Open access publications in the SLU publication database

Abstract

Afforestation of former arable land may serve many purposes and provide many benefits,including carbon sequestration, reduced nitrate pollution of water bodies, restoration of biodiversity and improved recreational possibilities. However, afforestation may also have adverse environmental effects such as reduction of water recharge to groundwater and surface water. This study evaluates the implications of a land use change from agriculture to forestry for N, C and water cycles, based on six afforestation chronosequences (species and age) in Sweden, Denmark and the Netherlands. Results showed that estimated losses by nitrate leaching varied considerably among these six chronosequences, but were at least 3-5 times lower than the reported nitrate leaching from arable land in the three countries. Compared with nutrient-poor sandy soils, nutrient-rich clayey soils appeared more vulnerable to disturbance of the N cycle and to increased N deposition, possibly leading to N saturation and enhanced nitrate leaching. Over approximately 35 years following afforestation, nitrate leaching from the root zone was generally higher below common oak than below Norway spruce. Simulated water recharge revealed a general pattern of decline during the first 30-40 years, followed by a recovery in older stands. Oak stands older than 20 years showed a 60-90 mm higher water recharge than adjacent stands of Norway spruce of similar age. The aboveground and belowground biomass accounted for about two thirds of the increase in ecosystem C, and the remaining one third was sequestered in the O horizon and the Ap horizon. The effect of time since afforestation on soil solution DOC (and DON) was partly masked by spatial variability in soil properties that influence DOM adsorption in the mineral soil. Concentrations of DOC in the A horizon at the sites were primarily related to the oxalate-extractable amounts of Al and Fe in the same horizon. It is evident that planning and planting new forests on arable land in an environmentally sound way requires a holistic and long-term perspective on the subsequent changes.