Relation between soil properties and tree species composition in a Scots pine-Norway spruce stand in southern Finland

It is commonly known in Finland that Scots pine (Pinus sylvestris L.) is a tree of dry soils and Norway spruce (Picea abies (L) Karst.) is a tree of fresh soils. However, the concepts of dry and fresh soils still lack a precise definition. Consequently, the discussion on which soil/site is a pine or spruce habitat has continued over several decades. Moreover, in forest regeneration, the practice of tree species selection between the pine and the spruce has varied. We investigated the relationship between soil properties and pine-spruce species composition in a mature, naturally regenerated stand in southern Finland. We applied spatial analysis to divide the stand area up into 3-7 classes based on selected soil properties and then investigated the variations in species composition among those classes. The pine-spruce basal area ratio (BA of pines / BA of spruces) increased along with increasing mean particle size and proportion of coarse sand and gravel particle size fraction (0.6-20 mm) of mineral soil, and was lowest in classes, with the highest proportions of fine texture fractions. The results suggest that in southern Finland on sorted soils, pine is more competitive in regeneration and growth than spruce when mean particle size is above 0.44 mm or percentage of coarse sand and gravel is higher than 50%.