Plant neighbor detection and response strategies are important mediators of interactions among species. Despite increasing knowledge of neighbor detection and response involving plant volatiles, less is known about how soil-borne signaling chemicals may act belowground in plant–plant interactions. Here, we experimentally demonstrate neighbor detection and allelopathic responses between wheat and 100 other plant species via belowground signaling. Wheat can detect both conspecific and heterospecific neighbors and responds by increasing allelochemical production. Furthermore, we show that (-)-loliolide and jasmonic acid are present in root exudates from a diverse range of species and are able to trigger allelochemical production in wheat. These findings suggest that root-secreted (-)-loliolide and jasmonic acid are involved in plant neighbor detection and allelochemical response and may be widespread mediators of belowground plant-plant interactions.

Summary1. Succession has been a focus of extensive ecological study for well over a century. Despite this sustained interest, succession remains a central theme in ecological research and is positioned to continue that prominence in this era of expanding human impacts. Community ecology is currently experiencing a profound conceptual expansion, providing many new insights into succession. 2. Here we present an existing conceptual framework of successional drivers that includes variation in site conditions, species availability and species performance, and expand it to include both evolutionary and geographic sources of variation. This framework is useful because it specifies relationships among individual drivers and is causally complete. While we generally think about succession as a within-site process, the inclusion of phylogenetic and geographic processes allows integration across broader scales. 3. We use the conceptual framework to highlight several opportunities for successional research that have developed within community ecology, but have not been fully integrated into succession work. These ideas represent not only individual drivers of succession, but also potential synergistic processes operating through interaction with other drivers. The complexity of drivers in succession strongly argues for the need to move away from single factor studies towards combinatorial studies that incorporate multiple drivers. 4. Utilizing a trait-based approach should allow researchers to address successional drivers at multiple ecological scales and lead to new insights that integrate ecological systems. Our ability to do this will depend on the availability of equivalent data across multiple systems, suggesting the need for more standardization in successional studies. 5. Addressing the research opportunities highlighted here will not only produce insights into successional systems, but also expand our understanding of fundamental questions in community ecology as a whole. Of particular importance is the ability to address broader scale questions that go beyond the idiosyncrasies of individual sites and systems. Understanding the dynamics of successional systems will remain critical to understanding, managing and predicting anthropogenic impacts on natural systems.

Ecological communities often transition from phylogenetic and functional clustering to overdispersion over succession as judged by space-for-time substitution studies. Such a pattern has been generally attributed to the increase in competitive exclusion of closely related species with similar traits through time, although colonisation and extinction have rarely been examined. Using 44 years of uninterrupted old-field succession in New Jersey, USA, we confirmed that phylogenetic and functional clustering decreased as succession unfolded, but the transition was largely driven by colonisation. Early colonists were closely related and functionally similar to residents, while later colonists became less similar to the species present. Extirpated species were generally more distantly related to residents than by chance, or exhibited random phylogenetic/functional patterns, and their relatedness to residents was not associated with time. These results provide direct evidence that the colonisation of distant relatives, rather than extinction of close relatives, drives phylogenetic and functional overdispersion over succession.

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Darwin's naturalisation conundrum describes the paradox that the relatedness of exotic species to native residents could either promote or hinder their success through opposing mechanisms: niche pre-adaptation or competitive interactions. Previous studies focusing on single snapshots of invasion patterns have provided support to both sides of the conundrum. Here, by examining invasion dynamics of 480 plots over 40 years, we show that exotic species more closely related to native species were more likely to enter, establish and dominate the resident communities, and that native residents more closely related to these successful exotics were more likely to go locally extinct. Therefore, non-random displacement of natives during invasion could weaken or even reverse the negative effects of exotic-native phylogenetic distances on invasion success. The scenario that exotics more closely related to native residents are more successful, but tend to eliminate their closely related natives, may help to reconcile the 150-year-old conundrum.

While exotic plant species often come to dominate disturbed communities, long‐term patterns of invasion are poorly known. Here we present data from 40 yr of continuous vegetation sampling, documenting the temporal distribution of exotic plant species in old field succession. The relative cover of exotic species decreased with time since abandonment, with significant declines occurring ≥20 yr post‐abandonment. The number of exotic species per plot also declined with time since abandonment while field‐scale richness of exotics did not change. This suggests displacement occurring at small spatial scales. Life history types changed from short‐lived herbaceous species to long‐lived woody species for both native and exotic plant species. However, shrubs and lianas dominated woody cover of exotic plants while trees dominated native woody cover. The species richness of exotic and native species was positively correlated at most times. In abandoned hay fields, however, the proportion of exotic plant cover per plot was inversely related to total species richness. This relationship suggests that it is not the presence, but the abundance of exotic species that may cause a reduction in community diversity. While the development of closed‐canopy forest appears to limit most introduced plant species, several shade‐adapted exotic species are increasing within the fields. These invasions may cause a reversal of the patterns seen in the first 40 yr of succession and may result in further impacts on community structure.

Whether plant communities in a given region converge towards a particular stable state during succession has long been debated, but rarely tested at a sufficiently long time scale. By analysing a 50-year continuous study of post-agricultural secondary succession in New Jersey, USA, we show that the extent of community convergence varies with the spatial scale and species abundance classes. At the larger field scale, abundance-based dissimilarities among communities decreased over time, indicating convergence of dominant species, whereas incidence-based dissimilarities showed little temporal tend, indicating no sign of convergence. In contrast, plots within each field diverged in both species composition and abundance. Abundance-based successional rates decreased over time, whereas rare species and herbaceous plants showed little change in temporal turnover rates. Initial abandonment conditions only influenced community structure early in succession. Overall, our findings provide strong evidence for scale and abundance dependence of stochastic and deterministic processes over old-field succession.

Introduction: This paper surveys a framework for vegetation dynamics to provide conceptual background for a series of papers addressing the role of vegetation dynamics in restoration. Richness of the foundation: Classical succession theory provides key ingredients for contemporary process studies of vegetation dynamics. The contemporary framework incorporates processes identified by Gleason and other critics of Clements' theory. Multiple causality: The Clementsian causes, when expanded to include interaction and to clarify net effects, accommodate those now recognized in vegetation dynamics. A mature successional framework: A hierarchical framework has emerged to evaluate the causes of vegetation dynamics. The framework identifies the general causes as site availability, species availability, and species performance. Differentials as drivers: Differentials in any of the three general causes can drive change in plant communities. Each general cause consists of specific mechanisms. A model template: To predict vegetation dynamics trajectories, models are required. A model template is presented to operationalize the hierarchical framework. Outcomes are contingent on species pools and environmental contexts and may be progressive or retrogressive. Relationships of frameworks: Other contemporary frameworks in biology relate to vegetation dynamics. Application to restoration: The vegetation dynamics framework is relevant to restoration through linkages with landscape ecology, disturbance ecology, competition, invasion ecology, and community assembly. The differentials of site availability, species availability, and species performance suggest the processes and strategies available for restoration. Conclusions: A synthetic framework of vegetation brings together the mechanisms required for successful restoration.