Metla Project 3277

Afforestation of cut-away peatlands and peat fields

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Duration: 2000-2003   Keywords: afforestation, cut-away peatlands, fertilization, peat fields
Research Programme: Ecologically and economically sustainable forestry on drained peatlands

Objectives

The project is divided in three parts. In the first part the effects of afforestation on the greenhouse balances of cut-away peatlands and peat fields are studied. The two other parts deal with specific problems of peat cut-away peatland and peat field afforestation.

A. Carbon and nutrient balance on afforested cut-away peatlands and peat fields.

The project will yield more definite information on the GHG balances of afforested cut-away peatlands and peat fields at the ecosystem level. The aim of this project is to determine the carbon and nutrient balance and the annual litter fall of planted Scots pine stands. This work will done in co-operation with University of Helsinki, Department of Ecology.

B. Sustainable tree growth on cut-away peatlands.

Nutrition and growth response of Scots pine and birch stands at different developmental stages will be studied on cut-away peatlands where the thickness of the remaining peat layer varies between 0 and 1 metres and the mineral soil texture from clay to coarse sand. Results will enable to define prospective need for refertilization and to optimize methods and nutrient amounts in the situation of nutrient application. The criteria of the suitability of cut-away peatlands for growing forest in various site conditions will be developed further (i.e. the thickness and the nutrient store of the remaining peat layer, mineral soil properties). Furthermore, the leaching of nutrients (e.g. phosphorus) will be studied.

C. Effect of soil properties on the afforestation of peat fields (2001-2003).

The effect of soil properties (e.g. nutrient amounts, ash content, bulk density, peat thickness) on the survival and growth of different tree species (Scots pine, Norway spruce, pubescent birch and silver birch) is studied on afforested peat fields. The need for fertilization is studied. The cirteria for suitability of growingforests on peatfields in various site conditions will be developed further. Soil classification based on the results will be constructed.

Results

A. Carbon and nutrient balance on afforested cut-away peatlands and peat fields. In Central Ostrobothnia on three peat fields afforested 1, 6 and 23 years ago the N2O and CH4 flows and soil respiration were studied during two summers. Peat fields are significant sources of CO2 and N20. According to preliminary results afforestation does not diminish the N2O emissions. In the beginning afforestation can increase CH4 emissions but when vegetations changes to forest vegetation emissions seem to end.

A static chamber technique was used to evaluate the fluxes of CH4, N2O and CO2 from three peat fields afforested 1, 6 or 23 years before study (Maljanen, M., Hytönen, J. & Martikainen ,P. 2001: Fluxes of N2O, CH4 and CO2 on afforested boreal agricultural soils. Plant and Soil 231:113-121). The mean emissions of CH4 and N2O durin the growing season did not correlate with the age of the tree stand. All sites were sources of N2O. The oldest site acted as small sink for methane, whereas the two youngests afforested fields were sources for methane. Soil respiration rates decreased with the age of forests. The results show that afforestatin of peat fields does not abruptly terminate the N2O emissions during the first two decades, and afforestation can even enhance methane emission for a few years. The carbon accumulation in the tree stand can partly compensate the carbon loss from soil.

B. Sustainable tree growth on cut-away peatlands. Cut-away peatlands are areas with varying thickness of remaining peat layer, low pH and unbalanced nutrition. Because of the high peat nitrogen stores cut-away peatlands have a high wood production potential if the mineral nutrition of trees is taken care of. This can be carried out by fertilization or soil preparation at the afforestation stage, but later the roots of grown up trees should be able to take nutrients also from the underlying mineral soil.

The root penetration of Pinus sylvestris and Betula pendula was studied (see Aro 2000). Root penetration was not significantly affected by mounding and fertilization in young seedling stands (range 17-33 cm). Results suggest that the thickness of the remaining peat layer should not exceed 30-35 cm in order to ensure mineral subsoil as a nutrient source for trees.

Relationships between some soil properties (thickness ofthe remaining peat layer, nutrient concentrations, minelral soil mixture and pH) and mortality, nutrition and height growth of Scots pine trees was studied on five afforestaton experiments on cut away peatlands (Aro & Kaunisto 2002). Peat thickness was in significant positive correlation with the needlen N content and in negative correlation with needle P and Ca content. The peat K concnetrations correlated positively with the needle potassium content and the height growth of trees increased with the needle K. Fertilization with phosphorus, potassium and boron increased significantly the height growth of Scots pine trees.

C. Afforestation of peat fields

Project leader: Hytönen, Jyrki
The Finnish Forest Research Institute, Kannus Office, Silmäjärventie 2, FI-69100 KANNUS, FINLAND
Phone: +358 29 532 3405
E-mail: jyrki.hytonen@metla.fi

Other researchers: Aro, Lasse, PA (2000-03), Heiskanen, Juha, SU (2001-03), Jylhä, Paula, KA (2003), Karsisto, Marjut, VA (2003), Komulainen, Veli-Matti (2000-01), Wall, Antti, KA (2001)


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Updated 12.06.2012
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