Manipulation of conventional forest management practices to increase forest growth—results from the Skogaby project

Abstract

Above ground dry mass production and N accumulation on an areal basis in stems, branches and needles as well as in litterfall in a Norway spruce stand in south Sweden treated with unlimited availability of water and nutrients (fertilisation with irrigation) or of water (irrigation) during a 6 year experimental period are presented. Fertilisation was made in liquid form on a weekly basis during the vegetation period with 100 kg N ha −1 year −1 during each year. The fertiliser also included a balanced composition of P, K, Ca, Mg and S as well as of micronutrients. Irrigation was carried out as soon as a 20 mm water storage deficit developed. It is concluded that there is a large potential to improve Norway spruce production through liquid fertilisation with irrigation. Stem and branch production of Norway spruce was almost doubled due to this treatment. Also, stand needle dry mass and litterfall were markedly increased in comparison with the control. Water and N availability were the two most limiting growth factors. During the experimental period, irrigation had a greater effect on growth than N addition. The gross N uptake increased by 450 kg ha −1 as a result of 600 kg ha −1 fertiliser addition. Needle retention was increased for irrigated trees but needle litterfall remained unchanged. Changing the forest management of Norway spruce to intensive cultivatation results in transitional carbon sequestration in both stand and soil compared with an untreated ecosystem. The largest long-term environmental value is, however, achieved if this cultivated renewable biomass is used as a substitute for fossil fuels. Wood utilisation options of intensively cultivated Norway spruce are discussed.