Plant diversity and land use under organic and conventional agriculture: a whole‐farm approach

Abstract

Summary 1.Organic farming is thought to lead to increased biodiversity and greater sustainability than higher-yielding conventional farming systems. It is usually assumed that organic farms have both larger and higher quality areas of semi-natural habitats, although this assumption has not been unequivocally tested. 2.Here we test the hypothesis that in comparison to conventional farms, organic farms have larger areas of semi-natural and boundary vegetation, and organic farms support higher levels of plant abundance, richness and diversity within cropped and semi-natural areas. 3. Our study compared whole-farms: 10 organic farms were paired with 10 conventional farms in a complex landscape in the south-west of England. On average, organic farms were 7·3 years post conversion. Plant abundance, species richness and diversity were measured in all crop and non-crop landscape elements on each farm. 4. Organic farms had greater total areas of semi-natural habitat (woodland, field margins and hedgerows combined). Woodland area on it's own was also significantly greater. Organic farms had more continuous blocks of woodland (with simpler perimeters than similarly sized patches on conventional farms), whereas woodland on conventional farms often consisted of more linear patches. 5. Semi-natural habitats on organic farms did not have higher plant abundance, richness or diversity than their conventional counterparts. The only landscape element that showed a significant increase in plant abundance, richness or diversity was arable fields. 6. Synthesis and applications . Even within a complex agricultural landscape differences do exist between organic and conventional farms, these differences being larger areas of semi-natural habitats on organic farms. However, with the exception of arable fields, no habitats on organic farms were yet of a better quality than their conventional counterparts in terms of plant abundance and diversity. Conventional farmers may be able to achieve an increase in plant diversity within arable fields by adopting some organic management practices at the field scale (e.g. exclusion of synthetic herbicides), and whole-farm conversion to organic practice might not be required. However, further work is needed to determine any biodiversity benefits of larger areas of semi-natural habitat on conventional farmland.

Consequences of organic and non-organic farming practices for field, farm and landscape complexity

“…the organic and non-organic farms within a pair were located within broadly the same landscape types as supported by comparisons at the 25km 2 scale. Results for the one and 9km 2 surrounding target fields and for habitat surveys indicated that even within similar relatively heterogeneous landscape types organic farms were characterised by higher landscape complexity than was found in their non-organic more arable dominated counterparts (see Gibson et al, 2007).…”

“…Other studies looking at biodiversity differences between organic and conventional systems have shown that complexity at the farm and landscape scale, independent of farming system, explained biodiversity differences between farms (Weibull et al, 2003;Clough et al, 2005;Purtauf et al, 2005). Recent work strongly suggests that for certain taxa, organic farming delivers fewer benefits when located within heterogeneous landscapes, with relatively large amounts of semi-natural vegetation, rather than simpler landscapes dominated by intensive farming (Roschewitz et al,2005b;Schmidt et al, 2005;Tscharntke et al, 2005;Rundlof and Smith 2006;Holzschuh et al, 2007) although differences may still exist (Gibson et al, 2007).…”

“…for birds; (Chamberlain and Wilson 2000;Freemark and Kirk 2001), for plants; (Aude et al, 2003;Roschewitz et al, 2005a;Gibson et al, 2007;Boutin et al, 2008) and for invertebrates; (Schmidt et al, 2005;Rundlof & Smith 2006;Holzschuh et al, 2007). Other studies looking at biodiversity differences between organic and conventional systems have shown that complexity at the farm and landscape scale, independent of farming system, explained biodiversity differences between farms (Weibull et al, 2003;Clough et al, 2005;Purtauf et al, 2005).…”

Does organic farming benefit farmland birds in winter?

“…It therefore remains unclear whether organic farms support greater biodiversity owing to management of inputs to the system (e.g. no synthetic pesticides or fertilizers), to heterogeneity in wider habitat composition (Chamberlain et al 1999;Gibson et al 2007) or both.…”

Invertebrates in field margins: taxonomic group diversity and functional group abundance in relation to age

“…markedly improved by the presence of semi-natural landscape elements and by management of the productive fields themselves (Duelli and Obrist 2003;Gibson et al 2007;Drapela et al 2008). Incorporation of semi-natural habitats on arable land and adoption of agri-environmental management are therefore seen as useful ways to promote biodiversity (e.g., Whittingham 2007).…”