DCA Ordination Research Articles

Integrated palaeoecological and historical data in the service of fine‐resolution land use and ecological change assessment during the last 1000 years in Rõuge, southern Estonia

AbstractAims Our aim is to reconstruct decadal scale development of historical landscapes during the last 1000 years by means of fossil pollen analysis of annually laminated lake sediments, and detailed historical maps and documents.Location Lake Rõuge Tõugjärv (Estonia), a small lake with annually laminated lake sediments situated in a dense prehistoric setting.Methods The chronology of the palaeodata is based on the annual laminations supported by AMS 14C and 210Pb dating and 137Cs, 241Am, and spheroidal carbonaceous particle marker horizons. The time‐scale and resolution allows fine sampling (the pollen samples generally comprise 3.5 years) and vegetation change reconstruction. Relevant source area of pollen (RSAP) of the lake was estimated, and the statistical zonation, rate of change, palynological richness, and DCA and PCA ordinations were generated on the basis of the pollen data. The historical calibration data set (maps, numerical information on population, domestic stock, farmland division, etc.) is based on archival material preserved in the Estonian Historical Archives.Results The topmost part (0–180 cm) of the sediment column of Lake Rõuge Tõugjärv, covering the last 1000 years, is visibly laminated carbonaceous gyttja. The varve chronology extends from ad 2000 to ad 1339, with a cumulative ± 9‐year error estimate. Beyond this the chronology is extrapolated using the 14C date and varve age–depth estimations. The simulation of the RSAP of Lake Tõugjärv shows that the major portion of the pollen loading originating from local vegetation is derived from plants growing within 2000 m of the sampling site. The pollen record divides into five statistically significant subgroups, which fall on the PCA plot into three clusters reflecting the general openness–closedness of the landscape. During the period between ad 1000 and 1200 (RT 1) the Rõuge area was generally wooded with birch, spruce and pine forests. The advancement of extensive farming gradually opened up the landscape between ad 1200 and 1650 (RT 2 and RT 3). The maximum openness of the landscape was reached between ad 1650 and 1875 (RT 4), with the most open period in the late eighteenth century. Historical maps from 1684 and 1870–99 and available quantitative data on population, domestic stock, farmland division, etc. show the same trend. The pollen data covering the last 125 years, and maps from 1935 and 1995, show the reduction of arable land in RSAP of the lake under investigation and the reduction of open land to an extent comparable with the end of the seventeenth century.Main conclusions The formation and development of the cultural landscape at Rõuge over the last 1000 years is characterized by rapid changes in floristic richness and rates of vegetation change attributed to certain historic processes in the RSAP. Five phases of landscape and social development are clearly distinguished during the last 1000 years. The decadal scale vegetation response to human‐induced forcing agrees with historical maps and documents and could be used for past landscapes prior to the period with solid historical data.

Bryophyte and vascular plant responses to base-richness and water level gradients in Western CarpathianSphagnum-rich mires

We investigated the importance of water chemistry and water regime for vascular plant and bryophyte species distribution in Western Carpathian mires dominated bySphagnum. Seventy-seven small circle plots distributed across a wide geographical area, a wide range of mineral richness and all possible microtopographical features were sampled in terms of species composition, physical-chemical water properties and water regime during one growing season. Both water chemistry and water regime were found to be important factors for vegetation composition. Bryophytes reflected only one clear gradient, connected to base-richness (pH, conductivity) and maximal water-level, whereas three different environmental gradients determined the occurrence of vascular plants: water-level amplitude, base-richness and an indistinct gradient presumably connected to peat layer thickness. When the entire data set was subjected to DCA ordination, the first resulting axis was governed by the bryophyte subset, whereas the second one was governed by the vascular plant subset. The species density of vascular plants was positively correlated with pH and conductivity. On the contrary, bryophyte species density showed no relationship to environmental factors. We further compared the pH values measured in groundwater and in water squeezed from bryophytes from the same plot; these plots were distributed along the base-richness gradient. Only in the acidic mires did the use of squeezed-water chemistry in the analyses give results similar to the use of groundwater pH. Further, we found thatSphagnum species with a similar response to the base-richness gradient had differentiated niches with respect to the water level gradient and vice versa.Sphagnum contortum andS. warnstorfii exhibiting the same demands for groundwater pH were segregated along the gradient of maximum water level. An analogous pattern was detected for acidophilous speciesSphagnum magellanicum andS. papillosum.

Diversity, floristic and structural patterns of cerrado vegetation in Central Brazil

The cerrado has been identified as one of the richest and most threatened biomes of the world, but few phytogeographical studies have been undertaken in the region. A total of 70 land systems based on climate, landscape and soils have been identified in the region, but it remains to be seen if the distribution and structure of the plant communities support these divisions. The aim of this work was to compare the floristic and structural similarity of cerrado sensu stricto within and between three physiographic units, named Pratinha, Veadeiros and Sao Francisco, which contain six land systems in central Brazil and cover 10 degrees of latitude and five degrees of longitude. The woody vegetation of 15 selected sites of the cerrado sensu stricto physiognomy was surveyed under a standardized methodology. The number of species per site varied from 55 to 97, with most sites having around 60 to 70 species, and Shannon´s diversity indices ranged from 3.44 to 3.73, with most sites around 3.5 suggesting high alpha diversity. Sorensen´s floristic similarity index was high, with all Figures above 0.5 between the sites in the same land system in each physiographic unit but low between sites in different land systems in the Veadeiros. Czekanowski similarity indices were lower than Sorensen’s in the comparisons due to a high structural differentiation between the sites. There is a large overlap in species occurrence in the sites but the size of their populations is very different at each site. Therefore, the high beta diversity is mostly due to differences in abundance of species between sites. The sites were separated by physiographic units, considering the first three divisions of TWINSPAN classification. The first axis of DCA ordination showed a gradient going from the cerrado on deep soils in Pratinha, through to those on sandy soils in Sao Francisco and ending on the shallower soils of the Veadeiros. Land systems conformed well with the floristic and structural variations of the vegetation, indicating their potential use in designing a network of conservation areas in the cerrado region and as a basis for decision-making on management.

Subsistence farming and conservation constrains in coastal peat swamp forests of the Kosi Bay Lake system, Maputaland, South Africa

Maputaland is a region of exceptionally rich biodiversity located in the north-eastern corner of Kwazulu-Natal and forms the southern most tip of the Mozambique coastal plain. It can be considered as the most southern end of the tropics in Africa and consequently many tropical species reach their southern most distribution boundary here. Maputaland is the largest peat containing region in South Africa with 60 % of the country’s peat present therein. Coastal peat swamps forests are more abundant in Maputaland than anywhere else in South Africa, but remain poorly studied as far as their vegetation composition, structure, functioning, and the nature and impact of exploitation on them are concerned. In this ongoing study an initial vegetation and environmental dataset of May 2003 was used to assess the impact of subsistence farming, predominately with madumbes (Colocasia esculenta) and bananas (Musa xparadisiaca), on coastal peat swamp forests. A TWINSPAN numerical classification resulted in the identification of 10 vegetation groups, exhibiting a gradient from pristine to highly disturbed peat swamp forests. The pristine peat swamp forest group is separated on the degree of wetness, ranging from wet to dry peat swamp forests, while the highly disturbed group is divided according to the presence or absence of active gardening. A Detrended Correspondence Analysis (DCA ordination) determined anthropogenic practices involving tree felling and peat draining as the main factors responsible for peat swamp forest habitat modification. The change in swamp forest structure and peat hydrology critically threatens the continued existence and ecological functioning of these systems. This impacts negatively on habitat and biodiversity loss and will eventually deprive the rural community of a sustainable gardening environment, bring about a change in the lake system’s nutrient balance, and even reduce available sources of clean and fresh water. The situation poses an urgent conservation challenge for the conservation agency and local community whose livelihood is intricately interwoven and pivoted around their peat swamp forest environments. Before progress can however be made trust needs to be established between the different stakeholders, looking beyond solutions of complete exclusion, but rather to mutual cooperation, involving practices such as wise use gardening management.

Development of vegetation in managed Scots pine ( Pinus sylvestris L.) stands in an oak–lime–hornbeam forest habitat

A regeneration process of oak–lime–hornbeam community ( Tilio-Carpinetum typicum Tracz., 1962), developing after a clear cutting followed by a plantation of Scots pine stand ( Pinus sylvestris L.), is analysed. A study material comes from managed and strictly protected (The Białowieża National Park) part of the Białowieża forest. A series of managed Scots pine stands, comprising developmental phases from thicket to old-growth, is compared with an analogical series of managed pedunculate oak stands – Quercus robur L. (in case of managed stands considered to be in a harmony with a target tree species composition for a given site type), as well as with a series of natural (strictly protected since ca. 80 years) stands, occurring in the Białowieża National Park. The three experimental variants, occurring in similar site conditions, are compared with regard to the vegetation and stand structure, as well as to the chemical properties of two uppermost soil layers. Analysis of vegetation includes, i.a., calculation of a species richness, a share of species typical for Scots pine and oak–lime–hornbeam forest, ecological indicator values, as well as an analysis of overall floristic similarity by means of DCA ordination method. Soil conditions are studied by analysis of, i.a. pH in KCl and base saturation. It is concluded that the development of Scots pine stands on the site of oak–lime–hornbeam community, under conditions of the Białowieża forest, has not brought about neither a persistent site degradation nor degeneration of the community. Some differences between pine and oak managed stands occurring on the site of oak–lime–hornbeam forest in the vegetation and chemical properties of the topsoil are generally confined to the comparatively short time period; from thicket to high polewood stages. The acidifying influence of pine needle litter on the site and ground layer vegetation is balanced, or even overridden, by processes associated with the regeneration of the phytocoenosis, first of all by the influence (shading and litter fall) of a rapidly developing hornbeam ( Carpinus betulus L.) layer. Intensive regeneration processes of natural oak–lime–hornbeam community, supported by site eutrophication, caused by the input of air-borne chemicals and climate warming, lead to the growing discrepancy between Scots pine stands and site conditions. The results obtained suggest that the restoration of more natural conditions in the replacement Scots pine stands can be achieved, in a greater extent than previously assumed, by a means of spontaneous regeneration processes.

DISTURBANCE SEVERITY AND COMMUNITY RESILIENCE IN A BOREAL FOREST

We studied the resilience of southeastern Norwegian old-growth Picea abies forest floor vegetation to experimental disturbance. Five treatments, differing in depth of removal of vegetation and soil layers and making up a gradient in disturbance severity, and three controls, were replicated 10 times. The experiment was analyzed with respect to the full species composition before and for seven years after treatment. The soil-buried propagule bank and local environmental conditions were recorded before treatment. Total cover of vascular plants and bryophytes and lichens increased slowly after treatment and was still below pre-disturbance levels after seven years. The rate of succession, measured as change in floristic dissimilarity between recordings made in successive years, declined with time for all treatments. The magnitude of vegetation change was strongly influenced by disturbance severity. DCA ordination revealed a main gradient in species composition from undisturbed forest floor to severely disturbed vegetation three years after disturbance, while in the fourth year, the direction of vegetation change turned in the direction of pre- disturbance positions. The turning point represented the maximum abundance of pioneer species (e.g., Luzula pilosa and Pohlia nutans) relative to dominant species before the disturbance (e.g., Dicranum majus and Hylocomium splendens). The return to pre-distur- bance positions from the fourth year was, however, slow and will probably take 5-25 more years to be completed if current trends continue. DCA ordination revealed two additional, interpretable, gradients in vegetation; one related to pulses of regeneration from the soil- buried propagule bank; the other represented a gradient in pre-disturbance environmental conditions. We demonstrate that one vegetation gradient related to time after disturbance is insufficient to account for the full complexity of revegetation processes following dis- turbance.

Inter-annual variation in the soil seed bank of flood-meadows over two years with different flooding patterns

Persistent soil seed banks are presumed to play a significant role in bridging and exploiting the effects of major flood disturbances in riparian systems. However, presently there is little empirical data on the correlation between flooding and seed bank dynamics. The objective of this study was to assess the impact of inter-annual flooding variation on soil seed bank dynamics in flood-meadows. We analysed seed bank composition at 46 plots along the northern Upper Rhine River, Germany, after two periods with contrasting flooding conditions (1996–1997: low and rare flooding; 1998–1999 high and very frequent flooding). Between both sampling occasions the total number of seedlings emerging from the seed bank decreased by 50% and average species-richness per sample by 30%, irrespective of the sampling depth. Similar decline occurred in mesophytes and wetland species as well as over different functional groups, with the exception of legumes. Considerable compositional changes in the seed bank were also indicated by shifts in DCA ordination and by the comparison of similarity matrices from both years with the Mantel test. The Mantel test also confirmed that compositional changes were more pronounced in the seed bank than in aboveground vegetation. There was poor correlation between the decline in total seed densities and species in the soil seed bank and environmental variables such as flooding duration and ecological groupings such as floodplain compartment and seed bank community types. Further distinct patterns of decline and persistence were evident only at the species level. While 21 species displayed a significant decline, only two species increased. Annual arable weeds and perennial ruderals with high temperature or nutrient requirements to break dark dormancy were amongst the most significantly declining species. In contrast, there was no decline in typical winter annuals and certain perennials that preferably germinate in autumn and fall into dormancy at the beginning of the warm period. Generally, differences in germination requirements and dormancy cycles of species gave the best explanation for the patterns of decline and persistence after intense flooding. Given these findings, the heavy depletion of the persistent soil seed bank we observed is most likely attributed to a post-flood germination flush due to very favourable recruitment conditions prevailing during the draw-down period after early summer flooding in 1999. The results of our study suggest that persistent soil seed banks are of outstanding importance to bridge and exploit the highly variable hydrological conditions that are typical of flood-meadows. Thus, they play a significant role in maintaining the floristic diversity of this habitat type over time and space.

The vegetation of three localities of the threatened butterfly species <i>Chrysoritis aureus</i> (Lepidoptera: Lycaenidae)

The vegetation and habitat characteristics of three localities of Chrysoritis aureus at theAlice Glockner Nature Reserve, Suikerbosrand Nature Reserve and Malanskraal farmnear Heidelberg in South Africa, were compared. A numerical classification technique,TWINSPAN, was used and refined by using Braun Blanquet procedures to classify thevegetation at the different localities. A DCA ordination was applied to confirm theresults of the classification. Although the general vegetation structure at the three habitats of Chrysoritis aureus were found to be similar, marked differences in the floristiccomposition were evidenced. A different sub-community, compared to the vegetation atSuikerbosrand and Alice Glockner Nature Reserve, was recorded at the Malanskraalhabitat of Chrysoritis aureus. These differences in floristic composition, but with similarities in vegetation structure, indicate the possible importance of fire for the ultimatesurvival of these butterflies in the Rocky Highveld Grassland. The host plant ofChrysoritis aureus, Clutia pulchella, collected at Malanskraal differed markedly andconsistently in their morphology, compared to the individuals from the habitats atSuikerbosrand and Alice Glockner Nature Reserve. These differences in the floristiccomposition of one of the habitats compared to the others, raise research questions concerning the butterfly metapopulation structure, since the subpopulations seem to beadapted to slightly different habitat conditions. The variation in the habitat suggests thatthe “last remaining locality scenario” for other localised butterflies in South Africa, suchas Orachrysops niobe, needs to be redressed. Management strategies are addressedwhile the importance of conserving rare, localised ecosystems are highlighted by thephytosociological study

Large-scale ordination and gradient analysis of salt-marsh communities in the Netherlands in the light of the Dutch National Vegetation Classification

In the development of the Dutch National Vegetation Classification, little emphasis was placed on ordination or gradient analysis. The current study provides a national-scale ordination analysis of salt-marsh communities in the Netherlands and presents it in the context of the National Classification. A series of 4 DCA ordinations derived from synoptic tables of 21 salt-marsh communities, each varying in their emphasis on dominant species, showed that the importance of dominance vs. overall assemblages of species in classifying communities varies with the communities in question: for species-poor communities such as the Spartinetea, T hero-Salicornietea, and portions of the Asteretea tripollii (Puccinellion maritimae and Puccinellio-Spergularion salinae), dominant species were critical in distinguishing communities while for more diverse communities (the Armerion maritimae and the Saginetea maritima of the Astereteae tripolii), total floristic composition was important and over-emphasis on dominant species obscured differences between several communities. Ordination scores were strongly correlated with mean Ellenberg indicator values for salinity and pH, but only weakly with moisture values. In this respect, Ellenberg values do not appear to reflect the critical conditions of duration and timing of flooding in Dutch salt-marsh vegetation. Ordinations based on both synoptic tables and on individual releves were carried out to study the validity of previously-reported classifications of several related associations. The analysis resolved the question of whether the Suaedetum maritimae is best placed in the Thero-Salicornietea or in the Cakiletea maritimae; it was clearly associated with the Thero-Salicornietea. As for the question of whether certain related associations better belong within the Lolio-Potentillion or within the saltmarsh alliance Armerion maritimae, both options are possible from the point of view of this study. The approach used here of ordinating synoptic tables to locate possible overlap between syntaxa and then using ordinations of individual releves within these to examine the problem areas further provides a useful method for verifying and revising classifications at the national level.

Species response curves along environmental gradients. A case study from SE Norwegian swamp forests

Abstract. Vegetation science has relied on untested paradigms relating to the shape of species response curves along environmental gradients. To advance in this field, we used the HOF approach to model response curves for 112 plant species along six environmental gradients and three ecoclines (as represented by DCA ordination axes) in SE Norwegian swamp forests. Response curve properties were summarized in three binary response variables: (1) model unimodal or monotonous (determinate) vs. indeterminate; (2) for determinate models, unimodal vs. monotonous and (3) for unimodal models, skewed vs. symmetric. We used logistic regression to test the influence, singly and jointly, of seven predictor variables on each of three response variables. Predictor variables included gradient type (environmental or ecocline) and length (compositional turnover); species category (vascular plant, moss, Sphagnum or hepatic), species frequency and richness, tolerance (the fraction of the gradient along which the species occurs) and position of species along each gradient. The probability for fitting a determinate model increased as the main occurrence of species approached gradient extremes and with increasing species tolerance and frequency and gradient length. Appearance of unimodal models was favoured by low species tolerance and disfavoured by closeness of species to gradient extremes. Appearance of skewed models was weakly related to predictors but was slightly favoured by species optima near gradient extremes. Contrary to the results of previous studies, species category, gradient type and variation in species richness along gradients did not contribute independently to model prediction. The overall best predictors of response curve shape were position along the gradient (relative to extremes) and tolerance; the latter also expressing gradient length in units of compositional turnover. This helps predicting species responses to gradients from gradient specific species properties. The low proportion of skewed response curves and the large variation of species response curves along all gradients indicate that skewed response curves is a smaller problem for the performance of ordination methods than often claimed. We find no evidence that DCA ordination increases the unimodality, or symmetry, of species response curves more than expected from the higher compositional turnover along ordination axes. Thus ordination axes may be appropriate proxies for ecoclines, applicable for use in species response modelling.

Succession in sub‐boreal forests of West‐Central British Columbia

Abstract. Structural and compositional changes were analysed over the course of 400+ yr of post‐fire succession in the sub‐boreal forests of west‐central British Columbia. Using a chronosequence of 57 stands ranging from 11 to 438 yr in age, we examined changes in forest structure and composition with complementary PCA and DCA ordination techniques. To determine stand ages and timing of tree recruitment, approximately 1800 trees were aged. Most early successional forests were dominated by Pinus contorta, which established rapidly following fire. Abies lasiocarpa and Picea glauca × engel‐mannii were also able to establish quickly, but continued to establish throughout the sere. Few Pinus contorta survived beyond 200 yr, resulting in major changes in forest structure. In some stands P. contorta never established, which led to considerable variation among stands less than 200 yr old. The oldest forests converged on dominance by Abies lasiocarpa. Vascular plant diversity decreased during succession whereas canopy structure became more complex as gap dynamics developed. Although these sub‐boreal forests contain few tree species, successional changes were pronounced, with structure changing more than composition across the chronosequence.

HABITAT AFFINITIES OF SPIDERS LIVING NEAR A FRESHWATER POND

Habitat ranges of ground-dwelling spiders were studied by pitfall trapping in and around a freshwater pond during the spring and summer of 1998 in central Alberta, Canada. Sixty species from 14 families were collected, and catches of several species suggested distinct habitat affinities along transects between the pond and adjacent terrestrial habitats. Variation in the catches of Pirata piraticus (Clerck 1757), Pardosa moesta Banks 1892, Pardosa fuscula (Thorell 1875), and immature Pirata species were partially explained by soil moisture at trap locations extending from the shore. We devised a “floating” pitfall trap that captured several species, including mature and immature Dolomedes triton (Walckenaer 1837), Pirata piraticus, and other immature Lycosidae, directly on the water surface. A DCA ordination revealed distinct spider assemblages were associated with three habitat types: 1) the water surface; 2) the moist habitats closely associated with the water's edge; and 3) the drier, terrestrial grassland habitats located >2 m from the shore. A new, more inclusive definition of semi-aquatic spiders was developed, based on knowledge about both male and female activity near the shore, and affinities towards soil moisture. Thus, Pirata piraticus, Dolomedes triton, and Pardosa fuscula were defined as semi-aquatic spiders.

Species response curves along environmental gradients. A case study from SE Norwegian swamp forests

Vegetation science has relied on untested para- digms relating to the shape of species response curves along environmental gradients. To advance in this field, we used the HOF approach to model response curves for 112 plant species along six environmental gradients and three ecoclines (as represented by DCA ordination axes) in SE Norwegian swamp forests. Response curve properties were summarized in three binary response variables: (1) model unimodal or monotonous (determinate) vs. indeterminate; (2) for determinate models, unimodal vs. monotonous and (3) for unimodal models, skewed vs. symmetric. We used logistic regression to test the influ- ence, singly and jointly, of seven predictor variables on each of three response variables. Predictor variables included gra- dient type (environmental or ecocline) and length (compo- sitional turnover); species category (vascular plant, moss, Sphagnum or hepatic), species frequency and richness, toler- ance (the fraction of the gradient along which the species occurs) and position of species along each gradient. The probability for fitting a determinate model increased as the main occurrence of species approached gradient extremes and with increasing species tolerance and frequency and gradient length. Appearance of unimodal models was favoured by low species tolerance and disfavoured by closeness of species to gradient extremes. Appearance of skewed models was weakly related to predictors but was slightly favoured by species optima near gradient extremes. Contrary to the results of previous studies, species category, gradient type and variation in species richness along gradients did not contribute inde- pendently to model prediction. The overall best predictors of response curve shape were position along the gradient (rela- tive to extremes) and tolerance; the latter also expressing gradient length in units of compositional turnover. This helps predicting species responses to gradients from gradient spe- cific species properties. The low proportion of skewed re- sponse curves and the large variation of species response curves along all gradients indicate that skewed response curves is a smaller problem for the performance of ordination meth- ods than often claimed. We find no evidence that DCA ordina- tion increases the unimodality, or symmetry, of species re- sponse curves more than expected from the higher compo- sitional turnover along ordination axes. Thus ordination axes may be appropriate proxies for ecoclines, applicable for use in species response modelling.

Succession in sub-boreal forests of West-Central British Columbia

Abstract Structural and compositional changes were analysed over the course of 400+ yr of post-fire succession in the sub-boreal forests of west-central British Columbia. Using a chronosequence of 57 stands ranging from 11 to 438 yr in age, we examined changes in forest structure and composition with complementary PCA and DCA ordination techniques. To determine stand ages and timing of tree recruitment, approximately 1800 trees were aged. Most early successional forests were dominated by Pinus contorta, which established rapidly following fire. Abies lasiocarpa and Picea glauca ×engelmannii were also able to establish quickly, but continued to establish throughout the sere. Few Pinus contorta survived beyond 200 yr, resulting in major changes in forest structure. In some stands P. contorta never established, which led to considerable variation among stands less than 200 yr old. The oldest forests converged on dominance by Abies lasiocarpa. Vascular plant diversity decreased during succession whereas canop...

Classification of ultracontinental boreal forests in central Yakutia

Using the Braun-Blanquet approach, five associations of boreal forests were distinguished in central Yakutia, the most continental part of eastern Siberia. Ecological features of the syntaxa were explained with the use of the DCA ordination of 50 relev?s. All available data from eastern Siberia were involved in the study for syntaxonomic analysis. Central Yakutian boreal forests were classified into two classes: Rhytidio-Laricetea sibiricae KOROTKOV et ERMAKOV 1999 - ultracontinental light coniferous hemiboreal forests, and Vaccinio-Piceetea BR.-BL. in BR.-BL. et al. 1939 - typical coniferous taiga forests of northern Eurasia. A new concept of higher syntaxonomic units of the class Vaccinio-Piceetea in eastern Siberia has been developed. Three orders represent the diversity of taiga forests: (1) Cladonio-Vaccinietalia KlELLAND-LUND 1967 (with alliances Hieracio umbellati-Pinion sylvestris ANENKHONOV et CHYTRY 1998 and Sax?frago bronchialis -Pinion sylvestris all. nov.) - light coniferous boreal forests occurring in dry and moderately dry oligotrophic sites in various climatic sectors of Northern Eurasia; (2) Lathyro humilis-Laricetalia cajanderi ord. nov. (with alliances Aulacomnio acuminati-Laricion cajanderi all. nov. and Rhododendro daurici-Laricion gmelinii all. nov.) - zonal boreal forests with xeric elements, which are typical of regions of northern Asia with cold, dry ultracontinental climate; (3) Ledo-Laricetalia cajanderi ord. prov. (with alliance Ledo-Laricion cajanderi prov.) - North Eurasian boreal forests occurring in cold sites with excessive soil moisture, sometimes water-logged. Phytogeography and ecology of these orders are discussed in comparison with other regions of northern Asia.

Characteristics, classification and ordination of riparian plant communities in the Three-Gorges areas

Sixteen different vegetation types of grassland and shrubland were selected to study the component and diversity of plant species of riparian plant communities along main channel in the Three-Gorges areas. Species richness (s), Simpson index (D), and Shannon-Weiner index (H) were used to study the biodiversity and the hierarchical classification was carried out by the methods of TWINSPAN and DCA ordination. The results showed that the components of flora were complex and dominated by the temperate type in the riparian plant communities. Species diversity was not different between the communities, but Shannon-Weiner indexes of different layers in some grassland were significantly different. TWINSPAN and DCA indicated that riparlan plant communities distributed along the gradient of moisture.

Conservation biology of an endangered grassland plant species, Pseudorchis albida, with some references to the closely related alpine P. straminea (Orchidaceae)

Pseudorchis albida s.s. is today a rather rare grassland orchid with a declining distribution in Scandinavia, as well as in other parts of Europe. This paper presents (a) ecological site descriptions from 30 Norwegian and Swedish sites, and (b) vegetation analyses from five Swedish populations of the closely related, alpine P. straminea, which enable some comparisons between taxa. A Detrended Correspondence Analysis ordination of vegetation data separated sites of P. albida rather well according to their geographical location. The Swedish south-west coast sites were particularly distinct. The Norwegian mid inland region constituted a transition zone between sites from the Norwegian west coast and sites from the Swedish eastern mountains. About 10 vascular plant species form a core group, common to nearly all sites. About 150 species occur in lower total frequencies than 50%. It is concluded that P. albida can occur in a wide array of plant communities. A Kendall correlation matrix for environmental variables for the P. albida sites and the site’s scores along the three first axes in the DCA ordination showed significant correlations between altitude, soil-pH, grazing, precipitation, mowing, ignition loss, and soil-potassium, with vegetation clusters. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society, 2002, 139, 47–66

Distribution pattern of rare plants along riparian zone in Shennongjia Area

Due to the importance of riparian zone in maintaining and protecting regional biodiversity, increasingly more ecologists paid their attentions to riparian zone and had been aware of the important effects of riparian zone in basic study and practical management. In this study, 42 sampling belts (10 m×100m) parallel to the bank of Xiangxi River at different elevations in Shennongjia Area were selected to investigate the riparian vegetation and rare plants. 14 species of rare plants were found distributing in riparian zone, accounting for 42.4% of the total rare plant species in Shennongjia Area. The main distribution range of the 14 rare plant species was the evergreen and deciduous mixed broadleaved forest at elevation of 1200–1800 m, where, species diversity of plant community was the maximum at the moderate elevation. The analysis of TWINSPAN divided the 14 rare species into 3 groups against the elevation, namely low elevation species group, moderate elevation species group, and high elevation species group. The analysis of DCA ordination showed similar results to that of TWINSPAN. In the paper, the authors discussed the reasons forming the distribution pattern of rare plant species, and pointed out that the important function of riparian zone on rare plant species protection.

Regeneration by seeds in alpine meadow and heath vegetation in sub‐arctic Finland

Abstract. This paper compares the regeneration by seeds of heath and meadow and studies relationships between the floristic composition of phases in the regeneration pathway. Seed densities in the seed rain and seed bank as well as the densities of emerged seedlings in gaps and in closed vegetation were greater in the meadow than in the heath. In the heath, environmental constraints hindered seedling emergence almost completely so seeds accumulated in the seed bank. In the meadow, the decrease in the seed bank was due to high seedling emergence. Within both plant communities, seedling emergence in gaps and in closed vegetation was comparable. In the meadow, the seed rain and seedling emergence in gaps, as well as the seed bank and seedling emergence in gaps were positively correlated. Differences in seed and adult plant sizes were reasons for the low correlation between the standing vegetation and the other phases. In DCA ordination the first axis separated the phase of seedling emergence in closed vegetation and seed bank. The second axis separated the standing vegetation from the other phases. The structure of the seed rain was more heterogeneous than that of other phases. In the heath, the standing vegetation and the seed rain were positively correlated. The ordination of these phases reflected the patchiness of standing vegetation and the ability of the diaspores of Betula nana to disperse over long distances.

Regeneration by seeds in alpine meadow and heath vegetation in sub-arctic Finland

Abstract This paper compares the regeneration by seeds of heath and meadow and studies relationships between the floristic composition of phases in the regeneration pathway. Seed densities in the seed rain and seed bank as well as the densities of emerged seedlings in gaps and in closed vegetation were greater in the meadow than in the heath. In the heath, environmental constraints hindered seedling emergence almost completely so seeds accumulated in the seed bank. In the meadow, the decrease in the seed bank was due to high seedling emergence. Within both plant communities, seedling emergence in gaps and in closed vegetation was comparable. In the meadow, the seed rain and seedling emergence in gaps, as well as the seed bank and seedling emergence in gaps were positively correlated. Differences in seed and adult plant sizes were reasons for the low correlation between the standing vegetation and the other phases. In DCA ordination the first axis separated the phase of seedling emergence in closed vegetat...