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- Materials and methods
- Supporting Information
Reptile and amphibian populations are experiencing unprecedented declines world-wide (Gibbons et al. 2000; Houlahan et al. 2000; Araujo, Thuiller & Pearson 2006; Sohdi & Erhlich 2010). This has raised concern among conservation biologists regarding our ability to maintain and improve biodiversity in commodity production landscapes (Whitfield et al. 2007; Wilson et al. 2010), an issue which is particularly poignant as increasing food demands are being met by intensifying agricultural practices (Fischer et al. 2008; Phalan et al. 2011; Tscharntke et al. 2012). Habitat fragmentation and agricultural intensification have been linked to herpetofaunal declines in Australia (Brown, Bennett & Potts 2008), Africa (Fabricius, Burger & Hockey 2003), South America (Whitfield et al. 2007) and Europe (Araujo, Thuiller & Pearson 2006; Ribeiro et al. 2009). Agricultural practices can lead to changes in plant species composition (Dorrough & Scroggie 2008), loss of vegetation structure (McIntyre & Tongway 2005) and altered soil chemistry (Benton, Vickery & Wilson 2003). Reptiles and amphibians are particularly sensitive to ground cover modification (Fischer, Lindenmayer & Cowling 2004; Jellinek, Driscoll & Kirkpatrick 2004; Brown, Dorrough & Ramsay 2011), primarily because many species are dependent on terrestrial retreat sites (Valentine, Roberts & Schwarzkof 2007), environments that are easily destroyed by agricultural practices (Cosentino, Schooley & Phillips 2011; Dorrough et al. 2012). Habitat specificity and poor dispersal ability in many species (Schutz & Driscoll 2008) also mean that reptiles and amphibians are prone to local extinction (Moore et al. 2008). Thus, the response of herpetofauna to native vegetation management in agricultural landscapes should be of importance to land managers but requires immediate investigation.
We sought to address this ecological knowledge gap using a landscape-scale study of agri-environment schemes (AES) in threatened semi-arid and temperate woodlands of south-eastern Australia – an area that has been subject to significant changes in vegetation cover over the past 150 years (Lindenmayer, Bennett & Hobbs 2010). The AES, initiated by the European Union's Common Agricultural Policy, were developed as a policy instrument to mitigate negative effects of agricultural intensification on biodiversity (Kleijn & Sutherland 2003). AES involve paying farmers to modify farming practices with the goal of providing environmental benefits such as increased biodiversity (Kleijn et al. 2006; Concepcion et al. 2012). However, many AES have been criticized for their lack of rigorous assessment, monitoring and evaluation (Zammit, Attwood & Burns 2010; Concepcion et al. 2012). Most studies that have evaluated the effectiveness of AES have focused on vegetation, invertebrate functional groups or particular avifaunal guilds (Whittingham 2007; Lindenmayer et al. 2012). Furthermore, few studies have evaluated the benefits of AES in protecting biodiversity relative to the broader farming landscape (Merckx et al. 2009), and no studies have explicitly evaluated the effectiveness of AES in protecting or increasing herpetofaunal diversity (Kleijn & Sutherland 2003; Kampmann et al. 2012). Thus, the value of AES in providing environmental benefits remains one of the most important policy-relevant ecological questions in recent times (Sutherland et al. 2006; Mauchline et al. 2012).
In south-eastern Australia, changes in the extent and quality of native vegetation occurred rapidly following European settlement (Yates & Hobbs 1997), with catastrophic effects on biodiversity (Lindenmayer, Bennett & Hobbs 2010). One agency responsible for managing natural resources in New South Wales is the Murray Catchment Management Authority (MCMA). The primary role of the MCMA is to prepare catchment action plans (CAP), manage financial incentive delivery programmes and allocate funds to develop property vegetation plans (PVP) to achieve natural resource management targets. Under the PVP, funds allocated by the Australian Government are awarded to landholders via a competitive grants process with the aim of, for example, improving vegetation condition and biodiversity outcomes (Murray Catchment Management Authority 2012).
We sought to determine whether the AES in the Murray catchment protect greater herpetofaunal diversity compared to the broader farming landscape, and whether levels of herpetofaunal diversity increase as a function of time-since-management intervention. We selected herpetofauna for detailed study because the group is relatively species rich within the Murray catchment (Michael & Lindenmayer 2010), includes threatened species of conservation concern, and a paucity of empirical data exists to evaluate responses to AES. Previous work in the woodlands of south-eastern Australia has shown that reptiles in particular are associated with local-scale attributes such as woody debris and native grass cover (Michael, Cunningham & Lindenmayer 2008; Brown, Dorrough & Ramsay 2011). These variables can be altered by agricultural practices and are expected to improve under AES. To evaluate the effectiveness of AES, we posed three main questions:
- Does herpetofaunal diversity differ among management regimes and broad vegetation communities?
- Are there particular environmental variables that relate to herpetofaunal occurrence patterns?
- To what extent can AES meet the objective of reversing herpetofaunal declines in rural landscapes?
Our questions were motivated by the knowledge that the MCMA invest in high-quality remnant vegetation, and these sites have the potential to support high levels of biodiversity (Lindenmayer et al. 2012). Management interventions such as reducing livestock grazing pressure and controlling invasive exotic plants are predicted to further improve the structure and condition of native vegetation condition, which in turn, may have positive benefits for herpetofauna. Based on habitat complexity theory (sensu MacArthur & MacArthur 1961), we expected to find a significant difference in species diversity between structurally complex vegetation under AES compared to structurally simple vegetation in the farming landscape, as well as gradients in species diversity in relation to time-since-management intervention. However, it is unclear what influence historical land-use practices and the prior filtering of species pools had on shaping patterns of herpetofauna in the region. Hence, the capacity for herpetofauna to respond to management remains unknown and is based on the assumption that travelling stock reserves (TSR) adequately reflect the biogeographic history of the region (Lindenmayer et al. 2012).
- Top of page
- Materials and methods
- Supporting Information
This study evaluated the effectiveness of an agri-environment scheme for protecting and improving herpetofaunal diversity. Several key findings emerged from this work, including: (i) relatively high regional reptile diversity, but low site-level diversity, (ii) no evidence to indicate that AES protect significantly more herpetofauna compared to the broader farming landscape, (iii) vegetation management increases the abundance of common species, (iv) vegetation type rather than management regime influences reptile assemblage structure, and (v) native plant diversity and woody debris are significant predictors of reptile occurrence. We further discuss the implications of our findings below in the context of improving AES.
Effect of Management on Species Diversity
At the onset of our study, we predicted that sites under AES would support higher species richness and that species richness would increase as a function of time-since-management intervention, with production areas and STC sites having lower species richness than LTC and TSR, a pattern reported for the region's avifauna (Lindenmayer et al. 2012). However, we found no significant differences in mean species richness among management classes for any response variable (Fig. 3). Only M. boulengeri showed a gradient in abundance, being recorded more frequently in TSR (Fig. 3). This implies that herpetofauna (reptiles in particular) may not be responsive to AES in the short term (<10 years). Benefits to reptiles from vegetation management appear to operate at the population level by increasing the abundance of common species and not at the community level by increasing local-scale species richness. For example, gradients in reptile abundance from PRD to TSR were evident across several vegetation types (e.g. FTW, IFW and RPW Fig. 3). This pattern is common among AES, where improvements in vegetation under AES benefit widespread and common species (Kleijn et al. 2006; Fuentes-Montemayor, Goulson & Park 2011; although see Merckx et al. 2010; Perkins et al. 2011). Two reasons why AES may fail to increase herpetofaunal diversity in this system could be due to the legacy of historical land-use practices (Harding et al. 1998) and the presence of dispersal barriers (Cosentino, Schooley & Phillips 2011). Many species of herpetofauna in temperate Australia have limited dispersal ability in modified landscapes (Schutz & Driscoll 2008; Williams, Driscoll & Bull 2012). Thus, the effectiveness of AES to improve herpetofaunal diversity is likely to depend on the distance to regional species pools, interpatch suitability and resource availability in the agricultural matrix (Donald & Evans 2006). Thus, a key management recommendation to improve AES is to restore habitat connectivity in the broader agricultural landscape by linking remnant vegetation.
Predictors of Species Richness and Abundance
We found several vegetation attributes to be positive predictors of herpetofaunal diversity (Tables 2 and 3), particularly native plant richness and bare ground cover (Fig. 4). Positive relationships between native plant richness and reptile diversity are well-established (Michael, Cunningham & Lindenmayer 2008; Schutz & Driscoll 2008; Brown, Dorrough & Ramsay 2011), as are negative relationships with exotic plant cover (Martin & Murray 2011). Several mechanisms may explain the avoidance of weed-infested areas by reptiles in particular, including unsuitable thermal conditions and low prey availability (Valentine, Roberts & Schwarzkof 2007). In grassy woodland ecosystems, native plant diversity and sward structure can be degraded by grazing pressure, fertilizer use and soil disturbance (McIntyre & Tongway 2005). Furthermore, it may take several decades before soil nutrients return to levels that can support native grasses and forbs (Dorrough & Scroggie 2008). Adopting a farm-scale approach to sustainable grazing may improve grassland condition and potentially benefit herpetofauna in the long term. Developing incentives around holistic rotational grazing systems should therefore be a high priority in future AES.
We found grazed woodland remnants (PRD) supported a similar number of reptile species compared to sites under AES (e.g. 16 species from 40 PRD cf. 19 species from 32 LTC sites). In grey box (FTW), species richness was highest in PRD (Fig. 3). Furthermore, the abundance of D. tessellatus, S. intermedius, C. pannosus, M. adelaidensis and Suta suta was also highest in PRD (Appendix S2, Supporting information), although low detections prevented formal analysis. When we examined reptile assemblages in more detail, we found no evidence to suggest that management influenced community composition (Fig. 5a, b). These findings are congruent with other studies which illustrate the value of remnant vegetation in production areas for maintaining reptile diversity (Fischer et al. 2005), but also highlights a limitation of AES, whereby parts of the landscape potentially rich in reptiles are not protected because they fail to meet investment criteria (e.g. minimum patch size and vegetation condition benchmarks). An alternative approach to conserving herpetofauna under AES may be to protect vegetation communities in various condition states, and at multiple spatial scales (Nicholson et al. 2006). This approach is likely to protect greater herpetofaunal diversity per unit area than investing in structurally homogeneous, high-quality vegetation.
In contrast to the lack of management effects, we found reptile assemblage structure varied significantly among vegetation types (Fig. 5a, b), whereby M. adelaidensis, Tiliqua rugosa and D. tessellatus were associated with boree woodland (RPW). Correspondence analysis revealed vegetation type, bare ground and organic litter to be key discriminating variables influencing assemblage structure. This relationship is underpinned by broad zoogeographical distribution patterns and life-form strategies. For example, the fossorial Lerista timida was associated with sandhill woodland (Fig. 6), a vegetation community found on sandy soils (Keith 2004). The arboreal C. pannosus was associated with black box (IFW) and grey box (FTW), eucalypt-dominated communities which produce large amounts of woody debris, and the arboreal S. intermedius (Fig. 6) shelters behind the bark of Callitris trees, a species associated with sandhill woodland (Keith 2004). Hence, strong habitat affiliations and vegetation heterogeneity may create natural dispersal barriers and limit the number of species potentially able to respond to AES in botanically diverse landscapes.
This study represents the first empirical investigation on the effectiveness of AES in protecting and improving herpetofaunal diversity. However, this study shares several limitations common to reptile studies in particular, notably, low site-level species richness. Some researchers have interpreted this pattern as reflecting an impoverished fauna (Brown, Bennett & Potts 2008; Brown, Dorrough & Ramsay 2011) resulting from prior filtering of regional species pools (Dorrough et al. 2012). However, because baseline data are lacking for herpetofauna in temperate woodlands, inferring pre-European assemblage structure is difficult. Nevertheless, our findings suggest that AES are unlikely to improve herpetofaunal diversity in the short term, emphasizing the need to develop new approaches to conserve low-vagility organisms such as frogs and reptiles in agricultural landscapes.
Our key recommendations for improving AES are to restore habitat connectivity to enhance local-scale diversity and protect mosaics of different vegetation types at multiple spatial scales (i.e. farm level to landscape level) to preserve regional diversity. These approaches are more likely to protect greater herpetofaunal diversity (Nicholson et al. 2006) than focusing solely on patch-scale management interventions. Future incentive schemes also should focus on improving sward structure, floristic diversity and increasing woody debris in the broader farming landscape to dissolve dispersal barriers created by past and present agricultural practices.