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Plants are responding to climate change by shifting their ranges to higher elevations. These range shifts are not happening at the same rate for all species, for example, subalpine species are generally moving faster upslope than alpine species, but with large variation within groups. This asymmetry in migration rates will result in novel communities and interactions between plant species that have not previously co-occurred. While seed dispersal is obviously critical for species’ range shifts, seedling emergence and survival are also major bottlenecks for successful colonization in new areas. As seedlings generally constitute the most vulnerable stages in the life-history of plants, variation in seedling establishment success can potentially be important determinants of species’ range shift rates. Previous studies have found that warming per se tends to increase seedling establishment in alpine climates, but it also increases plant productivity and thus competition for nutrients and light from the resident vegetation, which acts limiting on seedling establishment. This study will attempt to disentangle the relative importance of these abiotic and biotic factors on sub-alpine species’ seedling emergence and survival in alpine habitats, to help further understanding and prediction of future lowland plant colonization in alpine habitats. We will also explore if species’ life strategies impact their ability to colonize new locations, predicting that species with resource acquisitive traits will emerge earlier and faster than resource conservative species. To address these questions, we will perform a seed transplant experiment where we assess seedling emergence and establishment in the alpine. Seeds will be sown in plots with and without experimental warming, crossed with manipulation of biotic interactions, and using seeds from both resource conservative and resource acquisitive subalpine species. In addition, we will explore if the observed responses are general or context-dependent by replicating this experiment along a regional bioclimatic precipitation gradient.

Estimating the distribution of phenotypes in populations and communities is central to many questions in ecology and evolutionary biology. These distributions can be characterized by their moments: the mean, variance, skewness, and kurtosis. Typically, these moments are calculated using a community-weighted approach (e.g. community-weighted mean) which ignores intraspecific variation. As an alternative, bootstrapping approaches can incorporate intraspecific variation to improve estimates, and also quantify uncertainty in the estimate. Here, we compare the performance of different approaches for estimating the moments of trait distributions across a variety of sampling scenarios, taxa, and datasets. We introduce the traitstrap R package to facilitate inferences of trait distributions via bootstrapping. Our results suggest that randomly sampling ~9 individuals per sampling unit and species, focusing on covering all species in the community, and analysing the data using nonparametric bootstrapping generally enables reliable inference on trait distributions, including the central moments, of communities.

The coastal heathlands of North-west Europe are valuable cultural landscapes, created and maintained over millennia by a land-use regime involving burning and grazing. These heathlands are now critically threatened throughout their range by land-use change and, increasingly, climatic changes. The climatic change impacts are complex, as the coastal heathland regions are experiencing increased temperature and precipitation, but also increased frequency and severity of extreme events, such as drought. Previous studies reveal that established heathland vegetation, including Calluna, are vulnerable to drought, but also that these vulnerabilities vary throughout the range, and with successional stage after fire. Recruitment from seed is an important regeneration strategy for Calluna heathland vegetation after burning, and our study is the first to assess how the seed germination and early seedling growth of Calluna respond to drought. We will do this in a lab germination experiment, where we will expose Calluna seeds to five different drought treatments, from -0.25 MPa to -1.7 MPa, and measure germination, and record germination percentage, germination rates, and seedling growth, below-ground allocation, and functional traits (Specific Leaf Area, Specific Root Length). To allow assessment of variation in drought responses due to geographic origin, successional stage, and the maternal plants’ drought exposure, we will conduct this experiment on seeds from 540 Calluna plants sampled from across three drought treatments (control, 50%, and 90% coverage), in three successional stages after fire (pioneer, building, mature), in two regions (60N, 65N), using a factorial design.