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Mráz P. & Paule J. (2006): Experimental hybridization in the genus Hieracium s. str.: crosses between diploid taxa. – Preslia 78: 1–26.
The few attempts to produce artificial hybrids in the genus Hieracium s. str. have usually failed due to the use of polyploid parental taxa reproducing via agamospermy. Presented here for the first time are data on artificial hybridization in Hieracium s. str. which may help in understanding the microevolutionary processes resulting in the great morphological and genetic diversity in this genus. Diploid, sexually reproducing species (H. alpinum, H. pojoritense, H. transsilvanicum and two stable morphological types of H. umbellatum – of a low altitude and a high mountain type) were used as parent plants in experimental crosses. In most cases true hybrids, with intermediate morphology, were obtained. All the hybrids tested were diploid and produced a high amount of stainable pollen (65–92%). Hybrid progeny resulting from one cross exhibited a large range of morphological variation due to the combination of alleles from unrelated parental species. The percentage of welldeveloped achenes per capitulum, in capitula with at least one well-developed achene, in hybrids, ranged from 1.9 to 12.5% after free or controlled pollination, with an average of 4–5% per capitulum. Similar results (1.9–12.1%) were obtained from triple-cross hybrids. However, most of the capitula of hybrid progeny (either F1 or triple) were completely sterile after free or controlled pollination. Sterility is probably caused by genome incompatibility of unrelated parental taxa belonging to different sections. In two crosses, where strictly allogamous diploid plants of H. umbellatum (both morphotypes) were used as mother plants and F1 hybrids as pollen donors, some matroclinal progeny were obtained. This is a further example of the previously reported mentor effect. Diploid hybrids may be involved as pollen donors in gene flow as they produce uniformly sized and viable pollen. They are probably substantially less important as seed parents.

Kirschner J., Štěpánek J. & Klimeš L. (2006): Dandelions in Central Asia: A taxonomic revision of Taraxacum section Leucantha. – Preslia 78: 27–65.
A taxonomic revision of Taraxacum sect. Leucantha Soest is presented. Species in this section are mainly characterized by the pale bordered and appressed outer involucral bracts, achenes covered with subsparse coarse spinules, thick cylindrical cone and a relatively short, thicker rostrum, and often white or pale yellowish flowers. They occur in subsaline wet meadows and steppe depressions over a large area including Mongolia, South Siberia, NE, N and W China, Tibet, the Western Himalayas, Tadzhikistan, Kyrgyzstan and E and NE Kazakhstan. Eighteen species are recognized, seven of them described as new: Taraxacum niveum from the Altai and Dzhungaria, T. candidatum centred in Ladakh, Tadzhikistan and Kyrgyzstan, T. album from Kyrgyzstan, T. flavidum from Mongolia and Transbaikalia, T. occultum from East Mongolia, T. virgineum from Ladakh, India, and T. inimitabile from Gobi-Altai, Mongolia. An analysis of syntypes of the names T. dealbatum Hand.-Mazz. and T. sinense Dahlstedt is given. For the safe interpretation of the name T. luridum, epitype was designated. All the species are agamospermous but sexuality and diploidy is documented for a few Transbaikalian plants of the section Leucantha.

Jansová I. & Soldán Z. (2006): The habitat factors that affect the composition of bryophyte and lichen communities on fallen logs. – Preslia 78: 67–86.
The composition of cryptogam (bryophyte and lichen) communities on fallen logs was studied in two old-growth forests in the Czech Republic. Altogether, 85 species (22 liverworts, 44 mosses, and 19 lichens) were recorded. The presence and abundance of the different species on 350 logs was attributed to habitat factors (e.g. humidity, wood decay, wood softness, log diameter, bark cover, thickness of humus layer and tree species) that were recorded separately for each of the logs. The aim was to identify the factors significantly affecting the composition of cryptogam communities. For the different ecological groups of species (epiphytes, epixylic species, and ground flora) forwarded canonical correspondence analysis (CCA) selected thickness of humus layer and tree species as the factors explaining most variability. In addition, the extent of log surface covered by bark, humidity and log decay were selected as significant determinants of cryptogam community composition.

Havlová M. (2006): Syntaxonomical revision of the Molinion meadows in the Czech Republic. – Preslia 78: 129–136.
A syntaxonomical revision of meadows of the Molinion caeruleae Koch 1926 alliance in the Czech Republic is presented. Of ten associations reported previously for the Czech Republic only two were distinguished using the Cocktail method – Molinietum caeruleae Koch 1926 and Junco effusi-Molinietum caeruleae Tüxen 1954. The former occurs on more base-rich soils, while the latter is found in more acidic habitats and characterized by the occurrence of species of Nardus grasslands. Results of this classification were compared with classifications of Molinion meadows for other countries of Central Europe. Main environmental gradients responsible for variation in species composition of Czech Molinion meadows were revealed by detrended correspondence analysis. For interpretation of these gradients correlations with Ellenberg indicator values and altitude were used. The main gradient positively correlates with soil base status, continentality, temperature and nutrients, and negatively with altitude.

Lepší M. & Lepší P. (2006): Rubus kletensis, a new species from South Bohemia and Upper Austria. – Preslia 78: 103–114.
A new species of bramble, Rubus kletensis, of the section Corylifolii Lindley, series Sepincola (Focke) E. H. L. Krause occurring in South Bohemia and Upper Austria is described. The distance between the most distant localities exceeds almost 150 km. This distinct and relatively easily recognizable species grows in rather moist, eutrophic, synanthropic and sunny biotopes, and occurs most frequently in the vegetation of the class Galio-Urticetea, less frequently in that of the alliances Trifolion medii, Pruno-Rubion radulae, Sambuco-Salicion capreae, Berberidion and exceptionally in forest plantations and growths of pioneer saplings. A distribution map for this species and a list of all known localities are included, as well as a drawing of the species.

Vondrák J. & Prach K. (2006): Occurrence of heliophilous species on isolated rocky outcrops in a forested landscape: relict species or recent arrivals? – Preslia 78: 115–121.
Nineteen isolated rocky outcrops of different sizes, tops of which were covered with natural grassland vegetation, were studied in the forested submontane belt (630–1020 m a.s.l.) of the Šumava Mts in the southern part of the Czech Republic, Central Europe. The species of vascular plants present in the treeless sites at each locality were identified. Those species with an Ellenberg indicator value for light equal 6 or higher were considered to be heliophilous. The distance to the nearest secondary treeless area was measured. There were 43 heliophilous species (23%) recorded among the 184 species identified. The number of species and the number of heliophilous species varied independently of the altitude and extent of the treeless area on the rocky outcrops, but were significantly correlated only with the distance to man-made treeless areas. The highest number of heliophilous species was recorded within approximately 400 m from the nearest man-made treeless area. Although the relict occurrence of some of the heliophilous species on the rocky outcrops cannot be completely excluded, obviously most of the species colonized these localities from nearby secondary treeless areas since their creation in the Middle Ages.

Kropáč Z. (2006): Segetal vegetation in the Czech Republic: synthesis and syntaxonomical revision. – Preslia 78: 123–209.
A phytosociological synthesis of the segetal vegetation in the Czech Republic was performed using methods of the Zürich-Montpellier school. In total, 712 relevés made by the author in this country in 1955–2000 were classified, and 22 associations and one unranked community were distinguished. Each syntaxon is characterized by diagnostic species, documented by a synoptic table, and the syntaxonomy, structure, species composition, ecology, dynamics, distribution and variability of each syntaxon are commented on. Names are revised according to the rules of the International Code of Phytosociological Nomenclature. All syntaxa belong to the class Stellarietea mediae and associations are assigned to the orders Centaureetalia cyani (alliances Caucalidion lappulae, Fumario-Euphorbion, and Sherardion), Atriplici-Chenopodietalia (alliances Scleranthion annui, Polygono-Chenopodion polyspermi, Arnoseridion minimae, and Panico-Setarion), and Eragrostietalia (alliance Eragrostion).

Petřík P. & Wild J. (2006): Environmental correlates of the patterns of plant distribution at the meso-scale: a case study from Northern Bohemia (Czech Republic). – Preslia 78: 211–234.
The distribution of vascular plants in grid-cells and its relationship to the environmental correlates (driving factors) were studied using numerical methods (divisive classification and ordination). The first level of division in the classification distinguished forest and non-forest groups of grid-cells, and the second level four groups (containing predominantly species of base-rich forests at high altitudes, species of acidophilous mountain forests and small mountain grasslands, ruderal and meadows species at low altitudes, and species of thermophilous and basiphilous fringes and abandoned meadows). Within the study area, geographically consistent areas were delimited by correlating the groups, indicated by the divisive classification, with altitude and forest cover. Most differences in the Ellenberg indicator values for species in these groups for light, temperature, continentality, soil reaction and soil moisture were statistically significant. A number of variables were effective predictors (e.g. potential direct solar irradiation), physical geography (altitude, slope), land-cover (forest cover, area of urban zones) and geological bedrock were the key determinants of the species composition in the study area. However, even the most spatially correlated (according to Moran’s I measure) were the naturally contiguous variables such as topographical features (altitude, slope and aspect). Generally, the grid-cells at low altitudes contained more species due to the co-occurrence of man-made habitats with fragments of semi-natural habitats. A relatively large percentage of the variation (15.8%) was accounted for by the spatial structure of the data, the environmental factors explained 18.9%, but 65.3% of the floristic variance remained unexplained. The most spatially autocorrelated variables were also the most correlated with regard to species composition. However, the relatively high autocorrelation in the species data and their derivates had comparable or lower effect on species composition than the most autocorrelated environmental factors. The results were compared with those of other European studies, and possible bias due to the different ways of collecting and analysing data, and effect of different scales discussed.

Šumberová K., Lososová Z., Fabšičová M. & Horáková V. (2006): Variability of vegetation of exposed pond bottoms in relation to management and environmental factors. – Preslia 78: 235–252.
Species composition, structure and ecological characteristics of the vegetation of two pond types with different management, fishponds and storage ponds, in the Českobudějovická pánev basin (South Bohemia), were compared. A selection of 99 relevés from fishponds and 99 from storage ponds (small ponds used for the storage of marketable fish) made in 2000–2004 were analysed using direct and indirect ordination and ANOVA. The difference between storage ponds and fishponds was found to be more important than gradients correlated with temporal changes, soil moisture and mud depth. Storage ponds had a significantly higher mean number of species, bryophytes, archaeophytes and neophytes and beta-diversity. There were no significant differences in cover values, except of moss layer, which had significantly higher cover in storage ponds. Fishponds had significantly higher mean Ellenberg indicator values for light, continentality, moisture and nutrients. Oenanthe aquatica and Rumex maritimus are typical fishpond species and Amblystegium humile and Eleocharis palustris agg. typical storage pond species. The management of storage ponds is more varied and of different intensity than that of fishponds. It is assumed that management is a crucial factor determining the species richness and influencing the vegetation of these two habitats.

Neustupa J. & Šťastný J. (2006): The geometric morphometric study of Central European species of the genus Micrasterias (Zygnematophyceae, Viridiplantae). – Preslia 78: 253–263.
The relationships of 14 Central European species of the genus Micrasterias were analysed using landmark-based geometric morphometrics. The analysis of relative warps was used to depict the principal components of the variation in shape and cluster analysis to reveal the groupings of individual species within the genus. All the analysed cells were correctly placed in their appropriate species clusters on the basis of geometric morphometric data. The width of the polar lobe associated with depth of the incisions between lateral lobules is the dominant morphological trend in the data investigated.

Perglová I., Pergl J. & Pyšek P. (2006): Flowering phenology and reproductive effort of the invasive alien plant Heracleum mantegazzianum. – Preslia 78: 265–285.
Heracleum mantegazzianum is one of the most invasive species in the Czech flora. The present study describes its flowering phenology and assess the effectiveness of protandry in preventing selfing in this self-compatible species, describes the timing of flowering in a heavily invaded area of Slavkovský les (Czech Republic) and estimates fruit set in a large sample of plants, which provides reliable data on the often exaggerated fecundity of this species. The study of flowering phenology revealed that protandry is always effective only within individual flowers, where male and female flowering phases are completely separated. In contrast, anther dehiscence in some flowers can occasionally overlap with stigma receptivity in other flowers in the same umbel, providing an opportunity for geitonogamous (i.e. between-flower) selfing. Nevertheless, the potential for selfing in H. mantegazzianum is determined mainly by an overlap in the male and female flowering phases between umbels on the same plant; at least a short overlap between some umbels was observed in 99% of the plants at the Slavkovský les. Although the degree of protandry in H. mantegazzianum favours outcrossing, the opportunity to self may be of crucial importance for an invasive plant, especially if a single plant colonizes a new location. At Slavkovský les, flowering started within one week (from 20 to 27 June 2002) at all 10 sites. The duration of flowering of an individual plantwas on average 36 days,with maximum of 60 days, and increased significantly with the number of umbels on a plant. In the second half of August, the majority of the fruits were ripe and had started to be shed. The beginning of flowering of a plant was significantly negatively correlated with the number of umbels it had – the earlier a plant started to flower the more umbels it had produced. A significant negative relationship was also found between basal diameter and beginning of flowering; plants with large basal diameters started to flower earlier. An average plant at Slavkovský les produced 20,671 fruits. Of these, 44.6% were produced by the terminal umbel, 29.3% by secondary umbels on satellites, 22.6% by secondary umbels on branches and only 3.5% by tertiary umbels. The estimated fruit number of the most fecund plant was 46,470 – compared to an average plant, the proportional contribution of tertiary umbels increased relative to the primary umbel. This study revealed a significant positive relationship between fecundity and plant basal diameter. Although the results of this study indicate that the fecundity of this species is often overestimated in the literature, the number of fruits produced by H. mantegazzianum provides this invasive species with an enormous reproductive capacity.

Moravcová L., Pyšek P., Pergl J., Perglová I. & Jarošík V. (2006): Seasonal pattern of germination and seed longevity in the invasive species Heracleum mantegazzianum. – Preslia 78: 287–301.
We investigated the effects of different temperature regimes and dry storage on germination of H. mantegazzianum (Apiaceae, native to Caucasus) seeds in the laboratory and linked the results with studies of seasonal seed bank depletion in a common garden experiment and under field conditions. Seeds were collected at seven sites in the Slavkovský les region, Czech Republic, cold-stratified for 2 months and germinated at seven temperature regimes. Under all temperature regimes, fresh seeds germinated to significantly higher percentages than older (1, 2, 3 years) seeds. For all storage lengths, seeds germinated best at alternating day/night temperatures of 20/5 °C. The length of the germination period had a significant effect only at low constant temperatures of 2 and 6 °C, where germination percentage increased between 2 and 6 months. Seasonal germination exhibited a distinct pattern, with rapid depletion of seed bank by the first spring after seed burial. Non-dormant seeds were present in the soil early in spring and late in autumn. The higher summer temperatures prevented dormancy breaking and another cold period of at least two months below 10 °C was needed to bring non-germinated seeds out of dormancy. The results suggest that (1) seed dormancy of H. mantegazzianum was not completely broken until the first spring, but that some seeds re-enter or retain dormancy during high summer temperatures and that (2) the threshold needed for breaking the dormancy was achieved gradually during the cold autumn and winter months. However, in a small fraction of seeds the dormancy breaking process took several years. Of seeds buried in 10 different regions of the Czech Republic, on average 8.8% survived 1 year, 2.7% 2 years and 1.2% remained viable and dormant after 3 years of burial. The ability of even small fraction of H. mantegazzianum seeds to survive for at least 3 years can result in re-invasion of this species into controlled sites.

Kaplan Z. & Fehrer J. (2006): Comparison of natural and artificial hybridization in Potamogeton. – Preslia 78: 303–316.
The first attempt to artificially hybridize species of Potamogeton resulted in the hybrid P. perfoliatus × P. gramineus. The morphological features, reproductive behaviour and molecular markers of the offspring of this experimental hybridization were compared with those of the parental species and natural hybrids of the same assumed parentage. A phenotype corresponding to that of the natural hybrid P. × nitens was acquired from an experimental cross between P. perfoliatus and P. gramineus. All plants, both natural and artificial, of this hybrid were consistently sterile. They showed the ITS variants of both parental taxa, which is consistent with biparental inheritance of nuclear DNA. The experimental hybrid was used to test the maternal inheritance of chloroplast DNA in Potamogeton. Sequences of a chloroplast intergenic spacer (rpl20- rps12) were identical with those of the female parent. Then, the directions of the crosses resulting in the natural hybrids were investigated. Of five natural populations of P. × nitens, P. gramineus was the maternal parent of two and P. perfoliatus of three populations. The frequency of hybridization events and rise of hybrids are discussed.

Filipová L. & Krahulec F. (2006): The transition zone between Anthoxanthum alpinum and A. odoratum in the Krkonoše Mts. – Preslia 78: 317–330.
The distributions of the tetraploid Anthoxanthum odoratum and diploid A. alpinum were first studied in the Krkonoše Mts (part of the Sudetes Mts) to find the transition zone where both species occur together and then their ecological requirements in this zone were determined. The distribution was studied at two spatial scales, geographic and local; the latter included detailed distribution at a locality level, where the relationships of both species to plant communities were investigated. The zone where the overlap occurs is between 800–1290 m a.s.l. Anthoxanthum alpinum is able to descend to even lower altitudes, where it grows in vegetation dominaned by Nardus stricta. The species commonly occur in a fine mosaic of plant communities of Polygono-Trisetion (A. odoratum), Nardion (A. alpinum) or Nardo-Agrostion tenuis (both species). Anthoxanthum alpinum also occurs in areas that are currently not in direct contact with either alpine or subalpine vegetation (the Rýchory ridge, Černá hora Mt).

Dítě D., Navrátilová J., Hájek M., Valachovič M. & Pukajová D. (2006): Habitat variability and classification of Utricularia communities: comparison of peat depressions in Slovakia and the Třeboň basin. – Preslia 78: 331–343.
Vegetation with species of Utricularia and that dominated by Eleocharis quinqueflora, which occupy the same habitats. was studied in minerotrophic mires and oligotrophic wetlands associated with ponds. Relative towater and soil chemistry, the communities of Utricularia ochroleuca s.l. and U. intermedia occurred in mineral-poor and those of U. minor and U. australis in mineral-rich conditions. Rare stands with U. vulgaris occurred in conditions that were intermediate in mineral richness. Four communities belonging to the class Isoëto-Littorelletea were distinguished. Vegetation without bladderworts and dominated by E. quinqueflora occurs in calcareous fens and belongs to the class Scheuchzerio-Caricetea fuscae (the Caricion davallianae alliance). Vegetation with U. intermedia is characterized by high vascular plant cover and belongs to the class Scheuchzerio-Caricetea fuscae. Utricularia ochroleuca s.l. prefers open, acidic and waterlogged depressions in peat, whereas U. intermedia grows mostly in the shade under vegetation canopy. In this study, U. minor and U. australis have been found mainly in the more alkaline and mineral-rich habitats, and both species also tolerated extremely high mineral richness.

Štěpánková J. (2006): Karyotaxonomy of Myosotis alpestris group. – Preslia 78: 345–352.
Chromosome numbers of taxa belonging to the Myosotis alpestris group are provided and/or confirmed. A chromosome count is reported for the first time for M. olympica. A new ploidy level (2n = 24) was revealed within M. stenophylla for which previously only tetraploid cytotypes are reported. Myosotis stenophylla is identified for the first time from Greece. Previous chromosome counts for M. ambigens, M. alpestris, M. atlantica, M. corsicana, M. lithospermifolia, and M. suaveolens are confirmed based on plants originating from karyologically poorly investigated parts of the distribution areas of this polyploid complex.

Řezáčová M. (2006): Mallomonas kalinae (Synurophyceae), a new species of alga from northern Bohemia, Czech Republic. – Preslia 78: 353–358.
A new species of Mallomonas, M. kalinae, is described from a small peaty pool Ostrov in the Bohemian Switzerland National Park (northern Bohemia). The species is located in the section Papillosae and its morphological characteristics are closest to M. rasilis, M. calceolus, M. binocularis and M. paxillata. However, it can be distinguished from these species by differences in scale and bristle morphology. Itwas previously reported from different parts of theworld, but its taxonomic status remained unrecognized due to the lack of a detailed investigation of cultured material. The taxonomy and distribution of the species are discussed and compared with information in the literature.

Richardson D. M. (2006): Pinus: a model group for unlocking the secrets of alien plant invasions? – Preslia 78: 375–388.
The global-scale natural experiment created by the widespread dissemination of most of the 111 species of pines (genus Pinus, family Pinaceae) has shed light on many aspects of plant invasion ecology. Introductions and the fate of alien pines have been well documented worldwide, facilitating the accurate labelling of species as “naturalized”, “invasive”, or “non-invasive” using objective criteria. Thirty species are naturalized and 21 are invasive. Three life-history traits that clearly separate invasive from non-invasive taxa define the inherent ability of species to disperse over long distances, win in competition against other plants, and to survive or proliferate under a range of disturbance regimes. The realization of colonization opportunities for potentially invasive pines is determined by extrinsic factors, especially those that mediate seedling establishment. Meta-analysis of many introduction/invasion events revealed the interplay of factors. Detailed studies of pine invasions have elucidated the roles of long-distance seed dispersal and propagule pressure in driving invasions. Enhanced understanding of the ecology of pine invasions has improved our ability to manage these invasions. No other speciose genus of plants has yielded important insights on so many facets of invasion ecology.

Daehler C. C. (2006): Invasibility of tropical islands by introduced plants: partitioning the influence of isolation and propagule pressure. – Preslia 78: 389–404.
All else being equal, more isolated islands should be more susceptible to invasion because their native species are derived from a smaller pool of colonists, and isolated islands may be missing key functional groups. Although some analyses seem to support this hypothesis, previous studies have not taken into account differences in the number of plant introductions made to different islands, which will affect invasibility estimates. Furthermore, previous studies have not assessed invasibility in terms of the rates at which introduced plant species attain different degrees invasion or naturalization. I compared the naturalization status of introduced plants on two pairs of Pacific island groups that are similar in most respects but that differ in their distances from a mainland. Then, to factor out differences in propagule pressure due to differing numbers of introductions, I compared the naturalization status only among shared introductions. In the first comparison, Hawai‘i (3700 km from a mainland) had three times more casual/weakly naturalized, naturalized and pest species than Taiwan (160 km from a mainland); however, roughly half (54%) of this difference can be attributed to a larger number of plant introductions to Hawai‘i. In the second comparison, Fiji (2500 km from a mainland) did not differ in susceptibility to invasion in comparison to New Caledonia (1000 km from a mainland); the latter two island groups appear to have experienced roughly similar propagule pressure, and they have similar invasibility. The rate at which naturalized species have become pests is similar for Hawai‘i and other island groups. The higher susceptibility of Hawai‘i to invasion is related to more species entering the earliest stages in the invasion process (more casual and weakly naturalized species), and these higher numbers are then maintained in the naturalized and pest pools. The number of indigenous (not endemic) species was significantly correlated with susceptibility to invasion across all four island groups. When islands share similar climates and habitat diversity, the number of indigenous species may be a better predictor of invasibility than indices of physical isolation because it is a composite measure of biological isolation.

Stohlgren T., Jarnevich C., Chong G. W. & Evangelista P. H. (2006): Scale and plant invasions: a theory of biotic acceptance. – Preslia 78: 405–426.
We examined the relationship between native and alien plant species richness, cover, and estimated biomass at multiple spatial scales. The large dataset included 7051 1-m² subplots, 1443 10-m² subplots, and 727 100-m² subplots, nested in 727 1000-m² plots in 37 natural vegetation types in seven states in the central United States. We found that native and alien species richness (averaged across the vegetation types) increased significantly with plot area. Furthermore, the relationship between native and alien species richness became increasingly positive and significant from the plant neighbourhood scale (1-m²) to the 10-m², 100-m², and the 1000-m² scale where over 80% of the vegetation types had positive slopes between native and alien species richness. Both native and alien plant species may be responding to increased resource availability and/or habitat heterogeneity with increased area. We found significant positive relationships between the coefficient of variation of native cover in 1-m² subplots in a vegetation type (i.e. a measure of habitat heterogeneity), and both the relative cover and relative biomass of alien plant species. At the 1000-m² scale, we did find weak negative relationships between native species richness and the cover, biomass, and relative cover of alien plant species. However, we found very strong positive relationships between alien species richness and the cover, relative cover, and relative biomass of alien species at regional scales. These results, along with many other field studies in natural ecosystems, show that the dominant general pattern in invasion ecology at multiple spatial scales is one of “biotic acceptance” where natural ecosystems tend to accommodate the establishment and coexistence of introduced species despite the presence and abundance of native species.

Palmer M. W. (2006): Scale dependence of native and alien species richness in North American floras. – Preslia 78: 427–436.
I analyzed data from 1870 vascular floras from regions within North America to assess whether the determinants of native and alien diversity vary as a function of spatial grain. Moving window multiple regression revealed that richness of both native and alien species exhibit the expected species-area relationship, latitudinal gradient, elevation gradient, and year of publication effect. However, the strength of these factors varied between native and alien species, and as a function of scale. Alien diversity was more predictable than native diversity, and is more strongly related to elevation and latitude. For both groups, the latitudinal gradient is most pronounced at broad grains, and the elevational gradient is most pronounced at fine grains.

Pyšek P., Richardson D. M. & Jarošík V. (2006): Who cites who in the invasion zoo: insights from an analysis of the most highly cited papers in invasion ecology. – Preslia 78: 437–468.
The citation frequency of papers on invasion ecology published between 1981 and 2003 and that had accumulated at least 30 citations on the Web of Science on 9 August 2006 was analysed. The dataset comprised 329 papers and 27,240 citations. For each paper, the total number of citations was recorded and the annual citation rate (number of citations per year) was calculated. Papers were classified into broad research fields: plant invasions, animal invasions, biological control, and general papers (reviews and syntheses). Eight papers were cited more than 300 times, five of them dealt with general topics, and the mean value of the total number of citations across the whole data set is 82.8±73.1. The mean annual citation rate is 11.5±11.3 citations per year; six studies received on average at least 50 citations each year. About a half (50.8%) of papers in the data set deal with plant invasions. General papers are significantly more cited than papers from the other categories. The annual citation rate increased with time over the analysed period (1981–2003), by 1.0 citations per year. To compare the trends in invasion ecology with those in other fields of ecology, comparable data were compiled for population ecology and dynamics, and global change. The annual citation rate for invasion ecology as a whole increased faster than that for population ecology and dynamics, but not exponentially as is the case with studies on global change. The best-cited papers on invasion ecology were distributed among most of the top ecology journals. Those published in Oikos, Journal of Ecology, Ecological Applications and BioScience are cited 3.8–5.8 times more than the average for these journals (based on the impact factor). Papers on biodiversity, community ecology, impact, invasibility, dispersal, population ecology, competition, resources, genetical issues, biological control and species invasiveness received the highest total number of citations. However, measured by the annual citation rate, the hottest current topics in invasion ecology are the effect of global change on invasions, the role of natural enemies, character of the invasion process, evolutionary aspects, invasibility of communities and ecosystem processes. Some topics are disproportionally more cited than studied and vice versa. Studies on plant and animal invasions differ in focus: the topics of invasibility, biodiversity, resources, species invasiveness and population genetics are more emphasized in botanical studies, dispersal, competition, impact and pathways in papers dealing with animal invasions. Studies of grasslands and marine environment are most frequently cited in botanical and zoological studies, respectively. Most of the highly cited papers deal with multiple species; only 14 plant species and four animal species are the primary focus of one or more of the highly-cited papers. Twenty-two authors (4.5% of the total involved in the papers analysed), each with seven or more contributions cited at least 30 times, together contributed 49.4% of the most-cited papers, and attracted 55.6% of the total number of citations.

Prach K. & Řehounková K. (2006): Vegetation succession over broad geographical scales: which factors determine the patterns? – Preslia 78: 469–480.
We reviewed 37 studies on vegetation succession in which the succession started on bare ground, was followed in at least six sites, and where these sites were spatially separated over at least 10 km². The effect of environmental factors, which were explored in at least five studies, on the course of succession was assessed, based on the proportion of significant and non-significant results. Surrounding vegetation, macroclimate, soil moisture, amount of nitrogen and soil texture appeared to have the highest influence on the course of succession. Less influential were the size of a disturbed site, pH, organic matter and phosphorus content. Surrounding vegetation exhibited a significant effect in all cases where this was considered. These results imply that succession cannot be studied without the landscape context. The large-scale approach to succession has the potential to contribute substantially to both the theory of succession and practical applications, especially in restoration ecology.

Lepš J., de Bello F., Lavorel S. & Berman S. (2006): Quantifying and interpreting functional diversity of natural communities: practical considerations matter. – Preslia 78: 481–501.
Quantifying the functional diversity in ecological communities is very promising for both studying the response of diversity to environmental gradients and the effects of diversity on ecosystem functioning (i.e. in “biodiversity experiments”). In our view, the Rao coefficient is a good candidate for an efficient functional diversity index. It is, in fact, a generalization of the Simpson’s index of diversity and it can be used with various measures of dissimilarity between species (both those based on a single trait and those based on several traits). However, when intending to quantify the functional diversity, we have to make various methodological decisions such as how many and which traits to use, how to weight them, how to combine traits that are measured at different scales and how to quantify the species’ relative abundances in a community. Here we discuss these issues with examples from real plant communities and argue that diversity within a single trait is often the most ecologically relevant information. When using indices based on many traits, we plead for careful a priori selection of ecologically relevant traits, although other options are also feasible. When combining many traits, often with different scales, methods considering the extent of species overlap in trait space can be applied for both the qualitative and quantitative traits. Another possibility proposed here is to decompose the variability of a trait in a community according to the relative effect of among- and within-species differentiation (with the latter not considered by current indices of functional diversity), in a way analogical to decomposition of Sum of squares in ANOVA. Further, we show why the functional diversity is more tightly related to species diversity (measured by Simpson index) when biomass is used as a measure of population abundance, in comparison with frequency. Finally, the general expectation is that functional diversity can be a better predictor of ecosystem functioning than the number of species or the number of functional groups. However, we demonstrate that some of the expectations might be overrated – in particular, the “sampling effect“ in biodiversity experiments is not avoided when functional diversity is used as a predictor.

Krahulec F. (2006): Species of vascular plants endemic to the Krkonoše Mts (Western Sudetes). – Preslia 78: 503–516.
This paper summarizes the present state of knowledge of the vascular plants endemic to the Krkonoše Mts. The species given in previous lists but excluded from the present one are also discussed together with the history of opinion of their status. Some endemics are of Holocene age, e.g. Sorbus sudetica is the result of a past hybridization while others originated from continuous differentiation of small populations over time. Some endemic species of other genera, for example, Hieracium, Taraxacum and Alchemilla appear to be older in origin, representing relict populations which occurred at low altitudes at least during the last glacial period. Their age is unknown, because it is unknown, when and how they evolved.

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