Question: A set of easily-measured (‘soft’) plant traits has been identified as potentially useful predictors of ecosystem functioning in previous studies. Here we aimed to discover whether the screening techniques remain operational in widely contrasted circumstances, to test for the existence of axes of variation in the particular sets of traits, and to test for their links with ‘harder’ traits of proven importance to ecosystem functioning.

Location: central-western Argentina, central England, northern upland Iran, and north-eastern Spain.

Recurrent patterns of ecological specialization: Through ordination of a matrix of 640 vascular plant taxa by 12 standardized traits, we detected similar patterns of specialization in the four floras. The first PCA axis was identified as an axis of resource capture, usage and release. PCA axis 2 appeared to be a size-related axis. Individual PCA for each country showed that the same traits remained valuable as predictors of resource capture and utilization in all of them, despite their major differences in climate, biogeography and land-use. The results were not significantly driven by particular taxa: the main traits determining PCA axis 1 were very similar in eudicotyledons and monocotyledons and Asteraceae, Fabaceae and Poaceae.

Links between recurrent suites of ‘soft’ traits and ‘hard’ traits: The validity of PCA axis 1 as a key predictor of resource capture and utilization was tested by comparisons between this axis and values of more rigorously established predictors (‘hard’ traits) for the floras of Argentina and England. PCA axis 1 was correlated with variation in relative growth rate, leaf nitrogen content, and litter decomposition rate. It also coincided with palatability to model generalist herbivores. Therefore, location on PCA axis 1 can be linked to major ecosystem processes in those habitats where the plants are dominant.

Conclusion: We confirm the existence at the global scale of a major axis of evolutionary specialization, previously recognised in several local floras. This axis reflects a fundamental trade-off between rapid acquisition of resources and conservation of resources within well-protected tissues. These major trends of specialization were maintained across different environmental situations (including differences in the proximate causes of low productivity, i.e. drought or mineral nutrient deficiency). The trends were also consistent across floras and major phylogenetic groups, and were linked with traits directly relevant to ecosystem processes.

Nomenclature: Bolòs et al. (1990); Flora Iranica (1963 onwards); Stace (1991); Zuloaga et al. (1994); Zuloaga & Morrone (1996, 1999).

Question: Does disturbance reduce competition intensity and thus favour weak competitors that are presumably less affected by disturbance than strong competitors?

Methods: We used a single flooding event with increasing duration to simulate disturbance with increasing intensity. Six flood-plain grass species, typical of different flood regimes were grown in monocultures and in an additive species mixture. Flooding took place early in the first growing season and changes were monitored until the end of the second growing season.

Results: Longer flooding durations initially decreased competition, but only a single species (Agrostis) increased its abundance in mixtures after flooding. The two weakest competitors in our selection (Poa trivialis and Elytrigia repens) failed to benefit from flooding because direct losses from flooding exceeded gains from reduced competition. Accordingly, we found no trade-off between flooding tolerance and competitive ability indicating that floods affect strong and weak competitors equally, although some species tolerated floods better than others.

Conclusions: Since competition is only temporarily weakened after disturbance, increased competitive ability relative to other species may provide a more effective strategy for persistence in flood-disturbed sites. Above-ground runners seem an important prerequisite for enhanced competitive ability of clonal species in flood-disturbed sites.

Nomenclature: van der Meijden (1996).

Abbreviations: lnRR = natural log of the response ratio; LT₅₀ = number of days (‘lethal time’) after which 50% of individuals had died.

Question: In seeds which are regularly consumed by waterbirds in the field, how does gut–passage modify their response to salinity gradients?

Location: Doñana National Park salt marsh, south-west of Spain.

Methods: Seeds of Scirpus litoralis and Scirpus maritimus were collected and force fed to mallards (Anas platyrhynchos). Both the ingested seeds (passage) and non-ingested seeds (controls) were exposed, in germination chambers, to a salinity range similar to that observed in the field (0–32 dS/m). After 30 days, the total percentage germination, the duration of the dormancy period and the germination speed were computed. The response of the different germination parameters to ingestion and salinity was analyzed using generalized lineal models. Recovery tests on seeds that did not germinate in the various treatments and tests of the effect of ingestion on the intrinsic variability in seed response were also performed.

Results: An increase in salinity reduced germinability and increased the length of dormancy, while gut passage increased the intrinsic variability of the temporal seed response in both species. In S. litoralis there was a significant interaction between the effects of salinity and passage on germination rate. Passage increased germination rate at low salinities (≤2 dS/m) but decreased it at high salinities (≥4 dS/m).

Conclusion: Gut-passage by ducks significantly changes seed response to salinity. The outcome of plant-animal interactions can be influenced by environmental gradients. Studies of germination in response to gut passage that do not take such gradients into account may produce misleading results.

Abbreviation: GLM = Generalized linear model.

Question: How do distribution patterns change with increasing scale level, and can this shift be attributed to dispersal and/or niche limitation?

Location: Dune slacks at the Belgian and North French coast.

Method: Frequency distribution patterns of species were tested over different scale levels (ranging from 0.008 to 45 km²). Analyses were executed for the total species pool and for subsets of species with high and low dispersal rates and habitat generalist and specialist species.

Results: Species distributions for the total species pool on scale levels larger than 1.5 km² were unimodal, with an overrepresentation of rare species. With decreasing scale level, the proportion of common species increased, leading to weak bimodality. Distributions of subsets of slowly dispersing and habitat specialist species are on all scale levels characterised by a strongly unimodal pattern. The subset of species with high dispersal rates and habitat generalist species has a higher proportion of common species, leading to a significant core peak.

Conclusions: On all scale levels both dispersal and niche limitation are hampering the wider distribution of rare species. However, since isolation and habitat heterogeneity are limited on the smaller scale levels, a larger proportion of well dispersing and habitat generalist species is able to occupy a high number of patches, resulting in a significant core peak for the total species pool.

Nomenclature: Lambinon et al. (1998).

Questions: Are the vegetation attributes significantly different among lava domes and among geomorphologic units as a result of age and soil features? Are the successional rates equal in all the geomorphologic units of the domes? Are the colonizer species of lava domes totally replaced by other species in the late successional stages?

Location: Terceira Island, Azores (Portugal).

Methods: Three comparable domes of 240, 370 and 2080 yr old were selected. Data on floristic composition, vegetation bioarea (area occupied by plant species in transects), structure, demography and soil nutrients were collected. Quantitative and qualitative changes along the succession gradient were also analyzed.

Results: Vegetation attributes were consistent with the successional stage of each dome in the primary sere; however, the geomorphologic units did not follow the same pattern. The influence of the rates of plant colonization and soil formation are responsible for the decrease of the successional rates from footslopes, to summits, to slopes. The vegetation successionally changes from Juniperus scrub, to Juniperus wood and forest, and there is little species replacement since the similarity in species composition is high between the 3 domes.

Conclusions: This is a special type of direct succession that takes place mainly through an increase in biomass and structural complexity. We observed small wooded areas in the fissures of very young domes that are samples of later successional forests – a phenomenon that we call ‘zoom effect’.

Nomenclature: Hansen & Sunding (1993); Schäfer (2002).

Abbreviations: TIR = Terceira Três Irmãs; TLD = Terceira Lomba do Dias; TMN = Terceira Mistérios Negros.

Question: The relationship between carbon-13 in soil organic matter and C₃ and C₄ plant abundance is complicated because of differential productivity, litter fall and decomposition. As a result, applying a mass balance equation to δ¹³C data from soils cannot be used to infer past C₃ and C₄ plant abundance; only the proportion of carbon derived from C₃ and C₄ plants can be estimated. In this paper, we compare δ¹³C of surface soil samples with vegetation data, in order to establish whether the ratio of C₃:C₄ plants (rather than the proportion of carbon from C₃ and C₄ plants) can be inferred from soil δ¹³C.

Location: The Tsavo National Park, in southeastern Kenya.

Methods: We compare vegetation data with δ¹³C of organic matter in surface soil samples and derive regression equations relating the δ¹³C of soil organic matter to C₃:C₄ plant abundance. We use these equations to interpret δ¹³C data from soil profiles in terms of changes in inferred C₃:C₄ plant ratio. We compare our method of interpretation with that derived from a mass balance approach.

Results: There was a statistically significant, linear relationship between the δ¹³C of organic matter in surface soil samples and the natural logarithm of the ratio of C₃:C₄ plants in the 100m² surrounding the soil sample.

Conclusions: We suggest that interpretation of δ¹³C data from organic matter in soil profiles can be improved by comparing vegetation surveys with δ¹³C of organic matter in surface soil samples. Our results suggest that past C₃ plant abundance might be under-estimated if a mass balance approach is used.

Abbreviation: SOM = Soil organic matter.

Question: Do different competitive abilities of three fern species explain their different regional abundances?

Location: Estonia, Europe.

Methods: The factorial pot experiment, in which single individuals of three fern species were grown in natural soil with 0, 2, 4, and 8 neighbouring individuals of Deschampsia flexuosa.

Results: The response patterns of different biomass fractions and morphological parameters of fern species were similar to each other. The diploid D. expansa was the most vulnerable to competition, while tetraploid D. carthusiana and D. dilatata were more tolerant. D. carthusiana allocated relatively more to below-ground parts than the other two species and allocation to roots increased when neighbour density increased. For D. expansa and D. dilatata, allocation to below-ground parts decreased at high neighbour density, while in D. dilatata also the relative length of the stipe increased. Thus, the response of D. carthusiana corresponds to a ‘persistence type’ and that of D. dilatata to a ‘foraging type’.

Conclusions: Lower vulnerability of D. carthusiana to competition, compared to D. expansa, may explain the higher regional and local abundance of the former. The rarity of D. dilatata in Estonia, however, could rather be explained by the impact of climatic factors, since this species is near its northeastern distribution limit in Estonia.

Nomenclature: Fraser-Jenkins (1993).

Question: Is plant capacity to regrow under different herbivore treatments related to herbivore increaser/decreaser plant status?

Location: Grassland in Southeast England (GR 41/944691).

Methods: A field experiment was established in order to understand the role of plant tolerance to herbivory in explaining the abundance of nine grassland species previously known as herbivore increasers or decreasers. Tolerance was measured as a plant's capacity to regrow after exposure to herbivores. The experiment was designed to measure the impact of rabbits, molluscs, insects and clipping (artificial damage). Plants were propagated by stolons, exposed to different treatments in the field and then allowed to recover in the greenhouse for a month

Results: Previous studies have stated that plants that are able to persist in a herbivore environment could be tolerant or resistant, in agreement with the later our results showed that rabbit increaser plants were tolerant to herbivory in terms of biomass regrowth. Nonetheless, insect and mollusc increasers did not show any particular pattern related to plant compensation and some decreaser species were intolerant.

Conclusions: This study shows that tolerance to herbivory could be an important mechanism for rabbit increaser species survival in grazed ecosystems.

Nomenclature: Stace (1997).

Question: Can above-ground biomass of naturally growing Alhagi sparsifolia shrubs be estimated non-destructively?

Location: Qira oasis (37° 01′ N, 80° 48′ E, 1365 m a.s.l.) at the southern fringe of the Taklamakan desert, Xinjiang, NW China.

Methods: Two methods were compared to estimate above-ground biomass (AGB) of Alhagi. At first shrub AGB was estimated by manual ground measurements (called ‘allometric approach’) of length, width and height of 50 individuals. Subsequently regression equations were established between calculated shrub canopy volume and shrub AGB (r² = 0.96). These equations were used to calculate AGB from manual ground measurements in 20 sample plots within the Alhagi field. Secondly, kite-based colour aerial photography coupled with the use of a Geographic Information System (called ‘GIS approach’) was tested. First and second order polynomial regressions between AGB data of the 50 individual shrubs and their respective canopy area allowed to automatically calculate the AGB of all remaining shrubs covered by the photograph (r² = 0.92 to 0.96). The use of non-linear AGB regression equations required an automatised separation of shrubs growing solitary or in clumps. Separation criteria were the size and shape of shrub canopies.

Results: The allometric approach was more reliable but also more time-consuming than the GIS-based approach. The latter led to an overestimation of Alhagi dry matter in densely vegetated areas. However, this systematic error decreased with increasing size of the surveyed area. Future research in this field should focus on improvements of AGB estimates in areas of high shrub density.

Abbreviations: AGB = Above-ground biomass; DM = Dry matter.

Question: How do lawn floras compare with those of semi-natural grasslands? Are the compositions of lawn floras determined by local, within-garden factors (e.g. lawn management and size) or by regional factors (e.g. climate and location)? Are lawn floras nested (like semi-natural grasslands) or not (like cultivated parts of gardens)? Are there gradients of species composition within lawns?

Location: Sheffield, UK.

Methods: We examined the composition of the floras of entire lawns and of two 1-m² lawn quadrats in 52 gardens.

Results: A total of 159 species of vascular plants was recorded, 60 of them only once. Most lawn species were forbs, but most lawn cover consisted of grasses. Lawn species were predominantly natives. Bigger lawns had more species, but richness was not closely linked to other environmental or management variables. Composition of lawn floras varied with altitude, with woodland and wetland plants more common in the higher west of the city, and weeds of waste ground in the east. The species-area curve derived from 1-m² lawn quadrats was very similar to that of semi-natural grasslands. Lawn quadrats were significantly nested, with rarer species mostly confined to more species-rich quadrats. Trampling-tolerant Poa annua was more abundant in the part of the lawn nearer the house.

Conclusions: In most respects, lawns behaved much more like semi-natural grasslands than like cultivated flower beds and borders. Species composition of lawns is strongly influenced by local climate. Most lawns show an internal gradient of composition, linked to a gradient of intensity of use.

Nomenclature: Stace (1997).

Question: Is light available for subcanopy individuals of Fagus crenata spatiotemporally heterogeneous across patches with closed canopies of different foliage phenologies and gaps? Is local abundance of Sasa influenced by the composition of the canopy layer? If so, does the Sasa layer also affect the amount of light available to small F. crenata saplings? Is variation in F. crenata population structure consistent with the hypothesis that light is important?

Location: Mt. Kurikoma, Japan 780 m a.s.l.

Methods: Population structure of subcanopy individuals of Fagus crenata and importance of Sasa were examined in five patch types. The patch-types were Fc (F. crenata only in the crown), Qm (Quercus mongolica var. grosseserrata only in the crown), Mo (Magnolia obovata only in the crown), Fc′ (periphery of F. crenata) and Gap. Seasonal changes in light availability above and below the Sasa layer was examined by using hemispherical photographs and quantum sensors.

Results: Subcanopy individuals of F. crenata began unfolding their leaves approximately one month earlier than canopy trees of Q. mongolica var. grosseserrata and M. obovata, but a few days later than those of adult F. crenata. Accumulated photosynthetic photon flux density above the Sasa layer was greatest in Qm and Mo, and lowest in Fc. Importance of Sasa was highest in Gap. Maximum height and the number of subcanopy individuals of F. crenata were greatest in Qm, followed by Mo, and lowest in Fc.

Conclusions: Differences in canopy layer composition probably influence the regeneration of F. crenata both directly through their foliage phenologies, and also indirectly by determining the importance of Sasa.

Nomenclature: Ohwi & Kitagawa (1983).

Abbreviations: PPFD = Photosynthetic Photon Flux Density; RPPFD = Relative PPFD.

Question: We studied the development and persistence of the effects of nutrient pulses on biomass production and species composition in a fen meadow.

Location: Nature reserve, central Netherlands, 5 m a.s.l.

Methods: Single pulse fertilization with N and P in a factorial design on an undrained central and a drained margin site in a species-rich fen meadow (Cirsio dissecti-Molinietum). Biomass production and species composition were monitored during four years.

Results: At the central site, N addition boosted biomass production, but only during one year. The species composition was not changed. P fertilization increased the biomass production and changed the species composition from a vegetation dominated by Carex panicea to a grassland community with abundant Holcus lanatus, but not before the second year. At the margin site, P fertilization changed the species composition in a similar way, but biomass production was not increased. N fertilization had no effect. At both sites the P induced shift in species composition persisted for four years although the P effect declined during the experiment.

Conclusions: The biomass responses show that N was limiting in the central site. Another nutrient, besides N and P (probably K) must have been limiting in the marginal site. The fast decline of the N effect on biomass is ascribed to increased denitrification and biomass removal. The delay in the P effect on biomass and species composition and the persistence of the P effect on species composition are ascribed to fast immobilisation and subsequent slow release of fertilizer P in the peat soil. Recurrence of the P pulses is expected to cause permanent changes in species composition.

Nomenclature: van der Meijden (1990) for phanerogams and Schaminée et al. (1996) for syntaxa.

Question: Current climate changes in the Alaskan Arctic, which are characterized by increases in temperature and length of growing season, could alter vegetation structure, especially through increases in shrub cover or the movement of treeline. These changes in vegetation structure have consequences for the climate system. What is the relationship between structural complexity and partitioning of surface energy along a gradient from tundra through shrub tundra to closed canopy forest?

Location: Arctic tundra-boreal forest transition in the Alaskan Arctic.

Methods: Along this gradient of increasing canopy complexity, we measured key vegetation characteristics, including community composition, biomass, cover, height, leaf area index and stem area index. We relate these vegetation characteristics to albedo and the partitioning of net radiation into ground, latent, and sensible heating fluxes.

Results: Canopy complexity increased along the sequence from tundra to forest due to the addition of new plant functional types. This led to non-linear changes in biomass, cover, and height in the understory. The increased canopy complexity resulted in reduced ground heat fluxes, relatively conserved latent heat fluxes and increased sensible heat fluxes. The localized warming associated with increased sensible heating over more complex canopies may amplify regional warming, causing further vegetation change in the Alaskan Arctic.

Abbreviations: LAI = Leaf area index; SAI = Stem area index; PFT = Plant functional type; COV = Coefficient of variation.

Nomenclature: Hultén (1968).

Question: Are species-specific regeneration strategies and competition the dominant processes facilitating species coexistence in a Quercus liaotungensis dominated temperate deciduous forest?

Location: Dongling Mountains, North China, 1300 m a.s.l.

Methods: Ripley's K-function was used to characterize the spatial patterns and spatial associations of two dominant tree species, Quercus liaotungensis and Betula dahurica, and a common subcanopy species, Acer mono, at different growth stages (adult, sapling, seedling).

Results: Seedlings, saplings and adults of all three species exhibited clumped distributions at most spatial scales. Quercus seedlings and saplings were positively associated with conspecific adult trees and spatially independent of dead trees suggesting that seed dispersal and vegetative regeneration influenced the spatial patterning of Quercus trees. Betula seedlings and saplings were positively associated with both live and dead trees of conspecific adults at small scales (<5 m) but negatively associated with live and dead trees of other species indicating sprouting as an important mechanism of reproduction. Saplings of Acer had a strong spatial dependence on the distribution of conspecific adult trees indicating its limited seed dispersal range. Negative associations between adult trees of Betula and Quercus demonstrated interspecific competition at local scales (<5 m).

Conclusions: Different regeneration strategies among the three species play an important role in regulating their spatial distribution patterns, while competition between individuals of Betula and Quercus at the adult stage also contributes to spatial patterning of these communities. The recruitment limitations of Betula and Quercus may affect the persistence of these species and the long-term dynamics of the forest.

Nomenclature: He (1992).

Question: What are the main broad-scale spatial and temporal gradients in species composition of arable weed communities and what are their underlying environmental variables?

Location: Czech Republic and Slovakia.

Methods: A selection of 2653 geographically stratified relevés sampled between 1954–2003 was analysed with direct and indirect ordination, regression analysis and analysis of beta diversity.

Results: Major changes in weed species composition were associated with a complex gradient of increasing altitude and precipitation and decreasing temperature and base status of the soils. The proportion of hemicryptophytes increased, therophytes and alien species decreased, species richness increased and beta diversity decreased with increasing altitude. The second most important gradient of weed species composition was associated with seasonal changes, resulting in striking differences between weed communities developed in spring and summer. In summer, weed communities tended to have more neophytes, higher species richness and higher beta diversity. The third gradient reflected long-term changes in weed vegetation over past decades. The proportion of hemicryptophytes and neophytes increased, while therophytes and archaeophytes decreased, as did species richness over time. The fourth gradient was due to crop plants. Cultures whose management involves less disturbances, such as cereals, harboured less geophytes and neophytes, and had higher species richness but lower beta diversity than frequently disturbed cultures, such as root crops.

Conclusions: Species composition of Central European weed vegetation is mainly influenced by broad-scale climatic and edaphic factors, but its variations due to seasonal dynamics and long-term changes in agricultural management are also striking. Crop plants and crop-specific management affect it to a lesser, but still significant extent.

Nomenclature: Kubát et al. (2002).

Question: Which is the response of the evergreen Quercus ilex and the deciduous Q. cerrioides to repeated disturbances?

Location: central Catalonia (northeastern Spain), in the areas affected by two of the largest historically recorded wildfires in NE Spain: the Bages-Berguedà fire (24 300 ha forested area burned in July 1994), and the Solsonès fire (14 300 ha burned in 1998).

Methods: Survival and growth of individuals of Quercus ilex and Q. cerrioides were evaluated in plants subjected to different fire histories and experimental disturbances (burning, cutting or clipping) applied either before or after summer.

Results: Survival was high (> 99%), with both species showing a similar high resistance to disturbances. Growth after experimental disturbance was positively related to the size of the individual before the latest forest fire occurred. Fire history had a large effect on resprout growth, as the repeated incidence of disturbances lowered the capacity of individuals to grow. The type and season of experimental disturbance experienced by plants had a large effect. Individuals that experienced total above-ground loss had lower growth rates than those with partial loss. A similar pattern was observed in individuals disturbed after the summer in relation to those disturbed before summer.

Conclusions: The larger growth rates recorded in Q. cerrioides across all fire histories and experimental treatments, and the higher vulnerability of Q. ilex to increased fire frequency, intensity of experimental disturbance, and disturbance season, provide evidence for the relatively high susceptibility of the latter to repeated disturbances. This view disagrees with the larger resilience of this species compared to co-existing deciduous oaks, as reported.

Question: Does increasing Festuca canopy cover reduce plant species richness and, therefore, alter plant community composition and the relationship of litter to species richness in old-field grassland?

Location: Southeastern Oklahoma, USA.

Methods: Canopy cover by species, species richness, and litter mass were collected within an old-field grassland site on 16, 40 m × 40 m plots. Our study was conducted during the first three years of a long-term study that investigated the effects of low-level nitrogen enrichment and small mammal herbivory manipulations.

Results: Succession was altered by an increase in abundance of Festuca over the 3-yr study period. Species richness did not decline with litter accumulation. Instead, Festuca increased most on species-poor plots, and Festuca abundance remained low on species-rich plots.

Conclusions: Festuca may act as an invasive transformer-species in warm-season dominated old-field grasslands, a phenomenon associated more with invasions of cool-season grasses at higher latitudes in North America.

Nomenclature: Anon. (1986).