Miljøprojekt, 1120 – Sandsynlige konsekvenser af klimaændringer på artsudbredelser og biodiversitet i Danmark

Sandsynlige konsekvenser af klimaændringer på artsudbredelser og biodiversitet i Danmark

Summary and conclusions

The present report analyses the potential consequences of the climatic changes predicted to have occurred by year 2100 according to the A2 and B2 climate scenarios produced by the UN Intergovernmental Panel on Climate Change (IPCC) for 104 selected vascular plant species in Denmark. The chosen species include 88 so-called characteristic species under the EU Habitats Directive. These species represent a broad span of Danish vegetation types, from dunes and dry grasslands to meadows, bogs, and forests. In addition, the potential consequences are analysed for the two Danish plant species on the Habitats Directive’s annex 2, and for a suite of species from Central and Southern Europe, in order to evaluate to which degree the climatic changes might allow southern species to invade.

Using a bioclimatic habitat model we compute the potential distribution of each species under current conditions and under the B2 and A2 scenarios. Combining the results, we compute whether the changes in Denmark will be negative, neutral or positive.

The results in the present report suggest that 21^st century climate change, as represented by the B2 and A2 scenarios, must be expected to have a predominantly negative effect on the study species and probably also on the floristic diversity in Denmark in general. The results show that 67% of the species are expected to be negatively affected and 12% positively affected under the B2 scenario. For 21% of the species the impact will be neutral. Under the A2 scenario the corresponding figures are 78%, 10%, and 12%.

The expected impact varies considerably within Denmark. Generally, the south-eastern part of the country is more negatively affected than the western part, where negative and positive impacts largely balance out.

The impact also differ, albeit not significantly, between species characterising different habitat types. The figures suggest that species belonging to humid meadows and mesophile grasslands and, in particular, raised bogs, mires and fens will be most vulnerable to global warming.

The results indicate that 4% and 7% of the 84 native characteristic species will completely loose suitable climatic conditions under the B2 and A2 scenario, respectively. It is suggested that these species eventually would go extinct in Denmark. A total of 6% and 15% of the native characteristic species can be expected to experience climatic conditions under the B2 and A2 scenario, respectively, which are 80% less suitable than those they occur under in Denmark today. The occurrence of these species in Denmark would then be expected to come under pressure.

Dispersal is expected to become a particularly important constraint on the positive range response of plant species to future climatic changes. Most species will not have sufficient dispersal capacity to track climatic changes of the speed and strength described in the 21^st century climate scenarios. The extensive anthropogenic fragmentation of the natural habitats in Denmark and most of Europe exacerbates this problem.

It is concluded that it, with some care, is possible to use vascular plants as indicators of the climate change sensitivity of biodiversity in general. It is recommended to develop a progressive climate adaptation strategy based on the monitoring of habitat types and species. Such a monitoring could at least partly be based on the new NOVANA program, which monitors a large number of habitat types and species. By careful monitoring the expansions and declines of the long-term native as well as newly arrived species it becomes possible to use this monitoring as a basis for developing plans of actions.