Clear or open patches in forests
Overall effectiveness category Awaiting assessment
Number of studies: 8
Background information and definitions
Although many species of butterflies and moths live within woodland, many are reliant upon open glades, where sunlight can reach the understorey and create warm habitat patches and encourage the growth of flowers. Traditional woodland management, such as small scale wood harvesting, which created these habitats has declined, leading to the closure of woodland canopies (Bubová et al. 2015). Opening up patches within the forest may create new habitat for these species. However, some species, especially in tropical and sub-tropical regions, are dependent on the shade provided by continuous forest cover, and may be adversely affected by canopy clearance, so caution should be taken when applying this action.
Bubová T., Vrabec V., Kulma M. & Nowicki P. (2015) Land management impacts on European butterflies of conservation concern: a review. Journal of Insect Conservation, 19, 805–821.
Supporting evidence from individual studies
A replicated, site comparison study in 1980–1984 in 12 woodlands in Kent, UK (Warren 1987) found that woodland patches cleared two to four years ago had a higher abundance of heath fritillary Mellicta athalia than areas cleared more recently or longer ago. The number of heath fritillary recorded 2–4 years after a site had been cleared (108–410 individuals/site) was higher than in the first year after clearance (9 individuals/site), or 7–11 years after clearance (2–17 individuals/site). Some populations became extinct nine years after management. Twelve woodlands were managed by clearing patches to plant conifers, 1–11 years before surveying. From 1980–1984, the number of adult heath fritillary at each site was estimated from a combination of counts on regular transects throughout the season, single counts around the peak flight period, and mark-recapture of individuals.Study and other actions tested
A replicated, site comparison study in 1986 in a mixed woodland in Dorset, UK (Robertson et al. 1988) found that managed clearings within a woodland had a higher abundance and species richness of butterflies than other areas of the wood. In managed clearings, both the abundance (89 individuals/km) and species richness (19 species) of butterflies were higher than in coppiced woodland (abundance: 25 individuals/km; richness: 16 species), unmanaged broadleaved woodland (abundance: 2 individuals/km; richness: 4 species), or conifer plantations (abundance: 5 individuals/km; richness: 2 species). See paper for individual species results. The woodland contained patches managed in four ways: managed clearings (30–50 m wide and 100–150 m long) which were cleared of scrub every three years; open woodland with coppiced hazel; unmanaged broadleaved woodland with unmanaged hazel coppice; and conifer plantation. In July–August 1986, butterflies were surveyed six times on each of twenty-two 200-m transects: four in managed clearings, eight in open, coppiced wood, six in unmanaged wood and four in conifer plantation.Study and other actions tested
A replicated, controlled, before-and-after study in 1992–1997 in 18 deciduous woods in Östergötland, Sweden (Bergman 2001) found that clearing new woodland glades increased the population size of woodland brown Lopinga achine butterflies in five out of six woods. Over 4–5 years after glades were created, the population of woodland brown increased by 93–97% in five woods where glades were created, but decreased by 19–25% in nine woods where no glades were created. However, in a sixth wood cleared later, the population decreased by 27% in the first two years after glades were created, compared to a 9% decrease over the same time period in three other woods where no glades were created. The authors noted that populations only occurred at sites with >60% canopy cover, but sites with 70–75% canopy cover had the highest population density. From 1992–1995, irregularly-shaped glades (10–30 m long) were created in six woodlands (20 in one wood, and 5–6 in each of the others). Where possible, the longest side had a south-west to north-east orientation to maximize sun exposure. In July 1992–1997, the adult population size of woodland brown butterflies was estimated in six woods where glades were created, and in 12 woods where no glades had been created.Study and other actions tested
A replicated, controlled study in 2001–2004 in an urban evergreen forest in the Kansai region, Japan (Yamamoto & Tuhara 2004) found that small cleared patches in the forest had a higher abundance and species richness of butterflies than the forest interior, but both abundance and species richness decreased with time since clearing. Two to three years after clearing, the abundance (56–142 individuals) and species richness (14–19 species) of butterflies in cleared patches was higher than in uncleared patches in the forest interior (abundance: 11 individuals; richness: 9 species). However, in the four patches cleared in the first year, abundance and species richness were higher in the year after clearing (abundance: 161 individuals; richness: 20 species) than three years after clearing (abundance: 76 individuals; richness: 18 species). In 2001 and 2002, four patches/year (15 × 15 m each) were cleared within a mature ring-cupped oak Quercus glauca and Japanese bay tree Machilus thunbergii forest (0.16–0.20 trees/m2). From April–September 2004, butterflies were surveyed three times/month in each cleared patch, and in four nearby patches of forest interior, for 10 minutes/plot. The four patches cleared in 2001 were surveyed in the same way in 2001.Study and other actions tested
A replicated, site comparison study in 2010 in six deciduous woodlands in Hampshire and Wiltshire, UK (Merckx et al. 2012) found that wide woodland rides had a lower abundance, but similar species richness, of macro-moths than standard rides and mature forest. In wide woodland rides, the abundance of macro-moths (1,926 individuals) was lower than in standard rides (2,513 individuals) and mature forest (2,479 individuals). Species richness was similar between wide (175 species) and standard (176 species) rides and mature forest (180 species). However, wide rides and coppiced woodland supported 49 species not found in standard rides or mature forest, and 124 species were more abundant in wide rides and coppiced woodland than in standard rides and mature forest, especially ‘common but severely declining’ species (see paper for details). Only 22 species were found in standard rides or mature forest but not wide rides or coppiced woodland. Within six woodlands (8–711 ha), six areas under each of six management types were studied: young (1–2 years), medium (3–6 years) and old (7–9 years) coppice, wide (>20 m) and standard (<10 m) rides, and non-coppiced mature forest. From July–October 2010, macro-moths were sampled nine times/site using a 6 W Heath actinic light trap, over 27 nights (two sites/management type sampled/night).Study and other actions tested
A review in 2015 of 126 studies in Europe (Bubová et al. 2015) reported that maintaining sparse forest stands by clearing small patches benefitted 19 out of 67 butterfly species of conservation concern. Results were not tested for statistical significance. The review reported that 23 studies found that clearing and maintaining open areas in woodland benefitted 19 butterfly species. See paper for information on individual species. Clearings were created and maintained by felling trees, suppressing the growth of seedlings in glades, grazing forests, and coppicing. The review focussed on 67 butterfly species of conservation concern. The available information was biased towards studies in Northern and Western Europe.Study and other actions tested
A replicated, site comparison study in 2016 in 10 grasslands and forest clearings in Honshū, Japan (Ohwaki et al. 2018) found that clearcut forest patches attracted a similar number of butterfly species as semi-natural grasslands. In clearcut patches, the total number of butterfly species (22 species/site) and the number of threatened butterfly species (2 species/site) were not significantly different to semi-natural grasslands (total: 26 species/site; threatened: 6 species/site). However, 15 butterfly species (including five threatened species) were observed only in grassland, compared to six species (none threatened) which occurred only in clearcuts (statistical significance not assessed). From 2008–2012, five plantation patches (aged 27–88 years, 3.1–14.7 ha, >1.8 km apart) were clearcut. Two years after cutting, larch Larix kaempferi seedlings were planted at each site, with some broadleaved deciduous and evergreen coniferous trees. For 3–5 years after planting, summer mowing was used to suppress surrounding vegetation. Five semi-natural grasslands (15–1,900 ha, >3.5 km apart) were managed by burning in early spring (three sites) or had been abandoned since the 1950s (two sites). From May–October 2016, butterflies were surveyed once/month on three 200-m transects/site (six transects on the largest grassland).Study and other actions tested
A replicated, site comparison study in 2015 in a boreal forest in Alberta, Canada (Riva et al. 2018) found that larger cleared patches in forests had a higher abundance and species richness of butterflies than undisturbed forest, but smaller cleared patches did not. The abundance and species richness of butterflies in large clearings (abundance: 65 individuals/site; richness: 13 species/site) and wide corridors (abundance: 95 individuals/site; richness: 15 species/site) was higher than in undisturbed forest (abundance: 21 individuals/site; richness: 7 species/site). However, narrow corridors (abundance: 31 individuals/site; richness: 8 species/site) were similar to undisturbed forest. Of 43 species observed, 41 had a higher abundance in cleared sites than in undisturbed forest (statistical significance of individual species results not presented, see paper for details). From 2000–2005, clearings (60 × 60 m) and corridors (3 or 9 m wide) were created in a 25-km2 area of previously undisturbed forest by removing trees. From June–August 2015, butterflies were surveyed 11 times on five 200-m transects in each type of clearing, and in undisturbed forest patches which had received no wildfire or anthropogenic disturbance within 50 m for >80 years.Study and other actions tested