Prepare the ground before tree planting

Supporting evidence from individual studies

1. A replicated, randomized, controlled study in 1991-1996 in boreal forest in Sweden (Norberg et al. 1997) found that site preparation treatments increased the growth rate of planted Scots pine Pinus sylvestris seedlings. Seedling height was higher in scarification (300 mm) than control plots (250 mm), and highest in steamed plots (steamed: 350 mm; burned: 280). Stem basal area (mm²) differed among all treatments (control: 29; burned: 43; scarification: 55; steamed: 73). In August 1992, five plots (0.6 × 0.6 m) of each control (untreated), burned (ground vegetation and litter burned using a propane burner), scarification (humus layer removed from the mineral soil) and steamed (amount of steam equivalent to 13 L of water evenly sprayed over each plot for 2 minutes) treatments were replicated in 40 blocks that were clearcut in 1991–1992. In June 1993, one scots pine seedling was planted in each plot. Data were collected in 1996.

   Study and other actions tested

   Referenced paper

   Norberg G., Jäderlund A., Zackrisson O., Nordfjell T., Wardle D., Nilsson M. & Dolling A. (1997) Vegetation control by steam treatment in boreal forests: a comparison with burning and soil scarification. Canadian Journal of Forest Research, 27, 2026-2033.

2. A replicated, randomized, controlled study in 1986-1996 in boreal forest in Sweden (Örlander et al. 1998) found that site preparation treatments increased survival and biomass of planted lodgepole pine Pinus contorta and Norway spruce Picea abies seedlings. Survival rates were higher with all four site preparation treatments compared to controls for both pine (inverting: 98%; ploughing: 98%: mounding: 90%: disc-trenching: 86%; control: 72%) and spruce (inverting: 98%; ploughing: 100%: mounding: 96%: disc-trenching: 95%; control: 70%). biomass (g dry weight/seeding) of pine was higher in inverting and ploughing than the other three treatments (inverting: 392; ploughing: 338: mounding: 137: disc-trenching: 143; control: 36) . Biomass of spruce seedlings was higher in inverting than disc-trenching and control treatments, and higher in ploughing and mounding than control plots (inverting: 74; ploughing: 63: mounding: 63: disc-trenching: 32; control: 9). In 1986, five treatments: control (no soil scarification); disc trenching (with powered discs); mounding (with spades); ploughing (with tilt-plough); inverting (tilt-plough made furrows refilled with inverted soil) were randomly replicated eight times. Twenty spruce and 20 pine seedlings were planted in each treatment replicatein 1987. Survival and biomass data were collected 10 and four years after planting respectively.

   Study and other actions tested

   Referenced paper

   Örlander G., Hallsby G., Gemmel P. & Wilhelmsson C. (1998) Inverting improves establishment of Pinus contorta and Picea abies —10‐year results from a site preparation trial in Northern Sweden. Scandinavian Journal of Forest Research, 13, 160-168.

3. A replicated, controlled study in 1994-1997 in boreal forest in Alberta, Canada (Man & Lieffers 1999) found that site preparation treatments decreased the mortality of planted white spruce Picea glauca seedlings. Mortality was higher in control than in soil removal and soil mixed plots (control: 23%: soil removal: 7%; soil mixed: 9%). Seedling height increase (control: 23 cm: soil removal: 24 cm; soil mixed: 27 cm) and root-collar diameter (control: 6 mm: soil removal: 7mm; soil mixed: 7 mm) were not different between treatments. Data were collected in 1997 in four plots comprised of three treatment subplots (100 × 33 m): control, soil removal (top 11-13 cm of soil removed) and soil mixed (top 11-13 cm of soil mixed), in each of two blocks. Treatments and seedling planting were undertaken in 1994.

   Study and other actions tested

   Referenced paper

   Man R. & Lieffers V.J. (1999) Effects of shelterwood and site preparation on microclimate and establishment of white spruce seedlings in a boreal mixedwood forest. The Forestry Chronicle, 75, 837-844.

4. A replicated, randomized, controlled study in 1988-1995 in boreal forest in Sweden (Langvall, Nilsson & Örlander 2001) found no effect of mounding treatment on frost damage to planted Norway spruce Picea abies seedlings. The percentage of seedlings with frost injuries (site 1: 6-11%; site 2: 27-38%) was similar between treatments. Spruce seedlings were planted in five blocks of four mounds (50 × 50 cm, 10–20 cm high soil mounds created in the year of planting) and four control plots (4 × 4 m) that were established in 1988 in each of two sites. Data were collected in each plot two growing seasons after planting.

   Study and other actions tested

   Referenced paper

   Langvall O., Nilsson U. & Örlander G. (2001) Frost damage to planted Norway spruce seedlings—influence of site preparation and seedling type. Forest Ecology and Management, 141, 223-235.

5. A replicated, randomized, controlled study in 2001-2006 in temperate coniferous forest in Alberta, Canada (Landhäusser 2009) found that ground preparation treatments decreased the mortality of planted Lodgepole pine Pinus contorta seedlings. Mortality of planted seedlings was lower in soil mound (1%) and scarification (2%) than untreated plots (11%). Twelve mound, 12 scarification  and 12 control plots (30 × 30 m) were established in winter 2001 and planted with lodgepole pine (2,000 seedlings/ha) in 2002. Mortality of planted pines (2003-2006) was monitored by selecting 20 seedlings in each plot.

   Study and other actions tested

   Referenced paper

   Landhäusser S.M. (2009) Impact of slash removal, drag scarification, and mounding on lodgepole pine cone distribution and seedling regeneration after cut-to-length harvesting on high elevation sites. Forest ecology and management, 258, 43-49.

6. A replicated, randomized, controlled study in 2006-2008 in boreal forest in Sweden (Löf & Birkedal 2009) found that soil mounding increased the biomass of planted English oak Quercus robur seedlings, while all site preparation treatments decreased the biomass of ground vegetation. Dry biomass of English oak was higher in mounding (4-9 g/seedling) than in all other treatments (2-6 g/seedling). Five treatment plots (20×15 m): untreated control; disc trenching; patch scarification; top soil removal and mounding were established in 2006 in each of four blocks (0.35 ha). Data were collected in 2008.

   Study and other actions tested

   Referenced paper

   Löf M. & Birkedal M. (2009) Direct seeding of Quercus robur L. for reforestation: the influence of mechanical site preparation and sowing date on early growth of seedlings. Forest Ecology and Management, 258, 704-711.

7. A replicated, controlled study in 2010-2011 in temperate coniferous forest in Sweden (Wallertz & Malmqvist 2012) found that site preparation treatments decreased the mortality of planted Douglas-fir Pseudotsuga menziesii, but not of Norway spruce Picea abies seedlings. Mortality of Douglas-fir was higher in control than in all site-preparation treatments (control: 40%; scarified: 10%; mound: 6%; inverted: 11%; mixed: 8%). In contrast, mortality of Norway spruce was similar between all treatments (control: 2%; scarified: 4%; mound: 1%; inverted: 2%; mixed: 1%). Forty Norway spruce and 40 Dougla-fir seedlings were planted in May 2010 in four replicates (blocks) of five treatments: control (no treatment); scarified (scarified mineral soil patch); mound (inverted humus turf deposited on the forest floor capped with mineral soil); inverted (inverted humus turf, placed back in the pit covered with mineral soil); mixed (complete mixing of mineral soil and humus). Data were collected in 2010-2011.

   Study and other actions tested

   Referenced paper

   Wallertz K. & Malmqvist C. (2012) The effect of mechanical site preparation methods on the establishment of Norway spruce (Picea abies (L.) Karst.) and Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) in southern Sweden. Forestry, cps065.