Question: Which environmental variables affect the floristic composition of south Patagonian bog vegetation along a gradient of climate and biogeochemical changes with increasing distance from the Pacific ocean?

Location: Trans-Andean transect (53° S), southern Patagonia

Material and Methods: Floristic composition, peat characteristics (water level, decomposition, pH, total nitrogen, total carbon, ash content and plant available P, K, Na, Ca, Mg, Fe, Mn, Zn, and Al) and climatic constraints of ombrotrophic peatlands were measured at 82 plots along a gradient of increasing distance from the Pacific Ocean.

Results: Climatic constraints and biogeochemical peat characteristics significantly change with increasing distance from the Pacific. Peatland vegetation shifted from hyperoceanic blanket bogs dominated by cushion forming vascular plants to the west to Sphagnum bogs to the east. Climatic and biogeochemical variables explained a large proportion of the floristic variation along the first DCA axis. The second axis represented a water level gradient. When ‘distance to the Pacific’ was defined as a covariable in partial CCA, the proportion of variance explained declined for most other variables, especially in the case of annual precipitation and exchangeable base cations and related traits. The differences in biogeochemical characteristics related to peat were mainly attributed to the input of sea-borne cations.

Conclusions: While variation in vegetation composition along a longitudinal gradient crossing the southern Andes was attributed to climatic constraints as expected, vegetation composition was also strongly affected by the biogeochemical characteristics of peat. Sea spray was of high ecological importance to peat chemistry and, consequently, to floristic composition. Presumably, south Patagonian peat bogs represent a glimpse of pre-industrial environments, so that these peat bogs may act as reference systems with respect to atmospheric inputs in mire ecology research.

Question: Positive interactions are predicted to be common in communities developing under high physical stress or high herbivory pressure due to neighbour amelioration of limiting physical and consumer stresses, respectively. However, when both stress sources meet in the same community, the relative importance of the two facilitation mechanisms is poorly understood. We ask: What is the relative importance of abiotic vs. biotic mechanisms of facilitation of tree saplings by shrubs in Mediterranean mountain forests?

Location: Sierra Nevada, SE Spain (1800–1850 m a.s.l.)

Methods: Saplings of four tree taxa (Acer opalus ssp. granatense, Quercus ilex, Pinus nigra ssp. salzmanii and P. sylvestris var. nevadensis) were planted following a 2 × 2 factorial design: two levels of herbivory (control and ungulate exclusion) and two microhabitats (under shrubs and in open areas). Sapling survival and growth were monitored for five years.

Results: Shrubs had positive effects on sapling survival both in control and ungulate excluded plots. This effect was species-specific, with shrubs increasing the survival of Acer opalus and Quercus ilex three and twofold, respectively, but having a minor effect on the Pinus species. Herbivory damage was also species-specific, being much higher for Acer opalus than for any other species. Shrubs did not protect saplings of any species against ungulates. Thus, all Acer saplings (the most damaged species) suffered herbivory outside the exclosures, which largely reduced sapling height.

Conclusions: Protection from abiotic stress (summer drought and winter frost) was much more relevant than protection from biotic stress (herbivory). However, we propose that the final balance between the two mechanisms can be expected to vary strongly between sites, depending on the relative magnitude of the different sources of stress and the intrinsic traits (e.g. palatability) of the species interacting.

Nomenclature: Castroviejo et al. (1986–2001) for tree species, and Molero-Mesa et al. (1992) for shrub species.

Question: The mosaic-cycle concept of forest dynamics dominates in Central Europe. According to this concept intermediate-scale disturbances only accelerate the forest break-up under existing cycles of forest development. Is such an approach correct, or should new developmental cycles be elaborated for intermediate-scale disturbances?

Location: Near-natural Abies alba - Fagus sylvatica forests in the Świętokrzyski National Park in Central Poland. In these forests intermediate-scale disturbances occurred between 1970 and 1990.

Methods: Data were collected twice in areas surrounding 212 permanent sample points (in 1994 and 2004). Two increment cores were taken from 259 sample Abies trees. The effect of intermediate-scale disturbances on radial increment of Abies was assessed. Probabilities of stand transition during a 10-year period between individual stages and phases of development of the mixed forest were calculated. The development stages and phases were arranged into hypothetical succession series of successive changes.

Results: In 1994 70 stands and in 2004, 47 stands representing stages and phases containing the older generation formed by trees > 100–150 years were found. Also, in 1994 142 and in 2004, 165 stands representing stages and phases containing the younger generations only, formed by trees < 100–150 years, were recorded. Stages and phases containing only younger generations do not occur in the existing forest development cycle which does not consider the influence of intermediate-scale disturbances separately. Two developmental cycles, which take into account the presence of the older generation and the younger generations only (under conditions of the occurrence of intermediate-scale disturbances), are proposed.

Conclusion: The mosaic-cycle concept of forest dynamics can be used to analyse the dynamics of Central European near-natural mixed-species forests, but new developmental cycles should be elaborated for intermediate-scale disturbances.

Question: Are trait differences between grasses along a gradient related to climatic variables and/or photosynthetic pathway?

Location: Temperate grassland areas of South and North America.

Methods: In a common garden experiment, we cultivated C₃ and C₄ grasses from grasslands under different climatic conditions, and we measured a set of 12 plant traits related to size and resource capture and utilization. We described (1) interspecific plant trait differences along a climatic gradient defined by the precipitation and temperature at the location where each species is dominant and (2) the association between those plant trait differences and the photosynthetic pathway of the species.

Results: Trait differences between grasses were related to the precipitation at the area where each species is dominant, and to the photosynthetic pathway of the species. Leaf length, leaf width, plant height, leaf area per tiller, specific leaf area, leaf δ¹³C ratio, and nitrogen resorption efficiency increased while leaf dry matter content and nitrogen concentration in senesced leaves decreased as precipitation increased. A proportion of these changes along the gradient was related to the photosynthetic pathway because dominant grass species in cold areas with low precipitation are mainly C₃ and those from warm and wet areas are C₄.

Conclusions: A previous worldwide analysis showed that traits of graminoid species measured in situ changed slightly along climatic gradients (< 10% variance explained). In contrast, under a common environment we observed that (1) grass traits changed strongly along a climatic gradient (30–85% variance explained) and, (2) a proportion of those changes were related to the association between photosynthetic pathway of the species and precipitation.

Nomenclature: Cabrera & Zardini (1978); Correa (1971–1988); Anon. (2005).

Question: Insufficient tree regeneration threatens the long-term persistence of biodiverse Mediterranean open oak woodlands. Could shrubs, scarce due to decades of management (clearing and ploughing), facilitate holm oak recruitment at both acorn and seedling stages?

Location: Open oak woodlands in Central Spain.

Methods: Plots with four acorns were planted: (1) under the canopy of the spiny shrub Genista hirsuta, (2) in a small cage, protecting against ungulates, (3) in a shaded cage, protecting against ungulates and sun, and (4) in open grassland. Sets of these four treatments were spatially grouped according to a randomised block design, with 16 blocks near (< 10 m) and 16 away from (> 20 m) parent trees to test for distance-related survival. Plots were regularly checked for seed removal. After emergence one seedling per plot (97 in total) was selected and its survival monitored.

Results: Three months after sowing, 199 of 512 acorns were removed, predominantly by rodents. Acorn removal occurred at each treatment but was highest under shrubs. Eight months after sowing, seedling survival was highest under shrubs (50%), followed by shaded cages (16%), open grassland (4%) and cages (0%). Main mortality cause was drought (90%), killing most seedlings between June and July. No seedlings died from ungulate browsing.

Conclusion: Shrubs demonstrated clear net facilitative effects for Quercus ilex recruitment, despite higher seed removal. Shading appears the crucial factor facilitating seedling survival. We therefore propose that lack of shrubs contributes largely to tree recruitment failure in Mediterranean open woodlands; management should aim at conserving shrubs.

Questions: 1. Indicator values, such as those of Ellenberg, for different environmental factors are seen as independent. We tested for the presence of interactions between environmental factors (soil moisture and reaction) to see if this assumption is simplistic. 2. How close are Ellenberg indicator values (IVs) related to the observed optima of species response curves in an area peripheral to those where they have been previously employed and 3. Can the inclusion of bryophytes add to the utility of IVs?

Location: South Uist, Outer Hebrides, Scotland, UK.

Methods: Two grids (ca. 2000 m × 2000 m) were sampled at 50-m intervals across the transition from machair to upland communities covering an orthogonal gradient of both soil pH (reaction) and soil moisture content. Percentage cover data for vascular plants, bryophytes and lichens were recorded, along with pH and moisture content of the underlying sand/soil/peat. Reaction optima, derived from species response curves calculated using HOF models, were compared between wet and dry sites, and moisture optima between acidic and basic samples. Optima for the whole data set were compared to Ellenberg IVs to assess their performance in this area, with and without the inclusion of bryophytes.

Results: A number of species showed substantially different pH optima at high and low soil moisture contents (18% of those tested) and different soil moisture optima at high and low pH (49%). For a number of species the IVs were poor predictors of their actual distribution across the sampled area. Bryophytes were poor at explaining local variation in the environmental factors and also their inclusion with vascular plants negatively affected the strength of relationships.

Conclusions: A substantial number of species showed an interaction between soil moisture and reaction in determining their optima on the two respective gradients. It should be borne in mind that IVs such as Ellenberg's may not be independent of one another.

Nomenclature: Stace (1997) for vascular plants; Watson (1981) for mosses and liverworts; Jahns (1983) and Gilbert (2000) for lichens.

Question: How far can we simplify the floristic complexity of a tropical rainforest into functional groups in order to predict tree population dynamics after logging–induced disturbance?

Location: Paracou experimental site, French Guiana.

Methods: We used data from over 15 years in control and disturbed plots from a silvicultural trial started in 1984. We selected 53 common tree species assigned to five functional groups based on potential size and light requirement. For each species, we quantified: the fate, i.e. variation in population size, and dynamic processes, i.e. mortality, recruitment and growth, driving this fate. We investigated the links between dynamic processes, fate and functional groups.

Results: Disturbance stimulated growth and recruitment for most species, but had a heterogeneous impact on mortality. Species fate in disturbed plots depended on recruitment and was more favourable than in control plots. The functional classification was more predictive for most separate dynamic processes than for species fate: after disturbance, significant differences were found between all functional groups for growth. Pioneer heliophilous species showed significantly higher recruitment rates. Mortality of shade–tolerant species slightly increased and of mid–tolerant and heliophilous species decreased.

Conclusions: A combination of three species classifications separately built from the growth, recruitment and mortality processes is more informative than a global classification combining the processes. Identifying the pioneer heliophilous species on the basis of their growth rate is crucial to predict species fate after disturbance. We showed that potential growth rate could be used as a reliable indicator to identify this group.

Nomenclature: Hollowell et al. (2001) for Anthophyta families A–L;  http://www.mnh.si.edu/biodiversity/bdg/planthtml/index.html for other families.

Questions: Two hypotheses were tested: (1) physical features, such as wetland surface area and habitat diversity, together with water chemistry, are important determinants of species richness and composition of macrophyte assemblages and (2) species richness and composition of macrophyte assemblages differ between wetlands of different types (i.e., palustrine versus lacustrine) and between wetlands of different hydrologies (i.e. permanent versus intermittent).

Location: A subtropical coastal plain segment (2500 km²) of southern Brazil.

Methods: Quarterly collections were carried out in 15 wetlands (2004–2005) in southern Brazil. Differences in richness over time were tested using repeated measures ANOVA. Stepwise multiple regression was performed to investigate relationships between total richness and environmental variables. Significance of differences between wetland types and hydroperiods on species composition was verified by MRPP (Multi-Response Permutation Procedure). The influence of the environmental variables on species composition was assessed using CCA (Canonical Correspondence Analysis).

Results: Macrophyte species richness changed with time, was not significantly different between wetland types, but was higher in permanent wetlands than in intermittent ones. Area, habitat diversity and soluble reactive phosphorus concentration explained 76% of the variation in species richness. Species composition was different between permanent and intermittent wetlands, although it was not significantly different between wetland types. Area, habitat diversity and water chemistry explained 50.1% of species composition.

Conclusions: Species richness and composition of wetland macrophytes were mainly determined by area, habitat diversity and hydroperiod. These results can be used for the development of conservation and management programs in southern Brazil.

Nomenclature: Irgang & Gastal (1996).

Question: Several mechanisms have been proposed that control the spatio-temporal pattern of species coexistence. Among others, the species pool hypothesis states that the large-scale species pool is an important factor in controlling small-scale species richness through filtering of species that can persist within a species assemblage on the basis of their tolerance of the abiotic environment. Because of the process of environmental filtering, co-occurring species that experience similar environmental conditions are likely to be more taxonomically similar than ecologically distant species. This is because, due to the conservatism of many species traits during evolutionary diversification, the ability of species to colonize the same ecological space is thought to depend at least partially on their taxonomic similarity. The question for this study is: Under the assumption of trait conservatism, does environmental filtering lead to nonrandom species assemblages with respect to their taxonomic structure?

Methods: The significance of taxonomic filtering in regulating species coexistence is tested using data from 15 local species assemblages from the urban flora of Rome (Italy). To find out whether the taxonomic structure of the selected ‘local’ species assemblages was significantly different from random, we used a Monte Carlo simulation in which for each local species assemblage, the actual taxonomic diversity was compared to the taxonomic diversity of 1000 virtual species lists of the same size extracted at random from a larger ‘regional’ species pool.

Results: We found that in most cases the local species assemblages have a higher degree of taxonomic similarity than would be expected by chance showing a phenomenon of ‘species condensation’ in a small number of higher-level taxa.

Conclusions: Our observations support the species pool hypothesis and imply that environmental filtering is an important mechanism in shaping the taxonomic structure of species assemblages. Therefore, the incorporation of taxonomic diversity into landscape and community ecology may be beneficial for a better understanding of the processes that regulate species coexistence.

Nomenclature: Conti et al. 2005.

Questions: Are there interspecific differences in mortality and recruitment rates across life stages between two shade-tolerant dominant trees in a sub-alpine old-growth forest? Do such differences in demography contribute to the coexistence and co-dominance of the two species?

Location: Sub-alpine, old-growth forest on Mt. Ontake, central Honshu, Japan.

Methods: From 1980 to 2005, we recorded DBH and status (alive or dead) of all Abies mariesii and A. veitchii individuals (DBH ≥ 5 cm) in a 0.44-ha plot. Based on this 25 year census, we quantified mortality and recruitment rates of the two species in three life stages (small tree, 5 cm ≤ DBH < 10 cm; subcanopy tree, 10 cm ≤ DBH < 20 cm; canopy tree, DBH ≥ 20 cm).

Results: Significant interspecific differences in mortality and recruitment rates were observed in both the small tree and subcanopy tree stages. In this forest, saplings (< 5 cm DBH) are mostly buried by snow-pack during winter. As a consequence, saplings of A. mariesii, which is snow and shade tolerant, show higher rates of recruitment into the small tree stage than do those of A. veitchii. Above the snow-pack, trees must tolerate dry, cold temperatures. A. veitchii, which can more readily endure such climate conditions, showed lower mortality rate at the subcanopy stage and a higher recruitment rate into the canopy tree stage. This differential mortality and recruitment among life-stages determines relative dominance of the two species in the canopy.

Conclusion: Differential growth conditions along a vertical gradient in this old forest determine survival of the two species prior to reaching the canopy, and consequently allow co-dominance at the canopy stage.

Nomenclature: Kitamura & Murata (1994).

Question: Since increases in altitude and grazing intensity generally result in decreases in height growth of alpine grasslands, plant height may integrate effects of environmental stress and grazing disturbance and provide better assessments of the variation in root:shoot (R:S) biomass ratio than other variables. However, it is unclear if there is a general relationship between plant height and R:S ratio across grassland ecosystems. Such knowledge would be helpful for root biomass estimation in grasslands.

Location: An altitudinal transect in the Gonghe Basin (2880–4040 m a.s.l.), northeast Tibetan plateau.

Methods: We measured standing biomass both above-ground and below-ground, maximum plant height (MPH) and soil variables across 43 plots.

Results: Climatic variables explained the variations in MPH and R:S ratio of undegraded grasslands better than soil variables (46–50% vs <19%), while those of degraded grasslands generally showed insignificant correlations with climatic and soil variables. There was a general relationship between R:S ratio and MPH (negative, R² = 0.76, P < 0.001) across degraded and undegraded grasslands. The relationship was used to predict R:S ratio in 13 additional plots in steppe grasslands of Inner Mongolia, and good agreement of expected and observed values has been found (R² = 0.87, P < 0.001).

Conclusions: MPH, that is relatively easy to measure, can be used to predict R:S ratio at plot to regional scales. It is promising to develop a new method for large-scale estimation of root biomass in grasslands using MPH and shoot biomass avoiding tedious procedures of physical measuring of above and below-ground biomass.

Question: What is the effect of leaf litter on growth and mortality of feather mosses. Three experiments were conducted to isolate the shading effect from the effect of leaching of soluble compounds from the leaf litter effect on feather moss mortality and growth.

Location: Edmonton, Alberta and the northern boreal coniferous forest, west-central Alberta, Canada.

Methods: In a field experiment Populus tremuloides (aspen)leaf litter was applied to beds of feather mosses dominated by Hylocomium splendens. Treatments were one layer of leaves held in place with netting; one layer of leaves coarsely ground, sprinkled over the moss layer; a shade cloth equivalent to one layer of leaves; and a control. In two growth chamber experiments, the application of aqueous extracts of P. tremuloides and Pinus contorta leaf litter and the effect of shade and soluble carbohydrates were tested on the growth and mortality of Ptilium cristacastrensis.

Results: Mortality of Hylocomium was greatest under the intact leaves, followed by the treatments using shade cloth and ground leaves and finally the control. The application of aqueous extracts of aspen leaf litter resulted in senescence or death of nearly all Ptilium shoots compared to no effects for the control or for similar extracts of pine needle litter. Extracts from aspen litter had greater concentrations of phenolic compounds and soluble sugars than pine extracts. Addition of sugars to Ptilium allowed it to grow and accumulate carbohydrates, even in low light conditions.

Conclusions: Results suggest that broad-leaved deciduous overstory species can limit the growth of feather mosses through their leaf litter and by implication affect the humus form, nutrient cycling, and understory composition of these forests.

Nomenclature: Moss & Packer (1983); Lawton (1971).

Question: Are soil lichen communities structured by biotic interactions?

Location: Gypsum outcrops located next to Belmonte del Tajo, central Spain.

Methods: We sampled a total of 68 (50 cm × 50 cm) plots in gypsum outcrops from central Spain. Each plot was divided into 100 (5 cm × 5 cm) sampling quadrats, and the presence of all lichen species in every quadrat was recorded (6800 quadrats in total). We used two realistic null models to generate random communities unstructured by biotic interactions, and used them to test the hypothesis that soil lichen species co-occur less often than expected by chance.

Results: We found fewer species combinations and less co-occurrence than expected by chance. However, the latter result was dependent on the null model selected. The number of checkerboard pairs did not differ significantly from the null expectation.

Conclusions: Overall, our results suggest that gypsiferous soil lichen communities are structured by competitive interactions. They are consistent with studies conducted with a wide variety of taxa, and fill a gap in our knowledge of the factors driving the small-scale distribution of these important organisms.

Nomenclature: Tutin et al. (1964–1980) for vascular plants; Hladun & Llimona (2002–2007) and Breuss (1996) for lichens.

Questions: 1. Does random colonization predominate in early stages of primary succession? 2. Do pioneer species facilitate the establishment of later arriving species? 3. Does an initially random distribution change to an aggregated pattern with ongoing succession?

Location: Lignite mining region of Lower Lusatia, eastern Germany.

Methods: Individual plants were mapped along a 2 m × 28 m transect during three successive years and classified into two groups (1) the pioneer Corynephorus canescens and (2) ‘all other species’. Using the pair-correlation function, univariate point pattern analysis was carried out by applying a heterogeneous Poisson process as null model. Bivariate analysis and a toroidal shift null model were applied to test for independence between the spatial patterns of the two groups separately for each year, as well by exploring spatiotemporal patterns from different years.

Results: In the first year Corynephorus and ‘all other species’ showed an aggregated pattern on a spatial scale > 40 cm and in the second and third years a significant attraction for distances between 4 and 12 cm, with an increasing radius in the third year. The analyses of interspecific spatiotemporal dynamics revealed a change from independence to attraction between distances of 4 cm and 16 cm when using Corynephorus as focal species. However, applying ‘all other species’ as focal points results in a significant attraction at distances up to 60 cm in the first year and a diminishing attraction in the second and third years with distances ≤ 6 cm.

Conclusions: Facilitative species-species interactions are present in early stages of primary succession, resulting mainly from pioneer species acting as physical barriers and their ability to capture diaspores being drifted by secondary dispersal along the substrate surface. However, due to gradual establishment of perennial species and their ability of lateral extension by vegetative dispersal, facilitation may influence spatial pattern formation predominantly on short temporal and fine spatial scales.

Nomenclature: Wisskirchen & Haeupler (1998).

Questions: How does vegetation first establish on newly-formed lava substrates? Do very small (cm) and meso-scale (m) variations in the physical environment influence this process and subsequent vegetation development?

Location: Mount Hekla, southern Iceland (64°00′ N, 19°40′ W).

Methods: Data on vegetation structure and the incidence of ‘safe sites’ suitable for colonisation were collected from high and low points on the surfaces of lava flows emplaced during the 1991 and 2000 A.D. eruptions of Mount Hekla. Effects of flow age and meso-topographic position on vegetation structure (moss cover, patch density, stem length) were assessed by two-way analyses of variance. The distributions of colonisation events and available safe sites were analysed using point pattern techniques.

Results: Rapid colonisation of the lava surface was observed, despite stressful environmental conditions. The 1991 and 2000 flows differed significantly in vegetation structure, but there were no significant differences in moss cover, patch density and stem length between ‘high’ and ‘low’ sites.

Conclusions: Colonisation events are invariably associated with small-scale irregularities on the surface of the lava. The colonisation process appears to be spatially random. Development of the moss ‘carpet’ proceeds by vertical thickening and lateral growth and coalescence of moss patches that establish in ‘safe sites’. This process is rapid, with close to 100% of available safe sites exploited within 20 years. Topographic position makes no difference to the very early stages of vegetation development and cannot be used to ‘forecast’ the later stages of development.

Nomenclature: Purvis et al. (1994); Hansen & Anderson (1995); Kristinsson (2005); Smith (1996, 2004).