Effect of vegetation control on the survival and growth of Scots pine and Norway spruce planted on former agricultural land

Abstract

The effects of competing vegetation and various weed control methods (fibreboard mulch, cover crop of clover, and various herbicides) on the survival and growth of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) seedlings were compared based on 6- to 11-year data from a field experiment established as a randomized block design with three replications in southern Finland. The most effective herbicides significantly reduced the weed cover for 2 or 3 years. The mortality, basal diameter, height, and volume of Scots pine significantly correlated with percent cover of the ground vegetation. In the case of Norway spruce, only the stem diameter correlated significantly with percent cover of the competing vegetation. This was probably due to the severe frost damage that occurred in the third growing season. The mortality of pine began to increase only when the vegetation cover had exceeded 60%. After 11 years, the stand volume on the pine plots treated with terbuthylazine was almost double that of the untreated plots (32 vs. 17 m3·ha–1), but this difference was not statistically significant. Mulch and cover crop did not significantly affect pine growth or mortality. Recurrent frost damage may explain why none of the studied treatments significantly affected the mortality and volume growth of Norway spruce.