ALBERT

Description: Trait-based ecology has enjoyed increasing success, aided by the development of trait databases. However their reliability has hardly been tested. Sandel et al., in this issue, identified uncertainties in trait databases linked to missing species and variable sampling effort among species. This highlights the danger of using trait databases in a blind manner and the need for their thorough evaluation.

Description: Question For a desert where winter is the driest, harshest season we asked: does the effect of dominant shrubs ( Bulnesia retama ) on annual species depend on (1) the functional traits of the latter, (2) the season of the year, or (3) the activity of livestock? Location A low-density goat farm in central-northern Monte Desert, Argentina. Methods We estimated the effect of shrubs using a log response ratio based on annual species population sizes underneath shrub canopies and in open spaces. We collected density data of annual species in 18 visits between Aug 2010 and Apr 2013 in permanent 50-cm square areas laid out according to a split-plot design, in which the activity of livestock (fenced and unfenced; plots were 10-m squares) was the main factor, and microsite type (shrub and open) was the subordinate factor, with 20 replicates for each combination. We also gathered data on eight functional traits (characterizing whole plants, leaves, roots and seeds) from annual plants collected in the study site following standardized protocols. Results Annual species with acquisitive attributes (high specific leaf area, intermediate-to-low leaf dry matter content, large leaves and high specific root volume) were more benefited by shrubs compared to species with the opposite, relatively conservative attributes. Facilitative influences of shrubs were pervasive during winter, while competitive influences increased in frequency during summer, when total plant density was higher. This pattern was not affected by livestock. Conclusions The outcome of species interactions depended on the interplay between plant strategies and abiotic stress: facilitated species were mostly acquisitive, and shrub facilitation was more important during the harshest season (winter). Specific root volume, along with widely used functional traits (specific leaf area, leaf dry matter content, leaf size) delineated such strategies. This underlines the importance of considering below-ground traits when studying plant–plant interactions. Single traits achieved superior explanatory power of shrub effects than composite ones (i.e. principal component axes based on single traits), reinforcing the idea that single functional traits are themselves meaningful indicators of complex physiological trade-offs that ultimately affect community structure and dynamics. Whether functional traits determine species' abundance within a given community remains unresolved. We show that ecological strategies of desert annuals determined their abundance in relation to dominant shrubs: acquisitive species were facilitated, whereas conservative ones were repelled. Specific root volume, along with widely used functional traits (specific leaf area, leaf dry matter content, and leaf size) delineated such annual-plant strategies.

Description: Questions We analysed trait convergence and trait divergence assembly patterns across a metacommunity of grassland types (dry, wet and rocky) occurring along an edaphic gradient. We asked whether (1) floristics and phylogenetic structures vary among grassland types; (2) there is convergence and/or divergence in plant traits along the gradient; (3) the functional structure is influenced by phylogeny; and (4) abiotic or biotic filters generate the assembly patterns. Location Campos Gerais region, Paraná State, southern Brazil (ca. 25°15′02″ S, 49°59′59″ W). Methods We sampled plant functional traits and soil variables at 81.1-m 2 quadrats in three natural grassland vegetation types across three different sites. We analysed the relationship between species composition (abundance), phylogenetic relationships, functional traits and soil characteristics using matrix correlations, where soil characteristics were the predictors of functional and phylogenetic assembly patterns. Results A total of 168 plant species were sampled on the three vegetation types. Wet grassland quadrats were more similar to each other in species composition and phylogeny than with those on dry and rocky grasslands. We found trait convergence (not phylogenetically constrained) and trait divergence (phylogenetically constrained) assembly patterns in the three vegetation types along the edaphic gradient. Traits that generated convergence and divergence are related to strategies for survival in dry and low nutrient availability soils; nutritional soil gradient determined trait differences at small scales. Conclusion Species composition and phylogenetic structure of communities occurring in different grassland types are related to edaphic gradient. The occurrence of both trait convergence and trait divergence patterns suggests, respectively, that environmental filters and biotic filters (competition) are structuring the plant assemblages. This study shows that diversification in grassland types (wet, dry and rocky) are strongly related to edaphic gradient. Species occurring along the gradient presented trait specialization related to strategies for survival in dry and with low nutrient availability soils. The occurrence of trait convergence and divergence suggests that environmental and biotic filters (competition) are structuring the plant assemblages.

Description: Questions Has the observed decline in the willow Salix caprea L., one of the most common colonizers of post-mining sites in Central Europe, contributed to changes in the rest of the plant community on post-mining sites? How does S. caprea modify its understorey? How is the understorey vegetation affected by above-ground and below-ground competition with S. caprea ? Location Heaps after coal mining near Sokolov, Czech Republic (50°14′21″ N, 12°40′45″ E). Methods The effects of above-ground and below-ground competition with the willow S. caprea on its understorey plant community were studied in un-reclaimed post-mining sites. Below-ground competition was evaluated by comparing (1) frames inserted into the soil that excluded woody roots (frame treatment), (2) frames that initially excluded woody root growth but then allowed regrowth of the roots (open-frame treatment), and (3) undisturbed soil (no-frame treatment). These treatments were combined with S. caprea thinning to assess the effect of above-ground competition. Results Three years after the start of the experiment, above-ground competition from S. caprea (as modified by thinning of the S. caprea canopy) had not affected understorey biomass or species number, but had affected species composition. In contrast, below-ground competition significantly affected both the above-ground and below-ground biomass of the understorey. The above-ground biomass of the understorey was larger in the frame treatment (which excluded woody roots) than in the other two treatments. The below-ground biomass of the understorey was larger in the frame than in the open-frame treatment. Unlike above-ground competition (light availability), below-ground competition did not affect understorey species composition. Conclusions Our results suggest that S. caprea is an important component during plant succession on post-mining sites because it considerably modifies its understorey plant community. Below-ground competition is a major reason for the low cover and biomass of the herbaceous understorey in S. caprea stands on post-mining sites. We experimentally manipulated with aboveground and belowground competition of willow Salix caprea L., one of the most common colonizers of post mining sites in Central Europe, with its understory plant community. We found that biomass of understory is limited mainly by belowground competition, while species composition of understory community is driven mainly by aboveground competition for light.

Description: Aims Understanding the relationship between species and environments is at the heart of ecology and biology. Ranges of species depend strongly on environmental factors, but our limited understanding of relationships between range and trait stability of species across environments hampers our ability to predict their future ranges. Species that occur over a wide range (and thus have wide niche breadth) will have high variation in morpho-physiological traits in response to environmental conditions, thereby permitting stability of performance traits and enabling plants to survive in a range of environments. We hypothesized that species' niche breadth is negatively correlated with the rate of performance trait change along an environmental gradient. Location Northern China. Methods We analysed standing biomass and height of 48 species of Asteraceae ( Artemisia and its close relatives) collected from 65 sites along an environmental gradient across northern China. Results In support of our hypothesis, there were significant negative correlations between climatic niche breadth and rate of change in biomass, a performance trait, but not in height, which is both a morphological and a performance trait. Conclusions These findings have implications for risk assessment of species under climate change and prediction of unknown distributions of species. They also offer a new avenue of research for species distribution models. We show that there were significant negative correlations between climatic niche breadth and rate of change in biomass, a performance trait, but not in height, which is both a morphological and performance trait. Our findings have implications for risk assessment of species under climate change and prediction of unknown distributions of species.

Description: Questions Is there any evidence of coordination among leaf, stem and root traits, and thereby of the existence of a plant economics spectrum at the species and community level in Mediterranean forests? Are these traits related to plant size and seed mass? Location Mediterranean forests and shrublands, Sierra Morena mountains, Córdoba, southern Spain. Methods We selected nine woody plant communities along a natural local gradient of soil water and nutrient availability. We measured key leaf, stem, root and whole-plant traits for 38 dominant woody plant species. The variation across species of 15 functional traits (of the leaf, stem and root) was analysed and coordination among them was tested. We explored the relationships between these traits (hereafter ‘resource-use traits’ due to their close association with the acquisition–conservation trade-off) and plant height and seed mass. Finally, we compared results at species level with those calculated at community level, considering community-weighted means (CWMs). Results We found a significant coordination between traits belonging to different plant organs, and propose the existence of a plant economics spectrum in Mediterranean forests along the environmental gradient. However, weaker relationships were found within groups of species under similar environmental conditions. We did not find the expected orthogonal relationships between plant height, seed mass and resource-use traits. Relationships among functional traits were stronger at the community level than at the species level. Conclusions This study reveals a high degree of functional coordination between traits belonging to different plant organs at both species and community level, and suggests the existence of a plant economics spectrum across 38 Mediterranean woody plant species. However, this general trend of functional coordination between organs became weaker or disappeared when considering restricted groups of species belonging to environmentally similar sites (e.g. dry vs wet sites), suggesting that the diversification of strategies within communities is not related to the economics spectrum at a lower spatial scale. Interestingly, the high degree of coordination between resource-use traits and seed mass at the community level seems to support the tolerance–fecundity model, which predicts an inverse relationship between fecundity and stress tolerance. The main novelty of this study comes from the rigorous analysis of coordination among functional traits belonging to different plant organs (leaf, stem and root) related to resource-use strategies. In addition, we compared them with those related with competitive (plant height) and reproductive ability (seed mass). The study was carried out on Mediterranean woody plant communities along an environmental gradient in south Spain.

Description: Questions What are the prevailing types of intraspecific spatial distributions and interspecific association patterns at species and life stage levels of trees in a tropical rain forest? Which ecological processes could structure these patterns? Possible processes include dispersal limitation, self-thinning, facilitation and competition between species and life stages. Location A tropical broad-leaved forest in north-central Vietnam. Methods We used univariate and bivariate pair-correlation functions to investigate the spatial distribution and association patterns of 18 abundant tree species. To disentangle first- and second-order effects, we used a scale separation approach with the heterogeneous Poisson process as null model. Results (1) Sixteen of 18 species had aggregated patterns at various scales and regardless of their abundance. (2) Significant and aggregated patterns were found in 64% of all specific life stages. (3) At scales up to 15 m, 12.4% species pairs showed significant associations, among that 71% were spatial attractions, 5% were spatial repulsions and 24% were non-essential interactions. (4) In different life stage associations, attractions (81%) predominated over repulsions (19%) at small scales of up to 15 m. Conclusions Our findings provide evidence that dispersal limitation may regulate the spatial patterns of tree species. Moreover, positive spatial associations between tree species and life stages suggest the presence of species herd protection and/or facilitation in this forest stand, while the persistence of intraspecific aggregation through life stages suggests a very late onset or even absence of self-thinning. Habitat heterogeneity plays an important role for species distribution patterns, and the spatial segregation occurs at a scale around 15 m in this forest. This study contributes to a better understanding of the spatial regulation of species diversity in forests. It provides evidence that dispersal limitation and species herd protection may regulate the spatial patterns of tree species in a tropical broad-leaved forest in north-central Vietnam. The spatial segregation caused by habitat heterogeneity occurs at a scale around 15 m in this forest.

Description: Question Do precipitation, temperature and seasonality drive variation in the seed size of Amazonian tree genera? Location Amazonia. Methods We use a combination of global biodiversity information facility (GBIF) records, climatic data from BIOCLIM and seed size categories derived from the literature. Results Tree genera with very small seeds were associated with lower temperatures and higher seasonality, but not with precipitation; the opposite patterns being observed for trees with large seeds. These correlations remained even when the numerically dominant (and ecologically specialized) Fabaceae were removed from the analysis. Conclusions Our findings indicate that Amazonian tree genera with smaller seeds occur more frequently in transitional or seasonal forests, and genera with large seeds are more associated with climatically stable rain forests (warmer and less seasonality). These results are broadly consistent with the ‘recruitment hypothesis’, which predicts that large seeds have a competitive advantage in closed canopy forest vegetation. We use a combination of GBIF records, climatic data and seed size categories for Amazonian trees to assess macrogeographic variation in seeds size. Our findings indicate that Amazonian tree genera with smaller seeds occur more frequently in transitional or seasonal forests and genera with large seeds are more associated with climatically stable rainforests. These data provide support for the ‘recruitment hypothesis’.

Description: Questions How has the vegetation of the major biomes (Grassland, Nama-karoo, Albany Thicket, Azonal) of southeastern South Africa changed over the course of the 20th century? How do changes in climate and land-use drivers relate to long-term changes in vegetation? What are the implications of these findings for land degradation hypotheses and future climate change projections for the region? Location The biogeographically complex semi-arid, Karoo Midlands region of the southeastern part of South Africa. Methods We re-photographed 65 historical landscape photographs, the majority of which dated from 1950 to 1970, to measure long-term changes in the cover of grasses, dwarf shrubs, tall shrubs and alien plants. The cover of each growth form as well as total vegetation cover was estimated from matched photograph pairs with the aid of detailed cover estimates recorded in the field. The change in cover was relativized between sites by dividing the difference in cover between the two time steps by the number of years between photographs, expressed as the percentage change in cover per decade. Significant changes in mean annual rainfall and the standardized precipitation index (SPI) from 27 climate stations were assessed using a Mann-Kendall test for trend. This non-parametric test was also used to assess the significance of long-term trends in the number of cattle, sheep and goats in each of the biomes over the period 1911–1996. Results Grass cover and total vegetation cover had increased by between 1.0% to 4.5% per decade and 2.0% to 4.5% per decade, respectively, in all biomes investigated. In contrast, the cover of dwarf shrubs had decreased significantly by between 0.25% and 3.0% per decade, although not significantly so in the Nama-karoo biome. The change in tall shrub cover varied between different biomes but had generally increased in the study area. Alien plants were absent in the historical photographs and had increased significantly but only in Azonal habitats, where increases of 1.5% per decade were recorded. For the majority of climate stations no significant trend in mean annual rainfall and SPI values was recorded, while stocking rate had declined significantly in all biomes by between 36% and 48% from 1911 to 1996. Conclusions The findings support the hypothesis that vegetation cover and condition has improved in the semi-arid regions of South Africa. These findings are discussed in light of future projections for the region. We used historical landscape photos from the 20th century to demonstrate trajectories of vegetation change in three semi-arid, South African biomes. We show that grasses and tall shrubs have increased whereas dwarf shrubs have declined in most biomes. Drivers of change appear to be declining livestock densities, climatic change and possibly also CO2 enrichment.

Description: Question A better understanding of the response of Sphagnum mosses and associated vascular plants to climate warming is relevant for predicting the carbon balance of peatlands in a warmer world. Open-top chambers (OTCs) have been used to investigate the effect on soil biogeochemical processes in peatlands, but little information is available on the effects of OTCs on microclimate conditions and the associated response of the plant community. We aimed to understand how simulated warming and differences in soil moisture affect plant species cover. Location A Sphagnum -dominated peatlands in French Jura. Methods We used OTCs to measure the effect of a near-ground temperature increase (+1.5 °C on average) on vegetation dynamics over five growing seasons (2008–2012) in a Sphagnum -dominated peatland, in two adjacent microhabitats with different hydrological conditions – wet and dry. Microclimatic conditions and plant species abundance were monitored at peak biomass in years 1, 2, 3 and 5 and monthly during the plant growing season in year 5. Results The response to warming differed between vascular plants and bryophytes, as well as among species within these groups, and also varied in relation to soil moisture. Andromeda polifolia abundance responded positively to warming, while Vaccinium oxycoccus responded negatively, and Eriophorum vaginatum showed a high resistance. Conclusion Depth of rooting of vascular plants appeared to control the response in plant abundance, while moss abundance depended on various other interacting factors, such as shading by the vascular plant community, precipitation and soil moisture. We aimed to understand how in a Sphagnum -dominated peatland simulated warming using OTC's in combination with differences in soil moisture affect plant species cover. Depth of rooting of vascular plants appeared to control the response in plant abundance, while moss abundance depended on various other interacting factors, such as shading by the vascular plant community, precipitation and soil moisture. Significance codes for Linear Mixed Models are *** P 〈 0.001; ** P 〈 0.01; * P 〈 0.05; . P 〈 0.1.