EFFECT OF THINNING ON THE FOLIAR NUTRIENT STATUS OF SCOTS PINE STANDSON DRAINED BOREAL PEATLANDS

Foliar responses to thinning in midrotation stands of Scots pine (Pinu s sylvestris L.) were studied in six thinning experiments (0-50% of ba sal area removed) established on drained peatlands in northern Finland and southern Sweden. The trophic level of the sites varied from ombro trophic to meso-eutrophic. Needle sampling and analyses were carried o ut on individual trees of dominant and suppressed canopy layers. The v ariation in the needle dry mass and in the element concentrations and contents, calculated as plot means, was explained by thinning treatmen t, blocking by site groups and randoming blocking within the site. Thi nning increased foliar concentrations of P, needle size, and contents of N, P, and K in all the canopy layers. It was concluded that thinnin g improved the foliar nutrient status by reducing the competition for nutrients.