| 1. |
- Burli, S., et al.
(författare)
-
A common soil temperature threshold for the upper limit of alpine grasslands in European mountains
- 2021
-
Ingår i: Alpine Botany. - : Springer Science and Business Media LLC. - 1664-2201 .- 1664-221X. ; 131, s. 41-52
-
Tidskriftsartikel (refereegranskat)abstract
- While climatic research about treeline has a long history, the climatic conditions corresponding to the upper limit of closed alpine grasslands remain poorly understood. Here, we propose a climatic definition for this limit, the 'grassline', in analogy to the treeline, which is based on the growing season length and the soil temperature. Eighty-seven mountain summits across ten European mountain ranges, covering three biomes (boreal, temperate, Mediterranean), were inventoried as part of the GLORIA project. Vascular plant cover was estimated visually in 326 plots of 1 x 1 m. Soil temperatures were measured in situ for 2-7 years, from which the length of the growing season and mean temperature were derived. The climatic conditions corresponding to 40% plant cover were defined as the thresholds for alpine grassland. Closed vegetation was present in locations with a mean growing season soil temperature warmer than 4.9 degrees C, or a minimal growing season length of 85 days, with the growing season defined as encompassing days with daily mean >= 1 degrees C. Hence, the upper limit of closed grasslands was associated with a mean soil temperature close to that previously observed at the treeline, and in accordance with physiological thresholds to growth in vascular plants. In contrast to trees, whose canopy temperature is coupled with air temperature, small-stature alpine plants benefit from the soil warmed by solar radiation and consequently, they can grow at higher elevations. Since substrate stability is necessary for grasslands to occur at their climatic limit, the grassline rarely appears as a distinct linear feature.
|
|
| 2. |
- Pauli, H., et al.
(författare)
-
Recent Plant Diversity Changes on Europe's Mountain Summits
- 2012
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 336:6079, s. 353-355
-
Tidskriftsartikel (refereegranskat)abstract
- In mountainous regions, climate warming is expected to shift species' ranges to higher altitudes. Evidence for such shifts is still mostly from revisitations of historical sites. We present recent (2001 to 2008) changes in vascular plant species richness observed in a standardized monitoring network across Europe's major mountain ranges. Species have moved upslope on average. However, these shifts had opposite effects on the summit floras' species richness in boreal-temperate mountain regions (+3.9 species on average) and Mediterranean mountain regions (-1.4 species), probably because recent climatic trends have decreased the availability of water in the European south. Because Mediterranean mountains are particularly rich in endemic species, a continuation of these trends might shrink the European mountain flora, despite an average increase in summit species richness across the region.
|
|
| 3. |
- Dullinger, S., et al.
(författare)
-
Weak and variable relationships between environmental severity and small-scale co-occurrence in alpine plant communities
- 2007
-
Ingår i: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 95:6, s. 1284-1295
-
Tidskriftsartikel (refereegranskat)abstract
- 1. The stress gradient hypothesis suggests a shift from predominant competition to facilitation along gradients of increasing environmental severity. This shift is proposed to cause parallel changes from prevailing spatial segregation to aggregation among the species within a community. 2. We used 904 1-m(2) plots, each subdivided into 100 10 x 10 cm, or 25 20 x 20 cm cells, respectively, from 67 European mountain summits grouped into 18 regional altitudinal transects, to test this hypothesized correlation between fine-scale spatial patterns and environmental severity. 3. The data were analysed by first calculating standardized differences between observed and simulated random co-occurrence patterns for each plot. These standardized effect sizes were correlated to indicators of environmental severity by means of linear mixed models. In a factorial design, separate analyses were made for four different indicators of environmental severity (the mean temperature of the coldest month, the temperature sum of the growing season, the altitude above tree line, and the percentage cover of vascular plants in the whole plot), four different species groups (all species, graminoids, herbs, and all growth forms considered as pseudospecies) and at the 10 x 10 cm and 20 x 20 cm grain sizes. 4. The hypothesized trends were generally weak and could only be detected by using the mean temperature of the coldest month or the percentage cover of vascular plants as the indicator of environmental severity. The spatial arrangement of the full species set proved more responsive to changes in severity than that of herbs or graminoids. The expected trends were more pronounced at a grain size of 10 x 10 cm than at 20 x 20 cm. 5. Synthesis. In European alpine plant communities the relationships between small-scale co-occurrence patterns of vascular plants and environmental severity are weak and variable. This variation indicates that shifts in net interactions with environmental severity may differ among indicators of severity, growth forms and scales. Recognition of such variation may help to resolve some of the current debate surrounding the stress gradient hypothesis.
|
|
