Site preparation, planting position and planting stock effects on long-term survival, growth and stem form properties of Pinus contorta on southern Iceland

Abstract: In order to evaluate different afforestation methods for exposed heath lands a field experiment was established in Mosfell on southern Iceland in 1989. The trial comprised six different site preparation methods (control, herbicide application, tree shelters, patch scarification, TTS trenching and mounding). In total 960 container seedlings (1+0) and 960 Nisula roll transplants (2+1) of lodgepole pine were planted. Various planting positions (furrow, hinge, no site preparation (control) and on top of mounds) were tested within the site preparation treatments. This study involves renewed measurements and analyses of the trial.After 19 years the overall survival was 51,7 %. Patch scarification and herbicide application resulted in the highest survival (58 %) while tree shelters obtained the poorest survival (36%). Nisula rolls showed a significantly higher survival and stem form quality compared to container seedlings. Choice of planting stock had no effect on average height. Trees on control and mounded areas displayed the lowest (132 cm) respectively the highest (252 cm) mean height. Furrow planting generally affected survival and mean height in a negative way while hinge planting improved survival and mean height. In conclusion, scarification had a low impact on survival but enhanced height growth. Herbicide treatment increased mean height and mean diameter compared to control and is therefore an alternative to scarification. The use of tree shelters is not a sufficient site preparation method. The results of this study indicate that hinge planting offers an environment where seedlings are protected from wind, frost heaving and erosion while they at the same time are offered an adequate water and nutrient supply. Choice of planting spot was found to be crucial after mounding. A low planting position should be avoided regardless of site preparation method.