Some woodland management practices may improve structural diversity and benefit bats and other species, but our understanding of responses to alternative woodland management techniques remains limited. This paper addresses this knowledge gap for bats.
Conifer woodland covers 1.6 million hectares of the UK and is an important source of economic revenue. There is increasing recognition that commercial forests should deliver other benefits beyond timber production, including the provision of ecosystem services and habitat for biodiversity.
Plantations are often considered to be poor for bats because they typically show only limited structural diversity - the trees typically being the same age and height, etc. Some woodland management practices - notably irregular silviculture - may improve structural diversity and benefit bats and other species. Irregular silviculture involves the selective removal of individual trees or the felling of small groups of trees, and the maintenance of a permanent and irregular canopy. The practice is likely to benefit species associated with mature forest, small scale disturbances and specific habitat features (such as open canopy).
Using passive acoustic monitoring, the authors were able to record bat activity at two sites in southern England. Alongside this, data were collected on the habitat characteristics of a series of woodland plots at these sites, the plots varying in the type of management used. Some 13 bat species were recorded, including rare species like Barbastelle and the two horseshoe bats (Greater and Lesser).
Bat species richness and the activity of individual bat species were significantly influenced by seven structural variables describing the woodland habitat. For example, the activity levels of Common Pipistrelle and Soprano Pipipistrelle were strongly associated with plots that had greater canopy openness, and also showed higher levels of activity in plots with more deadwood snags and greater quantities of fallen deadwood.
The study helps us understand how bats respond to different approaches to the management of conifer plantations, and again underlines the valuable role that acoustic monitoring can play in answering key questions about how we manage land and its implications for biodiversity.
Conifer plantations are a major land use globally and provide a range of social, economic and environmental benefits, particularly the provision of timber. There is a growing interest in alternative forestry techniques, such as irregular silviculture, to create more sustainable and resilient plantations in response to climate change. Plantations are often considered poor for bats due to limited structural diversity. Irregular forestry increases structural diversity and reduces growing stocks, with potentially positive effects on bats, but this remains poorly understood in conifer plantations. At two estates in south-west Britain, we specifically tested whether bat species richness and activity respond to (1) the surrounding landscape cover types (2) habitat structure within irregular stands and (3) increasing progress along the transformation continuum in three continuous cover forestry stands undergoing transformation including irregular high forest. Stands further progressed along the transformation continuum had lower basal area, higher mean tree diameter, higher levels of fallen deadwood and greater canopy cover of broadleaf trees. A total of 13 species of bat, equivalent to 76% of the UK resident species were recorded. The activity of six species was significantly influenced by the proportion of four land use types (two positive and two negative associations with conifer woodland, one positive and one negative association with broadleaved woodland, two positive associations with improved grassland and two negative associations with arable) in the surrounding landscape at three spatial scales (500 m, 1500 m and 3000 m around each survey plot). Four species showed significant positive associations with habitat structural features including larger mean tree diameter, greater canopy openness, higher vertical structural complexity, higher quantities of standing and fallen deadwood, and higher canopy cover of broadleaved trees. Many of these habitat features were more prevalent in stands further progressed towards irregular high forest. We did not detect any significant differences in bat species richness or activity levels between the three stand stages, except for Plecotus auritus/austriacus which had higher activity in the Stage 3 stand compared to Stage 2, as the limited replication of our study may have precluded detection of any differences. Our study helps inform us on how bats populations respond to novel management of conifer plantations. Further research to determine thresholds for deadwood and broadleaved trees to further support bats in plantations would be beneficial.
Notes
We wish to thank the Stourhead Western Estate and National Trust Stourhead Estate for allowing access to conduct the research, in particular Nick Hoare, Henry Hoare and Kim Portnell. Forest manager, David Pengelly, provided important background information regarding the history of the stands, stand selection for the study and management of the stands.
Share this page