Distribution of alien vs. native plant species in roadside communities along an altitudinal gradient in Tenerife and Gran Canaria (Canary Islands)

Roadside plant communities were studied along two roads following an altitudinal gradient in Gran Canaria and Tenerife (Canary Islands). Our aim was to investigate variation in plant species richness, particularly of the alien flora, along a gradient from coastal shrubland to summit vegetation (1950 m a.s.l. in Gran Canaria, 2300 m in Tenerife) in relation to variation in habitat factors (altitude, habitat structure, roadside disturbance, distance to urban nuclei). We compared different species groups that were classified in terms of their biogeographical status, origin and life form. Altitude was the most important factor determining species richness and composition along both roadside transects. Alien plants showed a unimodal distribution pattern along the altitudinal gradient, with less species and lower abundance at low and high altitudes, and highest abundance at intermediate altitude. Alien plant species were also relatively more frequent near urban centres. The number of native and alien species was significantly positively correlated along the altitudinal gradient. Both alien and native, non-endemic species showed differences in their distribution along the altitudinal gradient according to their biogeographical affinities and climatic tolerances. Despite considerable differences in species pools these patterns were consistent among the two islands. Environmental (abiotic) stress is proposed as a primary, altitude-related factor acting as a filter against most alien plants at coastal and high-mountain altitudes. A higher frequency or intensity of disturbance at intermediate altitudes may be a further causal factor promoting alien plants in this zone. Future management efforts to control alien plants along roads should, therefore, concentrate on intermediate altitudinal zones of the higher Canary Islands.     

中国南部亚热带森林地表植被动态变化

系统研究了南方5个亚热带森林生态系统地表植被的动态变化情况.研究方法是:在每个研究区域内,按照地形梯度分别布设50个1m2 的样方,记录样方内所有物种的频度及相关的环境变量,5个研究区域共设250个样方,每个样方分别调查两次.通过单元及多元统计方法分析表明:维管植物物种频度在一个区域明显下降,另二个区域显著增加;苔藓物种频度在一个区域有明显下降,另一个区域明显增加;苔藓物种数量在3个区域显著增加,另二个区域显著下降;维管植物物种数量显著增加在二个区域;物种组成沿着第一个植被梯度轴DCA 1没有显著变化,沿着第二个植被梯度轴DCA 2在二个区域有显著变化.综合分析表明,苔藓对气候变化及其波动反映敏感,是较好的气候变化及气候波动生物指示因子,而管植物数量及频度的变化没有明显证据显示与土壤酸化和大气污染有紧密关系.     

Altitudinal pattern of vegetation variation on Tenerife

Abstract. The variation in structure and floristic composition of the vegetation of Tenerife is related to different environmental factors. 200 sample plots, stratified according to altitude, exposure to wind, kind and age of parent rock, inclination and degree of disturbance were analysed throughout the island. The resulting data were analysed using univariate statistics (altitudinal distribution profiles of the more frequent species) and multivariate methods (Correspondence, Cluster and Pattern Analysis). Altitude, exposure to wind and, to a lesser extent, disturbance were found to be the major determinants of vegetational variation, whereas parent rock and inclination were less important. Ordination results show a continuum in structural and floristic variation of the vegetation with species distributions varying continually along the altitudinal gradient. Nevertheless, altitudinally bound plant community types were recognized with Cluster Analysis. Vegetational discontinuities, which were also detected by pattern analysis, are more evident on the windward slope of the island; they have been attributed to the existence of a major underlying environmental discontinuity the ‘cloud sea’-which is associated with a climatic inversion. On the leeward slope, beyond the influence of the cloud sea, discontinuities are less evident and vegetational variation seems to be closer to a coenocline, i.e. a vegetational continuum.     

The altitudinal gradient of vascular plant richness in Aurland, western Norway

Differences in vascular plant species richness; along the altitudinal gradient in the Aurland area of western Norway have been investigated. Based on field surveys, as complete lists as possible of all vascular plants have been compiled for each 100 m altitudinal band, from sea level to the highest mountain (1764 m). For each of the 18 altitudinal bands, climatic data have been estimated. A total of 444 vascular plant species were recorded. Highest species richness (263 species) occurred in the 600–700 in band, whereas the uppermost band had only 10 species. There are minor differences in species number between the altitudinal bands < 1000 m. Partial least squares regression shows that species richness for the overall altitudinal gradient is well predicted by mean July and January temperatures and mean annual precipitation. Species turnover is highest in the 100–200 m. 600–700 m. and 1400–1500 m altitudinal bands. In terms of the gradient in summer temperature, the study supports the generally assumed linear relationship between July temperature and the number of vascular plant species between 700 and 1500 m corresponding with a mean July temperature range of 7–11°C. The study shows a decrease of ca 30 vascular plant species with a 1°C decrease in mean July temperature, and that the “climatic vascular plant limit” is here estimated to occur at a mean July temperature of 2.4°C. Above 1500 and below 700 m. species number is lower than expected based on summer iemperature conditions alone. The 700–800 m band represents the highest floristic difference compared to the other bands. Ordination and classification analyses of the floristic compositional data of all the bands highlight the 600–800 and 1500–1600 m altitudinal bands as the major biotic boundaries along the gradient. No major discontinuity in species richness, composition, or turnover was consistently found, however, at the 1100–1200 m band representing the forest-limit ecotone in Aurland.     

Multivariate approach to the classification and ordination of the forest ecosystem of Nandiar valley western Himalayas

QuestionsDoes the vegetation composition of the forests of Nandiar Valley correlate with climatic, topographic and edaphic variables? Is it possible to identify plant communities through indicator species in relation to environmental gradients? Can this approach of classification and ordination will be helpful for conservation planning?LocationForests of Nandiar Valley, Moist temperate Western Himalayas Pakistan.MethodsEighty stands were selected for quantitative and qualitative characteristic of vegetation between an elevations of 525–3817 m. Species composition was recorded by using 400 m long transects. GPS, climatic, edaphic and topographic data were recorded for each sampling site. The relationship between habitat types, species composition and distribution along with climatic, edaphic and topographic variables were analyzed using TWINSPAN, Cluster analysis and DCA ordination.ResultsSum 325 vascular plants species belonging to 97 families were recorded. Diversity index and species richness was maximum in the moist temperate zone. Classification and ordination showed that the variance in species data was 7.07. Two-ways indicator species analysis classified the vegetation into eight plant communities. Indicator species analysis revealed that slope aspect, wind speed, temperature, dew point, wet bulb, pH, organic matter and phosphorous were the strongest parameters (p ≤ 0.05) determining plant community composition and indicator species in each habitat. The results also show the strength of the environment – species relationship using Monte Carlo procedures. DCA ordination grouped different species having similar habitat and habitats having common species.ConclusionsThe multivariate analysis of the vegetation along with environmental variables of Nandiar valley confirmed the indicators of each sort of vegetation communities/microclimatic zones which could further be used in conservation planning and management not only in studied area but also in the adjacent regions as well as in the areas exhibit similar sort of climatic, edaphic and topographic conditions.     

Tree hydraulic traits are coordinated and strongly linked to climate‐of‐origin across a rainfall gradient

Plant hydraulic traits capture the impacts of drought stress on plant function, yet vegetation models lack sufficient information regarding trait coordination and variation with climate‐of‐origin across species. Here, we investigated key hydraulic and carbon economy traits of 12 woody species in Australia from a broad climatic gradient, with the aim of identifying the coordination among these traits and the role of climate in shaping cross‐species trait variation. The influence of environmental variation was minimized by a common garden approach, allowing us to factor out the influence of environment on phenotypic variation across species. We found that hydraulic traits (leaf turgor loss point, stomatal sensitivity to drought [P_gs], xylem vulnerability to cavitation [P_x], and branch capacitance [C_branch]) were highly coordinated across species and strongly related to rainfall and aridity in the species native distributional range. In addition, trade‐offs between drought tolerance and plant growth rate were observed across species. Collectively, these results provide critical insight into the coordination among hydraulic traits in modulating drought adaptation and will significantly advance our ability to predict drought vulnerability in these dominant trees species.     

Changes in plant species composition and litter production in response to roads and trails in the laurel forest of Tenerife (Canary Islands)

Abstract

Road density has increased in the Canary Islands' forests during the last century, affecting an unknown amount of forested area. We studied road effects on vegetation in the relict laurel forest of Tenerife. We assessed edge effects on plant species richness, plant composition and litter production. Effects of anthropogenic corridors on vegetation differed between paved roads and unpaved trails. Opportunistic species (shade intolerant) dominated road edges, but composition differed among all sites. Multivariate analysis revealed convergence in species composition along the corridor-interior gradient. For trails, both species richness and litter production did not differ significantly between edge and interior. Road edge effects on vegetation were detectable only within the first 10 m towards the interior. This suggests that the main effects of roads and trails on species richness are limited to the immediate edge of the laurel forest. Litter fall along road edges was half that of the interior. However, no significant differences were detected due to the high variability of the data. A buffer of approximately 10 m would result in the reduction of the total area of the remaining undisturbed laurel forest. Based on these results, the building of new paved roads should not be considered. Low human population inflow into the Anaga Rural Park needs to be maintained on a sustainable basis. Forest managers should take these road/trail effects into account when planning new road openings in this ecosystem.     

Effects of different cultivation types on native and alien weed species richness and diversity in Moravia (Czech Republic)

Changes in weed species richness and beta-diversity are partly attributable to different types and intensity of disturbance and partly to broad-scale variation in environmental conditions. We compiled a data set of 434 vegetation plots of weed vegetation in root crop and cereal fields in Moravia (eastern Czech Republic) to compare the effects of environmental conditions and different disturbance regimes on species richness and beta-diversity. To detect changes in species richness, we related the variation in species richness to individual environmental conditions. To assess differences in beta-diversity between the vegetation of cereal and root crop fields, we used Whittaker's measure of beta-diversity. The relative importance of each environmental variable for the variation in species composition was evaluated using canonical correspondence analysis. All analyses were done for all vascular plant species and separately for native species, archaeophytes and neophytes. A comparison of weed vegetation of root crops and cereals showed a distinct dichotomy between these two types of weed vegetation. There was no significant difference in total species richness and native species richness; however, cereal fields were richer in archaeophytes and root crop fields were richer in neophytes. The beta-diversity of weed vegetation was higher in root crops. Environmental factors explained a significant part of the variability in richness of both natives and aliens. The richness of native species increased and beta-diversity decreased with increasing precipitation. The opposite relationship was found for archaeophytes, in both cereals and root crops. These results confirmed the importance of climatic factors and management practices for changes in weed species composition. They also showed a distinct pattern of species richness and beta-diversity of native and alien weed species.     

The role of climate and plant functional trade‐offs in shaping global biome and biodiversity patterns

Aim Two of the oldest observations in plant geography are the increase in plant diversity from the poles towards the tropics and the global geographic distribution of vegetation physiognomy (biomes). The objective of this paper is to use a process‐based vegetation model to evaluate the relationship between modelled and observed global patterns of plant diversity and the geographic distribution of biomes. Location The global terrestrial biosphere. Methods We implemented and tested a novel vegetation model aimed at identifying strategies that enable plants to grow and reproduce within particular climatic conditions across the globe. Our model simulates plant survival according to the fundamental ecophysiological processes of water uptake, photosynthesis, reproduction and phenology. We evaluated the survival of an ensemble of 10,000 plant growth strategies across the range of global climatic conditions. For the simulated regional plant assemblages we quantified functional richness, functional diversity and functional identity. Results A strong relationship was found (correlation coefficient of 0.75) between the modelled and the observed plant diversity. Our approach demonstrates that plant functional dissimilarity increases and then saturates with increasing plant diversity. Six of the major Earth biomes were reproduced by clustering grid cells according to their functional identity (mean functional traits of a regional plant assemblage). These biome clusters were in fair agreement with two other global vegetation schemes: a satellite image classification and a biogeography model (kappa statistics around 0.4). Main conclusions Our model reproduces the observed global patterns of plant diversity and vegetation physiognomy from the number and identity of simulated plant growth strategies. These plant growth strategies emerge from the first principles of climatic constraints and plant functional trade‐offs. Our study makes important contributions to furthering the understanding of how climate affects patterns of plant diversity and vegetation physiognomy from a process‐based rather than a phenomenological perspective.     

Succession of terrestrial macrofungi along a deglaciation gradient at Glacier Blåisen, South Norway

A survey of terrestrial macrofungi along a deglaciation gradient from the glacier forefront to the established vegetation has been performed. The study was accomplished along a transect from Lake Finsevann to Glacier Blåisen, South Norway. Fortysix 6 m × 6 m plots divided into 9 subplots were positioned along this transect. The frequency of fruit bodies of each species in each plot was given on a 0–9 scale reflecting their occurrence in the subplots. Biotic and abiotic environmental variables for the plots were also recorded. The numerical methods used include principal component analysis (PCA), detrended correspondence analysis (DCA), and canonical correspondence analysis (CCA). Totally 99 species of macrofungi were recorded; 80.8 % of the species belonged to the Basidiomycota and 19.2 % to the Ascomycota. About one third of the species was only found once. In general, the species richness was highest on the glacier forefront, lowest in the most established vegetation. The proportion of species of Ascomycota was highest close to the glacier front. The main gradient in the data set was shown related to the primary ecological succession following the retreat of glaciers. The second gradient was possibly related to fine scale variation due to local moisture, microtopography, and secondary distribution. Of the variation in composition of species, 3 % can be ascribed to abiotic variance, 10 % to vascular plant variance, and 16 % to the combination of the abiotic and vascular plant component of variation. The results are discussed in the light of the time since deglaciation and the influence of certain biotic and abiotic environmental factors.     

Variation in species composition and vegetation structure of succulent scrub on Tenerife in relation to environmental variation

Abstract. On Tenerife, the occurrence of environmental gradients over short distances provides a unique opportunity to investigate the relationship between vegetation and environmental factors. In the semi‐arid coastal region of Tenerife, floristic composition, species richness and vegetation structure of perennial plants have been studied in 67 locations covering the existing precipitation gradient. On the island as a whole, variation in species composition could be best explained by mean annual precipitation; at coastal sites, substrate age and soil characteristics also played a significant role. On the other hand, substrate chemistry and the type of eruptive material explained little of the floristic variation. Stand biomass was strongly correlated with mean annual precipitation and was, on the youngest lava flows studied, also affected by substrate age. The native stem succulent species made up the bulk of total biomass along the whole precipitation gradient. Disturbed and undisturbed sites differed significantly in stand biomass and cover. Species richness was correlated with precipitation and substrate age. Distribution of plant functional types was also related to the precipitation gradient. The relative abundance of hemicryptophytes and shrubs with non‐hairy leaves increased with increasing precipitation whereas the ratio of shrubs with hairy/non‐hairy leaves and succulent plants decreased. Some alien plants were quite frequent at disturbed sites but, on the whole, they contributed little to the species spectrum and to the stand biomass. Undisturbed sites remained almost free of introduced species not considering annuals.     

Understorey vegetation in boreal Picea mariana and Populus tremuloides stands in British Columbia

Abstract. We compared the species composition and species density of vascular plants in the understorey vegetation of boreal forest between Picea mariana (Black spruce) and Populus tremuloides (Trembling aspen) stands in British Columbia, Canada, and related differences in species composition and species density between the two forest types to dominant canopy tree species as well as a wide variety of environmental factors. We analysed 231 stands, distributed in three different climatic regions representing drier, wetter, and milder variations of montane boreal climate. Of these stands 118 were dominated by P. mariana and 113 by P. tremuloides. P. tremuloides stands had higher species density than P. mariana stands in all climatic regions, but species density of each dominance type varied among climatic regions. The floristic composition of the understorey vegetation was markedly different for P. mariana and P. tremuloides dominated stands. A detailed study on the effect of canopy dominance and local environmental factors on the understorey vegetation of the boreal forest was conducted using 88 stands from one of the three climatic regions. Using a combination of ordination and variation partitioning by constrained ordination we demonstrated a small but unique effect of canopy dominance type on the understorey vegetation, while a larger amount of compositional variation was shared with other factors. Our results accord with a scenario in which differences in primary environmental factors and humus form properties, the latter accentuated by the canopy dominants themselves, are the most important causes of higher species density in P. tremuloides stands than in P. mariana stands, as well as differences in species composition among the two canopy dominance types. Processes and time scales involved in the small but significant direct and indirect effects of the canopy dominant on understo‐ rey species composition are discussed.     

Species richness, abundance, rarity and environmental gradients in coastal barren vegetation

Coastal barrens in Nova Scotia are heathlands characterised by short, predominantly ericaceous vegetation, sparse tree cover, exposed bedrock, pockets of Sphagnum bog, and stressful climatic conditions. Although coastal barrens are prominent in the physical and cultural landscape, they are largely unprotected. We selected six barrens along the Atlantic coast, and surveyed 20 1-m² plots at each barren for vascular plants, macrolichens, mosses and environmental factors. We recorded 173 species (105 vascular, 41 macrolichen, 27 moss), including six provincially rare vascular species found predominantly in nearshore areas with high levels of substrate salt and nutrients, variable substrate depth, and short vegetation. Although vascular plant and moss richness were similarly correlated with vegetation height, substrate depth, organic matter content, and rock exposure, there were no clear correlations between vascular plant, macrolichen and moss richness across all sites. Vascular plant rarity and species richness were not correlated, but had inverse relationships with key environmental gradients. Tailoring conservation efforts to protect areas of high richness may thus mean that rare species are missed, and vice versa. Ordination and ANOSIM show that barrens vegetation differs widely among sites; therefore, protecting any singular coastal barren will not protect the entire range of vegetation communities and species in this heathland type. Conservation planning should emphasize protecting environmental gradients correlated with richness, rarity and plant community structure, including substrate depth and moisture, and vegetation height. Additionally, protected areas should include a coastal-inland gradient and a diversity of substrate types, including exposed rock and trees.     

Fifteenth annual research symposium University of Glasgow, 1975

Background: All human land use (LU) affects the distribution of plant species; however, the impacts vary with the type/intensity of LU. For managing ecosystems, it is therefore essential to understand the effects of LU types on the distribution of plant species on a macroscale.

Aims: The objectives of our study were to quantify the effects of various LU types on the distribution of vascular plant species in Japan and to determine in particular the extent to which LU was an important factor for the distribution of common species.

Methods: Based on a logistic regression model and variation partitioning being applied to each plant species, we evaluated the partial deviance by six LU types, four climatic types and three topographic and geological factors for 647 plant species at 14,412 sites in Japan.

Results: The effect of LU was significant for species present at multiple sites. Of the six LU types, secondary vegetation and plantation were the most important factors determining species distribution for many species.

Conclusions: Our results suggest that distribution of the common species is largely affected by LU on macroscale. The design of LU relating to secondary vegetation and plantations will thus be important in determining changes in the vegetation composition within Japan.     

Biodiversity Characterization in Nubra Valley, Ladakh with Special Reference to Plant Resource Conservation and Bioprospecting

Trans-Himalayan mountains, owing to harsh climatic conditions and a short growing season support low vegetation cover (<20%), yet it is known to harbour a unique assemblage of flora and fauna which have not been systematically inventoried and documented so far. This paper deals with spatial and non-spatial information on landscape units, vegetation characteristics and plant species diversity of Nubra Valley in Ladakh, India. Based on digital – visual (on screen) interpretation of remote sensing data coupled with knowledge-based classification we delineated 19 cover classes (11 vegetation types and 8 non-vegetation categories). The vascular plants (angiosperms and gymnosperms) were systematically collected using stratified random sampling of different landscape/vegetation to characterize plant communities and assess the distribution patterns of species. The study reveals that nearly 78–80% of plant species in Nubra are restricted to the valley bottoms. In all, 414 species of vascular plants were recorded from the study area. These belongs to 56 families and 202 genera. Of these, 102 species were reported to be used in traditional system of medicine by Amchis over 80 species are largely associated with cultivated fields and human habitation. As many as 49 species were cultivated which include several varieties of crop plants especially those of barley and buckwheat. Aspects of bioprospecting and conservation of valuable species have been discussed.     

Stoichiometry of leaf nitrogen and phosphorus of grasslands of the Inner Mongolian and Qinghai-Tibet Plateaus in relation to climatic variables and vegetation organization levels

Nitrogen (N) and phosphorus (P) are most commonly the limiting essential elements that affect the functioning of plants and ecosystems. However, their stoichiometry in relation to climatic variables and vegetation organization levels has not been comprehensively characterized. N and P concentrations were measured for 329 leaf samples collected at 132 sites along the 5000 km long China Grassland Transect that traverses the Inner Mongolian and Qinghai-Tibet Plateaus. The patterns of these measurements were analyzed with reference to climate factors, plant species, plant functional groups, grassland communities and grassland ecosystems. The aim was to explore whether geographical patterns of plant leaf elements are related to zonal climatic variables, and at which vegetation organization levels changes of plant leaf N and P stoichiometric characteristics and pattern occur. Results showed that interspecific differences of N and P concentrations were most significant for the three vegetation organization levels of species, community and ecosystem. Plant leaf N and P concentrations were higher, coefficients of variation of N and P lower, and N/P, C/N and C/P ratios were also lower for leaf samples from the cold high altitude Qinghai-Tibet Plateau than for those from the relatively lower altitude and warmer Inner Mongolian Plateau. Correlation of N and P for Inner Mongolian grassland was higher than that for the Qinghai-Tibet Plateau. The study indicates plant species are the most basic unit influencing plant stoichiometric geographic patterns, and that climatic variables affect leaf element concentrations mainly through their effect on changes of plant species composition of vegetation.     

Diversity of Rich Fen Vegetation and Related Plant Specialists in Mountain Refugia of the Iberian Peninsula

In temperate mountains, fens have been reported as relict habitats subject to geographical fragmentation and broad climatic gradients, but few studies have analyzed the influence of these factors on plant diversity. Here we investigate the effect of isolation on the vegetation diversity of rich fens (Caricion davallianae) in the mountains of the Iberian Peninsula, the distribution limit of these habitats in south-western Europe. We used plot-based vegetation data from the Pyrenees and the Cantabrian mountain range to evaluate their regional species-pool, occurrence of specialists, beta-diversity and the effect of geo-climatic variables on their species-richness and species-composition. We found a lower ratio of rare specialists in the Pyrenees than in the Cantabrian range, but similar estimates in the species pools, total species-richness per plot and beta-diversity. The isolation of the two mountain regions resulted in different species assemblages best predicted by summer precipitation and bedrock types, showing region-based differences in the response of vegetation and plant specialists to the environment. The tighter correlation between local climate and diversity estimates in the Cantabrian range suggests relict character of rich fens in that region, where climatic conditions have restricted local distribution of formerly more widely distributed specialists. Although there is no relevant evidence of vegetation impoverishment in that region, historical isolation has probably resulted in the existence of fragmentary plant communities. We conclude that fen vegetation may experience long-time persistence in climatically sub-optimal mountain refugia, but related plant specialists may be sensitive to climatic changes and subject to the extinction of local populations.     

Plant species richness–environment relationships across the Subantarctic–Patagonian transition zone

Aim To evaluate the relative importance of climate, productivity, environmental heterogeneity, biotic associations and habitat use by cattle to account for the species richness of trees, shrubs and herbs across the Subantarctic–Patagonian transition. Location An area of c. 150 × 150 km, within the transition zone between the Subantarctic and Patagonian subregions on the eastern slope of the Andes (c. 39–42° S, 70–72° W). Methods All vascular plants found at each one of 50 (10 × 10 m) sampling plots were counted to estimate the local tree, shrub and herb species richness. Path analysis was used to evaluate the relationship between the richness of the three life‐forms and plant cover, dried litter biomass, mean annual temperature, annual precipitation, daily temperature range, substrate heterogeneity and number of faecal pats. Principal coordinates of neighbour matrices was used to model the spatial autocorrelation of the data. Results Total plant species richness showed a unimodal pattern of spatial variation across the transition. Richness responded positively to indirect effects of precipitation mediated through plant cover, but there was a negative overall effect of precipitation on richness towards the west of the transition, most strongly for trees. An increase in substrate heterogeneity promoted a local increase in herb and shrub richness; the richness of trees increased in sites with steeper slopes. Canopy closure had a direct negative impact on herb richness; it also increased the local accumulation of litter, which negatively affected shrub and herb richness. The impact of habitat use by cattle negatively affected herb richness in areas to the east of the biogeographical transition. Main conclusions We suggest that the importance of indirect climatic effects mediated by vegetation cover can account for species richness patterns across this transition, most strongly for woody species, which supports the productivity hypothesis. The southern temperate forests towards the west may represent a deviation from the predictions of the water–energy dynamics hypothesis. Dissimilar spatial patterns of variation in the richness of woody and herbaceous species, and their different responses to climatic and heterogeneity variables across the transition, suggest that plant life‐form influences the plant species richness–environment relationships.     

三峡水库蓄水对消涨带植被的初步影响

三峡库区消涨带植被一直受到广泛关注。为了研究水库蓄水对175 m以下消涨带原有植被的潜在影响,2008年8月在三峡大坝上游长江干流从巴南到秭归12个监测点,设立68个5 m×5 m永久监测样方,比较被水淹过的156 m以下与当时尚未水淹的156～175 m地段植被物种组分、物种多样性和草本层生物量的差异。结果表明：被水淹过与尚未水淹的植被物种组分存在显著差异,DCA可以将二者明显分开,156 m以上尚未水淹的植被以灌丛为主;156 m以下被水淹过的植被以草丛为主,优势种包括多年生草本：狗牙根（Cynodon dactylon）、牛鞭草（Hemarthria altissima）和硬秆子草（Capillipedium assimile）;一年生草本：狗尾草（Setaria viridis）、毛马唐（Digitaria ciliaris）和千金子（Leptochloa chinensis）。木本植物基本死亡,只有枫杨（Pterocarya stenoptera）、牡荆（Vitex negundo）和地瓜（Ficus tikoua）存活。此外,被水淹过的植被中灌木物种数比例显著降低,而一年生草本物种数比例显著增加。被水淹过和尚未水淹植被的物种多样性也存在显著差异,被水淹过植被物种总数、灌木和多年生草本物种数显著低于尚未被水淹过的植被,但一年生草本物种数没有显著差异。被水淹过的植被草本层生物量与尚未水淹的植被没有显著差异。可见,水淹显著改变了消涨带原有植被物种组分和物种多样性,但一年生草本物种数和草本层生物量没有显著差异。未来175 m以下的植被中,草本尤其是一年生草本将占据优势。在消涨带植被恢复选择适应水淹生境物种过程中,应分别从植物的生活史、生理学和形态学等角度进行筛选,尤其应重视生活史适应策略植物的应用。被水淹过的156 m以下现有优势草本和存活的灌木可以作为三峡库区未来消涨带植被恢复的备选物种。     

Microtopographic control of vascular plant, bryophyte and lichen communities on cliff faces

Cliff faces worldwide have recently been recognized as sites that harbour ancient forests, endangered biota and high levels of biodiversity, but knowledge is limited of the physical factors organizing cliff-face vegetation communities. Two large scale (geographic), five local, and eight fine scale (microtopographic) physical factors were examined using regression and Canonical Correspondence Analysis (CCA) to determine what scale of physical factors best explains variation in cliff-face vegetation on the 785 km long Niagara Escarpment in southern Ontario, Canada. The richness, frequency and community composition of vascular plants, bryophytes and lichens were determined for 72 cliff-face quadrats to discern whether these vegetation groups followed different patterns in their responses to the measured physical factors. A total of 124 different taxa (consisting of 50 vascular plant species, 21 bryophyte species, and 53 lichen taxa) were found on the cliff faces sampled in this study, though only 28 of these taxa were present in more than 10% of the sampled quadrats. Vascular plant and bryophyte species richness and frequency, and lichen frequency were only significantly correlated with microtopographic factors, while lichen species richness was correlated with a variety of fine and local scale physical factors. The fine scale factor ‘volume of soil’, in particular, was highly correlated with variation in richness or frequency for all vegetation groups, with increasing volume of soil correlated with increasing vascular plant richness and frequency and decreasing bryophyte richness and lichen frequency. A suite of local and fine scale physical factors also explained large proportions of variation in cliff-face vegetation community composition. A large scale gradient in the vegetation community was detected, though it resulted from fine scale physical differences between sites rather than from a latitudinal gradient. These results suggest that distinct subcommunities of vegetation exist on cliff faces and correlate with fine scale differences in microtopography.