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What Works in Conservation 2018

 | 
William J. Sutherland
, 
Lynn V. Dicks
, 
Nancy Ockendon
, 
et al.

5. Forest conservation

5.4 Threat: Biological resource use

Texte intégral

5.4.1 Thinning and wood harvesting

Beneficial

● Log/remove trees within forests: effects on understory plants

1Eight of 12 studies, including four replicated, randomized, controlled studies, in India, Australia, Bolivia, Canada and the USA found that logging increased the density and cover or species richness and diversity of understory plants. Two studies found mixed and three found no effect. Assessment: beneficial (effectiveness 65%; certainty 65%; harms 10%).

2http://www.conservationevidence.com/​actions/​1273

Likely to be beneficial

● Thin trees within forests: effects on understory plants

3Twenty five of 38 studies, including 12 replicated, randomized, controlled studies, across the world found that thinning trees increased the density and cover or species richness and diversity of understory plants. Nine studies found mixed and two no effects, and one found a decrease the abundance of herbaceous species. Assessment: Likely to be beneficial (effectiveness 58%; certainty 73%; harms 13%).

4http://www.conservationevidence.com/​actions/​1211

● Thin trees within forests: effects on young trees

5Six of 12 studies, including two replicated, randomized, controlled studies, in Japan and the USA found that thinning increased the density of young trees and a study in Peru found it increased the growth rate of young trees. One study found thinning decreased the density and five found mixed or no effect on young trees. One replicated, controlled study in the USA found no effect on the density of oak acorns. Assessment: Likely to be beneficial (effectiveness 60%; certainty 65%; harms 15%).

6http://www.conservationevidence.com/​actions/​1210

● Use shelterwood harvest instead of clearcutting

7Three replicated, controlled studies in Sweden and the USA found that shelterwood harvesting increased density of trees or plant diversity, or decreased grass cover compared with clearcutting. Assessment: Likely to be beneficial (effectiveness 75%; certainty 55%; harms 15%).

8http://www.conservationevidence.com/​actions/​1214

Trade-off between benefit and harms

● Thin trees within forests: effects on mature trees

9Eleven of 12 studies, including two replicated, randomized, controlled studies, in Brazil, Canada, and the USA found that thinning trees decreased the density and cover of mature trees and in one case tree species diversity. Five of six studies, including one replicated, controlled, before-and-after study, in Australia, Sweden and the USA found that thinning increased mature tree size, the other found mixed effects. One of three studies, including two replicated controlled studies, in the USA found that thinning reduced the number of trees killed by beetles. Assessment: trade-offs between benefits and harms (effectiveness 47%; certainty 55%; harms 35%).

10http://www.conservationevidence.com/​actions/​1209

Unknown effectiveness (limited evidence)

● Log/remove trees within forests: effects on young trees

11One of two replicated controlled studies in Canada and Costa Rica found that logging increased the density of young trees, the other found mixed effects. Assessment: unknown effectiveness (effectiveness 50%; certainty 18%; harms 10%).

12http://www.conservationevidence.com/​actions/​1272

● Use partial retention harvesting instead of clearcutting

13Three studies, including one replicated, randomized, controlled study, in Canada found that using partial retention harvesting instead of clearcutting decreased the density of young trees. Assessment: unknown effectiveness (effectiveness 5%; certainty 35%; harms 45%).

14http://www.conservationevidence.com/​actions/​1215

● Use summer instead of winter harvesting

15One replicated study in the USA found no effect of logging season on plant species richness and diversity. Assessment: unknown effectiveness (effectiveness 0%; certainty 13%; harms 0%).

16http://www.conservationevidence.com/​actions/​1216

Unlikely to be beneficial

● Remove woody debris after timber harvest

17Two studies, including one replicated, randomized, controlled study, in France and the USA found no effect of woody debris removal on cover or species diversity of trees. One of six studies, including two replicated, randomized, controlled studies, in Ethiopia, Spain, Canada and the USA found that woody debris removal increased young tree density. One found that it decreased young tree density and three found mixed or no effect on density or survival. One of six studies, including two replicated, randomized, controlled studies, in the USA and France found that woody debris removal increased understory vegetation cover. Five studies found mixed or no effects on understory vegetation cover or species richness and diversity. Assessment: unlikely to be beneficial (effectiveness 23%; certainty 50%; harms 10%).

18http://www.conservationevidence.com/​actions/​1213

Likely to be ineffective or harmful

● Log/remove trees within forests: effect on mature trees

19Three of seven studies, including two replicated, controlled studies, across the world found that logging trees decreased the density and cover of mature trees. Two found it increased tree density and two found no effect. Four of nine studies, including one replicated, randomized, controlled study, across the world found that logging increased mature tree size or diversity. Four found it decreased tree size or species richness and diversity, and two found no effect on mature tree size or diversity. One replicated, controlled study in Canada found that logging increased mature tree mortality rate. Assessment: likely to be ineffective or harmful (effectiveness 35%; certainty 50%; harms 30%).

20http://www.conservationevidence.com/​actions/​1271

● Log/remove trees within forests: effect on effects on nonvascular plants

21Two of three studies, including one replicated, paired sites study, in Australia, Norway and Sweden found that logging decreased epiphytic plant abundance and fern fertility. One found mixed effects depending on species. Assessment: likely to be ineffective or harmful (effectiveness 18%; certainty 40%; harms 50%).

22http://www.conservationevidence.com/​actions/​1270

● Thin trees within forests: effects on non-vascular plants

23Three of four studies, including one replicated, randomized, controlled study, in Canada, Finland and Sweden found that thinning decreased epiphytic plant abundance and species richness. Three found mixed effects depending on thinning method and species. Assessment: likely to be ineffective or harmful (effectiveness 20%; certainty 48%; harms 50%).

24http://www.conservationevidence.com/​actions/​1212

No evidence found (no assessment)

25We have captured no evidence for the following interventions:

  • Adopt continuous cover forestry
  • Use brash mats during harvesting to avoid soil compaction

5.4.2 Harvest forest products

Unknown effectiveness (limited evidence)

● Adopt certification

26One replicated, site comparison study in Ethiopia found that deforestation risk was lower in certified than uncertified forests. One controlled, before-and-after trial in Gabon found that, when corrected for logging intensity, although tree damage did not differ, changes in above-ground biomass were smaller in certified than in uncertified forests. Assessment: unknown effectiveness (effectiveness 50%; certainty 20%; harms 3%).

27http://www.conservationevidence.com/​actions/​1150

No evidence found (no assessment)

28We have captured no evidence for the following interventions:

29• Sustainable management of non-timber products

5.4.3 Firewood

No evidence found (no assessment)

30We have captured no evidence for the following interventions:

  • Provide fuel efficient stoves
  • Provide paraffin stoves.

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