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.
Questions:The coastal heathlands of northwest Europe are classified as highly endangered and a habitat of high conservation importance throughout their geographic range. Previous research into heathland vegetation dynamics has typically been carried out within single sites or regions, and hence little is known about the variability of land-use effects and successional dynamics along biogeographic gradients. We test the hypothesis that the bioclimatic gradient is a key factor shaping post-fire regeneration dynamics in Calluna heathlands, with progressively slower regrowth and lower post-fire pioneer species richness towards colder climates.Location: Wet and dry Calluna heath vegetation in five sites spanning a 340-km latitudinal gradient along the west coast of Norway (60.70°-63.79°N).Methods: A repeated measures design was used, with floristic data recorded from permanent plots in a number of experimental post-fire successions over a 3-yr period (n = 344). The data were analysed using multivariate ordination techniques: detrended correspondence analysis, partial redundancy analysis and principal response curves, and mixed effects models.Results: Regeneration rates decrease from south to north and the wet heath stands regenerate faster towards the pre-fire community composition than the dry stands. Calluna decreases immediately after fire in all sites, but increases from the second year onwards, with the southernmost site having the fastest return. Regeneration of grasses, herbs, mosses and lichens is also faster in the south. Across all sites, species richness decreased the first year after fire, followed by an increase that exceeds pre-fire levels by the second year. The number of pioneer species entering the heathlands after fire decreases northwards. Conclusions:We found considerable geographic variation, not only in species composition, but also in post-fire successional trends and dynamics. This is probably linked to higher productivity and larger pools of pioneer species in southern sites, and higher growth rates of shrubs and mosses in the wet heath habitat. This calls for conservation of a geographically diverse set of heathland sites, as well as development of regional-and site-specific management plans.
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