Oil Mallee Plantings Increase Diversity of Beetles (Coleoptera) and Other Terrestrial Invertebrates Within a Cropping Field

Open Journal of Forestry, 2018, 8, 167-181 http://www.scirp.org/journal/ojf ISSN Online: 2163-0437 ISSN Print: 2163-0429 Oil Mallee Plantings Increase Diversity of Beetles (Coleoptera) and Other Terrestrial Invertebrates within a Cropping Field Mei Chen Leng1,2, Jonathan Majer1,2,3 1Department of Environment and Agriculture, Curtin University, Perth, Australia 2School of Biological Sciences, University of Western Australia, Crawley, Australia 3Western Australian Museum, Perth, Australia How to cite this paper: Leng, M. C., & Abstract Majer, J. (2018). Oil Mallee Plantings In- crease Diversity of Beetles (Coleoptera) and Planting oil mallee (Eucalyptus spp.) belts in cropping fields introduces a new Other Terrestrial Invertebrates within a native, perennial-based habitat type to the previously homogenous, exotic, Cropping Field. Open Journal of Forestry, annual-based cropping environment. The purpose of this investigation was to 8, 167-181. determine if oil mallee plantings enhance the diversity and abundance of https://doi.org/10.4236/ojf.2018.82012 ground-dwelling invertebrates, especially beetles, in an agro-forestry land- Received: January 18, 2018 scape by comparing four habitat types (wheat field, oil mallee belts, remnant Accepted: March 19, 2018 woodland, and remnant roadside vegetation). Belts of oil mallees within a Published: March 22, 2018 cropping paddock had substantially different assemblages of ground dwelling Copyright © 2018 by authors and arthropod orders to the surrounding wheat crop. Of 93 coleopteran species Scientific Research Publishing Inc. trapped, 27 were found throughout all four habitats in the landscape, with the This work is licensed under the Creative remaining species creating a strong distinction between the assemblages in the Commons Attribution International cropped areas and other habitat types in terms of species competition, diver- License (CC BY 4.0). sity and abundance. Coleopteran assemblages in oil mallees were more similar http://creativecommons.org/licenses/by/4.0/ Open Access to those in woodland and roadside remnants than to those in the adjacent wheat crop. Arthropod assemblages, in particular coleopterans, within this agricultural environment were thus influenced by habitat type. Oil mallee farming systems appear beneficial for arthropod conservation in the wheat belt of Western Australia. Keywords Agriculture, Agroforestry, Hedgerows, Biodiversity, Conservation 1. Introduction Agricultural impacts such as land clearing, tillage, livestock trampling and the DOI: 10.4236/ojf.2018.82012 Mar. 22, 2018 167 Open Journal of Forestry M. C. Leng, J. Majer use of pesticides and fertilizers, can make for a hostile environment for many of the invertebrates inhabiting the region (Pywell et al., 2005). Due to crop rotation and use of land during different periods of the year, agricultural landscapes are seen as shifting mosaics of habitats for invertebrates (Holland et al., 2005). With a better understanding of insect dynamics and distribution, their populations may be better managed and utilized to increase diversity, as well as to assist in pest control in an agro-forestry farming system (Thomas et al., 2001). Non-cropped areas, such as vegetation belts or blocks and field margins, are more stable and less prone to disturbance, having different vegetation composi- tion structure than crop areas (Pywell et al., 2005). These areas are important sites for K-strategists, which tend to be slower growing and better long-term competitors (Knox et al., 2001). Amongst arthropods, K-strategists are rarely pests and are often beneficial (Price & Waldbauer, 1994; van Emden, 1976). Sus- taining populations of arthropods through non-cropped areas can also provide a food source for vertebrate fauna (Thomas & Marshall 1999). A British silvopas- toral study (Mcadam et al., 2007) demonstrated that the presence of trees on grasslands attracted terrestrial invertebrates and hence enhanced food supply, drawing avian fauna back into the area. By maintaining and establishing semi-natural habitats of appropriate spatial arrangement there is opportunity to create a heterogeneous mosaic of natural and semi-natural habitats and hope- fully conserve biodiversity (Magagula, 2003). Non-cropped areas also have implications for farming practices. They can provide areas from which re-colonization can occur after adverse farming pro- cedures, such as insecticide spraying (Mauremooto et al., 1995). One way to maintain invertebrate biodiversity within an agro farming industry is to protect large existing vegetation remnants, whilst establishing a network of connecting corridors to promote gene flown and re-colonization (Major et al., 1999). Joyce et al. (1999) determined that places where hedgerows and other field boundaries intersect, known as “nodes”, supported a higher number of forest carabids, probably due to nodes having higher plant species richness or providing a more stable environment. Migration of beetles within an agricultural environment between natural, semi-natural and managed habitats signifies the importance of topographically diverse habitats presented in an agricultural landscape. This is particularly significant for coleopteran recovery after disturbances (e.g., mowing, pruning, chemical treatment, etc.), coleopteran conservation and biotic diversity (Magagula, 2003). Western Australia (WA) currently has 4.3 million hectares affected by sec- ondary salinity, mostly in the wheatbelt area, and this is foreseen to double within 50 years (ECITA, 2006). Agro-forestry schemes involving native woody perennial crops are being assessed in low rainfall areas as a possible solution to salinity, and one such potential crop is oil mallee (Bell, 2005; Lefroy et al., 2005). Oil mallees are Eucalyptus species of a multi-stemmed shrubby nature possess- ing lignotubers. Several species (Eucalyptus kochii ssp kochii, ssp borealis and DOI: 10.4236/ojf.2018.82012 168 Open Journal of Forestry M. C. Leng, J. Majer ssp plenissima; E. horistes; E. angustissima; E. gratiae; E. loxophleba ssp lissophloia; and E. polybractea) have been selected for trials and commercial planting. Currently, around 10 million eucalypt oil mallee trees have been planted over thousands of hectares in the WA wheatbelt, arranged either in linear strips or belts (alley farming systems) or in blocks (Bell, 2005; Semple & Evans, 2004). The original aim of this enterprise was to produce bioenergy and also eucalypt oil. Unfortunately, the bioenergy aspect has not been successfully implemented, although there is still great interest in distilling the plant material to produce valuable eucalyptus oil. Our aim was to determine if oil mallee plantings increase the diversity and abundance of ground-dwelling arthropods, especially coleopterans, in a cropping field. We particularly focused on Coleoptera due to their high species richness and ecological (niche) diversity (Grove & Stork, 2000). We sought to com- pare both ordinal arthropod and beetle species data from pitfall trapping within four habitat types (wheat field, oil mallee belts, remnant woodland, and remnant roadside vegetation) and to observe temporal variation within these habitats. 2. Materials and Methods The study was conducted on a farm in the Cuballing region of the central wheatbelt of WA (32˚49'S, 117˚10'E). The site consisted of a 72 ha wheat field and 37 ha of adjacent remnant native woodland (Figure 1). The field is bounded by roads on two sides and strips of remnant vegetation approximately 5 m wide persist between the field edge and the road. The woodland was historically grazed by sheep but has been fenced off for the last 10 years to encourage natural regeneration. The field was developed and cleared around 1930 with a series of contour banks and dams installed in the late 1950’s to control erosion and catch water runoff. Linear strips of oil mallees (four tree rows wide) were planted along these contour lines in 1999. Two species of mallee trees were planted, Eu- calyptus loxophleba ssp lissophloia (York Gum Mallee), native to the south-western Australia and a small proportion of E. polybractea (Blue Mallee), native to south-eastern Australia. The field had been continuously cropped in recent years in a rotation of ce- reals, canola and lupins. When the study commenced there had been no spraying of pesticides since 2003, when Cypermethrin had been used as a blanket application for invertebrate pests. In the previous year (2002), Bifenthrin had been used for red-legged earth mite (Halotydeus destructor) control in the canola crop. At the beginning of 2006, there were sheep in the field to graze the crop stubbles but these were removed 2 weeks before sampling began. The surrounding agricultural lands were cultivated with cereal crops such as barley, oats (mixed with livestock grazing) and wheat. Wet pitfall traps were installed throughout the field and adjacent landscape to sample ground invertebrates in the four habitat types (Figure 1). Pitfall traps consisted of plastic vials that were 45 mm internal diameter and 85 mm in depth. They were placed at even intervals within habitat types in groups of 10, flush to DOI: 10.4236/ojf.2018.82012 169 Open Journal of Forestry M. C. Leng, J. Majer Figure 1. Aerial photograph of study site where oil mallee trees had been planted along contours. White lines denote the boundary fence and dots indicate pitfall trap positions. Habitats are coded accordingly; rem = woodland; road = roadside vegetation; M1 - M4 = oil mallees; P1 - P4 =

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