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  1. Ecological theory posits that temporal stability patterns in plant populations are associated with differences in species' ecological strategies. However, empirical evidence is lacking about which traits, or trade-offs, underlie species stability, especially across different biomes. We compiled a worldwide collection of long-term permanent vegetation records (greater than 7000 plots from 78 datasets) from a large range of habitats which we combined with existing trait databases. We tested whether the observed inter-annual variability in species abundance (coefficient of variation) was related to multiple individual traits. We found that populations with greater leaf dry matter content and seed mass were more stable over time. Despite the variability explained by these traits being low, their effect was consistent across different datasets. Other traits played a significant, albeit weaker, role in species stability, and the inclusion of multi-variate axes or phylogeny did not substantially modify nor improve predictions. These results provide empirical evidence and highlight the relevance of specific ecological trade-offs, i.e. in different resource-use and dispersal strategies, for plant populations stability across multiple biomes. Further research is, however, necessary to integrate and evaluate the role of other specific traits, often not available in databases, and intraspecific trait variability in modulating species stability. 
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    Free, publicly-accessible full text available June 28, 2024
  2. Abstract

    Extreme drought and increasing temperatures can decrease the resilience of plant communities to fires. Not only may extremely dry conditions during or after fires lead to higher plant mortality and poorer recruitment, but severe pre‐fire droughts may reduce the seed production and belowground vigor that are essential to post‐fire plant recovery, and may indirectly facilitate invasion. We studied survival, recruitment, and growth of shrubs and herbs in chaparral (shrubland) communities in Northern California after a 2015 fire that immediately followed California’s extreme 3‐yr drought. We followed the same protocols used to study similar, adjacent communities after a 1999 fire that did not follow a drought, and we compared the two recovery trajectories. Overall, the 2015 fire was not more severe than the 1999 fire, yet it caused higher mortality and lower growth of resprouting shrubs on fertile (sandstone) soils. In contrast, the 2015 fire did not affect the mortality or growth of resprouting shrubs on infertile (serpentine) soils, the density of shrub seedlings, or the richness or cover of native herbs differently than the 1999 fire. However, the 2015 fire facilitated a massive increase in exotic herbaceous cover, especially on fertile soils, possibly portending the early stages of a type conversion to exotic‐dominated grassland. Our findings indicate that the consequences of climate change on fire‐dependent communities will include effects of pre‐fire as well as post‐fire climate, and that resprouting shrubs are particularly likely to be sensitive to pre‐fire drought.

     
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  3. Abstract

    Competition, niche differences and chance all contribute to community assembly; yet, the role of reproductive interactions between species is often less appreciated. Closely related plant species that share floral form, phenology and habitat often interact through pollination. They potentially facilitate pollinator attraction, compete for pollination services and/or exchange pollen. If reproductive processes are important to co‐occurrence, we predicted that fitness costs of heterospecific pollen transfer or pollen limitation should result in lower rates of co‐occurrence among outcrossing congeners. In contrast, selfers, which may be less exposed to heterospecific pollen, and/or less negatively affected by it, should co‐occur more frequently.

    Flower size is an excellent proxy for mating system in clovers. Using herbarium records and three independent field datasets, we documented co‐occurrence patterns ofTrifoliumat 1 m2–1 km2scales in California. Using a randomization procedure to reshuffle matrices of community membership, we generated null hypotheses for the expected composition of large‐ and small‐flowered species inTrifoliumcommunities of different sizes.

    Across all spatial scales, large‐flowered outcrossers were over‐represented at sites lacking congeners, but under‐represented in communities with multiple congeners. Conversely, small‐flowered selfers often occupied sites with multiple otherTrifoliumspecies. Patterns for plant height and leaf size, which are weakly or strongly correlated with flower size, did not explain co‐occurrence patterns as robustly. Regression analysis and model selection corroborated the null model analyses, indicating that the likelihood of co‐occurrence decreased as flower size, and thus reliance on outcrossing, increased.

    Synthesis. This study suggests that reproductive traits and processes may be significant contributors to community assembly and co‐occurrence in flowering plants.

     
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  4. Premise

    Clouds have profound consequences for ecosystem structure and function. Yet, the direct monitoring of clouds and their effects on biota is challenging especially in remote and topographically complex tropical cloud forests. We argue that known relationships between climate and the taxonomic and functional composition of plant communities may provide a fingerprint of cloud base height, thus providing a rapid and cost‐effective assessment in remote tropical cloud forests.

    Methods

    To detect cloud base height, we compared species turnover and functional trait values among herbaceous and woody plant communities in an ecosystem dominated by cloud formation. We measured soil and air temperature, soil nutrient concentrations, and extracellular enzyme activity. We hypothesized that woody and herbaceous plants would provide signatures of cloud base height, as evidenced by abrupt shifts in both taxonomic composition and plant function.

    Results

    We demonstrated abrupt changes in taxonomic composition and the community‐ weighted mean of a key functional trait, specific leaf area, across elevation for both woody and herbaceous species, consistent with our predictions. However, abrupt taxonomic and functional changes occurred 100 m higher in elevation for herbaceous plants compared to woody ones. Soil temperature abruptly decreased where herbaceous taxonomic and functional turnover was high. Other environmental variables including soil biogeochemistry did not explain the abrupt change observed for woody plant communities.

    Conclusions

    We provide evidence that a trait‐based approach can be used to estimate cloud base height. We outline how rises in cloud base height and differential environmental requirements between growth forms can be distinguished using this approach.

     
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  5. The stability of ecological communities is critical for the stable provisioning of ecosystem services, such as food and forage production, carbon sequestration, and soil fertility. Greater biodiversity is expected to enhance stability across years by decreasing synchrony among species, but the drivers of stability in nature remain poorly resolved. Our analysis of time series from 79 datasets across the world showed that stability was associated more strongly with the degree of synchrony among dominant species than with species richness. The relatively weak influence of species richness is consistent with theory predicting that the effect of richness on stability weakens when synchrony is higher than expected under random fluctuations, which was the case in most communities. Land management, nutrient addition, and climate change treatments had relatively weak and varying effects on stability, modifying how species richness, synchrony, and stability interact. Our results demonstrate the prevalence of biotic drivers on ecosystem stability, with the potential for environmental drivers to alter the intricate relationship among richness, synchrony, and stability. 
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  6. Abstract

    Climate forecasts agree that increased variability and extremes will tend to reduce the availability of water in many terrestrial ecosystems. Increasingly severe droughts may be exacerbated both by warmer temperatures and by the relative unavailability of water that arrives in more sporadic and intense rainfall events. Using long‐term data and an experimental water manipulation, we examined the resilience of a heterogeneous annual grassland community to a prolonged series of dry winters that led to a decline in plant species richness (2000–2014), followed by a near‐record wet winter (2016–2017), a climatic sequence that broadly resembles the predicted future in its high variability. In our 80, 5‐m2observational plots, species richness did not recover in response to the wet winter, and the positive relationship of richness to annual winter rainfall thus showed a significant weakening trend over the 18‐year time period. In experiments on 100, 1‐m2plots, wintertime water supplementation increased and drought shelters decreased the seedling survival and final individual biomass of native annual forbs, the main functional group contributing to the observed long‐term decline in richness. Water supplementation also increased the total cover of native annual forbs, but only increased richness within nested subplots to which seeds were also added. We conclude that prolonged dry winters, by increasing seedling mortality and reducing growth of native forbs, may have diminished the seedbank and thus the recovery potential of diversity in this community. However, the wet winter and the watering treatment did cause recovery of the community mean values of a key functional trait (specific leaf area, an indicator of drought intolerance), suggesting that some aggregate community properties may be stabilized by functional redundancy among species.

     
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