Changes in Macronutrient Concentrations in Soil Solution Following Regeneration Felling in Pine and Spruce Stands: Whole-Tree Harvesting Versus Stem-Only Harvesting

Abstract

While conventional forest management in boreal and hemiboreal conditions has traditionally been targeted to use and enhance mainly provisioning services like timber production, the main goal of national and European forest policy is to ensure sustainable management of European forests in all aspects. Regeneration felling is a major disturbance in boreal and hemiboreal forests resulting in significant increase of organic matter on the forest floor in the form of logging residues (bark, small branches, tree tops) and severed roots (in case of stump harvesting), and can increase the risk of nutrient leaching. Recently, concern about the effect of forest management impact on macronutrient leaching potentially decreasing nutrient availability for the next forest generations and causing deterioration of water quality has been raised. In 2011, three objects to study the impact of different intensity regeneration felling (stem-only harvesting and whole-tree harvesting) were established in scientific research forests in Kalsnava forest district, eastern part of Latvia. Two sites were located on mineral soils (Myrtillosa and Hylocomiosa site type, dominant tree species Pinus sylvestris L.) and one on drained peat soil (Oxalidosa turf. mel. site type, dominant tree species Picea abies (L.) Karst.). Felling was performed in early spring 2013 with harvester, timber was extracted and logging residues were removed with forwarder, following "business as usual" principle. Soil solution samples were collected once or twice a month in 2012, 2013, 2014, 2015 and 2016. This study presents trends of pH and macronutrient (NO3 --N, PO43--P, K) concentrations during five years -one year before harvesting and four years following harvesting. In general, significant forest management impact expressed as increase of macronutrient concentrations in soil solution was detected in the second and third year after harvesting, but in the fourth year concentrations started to decrease again.