Root spatial distribution and biomass partitioning in Quercus robur L. seedlings: the effects of mounding site preparation in oak plantations

In a reforestation field experiment undertaken in southern Sweden and planted with pedunculate oak, three site preparation treatments (herbicide application (H), mounding site preparation (MSP) and combined herbicide and mounding treatment (H + MSP)) were compared to an undisturbed control (C). We analysed root spatial and biomass distribution in 48 harvested seedlings. Compared to the control, both MSP and H treatments resulted in a significantly higher root system biomass (means C: 16.4 g, H: 45.7 g, MSP: 41.4 g, MSP + H: 102.2 g). The proportion of lateral root biomass increased from 38% (C) to 62% (MSP + H), while the two remaining treatments (H, MSP) attained percentages of 48% and 51%, respectively. The treatments did not alter seedlings' allometry and root:shoot ratio significantly. However, biomass distribution of different root system parts varied among treatments, so that lateral root biomass increased relative to leaf biomass from C to MSP + H variant. Site preparation treatments (MSP, MSP + H) increased the horizontal extension of root biomass, compared to C and H variants. We conclude that mounding site preparation is an efficient method for the reforestation of pedunculate oak stands. Due to the comparative positive effects on root system development, MSP presents an alternative to herbicide treatment, particularly at sites where the use of chemicals is restricted.