The Role of Seeds in a Changing Climate - Linking Germination Ecophysiology to Population and Community Ecology

Recruitment from seed (germination and seedlings survival) is a key process in plant life story with consequences for species' distribution, evolution, and survival. Both the ecological role and the climate response of seed recruitment is best understood by putting this life-history stage in a wider context, and we study climate effects on the entire plant life cycle and on multiple levels; from seed ecophysiology via plant growth and resource allocation to population and community dynamics and diversity. SeedClim exploits the natural climatic gradients in Western Norway, from coastal to inland and from fjord to mountains, to explore how climate and climate change on plants and vegetation. Our 12 experimental sites fall into a climatic "network" which combine four levels of annual precipitation (600, 1200, 2000 and 2700 mm per year) with three levels of summer temperatures (average 7.5, 9.5, and 11.5 ° C in the four warmest months) while all other factors are kept as constant as possible. Climate stations monitor temperature, precipitation and soil moisture at each location. Between these places we transplanted intact vegetation mats (25 x 25 cm) and seeds of four focus species (two alpine specialists and two lowland generalists) towards warmer, wetter and warmer and wetter climates, paralleling the regional weather forecast for the future. This experimental setup allows us to investigate how seed germination and seedling recruitment in particular, as well as population and community dynamics in general, will be affected by climate change. We find, as expected, that the plants from warm climates generally flower more than those that of cold climates, but they actually allocate less of their total resources to flowers and roots and more leaves and stems. Precipitation has a more variable effect on flowering, and for some species flowering decreases towards the wettest regions. This may indicate that the highest amount of precipitation on the coast does not constitute a resource, but rather a problem for plants. Competition from grass and mosses, pests, and nutrients leaching may be explanations for this. When these results are extrapolated using regional climate models, we find that a temperature increase of 2°C will result in more flowering in western Norwegian landscapes, while a precipitation increase of 10% would have relatively limited effect. Meanwhile seedling recruitment is also limited by competition, especially under warm climates and in undisturbed vegetation,, which can delay the lowland species colonization of the mountains, especially in warmer climates and in areas with low grazing animals. These findings are reflected in the climate impacts on the entire plant life cycle. Alpine plants generally respond negatively to warming, while lowland species respond positively. The effect of increased rainfall remains variable, and the most interesting finding is that increased rainfall does not seem to be able to compensate for the negative temperature effect mountain plants experiencing. We also find clear patterns in vegetation composition along climatic gradients, and vegetation changes systematically in response to the experimental temperature and precipitation changes. An interesting finding is that the response to climate change is much faster in the dry than in humid regions. This is interesting because it confirms the experimental findings from a number of observational studies. Because we work experimentally, we have the opportunity to examine the ecological processes behind this pattern. We find that all alpine systems, regardless of where they are along precipitation gradient, are readily invaded by species from the lowlands. Invasions are slightly slower in oceanic regions, however. Meanwhile mountain plants are driven much faster to extinction by warming in dry than in oceanic areas. In dry areas exposed to increases in both temperature and precipitation changes this happens faster. It is here the impact of climate change is perceived to be the fastest. Graminoids (grasses and grasslike species) increase rapidly under these conditions, and competition from grasses may be an explanation for why alpine species disappears so quickly from dry regions under warming. Seedling recruitment is generally relatively high in the mountains, even in undisturbed vegetation. This means that all mountain areas will be readily invaded by lowland species, but that the invasion rate and the impact of invasions in driving alpine plants to extinction will be fastest in dry areas. We also find that even in this experimental context, where very small ecosystems (25 x 25 cm!) experience abrupt climate change of ca. 2 ° C warming and / or around 700 mm increase in precipitation, it takes several years, perhaps decades, for vegetation responses to catch up. This means that there will be significant delays in the alpine ecosystem responses to climate change.

In order to understand, and predict, the effects of climate change on the temporal and spatial scales relevant to the needs of society, we need approaches that enable us to scale up from detailed mechanistic studies of the effects on local ecological proc esses to landscape-scale or even regional-scale consequences. This project develops new methods that integrate observational and experimental approaches across broad-scale climate gradients to explore how climate, and climate change, affects the role o f seed recruitment across four levels of organization - from direct physiological effects via demographic responses to population and community dynamics. We focus on the seed regeneration stage because this is a key event in the life-histories of plants that affects their ability to disperse, to evolve, and to persist under unfavorable conditions. We therefore hypothesize that any impact of climate change on this life-history stage is likely to have strong effects on the fates of local populations and c ommunities. The ambitious goals will be achieved by a joining the forces of two strong ecological research groups in Norway with broad expertise in the ecological effects of climate change on terrestrial ecosystems (EECRG and NINA) in an interdisciplina ry collaboration with experts on down-scaling climate data in complex landscapes (met.no). International partners will contribute expertise on the effects of environmental change on different levels of ecological organization, from ecophysiology (Royal Bo tanical Gardens, UK) via populations (Charles University, CZ) to communities and ecosystems (University of Michigan, USA). This project will provide a new methodological framework for integrating population, community, and landscape ecology in environme ntal change research. The results will have implications for habitat management and nature conservation strategies under a changing climate.