Monitoring peatland vegetation by means of digitized aerial photographs.

Drainage-driven changes in peatland ecosystems in Finland were studied, using aerial photographs taken in 1995 and 1946. The species composition of the vegetation cover was examined in one drained and one undrained mire in 1995. The data were correlated with tone and texture values of digitized colour infrared aerial photographs taken the same year, using canonical correspondence analysis. The results obtained were used to reconstruct the vegetation cover of the aerial photograph from 1946. The analysis clearly differentiated drained and undrained mire site types from each other, forming the moisture gradient in the first axis. The undrained mire site types were distributed along the nutrient gradient, but the correlation between site types and different tone values was relatively weak. The main difference between 1946 and 1995 was that the open and sparsely forested peatland vegetation types diminished and two drained mire site types (drained, pine-dominated Vaccinium type and drained, pine-dominated dwarf shrub type) became dominant. Digitized aerial photographs were unable to identify the vegetation at the mire site-type level, especially in natural habitats. [ABSTRACT FROM AUTHOR]