Detecting changes in the state of reindeer pastures in northernmost Finland, 1995–2005.

Abstract

ABSTRACTThe state of pastures in the Finnish reindeer management area has been monitored since 1995 using remote sensing and field inventory. The first inventory was made in 1995–1996, updated in the beginning of 2000s and repeated in 2005–2008. By comparing results from 1995–1996 and 2005–2008 we can observe clear changes in forest cover, structure and ground lichen abundance. To evaluate pasture/vegetation changes on the basis of separate classifications we have used a grid approach. By implementing a 500 by 500 m grid network and summarizing pasture classes for every grid cell we can visualize and quantify intensity of change. By comparing 1995–1996 and 2005–2008 we can see a clear decrease in the number of cells classified old growth dominated forest, and also an increase of fragmentation can be detected. With a 7.5 ha threshold the amount of old growth forest was reduced by 5%, for 20 ha the decrease was 21%. This indicates a significant change in forest landscape structure, fragmentation and reduction of reindeer winter pasture value in large areas. Pixel wise comparison showed no substantial changes in pasture areas. There is a degree of uncertainty in change detection; changes in remote sensing instrument, changes in processing software and methodology, changes in field methods and ancillary data, and obviously also bias introduced by differences between analysts. When comparing reindeer lichen biomass between 1995–1996 and 2005–2008 on the basis of field site data, the measured lichen biomass has declined in 19 out of the 20 reindeer management districts. Only one district showed slight improvement, in three districts there was a notable drop in lichen biomass, from over 1500 kg/ha to about 500 kg/ha. Also amount of arboreal lichens declined due to felling of old growth forest, confirming the findings on the grid cell level. Consequently grass, shrub and sapling stands increased as felled areas start to grow graminoids and herbs.