![]() Microsite cover effects can be highly complex, with neighbouring vegetation positively or negatively affecting tree seedlings depending on vegetation type, species, demographic state, and prevailing weather conditions 29, 38. Early establishment is particularly limited by temperature and water availability 31, 32, 33, but other abiotic factors, such as snow cover duration and desiccating winds, may also affect seedling recruitment 34, 35, 36.īiotic interactions can be equally or even more important than abiotic factors in determining seed bed conditions 37. Abiotic factors are considered key drivers of seedling recruitment in climatically harsh environments 23. Seed bed quality is determined by a complex interplay of abiotic and biotic factors such as microclimatic conditions, the presence of neighbouring vegetation, and herbivory 30. Successful recruitment also depends on the availability of suitable microsites that provide the necessary conditions for emergence and establishment of seedlings 28, 29. Biotic interactions, such as pre-dispersal predation, may further constrain seed productivity at treeline 27, impacting future treeline range expansion. synchronous production of large seed crops 24, 25, 26. In treeline ecotones, viable seed availability commonly declines with elevation 13, 23 due to lower abundance of seed bearing trees and less frequent mast years, i.e. Hence, treeline responses to global warming vary among locations and are often asynchronous with the rate of climate change 17, 18, 19, 20, 21.Ĭlimate change-induced range expansion of treeline populations also depends on successful recruitment, which requires dispersal of viable seeds followed by successful establishment of individual propagules 22. ![]() However, global treeline dynamics are often modulated by regional-scale drivers such as historical land use changes 16 and biotic interactions 17. the range limit of forest ecosystems, is widely considered temperature sensitive and is thus expected to respond to climate warming 12, 13, 14, 15. There is increasing evidence for climate-induced latitudinal range shifts via increased shrub abundance in circumarctic tundra ecosystems 4, 5, 6 and elevational shifts of shrubs and trees in mountainous regions 7, 8, 9, 10, 11. Plant species are responding to recent global temperature increases 1 by shifting their ranges as populations track their fundamental niche 2, 3. ![]() This study demonstrates the importance of understanding multiple abiotic and biotic drivers of early seedling recruitment that should be incorporated into predictions of treeline dynamics under climate change. Post-dispersal predation, species, and provenance also affected emergence and early establishment. However, dense vegetation cover at lower elevations and winter mortality at higher elevations particularly limited early recruitment. ![]() Tree seedling emergence occurred at and several hundred metres above the current treeline when viable seeds and suitable microsites for germination were available. Seedling emergence and early establishment in treatment and in control plots were monitored over two years. In two consecutive years, we sowed seeds of low- and high-elevation provenances of Larix decidua (European larch) and Picea abies (Norway spruce) below, at, and above the current treeline into intact vegetation and into open microsites with artificially removed surface vegetation, as well as into plots protected from seed predators and herbivores. In this study, we evaluated the effects of several abiotic and biotic drivers of early tree seedling recruitment across an alpine treeline ecotone. Treeline responses to climate change ultimately depend on successful seedling recruitment, which requires dispersal of viable seeds and establishment of individual propagules in novel environments. ![]()
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