Complex Relationships between Competing Guilds along Large-Scale Environmental Gradients

Despite much research over the past 30 years there is still little general understanding of how the outcomes of interactions vary along environmental gradients, particularly at large geographic scales. A simple expectation is that decreasing environmental quality should reduce densities of competitors and hence the effects of competition should weaken in poorer environments. A counter-intuitive consequence is that associations between densities of competitors might change from negative to positive as environments decrease in quality. Here we test these predictions in a set of vascular plant communities where perennial species share space and resources with less competitive annuals. We surveyed nine grey dune communities annually for 5 years along a cross-European latitudinal gradient of habitat quality. We find that densities of annual and perennial species are negatively correlated at the high-quality end of the gradient, while at the low-quality end guild densities are uncorrelated or positively correlated, consistent with a weakening of competition linked to increasing environmental limitations. Our results suggest that even simple interactions can give rise to non-obvious changes in species associations along environmental gradients. They highlight that understanding the outcome of species interactions may require explicit characterization of their changing intensity with environmental quality, and that the factors limiting species’ co-distribution can vary along environmental gradients

A research agenda for seed-trait functional ecology

Trait-based approaches have improved our understanding of plant evolution, community assembly and ecosystem functioning. A major challenge for the upcoming decades is to understand the functions and evolution of early life-history traits, across levels of organization and ecological strategies. Although a variety of seed traits are critical for dispersal, persistence, germination timing and seedling establishment, only seed mass has been considered systematically. Here we suggest broadening the range of morphological, physiological and biochemical seed traits to add new understanding on plant niches, population dynamics and community assembly. The diversity of seed traits and functions provides an important challenge that will require international collaboration in three areas of research. First, we present a conceptual framework for a seed ecological spectrum that builds upon current understanding of plant niches. We then lay the foundation for a seed-trait functional network, the establishment of which will underpin and facilitate trait-based inferences. Finally, we anticipate novel insights and challenges associated with incorporating diverse seed traits into predictive evolutionary ecology, community ecology and applied ecology. If the community invests in standardized seed-trait collection and the implementation of rigorous databases, major strides can be made at this exciting frontier of functional ecology.Commonwealth Scientific and Industrial Research Organisation. Grant Number: R‐90470‐0

Fire seasonality effect on Post-Fire wind dispersal: Response to Keith, Dunker, and Driscoll

Letter to the Edito

Seed dormancy interacts with fire seasonality mechanisms

We recently published a framework of demographic mechanisms that may impact plant population responses to changes in fire seasonality [1]. This framework now includes eight mechanisms identified in [1,2] and further detailed in [3,4]. Subsequently, Cao et al. [5] have proposed that seed dormancy class, based on the dormancy classification scheme of Baskin and Baskin [6], should be recognised as an additional mechanism. Cao et al. [5] described for each seed dormancy class, how seed dormancy induction and loss, and germination timing, may be influenced by seasonal environmental cues (e.g., light and temperature) and, separately, how they interact with fire-related cues (e.g., heat and smoke). We agree that seed dormancy and germination traits are important to the regeneration of plants in fire-prone regions. However, as Cao et al. [5] do not identify how seed dormancy class determines seasonally varying resistant or vulnerable states required to create a fire seasonality effect beyond those already defined [1], it is not clear how dormancy class forms a new separate mechanism under a demographic framework

Success of post-fire plant recovery strategies varies with shifting fire seasonality

Wildfires are increasing in size and severity and fire seasons are lengthening, largely driven by climate and land-use change. Many plant species from fire-prone ecosystems are adapted to specific fire regimes corresponding to historical conditions and shifts beyond these bounds may have severe impacts on vegetation recovery and long-term species persistence. Here, we conduct a meta-analysis of field-based studies across different vegetation types and climate regions to investigate how post-fire plant recruitment, reproduction and survival are affected by fires that occur outside of the historical fire season. We find that fires outside of the historical fire season may lead to decreased post-fire recruitment, particularly in obligate seeding species. Conversely, we find a general increase in post-fire survival in resprouting species. Our results highlight the trade-offs that exist when considering the effects of changes in the seasonal timing of fire, an already present aspect of climate-related fire regime change

Fire seasonality mechanisms are fundamental for understanding broader fire regime effects

Letter to the edito