Estimating past floristic diversity in montane regions from macrofossil assemblages

The relationship between the diversity of higher plant macrofossils in surf ace sediments of lakes and the surrounding vegetation is examined in two mo untain regions; Grodalen in central Norway and the south-east Cairngorms in Scotland. Two lake sediment cores from each area were also analysed to exa mine vegetation history and to estimate changes in biodiversity through the Holocene. The diversity of present day vegetation in each region was estimated using both quadrat data and classified satellite images of the study areas. The m ean surface sample macrofossil representation of species recorded in quadra ts collected within 250m of the lakes was c. 17%. This figure drops to only c. 2% when the satellite imagery of the same area is used to provide a max imal species list. The macrofossil data from the Norwegian cores show that deglaciation in thi s region occurred earlier on the mountain summit than in the valley and tha t the maximum tree line elevation was during the interval 9100-4400 C-14 yr sp. In the Cairngorms the maximum tree line elevation was prior to c. 4500 C-14 yr BP. The changes in higher plant diversity recorded at these sites through the H olocene show that c. 4000 C-14 yr sp the reduction in the tree line resulte d in decreased P-diversity at higher altitudes but an increase at the lower altitude as the forest cover opened up. Under conditions of climatic warmi ng it is likely areas that come to lie below the tree line will experience reduced diversity and that a permanent loss of biodiversity would result fr om a severe reduction in the area above the tree line.