Lack of tree layer control on herb layer characteristics in a subtropical forest,China

Question: Knowledge of the interaction between understorey herb and overstorey tree layer diversity is mostly restricted to temperate forests. How do tree layer diversity and environmental variables affect herb layer attributes in subtropical forests and do these relationships change in the course of succession? Do abundance and diversity of woody saplings within the herb layer shift during succession? Location: Subtropical broad‐leaved forests in southeast China (29°8′18″‐29°17′29″N, 118°2′14″118°11′12″E). Methods: A full inventory of the herb layer including all plants below 1‐m height was done in 27 plots (10 × 10 m) from five successional stages (<20, <40, <60, <80 and ≥80 yr). We quantified the contribution of different life forms (herbaceous, woody and climber species) to herb layer diversity and productivity and analysed effects of environmental variables and tree layer diversity on these attributes. Results: Herb layer composition followed a successional gradient, as revealed by non‐metric multidimensional scaling (NMDS), but diversity was not correlated to the successional gradient. There was no correlation of diversity across layers. Herb layer productivity was neither affected by tree layer diversity nor by herb layer diversity. Although abundance of woody species in the herb layer decreased significantly during succession, woody species contributed extraordinarily to herb layer species diversity in all successional stages. All environmental factors considered had little impact on herb layer attributes. Conclusions: The subtropical forest investigated displays an immense richness of woody species in the herb layer while herbaceous species are less prominent. Species composition of the herb layer shows a clear successional pattern, however, the presence or absence of certain species appears to be random.     

The Contribution of Tropical Secondary Forest Fragments to the Conservation of Fruit-feeding Butterflies: Effects of Isolation and Age

Concomitant with the rapid loss of tropical mature forests, the relative abundance of secondary forests is increasing steadily and the latter are therefore of growing interest for conservation. We analysed species richness of fruit-feeding nymphalid butterflies in secondary forest fragments of different age and isolation and in mature forest at the eastern margin of the Lore Lindu National Park in Central Sulawesi, Indonesia. From April to August 2001 we collected 2322 individuals of fruit-feeding butterflies, belonging to 33 species. Butterfly species richness increased with succession, but was significantly higher in mature forests than in all types of secondary forest. Isolation of the forest fragments did not have a significant effect on butterfly species richness in the range of distances (up to 1700 m) studied. Rather it appeared to affect only a few species. Species richness of endemic species was higher than of non-endemic species. Although endemic species were most diverse in mature forests, many species captured were restricted to secondary forests. Our results show that mature forest is essential for the conservation of nymphalid butterflies and for the endemic species in this area. However, considering the relatively large number of species found in these rather small habitat islands, secondary forest fragments, especially older successional stages, can be taken into account in conservation efforts and thus contribute to the preservation of tropical biodiversity on a landscape scale.     

Persistent and pervasive compositional shifts of western boreal forest plots in Canada

Species compositional shifts have important consequences to biodiversity and ecosystem function and services to humanity. In boreal forests, compositional shifts from late‐successional conifers to early‐successional conifers and deciduous broadleaves have been postulated based on increased fire frequency associated with climate change truncating stand age‐dependent succession. However, little is known about how climate change has affected forest composition in the background between successive catastrophic fires in boreal forests. Using 1797 permanent sample plots from western boreal forests of Canada measured from 1958 to 2013, we show that after accounting for stand age‐dependent succession, the relative abundances of early‐successional deciduous broadleaves and early‐successional conifers have increased at the expense of late‐successional conifers with climate change. These background compositional shifts are persistent temporally, consistent across all forest stand ages and pervasive spatially across the region. Rising atmospheric CO₂ promoted early‐successional conifers and deciduous broadleaves, and warming increased early‐successional conifers at the expense of late‐successional conifers, but compositional shifts were not associated with climate moisture index. Our results emphasize the importance of climate change on background compositional shifts in the boreal forest and suggest further compositional shifts as rising CO₂ and warming will continue in the 21st century.     

长白山针阔混交林不同演替阶段的昆虫多样性

昆虫多样性变化对生态系统健康有重要的指示作用, 为研究昆虫群落变化与生境演替之间的关系, 本研究采用网捕、灯诱和诱捕法系统调查了长白山针阔混交林不同演替阶段（次生白桦林、次生针阔混交林、原始阔叶红松林）昆虫群落的组成和多样性, 分析了昆虫在森林演替过程中的规律及与植被群落之间的关系。系统调查共采集昆虫标本8 183头, 隶属于14个目699种, 其中鳞翅目和鞘翅目是主要优势类群。次生针阔混交林昆虫的个体数量最多, 原始阔叶红松林中物种数最多。不同演替阶段昆虫群落的物种数和个体数差异不显著, 但次生针阔混交林、原始阔叶红松林的Fisher’s α指数显著高于次生白桦林。目水平上的昆虫多样性未表现出显著性差异. 昆虫多样性在森林演替过程中和草本植物多样性的变化趋势相同;由于食性和生境选择的不同, 森林演替过程中鳞翅目昆虫多样性逐渐升高, 而鞘翅目多样性逐渐降低。     

Sapling communities in Amazonian white-water forests

Aim Structure and floristic composition of forest regeneration (trees between 1 and 10 cm diameter at breast height (d.b.h), ≥ 1 m growth height) was described in three forest types of Amazonian white‐water forests (várzea), in order to analyse whether floristic composition of saplings is related to the successional stage of the forests, whether it differs in comparision with the mature flora, and if there exists a zonation of sapling species along the gradients of flooding and irradiation. Location Mamirauá Sustainable Development Reserve, Western Brazilian Amazon. Methods The investigated forests were of the low and the high várzea type, on an annual average flooded around 4 and 1 months, respectively. The two low‐várzea forests belonged to the secondary and to the late‐successional stage, the high‐várzea forest also to the late‐successional stage. A total of 24 circular sample plots covering 1885 m² were installed. They were nested within three rectangular 1 ha permanent sample plots where individuals ≥ 10 cm d.b.h. were formerly inventoried. Average inundation and radiation [relative photosynthetically active radiation (rPAR)] at the forest floor was recorded in all inventoried plots. The Mean spatial Distribution Center (MDC; Ebdon, 1998 ) for all sapling species was calculated. Sapling species were grouped into associations with respect to their light‐demand and their location along the flood‐level gradient. Results Average flood height and average rPAR at the forest floor was highest in the secondary stage of the low várzea and lowest in the high‐várzea forest. Overall average density and basal area of the saplings averaged 2250 individuals and 2.3 m² ha^?1 in the secondary stage, 2330 individuals and 2.6 m² ha^?1 in the late‐successional stage of the low várzea and 5000 individuals and 4.8 m² ha^?1 in the high várzea. In all forest types, species richness of saplings was lower than species richness of trees ≥ 10 cm d.b.h., and amounted to 25 species in the secondary stage, to 35 species in the late‐successional stage of the low várzea and to 88 species in the high‐várzea forest. The amount of ‘immigrants’ ( Bazzaz, 1991 ) at the sapling level increased with proceeding forest succession and amounted to 24 and 29% in the low várzea and to 31% in the high várzea. Sapling species distribution, species richness and individual density was linked to both, the gradient of flooding and the gradient of irradiation. Species richness and individual density was highest in the high várzea and decreased with increasing influence of flooding. The high várzea was predominated by pronounced shade‐tolerant sapling species, whereas in the low várzea occured both, light demanding and shade‐tolerant species groups. Main conclusions Influence of flooding seems to be the main factor triggering species composition and structure of sapling communities in várzea forests. Proceeding forest succession reduces the impact of flooding because of the biogenical induced silting up of the forested sites. However, forest succession also alters forest architecture of the overstory and such the light conditions at the sapling level. Therefore, radiation is an important factor influencing species composition of sapling communities in várzea forests.     

Influence of Post‐Clearing Treatment on the Recovery of Herbaceous Plant Communities in Amazonian Secondary Forests

Secondary forests are an increasingly common feature in tropical landscapes worldwide and understanding their regeneration is necessary to design effective restoration strategies. It has previously been shown that the woody species community in secondary forests can follow different successional pathways according to the nature of past human activities in the area, yet little is known about patterns of herbaceous species diversity in secondary forests with different histories of land use. We compared the diversity and abundance of herbaceous plant communities in two types of Central Amazonian secondary forests—those regenerating on pastures created by felling and burning trees and those where trees were felled only. We also tested if plant density and species richness in secondary forests are related to proximity to primary forest. In comparison with primary forest sites, forests regenerating on non‐burned habitats had lower herbaceous plant density and species richness than those on burned ones. However, species composition and abundance in non‐burned stands were more similar to those of primary forest, whereas several secondary forest specialist species were found in burned stands. In both non‐burned and burned forests, distance from the forest edge was not related to herbaceous density and species richness. Overall, our results suggest that the natural regeneration of herbaceous species in secondary tropical forests is dependent on a site's post‐clearing treatment. We recommend evaluating the land history of a site prior to developing and implementing a restoration strategy, as this will influence the biological template on which restoration efforts are overlaid.     

The species richness–productivity relationship in the herb layer of European deciduous forests

Aim In contrast to non‐forest vegetation, the species richness–productivity (SR‐P) relationship in forests still remains insufficiently explored. Several studies have focused on the diversity of the tree layer, but the species richness of temperate deciduous forests is mainly determined by their species‐rich herb layer. The factors controlling herb‐layer productivity may differ from those affecting tree layers or open herbaceous vegetation, and thus the SR‐P relationship and its underlying processes may differ. However, the few relevant studies have reported controversial results. Here we explore the SR‐P relationship in the forest herb layer across different areas from oceanic to continental Europe, and put the effect of habitat productivity on species richness into context with other key factors, namely soil pH and light availability. Location North‐western Germany, Czech Republic, Slovakia and southern Urals (Russia). Methods We measured herb‐layer species richness and biomass, soil pH and tree‐layer cover in 156 vegetation plots of 100 m² in deciduous forests. We analysed the SR‐P relationship and the relative importance of environmental variables using regression models for particular areas and separate forest types. Results We found a consistent monotonic increase in the herb‐layer species richness with productivity across all study areas and all forest types. Soil pH and light availability also affected species richness, but their relative importance differed among areas. Main conclusions We suggest that the monotonically increasing SR‐P relationship in the forest herb layer results from the fact that herb‐layer productivity is limited by canopy shading; competition within the herb layer is therefore not strong enough to exclude many species. This differs fundamentally from open herbaceous vegetation, which is not subject to such productivity limits and consequently exhibits a unimodal SR‐P relationship. We present a conceptual model that might explain the differences in the SR‐P relationship between the forest herb layer and open herbaceous vegetation.     

Anthropogenic disturbances and plant biodiversity in forests of Uttaranchal,central Himalaya

Eight forest types varying in disturbance frequencies were identified along an elevational gradient in Uttaranchal, central Himalaya. Low elevation forests were close to human habitation and had high disturbance frequency, while high elevation forests were situated far from the human habitation and had low disturbance. The dominant tree species at low elevation were Pinus roxburghii and Quercus leucotrichophora, while Q. floribunda and Q. semecarpifolia dominated the high elevation forests. Pyracantha crenulata was the shrub present in all the forests except in Q. semecarpifolia forest and Anaphalis contorta, a herb species, was present in all the forests. Disturbance decreased the dominance of single species and increased the plant biodiversity by mixing species of different successional status. Species richness and diversity for all the vegetation layers were higher in low elevation–high disturbance forests. Mean tree density decreased from high to moderate and increased in low disturbance. The shrub density decreased from high to low disturbance while the reverse occured for herbs. High proportion of early successional species in disturbed forests indicated that disturbance induces succession. The mean number of young individuals increasing from high to low disturbance indicates that disturbance adversely affects regeneration. But, however, the high number of young individuals of Coriaria nepalensis, a small non-leguminous nitrogen fixing tree, in disturbed forests shows that the forest is regenerating. This species could be helpful in the re-establishment of original vegetation through triggering the regeneration of these forests. High elevation–low disturbed forests separated from low elevation–high disturbed forests. Forest type and elevation may have more influence on tree richness while shrub and herb richness may be more sensitive to disturbance and forest types.     

岷江冷杉林皆伐后次生群落结构和物种多样性的演替动态

为阐明岷江冷杉林皆伐后次生群落的演替过程,采用空间代替时间的方法,在川西米亚罗林区海拔3100—3600 m的阴坡选择岷江冷杉林皆伐后次生演替10、20、30、40和50a阶段的次生群落作为研究对象,对其群落结构和物种多样性的动态进行了研究。不同演替阶段的树木均呈显著聚集分布。按群落中优势种的重要值将该演替序列划分为3个类型:悬钩子-蔷薇灌丛、白桦阔叶林和桦木-岷江冷杉针阔混交林。随次生演替,乔木和灌木种的物种丰富度趋于增加,而草本种的物种丰富度趋于减少;乔木和灌木种的Shannon-Wiener多样性指数趋于增大,而草本的Shannon-Wiener多样性指数趋于减小;乔木、灌木和草本层的Pielou均匀度指数均趋于增大;乔木层的Simpson优势度指数趋于减小,灌木和草本层的Simpson优势度指数在演替0—40年阶段趋于增大,而在演替50a阶段趋于减小。在该演替序列中,乔木、灌木和草本层的物种组成均呈耐荫种替代非耐荫种的趋势。     

Tree species composition and diversity gradients in white-water forests across the Amazon Basin

Aim Attention has increasingly been focused on the floristic variation within forests of the Amazon Basin. Variations in species composition and diversity are poorly understood, especially in Amazonian floodplain forests. We investigated tree species composition, richness and α diversity in the Amazonian white‐water (várzea) forest, looking particularly at: (1) the flood‐level gradient, (2) the successional stage (stand age), and (3) the geographical location of the forests. Location Eastern Amazonia, central Amazonia, equatorial western Amazonia and the southern part of western Amazonia. Methods The data originate from 16 permanent várzea forest plots in the central and western Brazilian Amazon and in the northern Bolivian Amazon. In addition, revised species lists of 28 várzea forest inventories from across the Amazon Basin were used. Most important families and species were determined using importance values. Floristic similarity between plots was calculated to detect similarity variations between forest types and over geographical distances. To check for spatial diversity gradients, α diversity (Fisher) of the plots was correlated with stand age, longitudinal and latitudinal plot location, and flood‐level gradient. Results More than 900 flood‐tolerant tree species were recorded, which indicates that Amazonian várzea forests are the most species‐rich floodplain forests worldwide. The most important plant families recorded also dominate most Neotropical upland forests, and c. 31% of the tree species listed also occur in the uplands. Species distribution and diversity varied: (1) on the flood‐level gradient, with a distinct separation between low‐várzea forests and high‐várzea forests, (2) in relation to natural forest succession, with species‐poor forests in early stages of succession and species‐rich forests in later stages, and (3) as a function of geographical distance between sites, indicating an increasing α diversity from eastern to western Amazonia, and simultaneously from the southern part of western Amazonia to equatorial western Amazonia. Main conclusions The east‐to‐west gradient of increasing species diversity in várzea forests reflects the diversity patterns also described for Amazonian terra firme. Despite the fine‐scale geomorphological heterogeneity of the floodplains, and despite high disturbance of the different forest types by sedimentation and erosion, várzea forests are dominated by a high proportion of generalistic, widely distributed tree species. In contrast to high‐várzea forests, where floristic dissimilarity increases significantly with increasing distance between the sites, low‐várzea forests can exhibit high floristic similarity over large geographical distances. The high várzea may be an important transitional zone for lateral immigration of terra firme species to the floodplains, thus contributing to comparatively high species richness. However, long‐distance dispersal of many low‐várzea trees contributes to comparatively low species richness in highly flooded low várzea.     

Plant diversity patterns in subtropical evergreen broad-leaved forests of Yunnan and Taiwan

The subtropical evergreen broad-leaved forests of Yunnan and Taiwan were compared along environmental and successional gradients with the aim of identifying important taxon and species diversity as well as the drivers of mountain biodiversity patterns. A detrended correspondence analysis of an exhaustive set of data collected from 105 and 223 plots for Yunnan and Taiwan, respectively, was applied to classify natural mature forest types. Additional data from 72 and 68 plots for Yunnan and Taiwan, respectively, were used for analyses of secondary succession. The floristic richness and diversity index were calculated for each type of forest. In Yunnan, the monsoon forests in mesic-humid sites had more taxa and tended to show higher species diversity than the other two forest types. In Taiwan, species diversity values were significantly higher in the Machilus–Castanopsis zone in the middle altitudes (500–1500 m) than for the other three forest zones. For both Yunnan and Taiwan, the forests at the middle successional stage showed significantly higher species diversity than those at the early successional stage. Differences in diversity between the middle and late stages were not significant. These findings highlight the high species diversity of the natural mature evergreen broad-leaved forests of both Yunnan and Taiwan. In the secondary forests, as succession proceeds, species diversity comes to resemble that of the natural mature forests. In both ecosystems, the drivers of species diversity patterns are moisture, altitude, and succession/disturbance.     

海南岛霸王岭热带低地雨林植被恢复动态

热带次生林具有重要的物种保育和固碳功能, 然而高强度的干扰会导致次生林早期出现类似季雨林的阶段, 因而群落恢复速度和方向是当前热带生态学研究中最为关注的议题之一。该文以海南岛在刀耕火种弃耕地形成的不同演替阶段的次生林为研究对象, 比较森林不同恢复时间(12年、25年、55年)群落中的不同年龄(幼树、小树、成年树)个体与低地雨林老龄林的物种组成、多样性和群落结构差异, 探讨刀耕火种弃耕地恢复过程中的群落组配过程。首先, 在海南岛霸王岭林区内建立7个1 hm²(100 m × 100 m)的样地, 并调查样地内所有胸径≥ 1 cm的木本植物个体(不包括木质藤本)的种类、胸径大小和树高。无度量多维标定法(NMS)排序结果表明, 刀耕火种弃耕地恢复群落与老龄林的物种组成存在明显差异, 并且其物种组成差异随着径级增加而逐渐减小。刀耕火种弃耕地群落物种累积速度缓慢, 25年和55年恢复群落的种面积、种个体和种多度曲线无差异, 存在一个明显的停滞阶段。与物种组成相比, 群落结构恢复相对较迅速, 但仍没有形成老龄林阶段中的复杂结构。萌生个体在早期恢复群落中占有较高比例, 其个体密度和胸高断面积分别占总数的39.9%和55.9%, 但在恢复中后期迅速降低。刀耕火种弃耕地恢复群落中以先锋种和非先锋喜光种为主。虽然耐阴种随演替而逐渐增加, 但恢复中后期群落中的耐阴种重要值仅为老龄林的27.7%。这些结果表明, 虽然刀耕火种弃耕地恢复群落缓慢地逐渐接近最终恢复目标, 但仍然存在 很大的不确定性。刀耕火种弃耕地恢复过程中的异速恢复和停滞阶段需要纳入今后群落演替模型构建和森林固碳效益核甘共苦算中。     

甘肃小陇山林区不同生境类型蝶类多样性研究

于2006～2008年对甘肃小陇山林区不同生境类型中蝴蝶多样性进行了调查研究,研究中依据植被的不同将该林区的蝴蝶生境划分为6种类型:人工林、灌木丛和次生林、居民农田、针阔混交林、落叶阔叶林、针叶林。共获得蝴蝶标本5365只,隶属于11科116属210种。计算了6种生境类型中蝶类物种丰富度、相似性系数和多样性指数。不同生境中,灌木丛和次生林蝶类物种的多样性指数、丰富度和个体数量较高,人工林物种多样性指数、丰富度和个体数量较低;人工林与针叶林之间的相似性系数(0.4194)最高,针阔混交林与落叶阔叶林的相似性系数(0.2951)次之,人工林与灌木丛和次生林之间的相似性系数(0.0769)最低,表明各生境之间蝶类相似性系数很低。     

Density of herbaceous plants and distribution of western gorillas in different habitat types in south‐east Cameroon

The study of forest herb availability improves knowledge of ecology and conservation of gorillas that depend on such herbs. Density patterns of herbs and location of western gorilla nest sites were studied in different habitat types at a site in south‐east Cameroon to assess their relationship. Herb stems of the families Marantaceae and Zingiberaceae were identified and counted in 10,713 1‐m² plots distributed within six habitat types. Stem density correlated with light availability and ranged from 2.38 stems m^?² in near primary forest to 4.66 stems m^?² in light gaps. Gorillas showed marked preferences for habitats with high herb densities such as light gaps, swamps and young secondary forest. However, no clear relationship exists between terrestrial herbaceous vegetation and gorilla densities across Central Africa. It is suggested that differences in ecological factors and land use history within and between sites may explain differences in herb density and diversity which partly account for variations in the historical and present population distribution and density of western gorillas. Formerly logged and swamp forests, which are characterized by an abundance of herbs, may prove to be of great value in the conservation of western gorillas given appropriate forest management practices, adequate protection from poaching and limited human encroachment.     

Temporal variation in the influence of forest succession on caterpillar communities: A long‐term study in a tropical dry forest

Forest succession can influence herbivore communities through changes in host availability, plant quality, microclimate, canopy structure complexity and predator abundance. It is not well known, however, if such influence is constant across years. Caterpillars have been reported to be particularly susceptible to changes in plant community composition across forest succession, as most species are specialists and rely on the presence of their hosts. Nevertheless, in the case of tropical dry forests, plant species have less defined successional boundaries than tropical wet forests, and hence herbivore communities should be able to persist across different successional stages. To test this prediction, caterpillar communities were surveyed during eight consecutive years in a tropical dry forest in four replicated successional stages in Chamela, Jalisco and Mexico. Lepidopteran species richness and diversity were equivalent in mature forests and early successional stages, but a distinctive caterpillar community was found for the recently abandoned pastures. Species composition tended to converge among all four successional stages during the span of eight years. Overall, our results highlight the importance of both primary and secondary forest for the conservation of caterpillar biodiversity at a landscape level. We also highlight the relevance of long‐term studies when assessing the influence of forest succession to account for across year variation in species interactions and climatic factors. Abstract in French is available with online material.     

临安次生灌丛植物多样性对林火烈度空间异质性的响应

以同一过火3a后临安市太阳镇天然次生灌丛为对象,采用样地调查法按不同林火烈度设置火干扰样地进行植物群落调查,以检验林分内部的林火烈度异质性是否与局部的植物多样性变化相关。结果表明:研究区共有高等植物83种,分属于38科67属,群落区系组成以亚热带科属为主,表现出常绿阔叶林已退化过渡到位于演替早期阶段的落叶次生灌丛群落的性质;低林火烈度对灌木层的树种组成有影响,但不明显;中烈度林火对灌木层的物种组成影响较大;低、中林火烈度下草本层的物种组成变化都很明显;灌木层的物种数和多样性指数都表现出低烈度火未火烧中烈度火的趋势;草本层的物种数、多样性指数和均匀度指数表现出中烈度火低烈度火未火烧的趋势;草本层的物种组成和多样性受林火烈度的影响较灌木层更大。研究表明次生灌丛群落过火区内部林火烈度异质性在初期会引起植物多样性的响应差异;低烈度火干扰可以增加次生灌丛生物多样性、促进群落更新;中烈度火干扰下木本植物物种多样性丧失较大,而草本植物多样性显著增加,不利于群落的正向演替。     

Plant hydraulics and photosynthesis of 34 woody species from different successional stages of subtropical forests

It is important to understand the ecophysiological characters of plants when exploring mechanisms underlying species substitution in the process of plant succession. In the present study, we selected 34 woody species from different stages of secondary succession in subtropical forests of southern China, and measured their hydraulic conductivity, gas exchange rates, leaf nutrients and drought‐tolerance traits such as xylem resistance to cavitation, turgor loss point and carbon isotope ratio. Principal component analysis revealed that early‐, mid‐ and late‐successional species were significantly separated along axis 1, which was strongly associated with hydraulic‐photosynthetic coordination. In contrast to species distributed in late‐successional forest, early‐successional species had the highest hydraulic conductivity, net photosynthetic rates, photosynthetic nitrogen and phosphorus use efficiencies, but had the lowest photosynthetic water‐use efficiency. However, changes of the measured drought‐tolerance traits of the 34 species along the succession did not demonstrate a clear trend – no significant correlations between these traits and plant successional stages were found. Moreover, the trade‐off between hydraulic efficiency and safety was not identified. Taken together, our results suggested that hydraulic efficiency and photosynthetic function, rather than drought tolerance, play an important role in species distributions along plant succession in subtropical forests.     

海南岛吊罗山热带山地雨林两个演替阶段的种间联结性

种间联结一直是群落演替理论研究的焦点之一, 关于物种间相互作用与群落演替之间的动态关系仍然存在争议。本文中, 作者通过出现-不出现数据的方差比例、基于2×2列联表的种间联结分析和 ²检验, 对海南岛吊罗山热带山地雨林演替前期和演替后期群落的种间联结性进行了研究, 以揭示种间联结与群落演替的相互作用。结果表明: (1)在演替前期, 群落内所有树种间总体呈正联结, 但不显著; 发展至演替后期达到显著正联结。群落内所有物种间正、负联结种对数占总种对数的比例随演替进程呈现下降趋势, 而无联结种对数的比例则大幅上升; 优势种和伴生种间呈现相同的趋势。这表明群落演替正朝着有利于物种稳定共存的方向发展。(2)演替前期建群种和后期侵入种间正联结与无联结种对数的比例(分别为37.8%与41.5%)远大于负联结的比例(20.7%), 但正联结均不显著; 前期定居树种和后期侵入种通过分割资源而共存, 而且也趋于独立存在。(3)后期侵入种间不存在负联结, 所有正联结(占总对数的33.3%)均达显著水平, 显示它们对生境有相似的适应和相互重叠的生态位。     

Cryptogamic epiphytes in primary and recovering upper montane oak forests of Costa Rica – species richness,community composition and ecology

Species richness, community composition and ecology of cryptogamic epiphytes (bryophytes, macrolichens) were studied in upper montane primary, early secondary and late secondary oak forests of the Cordillera de Talamanca, Costa Rica. Canopy trees of Quercus copeyensis were sampled with the aim of getting insight in patterns and processes of epiphyte succession and recovery of diversity in secondary forest following forest clearing. Species richness of cryptogamic epiphytes in secondary and primary forests were nearly the same, showing that primary forests are not necessarily more diverse than secondary forests. High species richness of secondary forests was presumed due to the closed canopy, resulting in permanently high atmospheric humidity in these forests. Similarity in species composition of secondary and primary forests increases with forest age, but after 40 years of succession one third (46 species) of primary forest species had not re-established in the secondary forest. Community composition in primary and secondary forests differed markedly and indicates that a long time is needed for the re-establishment of microhabitats and re-invasion of species and communities adapted to differentiated niches. Genera and species exclusive to primary forests are relevant as indicator taxa and conservation targets. Forty percent (68 species) of all species recorded are restricted to secondary forests, indicating the important contribution of secondary forest diversity to total species richness of the oak forests of Costa Rica.     

Influences of herbaceous vines on community characteristics in pioneer succession stages

In the continental tropics, herbaceous vines and lianas are roughly equal in abundance, and the former are even more abundant in the temperate region. However, only little attention has been paid to the study of biological and ecological characteristics of herbaceous vines. In particular, research about effects of herbaceous vines acting as a biological control on plant communities has not been carried out in depth. Herbaceous vines are widely distributed and abundant also in humid subtropical areas, especially in the early stages of forest community succession, but their ecology is little known. The aim of our study is to understand the effect of local herbaceous vines on community characteristics in pioneer succession stages. The hypothesis was tested that herbaceous vines would have predominantly negative effects on co-occurring species, thereby reducing their diversity. Based on a quadrate method, a detailed survey of shrub and herb communities covered by herbaceous vines was conducted in the Jinyun Mountain Nature Reserve of Chongqing, SW China. The sample plots were selected based on the numbers and coverage of vines, distinguishing among high vine coverage plots, middle vine coverage plots and low vine coverage plots. All species in the plots with different herbaceous vine coverage were identified and measured. The measurements for each species included number, average height and coverage. Because of abundant tree seedlings in the habitat of forest edge plots, we only recorded the number of tree seedlings in those plots to evaluate the overall effects of vines on tree seedling regeneration. After the field investigation, herbaceous vines and other species in the plots were harvested respectively, then oven dried and weighed. The results showed that herbaceous vines had high productivity and produced a lot of branches, which caused above-ground competition and mechanical stress to other species. Herbaceous vines seriously affected species composition and species importance values of self-supporting species. In all three habitats, the number of species and families in low coverage samples was larger than that in high coverage samples, and furthermore the identities of species were different between them. Species richness significantly decreased with increasing herbaceous vine coverage, illustrating that some species disappeared. Herbaceous vines reduced species diversity of communities, and as a result, community complexity was decreased, which might also decrease community stability. Biomass of communities of self-supporting species significantly decreased with increasing herbaceous vine coverage, which suggested that herbaceous vines significantly decreased community productivity. The number of seedlings also significantly decreased with increasing herbaceous vine coverage, and seedlings were mainly distributed in lower coverage samples. Herbaceous vines reduced the light exposure in the understory, which may be the mechanistic explanation for the negative influence of vines on the performance of tree seedlings. It was concluded that herbaceous vines affected seedling quantitative dynamics and distribution, and inhibited the natural succession from shrub and herb communities to tree communities. Thus herbaceous vines not only had significant influences on community characteristics in pioneer succession stages, but also on subsequent succession stages.