The soil seed bank, an ecosystem component with a crucial role in the natural regeneration of plant communities, can be impacted by invasive non-native plants. The impact of non-native plants can be direct with the production of their own seeds or indirect without producing seeds, which has been less investigated. We determined the impact of an invasive seedless tree, non-native willow (Salix × rubens), on the soil seed bank in a riparian ecosystem.
Northwestern Patagonia, Argentina.
In autumn and spring 2022, we collected soil samples and estimated understorey cover, respectively, in plant communities invaded by willow and in uninvaded communities with a canopy dominated by native species. Over a year, we recorded the seedling emergence of soil samples to estimate the abundance, richness, and composition of the seed bank. We also compared the composition between the seed bank and understorey.
Total seed abundance and native woody species seed abundance decreased twofold and fourfold, respectively, in invaded plant communities in comparison with uninvaded communities. The most affected woody species was Ochetophila trinervis, a key tree species, because of its dominance in the canopy and understorey, and its role in various ecological processes (nitrogen cycling). In addition, willow invasion moderately changed the seed bank species composition producing species turnover. For both the seed bank and the understorey, species composition was more similar between invaded and uninvaded communities than between the seed bank and understorey. Willow invasion had more impact on understorey composition than on the seed bank.
Although willows do not produce seeds regionally, their invasion negatively impacts the soil seed bank by replacing native woody canopy species that supply seeds to the seed bank. These impacts could result in notable changes in the structure of the plant communities and the ecosystem dynamics of riparian areas.
Mammalian herbivory affects the structure and composition of plant communities, soil characteristics and intraspecific leaf traits. Understanding the effects of this type of herbivory is particularly relevant in grey dunes, a priority habitat type of the European Union Habitats Directive.
Sálvora island (NW Spain).
Vegetation surveys and sampling were carried out in a coastal grey-dune community, comparing the structure and composition of plant communities and soil characteristics in plots with herbivory exclusion and plots with herbivore activity, in autumn and spring. Changes in the specific leaf area (SLA), C/N ratio, δ13C and δ15N of two main plant species were also analysed.
The differentiation between treatments was low in autumn, in contrast to spring results, which demonstrated seasonal variation in the plant community and herbivore behaviour. Spring results showed lower above-ground dry mass in plots with herbivory due to defoliation, but greater richness and diversity, indicating that intermediate levels of disturbance reduced competition from dominant species. Herbivory treatments were different in terms of species composition, highlighting the positive effects of herbivory on the development of the threatened species Linaria arenaria. Soil temperature and moisture content were higher in herbivory plots because of the suppression of vegetation cover and the effect of trampling, respectively. No differences were detected in the chemical composition of the soil or the SLA, although the variability of these traits was greater in herbivory plots, indicating spatial heterogeneity generated by the activity of herbivores. No differences between treatments were obtained for % C and δ13C, whereas herbivory plots showed lower values of N content and δ15N as an adaptive response to herbivory pressure at the leaf and root level.
Our findings show that herbivory effects on plant communities vary by season — stronger in spring and weaker in autumn — emphasising the need for seasonal analysis and highlighting disturbance as a driver of spatial heterogeneity.
At high latitudes, anthropogenic climate change and invasive species threaten biodiversity, often with interacting effects. Climate change not only impacts native plant species directly by driving distribution and abundance of species, but indirectly through the influence on community dynamics and habitat suitability to invasive species. A key obstacle to quantifying vegetation change in the sub-Antarctic is the scarcity of cloud-free satellite imagery in a region with near-permanent cloud cover and lack of long-term plot data. In this paper, we aim to address the following questions: how has vegetation in the sub-Antarctic changed between 1965 and 2020? What are the roles of climate change and invasive species in driving these changes?
The study was conducted on Marion Island in the sub-Antarctica.
We quantified vegetation change by analysing repeat ground photography between 1965 and 2020, accompanied by an analysis of climate trends and invasive plant species’ cover changes over the same period.
Total vegetation cover was significantly higher in 2020 than in 1965 in all habitats other than in the coastal saltspray habitat, indicating an increase in overall biomass on the island. The more responsive ‘generalist’ plant species have expanded across the island, whilst the more ‘specialised’ plant species have not significantly changed in cover, with the exception of the mire graminoids, which have declined. Marion Island has thus undergone significant vegetation change, showing a greening trend across most habitats in the last five decades. This has been accompanied by aridification, an increase in mean air temperature, changes in wind direction and wind speed, and an increase in invasive mouse populations. The three most widespread invasive plant species have also expanded their ranges, especially in areas influenced by animal disturbance and nutrient input.
In congruence with research from Northern-hemisphere tundra and other islands in the sub-Antarctic, these results provide substantive empirical evidence for the interacting effects of climate change and invasive species on sub-Antarctic tundra vegetation, as has long been predicted.
How does the type of swamp, that is, riverine vs palustrine, shape understorey and overstorey plant communities? Beyond swamp type, how do spatial, topographic, soil and landscape characteristics determine the taxonomic and functional structure of swamp communities?
Southern Québec, Canada.
We sampled riverine and palustrine swamp plant communities in two watersheds within two ecoregions with contrasting land use. At the site scale (n = 56), we analyzed differences between riverine and palustrine swamps in plant richness and cover, species composition, and mean and dispersion values for ecological and morphological traits. At the plot scale (n = 213), we assessed the relative influence of a set of environmental parameters on species richness and cover, as well as on trait values using mixed models and on species composition using redundancy analysis.
Species composition and the mean value of traits varied significantly between the two types of swamps. While riverine swamps hosted more non-native species and were composed of more mesophilic species, shorter in height and with dominant resource acquisition strategies, palustrine swamps sheltered more non-vascular taxa and tall hygrophilous vascular species with more conservative resource strategies. The surrounding landscape and local microtopography within swamps had a significant effect on plant community structure. Species diversity and trait dispersion increased from agricultural-dominated to forest-dominated landscapes, and from homogeneous to heterogeneous substrates.
Habitats provided by riverine and palustrine swamps are complementary for wetland biodiversity. Our results underline the need to develop conservation plans to protect a wide variety of freshwater swamp types; for example, management actions that maintain or promote heterogeneous topographic forms at the site scale, and continuity of forest cover at the landscape scale.
How do local forest conditions and characteristics at the forest patch - scale and landscape - scale affect plot-scale plant diversity in Europe? Do these patterns vary between forest specialists and generalists? Do community saturation patterns differ between forests varying in their surrounding landscape type?
Deciduous forests sampled along a European gradient from southwest to northeast comprising eight regions in five countries (France, Belgium, Germany, Sweden, Estonia).
We examined the effects of local conditions assessed by means of Ellenberg indicator values (soil moisture, soil nitrogen, soil pH, light availability), patch-scale characteristics (patch-scale plant diversity, forest patch age, forest patch size) and a landscape-scale variable (representing low and high connectivity of forest patches) on plot-scale plant diversity, separately for forest specialist and generalist species. Additionally, we ran regression models to examine community saturation patterns.
We found patterns of niche partitioning among forest specialists and generalists. Low light availability and medium soil moisture favored forest specialists, while generalists were mostly present at higher light availability and medium and high soil moisture. In general, we found the highest plot-scale diversity at medium soil pH. Patch-scale diversity showed a positive impact on plot-scale diversity and plots in the high-connectivity landscape had a higher diversity than plots in the low-connectivity landscape. Further, we observed a high degree of community saturation in both landscape types.
The positive impact of a high connectivity of forest patches on local plant diversity emphasizes the importance of small semi-natural habitats like tree lines, unused field margins and hedgerows to enhance the potential dispersal of forest plants across agricultural landscapes. Community saturation patterns revealed the increasing relevance of local conditions and processes for plot-scale diversity when patch-scale diversity increases.
Environmental changes in Europe influence plant community composition, but the literature quantifying these changes often shows inconsistent trends, due mostly to heterogeneous survey methods. Here, we investigated temporal changes in plants over 12 years at the species and community level at a regional scale, using a standardized, plot-based monitoring scheme.
Data originated from 1,389 permanent plots of a standardized monitoring scheme targeting plant communities. Plots were distributed in the Burgundy region (France), initially grouped into 175 (2 km × 2 km) grid cells containing eight 10-m2 plots each, that were surveyed in at least 2 years between 2009 and 2020.
We characterized changes in vascular plants in 10-m2 plots by examining the temporal changes in the probability of occurrence of common species, changes in species diversity using species richness, Shannon–Wiener and Pielou's indices and changes in abundance-weighted mean community ecological preferences using Ellenberg indicator values.
Across 198 common species, probability of occurrence in the region has shown a decline since 2009. This decline is associated with a general decrease by 13% of both species richness and the Shannon index between 2009 and 2020. This trend was stronger in annual crops and grasslands, whereas forest diversity remained relatively constant over time. Pielou's index diminished on average, except in natural forests. Mean community Ellenberg indicator values suggested slight changes in plant community composition, with an increasing preference for nutrient-poor soils and Atlantic conditions over time.
The observed biodiversity loss in the Burgundy region is consistent with a widespread shift in community composition in response to environmental change. Existing conservation measures do not seem to compensate for the average losses, indicating that these measures are still inadequate to protect plant communities. Our approach also emphasizes the speed at which plant communities are changing and thus the need for better monitoring of the European flora.
Making predictions about species, including how they respond to environmental change, is a central challenge for ecologists. Because of the huge number of species, ecologists seek generalizations based on species’ traits and phylogenetic relationships, but the predictive power of trait-based and phylogenetic models is often low. Species co-occurrence patterns may contain additional information about species’ ecological attributes not captured by traits or phylogenies. We propose using a novel ordination technique to encode the information contained in species co-occurrence data in low-dimensional vectors that can be used to represent species in ecological prediction.
We present an efficient method to derive species vectors from co-occurrence data using Global Vectors for Word Representation (GloVe), an unsupervised learning algorithm originally designed for language modelling. To demonstrate the method, we used GloVe to generate vectors for nearly 40,000 plant species using co-occurrence statistics derived from sPlotOpen, an open-access global vegetation plot database, and tested their ability to predict elevational range shifts in European montane plant species.
Co-occurrence-based species vectors were weakly correlated with traits or phylogeny, indicating that they encode unique information about species. Models including co-occurrence-based vectors explained twice as much variation in species range shifts as models including only traits or phylogenetic information.
Given the widespread availability of species occurrence data, species vectors learned from co-occurrence patterns are a widely applicable and powerful tool for encoding ecological information about species, with many potential applications for describing and predicting the ecology of species, communities and ecosystems.
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