WP1: Processes controlling the establishment of range-expanding species
Task 1.1: Disentangling drivers of population establishment following range expansion (JA, VV, RC)
Objective: Determine the key processes underlying establishment success of range-expanding species.
Methods: We will conduct a replicated field experiment in climatically and socio-ecologically contrasting regions (Norway, Switzerland, South Africa), in which plant communities are “invaded” with native range- expanding species transplanted upwards from lower elevations. In each region, we will select ten plant species that share similar habitat requirements and upper elevation limits, but that vary in functional traits and (where information is available) in the magnitude of their range shifts following recent warming. Plants will be grown in a control “within-range” site near their current upper elevation limit, and in a higher elevation “beyond-range” experimental site with an approximately 2°C lower average mean annual temperature (i.e. corresponding to the theoretical upward range expansion given predicted warming this century). Experimental manipulations will be designed to test variation in novel species’ establishment at the beyond-4
range site due to (1) dispersal limitation (transplant into beyond-range plant community), (2) plant-plant interactions (intact vegetation vs. above-ground plant community removal), (3) soil abiotic and biotic conditions (growth on soil from within-range vs. beyond-range sites), and (4) temperature limitation (control vs. open-top chamber [OTC] warming treatment). The OTC treatment will be crossed with treatments 1-3, yielding six treatments at the beyond-range site. Within each beyond-range site, we will establish 10 replicate blocks, each consisting of six 1 m2 experimental plots randomly assigned to treatments. Within each plot, we will plant three individuals of each of the ten study species, yielding 30 replicate plants per species and treatment. We will initiate the experiment with both seedlings and seeds, and monitor key vital rates (germination and recruitment of transplanted seeds; growth, survival and reproduction of transplanted seedlings) of the focal species in each treatment across two growing seasons. We will use mixed-effects models to determine the contribution of each factor (dispersal limitation, plant-plant interactions, soil conditions, climate limitation) to establishment success (vital rates/population growth, estimated with integral projection models). We will examine variation across species and regions to test whether establishment success is predicted by plant functional traits, and how this differs across regions. Soils from the within-range and beyond-range sites will be collected for a lab experiment to assess soil biotic and abiotic impacts on establishment success (Task 1.2) and the experiment will be used to measure impacts on ecosystem processes (Tasks 2.2, 2.3). Task 1.2: Linking soil biota with novel species establishment (PK, JA)
Objective: Understand how interactions with soil biota influence novel plant establishment, and how these
depend on climate.
Methods: We will sample soils from the well-documented elevation transects established by MIREN, spanning climatic gradients in six globally-representative mountain regions (Switzerland, South Africa, Australia, Chile, Tenerife [Spain], Montana [USA]; with help of self-financed collaborators from MIREN). For these transects, data on plant distribution/novel species are already available (collected in 2020 in South Africa). Soil samples will be collected from three replicate elevational transects in each region, spanning temperature gradients of 2-5 °C, which can hence be used as a space-for time proxy for global warming. Each transect will consist of five plots (i.e. N=15 plots per region) positioned to cover the full spectrum of vegetation changes along the temperature gradient. Plots will be selected with known occurrences of range- expanding species, and within each plot we will collect pairs of soil samples from patches with high/zero cover of these species. Measurements of air temperature, soil temperature and soil moisture will be made at these plots using automatic loggers, contextualised against long-term climate records (chelsa-climate.org/). Soils will be analysed to determine physicochemical properties (texture, pH, total soil C/N, microbial biomass C/N, dissolved C/N, ammonium, nitrate; see Task 2.2) and community composition of microorganisms (bacteria, archaea, fungi) and nematodes41. We will then test for associations between soil properties and biota and the cover, diversity and traits (see Task 2.1) of range-expanding plant species (native and non- native). We will thus infer effects of temperature on plant-soil associations, how this varies across regions, and gain further insights into the role of soil biota on novel plant species establishment under warming. These measurements are low risk, using existing sites, data, and core methodology; but of high scientific impact as they will inform of factors underlying novel species establishment across a broad biogeographic context.
To further parse-out effects of soil abiotic versus biotic properties, and gain a more mechanistic understanding, we will conduct controlled soil inoculation experiments in climate chambers, following established protocols42. These experiments will run in parallel with Task 1.1, using soils and plants from the three field experiments. State-of-the-art climate chambers at SLU-Umeå will be programmed according to temperature scenarios simulated by the field experiments. Focal plants will be grown either in living soils collected from the “within-range” and “beyond-range” sites, or on sterilized soils re-inoculated with different subsets of soil biota (e.g. pathogens, mutualists). This design disentangles climate, soil properties and soil biota from within-range and beyond-range sites and allows testing for positive or negative effects of abiotic properties and soil organisms on plant establishment and performance beyond the current range limit.
Task 1.3: Assessing effectiveness of measures to control range-expanding species (RC, AP)
Objective: Test the effectiveness of novel plant removal as a management tool.
Methods: Species that expand their ranges with climate warming can pose a threat to native biodiversity. In coordination with local managers, we will conduct targeted removal experiments of range-expanding species in multiple regions (Switzerland, South Africa, Norway, Australia, Chile, Kashmir [India], Montana) and monitor the effectiveness of removal over two seasons (monitoring will continue beyond RangeX). Focal species will be primarily non-native, but we will also select relevant native species where available and recognized as a problem by local stakeholders. We will prioritize species for which there is currently no clear5
policy, or for which there are conflicting management guidelines (or major conflicts between utilitarian value, cultural bias, and negative ecosystem service impacts). Three ecologically contrasting species of management concern will be selected (in consultation with stakeholders) for the experiment in each region. We will match species across the different regions based on functional traits, to elucidate global management approaches for similar problem species in different regions. We will compare the effectiveness of removal at high (i.e. at the range edge) vs. low (i.e. in the range core) elevation, and relate removal effectiveness to indicators of population dynamics (see Task 3.1). In addition, for regions in which there are already data and management experience with non-native and native range-expanding species (e.g. South Africa and Australia), we will collate spatial, species, and temporal data from practitioners and managers (viz. conservation, private, contractors, government) for synthesis and determination of best practice guidelines for managing key range-expanding species in montane environments.