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A pertinent debate in plant ecology centers around the generality of the self‐thinning rule. However, studies focused on highly simplified settings such as even‐aged monospecific populations or optimal conditions. This neglects the fact that most natural communities, to which the classical self‐thinning slope is often applied, are age‐structured, composed of multiple species and exposed to various types of abiotic stress. With the help of an individual‐based model, we relax these simplified assumptions and systematically test for changes in the biomass–density relationships of uneven‐aged, functionally diverse plant communities across a complete stress gradient, using excessive to insufficient soil water as a case study. We show that frequent recruitment, which resulted in an uneven‐aged community, and stress intensity caused predictable changes in the entire biomass–density trajectory. Increasing stress resulted in steeper (more negative) slopes and increased the intercept in the classical self‐thinning section irrespective of excessive or insufficient soil water as a stress type. Recruitment steepened the slope, too and enabled a novel section in the biomass–density trajectory. This novel section represented a quasi‐steady state of the density‐dependent dynamics of new generations which occurred locally within patches of recruitment. At the community level, the slope of the biomass–density relationship at quasi‐steady state had a significantly flatter slope of −1.1 under optimal soil water conditions. Functional diversity showed little impact on density‐dependent mortality. Namely, it resulted in an earlier onset of mortality but not in changes in the values of the slope and intercept. We conclude that the classical −3/2 slope is not useful to describe the biomass–density relationship in natural and semi‐natural plant communities. The magnitude and direction of variation in the slope are related to the age‐structure and abiotic stress intensity in the plant community. [ABSTRACT FROM AUTHOR]

Abstract: Disturbances are characteristic for many ecosystems. However, we still lack generalizations concerning their role in shaping communities, particularly when disturbances co-occur. To study such effects, we used a novel modeling approach that is unrestricted by a priori tradeoffs among specific plant traits, except for those generated by allocation principles. Thus, trait combinations were emergent properties associated with biotic and abiotic constraints. Specifically, we asked which traits dominate under specific disturbance regimes, whether single and combined disturbance regimes promote similar trait tradeoffs and how complex disturbance regimes affect species richness and functional diversity. Overall, disturbances’ temporal properties governed the outcome of combined disturbances and were a stronger assortative force than spatial disturbance properties: low temporal predictability decreased seed-dispersability and dormancy, but increased competitive ability and disturbance tolerance. Evidence for tradeoffs between different colonization modes and between dormancy and disturbance tolerance were found, while surprisingly, the widely accepted colonization–competition tradeoff was not generated. Diversity was highest at intermediate disturbance intensity, but decreased monotonically with increasing unpredictability. In accordance with our results, future models should avoid restrictive assumptions about tradeoffs to generate robust and more general predictions about the role of disturbances for community dynamics. [Copyright &y& Elsevier]