EFFECTS OF THINNING ON GROWTH IN PINE AND SPRUCE DURING DROUGHT

Sammanfattning

As climate warms and droughts become more common, it is important to investigate how to manage forests to maintain productivity and maintain the important role that forests serve. This report investigates thinning and how it affected growth in Pine (Pinus sylvestris) and Spruce (Picea abies) during the dry year of 2018 in Sweden. The study was conducted by sampling 20 different trees from two sites in Remningstorp, Sweden. One site had been thinned in 2015, and the other had not been managed. The cores were measured to determine their ring width, and these values were then detrended by the Spline method before most of the statistical analysis took place. The results found that the control site grew 189% compared to the thinned site in 2018 (p<0.05), which was not expected as thinning was expected to decrease competition and therefore increase growth. Differences between the plots and increased evaporation after thinning are discussed as possible reasons behind this result. There was a significant difference between the two species in the thinned stand, where the Pine trees grew more than the Spruce during 2018 (p<0.05). One possible cause of this, which is discussed, is the difference between the two species root structure which may have affected the water uptake during dry periods. There was no significant difference found between the two species in the long term when comparing all trees, however there was a slight indication of a larger growth in Pine after thinning (p>0.05). Suggestions for further research include finding more similar plots, measuring more variables such as soil moisture and gathering a larger number of cores be able to analyze a larger sample size.