| 1. |
- Graae, Bente Jessen, et al.
(författare)
-
The effect of an early-season short-term heat pulse on plant recruitment in the Arctic
- 2009
-
Ingår i: Polar Biology. - : Springer Berlin/Heidelberg. - 0722-4060 .- 1432-2056. ; 32:8, s. 1117-1126
-
Tidskriftsartikel (refereegranskat)abstract
- Climate change will cause large-scale plant migration. Seedling recruitment constitutes a bottleneck in the migration process but is itself climate-dependent. We tested the effect of warming on early establishment of three Arctic pioneer species, while holding other environmental variables constant. Seeds and bulbils were sown in artificial gaps in dry Arctic tundra and subjected to a 13-day heating of the soil surface by 2-8°C, simulating temperature increases ranging from the general summer warming to heat waves projected to occur more frequently with global warming. All species showed decreased establishment with increasing soil surface temperature. The short-term heat pulse decreased establishment of Polygonum viviparum and Saxifraga cernua, whereas establishment of Cerastium alpinum decreased with temperature due to more permanent natural variation in micro-climate. The treatment effects increased by the quadrat of the temperature increase. Warming and in particular heat waves may result in declining establishment of Arctic plants in dry tundra regions. Electronic supplementary material The online version of this article (doi:10.1007/s00300-009-0608-3) contains supplementary material, which is available to authorized users.
|
|
| 2. |
- Milbau, Ann, et al.
(författare)
-
A hierarchical framework for integrating invasibility experiments incorporating different factors and spatial scales
- 2009
-
Ingår i: Biological Invasions. - : Springer Netherlands. - 1387-3547 .- 1573-1464. ; 11:4, s. 941-950
-
Tidskriftsartikel (refereegranskat)abstract
- Results from experiments studying different factors determining invasibility (e.g. land use, disturbance, biotic interactions) at different spatial scales are mainly used in isolation, probably because a methodology for integration is lacking. Recent studies show that factors affecting invasibility most likely do so in a hierarchical manner, with different factors acting more strongly at different spatial scales. Climate can be considered the dominant factor at the continental scale, while at regional and landscape scale topography, land cover and land use become increasingly important. At smaller spatial scales, soil type, disturbance, biotic interactions, resources, and microclimate may become significant. In the current paper, we propose a hierarchical framework for combining results from different types of studies. In this hierarchical system, factors operating at a smaller scale are subordinate to factors operating at a larger scale, but if conditions at higher levels are satisfied, the small-scale factors may become indispensable for making accurate predictions. Depending on the aim of the study, the accuracy of prediction can be selected by the researcher, which in its turn determines which data are required.We discuss several applications of the framework and indicate some options for future research. Although the complexity of natural systems presents fundamental limits to predictions, we think this framework can provide a useful tool for the identification of areas of risk for biological invasions, for improving our understanding of invasibility, and for identifying gaps in our current knowledge.
|
|
| 3. |
- Milbau, Ann, et al.
(författare)
-
Effects of a warmer climate on seed germination in the Subarctic
- 2009
-
Ingår i: Annals of Botany. - : Oxford University Press. - 0305-7364 .- 1095-8290. ; 104, s. 287-296
-
Tidskriftsartikel (refereegranskat)abstract
- Background and Aims In a future warmer subarctic climate, the soil temperatures experienced by dispersed seeds are likely to increase during summer but may decrease during winter due to expected changes in snow depth, duration and quality. Because little is known about the dormancy-breaking and germination requirements of subarctic species, how warming may influence the timing and level of germination in these species was examined. Methods Under controlled conditions, how colder winter and warmer summer soil temperatures influenced germination was tested in 23 subarctic species. The cold stratification and warm incubation temperatures were derived from real soil temperature measurements in subarctic tundra and the temperatures were gradually changed over time to simulate different months of the year. Key Results Moderate summer warming (+ 2.5 °C) substantially accelerated germination in all but four species but did not affect germination percentages. Optimum germination temperatures (20/10 °C) further decreased germination time and increased germination percentages in three species. Colder winter soil temperatures delayed the germination in ten species and decreased the germination percentage in four species, whereas the opposite was found in Silene acaulis. In most species, the combined effect of a reduced snow cover and summer warming resulted in earlier germination and thus a longer first growing season, which improves the chance of seedling survival. In particular the recruitment of (dwarf ) shrubs (Vaccinium myrtillus, V. vitis-idaea, Betula nana), trees (Alnus incana, Betula pubescens) and grasses (Calamagrostis lapponica, C. purpurea) is likely to benefit from a warmer subarctic climate. Conclusions Seedling establishment is expected to improve in a future warmer subarctic climate, mainly by considerably earlier germination. The magnitudes of the responses are species-specific, which should be taken into account when modelling population growth and migration of subarctic species.
|
|
| 4. |
- Vellend, Mark, et al.
(författare)
-
Homogenization of forest plant communities and weakening of species–environment relationships via agricultural land use
- 2007
-
Ingår i: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 95, s. 565-573
-
Tidskriftsartikel (refereegranskat)abstract
- 1Disturbance may cause community composition across sites to become more or less homogenous, depending on the importance of different processes involved in community assembly. In north-eastern North America and Europe local (alpha) diversity of forest plants is lower in forests growing on former agricultural fields (recent forests) than in older (ancient) forests, but little is known about the influence of land-use history on the degree of compositional differentiation among sites (beta diversity).2Here we analyse data from 1446 sites in ancient and recent forests across 11 different landscapes in north-eastern North America and Europe to demonstrate decreases in beta diversity and in the strength of species–environment relationships in recent vs. ancient forests.3The magnitude of environmental variability among sites did not differ between the two forest types. This suggests the difference in beta diversity between ancient and recent forests was not due to different degrees of environmental heterogeneity, but rather to dispersal filters that constrain the pool of species initially colonizing recent forests.4The observed effects of community homogenization and weakened relationships between species distributions and environmental gradients appear to persist for decades or longer. The legacy of human land-use history in spatial patterns of biodiversity may endure, both within individual sites and across sites, for decades if not centuries.
|
|
