Testing for consistency in ecosystem engineering : do cushion plants always turn up the heat?

Ecosystem engineers influence community structure and functioning by altering habitat and resource availability. However, few studies have assessed how consistent ecosystem engineers' impacts are on abiotic habitat conditions and/or community characteristics, either across species or between habitats. Here we test for the consistency of ecosystem engineering across, and within, cushion-forming plant species, a group of ecosystem engineers that are dominant in polar and alpine environments, by reviewing studies that document their effects on temperature. We find inconsistent effects, with cushion plants having contrasting impacts on temperatures in different studies. Even after limiting analyses to a single cushion plant morphology type or to just a single species, impacts on temperature were still inconsistent between studies. Therefore, while cushion plants have relatively consistent impacts on plant communities (e.g. increasing local species richness), their impact on temperature may not be the overarching abiotic mechanism driving this ecological effect. These results, therefore, highlight the need to explicitly test if ecosystem engineers’ biotic and abiotic impacts are consistent through space and time, and emphasize the importance of understanding context-dependence in the outcome of biotic interactions.The South African National Antarctic Programme of the South African National Research Foundation.https://www.elsevier.com/locate/actoechj2021Plant Production and Soil Scienc

Marine protected areas are insufficient to conserve global marine plant diversity

AIM : Marine plants are only incidentally included in conservation efforts for marine biodiversity. Here, for the first time, we apply phylogenetic methods to marine macrophytes (mangroves and seagrass species) to test for gaps in the current conservation network by identifying global diversity hotspots for these plant groups, and assess the degree to which hotspots are represented within the current network of marine protected areas (MPAs). LOCATION : Global. METHODS : We calculated five metrics of marine plant diversity: phylogenetic diversity, species richness, species endemism, phylogenetic endemism and ‘evolutionary distinctiveness and global endangerment’ (EDGE). RESULTS : Overall, the diversity of marine plants was poorly represented by current MPAs. Different measures of diversity showed spatial mismatch, demonstrating how strategies that maximize one diversity measure may be inefficient at protecting other facets of marine plant biodiversity. However, complementarity analyses revealed that complete representation can be achieved very efficiently with few additional locations. MAIN CONCLUSIONS : Our study highlights the need for an integrative approach to conserve both the species diversity and phylogenetic diversity of marine plants. While MPAs are a valuable instrument for conserving marine biodiversity, we now face the challenge of increasing coverage to protect other branches of the marine tree of life.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1466-8238hj2017Plant Production and Soil Scienc

Species differ in their responses to wind : the underexplored link between species fine-scale occurrences and variation in wind stress

Questions Species distribution models have traditionally relied heavily on temperature and precipitation, often ignoring other potentially important variables. However, recent advances have shown other climatic variables, including snow cover and solar radiation, may strongly improve predictions of species occurrence. Wind has long been known to have mechanical and physiological impacts on plants, but has not yet received adequate attention as a driver of species distributions. Location Marion Island, sub-Antarctic. Methods Using data from 1,440 plots in a chronically windy system, we test if wind stress (a combination of wind exposure and wind speed) improves species distribution models of vascular plant species, examining predictions for both species occurrence and cover. Results Wind stress was a significant predictor of the occurrence of 12 of the 16 species, even after accounting for seven other ecophysiologically important abiotic variables. Species showed differential responses to wind, but wind stress was among the four most important drivers for the majority of species when modelling occurrence patterns (10 of 16) and variation in cover (12 of 16). Further, wind stress was more important than all temperature and precipitation variables in predicting the occurrence of six species (and three species' cover). Conclusions Wind conditions were most influential for species that are characteristic of open, wet environments and for pteridophyte species, likely due to high wind speeds and exposure increasing the potential for moisture loss. This research highlights the value of incorporating wind metrics into species distribution models, particularly under changing wind patterns.Peer reviewe

Arctic-alpine vegetation biomass is driven by fine-scale abiotic heterogeneity

During recent decades large changes in vegetation biomass have been observed in arctic and alpine areas. While these temporal trends have been clearly linked to changing climatic conditions, the drivers of local spatial variation in biomass are still relatively poorly understood. Thus, we examine the effects of abiotic conditions (as measured by ten variables representing topography, soil properties and geomorphological processes) on variation in aboveground vascular plant biomass to understand the determinants of contemporary fine scale heterogeneity in this variable. We also compare the results from one destructive biomass estimation method (clipharvesting) to three non-destructive biomass estimates: vegetation cover, height and volume. To investigate the local drivers of biomass we analysed an extensive data set of 960 1 m2 cells in arctic–alpine tundra using spatially-explicit generalized estimation equations to conduct variation partitioning. The abiotic environment had a clear impact on the fine scale distribution of biomass (variance explained 32.89 % with full model for sampled biomass). Soil properties (temperature, moisture, pH and calcium content) were most strongly related to aboveground biomass (independent effect in variation partitioning 7.03 % and combined effect including joined effects with topography and geomorphology 19.6 %). Topography had only a small influence after soil and geomorphology were taken into account (independent effect only 2.23 % and combined effect 18.73 %), implying that topography has only indirect effects on vegetation biomass. Of the three non destructive biomass estimates, the results for vegetation volume were most similar to those for clipharvested biomass samples. Thus, we recommend utilizing vegetation volume as a cost-efficient and robust non-destructive biomass estimate in arctic-alpine areas. Our results indicate that the fine scale environmental variation has to be taken into account more carefully when modelling vegetation biomass and carbon budget, especially under changing climatic conditions.Academy of Finland (Project Number 1140873).http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1468-04592015-04-30hb201

Distribution of microarthropods across altitude and aspect in the sub-Antarctic : climate change implications for an isolated oceanic island

Current climate change is altering the distribution of species across both broad and fine scales. Examining contemporary species distributions along altitudinal gradients is one approach to predicting species future distributions, as species occurrence patterns at cold, high altitudes are expected to resemble the species distribution patterns currently observed at warmer, lower altitudes if warming occurs. Strong changes in climate have been observed in the sub-Antarctic over the last 50 years, with a 1.5 °C increase in mean temperature and a c. 30% decrease in mean precipitation recorded on Marion Island. In this study, the distribution patterns of mites and springtails inhabiting the cushion-plant Azorella selago were studied on Marion Island. Mite and springtail species richness and springtail abundance were significantly higher on the western aspect of the island, possibly due to higher rainfall and greater cloud cover on the windward side of the island. Mite abundance did not differ between aspects of the island, which may be due to the higher desiccation tolerance of mites. Mite and springtail species richness and springtail abundance were significantly lower at high altitudes coinciding with lower temperatures and generally harsher environment at higher altitudes. Plant characteristics generally did not contribute to explaining species patterns, suggesting that at the island-scale abiotic variables, rather than biotic factors, appeared to be the more important determinants of community structure. Therefore, despite species responding individualistically, it is clear that a warmer and drier climate will dramatically change the microarthropod community structure within A. selago on Marion Island.The National Research Foundation’s South African National Antarctic Programmehttp://www1.montpellier.inra.fr/CBGP/acarologiaam2019Plant Production and Soil Scienc

Outcomes of biotic interactions are dependent on multiple environmental variables

QUESTION : Can variation in the outcome of biotic interactions in relation to environmental severity bemore accurately predictedwhen consideringmultiple stress and/or disturbance variables? LOCATION : Arctic-alpine tundra in Kilpisj€arvi, North Finland. METHODS : To test the impact of including multiple environmental variables in analyses of the outcomes of biotic interactions, we modelled reproductive effort and cover of 17 arctic-alpine species as a function of Empetrum nigrum subsp. hermaphroditum cover, geomorphological disturbance and soil moisture with statistical interactions of the explanatory variables included.We implemented a best-subset approach using generalized linear models (GLM) and selected the bestmodel for each species based on Akaike’s information criterion (AIC). RESULTS : For the majority of species, models including multiple environmental variables were selected as best. Reproductive effort depended on one or both environmental variables for all species, and 14 species were additionally influenced by Empetrum,with the impact of Empetrum varyingwith abiotic conditions in all but one of those species. Moreover, the three-way interaction of three explanatory variables was included in the best-fit models for six species. The impact of Empetrum on species cover showed a similar pattern, with 11 species affected by Empetrum and its statistical interactions with one or both abiotic variables. CONCLUTIONS : Biotic interactions have an important role in arctic-alpine vegetation, but to fully understand variation in their effects multiple environmental factors should be explicitly considered. In this study, the outcome of biotic interactions was frequently dependent on two abiotic variables (and occasionally additionally on their statistical interaction). Therefore, we demonstrate that studies based on only one environmental factor may cause misleading interpretations of the nature of biotic interactions in plant communities where there are multiple independent variables underlying the habitat severity gradient.Academy of Finland (Project Number 1140873), the Nordenskiöld Foundation and the Department of Geosciences and Geography (University of Helsinki)http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1654-1103hb201

Repeated monitoring as an effective early detection means : first records of naturalised Solidago gigantea Aiton (Asteraceae) in southern Africa

Early detection ofemerging invasive plants depends onmaximizing the probability of detecting newpopulations. Repeated surveys along a gradient of environmental conditions or in areas exposed to high propagule pressure provide a potentially efficient strategy for early detection of alien species. The long-term monitoring of such an area resulted in the documentation of the first naturalised Solidago gigantea Aiton (Asteraceae) population for southern Africa. This population consisted of c. 45 individuals growing in two locations on unmanaged grassland in the Drakensberg Mountains at an elevation of 1619 m a.s.l. Solidago gigantea readily invades unmanaged European grasslands, altering biomass and transforming habitats. Moreover, since goldenrods (Solidago spp) are perennial species reproducing through a large number of wind-dispersed seeds and belowground rootstocks, these species appear well pre-adapted to the fire-prone grassland biome of South Africa. We therefore suggest early-stage eradication of S. gigantea before it potentially becomes an unmanageable and costly invasive species in this region. This study supports long-termmonitoring programmes as an effective means for early detection of new invasive species.DST-NRF Centre of Excellence for Invasion Biology, the University of Johannesburg and the University of Pretoria. JMK is currently supported by the long-term research development project no. RVO 67985939 (Academy of Sciences of the Czech Republic). The MazdaWildlife Fund.http://www.elsevier.com/locate/sajbhb201

Testing for consistency in the impacts of a burrowing ecosystem engineer on soil and vegetation characteristics across biomes

The impacts of ecosystem engineers may be expected to vary along environmental gradients. Due to some resources being more limited in arid than in mesic environments, disturbances created by burrowing mammals are expected to have a greater ameliorating effect in arid environments, with larger differences in microhabitat conditions expected between burrows and undisturbed areas. The aim of this study was to test if the impacts of a medium-sized burrowing mammal, the aardvark, on soil properties (soil temperature, moisture and compaction) and vegetation characteristics (plant cover, species richness and species composition) are consistent across three biomes that differ strongly in annual rainfall. Burrowing affected soil and vegetation attributes, but the direction and magnitude of these biogeomorphological impacts were not consistent across the different biomes. For example, plant species composition was altered by burrowing in the arid scrubland and in the mesic grassland, but not in the semi-arid savannah. Contrary to expectations, the difference in the impacts of burrowing between biomes were not related to rainfall, with burrowing having strong, albeit different, impacts in both the arid scrubland and the mesic grassland, but weaker effects in the semi-arid savannah. It appears, therefore, that the impacts of these biogeomorphic agents may be site-specific and that it may be difficult to predict variation in their biotic and abiotic effects across environmental gradients. As a result, forecasting the impacts of ecosystem engineers under different conditions remains a challenge to management, restoration and conservation strategies related to these types of species.http://www.nature.com/srepam2020Geography, Geoinformatics and MeteorologyPlant Production and Soil Scienc

Incorporating biotic interactions in the distribution models of African wild silk moths (Gonometa species, Lasiocampidae) using different representations of modelled host tree distributions

Biotic interactions influence species niches and may thus shape distributions. Nevertheless, species distribution modelling has traditionally relied exclusively on environmental factors to predict species distributions, while biotic interactions have only seldom been incorporated into models. This study tested the ability of incorporating biotic interactions, in the form of host plant distributions, to increase model performance for two host‐dependent lepidopterans of economic interest, namely the African silk moth species, Gonometa postica and Gonometa rufobrunnea (Lasiocampidae). Both species are dependent on a small number of host tree species for the completion of their life cycle. We thus expected the host plant distribution to be an important predictor of Gonometa distributions. Model performance of a species distribution model trained only on abiotic predictors was compared to four species distribution models that additionally incorporated biotic interactions in the form of four different representations of host plant distributions as predictors. We found that incorporating the moth–host plant interactions improved G. rufobrunnea model performance for all representations of host plant distribution, while for G. postica model performance only improved for one representation of host plant distribution. The best performing representation of host plant distribution differed for the two Gonometa species. While these results suggest that incorporating biotic interactions into species distribution models can improve model performance, there is inconsistency in which representation of the host tree distribution best improves predictions. Therefore, the ability of biotic interactions to improve species distribution models may be context‐specific, even for species which have obligatory interactions with other organisms.The University of Pretoria (RDP funding to Michelle Greve), the South African National Research Foundation and the South African National Biodiversity Institute.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1442-99932018-12-01hj2018Plant Production and Soil Scienc

Exposing wind stress as a driver of fine-scale variation in plant communities

The effects of temperature and precipitation, and the impacts of changes in these climatic conditions, on plant communities have been investigated extensively. The roles of other climatic factors are, however, comparatively poorly understood, despite potentially also strongly structuring community patterns. Wind, for example, is seldom considered when forecasting species responses to climate change, despite having direct physiological and mechanical impacts on plants. It is, therefore, important to understand the magnitude of potential impacts of changing wind conditions on plant communities, particularly given that wind patterns are shifting globally. Here, we examine the relationship between wind stress (i.e. a combination of wind exposure and wind speed) and species richness, vegetation cover and community composition using fine-scale, field-collected data from 1,440 quadrats in a windy sub-Antarctic environment. Wind stress was consistently a strong predictor of all three community characteristics, even after accounting for other potentially ecophysiologically important variables, including pH, potential direct incident solar radiation, winter and summer soil temperature, soil moisture, soil depth and rock cover. Plant species richness peaked at intermediate wind stress, and vegetation cover was highest in plots with the greatest wind stress. Community composition was also related to wind stress, and, after the influence of soil moisture and pH, had a similar strength of effect as winter soil temperature. Synthesis. Wind conditions are, therefore, clearly related to plant community characteristics in this ecosystem that experiences chronic winds. Based on these findings, wind conditions require greater attention when examining environment–community relationships, and changing wind patterns should be explicitly considered in climate change impact predictions.National Research Foundation.http://www.wileyonlinelibrary.com/journal/jechj2022Plant Production and Soil Scienc