Question: Do vascular epiphyte species have a metapopulation structure? What are the qualitative and quantitative long-term changes of the complete vascular epiphyte vegetation in a particular host tree species?

Location: Lowland forest on Barro Colorado Island (9°10′ N, 79°51′ W), Republic of Panama.

Methods: In 1994 and 2002 we conducted a census of all vascular epiphytes growing on more than 1000 Annona glabra trees (= patches). Epiphyte species abundances were recorded at the tree level in each census.

Results: The number of epiphyte individuals increased from ca. 15 000 to ca. 23 700 individuals during the census interval while the species composition on Annona glabra as a whole was rather stable. There was a strong positive relationship between occurrence in patches and local abundance of the species, and between species richness and host tree stand size. The dynamics of local populations of a given species were uncorrelated to each other; small and large local populations of most species had the same probability to go extinct. The frequency distribution of species on all host trees was not bimodal, but on a subset of heavily colonized host tree stands it was. Numbers of species and individuals were correlated with tree size which was not due to a correlation of tree size and tree age.

Conclusions: As far as the most abundant epiphyte species with metapopulation structures are concerned, these species belong to diverse families, e. g. Orchidaceae, Bromeliaceae and Polypodiaceae. Even ca. 80 years after the initial establishment of the host tree species in the study area epiphytes are still in the stage of initial colonization and have not reached a steady state as indicated by the strong increase in individuals and the ongoing colonization of empty trees.

Nomenclature: D'Arcy 1987) for flowering plants; Croat (1978) for ferns.

Question: Do severe winter flood events lift the nutrient limitation of biomass production in a river floodplain? How does this affect plant species richness? How long do the effects last?

Location: Floodplain grassland on calcareous sandy loam near river Rhine in The Netherlands.

Methods: Plots were fertilised with four treatments (control, N, P, N P) for 21 years; plant species composition, vegetation biomass and tissue nutrient concentrations were determined every year between 1985 and 2005.

Results: Fertilisation with N generally increased biomass production and reduced species richness, but these effects varied over time. During the first four years of the experiment, biomass production appeared to be co-limited by N and P, while N fertilisation dramatically reduced plant species richness; these effects became weaker subsequently. Following two extreme winter floods in 1993–94 and 1994–95 and a drought in spring 1996, the effects of fertilisation disappeared between 1998 and 2001 and then appeared again. Flooding caused an overall reduction in species richness (from c. 24 to 15 species m⁻²) and an increase in biomass production, which were only partly reversed after ten years.

Conclusions: Long time series are necessary to understand vegetation dynamics and nutrient limitation in riverfloodplains, since they are influenced by occasional flood and drought events, whose effects may persist for more than ten years. A future increase in flooding frequency might be detrimental to species richness in floodplain grasslands.

Nomenclature: van der Meijden (1996).

Question: Phytogenic mounds (nebkhas) – the natural accumulation of wind-blown sediments within or around the canopies of plants – have been proposed as important structures for locally maintaining high species richness in coastal and arid ecosystems. Nebkhas are assumed to increase habitat heterogeneity, but what is the importance of the nebkha host species relative to other nebkha characteristics in determining the associated plant assemblages? Are some host species more effective in creating diversity hotspots, or does a single species-area relationship apply to all nebkhas, regardless of host species? Can the influence of the host be ascribed to its indirect effects on abiotic attributes of the nebkha complex?

Methods and location: We investigated plant species richness and composition on nebkhas around six psammophytic species on Mediterranean coastal dunes of the Sinai Peninsula.

Results: Plant species richness was significantly related to nebkha size by the single power function according to the general prediction of island biogeography theory, but this relationship was modified – though to a limited degree – by nebkha host species identity. Canonical Correspondence Analysis revealed that nebkha host species identity and nebkha environmental and non-environmental factors significantly explained species composition on the nebkhas, but host species identity did so to a greater extent. The latter might reflect differences in seed trapping ability or free space for colonization between host species.

Conclusion: Differences in community composition and richness among nebkhas formed by different host species represent a key factor in the maintenance of plant diversity on arid coastal dunes.

Nomenclature: Täckholm (1974); Boulos (1995).

Question: What are the effects of grazing abandonment on the vegetation composition of Estonian coastal wetlands?

Location: Vormsi Island and Silma Nature Reserve in western Estonia, Europe.

Methods: Local knowledge and field reconnaissance were used to identify current and historical management levels of wetland sites within the west Estonian study area. Nine study sites, with varying management histories, were selected comprising an area of 287 ha. A total of 198 quadrats were taken from 43 distinct vegetation patches in five of the sites. TWINSPAN analysis was used to identify community type, and a phytosociological key was constructed for character taxa. This vegetation classification was then applied within a GIS-based context to classify all the study sites, using a ground survey technique and 1:2000 scale air photos.

Results: We identified 11 different brackish coastal wetland community types. Indicator species were defined with community characteristics for the seven main vegetation types readily recognisable in the field. Coastal wet grasslands were most extensive in grazed sites, or sites that had been more intensively grazed, while abandoned sites were largely composed of Phragmites australis stands, tall grassland, and scrub. Site variations based on vegetation composition were significantly correlated with past grazing intensity. Plant community types showed significant edaphic differences, with particularly low soil moisture and high conductivity and pH for open pioneer patches compared to other vegetation types.

Conclusion: Abandonment of traditionally grazed coastal grasslands threatens their characteristic biodiversity. This study found that grazing abandonment reduced the extent of coastal wetland grasslands of particular conservation value. Nevertheless, plant species of conservation interest were found across the sequence of community types described. The study shows that grazing is an important factor influencing coastal wetland plant communities but suggests that vegetation distribution is affected by environmental variables, such as topography.

Nomenclature: Stace (1999).

Question: What was the role of fire during the establishment of the current overstory (ca. 1870-1940) in mixed-oak forests of eastern North America?

Location: Nine sites representing a 240-km latitudinal gradient on the Allegheny and Cumberland Plateaus of eastern North America.

Methods: Basal cross-sections were collected from 225 trees. Samples were surfaced, and fire scars were dated. Fire history diagrams were constructed and fire return intervals were calculated for each site. Geographic patterns of fire occurrence, and fire-climate relationships were assessed.

Results: Fire was a frequent and widespread occurrence during the formation of mixed-oak forests, which initiated after large-scale land clearing in the region ca. 1870. Fire return ranged from 1.7 to 11.1 years during a period of frequent burning from 1875 to 1936. Fires were widespread during this period, sometimes occurring across the study region in the same year. Fires occurred in a variety of climate conditions, including both drought and non-drought years. Fires were rare from 1936 to the present.

Conclusions: A variety of fire regime characteristics were discerned. First, a period of frequent fire lasted approximately 60 years during the establishment of the current oak overstory. Second, fire occurred during a variety of climate conditions, including wet climates and extreme drought. Finally, there was within-site temporal variability in fire occurrence. These reference conditions could be mimicked in ongoing oak restoration activities, improving the likelihood of restoration success.

Nomenclature: Gleason & Cronquist (1991).

Question: Does ecosystem engineering by small mammals have a significant influence on vegetation patterns in the arid steppe vegetation of southern Mongolia?

Location: Gobi Altay Mountains, southern Mongolia.

Methods: We assessed the impact of the small lagomorph Ochotona pallasi on plant community composition, nutrient levels and biomass production in montane desert steppes. Data were derived from vegetation relevés, harvests of above-ground standing crop and a bioassay, followed by analyses of soil and plant nutrient contents.

Results: Although the local climate is arid with <150 mm annual precipitation, clear evidence of allogenic ecosystem engineering was found. Plant communities on burrows differed from those on undisturbed steppe in that they contained more species of annuals and dwarf shrubs, and a greater abundance of the important fodder grass Agropyron cristatum. Standing crop and nutrient concentrations were higher for plants growing on burrow soil. In situ measurements and a pot experiment showed that this effect was related to increased levels of soil nutrients (P, K, N) rather than moisture availability.

Conclusions: The study confirms that O. pallasi positively influences soil nutrient levels on its burrows, which leads to increased grassland productivity even under dry conditions. Thus, O. pallasi does not deteriorate site conditions, and the need for presently applied pest control schemes aimed at this species should be reassessed.

Nomenclature: Scientific names of plants follow Grubov (2001).

Question: Does overyielding of tree species mixtures in vertically stratified forests depend on complementary light use?

Location: Andes of south-central Chile.

Methods: Basal area data were obtained from 80 circular plots distributed regularly throughout old-growth stands with an emergent Nothofagus dombeyi tier over a canopy composed mainly of Laureliopsisphilippiana and Saxegothaea conspicua. Radial growth was measured from cores obtained from trees at the centre of each plot. The effects of competition on growth were evaluated through a competition index (CI) based on distances to and diameters of the two nearest neighbours.

Results: Overall, basal area of the canopy species was only weakly affected by the number of N. dombeyi per plot, and with basal area of N. dombeyi. However, the two main canopy species responded differently: whereas basal area of S. conspicua was negatively correlated with that of N. dombeyi, that of L. philippiana showed no response. Radial growth of S. conspicua was negatively correlated with CI calculated from canopy trees and more weakly so from emergent N. dombeyi. In contrast, radial growth of L. philippiana was not affected by competition with either canopy or emergent neighbours.

Conclusions: Results indicate that emergent N. dombeyi tend to depress growth and basal area of S. conspicua, but not of the more shade-tolerant L. philippiana. This supports the proposal that enhancement of wood production in stratified mixtures will be greatest when component species have strongly contrasting light use traits.

Question: Are competitive hierarchies, which are typically based on the results of pair-wise competition experiments, sensitive to the level of species interaction in the underlying competition experiments?

Location: Controlled greenhouse study using vegetation typical of old-fields in East Tennessee, USA.

Methods: We extend traditional competitive effect/response methods to incorporate data from competition experiments featuring any level of species interaction (i. e., 2,3,.,., n species interacting simultaneously) and develop an ordinal technique that makes hierarchies more robust to variation in the numerical values of relative yield. We apply these methodological techniques to empirical data from a greenhouse experiment wherein four old-field plant species were grown in pair-wise and tri-wise combination. We also demonstrate how resampling can be used to determine the variability of data and its consequences for development of competitive hierarchies.

Results: Different hierarchies were produced when we used different evaluation methods, different levels of species interaction, and different levels of replication. More acute resampling distributions and wider ranges of target/neighbor scores revealed that higher levels of species interaction lead to more distinct hierarchies.

Conclusions: Hierarchies developed from interactions among subsets of species may inadequately characterize relationships among the full community because of indirect or higher-order interactions within multi-species assemblages. Different evaluation methods can yield different hierarchies, and resampling is an effective tool to determine the sensitivity of resultant hierarchies to the level of replication. In sum, our new methodology can be used to control uncertainty in poorly-replicated experiments.

Nomenclature: Terrell (1967); Wofford & Kral (1993).

Questions: Is multi-stemming a survival strategy in response to chronic disturbance? Is multi-stemming under phylogenetic control? What environmental factors are associated with multi-stemming? When do trees initiate growth of multiple stems? Do multi-stemmed trees have limited stature?

Location: Subtropical Indian Ocean coastal dune forest at Cape Vidal in the Greater St. Lucia Wetland Park, northeastern South Africa.

Methods: Tree physiognomy and environmental conditions were sampled in 20 transects that were 300 m long and 5 m wide.

Results: 38.9 % of trees were multi-stemmed, with no correlation between multi-stemming and taxonomic grouping. The multi-stemming trait was most associated with stem decumbency and substrate erosion and multi-stemmed individuals were less common in protected dune slacks. Trees at Cape Vidal appear to facultatively produce multiple stems from an early stage. There was no trade-off between tree height and stem number.

Conclusions: Coastal winds and the unstable dune substrate are important environmental correlates of multi-stemming. Both short stature and the high incidence of multi-stemming are related to the tree-disturbance interaction. The taxonomically widespread phenotypic plasticity in this trait indicates the importance of multi-stemming to tree survival even under low levels of disturbance.

Nomenclature: Coates Palgrave (2002).

Questions: (1) What are the most important abiotic environmental variables influencing succession in central European man-made habitats? (2) How do these variables interact with one another and with variation in community properties?

Location: Central, western and southern parts of the Czech Republic. Habitats included old fields, urban sites, spoil heaps after coal mining, sites at water reservoirs, extracted sand pit and peatland and reclaimed sites in areas deforested by air pollution.

Methods: We investigated vegetation patterns on 15 successional seres, sampled by the same methods. Time of succession over which the data were available ranged from 12 to 76 years. The cover of vascular plant species (in %) was estimated in 5 m × 5 m plots. The relationships between vegetation characteristics (species composition, total cover, cover of woody species, species number and rate of dominant species turnover) and 13 abiotic site factors, including climatic and soil variables, were tested using CCA ordination and regression models.

Results: Substratum pH, the only substratum characteristic, and climate were the environmental variables significantly affecting the vegetation patterns in the course of succession. The rate of succession, measured as the turnover of dominant species, was significantly more rapid in lowland than in mountain climates. On alkaline soils, species numbers in succession increased towards warmer climates. However, acid soils prevented any increase in species numbers, regardless of the climate. Surprisingly, forms of nitrogen and contents of C, P and cations did not exhibit any significant effect on the vegetation characteristics studied.

Conclusions: Our approach, to compare a number of seres, can contribute not only to our understanding of succession, but also to help restoration projects to predict vegetation change because the crucial environmental variables, as identified by this study, are easy to measure.

Nomenclature: Tutin et al. (1964–1980).

Question: Does the upward shift of species and accompanied increase in species richness, induced by climate change, lead to homogenization of Alpine summit vegetation?

Location: Bernina region of the Swiss Alps.

Methods: Based on a data set from previous literature we expand the analysis from species richness to beta-diversity and spatial heterogeneity. Species compositions of mountain summits are compared using a two-component heterogeneity concept including the mean and the variance of Sørensen similarities calculated between the summits. Non-metric multidimensional scaling is applied to explore developments of single summits in detail.

Results: Both heterogeneity components (mean dissimilarity and variance) decrease over time, indicating a trend towards more homogeneous vegetation among Alpine summits. However, the development on single summits is not strictly unidirectional.

Conclusions: The upward shift of plant species leads to homogenization of alpine summit regions. Thus, increasing alpha-diversity is accompanied by decreasing beta-diversity. Beta-diversity demands higher recognition by scientists as well as nature conservationists as it detects changes which cannot be described using species richness alone.

Rationale: Few techniques exist for non-destructive measurement of the biomass of different co-occurring growth forms in a similar manner, and the available techniques tend to be tedious and time consuming.

Aim: This paper provides an alternative technique for the measurement of components of biomass (defined in terms of growth forms) and describes an apparatus effective to perform these measurements in samples of vegetation stands up to 1.5 meter tall.

Approach: The technique is based on a regression relationship between a number of probes [multiple height measurements of targeted growth forms with the help of mini disks (3 cm in diameter)] taken in a given area, and the dry biomass of these growth forms within that area.

Test: We tested the method in a multi-layered shrubland composed of three major growth forms (shrub, stoloniferous grass and tussock grass) to: (1) establish how accurate the new method predicts the biomass of different plant growth forms, and (2) determine the sampling intensity necessary for reliable results. The technique proved to be very effective in terms of predicting the biomass of the respective growth forms within sample plots, even at a very low density of probes.

Conclusion: The Multipoint Minidisk Meter method provides a good alternative biomass estimation method for vegetation composed of diverse growth forms, especially where sampling time is of essence. It will be especially useful to closely track changes in biomass within the same plot over time.

Question: How will changing climate and habitat structure interact to control the species diversity of lichen epiphytes?

Location: Scotland.

Method: Species richness (=diversity) of the epiphyte lichen community known as Lobarion (named after Lobaria pulmonaria) was quantified for 94 Populus tremula stands across Scotland, and compared in a predictive model to seven climate variables and eight measures of woodland structure. An optimum model was selected and used to project Lobarion diversity over the geographic range of the study area, based on IPCC climate change scenarios and hypothetical shifts in woodland structure.

Results: Species diversity of the Lobarion community was best explained by three climate variables: (1) average annual temperature; (2) autumn and winter precipitation; in combination with (3) historic-woodland extent. Projections indicate a positive effect of predicted climate change on Lobarion diversity, consistent with the physiological traits of cyanobacterial lichens comprising the Lobarion. However, the general response to climate is modified significantly by the effect on diversity of historic-woodland extent.

Conclusions: Historic-woodland extent may exert an important control over local climate, as well as impacting upon the metapopulation dynamics of species in the Lobarion. In particular, a temporal delay in the response of Lobarion species to changed woodland structure is critical to our understanding of future climate change effects. Future Lobarion diversity (e.g. in the 2050s) may depend upon the interaction of contemporary climate (e.g. 2050s climate) and historic habitat structure (e.g. 1950s woodland extent). This is supported by previous observations for an extinction debt amongst lichen epiphytes, but suggests an extension of simple climate-response models is necessary, before their wider application to lichen epiphyte diversity.

Background: Disturbances by avalanches have created unique habitats for animals and plants in subalpine ecosystems worldwide, but at the same time avalanches can pose a major threat to humans. Thus, avalanches are suppressed by means of avalanche barriers to protect settlements and infrastructures in populated areas of the European Alps. As a consequence, the disturbance regime in avalanche tracks has fundamentally changed.

Methods: In the present study we address ecological consequences of avalanche suppression on plant diversity. We analysed plant diversity and species composition in recent and old avalanche tracks with and without avalanche suppression and in undisturbed adjacent forests at high and low elevations.

Results: The number of species was higher in both active and inactive avalanche tracks as compared to undisturbed subalpine forest. The species composition indicated a wider range of ecological niches in active than in inactive avalanche tracks. The vegetation from active tracks showed lower indicator values for temperature and nitrogen availability. The proportion of alpine species was lower in formerly active tracks.

Conclusions: The conditions that exist in active avalanche tracks increase plant diversity in relation to undisturbed forest. In the few decades following avalanche suppression, species composition changes in tracks from which avalanches have been excluded. Continued suppression of avalanche disturbance may lead to a decline in plant and habitat diversity. Avalanche disturbance can exert an important influence on the biodiversity of subalpine forests and provide important habitats. Anthropogenic changes in the natural regime of avalanche disturbance are likely to contribute significantly to future landscape changes in subalpine forests.

Nomenclature: Lauber & Wagner (2000).

Question: Which are the gradients of floristic differentiation in Greek beech (Fagu sylvatica) forests? Which is the role of geographical and ecological factors in this differentiation?

Location: Beech forests of the plant geographical regions Northeast, North Central and East Central Greece.

Methods: A total of 1404 published and unpublished phytosociological relevés were used in the analyses. TWINSPAN and DCA were applied to classify and ordinate the relevés. Altitude, Indicator Values of relevés and their X and Y coordinates were used in a posteriori interpretation of the ordination axes. Kendall's correlation coefficients were calculated between DCA relevé scores and explanatory variables. Multiple linear regression was used to partition the variation explained by the first two DCA axes, between the geographical and the ecological variables.

Results: Classification resulted in 14 vegetation units defined by species composition. Two types of gradients, ecological and geographical, were revealed by the DCA of all relevés. The partition of the variation accounted for by the first and second DCA axis was attributed mainly to ecological and geographical variables, respectively.

Conclusions: Beech forests of northeast and Central Greece show phytogeographical differences, while ecologically similar vegetation units occur in both regions. A west-east gradient is revealed in Greek beech forest vegetation. The extent of the study area, its position along regional gradients and the comprehensiveness of the data set that is analysed determine the types of the gradients which can be revealed in a vegetation study.

Nomenclature: For names of mountains: Strid & Tan (1997). For names of plant taxa: Tutin et al. (1968–1993); Greuter et al. (1984–1989); Strid (1986); Strid & Tan (1991, 1997, 2002).

Question: Can non-parametric multiplicative regression (NPMR) improve estimates of potential direct incident radiation (PDIR) and heat load based on topographic variables, as compared to least-squares multiple regression against trigonometric transforms of the predictors?

Methods: We used a multiplicative kernel smoothing technique to interpolate between tabulated values of PDIR, using a locally linear model and a Gaussian kernel, with slope, aspect, and latitude as predictors. Heat load was calculated as a 45 degree rotation of the PDIR response surface.

Results: This method yielded a fit to a complex response surface with R² > 0.99 and eliminated the areas of poor fit given by a previously published method based on least squares multiple regression with trigonometric functions of the predictors.

Conclusions: Improved estimates of PDIR and heat load based on topographic variables can be obtained by using non-parametric multiplicative regression (NPMR). The main drawback to the method is that it requires reference to the data tables, since those data are part of the model.

Question: How do increases in soil nutrient and water availability alter the nutrient fluxes through the resorption and litter decomposition pathways and how do they affect litter nutrient pools in a low-productive alpine tundra ecosystem?

Location: An alpine lichen-rich tundra on Mt. Malaya Khatipara in the NW Caucasus, Russia (43°27′ N, 41°42′ E; altitude 2800ma.s.l.).

Methods: We conducted a 4-year fertilisation (N, P, N P, lime) and irrigation experiment, and analysed the responses of nutrient resorption from senescing leaves, leaf litter quality and decomposability of six pre-dominant vascular plant species, total plant community litter production and litter (nutrient) accumulation.

Results: Vascular plant litter [N] and [P] increased 1.5 and 10 fold in response to N and P additions, due to increased concentrations of the nutrients in fresh leaves and unchanged or reduced resorption efficiency. Litter decomposability was not affected by nutrient amendments. Fertilisation enhanced litter production (180%; N P treatment) and litter accumulation (80%; N P), owing to tremendously increased production and low decomposability of graminoids. Together with increased litter [N] and [P] this led to great increases in total litter nutrient pools.

Conclusions: Due to increased production of graminoids, nutrients added to the alpine tundra soil were mostly immobilised in recalcitrant, nutrient-rich litter. This suggests that changing species composition in low productive ecosystems may act as an internal buffer mechanism, which under increased soil nutrient availability prevents the community from rapidly acquiring features typical of a high productive ecosystem such as high decomposability and high nutrient availability.

Nomenclature: Vorob'eva & Onipchenko (2001).

Two alternatives are offered to Podani's proposals, based on the claim that Braun-Blanquet cover-abundance estimates cannot be properly analysed by conventional mul-tivariate methods.

1. The ordinal transform scale, based on an extended Braun-Blanquet cover-abundance scale, comes close to a metric cover percentage scale after (1) the abundance values r (very few individuals), (few ind.), 1 (abundant) and 2m (very abundant, cover < 5%) are replaced by cover percentage estimates and (2) the higher Braun-Blanquet values, notably 4 and 5, with cover intervals 50-75% and 75-100%, respectively, are interpreted as estimates of considerably higher cover values than the usual visual projection on the ground (because of the position of stems and leaves in several layers). I propose the equation ln C = (OTV -2)1 a, where C = Cover%, OTV is the 1 to 9 Ordinal Transfer Value and a is a factor weighting the cover values. With this equation cover values in a geometric series are achieved for the nine values in the extended Braun-Blanquet scale from 0.5 % (OTV 1) to 140% (OTV 9) for a = 1.415, and for a = 1.380 from 0.6 % to 160%.

2. This makes use of an earlier developed ‘optimum-transformation’ of cover-abundance values. For each species a frequency distribution of cover-abundance values is determined for a large data set, i.e. of dune slack vegetation. Tiny species have low values (OTVs 1-3) with high frequencies and hardly occur with higher OTV values; here all scores are considered ‘optimal’. In dominant species OTVs 7 to 9 have the highest frequencies and only these values are considered optimal. Species with intermediate OTV ranges have optimum ranges with low-bound OTV = 2,3,4 and 5, respectively. No species were found in the dune slack data set with a frequency distribution justifying an optimum range with low-bound OTV = 6.

For mathematically correct numerical treatments' optimum scores' can be converted to 1 and sub-optimal scores to 0 in order to approach a presence/absence situation.

Both alternatives are suggested to be acceptable approximations to a metric basis for numerical analyses.