Manage land under power lines for butterflies and moths
Overall effectiveness category Awaiting assessment
Number of studies: 6
Background information and definitions
Land under power lines offers a number of conservation opportunities. Management must maintain early successional habitats by suppressing the growth of woody species, to prevent interference with the electric lines. This could have benefits for butterflies and moths, which often favour these lightly disturbed habitats (Forrester et al. 2005). In addition, by running across the landscape, power lines may provide connectivity between other patches of suitable habitat. However, the methods used to control vegetation – primarily herbicide application or cutting – may affect the quality of the habitat created (Smallidge et al. 1996), while the frequency of management may be important for maintaining stretches of habitat in optimal conditions (Ravenscroft 2006).
For other studies on retaining or managing habitat connectivity along linear features, see “Restore or maintain species-rich grassland along road/railway verges” and “Habitat protection – Retain connectivity between habitat patches”.
Forrester J.A., Leopold D.J. & Hafner S.D. (2005) Maintaining critical habitat in a heavily managed landscape: Effects of power line corridor management on Karner blue butterfly (Lycaeides melissa samuelis) habitat. Restoration Ecology, 13, 488–498.
Ravenscroft N. (2006) Management for invertebrates in North Argyll and Lochaber: the effects of cyclical clearance of wayleaves on butterflies. Scottish Natural Heritage Commissioned Report No. 162 (ROAME No. F04LG01).
Smallidge P.J., Leopold D.J. & Allen C.M. (1996) Community characteristics and vegetation management of Karner blue butterfly (Lycaeides melissa samuelis) habitats on rights-of-way in east-central New York, USA. Journal of Applied Ecology, 33, 1405–1419.
Supporting evidence from individual studies
A site comparison study in 1990 along 16 power line rights-of-way in New York State, USA (Smallidge et al. 1996) found that the type of management used under power lines did not affect Karner blue butterfly Lycaeides melissa samuelis abundance. Karner blue population size was similar along power lines managed by cutting vegetation and those managed by applying herbicide (data presented as model results). The average number of years since management was not significantly different between sites with a large (3.3 years), small (3.0 years) or no Karner blue population (4.6 years). Sixteen power line rights-of-way were managed by applying herbicides or cutting vegetation on 3–8-year cycles, and data on at least the last two methods used at each site were available. Karner blue butterflies were surveyed at each site in 1990, and the maximum number seen during a visit was used as an estimate of population size. Sites were classified as having a large (>20 individuals), small (1–20 individuals) or no population of Karner blue butterflies.Study and other actions tested
A site comparison study in 1988–1996 along two power line rights-of-way in Wisconsin, USA (Swengel & Swengel 1997) found that one out of seven butterflies was more abundant on a right-of-way managed by mowing than on a right-of-way managed by cutting. Frosted elfin Callophrys irus were more abundant along a mown power line right-of-way (4 individuals/hour) than on a right-of-way managed by unintensive cutting (0 individuals/hour). Six other species (Olympia marble Euchloe olympia, Karner blue Lycaeides melissa samuelis, gorgone checkerspot Chlosyne gorgone, Persius duskywing Erynnis persius, Leonard’s skipper Hesperia leonardus leonardus, dusted skipper Atrytonopsis hianna) had a similar abundance on the mown and cut right-of-way (see paper for details). One power line right-of-way through pine barrens was managed by mowing, and a second was managed by unintensive cutting. Between 1988–1996, butterflies were surveyed on transects at each site, but not in every year.Study and other actions tested
A replicated, site comparison study in 2005 along 24 power lines through woodland in North Argyll and Lochaber, UK (Ravenscroft 2006) found that land under power lines managed within the last two years had more chequered skipper Carterocephalus palaemon than areas managed over four years ago, but numbers of small pearl-bordered fritillary Boloria selene were similar across time since management. In areas cut ≤2 years ago, there were more chequered skippers (1.4–1.7 individuals/minute) than in areas cut ≥4 years earlier (0.1 individuals/minute), and numbers were higher on 16–24-m-wide power lines (2.0 individuals/minute) than on 10–16-m-wide (1.3 individuals/minute) or 25–31-m-wide (1.0 individuals/minute) power lines. The number of small pearl-bordered fritillary was similar in areas cleared ≤1 year ago (1.4 individuals/minute) and 2–3 years ago (1.2 individuals/minute). Pearl-bordered fritillaries Boloria euphrosyne occurred at all four power lines cleared ≤1 year ago (0.8 individuals/minute), but at only two of 13 power lines cleared 2 years ago (0.2 individuals/minute), and were absent from ≥3-year-old clearances (statistical significance not assessed). Scrub under 24 power lines was normally cut in autumn or winter, and areas were last cut between 2000/01 and 2004/05. From May–June 2005, butterflies were surveyed weekly along one or more timed 100-m transects under each power line.Study and other actions tested
A replicated, paired, site comparison study in 2004–2006 in 15 drained pine mires under a power line in central Finland (Lensu et al. 2011, same experimental set-up as Komonen et al. 2013) found that land under power lines managed by mechanical cutting had a higher abundance and species richness of butterflies than nearby unmanaged land, and was similar to natural mires. In managed land under power lines, the abundance and species richness of both butterflies which depend on mires (abundance: 13–56 individuals/transect; richness: 4–5 species/transect) and other butterflies (abundance: 14–284 individuals/transect; richness: 6–9 species/transect), were higher than in nearby unmanaged areas (mire species: 3–8 individuals/transect, 1–2 species/transect; others: 4–50 individuals/transect, 3–4 species/transect). The abundance and species richness under power lines was also similar to natural mires (mire species: 17–43 individuals/transect, 3–5 species/transect; others: 18–107 individuals/transect, 4–5 species/transect). For 50 years, vegetation was cut every six years to maintain open, treeless habitat on drained mires under a 65-m-wide powerline, but was unmanaged next to the power line where forest developed. From June–August 2004 and June–July 2006, butterflies were surveyed every 5–10 days on paired 250-m transects within and 70 m outside the power line at 15 sites (1.5–4 ha, 0.5–18 km apart). Butterflies were also surveyed at five 2–6 ha undrained mires, 0.5–2 km from the drained mires. Butterflies which feed on plants that predominantly grow in mires were classified as mire-dependent species.Study and other actions tested
A replicated, site comparison study in 2004–2008 in 17 drained mires under a power line in central Finland (Komonen et al. 2013, same experimental set-up as Lensu et al. 2011) found that clearing trees and shrubs from under power lines increased the abundance and species richness of butterflies. Two–four years after clearing, the abundance of both mire-dependent (25–29 individuals/transect) and non-mire-dependent butterflies (103–126 individuals/transect) was higher than both one year after clearing (mire: 19 individuals/transect; non-mire: 61 individuals/transect) and 6–8 years after clearing (mire: 5–16 individuals/transect; non-mire: 6–47 individuals/transect). The species richness of non-mire butterflies was higher 1–3 years after clearing (7.4–8.1 species/transect) than 6–8 years after clearing (4.4–5.9 species/transect), but time since clearing did not affect the species richness of mire-dependent species (1–3 years: 4.0–4.4 species/transect; 6–8 years: 3.4–4.1 species/transect). See paper for individual species results. Between winter 1996–1997 and 2003–2004, seventeen drained mires (0.5–18 km apart) under a 65-m-wide power line were mechanically cleared of trees and shrubs. Ten of these sites were cleared again between winter 2004–2005 and 2007–2008. In June–July 2004 and 2006–2008, butterflies were recorded along one 250-m transect/site, 3–8 times/year at 5–10-day intervals. Two sites were only monitored in 2007 and 2008. Butterflies which feed on plants that predominantly grow in mires were classified as mire-dependent species.Study and other actions tested
A replicated, site comparison study in 2007–2008 along 52 power lines and road verges (collectively “transmission lines”) in Manitoba, Canada (Leston & Koper 2016) found that unmown transmission lines had more northern pearl crescent Phyciodes morpheus and pearl crescent Phyciodes tharos butterflies than lines mown twice/year, but mowing regime did not affect the abundance or species richness of other butterflies. There were more crescent butterflies on unmown transmission lines (2.7 individuals/visit) than on lines mown twice/year (0.1 individuals/visit). However, the abundance and species richness of other native butterflies was not significantly different between transmission lines which were not mown (abundance: 11 individuals/visit; richness: 32 species), mown once/year and not hayed (11 individuals/visit; 27 species), mown once/year and hayed (14 individuals/visit; 21 species), mown twice/year and sprayed with herbicide (10 individuals/visit; 21 species), and remnant tall-grass prairie fragments (12 individuals/visit; 20 species). See paper for species results. Fifty-two power lines and road verges (>30 m wide, >400 m long) were managed in one of four ways: 21 were neither mown nor sprayed with herbicide, but some trees were removed; 14 were mown twice/year with cuttings left on site and sprayed frequently with herbicide; 10 were mown once/year with cuttings left on site and sprayed infrequently with herbicide; seven were mown once/year with cuttings baled and removed with no spraying. Four similarly-sized remnant tall-grass prairie fragments (two urban, two rural) were managed by prescribed burning on a >3-year rotation. From 15 June–15 August 2007–2008, butterflies were surveyed on one 400- or 500-m transect at each site 2–4 times/year.Study and other actions tested