The International Tundra Experiment (ITEX) was founded in 1990 as a network of scientists studying responses of tundra ecosystems to ambient and experimental climate change at Arctic and alpine sites across the globe. Common measurement and experimental design protocols have facilitated synthesis of results across sites to gain biome-wide insights of climate change impacts on tundra. This special issue presents results from more than 30 years of ITEX research. The importance of snow regimes, bryophytes, and herbivory are highlighted, with new protocols and studies proposed. The increasing frequency and magnitude of extreme climate events is shown to have strong effects on plant reproduction. The most consistent plant trait response across sites is an increase in vegetation height, especially for shrubs. This will affect surface energy balance, carbon and nutrient dynamics and trophic level interactions. Common garden studies show adaptation responses in tundra species to climate change but they are species and regionally specific. Recommendations are made including establishing sites near northern communities to increase reciprocal engagement with local knowledge holders and establishing multi-factor experiments. The success of ITEX is based on collegial cooperation among researchers and the network remains focused on documenting and understanding impacts of environmental change on tundra ecosystems.
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Open top chambers (OTCs) were adopted as the recommended warming mechanism by the International Tundra Experiment (ITEX) network in the early 1990’s. Since then, OTCs have been deployed across the globe. Hundreds of papers have reported the impacts of OTCs on the abiotic environment and the biota. Here we review the impacts of the OTC on the physical environment, with comments on the appropriateness of using OTCs to characterize the response of biota to warming. The purpose of this review is to guide readers to previously published work and to provide recommendations for continued use of OTCs to understand the implications of warming on low stature ecosystems. In short, the OTC is a useful tool to experimentally manipulate temperature, however the characteristics and magnitude of warming varies greatly in different environments, therefore it is important to document chamber performance to maximize the interpretation of biotic response. When coupled with long-term monitoring, warming experiments are a valuable means to understand the impacts of climate change on natural ecosystems.more » « less
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Abstract Environmental changes can rapidly alter standing biomass in tundra plant communities; yet, to what extent can they modify plant‐community nutrient levels? Nutrient levels and their changes can affect biomass production, nutrient cycling rates and nutrient availability to herbivores. We examined how environmental perturbations alter Arctic plant‐community leaf nutrient concentrations (percentage of dry mass, i.e. resource quality) and nutrient pools (absolute mass per unit area, i.e. resource quantity).
We experimentally imposed two different types of environmental perturbations in a high‐Arctic ecosystem in Svalbard, spanning three habitats differing in soil moisture and plant‐community composition. We mimicked both a pulse perturbation (a grubbing event by geese in spring) and a press perturbation (a constant level of summer warming).
After 2 years of perturbations, we quantified peak‐season nitrogen and phosphorus concentrations in 1268 leaf samples from the most abundant vascular plant species. We derived community‐weighted nutrient concentrations and total amount of nutrients (pools) for whole plant communities and individual plant functional types (PFTs).
Spring grubbing increased plant‐community nutrient concentrations in mesic (+13%) and wet (+8%), but not moist, habitats, and reduced nutrient pools in all habitats (moist: −49%; wet, mesic: −31% to −37%). Conversely, summer warming reduced plant‐community nutrient concentrations in mesic and moist (−10% to −12%), but not wet, habitats and increased nutrient pools in moist habitats (+50%).
Fast‐growing PFTs exhibited nutrient‐concentration responses, while slow‐growing PFTs generally did not. Grubbing enhanced nutrient concentrations of forbs and grasses in wet habitats (+20%) and of horsetails and grasses in mesic habitats (+19–23%). Conversely, warming decreased nutrient concentrations of horsetails in wet habitats (−15%) and of grasses, horsetails and forbs in moist habitats (−12% to −15%). Nutrient pools held by each PFT were less affected, although the most abundant PFTs responded to perturbations.
Synthesis . Arctic plant‐community nutrient levels can be rapidly altered by environmental changes, with consequences for short‐term process rates and plant‐herbivore interactions. Community‐level responses in nutrient concentrations and pools were opposing and differed among habitats and PFTs. Our findings have implications for how we understand herbivory‐ and warming‐induced shifts in the fine‐scaled distribution of resource quality and quantity within and across tundra habitats. -
null (Ed.)Abstract Rapid climate warming is altering Arctic and alpine tundra ecosystem structure and function, including shifts in plant phenology. While the advancement of green up and flowering are well-documented, it remains unclear whether all phenophases, particularly those later in the season, will shift in unison or respond divergently to warming. Here, we present the largest synthesis to our knowledge of experimental warming effects on tundra plant phenology from the International Tundra Experiment. We examine the effect of warming on a suite of season-wide plant phenophases. Results challenge the expectation that all phenophases will advance in unison to warming. Instead, we find that experimental warming caused: (1) larger phenological shifts in reproductive versus vegetative phenophases and (2) advanced reproductive phenophases and green up but delayed leaf senescence which translated to a lengthening of the growing season by approximately 3%. Patterns were consistent across sites, plant species and over time. The advancement of reproductive seasons and lengthening of growing seasons may have significant consequences for trophic interactions and ecosystem function across the tundra.more » « less
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Snow is an important driver of ecosystem processes in cold biomes. Snow accumulation determines ground temperature, light conditions, and moisture availability during winter. It also affects the growing season’s start and end, and plant access to moisture and nutrients. Here, we review the current knowledge of the snow cover’s role for vegetation, plant-animal interactions, permafrost conditions, microbial processes, and biogeochemical cycling. We also compare studies of natural snow gradients with snow experimental manipulation studies to assess time scale difference of these approaches. The number of tundra snow studies has increased considerably in recent years, yet we still lack a comprehensive overview of how altered snow conditions will affect these ecosystems. Specifically, we found a mismatch in the timing of snowmelt when comparing studies of natural snow gradients with snow manipulations. We found that snowmelt timing achieved by snow addition and snow removal manipulations (average 7.9 days advance and 5.5 days delay, respectively) were substantially lower than the temporal variation over natural spatial gradients within a given year (mean range 56 days) or among years (mean range 32 days). Differences between snow study approaches need to be accounted for when projecting snow dynamics and their impact on ecosystems in future climates.more » « less
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The tundra phenology database: More than two decades of tundra phenology responses to climate changenull (Ed.)Observations of changes in phenology have provided some of the strongest signals of the effects of climate change on terrestrial ecosystems. The International Tundra Experiment (ITEX), initiated in the early 1990s, established a common protocol to measure plant phenology in tundra study areas across the globe. Today, this valuable collection of phenology measurements depicts the responses of plants at the colder extremes of our planet to experimental and ambient changes in temperature over the past decades. The database contains 150,434 phenology observations of 278 plant species taken at 28 study areas for periods of 1 to 26 years. Here we describe the full dataset to increase the visibility and use of these data in global analyses, and to invite phenology data contributions from underrepresented tundra locations. Portions of this tundra phenology database have been used in three recent syntheses, some datasets are expanded, others are from entirely new study areas, and the entirety of these data are now available at the Polar Data Catalogue (https://doi.org/10.21963/13215).more » « less
