Testing the role of functional trait expression in plant-plant facilitation

1. Positive biotic interactions between plant species may strongly affect species and community-level patterns, but the processes through which benefactor species alter the performance of interacting species (via, e.g. beneficial mechanisms like resource provisioning) are still inadequately understood. One poorly explored potential explanation is that plant–plant facilitation could occur through the impact of benefactor species on the functional trait expression of beneficiary species. Indeed, plant species that affect local conditions can modify functional trait expression of interacting species, thereby improving their performance and resulting in a facilitative interaction. However, the response of intraspecific trait variation to biotically driven microhabitat modification, and its role in determining the outcome of plant–plant interactions, has rarely been explored. 2. Here, we test whether growing with benefactor species affects the expression of functional traits of eight species, encompassing different plant growth forms, in two contrasting study systems. This is achieved using a paired sampling approach to compare values of seven functional traits of conspecific individuals growing within and adjacent to cushion plants (i.e. benefactor species which are known to strongly alter microhabitat conditions and to have positive effects on some of the focal species). In addition, we test whether the effect of biotic interactions on functional trait expression changes along elevational gradients, as the outcome of biotic interactions is expected to vary with elevation. 3. Contrary to predictions, in both systems, intraspecific trait variation was not well explained by the biotic interaction with the cushion plant species or the variation in abiotic conditions associated with elevational gradients. Where biotic interactions did affect functional trait expression and bivariate trait relationships, traits responded variably between species, suggesting that context specificity may be a constraint to predicting how intraspecific trait variation responds to plant–plant interactions, adding to the growing body of literature that challenges the generality and predictability of the drivers of intraspecific trait variation. 4. This research, therefore, suggests that benefactor species’ facilitative process is likely not through an impact on intraspecific trait expression, and that instead other processes may be more important for translating beneficial microhabitat modification or increased resource availability by benefactor species into positive impacts on beneficiary species.DATA AVAILABILITY STATEMENT : Data are available from TRY Plant Trait Database. Dataset ID 618 (Montane_grassland_FT) and 619 (sub-Antarctic_tundra_FT). URLs for the two datasets are below: https://www.try-db.org/TryWeb/Data.php#41 and https://www.try-db.org/TryWeb/Data.php#42.The National Research Foundation's South African National Antarctic Programme and the University of Pretoria Research Development Programme.http://www.wileyonlinelibrary.com/journal/fechj2022Plant Production and Soil Scienc

Can vegetation be discretely classified in species-poor environments? Testing plant community concepts for vegetation monitoring on sub-Antarctic Marion Island

DATA AVAILABILITY STATEMENT : Floristic plot data used in this manuscript is available on figshare at https://DOI.org/10.6084/m9.figsh are.21776477.The updating and rethinking of vegetation classifications is important for ecosystem monitoring in a rapidly changing world, where the distribution of vegetation is changing. The general assumption that discrete and persistent plant communities exist that can be monitored efficiently, is rarely tested before undertaking a classification. Marion Island (MI) is comprised of species-poor vegetation undergoing rapid environmental change. It presents a unique opportunity to test the ability to discretely classify species-poor vegetation with recently developed objective classification techniques and relate it to previous classifications. We classified vascular species data of 476 plots sampled across MI, using Ward hierarchical clustering, divisive analysis clustering, non-hierarchical kmeans and partitioning around medoids. Internal cluster validation was performed using silhouette widths, Dunn index, connectivity of clusters and gap statistic. Indicator species analyses were also conducted on the best performing clustering methods. We evaluated the outputs against previously classified units. Ward clustering performed the best, with the highest average silhouette width and Dunn index, as well as the lowest connectivity. The number of clusters differed amongst the clustering methods, but most validation measures, including for Ward clustering, indicated that two and three clusters are the best fit for the data. However, all classification methods produced weakly separated, highly connected clusters with low compactness and low fidelity and specificity to clusters. There was no particularly robust and effective classification outcome that could group plots into previously suggested vegetation units based on species composition alone. The relatively recent age (c. 450,000 years B.P.), glaciation history (last glacial maximum 34,500 years B.P.) and isolation of the sub-Antarctic islands may have hindered the development of strong vascular plant species assemblages with discrete boundaries. Discrete classification at the community-level using species composition may not be suitable in such species-poor environments. Species-level, rather than community-level, monitoring may thus be more appropriate in species-poor environments, aligning with continuum theory rather than community theory.https://onlinelibrary.wiley.com/journal/20457758am2024Plant Production and Soil ScienceSDG-15:Life on lan

TRY plant trait database – enhanced coverage and open access

Plant traits - the morphological, anatomical, physiological, biochemical and phenological characteristics of plants - determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait‐based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits - almost complete coverage for ‘plant growth form’. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait–environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives

Fine- and broad-scale distribution of a cushion plant species: Patterns and predictors for Euphorbia clavarioides

Cushion plants are a key Arctic, Antarctic, and alpine growth form, with many cushion-forming species strongly affecting community structure in abiotically stressful environments. Despite their ecological importance, there is little information about what drives the distribution of species exhibiting this growth form. This study investigates the determinants of the distribution of a cushion plant species, Euphorbia clavarioides at (1) a fine scale, using field-collected predictors from an alpine landscape; and (2) a broad scale, using distribution records and climate data across the species’ distributional range. At the fine scale, the species was locally rare (occurring in about 4 percent of samples) and may be limited to specific microsites by interspecific competition with taller-growing species. Broad-scale species distribution modeling showed that both temperature and rainfall are important in predicting the distribution of E. clavarioides with a higher probability of occurrence in areas with higher annual precipitation and mean annual temperatures < 15°C. Given the species’ sensitivity to competition and abiotic conditions (high temperatures and low precipitation), E. clavarioides may be vulnerable to environmental changes. Therefore, assuming that other cushion plant species exhibit similar patterns, species of this growth form may be particularly useful indicators of change in alpine, Arctic, and Antarctic areas

Ecosystem engineering through aardvark (Orycteropus afer) burrowing : mechanisms and effects

Burrowing mammals are often considered to be ecosystem engineers as burrowing disturbs the soil, thereby potentially changing resource availability and affecting habitat conditions for other species. After their excavation, burrows may strongly impact local plant communities through several mechanisms, including resource trapping, altered chemical and physical soil properties, and amelioration of microclimatic conditions. We studied ecosystem engineering by aardvark (Orycteropus afer) burrowing by comparing soil and vegetation characteristics between three microsites (burrow entrances, excavated soil mounds and adjacent control sites). We were able to identify several engineering effects and distinguish between potential mechanisms. Burrow soils were cooler, drier and less compact than the other microsites, with all three microsites representing unique combinations of abiotic conditions. Mean species richness was higher at older burrows than mounds and non-burrowed controls, despite burrows having a smaller seedbank and not differing in soil fertility from mounds and control sites. However, the opposite was observed at fresh burrows and mounds, where control plots contained more species on average than the other two types of microsites. Burrow age and microsite type also affected species composition, although only a small proportion of species were significantly associated with specific microsites and just two species were limited to a single microsite type. We suggest that trampling and the physical digging action at burrow entrances, and burial by deposited soil at mounds, prevents the establishment of many plant species at active burrows. However, once abandoned, burrow entrances provide good physical conditions for seedling survival, allowing the establishment of more species. Therefore, as suggested previously for other ecosystem engineers, it is important to explicitly consider the age and degradation processes of engineered structures. In addition, our results highlight biologically-important differences in engineering impacts between burrow entrances, where soil is removed, and mounds, where soil is deposited. Such microscale differences are important to consider when examining bioturbation or, more generally, ecosystem engineering.The National Research Foundation of South Africa for Grant No. 94103.http://www.elsevier.com/locate/ecoleng2019-08-01hj2018Geography, Geoinformatics and MeteorologyPlant Production and Soil Scienc

Ecosystem engineering through aardvark (Orycteropus afer) burrowing: Mechanisms and effects

Burrowing mammals are often considered to be ecosystem engineers as burrowing disturbs the soil, thereby potentially changing resource availability and affecting habitat conditions for other species. After their excavation, burrows may strongly impact local plant communities through several mechanisms, including resource trapping, altered chemical and physical soil properties, and amelioration of microclimatic conditions. We studied ecosystem engineering by aardvark (Orycteropus afer) burrowing by comparing soil and vegetation characteristics between three microsites (burrow entrances, excavated soil mounds and adjacent control sites). We were able to identify several engineering effects and distinguish between potential mechanisms. Burrow soils were cooler, drier and less compact than the other microsites, with all three microsites representing unique combinations of abiotic conditions. Mean species richness was higher at older burrows than mounds and non-burrowed controls, despite burrows having a smaller seedbank and not differing in soil fertility from mounds and control sites. However, the opposite was observed at fresh burrows and mounds, where control plots contained more species on average than the other two types of microsites. Burrow age and microsite type also affected species composition, although only a small proportion of species were significantly associated with specific microsites and just two species were limited to a single microsite type. We suggest that trampling and the physical digging action at burrow entrances, and burial by deposited soil at mounds, prevents the establishment of many plant species at active burrows. However, once abandoned, burrow entrances provide good physical conditions for seedling survival, allowing the establishment of more species. Therefore, as suggested previously for other ecosystem engineers, it is important to explicitly consider the age and degradation processes of engineered structures. In addition, our results highlight biologically-important differences in engineering impacts between burrow entrances, where soil is removed, and mounds, where soil is deposited. Such microscale differences are important to consider when examining bioturbation or, more generally, ecosystem engineering.The National Research Foundation of South Africa for Grant No. 94103.http://www.elsevier.com/locate/ecoleng2019-08-01hj2018Geography, Geoinformatics and MeteorologyPlant Production and Soil Scienc

TRY plant trait database - enhanced coverage and open access

10.1111/gcb.14904GLOBAL CHANGE BIOLOGY261119-18