Rare insects 'thriving' on harvested forestry plantations

The Forest Research survey – undertaken at Forestry and Land Scotland (FLS) sites in North Tummel Forest – looked at the importance of deadwood and early habitat on clearfell areas and found that a variety of spiders, moths, butterflies and beetles use these areas.

Amongst the rare moth species recorded were Northern Arches, Silvery Arches, Golden-rod Brindle and Cousin German; the latter is on the Scottish Biodiversity List as requiring conservation action.

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Although very little is known of its life-cycle or habitat requirements in Scotland, traps caught extraordinarily high numbers of Northern Arches– the Scottish populations of which are important on the European scale.

At the start of Insect Week 2024, FLS environment manager, Colin Edwards, said: “The presence of some of our rarest moths only goes to show how important these changing or ‘successional’ habitats are.

“As conifer plantations are adapted they increasingly incorporate a range of natural habitats that offer a refuge for many protected species.

“These plantations also provide ecological connectivity between patches of native woodland and can help many species to increase their range.

“Most people tend not to think about beetles, bugs and spiders when it comes to biodiversity but these invertebrates are like the plankton of the forest – they pretty much underpin the entire pyramid of life.”

When a site is clear felled a host of ‘pioneer’ species move in to work alongside the forest specialists, but as the vegetation changes some of these ‘pioneer’ species move on as the new canopy closes over.

For example, increased structural diversity of ground vegetation promotes spider diversity; hoverfly diversity is increased by provision of wet areas; proximity to broadleaved woodland increases moth and butterfly diversity; and more native vegetation and foodplants in open areas help sustain a variety of larvae and provide nectar sources and sunlight for adults. This temporary habitat supports important populations of some of Scotland’s rarest and most threatened butterflies and moths including, Kentish Glory, Pearl-bordered Fritillary and Chequered Skipper.

Spiders are found to inhabit clear-felled areas and early stage habitat on forestry sites (Image: Colin Edwards)

Report author and entomologist at Forest Research, Katty Baird, said: “The recording of four nationally scarce moth species including the Cousin German highlights the importance of recent clear fell and early-successional habitats in supporting some of our rarest moths.

“Clear-fell management provides important, though transient, open and scrubby habitats for 10-15 years post felling and is part of the mosaic of habitats needed to support a wide variety of insect species.”

Habitats other than the forest within plantation landscapes are important for many species with clear-fell rotations along with other open areas such as rides and wayleaves contributing the overall biodiversity within woodland and the wider landscape.

Some of the other insects to benefit from a diverse forest landscape include spiders, beetles, wasps, bees and pine hoverfly.

Tom Prescott, head of conservation at Butterfly Conservation Scotland, said: “Moths and butterflies play an important role in telling us about the health of our environment since they are widespread and found in many different habitats including harvested forestry sites.

“Their value as part of the food chain and in providing pollination services, as well as in providing cultural services, make them ideal indicator species.”