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Providing evidence to improve practice

Action: Log/remove trees within forests: effects on mature trees Forest Conservation

Key messages

  • Three of seven studies (including two replicated, controlled studies) in Bolivia, Central African Republic, China, Finland, Malaysia, Uganda and the USA found that logging trees in forests decreased the density and cover of trees. Two found it increased tree density and two found no effect of logging on tree density.
  • Three of six studies (including one replicated, randomized, controlled study) in Bolivia, Canada, China, Kenya, Malaysia and the USA found that logging trees in forests increased tree size. Two found it decreased tree size and one found no effect of  logging on tree size.
  • Two of four studies (including one paired site study) in Bolivia, China, Mexico and Papua New Guinea found that logging trees in forests decreased tree species richness and diversity. One study found it increased diversity and one found no effect of logging on tree species diversity.
  • One replicated, controlled study in Canada found that logging trees in forests increased tree mortality rate.

 

Supporting evidence from individual studies

1 

A replicated, controlled study in 1996-1999 in tropical forest in Bolivia (Fredericksen & Mostacedo 2000) found that selective logging decreased trees canopy cover. Tree canopy cover was higher in unlogged plots (logged: 18%; unlogged: 98%). The number of new commercial tree stems/m2 was similar in logged (11) and unlogged plots (11). Four logged (single tree selection in 1996 and 1997 on a diameter-limit basis) and four unlogged (control) plots (1 × 1 m) were replicated in nine block over a 200 ha area. Data were collected 14 months after treatment.

 

2 

A site comparison study in temperate coniferous forest in Colorado, USA (Kaufmann, Regan & Brown 200) found that tree density was generally higher in logged compared with unlogged area. Density of trees (trees/ha) over 1.4 m tall was higher in the logged area in east and west facing (logged: 728; unlogged: 350) and flat, high altitude plots (logged: 432; unlogged: 214), but similar between areas in north facing (1153-1229), south facing (219-402) and low altitude riparian plots (379-1148). Total basal area (m2/ha) was higher in logged flat high altitude plots (logged: 19; unlogged: 11), lower in logged north facing plots (logged: 24; unlogged: 31) and similar between areas in south facing (15-16), east and west facing (18-20) and low altitude riparian plots (21-22). Data were collected in five north facing, five south facing, five east and west facing, five flat high altitude and five low altitude riparian plots (0.1 ha) in each of logged (since the late 1800s) and unlogged (since end of 19th century) study areas (4 km2).

 

3 

A site comparison study in 1990-1998 in tropical rain forest in Papua New Guinea (Lindemalm & Rogers 2001) found that high intensity logging decreased tree species diversity. Species diversity was lowest in high intensity logging (Shannon-Weiner's index: 0.85) and similar in low intensity logging (1.08) and unlogged plots (1.14). Tree species diversity was calculated in six 0.2 ha plots (200 × 10 m) in each of high intensity logging (20 m2/ha of basal area removed using conventional high impact logging technics in 1990-1991), low-intensity logging (4.2 m2/ha of basal area removed using low impact portable sawmill in 1992) and unlogged sites. Data were collected six years after treatments.

 

4 

A replicated, controlled study in 1984-1996 in temperate coniferous forest in Finland (Lähde, Eskelinen & Väänänen 2002) found that cutting treatments decreased the wood volume but not the number of trees. Tree volume (m3/ha) was higher in uncut (248) than in six cutting treatments (32-153). However, there was no difference between treatments for the number of trees/ha (uncut: 2,226; cutting treatments: 1,684-2,669) or seedlings/ha (uncut: 6,156; cutting treatments: 6,109-15,625). Four replicates of seven treatment units (1-3 ha) were established in 1984: uncut; Norway spruce Picea abies shelterwood (330 spruce trees left); Scots pine Pinus sylvestris shelterwood (220 pine trees left); mixed shelterwood (450 trees left); single-tree selection; group selection (~25 m openings); diameter cutting (>25 cm DBH). Volume and number of trees (>1.3 m tall) were monitored in 1996 in one 40 × 40 m plot in each treatment unit. Seedlings (0.1-1.3 m tall) were monitored in 1991 in 16 subplots (10 m2) within each plot.

 

5 

A site comparison study in 2000 in tropical forest in Central African Republic (Hall et al. 2003) found that selective logging decreased the density of trees and shrubs over 18 months. The densities of trees (stems/ha) and shrubs 2.5-10 cm and >10 cm diameter at breast height were lower in 18 years post-logging (trees: 2,212; shrubs: 360) than in 6 months post-logging (trees: 2,806; shrubs: 451) and unlogged treatments (trees: 2,937; shrubs: 451). Species diversities (Shannon's index) were similar in all treatments (1.89, 2.00 and 1.94 for, 6-months-post-logging and 18-years-post-logging, respectively) as well as trees and shrubs basal areas (unlogged: 30; 6 months post-logging: 30; 18 years post-logging: 24 m2/ha). Monitoring was in sixteen 30 × 30 m plots in each of three forest sections of different logging histories: unlogged, 6 month and 18 years post-logging (selective logging of timber trees).

 

6 

A site comparison study in 1958-1997 in tropical rain forest in Malaysia (Okuda et al. 2003) found that logging decreased tree height and canopy size but not their density. Unlogged plots had greater canopy height (logged: 24.8 m; unlogged: 27.4 m), canopy surface area (logged: 19,272 m2/ha; unlogged: 27,845 m2/ha) and crown size of individual trees (logged: 42.9 m2; unlogged: 94.5 m2) compared to logged plots. However, the number of stems/ha was similar between treatments (logged: 6,067; unlogged: 6,418). Data were collected in 1997 using aerial photographs in a 6 ha logged site (all trees >45 cm diameter at breast height removed in 1958) and a 50 ha unlogged site, both divided into 50 × 50 m plots.

 

7 

A site comparison study in 2000-2003 in tropical moist lower montane forest in Kenya (Hitimana, Kiyiapi & Njunge 2004) found no effect of logging on forest structure. There was no difference between logged and unlogged sites for the maximum height of trees (logged: 25-30 m; unlogged: 26-34 m), height of shrubs (logged: 2.0-2.9 m; unlogged: 2.5 m) and herbaceous layers (logged: 0.4-1.4 m; unlogged: 1.0-1.3 m). Data were collected in 0.5-1.6 ha transects within each of three logged (logged at different time intervals in 1960-1998) and two unlogged sites (no evidence for logging).

 

8 

A replicated, controlled study in 2003-2005 in temperate coniferous forest in Montana USA (Fajardo et al. 2007) found that selective cutting increased the growth rate of trees. Tree basal area increase in ten years was higher in cut (137 cm2) than in uncut plots (75 cm2). One cut plot (modified individual tree selection cutting in 1992-1993) and one uncut plot (50 × 50 to 60 × 60 m) was established at each of three sites. Trees were measured in 1992-1993 and again in 2003.

 

9 

A replicated, controlled study in boreal mixed wood forest in Alberta, Canada (Bladon et al. 2008) found that harvesting increased tree mortality rate. Annual mortality was higher in harvested than in unharvested plots for balsam poplar Populus balsamifera (harvest: 9.4%; unharvested: 2.3%), paper birch Betula papyrifera (harvested: 8.7%; unharvested: 3.1%) and trembling aspen Populus tremuloides (harvested: 5.8%; unharvested: 1.7%). Annual mortality of white spruce Picea glaucae was similar between treatments (harvested: 2.6%; unharvested: 1.1%).  Fifty five harvested (retaining 10% of the trees) and 29 unharvested plots (100 m radius) were established within a 6,900 ha area. Harvesting was in 2000, data were collected annually 2001-2005.

 

10 

A replicated, randomized, controlled study in 2001-2006 in tropical moist forest in Bolivia (Peña-Claros et al. 2009) found that increased logging and silvicultural treatment intensity increased tree growth rate. Tree annual growth rate increased from unlogged (0.32 cm) to normal logging (0.38 cm) to light silviculture (0.42 cm) to intensive silviculture (0.48 cm) treatments. Four treatment plots (27 ha) were randomly established in each of three blocks in 2001-2002: unlogged; normal-logging (regular local logging technics); light silviculture (normal-logging with additional application of low-intensity silvicultural treatments) and intensive silviculture (logged at twice the intensity of the normal-logging treatment with application of intensive silvicultural treatments). Data were collected for four years after treatment.

 

11 

A replicated, study in 2004 in temperate broadleaf forest in Ontario, Canada (Jones, Domke & Thomas 2009) found that selective harvest increased the growth rate of shade-tolerant tree species. Annual increase of stem diameter (mm) for stems of the shade-tolerant species sugar maple Acer saccharum (Before: 1.3; after: 1.4), American beech Fagus grandifolia (Before: 1.3; after: 1.7) and eastern hemlock Tsuga canadensis (Before: 1.4; after: 1.6) was higher 4-15 years after harvest than in the five years before harvest. In contrast,  for the other less shade-tolerant species black  cherry Prunus serotina, white spruce Picea glauca, red maple Acer rubrum and yellow birch Betula alleghaniensis), stem diameter increase was similar between the two time-periods (1.2-1.6 mm/year). Annual increase of stem diameter was calculated by measuring stem cores extracted in 2004 from 4,127 trees in 174 plots representing nine years of harvest (retaining 15-18 m2/ha basal area): 1984, 1989, 1992, 1994, 1997, 1998, 2001, 2002, 2003. There were 16-20 plots for each harvest year.

 

12 

A site comparison study in 2008 in temperate mixed forest in China (Su et al. 2010) found that logging decreased tree size but increased tree density, species richness and diversity 37 years later. Overall, tree basal area (unlogged: 38 m2/ha; logged: 27 m2/ha) and average diameter at breast height (unlogged: 15 cm; logged: 8 cm) were higher in unlogged forest. In contrast, the number of trees/ha (unlogged: 994; logged: 1,921), tree species richness (unlogged: 15 species/0.04 ha; logged: 18 species/0.04 ha) and diversity (Shannon's index unlogged: 3.18; logged: 3.46) were higher in the logged forest. Data were collected in 2008 in four subplots (20 × 20 m) within each of 16 plots (40 × 40 m). Eight were in logged forest (timber harvest of 30% by volume in 1988) and eight in an unlogged primary forest site.

 

13 

A site comparison study in 2006 in tropical forest in Uganda (Bonnell, Reyna-Hurtado & Chapman 2011) found that moderate and heavy logging decreased the density of tree stems. Stem density was higher in unlogged and light-logged plots (470 and 480 stems/ha respectively) than in heavy-logged plots (300 stems/ha). There was no difference to other treatments in moderate-logged plots (350 stems/ha). Trees basal area was higher in unlogged (42 m2/ha) than in moderate-logged and heavy-logged plots (23 m2/ha in both). There was no difference to other treatments in light-logged plots (33 m2/ha). Twenty six 200 × 10 m plots were marked in four sites with different logging histories: heavy-logged (n = 5); moderate-logged (n = 4); light-logged (n = 6); and unlogged (n = 11). Logging was in 1969, data werecollected in 2006.

 

14 

A paired-site study in 1996-2006 in tropical moist forest in Mexico (Gutiérrez-Granados, Pérez-Salicrup & Dirzo 2011) found that logging decreased tree species richness and diversity. The number of tree species/0.1 ha was higher in unlogged than in logged sites for trees 1-5, 5-10 and 10-25 cm diameter at breast height (268 vs 160, 156 vs 114 and 146 vs 116 respectively) but similar for trees >25 cm (54 vs 41). Species diversity (Shannon's index) was higher in unlogged than in logged sites for trees 1-5 cm diameter at breast height (3.4 vs 2.6) but similar for trees 5-10, 10-25 and >25 cm (2.7 vs 2.3, 2.6 vs 2.4 and 2.3 vs 2.1 respectively). Two pairs of logged (in 1996) and unlogged areas were located at each of three forest sites. Sampling was in 2006 in ten 50 × 20 m transects (total of 0.1 ha) in each of the six logged and six unlogged areas.

 

15 

A replicated, randomized, controlled, before-and-after study in 2000-2008 in tropical forest in Bolivia (Carreño-Rocabado et al. 2012) found no effect of logging followed by silviculture treatments on tree species richness or diversity. There was no difference between before and eight years after treatments in numbers of species/ha (unharvested: 123-122; normal logging: 132-125; light-silviculture: 130-131; intensive-silviculture: 128-130) or diversity (Shannon's index unharvested: -3.06; normal: -0.27; light-silviculture: -0.71; intensive-silviculture: -1.26). Four 27 ha plots were randomly assigned to four treatments: unharvested; normal logging (logging using reduced-impact logging techniques); light-silviculture (logging plus light silviculture); and intensive-silviculture (double logging intensity plus intensive silviculture). Trees were monitored in 2000 and 2008 (before and after treatments) in four 1 ha subplots within each treatment plot.

 

 

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.