Aim s: We tested for the effect of final sowing plant density (i.e. density of established seedlings) on the values of biodiversity effects [transgressive overyielding, net effect, complementarity effect (CE) and selection effect (SE), trait-dependent complementarity and dominance effect] in a glasshouse pot experiment.Methods: We conducted a single-season (4 months) glasshouse experiment. Species monocultures and mixtures containing up to four common meadow species from different functional groups were sown and subsequently thinned to five density levels (8–128 individuals per pot, i.e. 200–3200 individuals m ?2). Community functioning was characterized by yield (both living and dead biomass) of all constituent species.Important Findings: Our results show that plant density (final sowing density in our case, but this finding can be generalized) affects the yields of both monocultures and mixtures. As these and their relationships are the basis for calculation of biodiversity effects, these effects also varied along the density gradient. Net biodiversity effect, CE and SE all increased with density. The net biodiversity effect and the CE switched from negative to quite positive in the four-species mixture. Using Fox's tripartite partitioning, trait-dependent complementarity was minor in comparison to the dominance effect. One of our experimental species did not follow the density-productivity relationship, called constant final yield (CFY), which was reflected in the biodiversity measures. The shape of the density-productivity relationship for experimental species affects also the values of biodiversity indices, particularly when species do not follow the CFY relationship. According to our data and recent simulation experiments, the values of commonly used biodiversity effects can be rather misleading if a species has, e.g. a unimodal dependence of yield for the density gradient and the density level used in the experiment is higher than the peak density.

Aims We analyze two continental data sets of forest communities from across the New World to examine the latitudinal gradients of beta diversity after accounting for gamma diversity and the latitudinal gradient of gamma diversity after accounting for beta diversity.
Methods Correlation and regression analyses were used to relate beta and gamma diversity to latitude along two latitudinal gradients in the New World (one including 72 forest sites located south of the equator and the other including 79 forest sites located north of the equator).
Important findings Beta diversity and gamma diversity were negatively correlated with latitude. Beta diversity was strongly and positively correlated with gamma diversity (Pearson's correlation coefficient: 0.783 for New World North and 0.848 for New World South). When beta diversity was regressed on latitude and gamma diversity, 69.8 and 85.7% of the variation in beta diversity were explained, respectively, for New World North and New World South. When gamma diversity was regressed on latitude and beta diversity, 81.8 and 84.3% of the variation in gamma diversity were explained, respectively, for New World North and New World South. After statistically removing the relationship between beta and gamma diversity, latitude has weak or no relationships with beta and gamma diversity. However, strong positive correlations between beta and gamma diversity may not be considered as evidence of one driving the other along a latitudinal gradient.

Aims Studying plant ecological succession provides insights into the spatiotemporal processes underlying community assembly and is of primary importance for restoration ecology. We investigate here colonization events and local community assembly over an original primary succession occurring on roadcuts after roadwork. For this, we addressed both the changes in species presence-absence (incidence data) to highlight pre-establishment filters and in species relative abundances to further assess the influence of local biotic processes.
Methods We studied 43 limestone roadcuts in Mediterranean France, covering five age classes up to an age of 80 years, along with 13 natural cliffs as a reference, and we counted 14322 plant individuals on these sites. We applied a constrained nonsymmetric correspondence analysis of both the incidence (presence-absence) and abundance data to assess the variation of these data along the chronosequence.
Important findings Along the first 30 years, the initially abundant short-lived species declined both in terms of incidence and abundance and were replaced by longer lived herbaceous and woody species. This first phase was characterized by species that are widespread in the surrounding scrublands and was comparable to an early secondary succession there. After 30 years, there were continuing changes in incidence data with age, but no more significant change in species' abundances. This second phase was marked by the late colonization of specialists that did not become dominant. Although colonization and establishment limitation was thereby apparent for specialist species, a slow convergence of community composition toward the situation of natural cliffs could be detected in the older stages of the chronosequence. These findings convey insights into the natural dynamics of man-made outcrop plant communities and may be useful for the ecological management and restoration of such contexts. It also illustrates the interest of comparing incidence and abundance data to investigate the relative influence of ecological determinants on the assembly of plant communities.

Aims We explore the possible role of leaf size/number trade-offs for the interpretation of leaf size dimorphism in dioecious plant species.
Methods Total above-ground biomass (both male and female) for three herbaceous dioecious species and individual shoots (from both male and female plants) for three woody dioecious species were sampled to record individual leaf dry mass, number of leaves, dry mass of residual above-ground tissue (all remaining non-leaf biomass), number of flowers/inflorescences (for herbaceous species) and number of branches.
Important findings For two out of three woody species and two out of three herbaceous species examined, male plants produced smaller leaves but with higher leafing intensity—i.e. more leaves per unit of supporting (residual) shoot tissue or plant body mass—compared with females. Male and female plants, however, did not differ in shoot or plant body mass or branching intensity. We interpret these results as possible evidence for a dimorphic leaf deployment strategy that promotes both male and female function, respectively. In male plants, capacity as a pollen donor may be favored by selection for a broadly spaced floral display, hence favoring relatively high leafing intensity because this provides more numerous axillary meristems that can be deployed for flowering, thus requiring a relatively small leaf as a trade-off. In one herbaceous species, higher leafing intensity in males was associated with greater flower production than in females. In contrast, in female plants, selection favors a relatively large leaf, we propose, because this promotes greater capacity for localized photosynthate production, thus supporting the locally high energetic cost of axillary fruit and seed development, which in turn requires a relatively low leafing intensity as a trade-off.

Aims Age structure and regeneration dynamics have been used to infer population response to environmental events and reconstruct forest development history. The aim of this study was to characterize and examine the differences of the age structure and regeneration dynamics of subalpine fir (Abies fargesii) forest across the altitudinal range in the north and south aspects in the Shennongjia Mountains, central China.
Methods Ten plots (20×20 m) at each altitudinal zone (i.e. the low elevation, the middle elevation and the high elevation) were established in both the north and south aspects of the Shennongjia Mountains, central China. Dendroecological techniques were applied to obtain information about ages of the trees in the plots. The population age structure was analyzed to investigate the regeneration dynamics across the altitudinal range.
Important findings Fir regeneration dynamics and age structure were similar in both aspects, and a unimodal population age structure was found at different altitudinal sites of both aspects, indicating that environmental factors might play an important role in shaping the regeneration dynamics and age structure of A. fargesii across its altitudinal range. There was a sustained recruitment during the 19th century, but the regeneration was rarer in the last century at low and midelevations. A significant greater number of fir seedlings and saplings recruited at high elevations in the last century, and fir tree density at high elevations was significantly higher than that at low elevations. Thus, the fir population at the high elevations showed a significant increase in recruitment and stem density in the last century, and we propose that the gradual infilling of fir seedlings might result in changes in regeneration dynamics and stand structure of the subalpine fir forest at high elevations in the Shennongjia Mountains, central China.

Aims Facilitation is widespread in plant communities and particularly common in highly stressful environments. In the semi-arid Mu Us sandland where soil water and nutrients are short and grazing is heavy, many species grow within the large patches formed by the dense individuals of the unpalatable clonal shrub Sabina vulgaris, the only natural evergreen shrub species in the Mu Us sandland. However, the interactions between S. vulgaris and these coexisting species remain unclear, and we hypothesize that S. vulgaris can facilitate at least some species because within the patches vegetation is not grazed and soil water and nutrients may also be higher.
Methods We measured the maximum height, coverage and number of individuals of each vascular species, little cover and thickness of biological crust at the soil surface in 1 m × 1 m plots in three types of microsites associated with 40 patches of S. vulgaris : (i) at the center, (ii) at the inner edge and (iii) outside the patches. We also took soil samples and measured soil water content and content of total N, P, K and organic matter.
Important findings Soil water, nitrogen, organic matter and litter cover were the highest at the patch center, lowest outside the patches and intermediate at the inner edge of the patches, whereas thickness of biological crust was greater outside than at the center or at the inner edge. Among the 32 species recorded, six species preferred to occur within the patches, suggesting that S. vulgaris can facilitate these species most likely by grazing exclusion, increasing water and/or nitrogen resources in soil. However, most (19) species did not show preference and seven preferred outside. Also, species richness, pooled cover and number of individuals of all species were greater outside than within the patches, and such effects did not vary with the size of the S. vulgaris patches. These results suggest that the dominant interactions between S. vulgaris and the coexisting species are competition. The findings add to our knowledge that facilitation can be shown even when the competitive effects from the potential nurse plants are very strong.

Aims The use of exotic species as taxon substitutes to restore lost ecological interactions is currently hotly debated. Aldabrachelys gigantea giant tortoises have recently been introduced to three islands in the Mascarene archipelago (Ile aux Aigrettes, Round Island and Rodrigues) to resurrect herbivory and seed dispersal functions once performed by extinct giant tortoises. However, potential unintended impacts by frugivore substitutes on native ecosystems, e.g. whether they will facilitate the germination of exotic plant species, are largely unknown. We investigated whether A. gigantea introduced to Rodrigues in 2006 could enhance the germination percentage of four widespread fleshy-fruited exotic species on the island. Using germination trials to forecast unintended impacts that could arise from the introduction of a frugivorous taxon substitute enables conservation managers to limit potential adverse negative interactions before they occur.
Methods In germination trials that ran over 4 months, we investigated the effects of ingestion (gut passage and deposition in faeces) by sub-adult and adult A. gigantea on the germination percentage of four exotic fleshy-fruited plant species introduced to Rodrigues. We fed fruits of these plant species to sub-adult and adult A. gigantea to test how variation in age and size of the frugivore would affect seed germination. Feeding of distinctly coloured plastic pellets together with the fruits allowed us to test for individual tortoise effects on seed germination.
Important findings Ingestion by A. gigantea increased the percentage of seeds germinating of Mimusops coriacea and Lantana camara, but not percentage of germination of Veitchia merrillii or Wikstroemia indica. Seeds were more likely to germinate following ingestion by sub-adult rather than adult tortoises, which may be a consequence of the shorter gut passage time observed for sub-adults. Our results demonstrate that introduced frugivorous taxon substitutes could facilitate germination of exotic and invasive plants and highlight the need for conservation managers to weigh the risk of taxon substitutes potentially facilitating the germination and recruitment of exotic fleshy-fruited plants against the benefit of restoring lost seed dispersal functions of threatened indigenous plants. Our findings also highlight the importance of considering age and size variation in frugivores, in particular in long-lived taxa such as giant tortoises, when studying ingestion effects on the germination performance of plants.

Aims Myriophyllum spicatum and Hydrilla verticillata are common submerged macrophytes in the Yangtze River basin. To investigate their tolerances and adaptations to water-level fluctuations, an experiment was conducted in a pond.
Methods We designed five different amplitudes of water-level fluctuations as static, ±15, ±30, ±60 and ±90 cm during the 74 days of the experiment. In each amplitude treatment, two cultivation methods were examined as monoculture and mixed culture.
Important findings The results showed that M. spicatum had greater morphological responses to water-level fluctuations than H. verticillata. Fluctuating amplitude had significant effects on branch number, shoot length and root dry weight (DW) of M. spicatum, whereas it only had significant effect on branch number of H. verticillata. Both fluctuating amplitude and cultivation method had significant effects on total DW of M. spicatum, which was higher in monoculture than mixed culture. The total DW of H. verticillata was affected by fluctuating amplitude only, and the largest biomass was in the amplitude of ±30 cm. Fruit DW of M. spicatum was largest in the amplitude of ±30 cm, high amplitude of water-level fluctuations would inhibit flowering and seed production. Root DW proportion was significantly affected by fluctuating amplitude and cultivation method in both species, and the root DW proportion of M. spicatum was significantly higher in the amplitude-of ±90 cm. We conclude that moderate amplitude of water-level fluctuations can promote the distribution and growth of both species, and in order to accelerate the restoration of both species in natural habitats, the optimum amplitude should be keep at ±15 to ±30 cm.

Aim s: The long-term effects of changing fire regimes on the herbaceous component of savannas are poorly understood but essential for understanding savanna dynamics. We present results from one of the longest running (>44 years) fire experiments in savannas, the experimental burn plots (EBPs), which is located in the Kruger National Park (South Africa) and encompasses four major savanna vegetation types that span broad spatial gradients of rainfall (450–700 mm) and soil fertility.Methods: Herbaceous vegetation was sampled twice in the EBPs using a modified step-point method, once prior to initiation of the experiment (1954) and again after 44–47 years. Different combinations of three fire frequency (1-, 2- and 3-year return intervals) and five season (before the first spring rains, after the first spring rains, mid-summer, late summer and autumn) treatments, as well as a fire exclusion treatment, were applied at the plot level (~7 ha each), with each treatment (n = 12 total) replicated four times at each of the four sites (n = 192 plots total). The effects of long-term alterations to the fire regime on grass community structure and composition were analyzed separately for each site.Important Findings: Over the 44+ years duration of the experiment, fires were consistently more intense on sites with higher mean annual rainfall (>570 mm), whereas fires were not as intense or consistent for sites with lower and more variable rainfall (<510 mm) and potentially higher herbivory due to greater soil fertility. Because the plots were open to grazing, the impacts of herbivory along with more variable rainfall regimes likely minimized the effects of fire for the more arid sites. As a consequence, fire effects on grass community structure and composition were most marked for the higher rainfall sites and generally not significant for the more arid sites. For the high-rainfall sites, frequent dry season fires (1- to 3-year return intervals) resulted in high grass richness, evenness and diversity, whereas fire exclusion and growing season fires had the lowest of these measures and diverged the most in composition as the result of increased abundance of a few key grasses. Overall, the long-term cumulative impacts of altered fire regimes varied across broad climatic and fertility gradients, with fire effects on the grass community decreasing in importance and herbivory and climatic variability likely having a greater influence on community structure and composition with increasing aridity and soil fertility.

Aims The study of deciduous phenology over boreal forest is important for understanding forest ecology and better management. In this paper, our objective was to determine the phenological stages of deciduous leaf out (DLO) over the deciduous-dominant [i.e. trembling aspen (Populus tremuloides)] stands in the Canadian Province of Alberta.
Methods During the period 2006–2008, we used Moderate Resolution Imaging Spectroradiometer (MODIS)-based 8-day surface temperature (T S) images to calculate accumulated growing degree days (AGDD: a favourable temperature regime for plant growth). The temporal dynamics of AGDD in conjunction with in situ DLO observations were then analysed in determining the optimal threshold for DLO in 2006 (i.e. 80 degree days).
Important findings The implementation of the above-mentioned optimal threshold revealed reasonable agreements (i.e. on an average 91.9% of the DLO cases within ±2 periods or ±16 days of deviations during 2007–2008) in comparison to the in situ observed data. The developments could be useful in various forestry-related applications, e.g. plant growth and its ability of exchanging atmospheric carbon dioxide, forest ecohydrology, risk of insect infestation, forest fire and impact of climate change, among others.

Aims Many resistance genes against fungal pathogens show costs of resistance. Genetically modified (GM) plants that differ in only one or a few resistance genes from control plants present ideal systems for measuring these costs in the absence of pathogens.
Methods To assess the ecological relevance of costs of pathogen resistance, we grew individual plants of four transgenic spring wheat lines in a field trial with three pathogen levels and varied the genetic diversity of the crop.
Important findings We found that two lines with a Pm3b transgene were more resistant to powdery mildew than their sister lines of the variety Bobwhite, whereas lines with chitinase (A9) or chitinase and glucanase (A13) transgenes were not more resistant than their mother variety Frisal. Nevertheless, in the absence of the pathogen, both the GM lines of Bobwhite as well as those of Frisal performed significantly worse than their controls, i.e. Pm3b #1 and Pm3b #2 had 39% or 53% and A9 and A13 had 14% or 23% lower yields. In the presence of the pathogen, all GM lines except Pm3b #2 could increase their yields and other fitness-related traits, reaching the performance levels of the control lines. Line Pm3b #2 seemed to have lost its phenotypic plasticity and had low performance in all environments. This may have been caused by very high transgene expression. No synergistic effects of mixing different GM lines with each other were detected. This might have been due to high transgene expression or the similarity between the lines regarding their resistance genes. We conclude that costs of resistance can be high for transgenic plants with constitutive transgene expression and that this can occur even in cases where the non-transgenic control lines are already relatively resistant, such as in our variety Frisal. Transgenic plants could only compete with conventional varieties in environments with high pathogen pressure. Furthermore, the large variability among the GM lines, which may be due to unpredictable transgene expression, suggests that case-by-case assessments are necessary to evaluate costs of resistance.

Aims The Gap Partitioning Hypothesis (GPH) posits that gaps create heterogeneity in resources crucial for tree regeneration in closed-canopy forests, allowing trees with contrasting strategies to coexist along resource gradients. Few studies have examined gap partitioning of temperate, ground-layer vascular plants. We used a ground-layer plant community of a temperate deciduous forest in northern Wisconsin, USA, as a model system to test whether the GPH extends to the relatively species-rich ground layer.
Methods We used a well-replicated experimental approach that included a gap opening gradient (five gap sizes, 6, 10, 20, 30 and 46 m diameter, and undisturbed reference areas), a within-gap location gradient (gap edge to center), and a temporal gradient (0, 2, 6 and 13 years after gap creation). The data were observations of ground-layer plant abundance, published plant traits, and a modeled index of understory light environments. We ordinated the plant abundance data and evaluated the relationships of composition, traits and light environment by gap size, location along the forest-gap transect and time, with several approaches such as correlations, descriptivestatistics, non-parametric tests of group differences and indicator species importance values.
Important findings Ground-layer plant composition and traits differed across gap sizes, within-gap locations and over time. Gaps of all sizes differed in composition from undisturbed areas, and all pair-wise combinations of gap size also differed in composition, except the 6 m from the 10-m gaps. Large gaps (46 m) also displayed within-gap compositional gradients from gap edge to center locations. Compositional differences in gap size were evident 2 years after gap creation and, contrary to our hypotheses, remained different over the 13-year period, even in gaps with crown closure. In contrast to the neutral theory, species functional traits and microenvironmental conditions were related to variation in ground-layer composition. Species with smaller seeds, lower shade tolerance, later bloom times, shorter stature and longer leaves were associated with higher light, more central gap locations, larger gap sizes and greater time since gap creation. The correlation between gap size and ground-layer plant composition and traits provides evidence for gap partitioning by the diverse ground-layer community in this temperate deciduous forest community.