Sylvi M. Sandvik

Local temperatures inferred from plant communities suggest strong spatial buffering of climate warming across Northern Europe

Recent studies from mountainous areas of small spatial extent (<2500 km(2) ) suggest that fine-grained thermal variability over tens or hundreds of metres exceeds much of the climate warming expected for the coming decades. Such variability in temperature provides buffering to mitigate climate-change impacts. Is this local spatial buffering restricted to topographically complex terrains? To answer this, we here study fine-grained thermal variability across a 2500-km wide latitudinal gradient in Northern Europe encompassing a large array of topographic complexities. We first combined plant community data, Ellenberg temperature indicator values, locally measured temperatures (LmT) and globally interpolated temperatures (GiT) in a modelling framework to infer biologically relevant temperature conditions from plant assemblages within <1000-m(2) units (community-inferred temperatures: CiT). We then assessed: (1) CiT range (thermal variability) within 1-km(2) units; (2) the relationship between CiT range and topographically and geographically derived predictors at 1-km resolution; and (3) whether spatial turnover in CiT is greater than spatial turnover in GiT within 100-km(2) units. Ellenberg temperature indicator values in combination with plant assemblages explained 46-72% of variation in LmT and 92-96% of variation in GiT during the growing season (June, July, August). Growing-season CiT range within 1-km(2) units peaked at 60-65°N and increased with terrain roughness, averaging 1.97 °C (SD = 0.84 °C) and 2.68 °C (SD = 1.26 °C) within the flattest and roughest units respectively. Complex interactions between topography-related variables and latitude explained 35% of variation in growing-season CiT range when accounting for sampling effort and residual spatial autocorrelation. Spatial turnover in growing-season CiT within 100-km(2) units was, on average, 1.8 times greater (0.32 °C km(-1) ) than spatial turnover in growing-season GiT (0.18 °C km(-1) ). We conclude that thermal variability within 1-km(2) units strongly increases local spatial buffering of future climate warming across Northern Europe, even in the flattest terrains.

Short-term effects of simulated environmental changes on phenology, reproduction, and growth in the late-flowering snowbed herb Saxifraga stellaris L.

Abstract Manipulations of temperature, soil nutrient, and light conditions were conducted over two years in alpine southwest Norway to simulate impacts of climate change in the late-flowering, perennial snowbed herb Saxifraga stellaris L. The temperatures were increased with Open Top Chambers by 1.6∞C (air) and 2.6∞C (soil) during daytime and light availability reduced for about seven hours per day by shading sheets. Reproduction and seasonal changes in plant size showed differential sensitivity to temperature and soil nutrient. In general, reproduction was more restricted by temperature than by soil nutrients, whereas plant size responded to nutrient addition and not to increased temperature. The experimentally warmed plants had shorter prefloration time and were capable of accelerating their seed maturation as compared to the control plants. This suggests that seed set may be more regular in a warmer climate. By contrast, shading exerted strong negative effects on both seed number and growth in the second year, but there was no significant impact of shading on pre- and postfloration time, fruit number per plant, or seed weight in the second year. Except for an interactive effect of soil nutrient addition and shading on seed weight, no other interactions between treatments were significant. Accelerated phenology and increased reproductive output of Saxifraga stellaris under warming may be particularly important for the species’ ability to accommodate to new available terrain at higher altitudes, where it may be displaced to in a future warmer climate.

Responses of alpine snowbed vegetation to long-term experimental warming

Abstract: In order to assess the influence of experimental warming on individual species response, species composition and richness, and the abundance of ramets in a wet late-melting snowbed, we established 20 open-top chambers (OTCs) permanently for 5 y (six growing seasons) at Finse, southwest Norway. Salix herbacea, Saxifraga stellaris, Omalotheca supina, Cerastium cerastoides, and Epilobium anagallidifolium increased in the experimentally warmed plots, while there was no significant response in Carex lachenalii, Deschampsia alpina, Poa alpina, Juncus biglumis, Saxifraga rivularis, or Veronica alpina. Species composition changed significantly with time both in the OTCs and in the control plots. Although invasion rates slightly increased in the OTCs compared to the controls, differences in overall species composition or richness were not significant between the OTCs and the control plots during the 5-y study. Our results suggest that vegetation change is going on naturally and that the effect of this change overrides the effect of the temperature treatment. We conclude that increased plant growth will result in denser vegetation in a warmer future. Whether the higher net invasion will result in more diverse vegetation is yet unclear, as the processes take more time than allowed for in this study.

Quantitative importance of staminodes for female reproductive success in Parnassia palustris under contrasting environmental conditions

The five sterile stamens, or staminodes, in Parnassia palustris act both as false and as true nectaries. They attract pollinators with their conspicuous, but non-rewarding tips, and also produce nectar at the base. We removed staminodes experimentally and compared pollinator visitation rate and duration and seed set in flowers with and with- out staminodes in two different populations. We also examined the relative importance of the staminode size to other plant traits. Finally, we bagged, emasculated, and supplementary cross-pollinated flowers to determine the pollination strategy and whether reproduction was limited by pollen availability. Flowers in both populations were highly depend- ent on pollinator visitation for maximum seed set. In one population pollinators primarily cross-pollinated flowers, whereas in the other the pollinators facilitated self-pollination. The staminodes caused increased pollinator visitation rate and duration to flowers in both populations. The staminodes increased female reproductive success, but only when pollen availability constrained female reproduction. Simple linear regression indicated a strong selection on staminode size, multiple regression suggested that selection on staminode size was mainly caused by correlation with other traits that affected female fitness.

Effects of simulated environmental changes on growth and growth form in a late snowbed population of pohlia wahlenbergii (Web. et Mohr) Andr

Abstract In a factorial field experiment we increased the temperature (Open Top Chambers) and nutrients (nitrogen, phosphorus, and potassium [NPK]) to simulate predicted future climate changes and studied the growth response of the acrocarpous bryophyte Pohlia wahlenbergii (Bryaceae) in a wet snowbed environment. The species shows a positive growth-length response to added nutrients and increased temperature. The stronger response to nutrients indicates a strong limitation of nutrients in the snowbed environment. There was an immediate response to nutrient treatment, whereas the temperature response was delayed. The growth response shows a clear interaction between temperature and nutrients. The immediate positive growth response is interpreted as a function of the wet habitat, since water makes the added nutrients immediately available to the plants. The growth form changed toward a more lax (loose) and desiccation-intolerant form with added nutrients. In a climate change scenario based on these results we hypothesize that bryophyte response will depend on the water availability from precipitation and from meltwater. In a drier environment we predict that bryophytes will become more constrained toward areas with a high continuity of meltwater, whereas increased precipitation may compensate for any changes in growth form, which would be positive for bryophytes.

Influence of Two N-Fixing Legumes on Plant Community Properties and Soil Nutrient Levels in an Alpine Ecosystem

Abstract Low nitrogen (N) supply is a limiting factor for plant growth in most terrestrial ecosystems. N-fixing legumes therefore have the potential to facilitate surrounding vegetation by increasing soil N levels. This effect should be especially pronounced in low-productivity habitats where ambient soil N levels are low, such as in alpine areas. We examined whether plant species composition, community diversity measures, and soil N levels differed with and without the presence of two alpine legumes, Oxytropis lapponica (Wahlenb.) Gay and Astragalus alpinus L., in a Dryas octopetala heath at Finse, Norway. Species composition and richness differed between plots with and without Oxytropis in one of two study sites, as other plant species were positively associated with the legume. None of the measured community properties differed between plots with and without the presence of Astragalus. The contrasting influence of the two legume species corresponds to our findings of higher soil N levels below Oxytropis, but not Astragalus. Differences in microhabitat N levels may explain why only Oxytropis acts as a facilitator. By affecting local species composition Oxytropis increases spatial heterogeneity, which may increase total species richness of the ecosystem.

Breeding System and Effects of Plant Size and Flowering Time on Reproductive Success in the Alpine Herb Saxifraga stellaris L.

The pollination and reproductive ecology of Saxifraga stellaris was investigated in alpine southwest Norway. A breeding system analysis, with performance of controlled crosses, revealed that S. stellaris is self-compatible and that reproductive success after crossand self-pollination is equal. Relative autodeposition efficiency (i.e. mean seed:ovule ratio in caged, nonmanipulated plants relative to mean seed:ovule ratio of control plants) was, however, low (0.29), suggesting that S. stellaris depends on insect visitation for maximum seed set. Seed set is not restricted by pollen availability, as indicated by a supplemental hand-pollination experiment. Plant size had a strong positive impact on ovule number, which in turn was positively correlated with seed number. Plant size also had a positive influence on seed weight. Seed weight was lowest for late-flowering plants, suggesting that shorter time for seed maturation and lower temperatures late in the season restrict seed weight. No correlations between flowering date and seed number were found, perhaps because the pollinators are relatively insensitive to temperature conditions and thus their activity does not change through the flowering season of S. stellaris.

Relationships between vegetation, air and soil temperatures on Norwegian mountain summits

ABSTRACT Geographic variations in air and soil temperatures are dependent on several biotic and abiotic factors. Air temperature has mostly been used to characterize thermal conditions for plant life, and studies of bioclimatic gradients. From a biological point of view, it is also essential to know to what extent soil temperature is coupled with air temperature. In this study, we have quantified the deviations between soil and air temperatures along gradients in latitude, altitude, and possible effects of the vegetation. Sixteen different temperature variables were estimated from 49 vegetation plots on 19 mountain summits along the high mountain range in Norway, ranging from 230 to 1780 m a.s.l., and from 59°N to 71°N. Soil and air temperature variables were estimated from the study plots during one year. All air and soil temperature variables were significantly correlated, but the rate of explanation was mostly relatively low (37.0–60.0%), except during the growing season. Start of the growing season, determined by air or soil temperatures, could deviate by 38 days mainly due to effects of frozen soils. Vegetation composition, especially the lichen cover, had a major impact on soil temperature, Dwarf shrub cover increased significantly with increasing July temperature. Lichen abundance and degree of soil frost were strongly correlated, and explained a major part of the variation in soil temperatures. The study indicates that air temperature is generally a poor proxy for soil temperature in cold areas, except during July.

Estimation of lichen biomass with emphasis on reindeer winter pastures at Hardangervidda, S Norway

Quantification of lichen abundance is important for management of reindeer populations. We measured dry lichen biomass in 876 micro plots (16.5 cm × 16.5 cm) systematically sampled within 219 vegetation plots (2 m × 2 m) from 7 different areas in S Norway. Lichen biomass was quantified as: (a) dry weight in g m-2, (b) lichen height in cm, (c) lichen cover, and (d) lichen volume (lichen height × lichen cover). Lichen biomass decreased with increasing precipitation and increasing altitude. On local scale, the variation in lichen biomass varied strongly with snow conditions. The grazed parts of Hardangervidda had in general a low average lichen biomass (an average mostly lower than 150 g m-2). Lichen biomass was much higher in area where reindeer migration was interfered by human activity. Lichen height and lichen volume were strongly linearly correlated with dry lichen biomass. These proxy methods may therefore be used to predict lichen biomass, but deviations from exact measurements should be expected.