Småskalig variation i arttätheten i hävdade växtsamhället
- en utvärdering av art/areaanalys för naturvården
Small-scale variation in species density in managed plant
communities
- an evaluation of species-area analysis for monitoring
The Swedish Environmental Protection Agency has promoted specis/area-analysis as a method for measuring biodiversity in meadows and pastures. To compare results from different investigations, an index that is based on the ratio between half the number of species found and the area is used. One of the aimes of my study was to find out whether this index is representative for a larger area with similar vegetation and habit factors. Ten species/area-sqares (2 x 2m each) was placed in similar vegetation in three cultivated meadows and pastured in the county of Gävleborg. I have also compared indices from a computer simulation and indices from a more extensive study made in the parish of Leksand. The results all show a large variation in indices within the same pasture.
Another aim was to evaluate species/area-analysis as a measurement of the state of grassland management. As there may be a ten-fold natural variation, both between indicec of two squares in the same area and from one year to another, the index is not a suitable variable for evaluating management status. The cause for this variation - both in time and space - is that the index is largely dependent on the number of species in the first square decimeter.
A further limitation of this method is that statistic tests of the results cannot be used since the data has been gathered in a cumulative way. Two indices related to different years or areas thus cannot be statistically compared, and therefor a qualitative evaluation of the management is not possible.
To determine how commonly the specis/area-analysis is used as a method in the environmental survey, I sent an inquiry to all the County Government Boards of Sweden. This shows that species/area-analysis is a very common method, used in 80% of the countys.