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.

Citation: Moeslund, J. E., L. Arge, P. K. Bøcher, T. Dalgaard, M. V. Odgaard, B. Nygaard, and J.-C. Svenning. 2013.Topographically controlled soil moisture is the primary driver of local vegetation patterns across a lowland region. Ecosphere 4(7):91. http://dx.doi.org/10.1890/ES13-00134.1Abstract. Topography is recognized as an important factor in controlling plant distribution and diversity patterns, but its scale dependence and the underlying mechanisms by which it operates are not well understood. Here, we used novel high-resolution (2-m scale) topographic data from more than 30500 vegetation plots to assess the importance of topography for local plant diversity and distribution patterns across Denmark, a 43000 km 2 lowland region. The vegetation data came from 901 nature conservation sites (mean size ¼ 0.16 km 2 ) distributed throughout Denmark, each having an average of 34 plots (five-meter radius) per site. We employed a variety of statistical measures and techniques to investigate scale dependence and mechanistic drivers operating within the study region. Ordinary Least Squares (OLS) multiple regression modeling scaled at different spatial resolutions (2 3 2, 10 3 10, 50 3 50, 100 3 100 and 250 3 250 m) was used to identify the horizontal resolution yielding the strongest vegetation-topography relationships. Using data scaled at this resolution, we quantified local (within-site) and regional (among sites) relationships between elevation, mechanistic topographic factors (slope, heat index, potential solar radiation, wind exposure, wetness index) and 10 vegetation measures representing species composition, richness and functional composition (average plant preferences along key environmental niche axes). We also investigated how overall site-level environmental characteristics affect the strength of these local relationships. Topography exerted the strongest effects at the 10 3 10 m horizontal resolution scale. Elevation exerted the strongest influence on vegetation, followed by slope and wetness. Topography generally affected all vegetation measures and exhibited the strongest local relationships with the main species-compositional gradient, the main functional gradient and the plant's average soil moisture preference. The strength of these relationships was strongly influenced by habitat and site-level average moisture conditions, with the strongest relationships found in wet habitats. Our findings show that finescale topography can strongly influence local vegetation patterns across a wide range of habitat types even in low-relief lowland regions. Notably, topography exhibited a consistently strong relationship with the main local floristic and functional compositional gradients. While a plurality of underlying mechanisms may contribute to the relationship between topography and vegetation patterns, topographically controlled soil moisture exerts primary control on the relationship.

International audienc

Salt meadows are thought to be vulnerable to habitat loss under future sea-level rise (SLR) due to inundation and compression of coastal environments (coastal squeezing). The extent of this threat is poorly understood due to the lack of geographically comprehensive impact assessments. Here, we linked vegetation data for Danish salt meadows to novel very fine-resolution digital elevation models. We developed statistical models relating plant species richness and average salt tolerance to elevation at different spatial scales. The best models were used to quantify potential impacts of SLR on Danish salt-meadow vegetation under five potential 21 st -century scenarios. Overall, species richness increased with elevation (average r 2 =0.21), while average salt tolerance decreased (average r 2 =0.45). Fine resolution (≤10-m) topography was required to fully represent vegetation-elevation relationships. At >50-m resolutions only feeble links were found. Under the worst scenarios 67-74% of the Danish saltmeadow area was projected to be lost. Notably, the relatively species-rich upper meadows were predicted to shrink drastically. If realized, these impacts may have severe consequences for salt-meadow biodiversity. We note that sedimentation, not accounted for here, may allow some salt meadows to partly keep up with SLR but the extent to which this will occur and where is uncertain.

Vegetation and chemical plant and soil data from 18 terrestrial non-forested natural habitat types have been collected each year since 2004 (Table 1). Presently, cover data of plant species measured by pinpoint (16 grid points in 0.5 m x 0.5 m frame) and plant frequency data (5 m circles) exist for more than 50,000 plots; the measuring of chemical properties in plant, soil, and water samples has been less intense. Presently there are more than 12,000 registrations of carbon content and 57,000 measurements of pH in topsoil. Soils are always samples from the top 5 cm. On heathland habitats the thickness of the mor layer is measured. All data are georeferenced and can be accessed at http://www.naturdata.dk/ The data comprises approximately 1,200 sites both within and outside of Natura 2000 areas. At each site the measurements were made at 20-60 randomly positioned plots. 70% of the plots have been revisited each year, whereas 30 % have only been visited once. Each year a total number of additional 5,000 sample plots and registrations will be performed. The protocols for the different measurement types (in Danish) may be downloaded from http://www.dmu.dk/fileadmin/Attachments/TAN1_106_01_FDCNY1.pdf. This report describes the available content in the vegetation-plot database NATURDATA.DK (GIVD ID EU-DK-001).Keywords: moss; nitrogen; pin point; plant cover; plant frequency; soil analysis. GIVD Database ID: EU-DK-001Last