Scaling up from plant traits to vegetation change in cold biomes: common patterns in the European Subarctic and the Caucasus Mountains?

To understand, predict and partly mitigate the impacts of global climate warming on terrestrial ecosystems is a great challenge to the international scientific community this century. The cold biomes of the Earth face big changes, because warming is predicted to be particularly strong there (IPCC 2001) and because carbon and nutrient cycling are limited by low temperatures and therefore responsive to warming. A crucial factor in climate driven ecosystem change is the replacement of plant species by species more adapted to new climate and soil conditions in a given location. Not the species identity will bring about ecosystem change, but rather their functional traits. For instance, interspecific variation in leaf traits control important feedbacks between vegetation productivity on one side of the ecosystem carbon and nutrient budget, and (via leaf afterlife effects), litter decomposition, nutrient mineralization and mycorrhizal association on the other side (Cornelissen et al. 2001, Oecologia 129). However, plant trait research in the biogeochemical cycling context has so far been biased towards temperate zones (Europe, N America, Australia), while it is in its infancy in cold biomes. Moreover, it has so far only addressed vascular plants (Wright et al. 2004, Nature 428), thus neglecting cryptogams. Yet, in cold biomes cryptogams are paramount determinants of ecosystem functioning because (1) they produce huge biomass; (2) they host nitrogen-fixing bacteria, providing major soil N input (lichens, bryophytes); (3) they control soil hydrology and temperatures, and soil chemistry and nutrition through accumulation of polyphenols (bryophytes); (4) they (lichens) provide a staple food to mammals such as reindeer, with important feedbacks to soils and biota; (5) they both facilitate and compete with vascular plants. We shall compare functional trait spectra in relation to climate-vegetation pattern between two distant regions, which however share many similarities in climate, soil, plant taxa and functional types. If there are common patterns in terms of climate-driven plant trait shifts, we should have a powerful tool to upscale ecosystem climate response to cold biomes elsewhere. The two sites representing these regions, both with a long tradition and international reputation of climate-soil-vegetation research, are (1) Teberda, NW Caucasus, Russia (Moscow University group); and (2) Abisko, N Sweden (www.ans.kiruna.se/ans.htm) (VU Amsterdam group: VUA). Both research groups have already started functional trait research, which will help our joint project to make a flying start. We plan two major field campaigns in N Sweden and the Caucasus (summers of 2006, 2007), when teams of Russian and Dutch scientists will together sample and measure vascular plants and cryptogams for key traits along natural climatic gradients. New trait assays are being tailor-made for cryptogams for this undertaking (2004/2005). Some of the analyses will be done both in the Moscow and the VUA labs according to standard protocols (e.g. specific leaf area as an indicator of potential growth rate and climate responsiveness, belowground traits). Other particular analyses (e.g. some cryptogam traits, stable isotope and certain chemical analyses), which depend on equipment only available at the VUA, will be done there by both Russian and Dutch partners. Analysing trait spectra at different points on the gradient will be accompanied by analyses of soil properties and vegetation composition. The final year (late 2007, 2008) will be for additional sampling and analyses, database completion, data processing and the preparation of scientific papers. The Russian young scientists will attend existing graduate courses in Soil-Plant Interactions (VUA), Writing Scientific English (VUA) and a cryptogam taxonomy and ecology course. Russian-Dutch exchange will further be optimized through a small organisatory meeting (Moscow, Oct. 2005), a larger project kick-off meeting (VUA, Jan. 2006), and a progress meeting reporting results and discussing output, with subsequent fieldwork in the Caucasus (summer 2007).