Question: Is a rapid decline in abundance of a dominant species in a bottomland hardwood forest evidence for a trade-off between flood-and shade-tolerance?

Location: Bottomland hardwood forest in east Texas, USA.

Methods: We used 23 years of data on marked individuals to examine abundance, mortality, recruitment and growth of trees before and after a long growing season flood.

Results: A decline of 47% in abundance and 49% in basal area of Carpinus caroliniana (Betulaceae) occurred between 1989 and 1994 in a bottomland hardwood forest following a long summer flood. Other major species showed little change in abundance or basal area. The Carpinus decline was greater at low elevations suggesting the importance of flooding. Carpinus is rated among the least flood-tolerant species in the system. It differs from other species of similar flood tolerance in adult stature (midstory) and shade tolerance (tolerant).

Conclusions: The trade-off between flood tolerance and shade tolerance can influence dynamics of floodplain forests.

Nomenclature: Burns & Honkala (1990) except for Ilex decidua Walt.

Question: In Amazonian moist forest, four questions arose: 1. Do tree species differ in their susceptibility to lianas? 2. What host tree traits (branch-free bole height, growth rate, bark type, leaf length and adult stature) are correlated with the susceptibility of tree species to lianas infesting the trunk and the crown? 3. To what extent do spatial variables (proximity to liana-infested trees and the light environment of the tree crown) affect the likelihood of liana infestation? 4. Are spatial variables or tree traits relatively more important in influencing the susceptibility of trees to lianas? We address all questions separately for trunk and crown infestation.

Location: Tambopata Nature Reserve, Peru.

Methods: We collected information on liana infestation, tree morphological traits, growth, light-environment and position for 3675 trees in seven 1-ha permanent sample plots. We separated trunk from crown infestation and used correlation and logistic regression analyses for tree species and individual tree-level analyses, respectively.

Results: Half of all trees were colonised by at least one liana. Of 41 relatively common dicot tree species, at least five have significantly greater and three significantly lower crown infestation rates than expected by chance. Trunk and crown infestation are influenced by different host traits – trunk infestation was only affected by bark type, while crown infestation is reduced when trees are fast-growing, tall, have low-density wood, long branch-free boles and long leaves. The likelihood of both trunk and crown infestation increases for trees growing in close proximity to another liana-infested tree, but is invariant with the light environment of tree crowns.

Conclusion: Crown and trunk infestation have not been properly distinguished before; it is important to do so as the factors determining the different modes of infestation differ fundamentally. The association between crown infestation and tree traits suggests that increases in liana dominance in Amazonian forests could cause changes in forest composition, including favouring faster growing tree species with low density wood, potentially reducing the carbon stored by mature forests.

Nomenclature: We used current nomenclature at the time of analysis as provided at TROPICOS  http://www.tropicos.org/

Question: What components of drought influence the drought limit of Fagus sylvatica forests? This study contributes to the ongoing discussion regarding the future of Fagus as a major component of central European forests.

Location: The drought limit of F. sylvatica at its ecotone with forest dominated by Quercus pubescens, Q. petraea and their hybrids in two limestone regions (Klettgau, Schwäbische Alb) in southwestern Germany was compared.

Methods: Vegetation relevés were classified and a gradient analysis was performed. The vegetation pattern was analysed with several drought relevant variables. Classification trees were used to determine the drought limits of the Fagus forest.

Results: The Fagus, Quercus and the ecotone forests were floristically characterized. The lower humidity in the submontane Klettgau, compared to the montane Schwäbische Alb, was compensated for by greater soil moisture (ASWSC). Therefore, Fagus forest in the Schwäbische Alb grew on sites with ASWSC values similar to those of ecotone forest in Klettgau.

Conclusions: The interaction between climatic and edaphic drought related factors demonstrates that drought is a complex edaphic-climatic factor. Both components contribute to limiting the distribution of Fagus. For the two regions in southwestern Germany, and under the existing climatic conditions, it could be shown that Fagus is able to dominate forests on soils with very low ASWSC (≥ 68 l.m⁻²).

Nomenclature: Oberdorfer (1994).

Question: To what extent do bison serve as seed dispersers via epizoochory and endozoochory in tallgrass prairie, and does this differ by age-sex class of bison and by month?

Location: Tallgrass Prairie Preserve, Osage County, Oklahoma, USA.

Methods: We collected bison hair from 19 bulls, 45 cows, and 47 juveniles in fall and we collected bison dung monthly for a year. We recovered and identified seeds from hair and dung samples, and classified seeds by size and diaspore characteristics.

Results: Bison hair samples contained 2768 seeds from at least 76 plant species. Several species found in hair did not feature specialized appendages for adhesive dispersal. Seed species composition differed in hair collected from bulls, cows and juveniles, possibly due to differential habitat use. Dung samples contained 7418 seeds from at least 70 species, from which graminoids accounted for 3936 seeds from 27 species. Species composition of seeds contained in dung samples differed among months, corresponding to availability. Grasses constituted about half the seeds in both dung and hair samples, but Asteraceae were more strongly represented in hair, while Scrophulariaceae and Solanaceae were more strongly represented in dung.

Conclusions: We conclude that bison are potentially important dispersers of forbs as well as graminoids. A high abundance and wide diversity of seeds were found in both bison hair and dung. The great majority of seeds found undamaged in bison dung were small seeds, which agrees with the ‘foliage is the fruit’ hypothesis. Dispersal by both epizoochory and endozoochory may play an important role in life history of many species in tallgrass prairie landscapes.

Nomenclature: Kartesz & Kartesz (1980).

Question: Diagnostic species are useful tools for the identification and ecological interpretation of community types. Vegetation databases facilitate the computation of diagnostic values of regional validity, but it is essential to understand the behaviour of fidelity measures in large data sets.

Methods: We focused our study on the phi-coefficient (Φ) of association and its limit value, the Ochiai index. The northeast Spanish relevé database was stratified using an arbitrary distance threshold in species composition. Diagnostic species analysis was undertaken using three methods of context selection: I. within a syntaxon of higher rank; II. including relevés with similar composition to that of the target unit; III. using the entire stratified database. Species diagnostic values were computed as well as bootstrap percentile confidence intervals.

Results: Many species deemed as diagnostic by method I have their optima in vegetation types neighbouring the unit chosen as context. In contrast, method II excluded many of these species. Φ-values and confidence intervals were similar to those obtained by the Ochiai indexwhen using a large dataset (method III) but this similarity was greater for low level syntaxa.

Conclusions: The diagnostic value of species in a given region is best assessed using the Ochiai index, since it can be split into two interpretable asymmetrical components. We recommend the determination of context-dependent differential species using the Φ-coefficient, and the assessment of species regional diagnostic value by means of a stratification procedure in combination with the Ochiai index.

Nomenclature: Bolòs et al. (1990).

Question: To what extent do tree growth, mortality, and long-term disturbance patterns affect stand structure and composition of an old-growth Picea abies forest?

Location: Boreal Sweden.

Methods: We linked data from three 50 m × 50 m permanent plots established in 1986 with dendrochronology data to evaluate tree growth and mortality over an 18-year period and to describe a several-hundred-year disturbance history for this forest type.

Results: Averaged over all diameters, P. abies trees had an annual mortality rate of 0.60%; however, diameter had a striking effect on both growth and mortality, with trees of intermediate diameters (ca. 20–30 cm) showing faster growth and lower mortality. Their increased vigor gave rise to a diameter distribution resembling the ‘rotated sigmoid’ (not reverse-J) proposed for such conditions, and it led to a deficit of snags of intermediate diameters. Slow-growing trees had an increased likelihood of dying. Although recruitment occurred in most decades over the past 400 years, two prominent recruitment peaks occurred (mid 1700s and 1800s), neither of which appeared to cause a shift in tree species composition. The lack of fire evidence suggests that fire was not responsible for these recruitment peaks.

Conclusions: Taken together, these results depict a rather impassive system, where canopy trees die slowly over decades. Field observations suggest that fungal infections, mediated by wind, account for much of the mortality during these periods of relative quiescence. However, these periods are at times punctuated by moderate-severity disturbances that foster abundant recruitment.

Nomenclature: Mossberg & Stenberg (2003).

Question: Is it possible to improve the general applicability and significance of empirical relationships between abiotic conditions and vegetation by harmonization of temporal data?

Location: The Netherlands.

Methods: Three datasets of vegetation, recorded after periods with different meteorological conditions, were used to analyze relationships between soil moisture regime (expressed by the mean spring groundwater level – MSL_t calculated for different periods) and vegetation (expressed by the mean indicator value for moisture regime F_m). For each relevé, measured groundwater levels were interpolated and extrapolated to daily values for the period 1970–2000 by means of an impulse-response model. Sigmoid regression lines between MSL_t and F_m were determined for each of the three datasets and for the combined dataset.

Results: A measurement period of three years resulted in significantly different relationships between F_m and MSL_t for the three datasets (F-test, p < 0.05). The three regression lines only coincided for the mean spring groundwater level computed over the period 1970–2000 (MSL_climate) and thus provided a general applicable relationship. Precipitation surplus prior to vegetation recordings strongly affected the relationships.

Conclusions: Harmonization of time series data (1) eliminates biased measurements, (2) results in generally applicable relationships between abiotic and vegetation characteristics and (3) increases the goodness of fit of these relationships. The presented harmonization procedure can be used to optimize many relationships between soil and vegetation characteristics.

Question: Does shifting cultivation contribute to plant diversity in an Afrotropical semi-deciduous forest lacking large-scale natural disturbance?

Location: Sanaimbo forest, Côte d'Ivoire (Ivory Coast).

Methods: We surveyed species assemblages, structural attributes of diversity, and life-history traits along a 30-year chronosequence of abandoned fields, comparatively to old-growth and selectively logged forest stands.

Results: Patterns of species assemblages strongly changed with fallow area age, with respect to species' light requirements, suggesting niche partitioning along the successional gradient. Species richness, diversity and equitability were all increasing along this gradient. There were clear shifts in life-history traits spectra as the forest recovered, especially regarding leaf shape, lifespan and hairiness, diaspore dispersal, seed size, resprouting capacity, and life forms. Early colonization by the invasive Chromolaena odorata did not appear to impair secondary succession. Soil type influenced old-growth forest vegetation but not fallow vegetation. After 30 years of forest regrowth, plant communities exhibited endemism rates similar to those of ancient forests.

Conclusions: Shifting cultivation appears to be a sustainable land use when small-sized fields are embedded in a forest matrix and when agriculture lasts only one to few years, preserves remnant trees, excludes fire and keeps several years between two clearing episodes. It may even contribute to the high biodiversity maintenance at the whole forest scale, by conserving the successional mosaic. However, conservation of old-growth forest patches is required for a number of climax tree species.

Nomenclature: Guillaumet & Adjanohoun (1971).

Questions: Do short-term seed-addition experiments reliably tell us about seed limitation of perennial species? Does seed provenance affect recruitment success?

Locations: Three dry grassland sites (Negrentino, Poma, San Giorgio), southern Switzerland.

Methods: 18 000 seeds of Bromus erectus of three provenances were sown in a reciprocal design with temporal replication. Frequent checks were made of all emerged individuals of two seed cohorts over three years and continued annual checks of one cohort until year eight. Performance was determined by number and size of emerging and surviving individuals and a combined measure of population vigour.

Results: From a three-year perspective, all sites appeared to be seed limited, and differences due to seed provenance were small. Over five years, two sites showed an increasingly superior performance of the local over the foreign populations. At one of these two sites, average individuals remained small and a decrease in number and individual phytomass since the fifth year suggested complete microsite limitation. Reproductive individuals only occurred at the other sites and confirmed seed limitation after eight years. The best performing site had the first reproductive individuals in the fourth year.

Conclusions: B. erectus showed a long pre-reproductive phase during which the prediction of establishment success by individual counts can be misleading if plant size is not also measured. The effect of seed provenance was clearly indicated where populations established most successfully and local-over-foreign superiority increased with time.

Question: Can a simple soil classification method, accessible to non-experts, be used to infer properties of the biological soil crust (BSC) communities such as species richness, evenness, and structure?

Location: Grand Staircase-Escalante National Monument, an arid region of the Colorado Plateau, USA.

Methods: Biological soil crusts are highly functional soil surface communities of mosses, lichens and cyanobacteria that are vulnerable to soil surface disturbances such as grazing. We sampled BSC communities at 114 relatively undisturbed sites. We developed an eight-tier BSC habitat classification based upon soil properties including texture, carbonate and gypsum content, and presence of shrinking-swelling clays. We used simple structural equation models to determine how well this classification system predicted the evenness, richness, and community structure of BSC relative to elevation and annual precipitation.

Results: We found that our habitat classification system explained at least 3.5 × more variance in BSC richness (R² = 0.57), evenness (R² = 0.59), and community structure (R² = 0.34) than annual precipitation and elevation combined. Gypsiferous soils, non-calcareous sandy soils, and limestone-derived soils were all very high in both species richness and evenness. Additionally, we found that gypsiferous soils were the most biologically unique group, harboring eight strong to excellent indicator species.

Conclusions: Community properties of BSCs are overwhelmingly influenced by edaphic factors. These factors can be summarized efficiently by land managers and laypeople using a simple soil habitat classification, which will facilitate incorporation of BSCs into assessment and monitoring protocols and help prioritize conservation or restoration efforts.

Nomenclature: Zander 2008 (Bryophytes); Esslinger 2008 (Lichen).

Question: Can mixing ratio and species affect the use of substrate-derived CO₂ by Sphagnum?

Location: Poor fen in south Sweden and greenhouse in Wageningen, The Netherlands.

Methods: Two mixing ratios of Sphagnum cuspidatum and S. magellanicum were exposed to two levels of CO₂ by pumping CO₂ enriched and non-enriched water through aquaria containing the species mixtures in the greenhouse.

Results: Enhanced CO₂ stimulated the production of S. cuspidatum, but only in aquaria co-dominated by S. magellanicum, coinciding with higher CO₂ concentrations in the water layer. The denser growing S. magellanicum seemed to reduce gas escape from the water, resulting in accumulation of dissolved CO₂. Adding CO₂ did not affect species replacement.

Conclusions: The use of substrate-derived CO₂ for Sphagnum production depended on species identity and mixing ratio. The effect of mixing ratio on CO₂ concentrations in the water layer suggests that species composition may affect both the efficiency with which substrate-derived CO₂ is trapped and subsequently used. This could result in hitherto unexplored feedbacks between vegetation composition and gas exchange.

Nomenclature: Daniels & Eddy (1990).

Question: Plant communities in Paleotropical savannas are regulated by a combination of bottom-up and top-down effects. However, the paucity of ungulates and other large herbivores in Neotropical savannas has led to speculation that these communities are primarily structured by physical factors such as fire, precipitation and soil chemistry. We addressed the following question: How much plant biomass is consumed by leaf-cutter ants in Neotropical savannas, and is it comparable to the amount of biomass consumed by herbivores in Paleotropical savanna sites?

Location: Our study was conducted at the Estação Ecológica do Panga, located 30 km south of Uberlândia, Minas Gerais, Brazil. All field work was conducted in the vegetation type known as cerrado sensu stricto.

Methods and Results: Using direct measurements of herbivory, coupled with estimates of plant productivity and ant colony density, we found that leaf-cutter ants (Atta spp.) consume 13–17% of the foliar biomass produced annually by woody plants in a Neotropical savanna (Brazilian cerrado). Although comparisons with other savanna systems are complicated by methodological differences among studies, the proportion of biomass consumed by Atta species is about 25% of that consumed by the entire ungulate community in some African savannas and greater than or comparable to the total herbivory observed in some terrestrial ecosystems.

Conclusions: We hypothesize that this intense biomass consumption by Atta will have important ecological consequences for the cerrado ecosystem, because leaf-cutter abundance increases in fragmented or degraded habitats. These effects are likely to be exacerbated as anthropogenic pressure in this biodiversity hotspot increases.

Questions: What are the colonization trends in vegetated vs. bare-ground plots over a 10-year period in a central Alpine glacier foreland? What are the long-term effects of artificial seed addition to these plots?

Location: Glacier foreland of the Rotmoosferner in the Central Alps, Obergurgl, Tyrol, Austria, 2380 – 2400 m a.s.l.

Methods: A total of 40 permanent plots were established on moraines ice-free for 35 and 50 years on vegetated and bare-ground areas. Half of them were treated with a seed mixture in 1996 and 1997. Number and cover of the species were recorded in 1996 and from 2002/2003 to 2006.

Results: Species richness doubled in the control plots and tripled in seeded plots on the 35-year-ice-free moraine. On the 50-year-ice-free moraine the increase in species number was more modest. Significant site, seeding and time effects were found. Seed addition had no effects in the bare-ground plots on the older moraine and low effects in those on the younger moraine. All plots showed significant changes in cover of single species. The pioneer species decreased significantly in both moraines, in the control as well as in the seeded plots. A disappearance during the next years is predicted.

Conclusions: Colonization in bare-ground plots is limited by a lack of safe sites, whereas vegetated plots facilitate recruitment and establishment. Colonization on the glacier foreland is also dispersal limited. Seed addition enhanced the presence of already established species, and late successional species were newly introduced.

Nomenclature: Fischer et al. (2005).

Question: What is the relative contribution of geographic distance, soil and topographic variables in determining the community floristic patterns and individual tree species abundances in the nutrient-poor soils of central Amazonia?

Location: Central Amazonia near Manaus, Brazil.

Methods: Our analysis was based on data for 1105 tree species (≥ 10 cm dbh) within 40 1-ha plots over a ca. 1000-km² area. Slope and 26 soil-surface parameters were measured for each plot. A main soil-fertility gradient (encompassing soil texture, cation content, nitrogen and carbon) and five other uncorrelated soil and topographic variables were used as potential predictors of plant-community composition. Mantel tests and multiple regressions on distance matrices were used to detect relationships at the community level, and ordinary least square (OLS) and conditional autoregressive (CAR) models were used to detect relationships for individual species abundances.

Results: Floristic similarity declined rapidly with distance over small spatial scales (0–5 km), but remained constant (ca. 44%) over distances of 5 to 30 km, which indicates lower beta diversity than in western Amazonian forests. Distance explained 1/3 to 1/2 more variance in floristics measures than environmental variables. Community composition was most strongly related to the main soil-fertility gradient and C:N ratio. The main fertility gradient and pH had the greatest impact of species abundances. About 30% of individual tree species were significantly related to one or more soil/topographic parameters.

Conclusions: Geographic distance and the main fertility gradient are the best predictors of community floristic composition, but other soil variables, particularly C:N ratio, pH, and slope, have strong relationships with a significant portion of the tree community.

Question: Can seeds in the seed bank be considered as a potential source of material for the restoration of European plant communities including forest, marsh, grassland and heathland?

Methods: This study reviews seed bank studies (1990–2006) to determine if they provide useful and reliable results to predict restoration success. We formally selected 102 seed bank studies and analyzed differences between four plant community types in several seed bank characteristics, such as seed density, species richness and similarity between seed bank and vegetation. We also assessed the dominant genera present in the seed bank in each plant community.

Results: We observed remarkably consistent trends when comparing seed bank characteristics among community types. Seed density was lowest for grassland and forest communities and highest in marshes, whereas species richness, diversity and evenness of the seed bank community was lowest in heathland and highest in grassland. Similarity between seed bank and vegetation was low in forest, and high in grassland. There was a lot of overlap of the dominant genera of seed bank communities in all studies.

Conclusions: The absence of target species and the high dominance of early successional species, in particular Juncus spp., indicate that restoration of target plant communities relying only on seed germination from the seed bank is in most cases not feasible. The exceptions are heathland and early successional plant communities occurring after temporally recurring disturbances. Restoration of plant communities composed of late successional species, such as woody species or herbaceous species typical of woodland or forest rely mainly on seed dispersal and not on in situ germination.

Questions: 1. Does tree growth differ among bedrock-controlled and depositional (floodplains and alluvial fans) riparian landforms? 2. Will the elemental composition of tree cores reveal long-term differences in nutrient availability among bedrock-controlled and depositional landforms? 3. Is understory vascular plant species richness higher on depositional landforms than bedrock-controlled landforms, and highest yet on floodplains?

Location: Lower Indian Creek watershed, a tributary of Turnagain Arm of Cook Inlet, Alaska, USA.

Methods: Sampling of riparian forests was stratified by landform type. Forest structure, tree growth characteristics, and the elemental composition of tree cores were assessed within point-centered-quarter plots (n = 30). Plots were oriented along transects bisecting the valley floor, along which 50 m × 2 m plots (n = 35) were also sampled for understory species composition and richness.

Results: Bedrock-controlled and depositional landforms supported mature trees that did not differ in age, yet structural differences were significant. Forests on depositional landforms were less dense, radial tree growth (cm.a⁻¹) and annual basal area increments were significantly higher, and tree cores revealed lower C : N ratios than trees growing on bedrock-controlled landforms. Species richness of vascular plants was higher on depositional landforms at the landform and plot (100m²) scale. Floodplains supported higher species richness than fans at the landscape scale yet differences at the plot scale were insignificant.

Conclusions: Stratification of sampling by landform showed that structural differences between landforms may strongly influence the ecology of riparian plants, and that studies conducted without regard to landform structure may overlook fundamental influences on the ecology of riparian forests.

Nomenclature: Hulten (1968).