Effect of mechanical site preparation methods on characteristics of the natural regeneration of Scots pine (Pinus sylvestris L.) in Spychowo Forest District

Abstract

Mechanical site preparation is recommended to create optimum conditions for seed germination and seedling growth in a clear−cut area. Lack of soil scarification or less−intense methods may be more suitable from an environmental point of view, but can result in a failure to obtain natural regeneration. This study compared the effects of three mechanical site preparation methods (SPM) characterized by different levels of soil scarification (i.e. double mould−board forest plough (LPz), active plough (PA) or forest mill (FL)), as well as a control variant without mechanical site preparation, on height, density, spatial distribution and survival among naturally regenerating Scots pines (Pinus sylvestris L.) in the first 2 years of growth in a clear−cut area of NE Poland. The experiment was based around a four−block randomized block design involving the four variants. Seedling height was measured at the end of the first and second growing seasons, with measurements performed on 8 meter−wide transects extending across the entire width of the cleat−cut. We found no effect of SPM on seedling height, though the density of seedlings regenerating naturally was found to be dependent. After two years, the highest density was achieved in the PA variant (8.1 seedlings/m2) and the FL variant (7.0 seedlings/m2). A significantly lower density characterized the LPz variant (5.1 seedlings/m2) and the lowest of all the variant without soil scarification (3.2 seedlings/m2). The most homogeneous natural regeneration was achieved following the use of PA (2.6% of 1 m2 plots without seedlings after two growing seasons), while the least homogeneous was the variant without soil scarification (22.4% of 1 m2 plots). Survival of pines after the second growing seasons was quite high (over 80%), and did not differ significantly depending on the SPM. Our research therefore confirmed that, in the absence of mechanical site preparation, natural regeneration of sufficient density and homogeneity cannot be obtained. The best natural regeneration was obtained on sites prepared with PA, and FL scarification being only slightly less favorable. The low density and uneven distribution of seedlings on the soil prepared with LPz was a surprising result. The probable reason for this lay in the high precipitation in the first growing season. On one hand, this provided very good moisture conditions for seed germination and seedling growth on a substrate with high porosity in the PA and FL variants, but on the other the high bulk density of mineral soil in the LPz variant led to oxygen deficit