This thesis was executed in the context of the historical metal pollution in the Campine (Kempen) region in north-eastern Belgium. Due to metal refining activities in the past, an extended area of about 700 km² is diffusely polluted with mainly cadmium (Cd) and zinc (Zn). The historical soil pollution is still causing human-toxicological and ecotoxicological risks, through metal leaching to groundwater and accumulation in the food chain. Moreover, the Campine region is characterized by poor sandy soils, aggravating the risks for metal dispersion in the environment. Conventional soil sanitation techniques are technically and financially inadequate to tackle the pollution problem, because of its spatial extent and the relatively moderate contamination levels. Hence, alternative remediation strategies, such as phytostabilization, are to be investigated. Sustainable phytostabilization projects require the metals to be stabilized in the soil and should thus aim at minimizing metal dispersion via both above- and below-ground pathways. As there is a clear tree species effect on metal uptake, on litter decomposition, on biogeochemical processes in the soil profile and on the water balance, the distribution and fluxes of metals in the forest-soil system will be tree species specific as well. Selecting appropriate tree species is thus crucial for achieving successful phytostabilization. The main objectives of this thesis were to assess the feasibility of phytostabilization by afforesting diffusely Cd and Zn contaminated sandy soils, and to determine the tree species effects on Cd and Zn cycling on these soils. Our study was carried out in ‘Waaltjesbos’, a young post-agricultural forest on a metal contaminated site on sandy soil. At the moment of our study, the trees were 10-15 years old. The six selected tree species were silver birch (Betula pendula), oak (Quercus robur and Q. petraea), black locust (Robinia pseudoacacia), aspen (Populus tremula), Scots pine (Pinus sylvestris) and Douglas fir (Pseudotsuga menziesii). We ...