Growth of broadleaved species on post-agricultural lands introduced during the process of stand conversion with a use of artificial gaps

Abstract This paper presents results on the restoration of Scots pine stands established on post-agricultural lands undergoing conversion into mixed stands. Sessile oak (Quercus petraea), common beech (Fagus sylvatica) and small-leaved lime (Tilia cordata) seedlings were planted in artificially created gaps (0.02 ha to 0.05 ha each) cut in six experimental plots (Forest Districts: Bielsk, Krynki, Sobibór, Dobieszyn, Skrwilno and Łupawa) located in 20–25-years-old pine stands. The experimental plots were spread across northern, central and eastern Poland and affected by root-rot fungus (Heterobasidion annosum). Nine years after planting, the number of individual trees and shrub species, their height sum and average height were calculated for fenced artificial gaps (LSO) as well as non-fenced artificial gaps (LSN) and compared to natural gaps (LN) and non-disturbed neighboring stands (D). Results were calculated separately for the planted species (oak, lime and beech) but combined for all other species. The results indicate satisfactory restoration in all of the investigated plots except in Krynki, which is located in a relatively poor site. Significant differences appeared between height sum as well as average height of planted species in fenced compared to non-fenced gaps. Furthermore, in both, natural and artificial gaps, the species composition of the young generation was enriched with natural regeneration of pioneer species, mainly silver birch (Betula pendula), rowan (Sorbus aucuparia) and aspen (Populus tremula).