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5. FOREST CONSERVATION

© W. Sutherland et al., CC BY 4.0 https://doi.org/10.11647/OBP.0179.05

Har’el Agra, Simon Schowanek, Yohay Carmel, Rebecca K. Smith & Gidi Ne’eman

Expert assessors

Rhett Harrison, Consultative Group on International Agricultural Research, Zambia

Keith Kirby, University of Oxford, UK

Gillian Petrokofsky, Biodiversity Institute Oxford, UK

Rebecca K. Smith, University of Cambridge, UK

William J. Sutherland, University of Cambridge, UK

Tom Swinfield, Royal Society for the Protection of Birds, UK

Scope of assessment: for the conservation of forest habitat (not specific species within forests), including tropical forests, temperate forests, woodland, scrubland, shrubland and dry forests.

Assessed: 2016.

Effectiveness measure is the median % score.

Certainty measure is the median % certainty of evidence, determined by the quantity and quality of the evidence in the synopsis.

Harm measure is the median % score for negative side-effects on the forest habitat of concern.

This book is meant as a guide to the evidence available for different conservation interventions and as a starting point in assessing their effectiveness. The assessments are based on the available evidence for the target habitat for each intervention. The assessment may therefore refer to different habitat to the one(s) you are considering. Before making any decisions about implementing interventions it is vital that you read the more detailed accounts of the evidence in order to assess their relevance for your study species or system.

Full details of the evidence are available at www.conservationevidence.com

There may also be significant negative side-effects on the target habitats or other species or communities that have not been identified in this assessment.

A lack of evidence means that we have been unable to assess whether or not an intervention is effective or has any harmful impacts.

5.1 Threat: Residential and commercial development

5.1.1 Housing and urban areas

Based on the collated evidence, what is the current assessment of the effectiveness of interventions for residential and commercial development in housing and urban areas?

No evidence found (no assessment)

Compensate for woodland removal with compensatory planting

Incorporate existing trees or woods into the landscape of new developments

Provide legal protection of forests from development

We have captured no evidence for the following interventions:

5.1.2 Tourism and recreation areas

Based on the collated evidence, what is the current assessment of the effectiveness of interventions for residential and commercial development in tourism and recreation areas?

No evidence found (no assessment)

Adopt ecotourism

Create managed paths/signs to contain disturbance

Re-route paths, control access or close paths

Use warning signs to prevent fire

No evidence found (no assessment)

We have captured no evidence for the following interventions:

5.2 Threat: Agriculture

5.2.1 Livestock farming

Based on the collated evidence, what is the current assessment of the effectiveness of interventions for livestock farming?

Likely to be beneficial

Use wire fences within grazing areas to exclude livestock from specific forest sections

Trade-offs between benefit and harms

Prevent livestock grazing in forests

Unknown effectiveness (limited evidence)

Reduce the intensity of livestock grazing in forests

Shorten livestock grazing period or control grazing season in forests

No evidence found (no assessment)

Provide financial incentives not to graze

Use wire fences within grazing areas to exclude livestock from specific forest sections

Three of four studies, including one replicated, randomized, controlled study in Kenya, Israel, Mexico and Panama found that excluding livestock using wire fences increased the size, density or number of regenerating trees. One study found no effect on tree size and decreased tree density. Four of eight studies, including two replicated, randomized, controlled studies across the world found that excluding livestock using increased biomass, species richness, density or cover of understory plants. Four studies found mixed or no effects on understory plants. Assessment: likely to be beneficial (effectiveness 58%; certainty 63%; harms 18%).

http://www.conservationevidence.com/actions/1205

Prevent livestock grazing in forests

One site comparison study in Israel found that preventing cattle grazing increased the density of seedlings and saplings. Two of three studies, including one replicated, controlled study, in Brazil, Costa Rica and the UK found that preventing livestock grazing increased survival, species richness or diversity of understory plants. One study found mixed effects. Assessment: trade-offs between benefits and harms (effectiveness 69%; certainty 45%; harms 20%).

http://www.conservationevidence.com/actions/1206

Reduce the intensity of livestock grazing in forests

Two studies, including one replicated, randomized, controlled study, in the UK and Greece found that reducing grazing intensity increased the number of tree saplings or understory total weight. Assessment: unknown effectiveness (effectiveness 78%; certainty 34%; harms 0%).

http://www.conservationevidence.com/actions/1207

Shorten livestock grazing period or control grazing season in forests

One of two studies, including one replicated, controlled study, in Spain and Australia found that shortening the grazing period increased the abundance and size of regenerating trees. One found no effect native plant species richness. One replicated study in the UK found that numbers of tree seedlings were higher following summer compared to winter grazing. Assessment: unknown effectiveness (effectiveness 58%; certainty 33%; harms 0%).

http://www.conservationevidence.com/actions/1208

We have captured no evidence for the following interventions:

Based on the collated evidence, what is the current assessment of the effectiveness of interventions for transport and service corridors?

No evidence found (no assessment)

Maintain/create habitat corridors

We have captured no evidence for the following interventions:

5.4.1 Thinning and wood harvesting

Based on the collated evidence, what is the current assessment of the effectiveness of interventions for thinning and wood harvesting?

Beneficial

Log/remove trees within forests: effect on understory plants

Likely to be beneficial

Thin trees within forests: effects on understory plants

Thin trees within forests: effects on young trees

Use shelterwood harvest instead of clearcutting

Trade-offs between benefit and harms

Thin trees within forests: effects on mature trees

Unknown effectiveness (limited evidence)

Log/remove trees within forests: effects on young trees

Use partial retention harvesting instead of clearcutting

Use summer instead of winter harvesting

Unlikely to be beneficial

Remove woody debris after timber harvest

Likely to be ineffective or harmful

Log/remove trees within forests: effect on mature trees

Log/remove trees within forests: effect on non-vascular plants

Thin trees within forests: effect on non-vascular plants

No evidence found (no assessment)

Adopt continuous cover forestry

Use brash mats during harvesting to avoid soil compaction

Log/remove trees within forests: effects on understory plants

Eight 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%).

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

Thin trees within forests: effects on understory plants

Twenty 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%).

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

Thin trees within forests: effects on young trees

Six 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%).

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

Use shelterwood harvest instead of clearcutting

Three 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%).

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

Thin trees within forests: effects on mature trees

Eleven 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%).

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

Log/remove trees within forests: effects on young trees

One 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%).

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

Use partial retention harvesting instead of clearcutting

Three 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%).

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

Use summer instead of winter harvesting

One 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%).

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

Remove woody debris after timber harvest

Two 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%).

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

Log/remove trees within forests: effect on mature trees

Three 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%).

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

Log/remove trees within forests: effect on effects on non-vascular plants

Two 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%).

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

Thin trees within forests: effects on non-vascular plants

Three 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%).

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

We have captured no evidence for the following interventions:

5.4.2 Harvest forest products

Based on the collated evidence, what is the current assessment of the effectiveness of interventions for harvesting forest products?

Unknown effectiveness (limited evidence)

Adopt certification

No evidence found (no assessment)

Sustainable management of non-timber products

Adopt certification

One 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%).

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

We have captured no evidence for the following interventions:

5.4.3 Firewood

Based on the collated evidence, what is the current assessment of the effectiveness of interventions for firewood?

No evidence found (no assessment)

Provide fuel efficient stoves

Provide paraffin stoves

We have captured no evidence for the following interventions:

5.5 Habitat protection

5.5.1 Changing fire frequency

Based on the collated evidence, what is the current assessment of the effectiveness of interventions for changing fire frequency?

Trade-offs between benefit and harms

Use prescribed fire: effect on understory plants

Use prescribed fire: effect on young trees

Likely to be ineffective or harmful

Use prescribed fire: effect on mature trees

No evidence found (no assessment)

Mechanically remove understory vegetation to reduce wildfires

Use herbicides to remove understory vegetation to reduce wildfires

Use prescribed fire: effect on understory plants

Eight of 22 studies, including seven replicated, randomized, controlled studies, in Australia, Canada and the USA found that prescribed fire increased the cover, density or biomass of understory plants. Six found it decreased plant cover and eight found mixed or no effect on cover or density. Fourteen of 24 studies, including 10 replicated, randomized, controlled studies, in Australia, France, West Africa and the USA found that fire increased species richness and diversity of understory plants. One found it decreased species richness and nine found mixed or no effect on understory plants. Assessment: trade-offs between benefits and harms (effectiveness 55%; certainty 70%; harms 25%).

http://www.conservationevidence.com/actions/1221

Use prescribed fire: effect on young trees

Five of 15 studies, including four replicated, randomized, controlled studies, in France, Canada and the USA found that prescribed fire increased the density and biomass of young trees. Two found that fire decreased young tree density. Eight found mixed or no effect on density and two found mixed effects on species diversity of young trees. Two replicated, controlled studies in the USA found mixed effects of prescribed fire on young tree survival. Assessment: trade-offs between benefits and harms (effectiveness 45%; certainty 55%; harms 23%).

http://www.conservationevidence.com/actions/1220

Use prescribed fire: effect on mature trees

Four of nine studies, including two replicated, randomized, controlled studies, in the USA found that prescribed fire decreased mature tree cover, density or diversity. Two studies found it increased tree cover or size, and four found mixed or no effect. Seven studies, including one replicated, randomized, controlled study, in the USA found that fire increased mature tree mortality. Assessment: likely to be ineffective or harmful (effectiveness 25%; certainty 50%; harms 50%).

http://www.conservationevidence.com/actions/1217

We have captured no evidence for the following interventions:

5.5.2 Water management

Based on the collated evidence, what is the current assessment of the effectiveness of interventions for water management?

No evidence found (no assessment)

Construct water detention areas to slow water flow and restore riparian forests

Introduce beavers to impede water flow in forest watercourses

Recharge groundwater to restore wetland forest

We have captured no evidence for the following interventions:

5.5.3 Changing disturbance regime

Based on the collated evidence, what is the current assessment of the effectiveness of interventions for changing the disturbance regime?

Trade-offs between benefit and harms

Use clearcutting to increase understory diversity

Use group-selection harvesting

Use shelterwood harvesting

Unknown effectiveness (limited evidence)

Thin trees by girdling (cutting rings around tree trunks)

Use herbicides to thin trees

Unlikely to be beneficial

Use thinning followed by prescribed fire

No evidence found (no assessment)

Adopt conservation grazing of woodland

Coppice trees

Halo ancient trees

Imitate natural disturbances by pushing over trees

Pollard trees (top cutting or top pruning)

Reintroduce large herbivores

Retain fallen trees

Use clearcutting to increase understory diversity

Three of nine studies, including four replicated, randomized, controlled studies, in Australia, Japan, Brazil, Canada and the USA found that clearcutting decreased density, species richness or diversity of mature trees. One study found it increased trees species richness and six found mixed or no effect or mixed effect on density, size, species richness or diversity. One replicated, randomized, controlled study in Finland found that clearcutting decreased total forest biomass, particularly of evergreen shrubs. Three of six studies, including five replicated, randomized, controlled studies, in Brazil, Canada and Spain found that clearcutting increased the density and species richness of young trees. One found it decreased young tree density and two found mixed or no effect. Eight of 12 studies, including three replicated, randomized, controlled studies, across the world found that clearcutting increased the cover or species richness of understory plants. Two found it decreased density or species richness, and two found mixed or no effect. Assessment: trade-offs between benefits and harms (effectiveness 63%; certainty 65%; harms 30%).

http://www.conservationevidence.com/actions/1222

Use group-selection harvesting

Four of eight studies, including one replicated, controlled study, in Australia, Canada, Costa Rica and the USA found that group-selection harvesting increased cover or diversity of understory plants, or the density of young trees. Two studies found it decreased understory species richness or and biomass. Three studies found no effect on understory species richness or diversity or tree density or growth-rate. Assessment: trade-offs between benefits and harms (effectiveness 50%; certainty 58%; harms 30%).

http://www.conservationevidence.com/actions/1224

Use shelterwood harvesting

Six of seven studies, including five replicated, controlled studies, in Australia, Iran, Nepal and the USA found that shelterwood harvesting increased abundance, species richness or diversity or understory plants, as well as the growth and survival rate of young trees. One study found shelterwood harvesting decreased plant species richness and abundance and one found no effect on abundance. One replicated, controlled study in Canada found no effect on oak acorn production. Assessment: trade-offs between benefits and harms (effectiveness 78%; certainty 70%; harms 28%).

http://www.conservationevidence.com/actions/1223

Thin trees by girdling (cutting rings around tree trunks)

One before-and-after study in Canada found that thinning trees by girdling increased understory plant species richness, diversity and cover. Assessment: unknown effectiveness — limited evidence (effectiveness 58%; certainty 13%; harms 0%).

http://www.conservationevidence.com/actions/1226

Use herbicides to thin trees

One replicated, controlled study in Canada found no effect of using herbicide to thin trees on total plant species richness. Assessment: unknown effectiveness — limited evidence (effectiveness 5%; certainty 13%; harms 0%).

http://www.conservationevidence.com/actions/1225

Use thinning followed by prescribed fire

Three of six studies, including one replicated, randomized, controlled study, in the USA found that thinning followed by prescribed fire increased cover or abundance of understory plants, and density of deciduous trees. One study found it decreased tree density and species richness. Three studies found mixed or no effect or mixed effect on tree growth rate or density of young trees. One replicated, controlled study Australia found no effect of thinning then burning on the genetic diversity of black ash. Assessment: unlikely to be beneficial (effectiveness 35%; certainty 40%; harms 15%).

http://www.conservationevidence.com/actions/1227

We have captured no evidence for the following interventions:

5.6 Threat: Invasive and other problematic species

5.6.1 Invasive plants

Based on the collated evidence, what is the current assessment of the effectiveness of interventions for invasive plants?

Unknown effectiveness (limited evidence)

Manually/mechanically remove invasive plants

Use herbicides to remove invasive plant species

No evidence found (no assessment)

Use grazing to remove invasive plant species

Use prescribed fire to remove invasive plant species

Manually/mechanically remove invasive plants

Two replicated, controlled studies in Hawaii and Ghana found that removing invasive grass or weed species increased understory plant biomass or tree seedling height. Two replicated, controlled studies in the USA and Hawaii found no effect of removing invasive shrubs or plants on understory plant diversity or growth rate of native species. Assessment: unknown effectiveness — limited evidence (effectiveness 40%; certainty 33%; harms 15%).

http://www.conservationevidence.com/actions/1228

Use herbicides to remove invasive plant species

One replicated, randomized, controlled study in the USA found no effect of controlling invasive plants using herbicide on native plant species richness. Assessment: unknown effectiveness — limited evidence (effectiveness 5%; certainty 10%; harms 0%).

http://www.conservationevidence.com/actions/1229

We have captured no evidence for the following interventions:

5.6.2 Native plants

Based on the collated evidence, what is the current assessment of the effectiveness of interventions for native plants?

No evidence found (no assessment)

Manually/mechanically remove native plants

We have captured no evidence for the following interventions:

5.6.3 Herbivores

Based on the collated evidence, what is the current assessment of the effectiveness of interventions for herbivores?

Likely to be beneficial

Use wire fences to exclude large native herbivores

Unknown effectiveness (limited evidence)

Use electric fencing to exclude large native herbivores

No evidence found (no assessment)

Control large herbivore populations

Control medium-sized herbivores

Use fencing to enclose large herbivores (e.g. deer)

Use wire fences to exclude large native herbivores

Two replicated, controlled studies in the USA found that excluding large herbivores increased tree density. One of three studies, including two replicated, paired-sites, before-and-after studies, in Canada, Bhutan and Ireland found that excluding large herbivores increased the biomass of young trees. One found it decreased the density of young trees and one found mixed effects on species. Five of 10 studies, including two replicated, randomized, controlled studies, across the world found that excluding large herbivores increased the cover or and size of understory plants. Six found no effect on the cover, seed density, species richness or diversity of understory plants. Assessment: Likely to be beneficial (effectiveness 50%; certainty 65%; harms 10%).

http://www.conservationevidence.com/actions/1230

Use electric fencing to exclude large native herbivores

One controlled study in South Africa found that using electric fencing to exclude elephants and nyalas increased tree density. Assessment: Unknown effectiveness (effectiveness 65%; certainty 10%; harms 0%).

http://www.conservationevidence.com/actions/1231

We have captured no evidence for the following interventions:

5.6.4 Rodents

Based on the collated evidence, what is the current assessment of the effectiveness of interventions for rodents?

Unknown effectiveness (limited evidence)

Control rodents

Control rodents

One controlled study in New Zealand found that rodent control decreased native plant species richness and had no effect on total plant species richness. Assessment: unknown effectiveness — limited evidence (effectiveness 10%; certainty 10%; harms 50%).

http://www.conservationevidence.com/actions/1232

5.6.5 Birds

Based on the collated evidence, what is the current assessment of the effectiveness of interventions for birds?

Unknown effectiveness (limited evidence)

Control birds

Control birds

One controlled study in Australia found that removing birds did not improve the health of the trees in a narrow-leaved peppermint forest. Assessment: unknown effectiveness — limited evidence (effectiveness 0%; certainty 15%; harms 0%).

http://www.conservationevidence.com/actions/1151

5.7 Threat: Pollution

Based on the collated evidence, what is the current assessment of the effectiveness of interventions for pollution?

Unknown effectiveness (limited evidence)

Maintain/create buffer zones

No evidence found (no assessment)

Remove nitrogen and phosphorus using harvested products

Maintain/create buffer zones

One site comparison study in Australia found that a forest edge protected by a planted buffer strip had higher canopy cover and lower stem density, but similar understory species richness to an unbuffered forest edge. Assessment: unknown effectiveness — limited evidence (effectiveness 50%; certainty 10%; harms 0%).

http://www.conservationevidence.com/actions/1168

We have captured no evidence for the following interventions:

5.8 Threat: Climate change and severe weather

Based on the collated evidence, what is the current assessment of the effectiveness of interventions for climate change and severe weather?

No evidence found (no assessment)

Prevent damage from strong winds

We have captured no evidence for the following interventions:

5.9 Habitat protection

Based on the collated evidence, what is the current assessment of the effectiveness of interventions for habitat protection?

Unknown effectiveness (limited evidence)

Adopt community-based management to protect forests

● Legal protection of forests

No evidence found (no assessment)

Adopt Protected Species legislation (impact on forest management)

Adopt community-based management to protect forests

Two studies, including one replicated, before-and-after, site comparison, in Ethiopia and Nepal found that forest cover increased more in community-managed forests than in forests not managed by local communities. However, one replicated, site comparison study in Colombia found that deforestation rates in community-managed forests did not differ from deforestation rates in unmanaged forests. Assessment: unknown effectiveness — limited evidence (effectiveness 60%; certainty 35%; harms 0%).

http://www.conservationevidence.com/actions/1152

Legal protection of forests

Two site comparison studies in Nigeria and Iran found that legal protection of forest increased tree species richness and diversity or the density of young trees. One replicated, paired site study in Mexico found no effect of forest protection on seed density and diversity of trees and shrubs. Assessment: unknown effectiveness — limited evidence (effectiveness 50%; certainty 20%; harms 0%).

http://www.conservationevidence.com/actions/1233

We have captured no evidence for the following interventions:

5.10.1 Restoration after wildfire

Based on the collated evidence, what is the current assessment of the effectiveness of interventions for restoration after wildfire?

Trade-offs between benefit and harms

Thin trees after wildfire

Unknown effectiveness (limited evidence)

Remove burned trees

Likely to be ineffective or harmful

Sow tree seeds after wildfire

No evidence found (no assessment)

Plant trees after wildfire

Thin trees after wildfire

Four of five replicated, controlled studies in Spain, Israel, Cananda and the USA found that thinning trees in burnt forest areas increased plant species richness, cover or survival of saplings. One study found thinning decreased plant biomass. One paired-site study in Canada found that logging after wildfire decreased species richness and diversity of mosses. Assessment: trade-offs between benefits and harms (effectiveness 50%; certainty 50%; harms 38%).

http://www.conservationevidence.com/actions/1234

Remove burned trees

Two replicated, controlled studies in Israel and Spain found that removing burned trees increased total plant species richness or the cover and species richness of some plant species. Assessment: unknown effectiveness (effectiveness 60%; certainty 20%; harms 25%).

http://www.conservationevidence.com/actions/1237

Sow tree seeds after wildfire

Three studies, including one replicated, randomized, controlled study, in the USA found that sowing herbaceous plant seeds in burnt forest areas decreased the density of tree seedlings or the number and cover of native species. All three found no effect of seeding on total plant cover or species richness. Assessment: likely to be ineffective or harmful (effectiveness 0%; certainty 43%; harms 40%).

http://www.conservationevidence.com/actions/1236

We have captured no evidence for the following interventions:

5.10.2 Restoration after agriculture

Based on the collated evidence, what is the current assessment of the effectiveness of interventions for restoration after agriculture?

Unknown effectiveness (limited evidence)

Restore wood pasture (e.g. introduce grazing)

Restore wood pasture (e.g. introduce grazing)

One replicated paired study in Sweden found that partial harvesting in abandoned wood pastures increased tree seedling density, survival and growth. Assessment: unknown effectiveness (effectiveness 65%; certainty 25%; harms 0%).

http://www.conservationevidence.com/actions/1164

5.10.3 Manipulate habitat to increase planted tree survival during restoration

Based on the collated evidence, what is the current assessment of the effectiveness of interventions for manipulating habitat to increase planted tree survival during restoration?

Unknown effectiveness (limited evidence)

Apply herbicides after restoration planting

Cover the ground using techniques other than plastic mats after restoration planting

Cover the ground with plastic mats after restoration planting

Use selective thinning after restoration planting

Apply herbicides after restoration planting

One replicated, randomized, controlled study in the USA found that controlling vegetation using herbicides after restoration planting decreased plant species richness and diversity. Assessment: unknown effectiveness (effectiveness 45%; certainty 25%; harms 40%).

http://www.conservationevidence.com/actions/1241

Cover the ground using techniques other than plastic mats after restoration planting

One replicated, randomized, controlled study in the USA found that covering the ground with mulch after planting increased total plant cover. Assessment: unknown effectiveness (effectiveness 30%; certainty 15%; harms 10%).

http://www.conservationevidence.com/actions/1240

Cover the ground with plastic mats after restoration planting

One replicated study in Canada found that covering the ground with plastic mats after restoration planting decreased the cover of herbecous plants and grasses. Assessment: unknown effectiveness (effectiveness 40%; certainty 20%; harms 0%).

http://www.conservationevidence.com/actions/1239

Use selective thinning after restoration planting

One replicated, paired sites study in Canada found that selective thinning after restoration planting conifers increased the abundance of herbaceous species. Assessment: unknown effectiveness (effectiveness 43%; certainty 18%; harms 0%).

http://www.conservationevidence.com/actions/1238

5.10.4 Restore forest community

Based on the collated evidence, what is the current assessment of the effectiveness of interventions for restoring a forest community?

Unknown effectiveness (limited evidence)

Build bird-perches to enhance natural seed dispersal

Plant a mixture of tree species to enhance diversity

Sow tree seeds

Water plants to preserve dry tropical forest species

No evidence found (no assessment)

Restore woodland herbaceous plants using transplants and nursery plugs

Use rotational grazing to restore oak savannas

Build bird-perches to enhance natural seed dispersal

One replicated, randomized, controlled, before-and-after study in Brazil found that sowing tree seeds increased the density and species richness of new trees. Assessment: unknown effectiveness (effectiveness 50%; certainty 13%; harms 0%).

http://www.conservationevidence.com/actions/1245

Plant a mixture of tree species to enhance diversity

One replicated, randomized, controlled study in Brazil found that planting various tree species increased species richness, but had no effect on the density of new trees. One replicated, controlled study in Greece found that planting native tree species increased total plant species richness, diversity and cover. Assessment: unknown effectiveness (effectiveness 50%; certainty 28%; harms 0%).

http://www.conservationevidence.com/actions/1243

Sow tree seeds

One replicated, randomized, controlled, before-and-after study in Brazil found that sowing tree seeds increased the density and species richness of new trees. Assessment: unknown effectiveness (effectiveness 60%; certainty 13%; harms 0%).

http://www.conservationevidence.com/actions/1244

Water plants to preserve dry tropical forest species

One replicated, controlled study in Hawaii found that watering plants increased the abundance and biomass of forest plants. Assessment: unknown effectiveness (effectiveness 65%; certainty 18%; harms 0%).

http://www.conservationevidence.com/actions/1242

We have captured no evidence for the following interventions:

5.10.5 Prevent/encourage leaf litter accumulation

Based on the collated evidence, what is the current assessment of the effectiveness of interventions for preventing/encouraging leaf litter accumulation?

Unknown effectiveness (limited evidence)

Remove or disturb leaf litter to enhance germination

No evidence found (no assessment)

Encourage leaf litter development in new planting

Remove or disturb leaf litter to enhance germination

One of two replicated, controlled studies in Poland and Costa Rica found that removing leaf litter increased understory plant species richness. The two studies found that removal decreased understory plant cover or the density of new tree seedlings. Assessment: unknown effectiveness (effectiveness 40%; certainty 25%; harms 23%).

http://www.conservationevidence.com/actions/1246

We have captured no evidence for the following interventions:

5.10.6 Increase soil fertility

Based on the collated evidence, what is the current assessment of the effectiveness of interventions for increasing soil fertility?

Likely to be beneficial

Use vegetation removal together with mechanical disturbance to the soil

Trade-offs between benefit and harms

Add organic matter

Use fertilizer

Use soil scarification or ploughing to enhance germination

Unknown effectiveness (limited evidence)

Add lime to the soil to increase fertility

Use soil disturbance to enhance germination (excluding scarification or ploughing)

Likely to be ineffective or harmful

Enhance soil compaction

Use vegetation removal together with mechanical disturbance to the soil

Three studies, including one replicated, randomized, controlled study, in Portugal and France found that vegetation removal together with mechanical disturbance of the soil increased the cover or diversity of understory plants, or density of young trees. One of the studies found it decreased understory shrub cover. Assessment: Likely to be beneficial (effectiveness 61%; certainty 40%; harms 15%).

http://www.conservationevidence.com/actions/1274

Add organic matter

One of two studies, including one replicated, randomized, controlled study, in Brazil and Costa Rica found that adding leaf litter increased species richness of young trees. One found it decreased young tree density in artificial forest gaps and both found no effect on the density of tree regenerations under intact forest canopy. One of two replicated, controlled study in Portugal and the USA found that adding plant material increased total plant cover. One found mixed effects on cover depending on plant group. Assessment: trade-offs between benefits and harms (effectiveness 45%; certainty 43%; harms 28%).

http://www.conservationevidence.com/actions/1250

Use fertilizer

Six of eight studies, including five replicated, randomized, controlled, in Europe, Brazil, Australia and the USA found that applying fertilizer increased total plant cover, understory plant biomass, size of young trees, biomass of grasses or cover of artificially seeded plant species. Five of the studies found no effect on plant biomass, cover, seedling abundance, tree growth or tree seedling diversity. Assessment: trade-offs between benefits and harms (effectiveness 55%; certainty 65%; harms 25%).

http://www.conservationevidence.com/actions/1248

Use soil scarification or ploughing to enhance germination

Two studies, including one replicated, randomized, controlled study, in Portugal and the USA found that ploughing increased the cover or diversity of understory plants. Two of five studies, including two replicated, randomized, controlled, in Canada, Brazil, Ethiopia and Sweden found that ploughing increased the density of young trees. One found a decrease in density and two found mixed effects depending on 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. Assessment: unknown effectiveness (effectiveness 60%; certainty 50%; harms 25%).

http://www.conservationevidence.com/actions/1251

Add lime to the soil to increase fertility

One replicated, randomized controlled study in the USA found that adding lime increased vegetation cover. Assessment: unknown effectiveness (effectiveness 80%; certainty 18%; harms 0%).

http://www.conservationevidence.com/actions/1249

Use soil disturbance to enhance germination (excluding scarification or ploughing)

Two replicated, controlled studies in Canada and Finland found that disturbance of the forest floor decreased understory vegetation cover. Assessment: unknown effectiveness (effectiveness 30%; certainty 35%; harms 40%).

http://www.conservationevidence.com/actions/1252

Enhance soil compaction

Two of three studies, including two replicated, randomized, controlled studies in Canada and the USA found that soil compaction increased understory plant cover and density. Two found it decreased tree regeneration height or density and understory plant species richness. Assessment: likely to be ineffective or harmful (effectiveness 28%; certainty 40%; harms 45%).

http://www.conservationevidence.com/actions/1253

5.11 Actions to improve survival and growth rate of planted trees

Based on the collated evidence, what is the current assessment of the effectiveness of interventions to improve the survival and growth rate of planted trees?

Beneficial

Prepare the ground before tree planting

Use mechanical thinning before or after planting

Likely to be beneficial

Fence to prevent grazing after tree planting

Use herbicide after tree planting

Trade-offs between benefit and harms

Use prescribed fire after tree planting

Unknown effectiveness (limited evidence)

Apply insecticide to protect seedlings from invertebrates

Add lime to the soil after tree planting

Add organic matter after tree planting

Cover the ground with straw after tree planting

Improve soil quality after tree planting (excluding applying fertilizer)

Manage woody debris before tree planting

Use shading for planted trees

Use tree guards or shelters to protect planted trees

Use weed mats to protect planted trees

Water seedlings

Unlikely to be beneficial

Mechanically remove understory vegetation after tree planting

Use different planting or seeding methods

Use fertilizer after tree planting

No evidence found (no assessment)

Apply fungicide to protect seedlings from fungal diseases

Infect tree seedlings with mycorrhizae

Introduce leaf litter to forest stands

Plant a mixture of tree species to enhance the survival and growth of planted trees

Reduce erosion to increase seedling survival

Transplant trees

Use pioneer plants or crops as nurse-plants

Prepare the ground before tree planting

Six of seven studies, including five replicated, randomized, controlled studies, in Canada and Sweden found that ground preparation increased the survival or growth rate of planted trees. One study found no effect of creating mounds on frost damage to seedlings. Assessment: beneficial (effectiveness 78%; certainty 73%; harms 0%).

http://www.conservationevidence.com/actions/1263

Use mechanical thinning before or after planting

Five of six studies, including two replicated, randomized, controlled studies, in Brazil, Canada, Finland, France and the USA found that thinning trees after planting increased survival or size of planted trees. One study found mixed effects on survival and size and one found it decreased their density. One replicated study in the USA found that seedling survival rate increased with the size of the thinned area. Assessment: beneficial (effectiveness 75%; certainty 63%; harms 10%).

http://www.conservationevidence.com/actions/1261

Fence to prevent grazing after tree planting

Four of five studies, including two replicated, randomized, controlled studies, in Finland, Australia, Canada and the USA found that using fences to exclude grazing increased the survival, size or cover of planted trees. Two studies found no effect on survival rate and one found mixed effects on planted tree size. Assessment: Likely to be beneficial (effectiveness 70%; certainty 50%; harms 0%).

http://www.conservationevidence.com/actions/1254

Use herbicide after tree planting

Two of three studies, including two replicated, randomized, controlled studies, in Sweden and the USA found that using herbicide increased the size of planted trees. One study found no effect. One replicated, randomized, controlled study in Sweden found no effect of using herbicide on frost damage to seedlings. Assessment: unlikely to be beneficial (effectiveness 58%; certainty 45%; harms 0%).

http://www.conservationevidence.com/actions/1262

Use prescribed fire after tree planting

Two of four studies, including one replicated, randomized, controlled study, in Finland, France and the USA found that using prescribed fire after planting increased the survival and sprouting rate of planted trees. One study found fire decreased planted tree size and one found no effect on the size and survival rate. Assessment: trade-offs between benefits and harms (effectiveness 50%; certainty 43%; harms 20%).

http://www.conservationevidence.com/actions/1255

Apply insecticide to protect seedlings from invertebrates

One randomized, replicated, controlled study in the USA found that applying insecticide increased tree seedling emergence and survival. Assessment: unknown effectiveness (effectiveness 70%; certainty 13%; harms 0%).

http://www.conservationevidence.com/actions/1149

Add lime to the soil after tree planting

One of two replicated, randomized, controlled studies in the USA found that adding lime before restoration planting decreased the survival of pine seedlings. One found no effect on seedling growth. Assessment: unknown effectiveness (effectiveness 0%; certainty 30%; harms 50%).

http://www.conservationevidence.com/actions/1259

Add organic matter after tree planting

Two replicated, randomized, controlled studies in the USA found that adding organic matter before restoration planting increased seedling biomass, but decreased seedling emergence or survival. Assessment: unknown effectiveness (effectiveness 20%; certainty 25%; harms 50%).

http://www.conservationevidence.com/actions/1258

Cover the ground with straw after tree planting

One replicated, randomized, controlled study in the Czech Republic found that covering the ground with straw, but not bark or fleece, increased the growth rate of planted trees and shrubs. Assessment: unknown effectiveness (effectiveness 75%; certainty 20%; harms 0%).

http://www.conservationevidence.com/actions/1266

Improve soil quality after tree planting (excluding applying fertilizer)

Two randomized, replicated, controlled studies in Australia found that different soil enhancers had mixed or no effects on tree seedling survival and height, and no effect on diameter or health. Assessment: unknown effectiveness (effectiveness 25%; certainty 23%; harms 13%).

http://www.conservationevidence.com/actions/1153

Manage woody debris before tree planting

One replicated, randomized, controlled study in Canada found that removing woody debris increased the survival rate of planted trees. One replicated, controlled study in the USA found mixed effects on the size of planted trees. Assessment: unknown effectiveness (effectiveness 40%; certainty 25%; harms 13%).

http://www.conservationevidence.com/actions/1257

Use shading for planted trees

One replicated, controlled study in Panama found that shading increased the survival rate of planted native tree seedlings. Assessment: unknown effectiveness (effectiveness 85%; certainty 23%; harms 0%).

http://www.conservationevidence.com/actions/1269

Use tree guards or shelters to protect planted trees

One replicated, randomized, controlled study in the USA found that using light but not dark coloured plastic tree shelters increased the survival rate of planted tree seedlings. One replicated, controlled study in Hong Kong found that tree guards increased tree height after 37 but not 44 months. Assessment: unknown effectiveness (effectiveness 60%; certainty 28%; harms 20%).

http://www.conservationevidence.com/actions/1268

Use weed mats to protect planted trees

One replicated, controlled study in Hong Kong found no effect of using weed mats on seedling height. Assessment: unknown effectiveness (effectiveness 0%; certainty 18%; harms 0%).

http://www.conservationevidence.com/actions/1267

Water seedlings

One replicated, randomized, controlled study in Spain found that watering seedlings increased or had no effect on seedling emergence and survival, depending on habitat and water availability. Assessment: unknown effectiveness (effectiveness 45%; certainty 20%; harms 0%).

http://www.conservationevidence.com/actions/1154

Mechanically remove understory vegetation after tree planting

Four of five studies, including three replicated, randomized, controlled studies in France, Sweden, Panama, Canada and the USA found no effect of controlling understory vegetation on the emergence, survival, growth rate or frost damage of planted seedlings. One found that removing shrubs increased the growth rate and height of planted seedlings, and another that removing competing herbs increased seedling biomass. Assessment: unlikely to be beneficial (effectiveness 20%; certainty 50%; harms 0%).

http://www.conservationevidence.com/actions/1256

Use different planting or seeding methods

Four studies, including one replicated, randomized study, in Australia, Brazil, Costa Rica and Mexico found no effect of planting or seeding methods on the size and survival rate of seedlings. One replicated, controlled study in Brazil found that planting early succession pioneer tree species decreased the height of other planted species. Assessment: unlikely to be beneficial (effectiveness 0%; certainty 43%; harms 13%).

http://www.conservationevidence.com/actions/1264

Use fertilizer after tree planting

Two of five studies, including two randomized, replicated, controlled studies, in Canada, Australia, France and Portugal found that applying fertilizer after planting increased the size of the planted trees. Three studies found no effect on the size, survival rate or health of planted trees. One randomized, replicated, controlled study in Australia found that soil enhancers including fertilizer had mixed effects on seedling survival and height. Assessment: unlikely to be beneficial (effectiveness 38%; certainty 45%; harms 3%).

http://www.conservationevidence.com/actions/1260

We have captured no evidence for the following interventions:

5.12 Education and awareness raising

Based on the collated evidence, what is the current assessment of the effectiveness of interventions to improve education and awareness raising?

No evidence found (no assessment)

Provide education programmes about forests

Raise awareness amongst the general public through campaigns and public information

We have captured no evidence for the following interventions: