A conceptual model of vegetation dynamics on gravel bars of a large Alpine river

The concepts of large river systems have been advanced with limited empirical knowledge of natural systems. In particular, virually all large Alpine European rivers were trained during the 19th century. Without first hand knowledge of natural systems we lack baseline data to assess human impacts and to address restoration and conservation strategies. An exception is the River Tagliamento which rises in the limestone Alps of northern Italy and flows for 172 km to the Adriatic Sea. Following a very high flood, we observed the first stages of succession within the river's active zone. This article presents a conceptual model of vegetation dynamics on gravel bars based upon those observations. Thousands of trees and other large woody debris (LWD) lay scattered across the active zone after the flood. The larger pieces of debris had a marked influence on the deposition of sediments and other debris, and were sites of colonization by pioneer plants. They represent the first stage in the development of vegetated islands that have the potential to increase in size during subsequent floods. Islands are also eroded, particularly by lateral channel erosion, and the materials may be reincorporated into new islands downstream. The island vegetation is dominated by five Salix species and Populus nigra. The dynamics of vegetated islands results from the interaction between the fluvial regime and the dominant woody species, the Salicaceae. These plants act as autogenic ecosystem engineers, because the plant structures themselves alter the environmental conditions through trapping sediment and organic debris. These processes may help to maintain an island-braided channel system that supports a high habitat diversity. Management of the river to regulate flow or to reduce the supply of LWD is likely to result in a loss of the habitat heterogeneity produced by island dynamics.     

植被原生演替研究进展

对植被原生演替的国内外研究进展进行了评述。植被原生演替过程受到生物因素和非生物因素的共同影响。生物因素包括种子的传播方式、对原生环境的适应能力及物种之间的关系等,依靠风力传播、对裸地的极端环境具有较强适应能力的物种更容易成为原生裸地的早期定居者,某些微生物在植物的定居具有非常重要的作用。非生物因素则包括裸地表面的形状(凹、凸、平)、粗糙度、与岩石的距离等,一些特殊的微环境能够为植物的定居创造更为优越的水分、养分条件,促进植物的定居。植被原生演替是生物驱动因素与环境阻力相互作用的结果,二者的消长决定原生演替进行的模式。大量的研究表明,植被原生演替过程并不完全遵循地衣-苔藓-草本植物-木本植物的顺序,不同环境条件下的植被原生演替过程表现出明显的复杂性,这种复杂性与原生裸地环境条件的复杂性有关。该领域的研究将侧重于以下两个方面:早期定居种的适生特征(包括解剖的和生理的)以及各种微生物对植物定居过程的影响;各种非生物环境因素对植物定居的影响。     

Towards the analysis of vegetation succession

Attention is drawn to canonical analysis as a plausible model for analyzing vegetation succession. An assessment of the opportunities afforded by canonical analysis for this purpose is then made by reference to two applications of the method. The applications deal with characteristics of hydroseral processes and with the dynamic status of an area of lowland tropical rain forest. On the basis of these and other studies the conclusion is drawn that canonical analysis could contribute usefully in efforts to place the study of dynamic ecosystem processes on a more analytic footing.This work was supported by a Natural Sciences and Engineering Research Council award to L. Orlóci. It is a pleasure to acknowledge my indebtedness both to Dr. Orlóci for his support and encouragement and to the Department of Plant Sciences at the University of Western Ontario for hospitality and help. Appreciation is expressed also to Dr. John Ogden, Research School of Pacific Studies, The Australian National University, Canberra for kindly placing his rain forest data at my disposal and for his invaluable help in interpreting the results of analyses of these data.     

Increasing topographic influence on vegetation structure during primary succession

Mount Pinatubo, Philippines (15.14°N, 120.35°E) erupted violently in 1991 to initiate significant primary succession. Aspect, the direction faced by a slope, affects patterns of vegetation at higher latitudes, but such effects remain unreported in the wet tropics. Therefore, we monitored species composition and cover in established plots during 2006, 2010, and 2013 to characterize how aspect affected primary succession. We used redundancy analysis (RDA) to assess vegetation change in response to time and environmental factors. Vegetation cover increased from 153 to 245% on north-facing slopes, and from 174 to 230% in south-facing slopes while species richness and diversity indices also increased. From 38 to 63% of the species were restricted to one aspect, depending on the year of study. Redundancy analysis demonstrated that aspect strongly affected species composition and that its effects persist. Fabaceae was concentrated on south-facing slopes, which suggested that aspect effects might be accentuated due to enhanced soil nitrogen. Vines, grasses, and forbs, all typical of habitats with greater insolation, were more abundant on south aspects, while trees and ferns were more common on the north aspects. This is the first survey of vegetation dynamics using permanent plots on new volcanic surfaces in this region. Aspect differences produced distinct insolation and moisture patterns that enhanced habitat diversity and altered species composition. This effect has not been noted in monsoon forests. Aspect may continue to initiate divergence in succession trajectories as soils and vertical canopy structure develop differentially in response to differential dominance.     

Chemistry and vegetation of highly acidic streams

An account is given of the water chemistry and photosynthetic flora of waters in England with a pH value of 3.0 or less. Of the fifteen sites found, thirteen were associated with coal-mining, one with a barytes mine and one was an industrial effluent. Flowing waters predominated, but in some cases pools in direct contact with the streams were also present. All waters carried high levels of heavy metals and silicate, and most carried moderately high levels of phosphate and combined inorganic nitrogen. The total flora consisted of twenty-four algae, two mosses and two flowering plants. Of these, three algae and one flowering plant were found in pools only. Euglena mutabilis was both the most widespread species, and often also the most abundant. The number of species present in a reach showed a positive correlation with pH during late summer, and a negative correlation with total acidity in winter. Only four of the algal species found in England are certainly included in the U.S.A. literature. Some, but not all, the apparent differences between the two floras are very probably due simply to taxonomic problems.     

Rates of change in vegetation during secondary succession

Plant Ecology - For a number of experiments on secondary succession on different soils (lasting 9–23 yf) calculations were made of: a) rates of floristic change as measured with the community...     

Development of vegetation patterns in early primary succession

Question: We investigated colonisation filters in early plant community development on a glacial outwash plain. We asked if these were related to seed limitation or to a lack of safe sites, if topographical heterogeneity affected species patchiness and how species life cycles influence successional trajectories. Location: An outwash plain (Skeiðarársandur) in southeast Iceland. Methods: We identified surface heterogeneity at two different scales, ca. 10–15 cm (larger stones and established plants) and ca. 50 m (shallow depressions representing dry river beds) at two study sites. We quantified species cover, flowering plant density, seed production, seed rain, seed bank density, seedling emergence and seedling survival from June 2005 to June 2007 for the whole plant community, and measured seed production for five species. Results: Mean vegetation cover was <2.5% at the sites. Low emergence rates and high seedling mortality were the two main recruitment filters. Only 1.4% of seedlings emerging in 2005 survived into the 2007 growing season. Topographical heterogeneity had little effect on plant colonisation. High annual variation was recorded, and the two study sites (ca. 2 km apart) differed in their colonisation success. Of the five species, establishment of Cerastium alpinum and Silene uniflora was most limited by lack of seeds, whereas establishment of Luzula spicata, Poa glauca and Rumex acetosella was most limited by safe sites. Conclusions: We conclude that colonisation processes and patterns in early primary succession on Skeiðarársandur were largely influenced by stochastic factors.     

Effects of winter mowing on vegetation succession in a lakeshore fen

Abstract. To assess whether winter mowing in wetlands fulfils the aim of preventing succession towards drier communities, 34 permanent quadrats (15 m²) were surveyed annually from 1984–1985 to 2000 within large mown and unmown (control) areas (several ha) in a calcareous lake shore fen (W Switzerland). Three trends were noticed: decrease of aquatic species, spread of Cladium mariscus and establishment of woody species (especially Alnus glutinosa and Frangula alnus). None of these trends was prevented by mowing, but mowing did prevent the accumulation of C. mariscus litter and kept woody saplings small. Succession was generally slow and often occurred in the form of sudden, discrete changes. Plant species richness increased with mowing and remained constant without mowing. Soil disturbance by the mowing machine contributed more to the effects of management on species composition than the periodic removal of biomass. It is concluded that mowing every three years in winter is insufficient to preserve semi‐aquatic communities against succession but sufficient to maintain the plant species richness of a low productive, regularly flooded fen.     

江苏省海滩植被演替的研究

江苏省海滩植被可分为滨海盐土植被、盐沼植被及海滩沙生植被三个基本类型。本文论述了这些植被类型的演替规律。滨海盐土植被与盐沼植被的演替,外因于土壤盐分含量递减与有机质含量的递增;海滩沙生植被的演替,外因于土壤沙颗粒大小及其相应的土壤含水量的变化,所以海滩植被演替为外因动态演替。     

子午岭次生林植被演替过程的土壤抗冲性

在水土流失极为严重的黄土高原地区,土壤抗冲性决定着土壤的可蚀性.于2004年5月在黄土高原惟一的次生林区——子午岭林区,通过原状土冲刷实验对不同植被演替阶段下的土壤抗冲性进行了研究.结果表明： （1）随植被的正向演替,表层土壤（0～15cm）的抗冲性明显增大,但亚表层（15～30cm）和底层（30～50cm）土壤抗冲性则没有太大的变化;（2）植物根系能显著的增强土壤抗冲性,土壤抗冲系数与单位土体根系表面积具有极显著的（p＜0.001）线性相关关系;（3）土壤抗冲系数随土壤中水稳性团聚体含量和微生物量的增加而增大,且其相关关系极显著（p＜0.001）.综合根系（x1）、水稳性团聚体（x2）以及微生物（x3）对土壤抗冲性的影响,建立黄土高原地区土壤抗冲性方程： y=-4.89＋1.27x1＋0.079x2＋1.94E-3x3 （R^2=0.914 p＜0.001）.     

Probing time series vegetation data for evidence of succession

A subset of Stephens & Waggoner's (1970) data, spanning 40 years of recording at the same site, is analysed by AOC for trends in density fluctuations. The results suggest that the recording period is sufficiently long for trends to be detected. A dominant trend depicts density changes as simple monotone functions of time. Other lesser trends signify cyclic changes of different lengths. The fact that a dominant monotone trend exists is interpreted as evidence of succession.Nomenclature follows Little (1953)     

A Markov approach for describing post-fire succession of vegetation

Vegetation dynamics in the coastal area of the Seto Inland Sea region in Japan, where wild fires occur frequently, were described using a stationary Markov model. In this region, vegetation types ofMiscanthus-Pleioblastus grassland,Lespedeza-Mallotus scrub,Pinus-Rhododendron forest andCrassocephalum-Erechtites community have been identified, and these show cyclic succession under the influence of fires. The model uses parameters determining fire frequency and rate of successional change to analyze the effect of variation in these parameters on the areal ratio of each vegetation type at equilibrium and on the time taken for one vegetation type to succeed another (elapsed successional time). The effect of fire frequency differs between hypothetical habitats with high and low productivity. A policy for vegetation management in areas of high and low productivity is proposed. The advantages and limitations of applying Markov models to studies of vegetation succession are also discussed.     

Limits to convergence of vegetation during early primary succession

Questions: Primary succession, measured by changes in species composition, is slow, usually forcing a chronose‐quence approach. A unique data set is used to explore spatial and temporal changes in vegetation structure after a 1980 volcanic eruption. On the basis of data from a transect of 20 permanent plots with an altitudinal range of 250 m sampled through 2005, two questions are asked: Do changes along the transect recapitulate succession? Do plots converge to similar composition over time? Location: A ridge between 1218 and 1468 m on Mount St. Helens, Washington, USA. Methods: Repeat sampling of plots for species cover along a 1‐km transect. Floristic changes were characterized by techniques including DCA, clustering and similarity. Results: Species richness and cover increased with time at rates that decreased with increasing elevation. The establishment of Lupinus lepidus accelerated the rate of succession and may control its trajectory. Diversity (H) at first increased with richness, then declined as dominance hierarchies developed. Primary succession was characterized by overlapping phases of species assembly (richness), vegetation maturation (diversity peaks, cover expands) and inhibition (diversity declines). Each plot passed through several community classes, but by 2005, only four classes persisted. Succession trajectories (measured by DCA) became shorter with elevation. Similarity between groups of plots defined by their classification in 2005 did not increase with time. Similarity within plot groups converged slightly at the lower elevations. Despite similarities between temporal and spatial trends in composition, trajectories of higher plots do not recapitulate those of lower plots, apparently because Lupinus was not an early colonist. Any vegetation convergence has been limited to plots that are in close proximity.     

Glacial loss and its effect on riparian vegetation of alpine streams

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High vegetation and environmental diversity during the Late Glacial and Early Holocene on the example of lowlands in the Czech Republic

The diversity of vegetation and the environment in the Late Glacial period in the Elbe region is illustrated by a comparison of three palynological localities. The localities differ in their history, profile lithology and position relative to the Elbe river. The Hrabanovská ?ernava profile holds a record of the development of a shallow lake, which was surrounded by a cold continental steppe in the Early Dryas. Evidence of a pine forest in the Late Glacial period is captured in the surroundings of the profile Chrást. The Mělnický úval — P?ívory locality is an interdune infill, where marl sediments redeposited in shallow water. The surrounding vegetation was diffuse and influenced by erosion. In the Early Holocene, the landscape was covered by an open birch-pine forest. Broad-leaved woody species appeared later. Localities in the Elbe region share a high proportion of Pinus throughout the Holocene as a result of the spread of drift and terrace sands. The human impact in the mid Holocene manifests as evidence of intensive charring of localities.     

长白山植被类型特征与演替规律的研究

根据多次对长白山植被调查和长期定位观测资料 ,全面系统地总结了长白山植被类型特征和演替规律 ,详细描述了长白山地带性和非地带性植被类型的性质、组成、结构和分布规律 ,探讨了长白山植被演替与火山爆发的关系。提出长白山植被垂直分布基带应是红白松阔叶混交林 ,也是长白山地带性植被类型。但由于长期受人类活动影响 ,削弱了地带性表现 ,形成大面积的天然次生林和耕地。据此不应该认为 ,人类能消灭客观自然规律的植被分布的地带性 ,为了恢复地带性植被和定向改造自然 ,应引进地带性树种 ,营造结构合理、种类多样和稳定性强的森林群落。     

Early succession of butterfly and plant communities on set-aside fields

 Hypotheses on secondary succession of butterfly and plant communities were tested using naturally developed 1- to 4-year-old set-aside fields (n = 16), sown fields (n = 8) and old meadows (n = 4) in 1992 in South Germany. Pioneer successional fields (1st and 2nd year of succession, dominated by annuals) and early successional fields (3rd and 4th year of succession where perennials, especially grasses became dominant) had fewer plant species than mid-successional fields (old meadows). In contrast to established hypotheses, mean number of plant species decreased from 1- to 4-year-old set-aside fields. Species richness of butterfly communities did not change during the first four years of succession, but species composition changed greatly. Pioneer successional fields were characterized by (1) specialized butterflies depending on annual pioneer foodplants (e.g. Issoria lathonia), and (2) species preferring the pioneer successions despite their host plants being more abundant on early and mid-successional fields (e.g. Papilio machaon). The variability in butterfly species richness was best explained by flower abundance which was closely correlated with plant species richness. Species whose abundance was correlated with habitat connectivity were significantly smaller than species which correlated with flower abundance. Numbers of caterpillar species were correlated with numbers of adult butterfly species. Life-history features of butterflies changed significantly from pioneer to early and mid-successional fields. We found decreasing body size and migrational ability, decreasing numbers of species hibernating as imago, decreasing numbers of generations and increasing larval stage duration with age of succession, but, contrary to expectation, host plant specialization, numbers of egg-cluster laying species and egg diameter did not change with successional age. Received 18 September 1995 / Accepted: 17 July 1996