Metla Project 3310

Effect of final cutting on the water, carbon and nutrient stores and fluxes in boreal forest

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Duration: 2001-2003   Keywords: biomass, boreal forest, carbon, clear-cutting, decompostion, ground water, leaching, mineralisation, nutrients, soil scarification

Objectives

The objective is to study the effects of final cutting and soil scarification on the 1) carbon and nutrient stores in forest vegetation and soil 2) water, carbon and nutrient fluxes through the forest canopy and soil 3) carbon, nutrient and water input and output from forested catchments and 4) changes in the quality of ground water in the ground water areas. Also the carbon and nutrient stores and fluxes will be evaluated on pristine areas. The study utilizes the material which has been and will be collected from long term study areas established in the beginning of 1990s.

Sub-projects:


Results

Monitoring of the VALU catchments started 6 years before forestry operations were carried out (logging was done in 1996, soil scarification in 1998 and Scots pine seedlings planted in 1999) and have continued to the present. Stem-only harvesting was done and a considerable amount of logging residues (branches, needles and leaves, roots and stumps) was left at the site. Nutrients released from either the logging residues or from the soil are susceptible to leaching as a result of increased infiltration of precipitation and reduced uptake related to the removal of trees and damage to and changes in the ground vegetation.

We observed runoff from the catchments in which clear-cutting had been carried out increased 5 to 9 mm per logged 10 m3 of stem wood. Decomposition of the finest logging residue fraction (fine roots, fine branches and foliage) started soon after cutting, and releasing of phosphorus (P) and potassium (K)]. Three years after harvesting13 kg P per ha and 65 kg K had been released from the fine fraction. No increase in the release of nitrogen (N) was observed over this time, however, with the logging residues [microbial community] retaining N in this early stage of decomposition.

However, our leaching results showed that, with the exception of K, nutrients released from logging residues, organic layer and upper soil were efficiently retained deeper in the mineral soil (B-horizon) at the clear-cut sites. The leaching of K was observed as increased concentrations (83-352%) in the monthly outlet stream water samples compared to the period before cutting. The concentration of suspended solids in stream water also increased after harvesting (41-192%) as did occasionally that of total N, nitrate N and total P. After harvesting we also observed increased nitrate and phosphate concentrations in groundwater down slope from the clear cut areas on occasions. Our VALU results agree with those of an earlier study in the region (the Nurmes project), but the amounts of nutrients leaching were much smaller. In our study, the logging was carried out in accordance with current management practice, including the requirement for a buffer zone near water courses. This buffer zone, which was peatland, evidently retained some of the solid material and nutrients. The increased concentrations of P in stream water after the clear-cutting may have been due to the flow of P enriched water over or through the surface layer of the riparian zone or related to the increased leaching of suspended solids rich in P, as P leaching through the mineral soil at the clear cut sites was effectively retained in the B-horizon.

Project leader: Piirainen, Sirpa
The Finnish Forest Research Institute, Joensuu Office, PL 68, FI-80101 JOENSUU, FINLAND
Phone: +358 29 532 3188
E-mail: sirpa.piirainen@metla.fi

Other researchers: Alm, Jukka, JO (2002), Domisch, Timo, JO (2003-04), Finér, Leena, JO (2001), Laurén, Ari, JO (2001-03), Palviainen, Marjo (2001), Starr, Michael, VA (2001-03)


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Updated 12.06.2012
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