Agriculture, Ecosystems and Environment 78 (2000) 115–122 Effect of woody borders on insect density and diversity in crop fields: a landscape-scale analysis Jeff Holland, Lenore Fahrig * Ottawa-Carleton Institute of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, Canada K1S 5B6 Received 18 November 1997; received in revised form 25 September 1998; accepted 16 August 1999 Abstract The relationship between density and richness of herbivorous insects in alfalfa fields, and the amount (total length) of woody field border in the landscapes surrounding the fields was studied. Insects (predominantly herbivorous) were sampled in 35 alfalfa fields in 1995 and 24 fields in 1996, and the total length of woody field borders within the 1 km radius circular landscape surrounding each field was measured. There was no effect of amount of woody border in the landscape on insect density. There was a significant positive effect of amount of woody border in the landscape on overall family richness of insects in the alfalfa fields. The results of this study suggest that woody borders increase diversity but not density of herbivorous insects within crop fields in agro-ecosystems. This suggests that woody borders play a role in maintaining biodiversity in agro-ecosystems, and that this role extends beyond the borders themselves, into the crop fields. ©2000 Elsevier Science B.V. All rights reserved. Keywords: Woody borders; Insect density; Insect diversity; Dispersal; Agricultural landscapes; Fencerows; Biodiversity; Canada 1. Introduction Woody borders around fields are a common element in the agricultural landscape of many areas. Conserva- tion groups have placed great value on woody borders because they provide habitat for many species. How- ever, farmers often view these borders as harbouring weed and insect pests (Marshall and Smith, 1987) and reducing insolation and drying of the soil by wind action. The large-scale effects of woody borders on insect fauna in crop fields are not well known. Patch boundaries can represent barriers to dispersal for many insects, depending on the structure of the * Corresponding author. Tel.: +1-613-520-3856; fax: +1-613-520-4497. E-mail address: lfahrig@ccs.carleton.ca (L. Fahrig). border and the type of insect (Duelli et al., 1990; Frampton et al., 1995). Studies have found that hedgerows can reduce the dispersal of some insects (Lewis, 1969; Bowden and Dean, 1977; Fry, 1994, Mauremooto et al., 1995) and some spiders (Thomas, in Frampton et al., 1995). Forman and Baudry (1984) have called for research on the effects of woody margins on insect movement at a landscape scale. Fry (1994) states that field borders may affect the habitat searching of insects, possibly making large monoculture crops harder for pest insects to locate. Bach (1988) cited research demonstrating that non-host plants can reduce the ability of herbivo- rous insects to find habitat patches, and also stated that vegetation height has important effects on insect dispersal. This suggests that the presence of woody borders in a landscape may affect the insect popula- 0167-8809/00/$ – see front matter ©2000 Elsevier Science B.V. All rights reserved. PII:S0167-8809(99)00123-1