Effects of mechanical site preparation and slash removal on long-term productivity of conifer plantations in Sweden

Abstract

Mechanical site preparation is commonly used to increase survival and early growth of newly planted seedlings. Ideally, any early positive effects of site preparation should persist for a long time, but concerns have been raised as to whether intensive site preparation might have a negative effect on the long-term productivity of a stand. The present study was therefore designed to investigate the long-term effects of different site-preparation methods on productivity and determine any possible interactions with tree species and site fertility. In the 1980s, a randomized block experiment was established at sites throughout Sweden. Four site-preparation methods of various intensities were performed on different sites: (i) an untreated control, (ii) disc trenching, (iii) mounding, and (iv) ploughing. As a complementary treatment, slash was either retained or removed from some plots. Depending on soil moisture class, geographical position, and site index, Norway spruce (Picea abies (L.) Karst.), Scots pine (Pinus sylvestris L.), or lodgepole pine (Pinus contorta Douglas ex Loudon) were planted in pure stands. Growth variables such as height and diameter were measured during the first years after establishment. After about 30 years, these variables were remeasured at the level of individual trees. Overall, an increased production of the planted trees after site preparation was found. Neither intensive site preparation (such as ploughing) nor slash removal had any negative effect on the long-term productivity of these experimental stands.

Survival and growth of Scots pine (Pinus sylvestris) seedlings in north Sweden: effects of planting position and arginine phosphate addition

“…This finding emphasizes the difference between the two planting positions in respect of the risk to planted seedlings when exposed to drought. This variation in drought sensitivity depending on planting position might be one of the reasons why a large variation in survival between sites has been seen in other studies of forest regeneration in the Nordic countries (Hjelm et al 2019;Sikstrom et al 2020). The mortality of P. sylvestris seedlings has also been found to be strongly related to the number of dry days during the month the seedlings were planted (Sukhbaatar et al 2020) and seedling mortality is associated with drought stress, even on sites where soil moisture is only low on rare occasions (Burton et al 2000).…”

“…The lack of general superior growth in capped mounds is, however, not unique to our study. In a study by Hjelm et al (2019), no significant difference in tree volumes was found after 30 years between trees planted in the mineral soil close to the berm after disc trenching and trees planted in capped mounds after mounding.…”

Management of spontaneously regenerated mixed stands of birch and Norway spruce in Sweden

“…Although artificial regeneration practices in boreal forest, with soil scarification and planting of conifers, have proven highly efficient (Örlander et al 1998;Hjelm et al 2019) and profitable (Sikström et al 2018), there is a need for management practices in areas where mixed forests spontaneously regenerate (Coll et al 2018;Löf et al 2018). Spontaneous regeneration is an opportunity for the forest owner to combine production and biodiversity on the same clearcut by leaving different tree species during pre-commercial thinning to create a mixed-species stand (Felton et al 2016;Holmström et al 2016).…”

Long-term growth response of Norway spruce in different mounding and vegetation control treatments on fine-textured soils

“…is the most planted tree species in boreal forests of northern Europe (Peltola et al 2019;Sikström 2020). Nowadays mechanical site preparation (MSP) commonly precedes spruce planting since it has been found to facilitate the planting work and expedite the survival and early growth of planted seedlings (Ritari and Lähde 1978;Örlander et al 1990;Sutton 1993;Hallsby and Örlander 2004;Boateng et al 2006;Nilsson et al 2010;Wallertz and Malmqvist 2013;Wallertz et al 2018;Hjelm et al 2019;Sikström et al 2020). Mounding has shown better plantation establishment than patch scarification or disc trenching (Hallsby and Örlander 2004;Saksa et al 2005;Kankaanhuhta et al 2009;Korhonen et al 2010;Uotila et al 2010;Saksa 2011;Sikström et al 2020), and it is currently one of the mostly used methods in Fennoscandia (Peltola et al 2019).…”