聊城地区经过３年育苗试验，６年造林试验，对其育苗方法、苗期和幼树生长规律、生态学特性、抗性等方面进行了系统研究，取得了稳定效果，确认绒毛白蜡既是内陆盐碱撩荒地或低洼地造林的优良树种，又是树形美观的城镇绿化树种．     

极小种群梓叶槭种群结构及动态特征

【目的】分析中国特有濒危极小种群梓叶槭(Acer catalpifolium)的年龄结构和动态特征,揭示种群与环境之间的相互关系,预测种群发展动态,探索其濒危机制,提出野生梓叶槭种群的保护和恢复对策。【方法】通过对集中分布于四川峨眉山和都江堰的梓叶槭种群进行样地调查,采用样方调查法,将各样地划分为1～4个20 m×20 m的样方,再将每块样方划分为16个5 m×5 m的小样方; 对样方内的梓叶槭植株进行每木调查,调查内容包括个体数、树高、胸径等生长因子,同时记录各样地海拔、经纬度、坡向、坡度、林分郁闭度、植被群落以及土壤类型等生境因子; 以梓叶槭个体的胸径代替龄级来反映种群结构,将梓叶槭胸径大小划分为11个径级(Ⅰ-Ⅺ,设置DBH>50 cm为Ⅺ级,每级间隔5 cm),龄级与胸径大小级对应,绘制梓叶槭种群的径级结构图; 编制了种群的特定时间生命表,分析其存活曲线、死亡率曲线等重要参数; 运用时间序列预测模型分析种群数量动态和发展趋势。【结果】梓叶槭在峨眉山和都江堰地区的种群差异明显,峨眉山种群共有105株,都江堰种群共有81株,种群龄级结构完整,种群径级结构表现为中龄级所占比例较大、幼龄级和老龄级比例次之的纺锤形结构。梓叶槭种群年龄结构动态变化指数表明,两个地区受随机干扰时的种群年龄结构动态指数(V_pi')分别为0.011 6和0.004 2,均趋近于0,总体上表现出由稳定型向衰退型转化的衰退型结构; 生命表及相关曲线分析显示,梓叶槭早期个体死亡数较高,存活数随龄级的增加而减少,对环境的选择作用强; 存活曲线趋于Deevey-Ⅱ型,各龄级种群有相近死亡率; 生存函数分析表明,两个种群的生存率函数S(t)均随着龄级的增大呈单调下降的趋势,而累计死亡率F(t)则呈单调上升趋势,两个函数曲线变化呈现互补的现象; 时间序列预测分析表明,2、4、6、8龄级时间后梓叶槭老龄级个体逐渐增多,幼龄级个体则有所降低,种群稳定性降低,难以长期维持; 如果种群中幼苗难以补充,幼树不充足,再经过4个龄级后梓叶槭种群将成为衰退型种群。【结论】导致梓叶槭濒危的原因可能是梓叶槭的生物学特性和人为干扰; 应加强对梓叶槭种群及栖息地的保护,保护梓叶槭现有的成年个体,促进种子的萌发和幼苗的更新,防止栖息地及生态系统的破坏; 还要深入开展梓叶槭生物学及繁育特征研究,提高梓叶槭种子萌发率和成苗率,促进其种子向幼苗转化。另外,在天然林更新中,应采取人工抚育等措施来加强对中小径级梓叶槭个体及生境的保护,促进梓叶槭种群的自然更新和恢复。     

海南热带雨林树木生长空间测度的研究

针对海南热带雨林林分特征,提出了新的测度指标体系,对热带雨林树木生长及其竞争的关系进行了研究。结果表明,所提出的生长竞争测度指标能客观地反映林木生长势态,较大地提高了生长模型的估计精度。该研究为进一步揭示热带雨林生长规律,研究稳定、持续的生态系统提供了理论基础。     

苗木移栽条件下的滨海盐渍土水盐动态变化

 在河北唐山南堡开发区, 结合穴状衬膜改土整地, 移栽了绒毛白蜡、国槐、桧柏、柳树等研究用苗木, 以土钻取土法进行两年土壤水盐动态定期监测, 研究了移栽苗木对滨海盐渍土水盐动态规律的影响, 以期为滨海泥质盐碱地造林绿化的树种选择提供理论依据。结果表明, 与未移栽苗木的处理(对照组)相比, 移栽苗木会降低土壤含水量和电导率, 并增大二者的月际变化幅度, 但对土壤含水量和电导率的总体变化趋势影响不大。苗木的生长季、树冠结构和根系吸水是移栽苗木后影响土壤水盐动态变化的主要因素, 其中苗木的生长季影响主要表现为同一时期, 各种苗木所在土壤含水量差异较大;苗木的冠型结构主要影响表层土的土壤含水量;根系吸水作用则是改变了土壤含水量和盐分的垂直分布。4 种苗木间对比, 土壤含水量动态变化无明显差异;土壤电导率动态变化呈显著差异, 其中以桧柏对土壤电导率动态变化影响较为显著、脱盐降盐效果最好。     

广西防城港市万鹤山鹭林植物的初步研究

用样方调查结合实地逐株统计方法，调查广西防城港市万鹤山鹭林植物，结果表明，万鹤山鹭鸟几乎全部聚集在以许氏家族房屋为中心直径为800m^2左右的半圆范围内的次生林中，白鹭的营巢植物群落的乔木层主要是马尾松（Pinus massoniana Lamb.）。郁闭度0．6，下层以三叉苦（E.lepta(Spreng.)Merr.）占优势，灌木层盖度40％与草本层成团状分布；营巢树共有12种，马尾松和三叉苦均为10巢／株，其余10种平均单株营巢数为2－8株，夜鹭的营巢植物群落为典型的马尾松－桃金娘－五节瓦＋铁芒萁群落，林分郁闭度0．7，营巢树仅为马尾松，鹭 取食的的任何部分，但在权桠建巢，常到树冠顶部了望和停留，挤压幼枝、损折干枝，破损树皮以及所排粪便覆盖和污损树叶等，影响鹭林植群的演替，但不改变演潜方向，而且鹭林植物群落及周围森林无明显病虫害发生，建议建立自然保护区，有效保护近海水域及周围森林，宣传教育群众爱护鹭鸟。     

Host specificity of Lepidoptera in tropical and temperate forests

For numerous taxa, species richness is much higher in tropical than in temperate zone habitats. A major challenge in community ecology and evolutionary biogeography is to reveal the mechanisms underlying these differences. For herbivorous insects, one such mechanism leading to an increased number of species in a given locale could be increased ecological specialization, resulting in a greater proportion of insect species occupying narrow niches within a community. We tested this hypothesis by comparing host specialization in larval Lepidoptera (moths and butterflies) at eight different New World forest sites ranging in latitude from 15 degrees S to 55 degrees N. Here we show that larval diets of tropical Lepidoptera are more specialized than those of their temperate forest counterparts: tropical species on average feed on fewer plant species, genera and families than do temperate caterpillars. This result holds true whether calculated per lepidopteran family or for a caterpillar assemblage as a whole. As a result, there is greater turnover in caterpillar species composition (greater beta diversity) between tree species in tropical faunas than in temperate faunas. We suggest that greater specialization in tropical faunas is the result of differences in trophic interactions; for example, there are more distinct plant secondary chemical profiles from one tree species to the next in tropical forests than in temperate forests as well as more diverse and chronic pressures from natural enemy communities.     

广东黑石顶森林群落黄果厚壳桂(Cryptocary aconcinna)幼苗生长与环境因子的相关分析

对黑石顶森林群落中黄果厚壳桂幼苗一年的生长与影响幼苗生长因子的相关性分析结果表明,土壤中氮、磷、钾含量与幼苗生长呈正相关,土壤有机质含量和pH值也间接影响幼苗生长,在水发和光照强度产大的群落中,幼苗生长与土壤水分含量呈正相关,与林内光照强度呈负相关,群落中幼苗密度较大将促进1年生幼苗的生长,各影响因子主要与1－3年生幼苗的生长具有显著的相关性,而3龄以上幼苗的生长与各因子间无显著的相关性。     

基于EST-SSR标记鉴定猴耳环自由授粉的全同胞子代

【目的】猴耳环是重要的药用树种,具有较好的工业应用价值。利用EST-SSR标记对猴耳环自然群体1株母树的自由授粉子代进行父本鉴定,从而确定全同胞子代,为基于全同胞家系的后续研究提供材料基础。【方法】以自然群体中母树ELS31自由授粉产生的1 489株子代及该群体内挂果的38株候选父本为材料,利用15个EST-SSR标记检测子代多样性和标记多态性,基于最大似然法鉴定各子代的父本,母本父本均相同的子代即构成全同胞家系,并估算群体内花粉传播距离,检验各父本对应的全同胞家系的多样性,通过卡方检验判断标记是否合乎预期的孟德尔分离比。【结果】15个EST-SSR标记的引物(对)共扩增出89个等位片段。子代群体期望杂合度(H_e)为0.525,表明群体多样性为中等水平;基于自然群体18株无亲缘关系的单株估算的标记平均多态性信息量(PIC)为0.736,表明标记多态性高。在1 489株自由授粉的子代中,确定了857株子代(57.6%)的34株父本。子代数最多的10个父本产生的子代数为26~184株,其他24个父本仅共产生子代139株。未发现自交子代,表明猴耳环是异交物种,自交的可能性极低。对子代数量20株以上的10个父本对应的全同胞家系观测杂合度(H_o)为0.502~0.693,H_e为0.417~0.544,各家系均是H_o大于H_e,表明存在一定程度的杂合子过剩。花粉传播的范围为10.0~559.1 m,平均119.2 m,但主要传播距离在150 m以内。716株子代(83.5%)的父本(10株)与母树距离在150 m以内。距离最远的父本ELS01 (559.1 m)和ELS02 (552.2 m)分别仅产生了9和12株子代。15个标记在子代20株以上的部分或全部全同胞家系中均有不同程度的偏分离,平均每家系的偏分离标记数为8.6个;偏分离最严重的是标记ARCeSSR141,在父本ELS30的全同胞家系中卡方(χ²)值为164.55。【结论】基于15个EST-SSR标记鉴定了猴耳环自然群体1株母本的1 489株自由授粉子代的父本,获得了子代20株以上的10个父本的全同胞家系。这为后续遗传测定、遗传图谱构建和数量性状位点定位等研究提供了材料基础。