Use selective or reduced impact logging instead of conventional logging
Overall effectiveness category Awaiting assessment
Number of studies: 4
Background information and definitions
Harvesting timber within forests can be carried out by clearcutting sites or by various methods of harvesting a proportion of trees. Selective logging is the removal of selected trees within a forest based on criteria such as diameter, height, or species. Remaining trees are left in the stand, as opposed to conventional clearcutting where all trees are felled. Reduced impact logging is a sustainable harvesting and management method that aims to minimize ecological disturbance. It involves selective logging as well as other practices such as mapping large target trees prior to felling, limiting the number of trees which can be felled/hectare, pre-cutting heavy vines and controlling the direction in which trees fall to minimize collateral damage, and planning the routes of access roads to reduce disturbance (Montejo-Kovacevich et al. 2018, Ribeiro & Freitas 2012). The aim is to preserve the integrity of the forest structure, which may also be termed “continuous cover forestry” if the canopy remains intact.
For other options for harvesting timber, see “Harvest groups of trees or use thinning instead of clearcutting”, “Use patch retention harvesting instead of clearcutting”, “Use leave-tree harvesting instead of clearcutting”, “Use shelterwood harvesting instead of clearcutting” and “Retain riparian buffer strips during timber harvest”.
Montejo-Kovacevich G., Hethcoat M.G., Lim F.K.S., Marsh C.J., Bonfantti D., Peres C.A. & Edwards D.P. (2018) Impacts of selective logging management on butterflies in the Amazon. Biological Conservation, 225, 1–9.
Ribeiro D.B. & Freitas A.V.L. (2012) The effect of reduced-impact logging on fruit-feeding butterflies in Central Amazon, Brazil. Journal of Insect Conservation, 16, 733–744.
Supporting evidence from individual studies
A replicated, randomized, paired, controlled study in 1992 in three boreal forests in Lapland, Sweden (Atlegrim & Sjöberg 1996) found that bilberry Vaccinium myrtillus plants in selectively logged forests had a higher abundance of exposed moth caterpillars, but not concealed caterpillars, than clearcut forests. The abundance of exposed caterpillars (Geometridae and Noctuidae, which crawl on leaves while feeding) in selectively logged forests (2.3–3.5 individuals/m2) was higher than in clearcut forests (0.3–1.3 individuals/m2), and similar to undisturbed forests (3.0–5.7 individuals/m2). However, the abundance of concealed caterpillars (Tortricidae and Pyralidae, which spin leaves together and live between them) was not significantly different in selectively logged (0 individuals/m2), clearcut (0–0.3 individuals/m2) and undisturbed (0–1.3 individuals/m2) forests. Three forests were each divided into three 20-ha stands, which were randomly assigned to three treatments: selective logging (30% of trees and 45–50% of tree volume removed), clearcutting (all trees removed, followed by soil scarification and artificial regeneration), and undisturbed. Felling was staggered between winter 1987/88 and 1991/92. From late June–early July 1992, caterpillars feeding on bilberry were counted in three randomly placed 0.1-m2 plots in each of 10 sites within each stand.Study and other actions tested
A replicated, controlled, before-and-after study in 2007–2009 in three hardwood forests in Indiana, USA (Summerville 2011) found that timber harvesting method, including selective logging, did not affect the number of moth species, but all harvested forest stands had fewer species than unharvested stands. One year after harvesting, there was no significant difference in the number of moth species between stands subjected to single-tree harvesting (39 species), group-selection harvesting (40 species) or shelterwood harvesting and clearcutting (46 species, data not separated), but all harvested stands had fewer species than unharvested stands (56 species). One year before harvesting, all stands had a similar number of moth species (single-tree: 85; group-selection: 100; shelterwood/clearcutting: 96; unharvested: 90 species). In 2008, forest stands (3–5 ha, 150–350 m apart) in three watersheds (500 ha, 10 km apart) were logged. In one watershed, four stands had random single trees removed, and four stands were harvested by group-selection (80% of trees removed). In a second watershed, three stands were shelterwood harvested (15% of trees removed), two stands were clearcut (100% of trees removed), and three stands were unharvested (no trees removed). In the third watershed, all four stands were unharvested. All stands had been clearcut around 60 years earlier. From June–August 2007 and 2009, moths were surveyed every 14 nights (five times/year) from 8pm–7am using a black-light trap placed 2 m above the ground in the centre of each forest stand.Study and other actions tested
A site comparison study in 2007 in a rainforest in Amazon State, Brazil (Ribeiro & Freitas 2012) found that forests managed by reduced impact logging had a higher abundance, but similar species richness and diversity, of butterflies than unlogged, primary forest. In a forest managed by reduced impact logging, the abundance of butterflies (644 individuals) was higher than in an unlogged forest (447 individuals), but the species richness was not significantly different between reduced impact logging (62 species) and unlogged (54 species) forest. The diversity of butterflies was also similar between forest types (data presented as model results). See paper for individual species results. An 8,100-ha area of forest was managed under reduced impact logging for three years. Trees of 70 valuable species, >50 cm diameter at breast height, were selected and harvested by directional felling. A maximum of six trees/ha could be felled every 30 years. A 7,500-ha primary forest, which had never been logged, was also studied. From July–November 2007, butterflies were sampled for 14 days/month using 50 baited traps/forest. Traps were placed in groups of ten, 900 m apart. Within each group, traps were 100 m apart and alternated between the understorey (1.5 m above ground) and the canopy (20 m above ground). Traps were visited every 48 hours to replace bait and collect captured butterflies.Study and other actions tested
A replicated, site comparison study in 2015–2016 in 40 tropical forest sites in Rondônia, Brazil (Montejo-Kovacevich et al. 2018) found that intermediate intensity reduced impact logging (RIL) produced higher fruit-feeding butterfly (Nymphalidae) abundance, but not species richness, compared to low or high intensity RIL. Three to five years after logging, RIL sites logged at intermediate intensity had a higher abundance of butterflies (7.7 individuals/site/48 hours) than RIL sites logged at low (2.9 individuals/site/48 hours) or high (3.0 individuals/site/48 hours) intensity. Species richness was similar at intermediate (1.9 species/site/48 hours), low (1.7 species/site/48 hours) and high (1.7 species/site/48 hours) intensity RIL sites. However, community composition at logged sites was different to pristine forest (data presented as model results). From 2011–2012, reduced impact logging was conducted at 40 sites (>100 m apart, >250 m from roads or rivers). All timber trees >40 cm diameter were mapped prior to logging, and pre-felling vine cutting and directional felling were used to minimize disturbance. Logging intensity ranged from 0 (low) to 36.9 (high) m3 timber/ha (0–6 trees/ha), with intermediate logging at 18.6 m3 timber/ha. In the 2015 and 2016 dry seasons, fruit-feeding butterflies were sampled in 50-m radius plots at 40 logged sites and 20 pristine forest sites. Three baited cylindrical traps/plot were suspended 15–25 m apart, 1 m above the ground, and the surrounding undergrowth was cleared. Traps were open for 12 consecutive days, and visited every 48 hours to replace bait and record butterflies.Study and other actions tested