林隙与林下环境对锐齿槲栎和米心水青冈种群更新的影响

锐齿槲栎 (Quercusalienavar.acuteserrata ) 和米心水青冈 (Fagusengleriana) 是广泛分布在我国暖温带和亚热带山地中海拔地段的主要建群种, 对水土保持和维持生态系统稳定具重要意义。该文通过在神农架地区的典型样地调查, 分析了这 2个种群在林隙和林下不同光环境中的更新状况和径级结构 ;利用便携式Licor₆ 4 0 0光合仪测量了 2种苗木的光饱和及光诱导曲线, 探讨了光对这 2个树种更新的影响机理。实验结果表明, 在所调查的林地中, 锐齿槲栎和米心水青冈种群都有充足的幼苗库, 锐齿槲栎幼苗以实生为主, 米心水青冈幼苗以萌生为主 ;从幼苗到幼树的转化过程中, 锐齿槲栎的成活率几乎为零, 而米心水青冈的成活率约为 6 %~ 8% ;在两者的混交林中, 米心水青冈种群呈稳定的金字塔形年龄结构, 而锐齿槲栎则是某一生长阶段的种群占据主导地位。光饱和曲线显示, 对 2年生同生群苗木, 在林窗下, 锐齿槲栎的最大净光合速率 (4.6 1μmol·m-2 ·s-1) 比米心水青冈的 (4.16 μmol·m-2 ·s-1) 要高 ;而在林冠下, 米心水青冈的最大净光合速率 (Pn=3.89μmol·m-2 ·s-1) 比锐齿槲栎的最大净光合速率 (Pn=3.6 8μmol·m-2 ·s-1) 要高。无论在林窗下或林冠下, 米心水青冈幼苗的光饱和点比锐齿槲栎的要低。两者混交林下的光诱导曲线显示, 与米心水青冈幼苗相比, 锐齿槲栎幼苗对光的反应速度较慢, 最大净光合速率也较低, 在林冠下表现出较弱的竞争力。资源分配试验证明, 锐齿槲栎在幼苗阶段以地上部分生长为主, 而米心水青冈倾向于把更多的干物质贮藏在根部, 显示出不同的光利用策略。     

啮齿动物捕食和搬运蒙古栎种子对种群更新的影响

2010-2011年,在东北林业大学城市林业示范基地研究了啮齿动物对蒙古栎种子的捕食和搬运。结果表明,蒙古栎种子捕食率在年际间无显著差异,但2010年的蒙古栎种子搬运率显著高于2011年,存留率显著低于2011年。啮齿动物在胡桃楸林、樟子松林、水曲柳林和白桦林内对蒙古栎种子的总捕食率和总搬运率分别达到(5.7±13.5)%和(27.1±37.1)%。蒙古栎种子在樟子松林内的捕食率和搬运率均最高,胡桃楸林内蒙古栎种子存留率最高;2010年蒙古栎种子在与蒙古栎林边缘距离0,10,20,30,40,50m组间的捕食率无显著差异,搬运率和存留率有显著差异,但2011年蒙古栎种子在不同距离组间的捕食率呈显著差异,搬运率和存留率无显著差异。与蒙古栎林边缘距离20m处蒙古栎种子的捕食率最高。2010年和2011年,分别有(37.8±49.7)%和(27.7±49.8)%的蒙古栎种子被啮齿动物利用,这表明啮齿动物是林业示范基地内蒙古栎地表种子的主要捕食者。冬季食物匮乏秋季贮藏种子是造成啮齿动物对蒙古栎种子有较大捕食、扩散压力的主要原因。因此,啮齿动物对蒙古栎种子的捕食和搬运影响了蒙古栎林的种群更新。     

太阳坪米心水青冈林林窗更新动力学的初步研究

研究了太阳坪米心水青冈林中林窗的特征和更新行为。在５０００ｍ＾２的研究样地中,观察到林窗１０个,林窗面积占研究面积的４０．１％,平均大小２０１ｍ＾２。探讨了林窗的形成原因,米心水青冈的更新成分与林窗的大小呈正相关性。米心水青冈的更新是在由一个或几个林冠层树种死亡后形成的林窗中进行的。     

钱江源国家公园古田山常绿阔叶林木本植物的萌生更新特征

萌生更新是木本植物在原位进行更新的有效手段,使群落具有较强的恢复力。但以往研究侧重于实生更新,森林中木本植物的萌生更新特征及其在森林群落中的地位仍未得到足够理解。基于钱江源国家公园古田山国家级自然保护区内5 hm2亚热带常绿阔叶林样地的群落数据,分析木本植物萌生更新的数量特征,同时对不同分类单元、不同功能类群的萌生能力等进行比较。结果表明:(1)样地内64%的物种、20%的实生个体已经发生萌生更新现象,且萌生茎的数量占样地总个体数量的24%;(2)物种水平与科水平上,萌生能力均表现为显著差异(F=13.11,P0.001;F=27.45,P0.001)。腺蜡瓣花、柳叶蜡梅、宜昌荚蒾、窄基红褐柃、美丽马醉木等物种的萌生能力较强,蜡梅科、忍冬科、木兰科、壳斗科等类群的萌生能力较强;(3)不同垂直结构层次(林冠层、亚乔木层、灌木层)的萌生能力差异显著(F=117.5,P0.001),灌木层物种的萌生能力是林冠层与亚乔木层的1倍左右。不同生活型(常绿组分与落叶组分)的萌生能力差异显著,常绿类群的萌生能力显著高于落叶类群(P0.001)。萌生更新在亚热带常绿阔叶林中具有重要地位,可能是物种多样性维持、群落更新与演替的机制之一。灌木物种与常绿物种有着较强的萌生能力,暗示着萌生可能是植物适应荫蔽环境的生态策略之一。     

天目山米心水青冈群落物种组成特点与萌条更新

由于特定的温湿需求,中国的水青冈多分布于亚热带山地,而分布于欧洲和北美的水青冈则为温带的优势种。本文对浙江天目山自然保护区内米心水青冈群落物种组成特点和更新进行了研究。结果表明：在3个30 m×30 m样方中共发现132种高等植物,分属于51科86属;种-面积关系符合Arrhenius模型,lg S=0.384 lg A+0.6443;log-series模型能很好地模拟米心水青冈群落中乔木层种-多度关系(R²=0.9596);乔木层优势种为壳斗科的米心水青冈、短柄枹、锥栗等;灌木层优势种有伞形绣球、宜昌荚蒾等;草本层优势种为箬竹、苔草等;群落物种多样性较高,而灌木层和草本层物种多样性与乔木层多样性呈负相关;群落结构表明,天目山米心水青冈群落是稳定的顶极群落,萌条更新在米心水青冈群落中十分常见,55%的乔木层物种具有萌条现象;尤其是米心水青冈,萌条数与母株的胸径呈显著的正相关。     

木本植物萌生更新研究进展

萌生是植物营养繁殖的方式之一.本文综述了萌生与实生这2种更新方式的差异、植物萌生能力的测定、影响植物萌生能力的因素以及萌生指数在生态系统评估中的意义.与实生相比,萌生具有抗干扰能力强、幼年期生长迅速等优点,因而它在植被演替的前期阶段发挥着明显的促进作用;而当干扰强度较低、种间竞争关系稳定时,物种更倾向于采取实生更新的策略.植物的萌生具有较大的不确定性.影响植物萌生的内在因素主要包括残桩高度、萌枝长出的位置、根的生物量与长度等;环境因素主要包括干扰方式和程度、光照、养分资源的可利用性等.从理论上讲,在一个稳定的、健康的森林生态系统中,其萌生指数应该有一个最佳值范围.     

神农架地区米心水青冈萌枝过程的研究

米心水青冈是水青冈属３种多主干的树种之一,萌枝是它的主要更新方式。本文通过样方法和树木年代学方法对神农架地区米心水青冈的萌枝更新过程进行了研究。结果表明,米心水青冈的萌枝现象是普遍存在的,但萌枝数量不同地点差异较大。９丛米心水青冈完整的年轮分析结果表明,它们萌枝的时间不是连续的,而与森林的受干扰有关。根据８３个圆盘和生长锥芯资料,米心水青冈在萌枝后成长为乔木层或林冠层的过程中,径向生长表现为５种模式,这是根株内竞争的结果。萌枝在米心水青冈林的维持和发展过程中,具有重要的生态学作用。     

木论喀斯特常绿落叶阔叶林木本植物萌生特征

萌生更新是植物进行自我更新的重要方式之一。为了阐明喀斯特常绿落叶阔叶林植物的萌生特征,基于木论25 hm²动态监测样地的调查数据,分析了木本植物萌生更新数量特征、不同生活型植物萌生能力的差异、萌生能力与地形因子和萌生能力与物种多样性的关系。研究结果表明：样地具有萌生现象的木本植物共有197种,隶属59个科137个属,分别占样地植物科属种的86.8%、93.7%、91.3%。萌生现象在样地内各物种中普遍存在,滇丁香、长管越南茜、火棘、香叶树等物种的萌生能力较强。不同生活型的植物的萌生能力存在显著差异,常绿树种的萌生能力显著高于落叶树种（P<0.001）。萌生物种丰富度比例及萌生物种个体比例都与群落物种多样性呈显著正相关。萌生能力与土层厚度呈显著负相关,与凹凸度呈显著正相关,此外萌生物种丰富度比例还与海拔呈正相关关系,而萌生物种个体比例与岩石出露率和土壤坡度呈正相关关系。由此可见,作为喀斯特森林群落更新中一种占优势的更新方式,萌生更新在一定程度上能够增加群落物种多样性,萌生能力与地形因子存在一定关联。     

神农架地区米心水青冈-曼青冈群落的结构与格局研究

 米心水青冈(Fagus engleriana)-曼青冈(Cyclobalanopsis oxyodon)常绿落叶阔叶混交群落是神农架山地植被垂直带谱的重要类型。通过分析乔木层结构及优势种的分布格局,探讨群落的特点及动态。结果表明,群落乔木层可分为3个亚层：第一亚层落叶阔叶树种占优势,势树种为米心水青冈;第二及第三亚层以常绿树种为主,优势种为曼青冈。应用偏离指数、Lloyd的平均拥挤度和聚块性指数及Morisita指数,在8个尺度下对米心水青冈及曼青冈两种优势树种进行格局分析,发现两者总体上均为聚集分布,米心水青冈的聚集强度高于曼青冈。按1～4cm, 4～8cm及8cm以上３个径级对曼青冈分布格局进行比较,各径级间聚集强度相似,没有自疏现象。由于米心水青冈及曼青冈占据乔木层不同的高度,且均不缺乏更新贮备,因此形成稳定共存的群落。     

基于种群分布地形格局的两种水青冈生态位比较研究

提出了根据不同植物种在地形梯度上的分布格局测度和比较其生态位的思路.将地形分解为海拔、坡向、坡位和坡度4个属性指标,作为多维生态位空间的环境梯度轴.根据对三峡大老岭地区米心水青冈(Fagusengleriana)和亮叶水青冈(F.lucida)群落样方及其地形因子调查,分析了两个种的多维生态位宽度及种间的生态位重叠.结果1)大老岭米心水青冈种群的生态位宽度总体上大于亮叶水青冈.亮叶水青冈在坡向梯度上的生态位较宽;米心水青冈在海拔、坡位和坡度梯度上的生态位较宽;2)两个种在海拔、坡向、坡位和坡度梯度上的生态位重叠度分别为0.259、0.831、0.670、0.676,其总体重叠度为0.087;3)亮叶水青冈和米心水青冈分布的海拔范围分别为1300～2000m和1450～2600m.米心水青冈主要分布于NW80°～NE80°之间的阴坡和半阴坡;亮叶水青冈集中于NW20°～SW10°和NE20°～SE10°的半阴半阳坡.亮叶水青冈不见于沟谷底部,其重要值随坡位上升而增大;而米心水青冈在湿润稳定的中、下坡位重要值最高.米心水青冈适应的坡度范围很宽,主要在20°～40°;而亮叶水青冈集中在35°～45°的坡度范围.上述结果表明在景观尺度上,采用地形因子表征植物多维生态位空间的梯度特征是一个有效而可行的途径,能够很好地反映两种植物生态位的差异.最后讨论了不同尺度上生态位测度的相互验证问题.     

The evolutionary ecology of nut dispersal

A variety of nut-producing plants have mutualistic seed-dispersal interactions with animals (rodents and corvids) that scatter hoard their nuts in the soil. The goals of this review are to summarize the widespread horticultural, botanical, and ecological literature pertaining to nut dispersal inJuglans, Carya, Quercus, Fagus, Castanae, Castanopsis, Lithocarpus, Corylus, Aesculus, andPrunus; to examine the evolutionary histories of these mutualistic interactions; and to identify the traits of nut-bearing plants and nut-dispersing rodents and jays that influence the success of the mutualism. These interactions appear to have originated as early as the Paleocene, about 60 million years ago. Most nuts appear to have evolved from ancestors with wind-dispersed seeds, but the ancestral form of dispersal in almonds (Prunus spp.) was by frugivorous animals that ingested fruit. Nut-producing species have evolved a number of traits that facilitate nut dispersal by certain rodents and corvids while serving to exclude other animals that act as parasites of the mutualism. Nuts are nutritious food sources, often with high levels of lipids or proteins and a caloric value ranging from 5.7 to 153.5 kJ per propagule, 10–1000 times greater than most wind-dispersed seeds. These traits make nuts highly attractive food items for dispersers and nut predators. The course of nut development tends to reduce losses of nuts to insects, microbes, and nondispersing animals, but despite these measures predispersal and postdispersal nut mortality is generally high. Chemical defenses (e.g., tannins) in the cotyledons or the husk surrounding the nut discourage some nut predators. Masting of nuts (periodic, synchronous production of large nut crops) appears to reduce losses to insects and to increase the number of nuts dispersed by animals, and it may increase cross-pollination. Scatter hoarding by rodents and corvids removes nuts from other sources of nut predation, moves nuts away from source trees where density-dependent mortality is high (sometimes to habitats or microhabitats that favor seedling establishment), and buries nuts in the soil (which reduces rates of predation and helps to maintain nut viability). The large nutrient reserves of nuts not only attract animal dispersers but also permit seedlings to establish a large photosynthetic surface or extensive root system, making them especially competitive in low-light environments (e.g., deciduous forest) and semi-arid environments (e.g., dry mountains, Mediterranean climates). The most important postestablishment causes of seedling failure are drought, insufficient light, browsing by vertebrate herbivores, and competition with forbs and grasses. Because of the nutritional qualities of nuts and the synchronous production of large nut crops by a species throughout a region, nut trees can have pervasive impacts on other members of ecological communities. Nut-bearing trees have undergone dramatic changes in distribution during the last 16,000 years, following the glacial retreat from northern North America and Europe, and the current dispersers of nuts (i.e., squirrels, jays, and their relatives) appear to have been responsible for these movements.     

米心水青冈种群萌条更新与高度生长

萌条是许多木本植物更新的重要方式,尤其是在干扰生境中.有种观点认为萌条需要消耗大量资源,导致其他方面投入减少,据此提出萌条数-高度的权衡假说.对该假说的检验多比较萌条和非萌条同属植物的高度,然而由于生活史以及其他生物学习性的差异,可能使这一比较的基础不成立.在米心水青冈中比较萌条现象不同的个体间高度来检验该假说,结果表明米心水青冈萌条和非萌条个体间的高度不存在显著差异(p=0.873),多茎干和少茎干成体间的高度也没有显著差异(p=0.559),并且个体的高度与茎干数存在显著的正相关,表明在米心水青冈中不存在茎干数-高度的权衡关系,其原因是由于萌条的叶片也具有光合能力,向萌条的资源运输随着萌条的长大而逐渐减少,直至中止.在调查的米心水青冈种群中,多干指数达到96.4%,几乎所有的幼苗、幼树和小树都是通过萌条形成的,表明萌条在种群的更新中起着关键作用.     

Geographical variation in the early regeneration process of Siebold's Beech (Fagus crenata BLUME) in Japan

The causes and timing of seed death in early regeneration process of Siebold's beech (Fagus crenata Blume) was studied at 15 sites along a snowfall gradient in Japan, in order to clarify why the seedling density of the species has geographic difference remarkably. Seed production did not significantly differ along the snowfall gradient. Pre-dispersal seed mortality by insect damage was higher at sites with light snowfall than at sites with heavy snowfall, but this only seemed to be a minor factor influencing the population. A large proportion of the viable nuts that fall in autumn ware killed in winter before germination. Winter mortality was much higher at sites with thin snow cover than that at sites with thick snow cover, and this factor was strongly correlated with the geographic variation of seedling regeneration probability. There was little seed mortality by winter desiccation. The main factor contributing to the geographic difference seemed to be a seed predation by rodents in winter. Deep snow cover may reduce the success of rodents finding seeds in winter. Thus the observed relationship between snowpack depth and early mortality may be due to an indirect effect through the process of seed predation.p>     

History of Disturbance and Regeneration Strategies of Fagus engleriana and Quercus aliena var. acuteserrata Forests in Shennongjia,Hubei Province

Based on plot investigation, stem analysis and radial growth pattern, the authors studied the history of suppression, release and regeneration strategies of Fagus engleriana Seem. and Quercus aliena var. acuteserrata Maxim. forests, which were widely distributed in Shennongjia of Hubei Province. It was found that (85.9 ± 6.9) % of the Fagus engleriana samples showed periods of suppression during their canopy recruitment. The average number of suppression periods was 2.1 ± 0.8, the average total length of suppression time was (47 ± 24.1) a, the length of longest suppression time was 73 a, the average number of periods of release was 1.6±0.7, and the average total length of release time was 23 a. (60.83±17.3)% of the Quercus aliena var. acuteserrata samples showed periods of suppression but without release. Combined with height and radial growth characteristics, these suggest that Fagus engleriana was shade-tolerant species, and its regeneration strategies was release from seedling sprouts in canopy gaps, while Quercus aliena var. acuteserrata was shade-intolerant species, and its regeneration strategies was seedling establishment and growth in large canopy gaps by producing large amount of seeds.     

Predation and dispersal of large and small seeds of a tropical palm

Seed size may vary greatly among individuals within plant species. What effects the extremes of this variation have for seeds taken by small mammals are poorly understood. Not all seeds removed by small mammals are necessarily eaten. Small rodents are common seed predators, but they may disperse a significant proportion of seeds by scatter hoarding them via burial. Size-dependent predation and dispersal of seeds has not been directly tested within a plant species for tropical rodents. This study tested whether or not large and small nuts of Astrocaryum mexicanum (Palmae) differed in their fates due to handling by the spiny pocket mouse Heteromys desmarestianus (Heteromyidae). Exclosures were used to give small rodents exclusive access to A. mexicanum nuts. H. desmarestianus preferentially consumed large over small A. mexicanum nuts, but cached (in burrows and by scatter hoarding) similar proportions of these nuts by size. Small nuts tended to be buried farther away from exclosures than large nuts. Although sample sizes of buried nuts were small, the rodents retrieved all buried large nuts, but 30% of the small nuts remained buried long enough to germinate. I also examined predispersal predation by insects and found that insects appear to have no size preference for A. mexicanum nuts, but insect predation appears to hinder nut development. Thus, nuts attacked by insects develop to be significantly smaller, with a low proportion of undamaged endosperm, than uninfested nuts. It is hypothesized that the preferential predation of large A. mexicanum nuts by H. desmarestianus is a response by these rodents to insect predation.     

Nut predation and dispersal of Harland Tanoak Lithocarpus harlandii by scatter-hoarding rodents

Plants that use the propagule to co-opt animals as dispersal agents must balance the costs of seed predation with the benefits of dispersal. Successful post-dispersal germination is a key metric that reflects these costs and benefits. By tracking individual nuts with coded tin-tags over 3 years (2000–2003), this study quantified nut predation and dispersal of harland tanoak (Lithocarpus harlandii) by seed-caching rodents in a subtropical evergreen broadleaved forest in the Duiangyan Region of Sichuan Province, Southwest China. We found that tanoak seedlings established from rodent-generated caches in the primary stands over a 12-month post-dispersal period. Our results indicate that seed-caching rodents are effective dispersers of tanoak nuts, but dispersal effectiveness varies among years and stands, probably due to mast seeding of harland tanoak or community-level seed availability according to the predator satiation hypothesis. Some nut traits in tanoak species, e.g. large seed size, hard nut husk, lower tannin and mast seeding, are important characteristics for seed dispersal by scatter-hoarding rodents, compared with oak species with higher tannin content.     

Experimental field test of spatial variation in rodent predation of nuts relative to distance and seed density

The spatial context in which seed predation occurs may modify the spatial structure of recruitment generated by seed dispersal. The Janzen–Connell (J-C) model predicts that granivores will exert greater pressure on the parent plant or at those sites where the density of dispersed seeds is higher. We have investigated how the probability of post-dispersal survival of Juglans australis varies with nut density across a hierarchy of spatial scales. We experimentally evaluated the survival of 3,120 nuts at three spatial scales: meso-scale (≤1.5 ha), as forest sites with two densities of fruiting J. australis individuals; intermediate scale (<0.2 ha), as individual trees with two experimental crop sizes; small scale (<0.1 m²), as microsites with two factors (number of nuts and distance from source). Nut removal coincided with seed predation, a condition that allowed us to test the density-dependent seed predation hypothesis. We found that the probability of nut survival was greater at forest sites with higher J. australis density. Nut survival was not affected by nut density in the seed shadow of individual specimens: at sites where J. australis density was greater, the proportion of surviving nuts did not differ between microsites located at different distances from the parent plant, but it was greater at microsites with greater initial nut density. Nut survival depended on the scale at which rodents responded to nut density, being negatively density dependent at the meso-scale and spatially random at intermediate and small scales. At the meso-scale, excess nut supply increased the probability of nut survival, which is in agreement with a model of granivore satiation near the seed source. Rodent satiation at the meso-scale may favour maintenance of sites with high J. australis density, where individual trees may have greater probabilities of passing their genes onto the next stage of the dispersal cycle.     

Ecological benefits of myrmecochory for the endangered chaparral shrub Fremontodendron decumbens (Sterculiaceae)

Fremontodendron decumbens grows in a single county in central California, USA. Prior research showed that its elaiosome-bearing seeds are dispersed by the harvester ant Messor andrei. I tested several hypotheses regarding the positive role of ant-mediated dispersal to F. decumbens: (1) Does ant-mediated seed dispersal facilitate seed escape from rodent predation?; (2) Does ant processing of seeds stimulate germination?; (3) Are ant middens more suitable microsites for seed or seedling survival in unburned chaparral areas?; and (4) Do survival benefits of dispersal occur post-fire in the form of differences in seedling survival probabilities and, if so, why? Results of tests of each hypothesis were: (1) similar percentages of seeds placed on ant middens and under F. decumbens shrub canopies were destroyed by rodents, but seeds from which elaiosomes had been removed were more likely to escape rodent predation; (2) seeds processed by ants did not germinate more readily than seeds removed directly from shrub branches; (3) seedling predation was a major cause of mortality in unburned chaparral on both ant middens and under shrubs, and overall seedling survival did not differ between the two microsites; (4) post-burn seedling survival was significantly greater for seedlings dispersed away from F. decumbens shrub canopies, because dispersed seedlings were both less likely to be killed by predators and more likely to be growing in a gap created by the fire-caused death of an established shrub. I concluded that the major ecological benefit to F. decumbens of ant-mediated seed dispersal was elevated post-fire seedling survival resulting from enhanced escape by dispersed seedlings from both predation and competition.