The impact of grassy field margins on macro-invertebrate abundance in adjacent arable fields

Abstract

Grassy field margins are thought to be an important feature for a variety of species in arable landscapes. However, not many studies address the impact of such margins in arable landscapes on the abundance of macro-invertebrates in arable fields. We estimated the abundance of earthworms, gastropods and carabids in fields with and without a grassy margin. Additionally, fields were sampled along the edge and further in the field.

From our findings we can conclude that the presence of grassy field margins in arable landscapes increases the abundance of carabids and earthworms but decreases the abundance of gastropods. These effects were mainly noticeable on the edge of the field, but appear to be occurring further in the field as well.

Introduction

About 38% of the total land area of the world was used for agricultural purposes in 2004 (Clay, 2004), an area potentially valuable for an array of species (e.g. Chamberlain et al., 2000, Robinson and Sutherland, 2002). However, especially after the Second World War, farm management rapidly changed and intensified resulting in a reduction in diversity of landscapes (Robinson and Sutherland, 2002, Foley et al., 2005). Consequently, changes in agricultural management have frequently been mentioned as one of the major causes for the loss of species diversity and abundance (e.g. Krebs et al., 1999, Donald et al., 2001, Robinson and Sutherland, 2002, Foley et al., 2005).

Agri-environment schemes were introduced into the agricultural policy of the USA, Australia and in the European Union, during the last few decades, partly with the aim of protecting biodiversity and also in an attempt to reverse some of the negative impacts of agricultural intensification on wildlife and the environment (Australian Government, 2009, European Commission, 2009, USDA, 2009). Many existing agri-environment schemes have provision for grassy, or uncultivated, field margins (e.g. Benton, 2007, Butler et al., 2007). Many studies focus on the effect of different arable field margin management strategies on invertebrates (e.g. Morris and Webb, 1987, Kromp and Steinberger, 1992, Baines et al., 1998, Asteraki et al., 2004, Woodcock et al., 2005, Woodcock et al., 2007). However few studies investigated the impact of the presence of a grassy field margin in itself in comparison with its absence (Yu et al., 2006). More studies investigate whether a possible positive effect of grassy field margins on invertebrate abundance extends to surrounding arable fields (Kromp and Steinberger, 1992, Kádár et al., 2004, Saska et al., 2007, Smith et al., 2008, Werling and Gratton, 2008, Twardowski and Pastuszko, 2008), but many of these studies focus on a specific group of invertebrates.

Marshall et al. (2006) investigated the impact of agri-environment field margins and found positive impacts on diversity or abundance for flora, bees and orthoptera, but not for birds, spiders and carabids. However, it has also been found that undisturbed boundaries such as hedges and beetle banks, may act as winter reservoirs for some species of carabids in arable landscapes (Sotherton, 1984, Sotherton, 1985, Morris and Webb, 1987). Dennis and Fry (1992) found that the predatory arthropod species diversity is higher near grassy field boundaries. Whether the abundance of earthworms and gastropods may be enhanced in arable fields by the presence of an unmanaged boundary is currently not well studied and might be important with respect to the conservation of invertebrates and their predators, and to pest management. Complementary to the available literature, this paper investigates if the presence of grassy field margins affects the abundance of macro-invertebrates (earthworms, gastropods and carabids) in the field margin, and in adjacent arable fields.