26 - Cautious reforestation of a wetland after clearfelling

Summary

ABSTRACT A small forest catchment in Sweden is drained via a peatland. The mature spruce stand (108 years) was clearcut after which a younger stand (60 years) on the peatland was accidentally stormfelled the next year. The clearcutting causes nitrification in the upland. To maintain the nitrogen reduction function of the peatland, planting on mounds was practiced instead of the conventional fishbone drainage pattern. During the fourth and fifth years after the clearcutting the nitrogen flux from the upland to the peatland was 17 kg ha⁻¹.a while only 7 kg left the peatland. While about 85% of the nitrogen entering the peatland was in the form of nitrate, the fraction of nitrate in the runoff was only 40%. The establishment of new forest stands on peatland soils by planting on mounds gives considerable environmental advantages as compared to conventional drainage. Both fluxes of nutrients and suspended matter are decreased. Spontaneous regeneration of the wetland spruce stand results in loss of about ten years of growth and a younger stand on the wetland than on the upland with the risk of the stormfelling being repeated after the upland forest has been harvested.

INTRODUCTION

Most of the Swedish forest land is drained by a system of ditches. Draining has been done for the purpose of increasing forest production. A peak in the draining operations was seen in the 1930s and it has again increased during the last decades (Löfroth, 1991). A maximum of 12 000 km of drains have been dug yearly, equal to the distance from Stockholm to Vladivostok and back again, much through the same terrain.