Plant communities and landscape diversity along a Canadian Arctic river

Abstract. We analysed the structure and diversity of the vegetation along an Arctic river to determine the relationship between species richness and plant community structure. We examined whether variation in species richness along the corridor is structured as (1) an increase in the number of communities due to increasing landscape heterogeneity, (2) an increase in the floristic distinctiveness (β-diversity) of communities, or (3) an increase in within-community richness (α-diversity) as species-poor communities are replaced by species-rich communities. We described 24 community types and analysed the relationship between site vascular species richness (γ-diversity) and β-diversity, α-diversity, site environmental heterogeneity, and the number of distinct plant communities. We also measured diversity patterns of vascular, bryophyte, and lichen species within communities and examined their relationship to community-level estimates of environmental factors. We found that an increase in site species richness correlated with an increase in the number of communities (r²= 0.323, P= 0.0173) and β-diversity (r²= 0.388, P= 0.0075), rather than an increase in the α-diversity of individual communities. Moisture and pH controlled most of the differences in composition between communities. Measures of species richness and correlations with moisture and pH within communities differed among vascular, bryophyte, and lichen species. Bryophyte richness was positively correlated with moisture (r²= 0.862, P= 0.0010) and lichen richness was negatively correlated with moisture (r²= 0.809, P= 0.0031). Vascular plants had a peak in richness at pH 6.5 (r²= 0.214, P < 0.0001). We conclude that site variation in vascular richness in this region is controlled by landscape heterogeneity, and structured as variation in the number and distinctiveness of recognizable plant communities.     

Restoration of alpine spoil heaps: Successional rates predict vegetation recovery in 50 years

Human disturbances in the alpine region can have long-lasting ecosystem effects because biological recovery in harsh environments proceeds slowly. As a by-product of the exploitation of hydroelectricity, surplus masses from tunnel excavations are deposited as spoil heaps in the alpine landscape. The typical management goal for such spoil heaps is that their species composition converges towards that of their undisturbed surroundings. At present we lack knowledge of the rate as well as the direction of these successions. We examined the species composition of five alpine spoil heaps in western Norway at two points in time, after 6-16, and 24-34 years of succession, with regard to vegetation cover, species richness, species composition and soil conditions. We also compared the vegetation of spoil heaps with that of their surroundings. After ca. 30 years, bryophyte and lichen cover and species richness were similar to those of their surroundings, while cover of vascular plants and species richness recovered more slowly. The vegetation development of spoil heaps appears safe-site limited rather than dispersal limited. Topsoil development was slow, but some accumulation of organic matter was observed. The species composition followed a successional trajectory in direction of the vegetation of the surroundings. Estimated linear successional rates indicate that 35-48 years are needed from construction of spoil heaps till a species composition more or less similar to their surroundings has been reached. However, these estimates are likely to be over-optimistic because successional rates tend to decrease with time. Based on our results we propose three changes to the current spoil-heap construction practice that will improve their restoration: (1) to increase surface unevenness, by which the number of safe sites will increase and germination and establishment success will be enhanced; (2) to increase substrate variability, by adding more of fine-grained materials more species will establish in shorter time; and (3) to use seed from local sources or to let the spoil heaps regenerate naturally.     

The role of cattle in maintaining plant species diversity in wet dune valleys

The succession of species-rich wetland vegetation in dune valleys into species-poor dwarf shrub vegetation was followed by means of permanent vegetation plots, in which the cover of vascular plant, moss and lichen species were recorded over a period of up to 33 years. Low density cattle grazing is an effective substitute for rabbits in stalling this succession, thus preserving the local plant species diversity. The influence of direct rabbit grazing pressure on the vegetation was studied in exclosures. The differences were significant, but not long-lasting after the exclosures had been opened again to the rabbits. Cladina lichen-rich Empetrum-heathland in the dunes is a stage in a probably cyclic succession that might be triggered by grazing. The total vascular plant, moss and lichen diversity of the dune ecosystem can be maintained by a combination of extensive cattle grazing and a regular but limited re-creation of pioneer situations.     

Vegetation of Barton Peninsula in the neighbourhood of King Sejong Station (King George Island,maritime Antarctic)

Plant communities were studied on Barton Peninsula around King Sejong Station on King George Island, maritime Antarctic. The objective of this study was to document the occurrence and distribution of plant assemblages to provide the bases for monitoring the effects of environmental changes and human impact on the vegetation of this area. Approximately 47% of the investigated area was covered by vegetation. Crustose lichens showed the highest mean cover (21%) among vegetation components. The total mean cover of the four dominant taxa, together with the other three major subdominant components, i.e., Usnea spp., Andreaea spp. and Sanionia georgico-uncinata, was 78.2% of the total cover of all the species. Lichen cover and species diversity increased with altitude and the time of exposure from snow. Lichens contributed substantially more to the increased species density and diversity than did bryophytes. Ten plant communities were recognized within the study area. All of them belong to the Antarctic cryptogam tundra formation; they were grouped into four subformations: fruticose lichen and moss cushion subformation, crustose lichen subformation, moss carpet subformation and moss hummock subformation. The moss turf subformation was not found on this region. The Antarctic herb tundra formation was also not found; however, the populations of both Antarctic vascular plants have rapidly expanded around Barton Peninsula in recent years, which may allow development of the Antarctic herb tundra formation in the future.     

Vegetation structure in gullies developed by the melting of ice wedges along Kolyma River, northern Siberia

Vegetation structure was surveyed in gullies developed by the melting of ice wedges along the Kolyma River, northern Siberia, using 72–50 × 50 cm plots. The mean total plant cover was approximately 50% on gley soils, which were only distributed in the gullies. Based on twinspan cluster analysis, four vegetation types were recognized: (i) Agrostis purpurascens grassland with Ceratodon purpureus moss carpet; (ii) Matricaria matricarioides forbland; (iii) Chamaenerium angustifolium and M. matricarioides forbland; and (iv) Descurainia sophia grassland. Species that produce seeds capable of long-distance dispersal established well. Of the environmental factors surveyed, the gully scales (height and width) and elevational difference within a plot were primarily related to the vegetation development. The gully height was correlated with soil pH and compaction that might be related to intensities of ground surface disturbances. Agrostis purpurascens established in large gullies, while Equisetum arvense and Salix alaxensis established in small gullies. Soil compaction was also related to the vegetation establishment patterns (e.g. Rumex sibirica did not establish on hard soils). We concluded that the gully scales primarily determine soil conditions, including ground surface instability as a function of slope and soil compaction, and subsequent community structure.     

Distribution and abundance of small insects and arachnids in relation to structural heterogeneity of grazed, indigenous grasslands

1. The species composition and spatial distribution of small insects (Hemiptera, Coleoptera, Lepidoptera) and arachnids (Araneae, Opiliones, and Pseudoscorpiones) were investigated in three indigenous, upland grasslands identified as the National Vegetation Classification Festuca–Agrostis–Galium typical subcommunity (code U4a), Festuca–Agrostis–Galium, Vaccinium–Deschampsia subcommunity (code U4e), and Nardus stricta species-poor sub-community (code U5a), on which grazing management was manipulated experimentally. 2. Two hypotheses were tested that predicted arthropod diversity in upland grasslands. The habitat heterogeneity hypothesis predicts that the species number and abundance of arthropods will have an asymptotic relationship with increasing numbers of plant species and greater structural heterogeneity in the vegetation. The symbiosis between patches hypothesis states that the species number and abundance of arthropods will express a unimodal relationship with the grain size of sward patches created by grazing. The sward patches must be large enough to be apparent to, and support populations of, arthropods, but small enough that interspersed tussocks provide shelter from weather and a deterrent to disturbance by grazers. 3. The hypotheses were tested by sampling arthropods from the geometrical patterns represented by the individual tussocks and intermediate sward components of three indigenous grasslands produced by different grazing treatments. Paired samples of arthropods were taken by motorized suction sampler, the first of the pair from the grazed sward and the second, the accumulated samples from the surrounding triad of tussocks (U4a and U5a grasslands) or hummocks (U4e grassland). The paired samples were taken from six randomly-selected locations across both replicates of each of the grazing treatments. 4. Arthropod species composition and abundance were compared between the paired sward and tussock samples and in turn with measures of the vertical and horizontal components of vegetation structure, i.e. the variance in vegetation height per unit area and the area covered by tussock compared with sward. 5. There were consistently more species and a greater abundance of arthropods associated with tussocks than with swards and the average species number and abundance for the combined pair of samples declined with increased grazing pressure. The relationship between vertical and horizontal components of vegetation structure and the species number and abundance of selected arthropods was asymptotic as opposed to unimodal, supporting the habitat heterogeneity hypothesis, rather than the symbiosis between patches hypothesis. 6. Small and relatively sedentary insects and arachnids are more sensitive to grazing intensity and species of grazer in these upland, indigenous grasslands than are larger Coleoptera and Araneae, which respond less directly to varied grazing management. The overall linear reduction of small herbivorous and predatory arthropods with increased grazing intensity was buffered in grasslands with substantial tussock patches.     

Sixty years of vegetation dynamics in a south boreal coniferous forest in southern Norway

Abstract. Vegetation data from permanent plots were collected in 1931, 1961 and 1991 in a south boreal forest 20 km north of Oslo in southern Norway. Major changes were found in the vegetation composition during those 60 years. The main changes were a reduction in the frequency of species and the frequency of joint occurrences of vascular species such as Andromeda polifolia, Calluna vulgaris, Cornus suecica, Eriophorum vaginatum, Maianthemum bifolium, Melampyrum pratense, Trientalis europaea, Vaccinium uliginosum and V. oxycoccus, and mosses, e.g. Dicranum fuscescens, Hylocomium splendens, Pleurozium schreberi, Ptilidium ciliare and Ptilium crista-castrensis. The observed changes were interpreted as being induced by internal processes e.g. notably a long-term change from paludified forest to mesic forest. In particular the growth of Picea abies seems to be a main driving force. The dominance of Picea abies and Vaccinium myrtillus appears to have rendered the conditions more unfavourable for other species. A doubling of the living stem biomass of P. abies during the last 67 yr shows that this old-growth forest has not yet reached a steady state. It was demonstrated that species such as Deschampsia flexuosa and Molinia caerulea did not increase in frequency in response to nitrogen deposition, as has occurred elsewhere in northern Europe. pH in the humus layer increased with 0.2 unit from 1961 to 1991. The results of this study indicate that protection from logging has initiated the reduction of species in the field layer and bottom layer. This study questions if monitoring of forest vegetation should be restricted to protected forests as is the practice in Scandinavia today. We recommend that also areas with some kind of selective cutting will be used for monitoring of forest vegetation.     

Disturbance‐induced changes in a high‐alpine cushionfield community,south‐central New Zealand

Long‐term effects of two nearby disturbances, mechanical blading 34 years ago and an approximately century‐old sheep graveyard, in high‐alpine cushionfield share certain vegetation features despite their contrasting soil nutrient status. Secondary succession following blading has continued beyond that recorded over the first 24 years with continued trends towards the adjacent undisturbed cushionfield: increased cover of several cushion species and the lichen Cetraria islandica ssp. antarctica. Several mid‐seral species remain prominent while bare soil and stone pavement continue to decrease. Additional shelter, facilitated by tall snow tussocks planted locally at near‐natural density on part of the bladed site, allowed establishment of some larger, thin‐leaved species. Soil factors remain little affected by the mechanical disturbance compared with the general enrichment persisting at the graveyard. Here three small indigenous grasses, which dominated 50 years earlier (Trisetum spicatum, Agrostis muelleriana, Poa colensoi), remain prominent among the relatively diverse community (50 species, including several calciphilic lichens on the degrading bones). By contrast, frequency of the cushionfield dominant, Dracophyllum muscoides and the lichen Alectoria nigricans, are negatively correlated with the presence of bones. The post‐disturbance temporal community changes are assessed in the context of the initial productivity of the habitat, competitive exclusion and the intermediate disturbance hypothesis.     

Trends in species diversity and composition of urban vegetation over three decades

Question: What was the change in diversity of urban synantropic vegetation in a medium‐sized Central European city during the period of increasing urbanization (1960s‐1990s)? Location: The city of Plzeň, an industrial centre of the western part of the Czech Republic. Methods: Sampling of various types of synanthropic vegetation, conducted in the 1960s, was repeated by using the same methods in the 1990s. This yielded 959 relevés, of which 623 were made in the 1960s and 336 in the 1990s. The relevés were assigned to the following phytosociological classes: Chenopodietea, Artemisietea vulgaris, Galio‐Urticetea, Agropyretea repentis and Plantaginetea majoris. Total number of vascular plant species, evenness index J, number of alien species (classified into archaeophytes and neophytes), and mean Ellenberg indicator values for light, temperature, continentality, moisture, soil reaction, and nutrients were obtained for each relevé. Results: From 1960s to 1990s, there was a significant decrease of species richness and diversity in synanthropic vegetation. The proportion of archaeophytes decreased in most vegetation types, indicating the contribution of this group of species, often confined to specific rural‐like habitats, to the observed impoverishment of ruderal vegetation. The proportion of neophytes did not change between the two periods. Comparison between 1960s and 1990s indicated a decrease in light, temperature, moisture, soil reaction and nutrient indicator values in some vegetation types. In both periods, Artemisieta, Galio‐Urticetea and Chenopodietea formed a distinct group harbouring more species than Agropyretea and Plantaginetea. Neophytes, i.e. recently introduced species, were most represented in the early successional annual vegetation of Chenopodietea, rather than in perennial vegetation of the other classes. Conclusions: Synanthropic vegetation of Plzeň exhibited a general trend of decrease in species diversity.     

Leaf demography and leaf traits of temperate-deciduous and tropical evergreen-broadleaved trees in a Mexican montane cloud forest

The spatial variation in epilithic lichen community structure was investigated as part of a larger study of the vegetation and ecology of the tall limestone cliffs within the Niagara Escarpment Biosphere Reserve in southern Ontario, Canada. The cover of all lichen taxa was visually estimated for a total of 199 samples taken from the top, middle, or bottom of the cliff face at five sites. Twelve environmental variables were also measured. Twenty-seven lichen taxa were identified on the samples. Multivariate ordinations of species composition (DCA, CCA, PCCA) revealed variation in community structure on multiple scales, but no groupings of sites that would have suggested the presence of several distinct species assemblages. A gradient in species composition from north to south, most clearly reflected in the decreasing cover of foliose and fruticose species, may reflect a gradient in human disturbance. There was also intermediate-scale patchiness in species composition in a horizontal plane across cliffs, but despite earlier claims made in the literature, no evidence of vertical zonation of the lichens on cliffs was found. Species composition also responded to small-scale factors possibly related to exposure, light, or moisture. Unlike community composition, the total cover of all lichens was homogeneous over large spatial scales and varied only on a small scale, illustrating that scale as well as resolution of a study may influence the ecological patterns seen. More than half of the species found on the Niagara Escarpment are rare on rock substrates elsewhere in southern Ontario, and two are new for North America (Candelariella heidelbergensis (Nyl.) Poelt and Lecanora perpruinosa Fröberg). The result that cliffs support a distinct flora containing many rare species suggests that they are a reservoir for biodiversity not just for vascular plants, but also for lichens.     

Biodiversity in montane Britain: habitat variation,vegetation diversity and some objectives for conservation

The montane (low- to mid-alpine) zone in Great Britain (GB) lies above the potential tree-line (700–800 m, but descending to 200 m in the north). It is composed of moss and lichen heaths, snowbeds, blanket bog and dwarf-shrub (Ericaceae) health-covered solifluction/gelifluction terraces (38 communities/sub-communities). Approximately 3.0% of the land surface is covered by this- the most extensive predominantly near-natural terrestrial habitat in GB. Internationally distinctive features include oceanic and southern biotic outliers of arctic-alpine fellfield and mountain tundra, and plant communities that are either globally rare/localised or especially well represented in GB. The absence of extensive sub-alpineBetula spp. andSalix spp. scrub is striking.The main sources of habitat diversity are climate, regional variation in topography and geology, and regional modifications due to land-use impact. Over 50 examples are given. Five important gradients in Scottish Highland vegetation are described. Only some 15% of the sampled montane vegetation is anthropogenic; the rest is semi- or near-natural. The vegetation is divided into 5 functional groups: chionophobous (avoids snow), chionophilous (prefers snow), species-rich, mires (including springs and flushes), and anthropogenic. Chionophobous and then chionophilous communities contribute most to montane vegetation diversity (calculated here as the ShannonH diversity index).H diversity increases asymptotically with montane site area but linearly with the number of communities present. A more varied topography, geology and topo-climate gives the highestH diversity.Two examples of montane biodiversity reductions south of the Highlands are the loss of prostrateCalluna vulgaris heaths and modification ofRacomitrium lanuginosum healths. Five objectives for nature conservation are proposed, covering restoration of montaneR. lanuginosum healths, prostrate dwarf-shrub dominated heaths, sub-alpine scrub and upper treelines, and the extension of the breeding ranges of both ptarmigan (Lagopus mutus) and dotterel (Charadrius morinellus) south of the Scottish Highlands. International support for monitoring is sought.     

Natural CO2 springs in Italy: a resource for examining long-term response of vegetation to rising atmospheric CO2 concentrations

It is estimated that more than 100 geothermal CO₂ springs exist in central-western Italy. Eight springs were selected in which the atmospheric CO₂ concentrations were consistently observed to be above the current atmospheric average of 354μmol mol^-1. CO₂ concentration measurements at some of the springs are reported. The springs are described, and their major topographic and vegetational features are reported. Preliminary observations made on natural vegetation growing around the gas vents are then illustrated. An azonal pattern of vegetation distribution occurs around every CO₂ spring regardless of soil type and phytoclimatic areas. This is composed of pioneer populations of a Northern Eurasiatic species (Agrostis canina L.) which is often associated with Scirpus lacustris L. The potential of these sites for studying the long-term response of vegetation to rising atmospheric CO₂ concentrations is discussed.     

The vegetation of ultrabasic soils on the Isle of Rhum II. The causes of the debris

Summary

The relationship between the Rhum ultrabasic skeletal soils and their debris vegetation was investigated by plant analyses and field and laboratory experiments. Samples of Agrostis vinealis, Arenaria norvegica ssp norvegica, Calluna vulgaris, Festuca vivipara, Plantago maritima and Racomitrium lanuginosum from these soils usually had low concentrations of potassium and calcium, and high concentrations of sodium, magnesium (and high Mg/Ca quotients), iron and nickel. There were instances of very high iron concentrations (up to 22.4mg g^?1 in Plantago maritima), very high Mg/Ca quotients (up to 27.8 in Arenaria novegica spp. norvegica) and high nickel concentrations (up to 0.48mg g^?1 in Plantago maritima). A nutrient addition experiment which was set up in 1965 on an exposed barren area had in 1982 over twice as many species as originally recorded and a nearly complete plant cover. Shorter-term work has confirmed that nutrient availability limits the ultrabasic vegetation. An experiment on Agrostis vinealis in simulated soil solutions showed that a gabbro (non-ultrabasic) clone had a higher R.G.R. (relative growth rate), even at the higher of two experimental Mg/Ca quotients, than two peridotite (ultrabasic) clones and was moreover not significantly affected by the higher nickel concentration used. It is concluded that the low vegetation cover on the skeletal soils is maintained by low soil nutrients which might interact with the coarsely sandy texture in exacerbating the effects of periodic drought and frost heaving. There is no unequivocal evidence for plant toxicities associated with high magnesium or nickel in the Rhum soils.     

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.     

The core microbiome bonds the Alpine bog vegetation to a transkingdom metacommunity

Bog ecosystems fulfil important functions in Earth's carbon and water turnover. While plant communities and their keystone species Sphagnum have been well studied, less is known about the microbial communities associated with them. To study our hypothesis that bog plants share an essential core of their microbiome despite their different phylogenetic origins, we analysed four plant community plots with 24 bryophytes, vascular plants and lichen species in two Alpine bogs in Austria by 16S rDNA amplicon sequencing followed by bioinformatic analyses. The overall bog microbiome was classified into 32 microbial phyla, while Proteobacteria (30.8%), Verrucomicrobia (20.3%) and Planctomycetes (15.1%) belonged to the most abundant groups. Interestingly, the archaeal phylum Euryarcheota represented 7.2% of total microbial abundance. However, a high portion of micro‐organisms remained unassigned at phylum and class level, respectively. The core microbiome of the bog vegetation contained 177 operational taxonomic units (OTUs) (150 526 seq.) and contributed to 49.5% of the total microbial abundance. Only a minor portion of associated core micro‐organisms was host specific for examined plant groups (5.9–11.6%). Using our new approach to analyse plant–microbial communities in an integral framework of ecosystem, vegetation and microbiome, we demonstrated that bog vegetation harboured a core microbiome that is shared between plants and lichens over the whole ecosystem and formed a transkingdom metacommunity. All micro‐ and macro‐organisms are connected to keystone Sphagnum mosses via set of microbial species, for example Burkholderia bryophila which was found associated with a wide spectrum of host plants and is known for a beneficial plant–microbe interaction.     

Plant and lichen colonization in an asbestos mine: Spontaneous bioattenuation limits air dispersion of fibres

Abstract

Plant and lichen phytosociological studies describe the different dynamic stages of colonization. This approach has been applied to the Balangero asbestos mine, the most important of Western Europe up to 1990, which is a potential source for the air-dispersion of carcinogenic fibres. Vegetation relevés and maps have shown that plants and lichens develop spontaneously on the asbestos-rich substrates. Early colonization stages with low-covering hyperaccumulators, such as Thlaspi sylvium and Minuartia laricifolia, and with Thymus alpestris and T. cfr. humifusus, are followed, some decades later, by mature plant communities, which completely cover the asbestos-rich debris, thereby limiting the dispersion of fibres. Lichen colonization, even when limited to low covering early stages with pioneer crustose species, such as Scoliciosporum umbrinum and Candelariella vitellina, and young foliose thalli of Xanthoparmelia tinctina, is important whenever asbestos veins are exposed on serpentinite blocks and walls. Plants and lichens can be considered as bioattenuation (spontaneous bioremediation) agents in ecological recovery.     

Plant Communities in Multi-Metal Contaminated Soils: A Case Study in the National Park of Alta Murgia (Apulia Region - Southern Italy)

A phytosociological study was conducted in the National Park of Alta Murgia in the Apulia region (Southern Italy) to determine the adverse effects of metal contamination of soils on the distribution of plant communities. The phytosociological analyses have shown a remarkable biodiversity of vegetation on non-contaminated soils, while biodiversity appeared strongly reduced on metal-contaminated soils. The area is naturally covered by a wide steppic grassland dominated by Stipa austroitalica Martinovský subsp. austroitalica. Brassicaceae such as Sinapis arvensis L. are the dominating species on moderated contaminated soils, whereas spiny species of Asteraceae such as Silybum marianum (L.) Gaertn. and Carduus pycnocephalus L. subsp. pycnocephalus are the dominating vegetation on heavily metal-contaminated soils. The presence of these spontaneous species on contaminated soils suggest their potential for restoration of degraded lands by phytostabilization strategy.     

Vegetation at the Limits for Vegetation: Vascular Plants, Bryophytes and Lichens in a Geothermal Field

The effects of the chemical and physical factors associated with geothermal activity on plant community structure and composition were investigated in one of the largest geothermal fields of central Italy. The study site was located in the geothermal area of Sasso Pisano – Monte Rotondo Marittimo, Southern Tuscany. The percentage cover of all vascular plant, bryophyte and lichen species was estimated within 119 circular plots of 0.25 m². For each plot the soil pH, soil temperature, slope, aspect, incident radiation, soil nitrogen and carbon contents were also quantified. Two vascular plants, Calluna vulgaris and Agrostis castellana, were found to be the most widespread species tolerating the harshest conditions in terms of low soil pH and high soil temperature. The most widespread cryptogam species was Hypnum cupressiforme. Spatially autoregressive models showed that a proportion of about 41–51% of the variance in species richness of one group of plants (vascular or cryptogamic plants) could be modelled by using three or four uncorrelated environmental factors respectively (soil temperature, soil nitrogen and soil C/N ratio and these three plus incident radiation). For the total number of species (vascular and cryptogamic plants), the variance explained by the same three uncorrelated variables was about 57%. This study evidenced a strong environmental control of community composition and species richness, in a site subjected to extreme soil values of soil pH and temperature. The dominance of vascular over cryptogamic vegetation in this geothermal site can be explained by the combined effects of geothermal stress (low soil pH and high soil temperature) with the summer drought typical of the Mediterranean climate.     

新疆阿勒泰山两河源自然保护区地面生地衣的物种多样性

阿勒泰山地是我国著名水系额尔齐斯河和乌伦古河的发源地,该山地地衣植物的研究在中国乃至中亚都占有非常重要的科学地位。新疆阿勒泰山两河源自然保护区位于阿勒泰山东段,气候在新疆最为潮湿,其地衣植物种类十分丰富。作者在该保护区选择6个植被带类型,即山地荒漠带、山地草原带、针阔混交林带、针叶林带、亚高山草甸带、高山草甸带,研究了其地面生地衣植物的物种多样性特征。结果表明:阿勒泰山两河源自然保护区地衣植物区系成分丰富而且复杂,共有地面生地衣植物5科6属46种,以石蕊科种类最为丰富,约32种。该地区不同植被带类型下地面生地衣植物物种的S?renson相似性系数在0.200–0.739之间,以针阔混交林和针叶林带的相似性为最高(0.739),针阔混交林和高山草甸带地衣植物物种相似性最低(0.200)。各植被带地衣优势种中白边岛衣(Cetrarialaeuigata)、林鹿蕊(Cladoniaarbuscula)、佐木氏珊瑚枝(Stereocaulonsasakii)、鳞地卷(Peltigeralepido-phora)、喇叭粉石蕊(Cladoniachlorophaea)、东方鹿蕊(Cladinagrisea)等的重要值在0.5以上,其余优势种的重要值均在0.5以下;山地森林带地衣植物物种多样性最为丰富,在整个阿勒泰山两河源自然保护区地面生地衣植物群落中占据优势地位,为该地区地衣植物多样性的分布中心,是地衣植物多样性保护的关键地区。