Establishment of direct seeded seedlings of Norway spruce and Scots pine: Effects of stand conditions, orientation and distance with respect to shelter tree, and fertilisation

Abstract

Abstract The objectives of this work were to quantify the effects of stand stem density (SSD), orientation and distance with respect to shelter tree, and fertilisation on the establishment of Pinus sylvestris L. and Picea abies (L.) Karst. regenerated by direct seeding on different soil preparations. The field experiment was performed on South (64°14′N, 19°46′E, 225 m a.s.l.) and North (64°09′N, 19°36′E, 274 m a.s.l.) slopes in boreal Sweden. Regeneration and height growth in three SSDs with different light regimes, i.e. uncut forest (∼500 stems/ha), shelterwood (∼150 stems/ha), and clear-cut, were compared. Sowing was done in 2001, after using two soil preparations (mineral soil and a mixture of mineral soil and humus layer ground to a fine texture), at six distances to shelter trees (0.5, 1, 1.5, 2, 4 and 6 m). Half of the seedlings were also irrigated with fertiliser (10 mM N) from the second to the fourth growing season after seeding, i.e. until final inventories were made. The light environment did not differ significantly between different orientations and distances with respect to trees, but it was clearly different between SSDs. The establishment and growth of direct seeded seedlings depended on species and SSD as well as on soil preparation. On the North slope, the emergence was highest (50 seedlings in percent of germinable seeds for P. sylvestris and 44% for P. abies ) in SSD 150. On the other hand, on the South slope the conditions in SSD 0 favoured the high emergence of P. sylvestris (41%), whereas for P. abies there was no difference between SSD 0 and SSD 150 (28% versus 30%, respectively). The soil preparation that created a mixture of mineral soil and humus layer generally favoured seedling emergence. Only for P. abies on the North slope, fertilised seedlings were taller (ca. 20%) than non-fertilised seedlings. After four years, P. abies on the North slope was most successful with nine seedlings in percent of germinable seeds remaining out of 24% emerged. The main conclusion is that for plant establishment from seed, the general conditions of the stand matter more than the orientation and distance with respect to the nearest tree and the light environment is more important than the nutritional status, i.e. light requirements cannot be moderated by nutrient supply.