Directional trends in species composition over time can lead to a widespread overemphasis of year‐to‐year asynchrony

Questions: Compensatory dynamics are described as one of the main mechanisms that increase community stability, e.g., where decreases of some species on a year‐to‐year basis are offset by an increase in others. Deviations from perfect synchrony between species (asynchrony) have therefore been advocated as an important mechanism underlying biodiversity effects on stability. However, it is unclear to what extent existing measures of synchrony actually capture the signal of year‐to‐year species fluctuations in the presence of long‐term directional trends in both species abundance and composition (species directional trends hereafter). Such directional trends may lead to a misinterpretation of indices commonly used to reflect year‐to‐year synchrony. Methods: An approach based on three‐term local quadrat variance (T3) which assesses population variability in a three‐year moving window, was used to overcome species directional trend effects. This “detrending” approach was applied to common indices of synchrony across a worldwide collection of 77 temporal plant community datasets comprising almost 7,800 individual plots sampled for at least six years. Plots included were either maintained under constant “control” conditions over time or were subjected to different management or disturbance treatments. Results: Accounting for directional trends increased the detection of year‐to‐year synchronous patterns in all synchrony indices considered. Specifically, synchrony values increased significantly in ~40% of the datasets with the T3 detrending approach while in ~10% synchrony decreased. For the 38 studies with both control and manipulated conditions, the increase in synchrony values was stronger for longer time series, particularly following experimental manipulation. Conclusions: Species’ long‐term directional trends can affect synchrony and stability measures potentially masking the ecological mechanism causing year‐to‐year fluctuations. As such, previous studies on community stability might have overemphasised the role of compensatory dynamics in real‐world ecosystems, and particularly in manipulative conditions, when not considering the possible overriding effects of long‐term directional trends

LOTVS: a global collection of permanent vegetation plots

Analysing temporal patterns in plant communities is extremely important to quantify the extent and the consequences of ecological changes, especially considering the current biodiversity crisis. Long-term data collected through the regular sampling of permanent plots represent the most accurate resource to study ecological succession, analyse the stability of a community over time and understand the mechanisms driving vegetation change. We hereby present the LOng-Term Vegetation Sampling (LOTVS) initiative, a global collection of vegetation time-series derived from the regular monitoring of plant species in permanent plots. With 79 data sets from five continents and 7,789 vegetation time-series monitored for at least 6 years and mostly on an annual basis, LOTVS possibly represents the largest collection of temporally fine-grained vegetation time-series derived from permanent plots and made accessible to the research community. As such, it has an outstanding potential to support innovative research in the fields of vegetation science, plant ecology and temporal ecology

aboveground and belowground data

Plotwise ramet counts and belowground root densities of 13 species in 18 plots. Readme file is a part of the archive

Data from: Root:shoot ratio in developing seedlings: how seedlings change their allocation in response to seed mass and ambient nutrient supply

1) Root:shoot (R:S) biomass partitioning is one of the keys to the plants' ability to compensate for limiting resources in the environment and thus to survive and succeed in competition. In adult plants, it can vary in response to many factors, such as nutrient availability in the soil or reserves in the roots from the previous season. The question remains whether, at the interspecific level, reserves in seeds can affect seedlings’ R:S ratio in a similar way. Proper allocation to resource-acquiring organs is enormously important for seedlings and is likely to determine their survival and further success. Therefore, we investigated the effect of seed mass on seedling R:S biomass partitioning and its interaction with nutrient supply in the substrate. 2) We measured seedling biomass partitioning under two different nutrient treatments after two, four, six and twelve weeks for seventeen species differing in seed mass and covering. We used phylogenetically informed analysis to determine the independent influence of seed mass on seedling biomass partitioning. 3) We found consistently lower R:S ratios in seedlings with higher seed mass. Expectedly, R:S was also lower with higher substrate nutrient supply, but substrate nutrient supply had a bigger effect on R:S ratio for species with higher seed mass. These findings point to the importance of seed reserves for the usage of soil resources. Generally, R:S ratio decreased over time and, similarly to the effect of substrate nutrients, R:S ratio decreased faster for large-seeded species. 4) We show that the seed mass determines the allocation patterns into new resource-acquiring organs during seedling development. Large-seeded species are more flexible in soil nutrient use. It is likely that faster development of shoots provides large-seeded species with the key advantage in asymmetric above-ground competition, and that this could constitute one of the selective factors for optimum seed mass

Root:Shoot ratio of seedlings

Above- and below- ground biomass of seedlings of 17 species growing in two nutrient supply treatement and measured in four time cuts

Data from: Environmental drivers and phylogenetic constraints of growth phenologies across a large set of herbaceous species

1. Because perennial herbs of temperate climates develop their aboveground parts every year anew, their success critically depends on the timing and speed of this growth (growth phenology). These parameters can play a role in species coexistence and may differ along environmental gradients. Still, we know little about them, as most phenological data come from observations of flowering and to a lesser degree leafing onset. 2. We collected data on growth phenology of about 400 perennial herbs in a botanical garden to make the results independent of local differences in climatic drivers as much as possible. Using these data, we determined species-specific parameters of Day of peak growth, Day of maturity, and two types of growth rates associated with the change in plant size. Environmental conditions in which these species occur in the field were assessed using Ellenberg indicator values, which express species' optima along gradients of moisture, nutrients and temperature. 3. Both timing and speed of growth estimated in the common garden were affected by light and moisture conditions of the habitats where the species typically occur. All parameters showed phylogenetic conservatism. 4. We identified two relationships among these parameters of growth phenology: (i) species with early peak growth had high relative growth rates in contrast to late species; (ii) tall species showed later peak growth than short species which more often grew early. The first relationship is associated with survival under forest canopy, where species are selected to grow early and fast before trees leaf out, which restricts their size. The latter is associated with (asymmetric) competition for light in open habitats, where the main selection factor is for tall stature, which cannot be attained early in the season. 5. Synthesis: We show that large differences in size growth dynamics among herbaceous species are constrained by a few key tradeoffs involving height at maturity, rate of growth, and time when maximum height is attained. These tradeoffs correspond to major selective forces acting on herbaceous plants in temperate climates

Data from: Effects of disturbance frequency and severity on plant traits: an assessment across a temperate flora

(1) Recent analyses of plant traits across large sets of species have revolutionized our understanding of plant functional differentiation. However, understanding of ecological relevance of this differentiation is contingent upon knowledge of environmental preferences of species, namely along gradients of disturbance and productivity for which no quantitative data were available until recently. (2) We examined the relationships of key functional traits (life-history categories, leaf-height-seed traits, clonal growth and bud bank traits) in the herb-dominated flora of Central Europe to species niche positions along the gradients of disturbance frequency, disturbance severity and productivity. (3) Life-history categories and bud bank size showed the strongest response to disturbance and productivity, whereas relationship of leaf-height-seed traits were much weaker. A number of traits, including clonal growth form and bud bank size, showed significantly unimodal response to disturbance frequency. Responses of many traits to disturbance frequency were different from their responses to disturbance severity. (4) Our findings support the notions that disturbance and productivity are key gradients of species functional differentiation and that disturbance severity and frequency select for different trait suites. Further the data indicate that in a predominantly herbaceous flora the traits of lifespan, clonal growth and resprouting show stronger relationship to the environment than the leaf-height-seed traits, which are more important in floras with high proportions of woody species. Since most previous trait analyses are based on woody-plant-dominated floras, patterns revealed in a herb-dominated flora deepen our understanding of the full range of variation within the plant kingdom

Data from: Root foraging performance and life-history traits

Plants use their roots to forage for nutrients in heterogeneous soil environments, but different plant species vastly differ in the intensity of foraging they perform. This diversity suggests the existence of constraints on foraging at the species level. We therefore examined the relationships between the intensity of root foraging and plant body traits across species in order to estimate the degree of coordination between plant body traits and root foraging as a form of plant behavior. We cultivated 37 perennial herbaceous Central European species from open terrestrial habitats in pots with three different spatial gradients of nutrient availability (steep, shallow and no gradient). We assessed the intensity of foraging as differences in root placement inside pots with and without a spatial gradient of resource supply. For the same set of species, we retrieved data about body traits from available databases: maximum height at maturity, mean area of leaf, specific leaf area, shoot lifespan, ability to self-propagate clonally, maximal lateral spread (in clonal plants only), realized vegetative growth in cultivation and realized seed regeneration in cultivation. Clonal plants and plants with extensive vegetative growth showed considerably weaker foraging than their non-clonal or slow-growing counterparts. There was no phylogenetic signal in the amount of expressed root foraging intensity. Since clonal plants foraged less than non-clonals and foraging intensity did not seem to be correlated with species phylogeny, we hypothesize that clonal growth itself (i.e. the ability to develop at least partly self-sustaining ramets) may be an answer to soil heterogeneity. Whereas unitary plants use roots as organs specialized for both resource acquisition and transport to overcome spatial heterogeneity in resource supply, clonal plants separate these two functions. Becoming a clonal plant allows higher specialization at the organ level, since a typical clonal plant can be viewed as a network of self-sustainable harvesting units connected together with specialized high-throughput connection organs. This may be an effective alternative for coping with spatial heterogeneity in resource availability

Data from: Philip Grime's fourth corner: are there plant species adapted to high disturbance and low productivity?

Grime's CSR species life-strategy theory (competition-stress-ruderality) provides a conceptual framework to classify species into competitive (high productivity, low disturbance), stress-tolerant (low productivity, low disturbance) and ruderal (high productivity, high disturbance). Importantly, this classification is based on the assumption that the niche space of disturbance and productivity is filled unevenly: while in productive habitats species can adapt to different disturbance regimes, species of low-productivity and disturbed habitats do not exist, resulting in a triangular distribution of species optima along axes of disturbance and productivity. This assumption has often been criticised, but it has not yet been put under a rigorous test. Here we use existing data on niche positions of Central European plant species to test this hypothesis, namely its prediction that species adapted to jointly stressed (low-productive) and disturbed habitats do not exist. We use Ellenberg indicator values and newly developed indicator values for disturbance as proxies of species positions in the space of productivity and disturbance. We found that positions of species optima along the gradients of productivity and disturbance severity are not independent of each other, with very few species adapted to low-productive and severely disturbed habitats. In contrast, there is no relationship between productivity and disturbance frequency; a number of species occur in low-productive and frequently disturbed habitats. The relationship between productivity and disturbance severity can be either due to tradeoffs between life history traits responsible for response to disturbance and productivity (as originally assumed by Grime) or due to historical rarity of severely disturbed habitats in unproductive conditions and consequent absence of evolution of species adapted to them. Our data are based on one specific flora, shaped by glaciations and early introduction of agriculture, but the question of what causes this pattern can be resolved by future analyses of floras with different evolutionary and ecological histories

root biomass per pot half

Root foraging data for 37 plant species. The experiment was run in two years. Each row corresponds to a pot. In each pot, there was either no spatial gradient of nutrients, or shallow gradient or steep gradient (column "contrast"). Dry belowground biomass is reported for each half of the pot (root biomass content in the nutrients-poor half: column "lowconc_half_roots[g]"; root biomass content in the nutrients-rich half: column "highconc_half_roots[g]"); for pots with no gradient, identity of halves was chosen at random. Aboveground dry biomass and sum of the belowground halves are reported, too