Growth responses of Pinus sylvestris and Picea abies after ditch cleaning – a survey in Sweden

Abstract

ABSTRACTIn drained forest sites, ditch cleaning (DC) may be needed to restore the drainage function of ditches and maintain favourable growing conditions. The main aims of this study were (i) to estimate the growth responses of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies L. Karst) stands following DC, and (ii) to test the hypothesis that stand stocking should be less than 150 m3 ha−1 at DC to obtain a growth response. This survey included 14 ditched stands in Sweden on both mineral and peat soils. The methodology was based on evaluating growth rates before and after the DC operation (growth ratio), reconstructing the growth by taking increment cores from the tree trunks. The measured growth was related to growth derived using a growth simulator as if DC had not been conducted. The results showed an average growth increase of 1.6 m3 ha−1 yr−1 for about 25 years after DC in the stands containing 50–200 m3 ha−1. The growth response appeared to be positively related to stand age, trees ha−1 and site index, and negatively related to stand volume, supporting the hypothesis that stand stocking is an important factor to consider when assessing the need for DC.