Above-ground growth and temporal plant–soil relations in midterm hybrid aspen (Populus tremula L. × P. tremuloides Michx.) plantations on former arable lands in hemiboreal Estonia

Short-rotation forestry with hybrid aspen is a novel silvicultural system in northern Europe on former arable lands. However, knowledge about hybrid aspen growth potential in different soil types and the impact of soil physico-chemical properties on tree productivity in the long term is still scanty. We used repeated monitoring of soil properties and tree growth in young (5-year) and midterm (15-year) hybrid aspen plantations in various soil types (corresponding to four forest site types) to determine the temporal changes in tree growth–soil relationships. Growth of midterm hybrid aspen plantations exceeded same-aged native European aspen stands about two-fold. Growth had improved on Aegopodium, remained moderate on moist Dryopteris and was increasingly suppressed on dry Hepatica soils. The pH_KCl, available Ca, content of clay and layer thickness of the soil A-horizon had a significant effect on tree growth in young plantations, but these effects disappeared in the midterm age. The soil water-holding capacity and available P in the A-horizon had a significant growth-controlling effect on tree growth in both ages. We concluded that former arable soils provide a sufficient supply of major nutrients in midterm hybrid aspen plantations whereas minor changes have occurred in growth–soil relationships between young and midterm age.