Impact of environmental variables on tundra vegetation onset of flowering explained by survival modelling

Abstract: Timing of phenological events are highly related to climate and is one of the first signs of ecosystem responses to the climate change. Timing of flowering phenology is an important trait influencing the distribution and fitness of plants species. Tundra ecosystems are particularly important to study these effects due to short growing seasons, poor pollinator community and a particularly pronounced expected climate change. In this study proportional hazard models are used to explain the impact of environmental variables and experimental warming tundra plant species’ onset of flowering. The results show that global radiation and precipitation are negatively linked to onset of flowering, whereas thawing degree days only showed some weak relationship to flowering. The negative impact of both radiation and precipitation are addressed to cooling the soil surface temperature and indicate further that local air temperature is not sufficient for explaining changes in onset of flowering. In concordance with earlier research higher TDD sum previous year show a negative effect on the timing following year. The effect was particularly large on the early flowering species. Responses to experimental warming were stronger among late flowering dwarf shrubs, although the effect on early flowering species may have been out competed by snow melt dates. The study further suggests that survival modelling can be successfully used in phenology research providing accurate predictions of onset of flowering. Further studies of how the model application perform beyond the study area still needs to be tested.