Question: What is the relative importance of fire-induced canopy mortality, soil burning and post-fire herbivory on tree seedling performance?

Location: Subalpine Nothofagus pumilio forests at Challhuaco valley (41°13′S, 71°19′W), Nahuel Huapi National Park, Argentina.

Methods: We fenced and transplanted soils of three burning severities along a fire severity gradient produced by a fire in 1996. Over two growing seasons we monitored soil water, direct incoming solar radiation, seedling survival, final seedling total biomass and root/shoot ratio. Additionally, we assessed severity-related changes in soil properties.

Results: Incoming radiation (an indicator of the amount of canopy cover left by the fire) was the primary factor influencing spring and summer top soil water availability, first and second-year seedling survival and seedling growth. While seedling survival and soil water content were negatively affected by increased radiation, seedling final biomass was highest in very open microsites. Burned soils showed lower water holding capacity and soil carbon; however these changes did not affect topsoil water, and, contrary to expectation, there was a slight tendency toward higher seedling survival on more heavily burned soils. Herbivory significantly reduced seedling survival, but only under high-radiation conditions. While the effect of radiation on final seedling biomass was not affected by herbivory, R/S ratios were significantly reduced by herbivory in high radiation microsites.

Conclusions: Despite inducing faster aerial growth, increased radiation and herbivory in severely burned sites may effectively prevent post-fire regeneration in north Patagonian subalpine forest where seed sources are not limiting.

Nomenclature: Correa (1969–1984).

Abbreviations: HEF = herbivory effect; R/S = root:shoot final seedling biomass ratio; RAD = Direct incoming spring-summer integrated radiation; SBS = soil burning severity treatments; SWC = Gravimetric top soil water content.

Question: Which are the structural attributes and the history of old-growth Fagus forest in Mediterranean montane environments? What are the processes underlying their structural organization? Are these forests stable in time and how does spatial scale affect our assessment of stability? How do these forests compare to other temperate deciduous old-growth forests?

Location: 1600–1850 m a.s.l., Fagus forest near the tree line, central Apennines, Italy.

Methods: An old-growth Fagus forest was studied following historical, structural and dendroecological approaches. History of forest cover changes was analysed using aerial photographs taken in 1945, 1954, 1985 and 1994. The structural analysis was carried out in the primary old-growth portion of the forest using 18 circular and two rectangular plots. Dendroecological analyses were conducted on 32 dominant or co-dominant trees.

Results: These primary old-growth Fagus remnants consist of four patches that escaped logging after World War II. Both living and dead tree components are within the range of structural attributes recognized for old-growth in temperate biomes. Dendroecological analyses revealed the roles of disturbance, competition and climate in structuring the forest. We also identified a persistent Fagus community in which gap-phase regeneration has led to a mono-specific multi-aged stand at spatial scales of a few hectares, characterized by a rotated-sigmoid diameter distribution.

Conclusion: Even at the relatively small spatial scale of this study, high-elevation Apennine Fagus forests can maintain structural characteristics consistent with those of old-growth temperate forests. These results are important for managing old-growth forests in the Mediterranean montane biome.

Nomenclature: Pignatti (1982).

Abbreviations: BAI = Basal area increment; CCTRMD = Computer controlled tree ring measuring device; CV = Coefficient of variation; CWD = Coarse wood debris; DBH = Diameter at breast height; DIB = Diameter inside bark; IGM = Istituto Geografico Militare; OG = Old-growth; PGC = Percentage growth change; PNA = Abruzzo National Park; UTM = Universal transverse Mercator.

Aim: Patterns of plant functional traits related to clonality (clonal growth modes; CGM) in plant communities were studied and hypotheses on the importance of the selected traits in plant communities supported by soils differing in moisture and nutrient status were tested.

Material and Methods: Selected plant functional traits, such as the position of the mother-daughter plants connections, length of spacers, frequency of multiplication, persistency of ramets connections, presence of storage organs and bud protection were studied in two contrasting plant communities (xeric and mesic abandoned pastures) typical of central Apennines, Italy.

Results and Discussion: Clonality was shown to be of great importance in both mesic and xeric grasslands. The major differences between the two communities were due to the dominant CGMs: turf graminoids (having effective protection of growth meristems in dense tussocks) dominated xeric grasslands, while rhizomatous graminoids (typical of competitive resource-rich environments) dominated mesic grasslands. Below-ground CGOs (clonal growth organs), shorter spacers, higher multiplication potential, permanent ramet connection, large bud bank and increased importance of bud protection were found to be of importance in water stressed xeric grassland. Contrary to our expectations, the mesic (less stressed) grasslands have the higher number of clonal plants possessing storage organs.

Nomenclature: Pignatti (1982) for taxa; Venanzoni & Kwiatkowski (1995) for the syntaxa mentioned in ^{Table 1}.

Abbreviations: CGM = Clonal growth mode; CGO = Clonal growth organ.

Question: Underlying ecological processes have often been inferred from the analysis of spatial patterns in ecosystems. Using an individual-based model, we evaluate whether basic assumptions of species' life-history, drought-susceptibility, and shade tolerance generate dynamics that replicate patterns between and within forest stands.

Location: Virginia piedmont, USA.

Method: Model verification examines the transition in forest composition and stand structure between mesic, intermediate and xeric sites. At each site, tree location, diameter, and status were recorded in square plots ranging from 0.25 to 1.0 ha. Model validation examines the simulated spatial pattern of individual trees at scales of 1–25 m within each forest site using a univariate Ripley's K function.

Results: 7512 live and dead trees were surveyed across all sites. All sites exhibit a consistent, significant shift in pattern for live trees by size, progressing from a clumped understorey (trees ≥ 0.1 m in diameter) to a uniform overstorey (trees > 0.25 m). Simulation results reflect not only the general shift in pattern of trees at appropriate scales within sites, but also the general transition in species composition and stand structure between sites.

Conclusions: This shift has been observed in other forest ecosystems and interpreted as a result of competition; however, this hypothesis has seldom been evaluated using simulation models. These results support the hypothesis that forest pattern in the Virginia piedmont results from competition involving species' life-history attributes driven by soil moisture availability between sites and light availability within sites.

Nomenclature: Harlow et al. (1996).

Abbreviations: ALB = Above-ground live biomass; BA = Basal area; CSR = Complete spatial randomness; DBH = Diameter at breast height; LAI = Leaf area index; MUSE = Multistrata spatially explicit model; PET = Potential evapo-transpiration.

Question: The aim of the present study is to determine whether seed/seedling predation will increase and Fagus survival will decline with the recovery of the Sasa cover.

Methods: We examined Fagus crenata regeneration for seven years in an old-growth Fagus-Sasa forest near Lake Towada, northern Japan, by examining the effects of simultaneous death of Sasa, tree canopy gap formation, mast seeding of Fagus and seed and seedling predation by rodents on the survival of Fagus seeds and current year seedlings. We established four types of sites differing in forest canopy (closed or gap) and Sasa status (dead or alive) following the simultaneous flowering and death of Sasa kurilensis (dwarf bamboo) in 1995.

Results: Fallen Fagus seed was abundant in 1997 and 2000 (mast years). In sites with alive Sasa, survival from the first growing season was low due to high seed and seedling predation. In sites with dead Sasa, seed survival under the canopy was high for both mast years, but in gaps it varied between years. Seedling survival was highest in canopy gaps with dead Sasa (gap-dead) in 1998, because of higher light levels and lower predation by rodents. However, seedling survival in these plots was low in 2001, apparently because rapid Sasa recovery favoured rodent predation. In both mast years, Sasa die-back had significant positive effects on seed and seedling survival under closed canopies because the seedlings there were more successful in escaping predation.

Conclusion: The change in successful sites for the early stage of regeneration of Fagus appears to reflect the combined effects of canopy gap, seed/seedling predation and revegetation of Sasa.

Nomenclature: Satake et al. (1989).

Abbreviations: PPFD = Photosynthetic photon flux density; RPPFD = Relative photosynthetic photon flux density.

Question: What are the grazing effects in the spatial organization and the internal structure of high and low cover patches from a two-phase vegetation mosaic?

Location: Patagonian steppe, Argentina.

Methods: We mapped vegetation under three different grazing conditions: ungrazed, lightly grazed and heavily grazed. We analysed the spatial patterns of the dominant life forms. Also, in each patch type, we determined density, species composition, richness, diversity, size structure and dead biomass of grasses under different grazing conditions.

Results: The vegetation was spatially organized in a two-phase mosaic. High cover patches resulted from the association of grasses and shrubs and low cover patches were represented by scattered tussock grasses on bare ground. This spatial organization was not affected by grazing, but heavy grazing changed the grass species involved in high cover patches and reduced the density and cover of grasses in both patch types. Species richness and diversity in high cover patches decreased under grazing conditions, whereas in low cover patches it remained unchanged. Also, the decrease of palatable grasses was steeper in high cover patches than in low cover patches under grazing conditions.

Conclusions: We suggest that although grazing promotes or inhibits particular species, it does not modify the mosaic structure of Patagonian steppe. The fact that the mosaic remained unchanged after 100 years of grazing suggests that grazing does not compromize population processes involved in maintaining patch structure, including seed dispersal, establishment or biotic interactions among life forms.

Nomenclature: Correa (1971–1984).

Abbreviations: CSR = Complete spatial randomness; INTA = Instituto Nacional de Tecnología Agropecuaria.

Question: Does the influence of plant canopy on seedling establishment interact with climate conditions, and particularly, do intensified drought conditions, enhance a positive effect of the vegetation canopy on seedlings in Mediterranean-type ecosystems.

Location: Mediterranean shrubland near Barcelona, Spain at 210 m a.s.l.

Methods: Over the course of four years we recorded seedling emergence and survival in open areas and below vegetation under control, drier and warmer experimental climatic conditions.

Results: Seedling emergence is more sensitive to climate conditions than later stages of growth. When considering the whole set of species, the total number of established seedlings at the end of the experiment was lower in the drought and warming stands than in control ones, and vegetation canopy increased the number of these seedlings in the drought stands. Drought reduced seedling emergence but not warming, while the interaction between climate treatments and vegetation canopy was not significant. Seedling survival was lower in the warming treatment than in the control. Under drought conditions, vegetation canopy increased seedling emergence of the dominant Globularia alypum. In control stands, vegetation canopy reduced their survival. Vegetation canopy increased the survival of the dominant Erica multiflora in warming stands, and it reduced the survival of G. alypum in drought stands. No significant effects of drought and warming were observed in the seed rain of these two species.

Conclusions: The balance of the facilitation-competition interactions between vegetation canopy and seedling establishment in Mediterranean-type ecosystems determined by water availability, and drought conditions enhance the positive effect of vegetation canopy. This interaction is species-specific and shows important between-year variability.

Nomenclature: Bolós et al. (1990).

Question: The use of plant traits to predict weed impact is a long-standing goal in weed ecology. In particular, trait plasticity, i.e. the variability of a trait response to environmental change, is widely considered to contribute to weed success. However, the generality of the role of trait plasticity in determining weed impacts has never been systematically tested.

Methods and location: We tested the hypothesis that high-impact environmental weeds have greater plasticity in growth responses to nutrient availability than low-impact species. In a glasshouse experiment, we supplied a complete nutrient solution at five different concentrations to seedlings of 24 species of high- and low-impact environmental weeds from south east Queensland, Australia.

Results: Almost all species showed plasticity in biomass accumulation in response to the nutrient treatments, but plasticity in biomass accumulation did not differ between related high- and low-impact species. There was no evidence of nutrient-related plasticity in root:shoot allocation. Seedling survival was greater at higher nutrient concentrations, and also differed greatly between families. Survival among low-impact species was marginally (p = 0.0610) lower than among high-impact species.

Conclusion: We conclude that the impact of environmental weeds in south east Queensland cannot be predicted from nutrient-related plasticity in seedling growth. The effects of nutrients on seedling survival warrant further research.

Nomenclature: Stanley & Ross (1983–1989); Richardson et al. (2000).

Question: Which factors influence the effectiveness of biotic refuges for harbouring grazing-sensitive species in pastures with a long history of grazing by large herbivores? Previous research showed that spiny clumps of the cactus Opuntia polyacantha provided refuges from cattle grazing for plants and for inflorescence production on short-grass steppe. In this paper, seven factors that may have a potential positive influence on the refuge effects of cactus at a landscape scale were assessed.

Location: Short-grass steppe of the Great Plains of North America.

Methods: The study was conducted in eight long-term grazed pastures and their respective ungrazed controls that were established 60 years ago.

Results: Heavy grazing intensities were necessary for some positive effects of cactus to manifest, and some refuge effects changed to negative effects under lower grazing pressure. Refuge effects increased with plant community productivity due to greater abundances of grazing-sensitive species, and greater grazing intensities in the more productive areas. Cover of cactus cladodes (spine-covered pads) inside clumps appeared to be the main limiting factor for refuge effects, probably by limiting available space for grazing-sensitive species in the clumps. Other factors such as size and density of cactus clumps, and the presence of large refuges in the proximity of clumps had minor influence on the effectiveness of cactus refuges.

Conclusions: The effects of biotic refuges largely varied with ecological conditions and structural characteristics of the refuge. Refuge effects were mainly influenced by grazing intensity, plant community productivity, and structural characteristics of the biotic refuges. A conceptual model of factors influencing refuge effects at a local landscape scale in plant communities grazed by large herbivores is presented.

Question: What is the long-term influence of nutrient availability, productivity and soil pH on grassland community organization?

Location: Ukulinga research farm, KwaZulu-Natal, South Africa.

Methods: The influence of fertilization on soil pH, nitrogen (N) and phosphorus (P) on variation in plant traits, community composition and species richness were examined in a 50-year grassland fertilization experiment.

Results: Averaged over 30 years, above-ground net primary production (ANPP) was 337, 428 and 518 g.m⁻² in sites not fertilized, fertilized with N, and fertilized with N plus P respectively. ANPP depended directly on N-fertilization but not on P-fertilization or liming, and responded positively to the interaction of N (first limiting nutrient) and P (second limiting nutrient). Short narrow-leaved grass species – Themeda triandra, Tristachya leucothrix and Setaria nigrirostris – dominated sites of lowest ANPP where N was limiting (unfertilized, P-fertilized or limed sites). A tall narrow-leaved species, Eragrostis curvula, dominated sites of intermediate ANPP where P was limiting (N-fertilized sites). By contrast, a tall broad-leaved species, Panicum maximum, dominated the most productive sites where neither N nor P were limiting (N- and P-fertilized sites). Certain species responded to liming and type of N-fertilizer apparently because of their effects on soil pH. N-fertilization reduced the density of herbaceous dicots (forbs) from 14 (unfertilized) to two (high N, no P, no lime) and five species per m² (high N, no P, limed). This effect was attributed to increased ANPP and a decrease in soil pH from 4.6 (KCl) in unfertilized sites to 3.49 (high N, no lime) and 4.65 (high N and lime). Soil acidification had no effect on grass species richness but influenced the abundance of certain species.

Conclusions: Grassland community organization is determined not only by the influence of N availability, but also by the hierarchical interaction of N and P availability, in part through their compounded effect on ANPP, and by individualistic species responses to soil pH.

Nomenclature: Arnold & De Wet (1993)

Question: Along river floodplains lower distribution limits of plant species seem largely determined by their tolerance to rarely occurring floods in the growing season. Such distribution patterns remain fixed for many years suggesting additional effects of winter floods at lower positions. Our objective was to investigate the direct and indirect effects of winter floods on colonization of floodplains in a series of field experiments.

Location: River Rhine, The Netherlands.

Methods: We measured the direct effects of winter floods on seedling survival and seed removal and survival at low and high floodplain elevation. Indirect effects of winter flooding through changes in the soil were investigated by measuring seedling emergence on soil transplants that were exchanged between high and low floodplain elevation. To investigate indirect effects of floods on the germination environment through changes in the vegetation structure, we measured the effects of vegetation removal on recruitment of sown species. Results: Recruitment was seed limited at both floodplain elevations. An additional effect of vegetation removal on seedling emergence was also observed. Soil types from both zones did not differently affect seedling emergence. Seeds were not removed from the soil surface by a single winter flood. Moreover, seeds remained viable in the soil for at least two years, while the experimental plots were flooded several times during the experimental period. During one of those floods a thick sand layer was deposited at the low zone and subsequently no seedlings were observed anymore.

Conclusions: Colonization of low floodplain zones in years between subsequent summer floods is prevented by seed limitation while the direct effects of winter floods are limited except for irregularly occurring sand depositions.

Nomenclature: van der Meijden (1996).

Question: The significance of disturbances caused by periodical inundation was investigated with respect to its effects on vegetation dynamics, species richness and fluctuations, and to the relevance of certain plant properties.

Location and Method: At a sod-cut stand within nutrient-poor inland sand dunes, permanent plots along a transect were surveyed over a period of up to nine years after sod cutting.

Results: In contrast to never inundated plots, periodically inundated plots were characterized by low vegetation cover and by high numbers of species belonging to many different communities, each of them with a low cover. Periodical inundations favoured the presence of pioneers, species tolerant of disturbances, species adapted to wet conditions and stoloniferous species. Furthermore, annual fluctuations of species within each plot were higher and most species occurred only sporadically.

Discussion: A comprehensive model is presented describing the relevant processes identified in the littoral zone. Changing water tables result in the creation of gaps. The re-colonization of these gaps follows mainly from vegetative regeneration and less to the dispersion of diaspores. Highest species numbers in the zone of moderate disturbances result from a high rate of re-colonization in spite of local extinctions following each disturbance event. It is suggested that colonization abilities are among the most important features for species occurrence at a site rich in disturbances (more important than competitive abilities and more important than a slow rate of displacement). For nature conservation such sites are very important, because they allow (rare) pioneer species to survive for longer periods of time.

Nomenclature: Wisskirchen & Haeupler (1998). For categories of endangerment, see Garve (2004).

Question: Does the degree and timing of disturbance contribute significantly to the pattern and process of regeneration in plant communities as a consequence of the availability and number of species of propagules present?

Location: Acid grassland at 230 m a.s.l., eastern Scotland, UK.

Methods: Plots were surface disturbed or had their soil profile inverted at monthly intervals at 12 dates during a year. Seed bank and seed rain were assessed at each treatment time. The effect of disturbance intensity and timing on the regenerating vegetation was assessed.

Results: Removing the seed bank significantly slowed regeneration, as it contributed 43 % of developing cover after one year where it was present.

At an individual seed level, seed in the seed rain had a much higher likelihood of contributing to the regenerating vegetation than a seed in the seed bank. Some species showed a reliance on the seed bank for regeneration, and hence there was a significant difference in the vegetation that developed between plots with the seed bank intact and those where it was removed. Winter disturbed plots (little seed rain) had slower rates of re-vegetation than summer disturbed plots. Timing had little effect on species composition, though a significantly higher cover of perennial forb species developed on the winter disturbed plots.

Conclusion: Removing the contribution of the seed bank had a greater effect on the composition of regenerating vegetation than the effect of seasonal variation on the seed rain.

Nomenclature: Stace (1997).

Question: Is it possible to determine the species composition of root samples containing multiple species, without first disentangling individual roots?

Methods: The internal transcribed spacer (ITS) region of nuclear ribosomal DNA was amplified and sequenced from four California annual grassland species (two Poaceae and two Asteraceae). Restriction enzymes that cut the ITS region of each species into uniquely sized fragments were identified based on DNA sequence variation of the ITS regions. Mixed root samples were analysed to test the ability of the method to identify the presence or absence of each species in multi-species samples.

Results: The technique successfully identified species present in multi-species samples. ITS regions were shorter in Poaceae than in Asteraceae, so size differences alone were sufficient to distinguish these taxonomic groups. At the species level, digestion of ITS regions with the appropriate restriction enzymes yielded at least one uniquely sized fragment for each species.

Conclusions: This method is the first to identify the species composition of mixed root samples. It should be applicable to most plant species because the ITS region is flanked by universal primers and most species have unique ITS sequences. The ability to determine species-specific rooting distributions has broad applications in vegetation science.

Abbreviations: CAPS = Cleaved amplified polymorphic sequences; DNA = Deoxyribonucleic acid; ITS = Internal transcribed spacer; PCR = Polymerase chain reaction.

Nomenclature: Hickman (1993).

Question: How do Coriaria arborea, an N-fixing native shrub, and Buddleja davidii, a non-N-fixing exotic shrub, affect N:P stoichiometry in plants and soils during early stages of primary succession on a flood-plain?

Location: Kowhai River Valley, northeast South Island, New Zealand.

Methods: We measured soil and foliar nutrient concentrations, light levels, plant community composition and the above-ground biomass of Coriaria and Buddleja in four successional stages: open, young, vigorous and mature.

Results: Coriaria occurred at low density but dominated above-ground biomass by the vigorous stage. Buddleja occurred at 5.3 ± 1.0 stems/m² in the young stage and reached a maximum biomass of 520–535 g.m⁻² during the young and vigorous stages. Mineral soil N increased with above-ground Coriaria biomass (r² = 0.45), but did not vary with Buddleja biomass. In contrast, soil P increased with Buddleja biomass (r² = 0.35), but not with Coriaria biomass. In early successional stages, 70–80% of the species present were exotic, but this declined to about 15% by the mature stage. Exotic plant species richness declined with increasing Coriaria biomass, but no other measures of diversity varied with either Coriaria or Buddleja biomass.

Conclusion: These results demonstrate that Buddleja dominates early succession and accumulates P whereas Coriaria dominates later succession and accumulates N. A key ecosystem effect of the invasive exotic Buddleja is alteration of soil N:P stoichiometry.

Nomenclature: Allan (1961) with amendments suggested by Connor & Edgar (1987), and Webb et al. (1988).