Differences in early dynamics and effects of slope aspect between naturally regenerated and planted Pinus sylvestris woodland on inland dunes in Poland

There is little knowledge of the effects of landform relief on early growth dynamics and competitive interactions of Pinus sylvestris (Scots pine) stands on inland dunes, which could potentially be substantial. The goal of this study was to examine and compare early dynamics (based on growth parameters and properties of the understorey vegetation) and the effects of slope aspect in naturally regenerated and pine-planted woodland on inland dunes in northern Poland. Growth parameters, tree density, and understorey vegetation were monitored on north- and south-facing slopes in a 26.3 ha post-fire area with natural secondary succession and eight even-aged pine-planted stands, 5-34 years old. Clear differences were detected between the woodland types, in both growth parameters of pines with similar ages and effects of slope aspect on the pines. In the natural regeneration area north-facing slopes provided favorable conditions for natural encroachment by pines. Tree density was higher, and the pines were taller and thicker, on north-facing than on south-facing slopes. In contrast, in the pine-planted area pines were larger on south-facing slopes, although growth conditions were less favorable than on north-facing slopes. However, in the pine-planted area the north-facing slopes had significantly higher herb cover, dominated by Deschampsia flexuosa, indicating that even the presence of a relatively low grass species can impede early growth of Scots pine. The understorey species composition differed in the natural regeneration area, being dominated by Calluna vulgaris on north-facing slopes and Corynephorus canescens on south-facing slopes. The results reveal that interactions between landform, natural dynamics, planting practices, and competitive interactions in woodlands on inland dunes are complex, and should be considered in efforts to manage them efficiently.