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Forests and water (H2O) 2013-2017

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Photo: Metla/Erkki Oksanen.

The effects of and need for ditch network maintenance

In the Finland’s National Forestry program it is estimated that to sustain the current level of growth in peatland forests it is necessary to maintain 100 000 ha of peatland ditch networks annually. Studies have shown that ditch network maintenance increases stand growth and it is an economically feasible action, although the additional growth e.g. in southern Finland may remain marginal.

On the other hand, ditch network maintenance is the most harmful forestry operation because of the related loads of suspended solids to water courses. About 90 per cent of loads of suspended solids from forestry are due to ditch network maintenance resulting muddy waters and blocking of spawning gravels for salmonids. Additionally, phosphorus leaching is significant and small amounts nitrogen and dissolved organic carbon also will be released in ditch network maintenance.

Several water protection measures connected to ditch network maintenance have been developed, but none of those can completely prevent all loads in all conditions. The most effective way to constrain the load is to concentrate ditch network maintenance operations only in stands which clearly can benefit from the action. How these areas can be detected, necessitates investigations of the role of evapotranspiration of the tree stand and climate on drainage of the site. Further, it is necessary to find out water retention characteristics of different peats. Based on field and laboratory studies, models will be developed for describing peatland forests and the hydrological processes in the peatland ecosystem.

The models will be applied in simulation studies by forecasting development of stand characteristics and site condition from different initial conditions (stand stocking, climate, peat properties) with or without ditch network maintenance. In two forestry centers future timber yields with or without ditch network maintenance will be estimated using actual data of forest resources and peatland areas. Financial effects and impacts on water quality will be also assessed.

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Updated: 27.02.2014/MLin  |  Photo: Erkki Oksanen, Metla, unless otherwise stated  |  Copyright Metla  |  Feedback