Moving out of town? The status of alien plants in high‐Arctic Svalbard, and a method for monitoring of alien flora in high‐risk, polar environments

Abstract Rising human activity in the Arctic, combined with a warming climate, increases the probability of introduction and establishment of alien plant species. While settlements are known hotspots for persistent populations, little is known about colonization of particularly susceptible natural habitats. Systematic monitoring is lacking and available survey methods vary greatly. Here, we present the most comprehensive survey of alien vascular plant species in the high‐Arctic archipelago of Svalbard to date, aimed at (i) providing a status within settlements; (ii) surveying high‐risk habitats such as those with high visitor numbers and nutrient enrichment from sea bird colonies; (iii) presenting a systematic monitoring method that can be implemented in future work on alien plant species in Arctic environments; and (iv) discuss possibilities for mapping alien plant habitats using unmanned aerial vehicles. The systematic grid survey, covering 1.7 km2 over three settlements and six bird cliffs, detected 36 alien plant species. Alien plant species were exclusively found in areas of human activity, particularly areas associated with current or historic animal husbandry. The survey identified the successful eradication of Anthriscus sylvestris in Barentsburg, as well as the rapid expansion of Taraxacum sect. Ruderalia over the last few decades. As there is currently no consistent method for monitoring alien plant species tailored to polar environments, we propose a systematic methodology that could be implemented within a structured monitoring regime as part of an adaptive monitoring strategy towards alien species in the Arctic

Global maps of soil temperature

Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km2 resolution for 0–5 and 5–15 cm soil depth. These maps were created by calculating the difference (i.e. offset) between in situ soil temperature measurements, based on time series from over 1200 1-km2 pixels (summarized from 8519 unique temperature sensors) across all the world\u27s major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (−0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications

Highways up the mountains: Trails as facilitators for redistribution of plant species in mountain areas.

To protect mountain ecosystems, their biodiversity, ecosystem services, and other contributions to people, it is necessary to understand how climate and disturbances affect them. Trails may change seed dispersal and disrupt biotic interactions between plants, thereby creating opportunities for recruitment in locations where seeds did not arrive or competition prevented establishment. This could change plant distributions in mountain areas. Colonization opportunities may also allow species that are non-native in a particular mountain ecosystem to establish. Such changes in species distributions can influence ecosystem functions, services, and benefits. The aim of this thesis is to improve our understanding of trails' impacts on species’ distributions in the Scandes and to improve knowledge on the impact of invasive species in mountain ranges as they are perceived by stakeholders. I conducted systematic observational surveys along hiking trails in Norway and Sweden and examined the effect of hiking trails on seed rain, seed bank abundance, seedling recruitment, and species’ realized climatic niches. For further insights in establishment and persistence of species, I investigated the importance of positive and negative neighbour interactions on different species and life stages in a field experiment manipulating environmental stress and distance to neighbouring vegetation. Using a global survey, I evaluated stakeholder perceptions of invasive species’ impacts on ecosystem functions and services in mountains. Seed rain, seed bank, and seedling recruitment were strongly elevated along trails and trail disturbances reached far into the vegetation. Along trails, alpine species shifted their warm climatic niche edges and optima towards warmer locations, leading to an increased overlap in species' climatic niches. This was reflected by a greater species richness in trailside vegetation than in the vegetation far from trails. Recipient community and distance to anthropogenic structures modulated this increase in species richness in trailsides. Gap size influenced the microclimate within vegetation gaps. Increased seedling establishment in small gaps appeared to be a result of reduced competition for light, which masked the amelioration of climate by neighbouring vegetation that becomes apparent when including larger gaps sizes. Facilitation by neighbouring vegetation was important throughout the life cycle under stressful conditions. Stress type mattered for the importance of facilitation, with seedlings more susceptible to acute stress. Stakeholders across regions ranked impacts of invasive species on biodiversity and ecosystem functions predominantly negative, while the ranking of impacts on ecosystem functions and benefits also included positive perceptions. Stakeholder groups varied in their perception of impacts, with on-the-ground stakeholders more frequently reporting positive impacts. Conflicting views on impacts may be a reason for the large proportion of species that currently have no management plan. This thesis illustrates that trailsides may provide temporary escape routes from strongly competitive lowland plants for pressed alpine species, and locally increase species richness in the Scandes. When examining biotic interactions, the spatial scales on which different stresses act and target species tolerances to them should be considered. Further research on changes in native and non-native species distributions should consider impacts beyond biodiversity

Hiking trails as conduits for the spread of non-native species in mountain areas

Roadsides are major pathways of plant invasions in mountain regions. However, the increasing importance of tourism may also turn hiking trails into conduits of non-native plant spread to remote mountain landscapes. Here, we evaluated the importance of such trails for plant invasion in five protected mountain areas of southern central Chile. We therefore sampled native and non-native species along 17 trails and in the adjacent undisturbed vegetation. We analyzed whether the number and cover of non-native species in local plant assemblages is related to distance to trail and a number of additional variables that characterize the abiotic and biotic environment as well as the usage of the trail. We found that non-native species at higher elevations are a subset of the lowland source pool and that their number and cover decreases with increasing elevation and with distance to trails, although this latter variable only explained 4–8% of the variation in the data. In addition, non-native richness and cover were positively correlated with signs of livestock presence but negatively with the presence of intact forest vegetation. These results suggest that, at least in the region studied, hiking trails have indeed fostered non-native species spread to higher elevations, although less efficiently than roadsides. As a corollary, appropriate planning and management of trails could become increasingly important to control plant invasions into mountains in a world which is warming and where visitation and recreational use of mountainous areas is expected to increase.(c) The Author(s) 201

Global maps of soil temperature

Abstract Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km² resolution for 0‐5 and 5‐15 cm soil depth. These maps were created by calculating the difference (i.e. offset) between in situ soil temperature measurements, based on time series from over 1200 1‐km² pixels (summarized from 8519 unique temperature sensors) across all the world's major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10° degrees C (mean = 3.0 +/‐ 2.1° degrees C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 +/‐2.3° degrees C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (‐0.7 +/‐ 2.3° degrees C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications

SoilTemp: A global database of near‐surface temperature

Current analyses and predictions of spatially explicit patterns and processes in ecology most often rely on climate data interpolated from standardized weather stations. This interpolated climate data represents long‐term average thermal conditions at coarse spatial resolutions only. Hence, many climate‐forcing factors that operate at fine spatiotemporal resolutions are overlooked. This is particularly important in relation to effects of observation height (e.g. vegetation, snow and soil characteristics) and in habitats varying in their exposure to radiation, moisture and wind (e.g. topography, radiative forcing or cold‐air pooling). Since organisms living close to the ground relate more strongly to these microclimatic conditions than to free‐air temperatures, microclimatic ground and near‐surface data are needed to provide realistic forecasts of the fate of such organisms under anthropogenic climate change, as well as of the functioning of the ecosystems they live in. To fill this critical gap, we highlight a call for temperature time series submissions to SoilTemp, a geospatial database initiative compiling soil and near‐surface temperature data from all over the world. Currently, this database contains time series from 7,538 temperature sensors from 51 countries across all key biomes. The database will pave the way toward an improved global understanding of microclimate and bridge the gap between the available climate data and the climate at fine spatiotemporal resolutions relevant to most organisms and ecosystem processes