Shelter Benefits Less Mobile Moth Species: the Field-Scale Effect Of
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Agriculture, Ecosystems and Environment 138 (2010) 147–151 Contents lists available at ScienceDirect Agriculture, Ecosystems and Environment journal homepage: www.elsevier.com/locate/agee Shelter benefits less mobile moth species: The field-scale effect of hedgerow trees Thomas Merckx a,∗, Ruth E. Feber a, Claire Mclaughlan a, Nigel A.D. Bourn b, Mark S. Parsons b, Martin C. Townsend a, Philip Riordan a, David W. Macdonald a a Wildlife Conservation Research Unit, Department of Zoology, University of Oxford, The Recanati-Kaplan Centre, Tubney House, Abingdon Road, Tubney, Abingdon, OX13 5QL, UK b Butterfly Conservation, Manor Yard, East Lulworth, Wareham, BH20 5QP, UK article info abstract Article history: Agri-environment schemes are the main policy instruments for reversing declines in farmland Received 15 October 2009 biodiversity, but there is scope for improvement. Within an intensive agricultural landscape, a mark- Received in revised form 15 April 2010 release-recapture experiment was used to investigate the relative effects on the number of adults of Accepted 19 April 2010 23 moth species of two landscape features (wide field margins and hedgerow trees) that may feature Available online 21 May 2010 within agri-environment schemes. Species belonged to either the grass/herb- or shrub/tree-feeders’ guild. Margin width did not affect the number of individuals, in either guild. Numbers of shrub/tree- Keywords: feeding individuals were higher at sites with hedgerow trees, but not so for this guild’s two most mobile Agri-environment schemes Field margins species, nor for the grass/herb-feeders, which were 30% more mobile. The results show that hedgerow Habitat resources trees increase adult moth numbers because they are shelter-providing resources in typically exposed Landscape-scale conservation agricultural landscapes, rather than due to being larval food resources. Hedgerow tree retention and Lepidoptera establishment options should be part of efficient general agri-environment schemes, while grassy wide Macro-moths field margins may not always deliver gains, at least not when implemented at the field-scale. Shelter © 2010 Elsevier B.V. All rights reserved. Spatial scale 1. Introduction Although proactive conservation management of hedgerow trees was until recently not financially rewarded in any of the EU coun- Agri-environment schemes (AES) are considered to be the only tries, it is now a recent addition to the set of general AES options realistic policy instruments for reversing widespread biodiver- within England (DEFRA/NE, 2009) (see also the new Scottish Rural sity declines in agricultural landscapes (Donald and Evans, 2006). Development Priorities). This paper concerns the relative impacts on two moth guilds of Larger moths (macro-moths) are a species-rich group, playing two prominent landscape features (wide grassy field margins and important ecological roles within many terrestrial ecosystems, and hedgerow trees) with potential to feature within national AES. occurring often abundantly in farmed landscapes. Rapid and signif- Wide field margins are an important conservation tool (Macdonald icant declines have been recorded for the majority of common and et al., 2000). Their management is financially rewarded in a number widespread macro-moth species that inhabit farmland in the UK of EU countries. By early 2008 more than half of agricultural land (Conrad et al., 2006), and it seems likely that a similar trend is occur- in England was under AES, and grass/buffer strips on arable land ring in other temperate-zone industrialized regions (Groenendijk were one of the most popular scheme options (DEFRA/NE, 2008). and Ellis, in press). Partly because of their ecological diversity and Hedgerow trees are characteristic of many European agricultural species richness, they are considered a sensitive indicator group for landscapes. In England, their abundance has dramatically declined biodiversity in terrestrial ecosystems (New, 2004; Thomas, 2005), since the late 18th century to an estimated 1.6 million, of which the suggesting that findings for this group may have relevance for the annual recruitment is currently only half the level required to main- conservation of other winged insects on farmland. tain a healthy population (Stokes and Hand, 2002; DEFRA, 2010). Hedgerow trees have a larger impact on macro-moth abundance and diversity than the 6 m wide grassy field margins (data on 243 species: Merckx et al., 2009a). However, what remains unclear is ∗ Corresponding author. Tel.: +44 01865 393104; fax: +44 01865 393101. the mechanism behind the observed effect of hedgerow trees. It is E-mail addresses: [email protected] (T. Merckx), difficult indeed to disentangle the relative effect of shelter vs. lar- [email protected] (R.E. Feber), [email protected] (C. Mclaughlan), val foodplant, since the sampled hedgerow trees in the study were nbourn@butterfly-conservation.org (N.A.D. Bourn), predominantly pedunculate oak Quercus robur. Although overall mparsons@butterfly-conservation.org (M.S. Parsons), species not dependent on Q. robur as a larval foodplant benefited [email protected] (M.C. Townsend), [email protected] (P. Riordan), [email protected] (D.W. Macdonald). (+43%) from their presence, which points to an effect of shelter, 0167-8809/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2010.04.010 148 T. Merckx et al. / Agriculture, Ecosystems and Environment 138 (2010) 147–151 there was a much stronger response (+300%) to the presence of Acer campestre, sycamore A. pseudoplatanus, common hazel Cory- these trees for those moth species that use Q. robur as a larval food- lus avellana, lime Tilia sp., horse-chestnut Aesculus hippocastanum, plant, which would point to a combined effect of foodplant and European holly Ilex aquifolium, larch Larix sp., pine Pinus sp.). Thus, shelter. there were four different experimental groups: (i) tree + wide mar- Here, a mark-release-recapture (MRR) experiment was con- gin, (ii) no tree + wide margin, (iii) tree + standard margin, (iv) no ducted at a field-scale that allows addressing this remaining tree + standard margin. Sampling sites were carefully selected so question: do hedgerow trees increase moth numbers mainly that the variation in hedgerow tree and margin characteristics because they are shelter-providing resources, or because they are (e.g. botanical composition and management) other than the sub- larval food resources? This question is of particular relevance for ject variables was minimal throughout. All sites were fixed, were designing effective AES. In case of the latter outcome, (i) hedgerow located in margins and 1 m from hedgerows, and were more than tree options will favour significantly less species, and (ii) spatial 100 m apart in order to exclude interference between light traps. abundance of not only hedgerow trees in general, but also of spe- Sampling at hedgerow intersections was avoided to reduce bias cific tree species need to be taken into account in order to optimise due to local aggregation of individuals that use hedgerows as flight the biodiversity gain from AES. Instead of using predominantly Q. corridors (e.g. Maudsley, 2000). robur as hedgerow trees, a whole variety of tree species (see Section 2) was now used so as to avoid a strong biased response towards 2.1. Sampling one specific tree species. Moreover, eight out of the 13 selected moth species of the shrub/tree-feeding guild did not use this par- We used Heath pattern actinic light traps (6W) (Heath, 1965) ticular set of tree species as hostplants, as they feed on other plant to capture moths. These operate on the ‘lobster-pot principle’, species associated with hedgerows (such as traveller’s-joy Clematis whereby moths are drawn to an actinic tube secured vertically vitalba, blackthorn Prunus spinosa, hawthorn Crataegus monogyna, between baffles, fall unharmed down a funnel, and rest on the inside spindle Euonymus europaeus, brambles Rubus sp., and other berries; of the trap or on pieces of egg-tray provided. Traps were operated Waring and Townsend, 2009). The hypothesis is that if the positive from dusk to dawn, when the live sample of selected species was effect of hedgerow trees on adult moth numbers can mainly be marked (at first capture) by writing a unique number on the left ascribed to the shelter they provide, one would under this partic- forewing with a fine (0.4 mm), non-toxic, permanent waterproof ular experimental set-up still see numbers of moths to be higher marker (Staedtler Lumocolor 313) and released in situ into nearby at sites with hedgerow trees than at sites without them. Also, one tall vegetation. would expect this effect to be stronger for less mobile species as Sampling followed a strict protocol to control for confounding poorer fliers would generally be more prone to convective cool- factors between sites and between sampling events. The protocol ing, and would hence rely more strongly on shelter in typically was designed to ensure that sampling was conducted in simi- exposed agricultural landscapes (Dover and Sparks, 2000; Pywell lar, sufficiently favourable conditions to minimise bias, as activity et al., 2004). levels of nocturnal flying insects are affected by a number of This study also looks at the effect of wide field margins on the variables. Sampling occurred under pre-defined weather forecast adult abundance of the 23 selected moth species belonging to either criteria of minimum night temperature (10 ◦C), maximum