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Community change is one of the few constants in nature, and the balance of mechanisms influencing this change is central for understanding the structure and functioning of communities and ecosystems. Newly established communities undergo succession and can change in diversity and composition as local environmental change, interspecific interactions and immigration play out over time. Understanding the influence of initial conditions and priority effects (long‐term consequences of the initial community composition and species identity) on community change is critically important for both evaluating ecological theory and predicting restoration outcomes.Here I evaluate how initial experimental conditions in 2012, like initial sown species richness, phylogenetic diversity and early biomass production, along with priority effects caused by the identity of sown species, influence subsequent herbaceous plant community composition and the number of colonizing species after 9 years of uninterrupted natural colonization.I found that sown phylogenetic diversity (measured as mean pairwise distance) indirectly affected the number of colonizing species by increasing biomass production early on and plots with more biomass in 2012 were colonized by fewer species. Individual species influenced the number of colonizing species with taller species reducing the number of colonists and some shorter species subject to a greater number of colonists.Synthesis. Taken together, these results indicate that initial composition influences the number of colonizing species via community‐wide competition. These findings suggest that restoration outcomes can be greatly influenced by decisions about sown species composition and early management practices. [ABSTRACT FROM AUTHOR]

Plant species invasion represents one of the major drivers of biodiversity change globally, yet there is confusion about the nature of nonindigenous species (NIS) impact. This confusion stems from differing notions of what constitutes invasive species impact and the scales at which it should be assessed. At local scales, the mechanisms of the impact on local competitors can be classified into four scenarios: (1) minimal impact from NIS inhabiting unique niches; (2) neutral impact spread across the community and proportional to NIS abundance; (3) targeted impact on a small number of competitors with overlapping niches; and (4) pervasive impact that is disproportionate to NIS abundance and caused by modifications that filter out other species. I developed a statistical test to distinguish these four mechanism scenarios based on plant community rank‐abundance curves and then created a scale‐independent standardized impact score. Using an example long‐term dataset with high native plant diversity and an abundance gradient of the invasive vine, Vincetoxicum rossicum, I show that the impact resulted in either targeted or pervasive extirpations. Regardless of whether the NIS impact is neutral, targeted, or pervasive, the net outcome will be the homogenization of ecosystems and reduced biodiversity at larger scales, perhaps reducing ecosystem resilience. The framework and statistical evaluation of impact presented in this paper provide researchers and managers with an objective approach to quantifying NIS impact and prioritizing species for further management actions. [ABSTRACT FROM AUTHOR]

One of the central questions in ecology is why some species are abundant while others are rare. In plant communities, some studies show that rare plant species are rare because they suffer stronger negative density‐dependent effects from pathogens compared to abundant plant species. Moreover, such pathogen effects are also suggested to be related to phylogenetic distance among plant species. However, the importance of pathogens has been commonly inferred by treating the entire pathogen community as a "black box" without explicitly characterizing pathogen richness and community composition.Here, we test two predictions. First, if rare plant species are more susceptible to pathogens, we predict that rare plant species are associated with a higher richness of specialists (i.e., pathogens that attack only a single plant species) and/or the total pathogen community. If phylogenetically distinct plant species are less susceptible to pathogens, we predict that plant species with higher phylogenetic distinctiveness (i.e., a measure of how phylogenetically distant a species is from other co‐occurring species) are associated with a lower richness of phylogenetic specialists (i.e., pathogens that attack closely related plant species) and/or the total pathogen community.We conducted a survey of the root‐associated pathogen communities from 45 plant species in a subtropical forest. We showed that approximately 40% and 25% of the pathogens were specialists and phylogenetic specialists respectively. In contrast to our first prediction, the richness of the total pathogen community but not the richness of the specialists was found to be positively related to plant species abundance, indicating that rare plant species suffer less from pathogens. Consistent with our second prediction, both the richness of the phylogenetic specialists and the total pathogen community were found to be negatively related to plant species phylogenetic distinctiveness. Furthermore, these correlations were stronger at the earlier plant life stages examined.Synthesis. We found that the root‐associated pathogen communities were less diverse in rare plant species and plant species with few close relatives. These associations varied across multiple plant life stages, suggesting that the strength of the above‐ground–below‐ground interactions change dynamically across plant life span. [ABSTRACT FROM AUTHOR]