RESTORATION EVIDENCE

Action: Use soil scarification or ploughing to enhance germination Forest Conservation

Key messages

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  • Two studies (including one replicated, randomized, controlled study) in Portugal and the USA found that ploughing increased the cover and diversity of understory plants.
  • Two of three studies (including two replicated, randomized, controlled) in Canada and Brazil found that ploughing increased,  and one found it decreased the density of young trees. Two replicated, controlled studies in Ethiopia and Sweden found mixed effects of tilling on different tree species.
  • One replicated, before-and-after trial in Finland found that ploughing decreased the cover of plants living on wood surface.
  • One replicated, controlled study in the USA found that ploughing did not decrease the spreading distance and density of invasive grass seedlings.

 

Supporting evidence from individual studies

1 

A replicated, controlled study in 1992 in Afro-montane forests in Ethiopia (Sharew, Legg & Grace 1997) found that ploughing after clearcutting increased seedling establishment of African juniper Juniperus procera but not of East African yellowwood Afrocarpus gracilior trees. Seedling density of African juniper (control: 0-13; ploughing: 5-14 individuals/m2) was higher in ploughing, while density of East African yellowwood (control: 1-5; ploughing: 3-5) was similar between treatments. Data were collected in December 1992 in three pairs of control and ploughing (ploughed to 30 cm depth and raked) subplots (1 × 2 m) in each of nine plots (10 × 10 m) established in a clear-felled site (40 × 40 m) in March-April 1992.

 

2 

A replicated, randomized, controlled study in 1993-1996 in temperate coniferous forest in Alberta, Canada (Stewart et al. 2000) found that mechanically scratching the land (scarification) increased the density of white spruce Picea glauca seedlings under trembling aspen Populus tremuloides canopies. The density of white spruce under natural regeneration (scarification: 11-16; control: 0 seedlings/ha) and under artificial seeding (scarification: 14-17; control: 0) was higher in scarification plots than controls. Four treatment strips (50 × 6 m): control (undisturbed) and three scarification treatments: light (upper litter layer removed), heavy (humus and litter-layer removed) and heavy with ridge (heavy scarification plus second pass to create a ridge of soil) were established in 1993 in each of three blocks within each of six sites. All sites were dominated by aspen trees. Data were collected in August 1996 in three natural regeneration (not seeded) plots (50 × 100 cm) and three artificially –seeded (100 white spruce seeds in May 1994) plots (50 × 50 cm) in each treatment strip.

 

3 

A replicated, randomized, controlled study in 1999-2002 in temperate broadleaf forest in Illinois, USA (Baer & Groninger 2004) found that ploughing before reforestation planting increased plant species diversity. Plant diversity was higher in ploughing (Shannon's index of diversity: 1.7) than in control plots (1.4). Data were collected in 2002 in a 0.5 m2 plot around each of 60 ash seedlings (planted in 1999) in each control and ploughing (disked to 15 cm depth before planting) treatments (9 × 90 m) replicated in four blocks.

4 

A replicated, controlled study in 1993-2000 in temperate forest in Sweden (Karlsson & Nilsson 2005) found that mechanical soil scarification increased the cover of herbaceous plants; increased the density of young Scots pine Pinus sylvestris, downy birch Betula pubescens and silver birch B. pendula after shelterwood logging; increased pine but decreased birch density after clearcutting; did not affect the density of Norway spruce Picea abies seedlings or the cover of grasses and dwarf shrubs. Density of pine seedlings was higher following scarification in both shelterwood (scarification: 23,000; control: 18,000 seedlings/ha) and clearcut sites (scarification: 6,500; control: 3,000). Birch density was higher in scarification plots in shelterwood sites (scarification: 18,000; control: 3,000) and higher in control plots in clearcut sites (scarification: 7,000; control: 15,000). The density of spruce seedlings was similar between treatments in both shelterwood (17,000-20,000) and clearcut sites (2,500-3,000). Cover of herbaceous plants was higher in scarification plots in both shelterwood (scarification: 9; control: 5%) and clearcut sites (scarification: 11; control: 9%). Cover of grasses and dwarf-shrubs was similar between treatments in both shelterwood (scarification: 19-20; control: 16-18%) and clearcut plots (scarification: 32-35; control 11-12%). Scarification and control treatments were established in each of eight shelterwood (40% of tree volume cut) and eight clearcut plots (0.4 ha). Scarification treatment was applied in 1994-1996, two to14 months after cutting. Data were collected in 2000.

 

5 

A replicated, randomized, controlled, before-and-after study in 2004-2005 in subtropical forest in Brazil (Sampaio, Holl & Scariot 2007) found that ploughing decreased the density of young trees and had no effect on species richness of new trees. The change (after minus before) in young tree density was more negative in ploughed plots (ploughing: -4,000; control: 1,000/ha). The number of species/plot (ploughing: -2; control: 0) was similar between treatments. Data were collected immediately before (January 2004) and one year after treatment (March 2005) in four replicates of adjacent control and ploughing (to a 10 cm depth) plots (10 × 10 m).

 

6 

A replicated, controlled study in 2005–2007 in temperate broadleaf forest in Tennessee, USA (Marshall & Buckley 2008) found no effect of soil disturbance on the spreading distance or on the number of invasive grass Japanese stiltgrass Microstegium vimineum seedlings. Average spread distance (disturbed: 13 cm; control: 10 cm) as well number of seedlings (1 to >100 seedlings/m2) was similar between treatments. Data were collected in 2006-2007 in three disturbed (soil disturbed using a sharpshooter shovel in 2005-2006) and three control plots (1 m2) in each of three blocks.

 

7 

A replicated, randomized, controlled study in 2001-2006 in temperate coniferous forest in Alberta, Canada (Landhäusser 2009) found that mechanical soil scarification increased the density, but not the height of naturally regenerated pine seedlings. The density of pine seedlings was higher in scarification plots (scarification: >10,000; control: <1,000 seedlings/ha), while their height was similar between treatments (18-25 cm). Twelve scarification (in winter 2001) and 12 control plots (30 × 30 m) were established in 2002. Density and height of pine seedlings was measured in 2006 in five subplots (10 m2) within each plot.

 

8 

A replicated, controlled study in 1998-2007 in Mediterranean oak woodland in Portugal (Canteiro et al. 2011) found that ploughing increased plant cover nine years after treatment. Total plant cover was higher in ploughing plots (87% in both) than control plots (82%). In June 1998, ploughing (incorporating plant matter into the soil) and control treatments were each applied to three plots (50 × 14 m). Total plant cover was measured in 2007 in five subplots (2 × 2 m) in each treatment plot.

 

9 

A replicated, before-and-after study in 1998-2000 in boreal Norway spruce Picea abies forest in Finland (Hautala, Laaka-Lindberg & Vanha-Majamaa 2011) found that soil scarification after tree felling decreased the cover and number of plant species that living on the surface of wood (epixylic species). The cover of all epixylic species groups were lower after scarification (vascular plants: before 0.8%, after 0.0%; bryophytes: before 7.0%, after 2.5%; lichens: before 1.1%, after 0.4%). The same was true for the total number of epixylic species (before: 2; after: 1/plot). Epixylic species were monitored before (1999) and after soil scarification in 2000, in approximately 500 plots (200 cm2) marked on 66 logs in an area that was clear-felled in 1998.

Referenced papers

Please cite as:

Agra H., Schowanek S., Carmel Y., Smith R.K. & Ne’eman G. (2018) Forest Conservation. Pages 285-328 in: W.J. Sutherland, L.V. Dicks, N. Ockendon, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2018. Open Book Publishers, Cambridge, UK.