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Land-use Intensity, Effects of Organic Farming on Biodiversity

29 March 2014

Organic farming, in which insecticides, herbicides and inorganic fertilizers are entirely or largely avoided, is generally thought to be more environmentally benign than its conventional farming cousin.

However, the overall benefits of organic farming for biodiversity, the environment in general, human health and food security have been intensely debated in recent years. The debate turns on whether or not the decreased yields from organic farms negate any local benefits, for example, to biodiversity, that such methods deliver. The logic of this argument runs as follows: lower yields push up food prices, and as a consequence, more wild or marginal land is brought into agricultural production. This wild land is likely to have supported even higher biodiversity than the organic farm; hence, begging the question, is there an overall cost of organic farming to biodiversity?

Organic farming provides shared benefits to both humans and wildlife, while conventional farming, at least in the short term, maximizes yields – thus potentially sparing wild lands elsewhere – therefore this argument is often naively framed as ‘land sharing’ vs. ‘land sparing’ although recently the debate has moved away from such overly simplistic dichotomies. For example, it has been argued that decisions about land sparing vs. sharing are contingent on the landscape and potential yields.

It is also clear that some organisms are necessary on the farm to support essential ecosystem services, for example, pollination and pest control, which contribute to yield. Therefore, species in farmland cannot be entirely sacrificed in order to preserve biodiversity elsewhere. In addition, some species, particularly in Europe where farming has been an integral part of the landscape for thousands of years, thrive in extensively managed farmland and are clearly threatened by agricultural intensification (Chamberlain et al. 2000).

These species are an integral part of the European cultural landscape, and their loss has provoked both public and political outcry, leading the British Government, for example, to pledge to reverse such declines by 2020. Thus, organic farming, which generally increases both crop and landscape heterogeneity, may be one component of a land-sharing strategy, delivering wider ecosystem services including amenity and conservation of culturally important species (Vandermeer & Perfecto 2007; Gabriel et al. 2013). In this light, quantifying the precise benefits delivered by organic farming is essential.

While there is a general consensus that organic farming increases biodiversity when compared to conventional agriculture, the magnitude of this effect seems to vary greatly, particularly among organism groups and across landscapes. Bengtsson, Ahnstr€om and Weibull (2005) suggested that the effects of organic farming on biodiversity were likely to be greatest in intensively managed agricultural landscapes, while Tscharntke et al. (2005) argued that agrienvironment schemes would have larger effects in simple than in complex landscapes.

Some of these predictions have been borne out by individual studies and by meta-analysis in which landscapes were classified as either simple or complex. However, different studies have defined ‘simple’ and ‘complex’ in different ways, whereas it would be preferable to have some more objective, continuous measurement of land-use intensity with which to test these ideas more fully.

While there have been previous meta-analyses comparing conventional vs. organic farming and their biodiversity and environmental impacts, we believe that a new analysis is still timely. First, previous meta-analyses have not taken account of the hierarchical structure of the data; secondly, a large number of new studies have been published in recent years; and thirdly, we include here three objective and standardized measures of land-use intensity and landscape complexity measured on a continuous scale, newly obtained for each of the studies. Using an extended data set compared with Bengtsson, Ahnstrom and Weibull (2005), we can therefore ask the following questions: (i) By how much does organic farming increase biodiversity compared with conventional agriculture? (ii) Do the effects of organic farming depend on the organism or functional group, land-use intensity and structure, and crop type? (iii) Has the reported effect size of organic farming on biodiversity decreased or remained stable over time? (iv) Is there evidence for publication bias in the literature, either because studies with negligible or negative effects of organic farming remain unpublished or because the present studies of organic farming, which are often performed in Europe or the US, are unrepresentative of the crops and regions in which organic farming is conducted globally?


The overall mean log response ratio was 0.296 (95 per cent CI: 0.231–0.361); this indicates that species richness on organic farms is on average 34 per cent (95 per cent CI: 26–43) higher than conventional. The estimated standard deviation of the true effect sizes, ω, was 0304 (variance for ω = 00004). This true variance among effect sizes comprised an overwhelming proportion of total variance (I2 = 974 per cent). These results reveal substantial heterogeneity among effect sizes, although many studies showed a large positive effect of organic farming on biodiversity relative to conventional farming. The estimate for hierarchical dependence was positive, meaning that the covariance among within-publication effect sizes will downweight large groups of effect sizes that would otherwise have an excessive effect on the overall result.

We found large differences in the effect of organic farming on different taxonomic and functional groups (Fig. 1a,b; Table S2, Supporting information). For example, among taxonomic groups, plants benefited the most from organic farming (Fig. 1b). Arthropods, birds and microbes also showed a substantial positive effect. Disaggregating organisms into functional groups showed a variety of responses: among functional groups, the largest effect size was found for pollinators while decomposers showed little effect (Fig. 1a). The crop types showed varying responses, with large positive effect sizes in cereals and mixed farming, and moderate positive effect sizes for all others (Fig. 1c).

Fig. 1. The difference in species richness ( per cent) on organic farms, relative to conventional, classified: (a) by functional group (n: decomposers = 19, herbivores = 6, other = 27, pollinators = 21, predators = 49, producers = 62), (b) by organism group (n: arthropods = 89, birds = 17, microbes = 6, plants = 62) and (c) by crop types (n: cereals = 100, grasses = 13, mixed = 40, orchard = 9, unspecified = 6, vegetables = 16). The grand mean is shown in black, accompanied by the black line. The dashed lines show the zero line. 95 per cent credible intervals are calculated from posterior standard errors.

The percentage arable fields had a positive effect on the magnitude of the effect size (slope log(RR) = 0442, 95 per cent CI: 0089 to 0973; Fig. 2). To assess the sensitivity of this slope estimate to the largest (‘outlying’) effect sizes, we removed the four data points with log(RR) >2 and reperformed the analysis; there was a small reduction in the slope estimate (0396). Other landscape metrics had slope estimates close to zero (number of habitats: log(RR) = 0006, 95 per cent CI: 0019 to 0031; average field size: log(RR) = 0001, 95 per cent CI: 0001 to 0002). When the percentage of arable fields was fitted as an interaction with functional group, there was substantial heterogeneity in the resulting slopes. However, there was significant uncertainty in these estimates, possibly due to small sample sizes within some functional groups; thus, we choose to report this result qualitatively: increasing landscape intensity affected the magnitude of the effect size in the order: herbivores > ‘other’ > predators > producers > decomposers > pollinators. The sampling scale of species richness observation did not appreciably change the effect size (farm = 0249, 95 per cent CI: 0161 – 0338; treatment contrasts with farm scale: field = 0139, 95 per cent CI: 0002 to 0279; plot = 0017, 95 per cent CI: 0222 to 0187).

Fig. 2. The relationship between the effect size and the proportion of the landscape covered by arable fields showing a regression slope with 95 per cent confidence intervals.

The representation of different crop types in the meta-analysis was comparable with the global FAO statistics; there were similar proportions of cereals, vegetables and orchards (fruit; Fig. 3a), although fibre and oil crops were underrepresented. The geographical representation in our data set, however, showed much less congruence (Fig. 3b): Western and Northern Europe, and to some degree North America, were highly overrepresented, while studies were largely lacking from most other geographical regions, especially Asia, Africa and Australia.

Fig. 3. Top row: proportions of different crop types present in the meta-analysis data set compared with the frequency of the most commonly grown organic crops world-wide. Bottom row: geographical origin of studies in the meta-analysis data set compared with the area under organic production in different regions of the world. FAO data obtained from their website (FAOSTAT 2013).

The funnel plot (Fig. 4a) showed some positive bias. A trim and fill assessment of how publication bias could impact our inference, after correcting for positive funnel plot skew, produced a negligible reduction in the effect size (00001, three studies added). This suggests that, if publication bias is evident, the reported effect size is robust to its impact. Investigating further, the cumulative meta-analysis of effect sizes sorted by sampling variance showed that less reliable studies caused the grand mean to increase, but not drastically so (Fig. 4b). If we assume that this was due to publication bias then the most conservative effect size estimate is 0190 (95 per cent CI: 0135– 0246), which still corresponds to a >20 per cent increased species richness on organic farms. This was the minimum value obtained from the cumulative plot and was reached after c. 80 observations (out of 184) were included. This reduced effect size did not greatly alter our interpretation of the magnitude of organic farming’s positive effect on biodiversity. The relationship between sampling variance and the effect size had a positive slope (0022, 95 per cent CI: 0056 to 0101), which confirms the positive association seen in Fig. 4.

Fig. 4. (a) Funnel plot showing asymmetry in the spread of residuals around the mean, created using the R package meta (Schwarzer 2010). The dashed line shows 95 per cent confidence limits. (b) Cumulative meta-analysis forest plot of data sorted by increasing sampling variance. (c) Cumulative meta-analysis forest plot of data sorted by increasing publication date.

The cumulative meta-analysis plot for data sorted by publication date (Fig. 4c) showed that the grand mean effect size estimated from our model was robust over time, although, interestingly, many of the earliest studies reported very high effect sizes. The lack of change with time was supported by a slope estimate close to zero (0003, 95 per cent CI: 0007 to 0013).


Our updated meta-analysis shows that organic farming on average increases biodiversity (measured as species richness) by about one-third relative to conventional farming. This result has been robust over the last 30 years of published studies and shows no sign of diminishing. Organic farming is therefore a tried and tested method for increasing biodiversity on farmlands and may help to reverse the continued declines of formerly common species in developed nations (Burns et al. 2013). Similar results have been previously obtained (Bengtsson, Ahnstrom & Weibull 2005; Fuller et al. 2005; Hole et al. 2005; Batary et al. 2011; Garratt, Wright & Leather 2011), but our study is the most up to date, deals with the hierarchical structure of multiple within-publication effect sizes and includes standardized measures of land-use intensity and heterogeneity across all studies.

In other areas of biology and medicine, it has been noted that, with the addition of further evidence, effect sizes concerning a particular question often decrease over time (Jennions & Møller 2002). This is thought to occur because of initial publication bias against non-significant or negative results that is eventually corrected. The effect size in our new study is slightly lower than the one reported in Bengtsson, Ahnstrom and Weibull (2005); however, our analysis reveals that the grand mean effect size is robust over time (Fig. 4c). There is therefore no sign of a dwindling effect size with the addition of further evidence. This implies that the increase in diversity with organic farming that we report here is robust, given the choice of crops and study areas included (see below for a discussion of the representativeness of our study).

Land-use Intensity Effects

Many authors have speculated on and investigated the importance of landscape characteristics in shaping the likely effect of organic farming on biodiversity (Bengtsson, Ahnstrom & Weibull 2005; Rundlof & Smith 2006; Rundlof, Bengtsson & Smith 2008; Rundlof, Nilsson & Smith 2008; Batary et al. 2011). Here, we calculated three standardized measures of land-use intensity and heterogeneity for all studies: the proportion of arable fields, the typical field size and the number of habitats. Only the proportion of arable fields in the landscape had any significant overall effect. The difference in diversity between organic and conventional farming generally increased with increasing proportion of arable fields, although there was large variation around the estimated slope. Some of this variance may be due to different responses between functional groups (Batary et al. 2011). The slope of this relationship decreased in the order: decomposers > ‘other’ > predators > herbivores > producers > pollinators, suggesting that the effect of organic farming on predators is greater in intensively managed landscapes, whereas the effect of organic farming on pollinators does not increase much with land-use intensity. These differences may be due to the importance of local actions relative to regional actions and to the movement of organisms and chemicals across the landscape. For example, some pollinators are known to be sensitive to certain pesticides (Goulson 2013), leading to an EU moratorium on neonicotinoids. If an organic farmer refrains from using pesticides, then local pollinator richness might increase; however, given that these chemicals might drift substantially, and that pollinators on an organic farm will likely visit neighbouring farms, the impact of this local action might have no more effect in an intensively managed landscape compared with an extensive one.

Organism Groups, Crop Types and Spatial Scale

We expected that the magnitude of the positive effect of organic farming would vary among organism groups, as this has been found repeatedly (Bengtsson, Ahnstrom & Weibull 2005; Fuller et al. 2005; Batary et al. 2011; Garratt, Wright & Leather 2011; Winqvist et al. 2011; Winqvist, Ahnstrom & Bengtsson 2012). As in previous studies, we found that plants benefited most from organic farming, probably because of restricted herbicide use (Roschewitz et al. 2005; Rundl€of, Edlund & Smith 2010). Arthropods, birds and microbes also benefited, with varying levels of estimated confidence. Accordingly, most functional groups – herbivores, pollinators, predators and producers – were more diverse in organic farming, with the exception of decomposers. The lack of positive effects on decomposers, which are mostly soil fauna, is surprising given that there are positive effects of organic farming on soil conditions and soil carbon (Mader et al. 2002; Gattinger et al. 2012). This may be because variation in soil type and structure is more important for soil organisms than the farming system itself. Such interactions between factors influencing the diversity and abundance of soil organisms would repay more investigation. The strong positive effects of organic farming on herbivores and pollinators are consistent with other studies (Rundlof & Smith 2006; Holzschuh, Steffan- Dewenter & Tscharntke 2008; Rundlof, Bengtsson & Smith 2008; Garratt, Wright & Leather 2011).

We found significant differences in the effect of organic farming among crop types. In cereal fields, which comprised >50 per cent of the studies, organic farming had large effects, significantly higher than in vegetable crops and orchards (Fig. 1c). This might reflect the intensive management of conventional cereal crops, with repeated applications of inorganic fertilizers and fungicides. The effect size in both vegetable crops and orchards, although positive, did not differ significantly from zero, but this could be due to small sample sizes. A lower but still significant effect was found in grasslands (pastures and permanent or semi-permanent leys), which are generally not so intensively managed. The number of studies in grasslands, vegetables and orchards was quite low, and we recommend that these crops are given more attention in the future.

In a previous meta-analysis (Bengtsson, Ahnstrom & Weibull 2005), small-scale studies (on the plot or single field scale) showed much larger effect sizes than studies on larger spatial scales. However, we found negligible differences across scales. This suggests that the general benefit of organic farming is robust across sampling scales, in contrast to recent work that suggests that this benefit diminishes at larger scales (Gabriel et al. 2010; Crowder et al. 2012). The previous meta-analysis result may have been due to small sample size or publication bias, which highlights the importance of updating meta-analyses with additional evidence. We note that most of the recent studies have been conducted at the farm scale, which is the most relevant scale for evaluating both organic farming as an agri-environmental scheme for biodiversity, and for the sustainability of farming systems in general.

Publication Bias

The funnel plot suggests a positively biased spread of effect sizes (Fig. 4a), which could be interpreted as a tendency for studies showing large positive effects of conventional farming on biodiversity to remain unpublished. However, an alternative interpretation may be that large positive effects of organic farming occur occasionally, while large positive effects of conventional farming are exceptionally unlikely. This seems reasonable given the nonlinear nature of many natural processes, for example population growth, which could occasionally fuel very large impacts of not controlling certain groups of organisms. In any case, the positive bias is slight and has been shown to not affect our result.

Previous studies of organic farming on biodiversity have been strongly biased towards temperate Western and Northern Europe and North America (Fig. 3), that is, intensive farming systems in developed countries. There is extremely limited data available from other areas of the world, for example, Eastern Europe, Asia, Africa, Central and Southern America, a bias also noted by Batary et al. (2011), Martin, Blossey and Ellis (2012), and Randall and James (2012). We therefore recommend that studies of organic farming practices on diversity in tropical and subtropical areas (e.g. Deb 2009; Zhang et al. 2013) should receive high priority. It is, for example, surprising that there are no studies on organic bananas or cacao, despite these products being widely available in European supermarkets. Mediterranean climates are also underrepresented, although a few studies from California (Drinkwater et al. 1995; Letourneau & Bothwell 2008; Kremen, Iles & Bacon 2012) and South Africa (Kehinde & Samways 2012) exist.

The Organic Controversy

The yields from organic farms are generally lower than conventional yields, although some controversy exists concerning the size of this effect and whether it is more prominent in developed countries (Badgley et al. 2007; De Ponti, Rijk & van Ittersum 2012; Dobermann 2012; Reganold 2012; Seufert, Ramankutty & Foley 2012). As outlined in the introduction, this implies a potential trade-off between biodiversity and crop yields. For example, Gabriel et al. (2013) in a study of cereal crops in Southern England concluded that the benefits of organic farming to biodiversity were entirely bought at the cost of reduced yield. They further suggested that the lower yields of organic farming may therefore have the unfortunate result of increasing the total area of land under agricultural production. However, there are other, often unmeasured, potential positive environmental benefits of organic farming. For example, nitrogen and phosphorus pollution caused by leaching from intensively managed fields is still a major problem in many countries and incurs significant costs to society (Heathwaite, Sharpley & Gburek 2000). An overall evaluation of organic farming in relation to crop yields therefore needs to account for the effects of farming practice on a wider range of environmental factors (Mondelaers, Aertsens & Huylenbroeck 2009; Sandhu, Wratten & Cullen 2010; Gattinger et al. 2012; Bommarco, Kleijn & Potts 2013).

Synthesis and Recommendations

This analysis affirms that organic farming usually has large positive effects on average species richness compared with conventional farming. Given the large areas of land currently under agricultural production, organic methods could undoubtedly play a major role in halting the continued loss of diversity from industrialized nations. The effect of organic farming varied with the organism group and crop studied, and with the proportion of arable land in the surrounding landscape. We found larger effects in cereals, among plants and pollinators, and in landscapes with higher land-use intensity. Despite the fact that organic farming has been suggested to have large effects on soil conditions, its effects on soil organisms were ambiguous and in general understudied. Finally, it is clear that three decades of studying the effects of organic farming on biodiversity have been heavily biased towards agricultural systems in the developed world, especially Europe and North America. We therefore recommend that other regions and agricultural systems are given much greater attention. In particular, more studies are needed in tropical, subtropical and Mediterranean climates. Studies at any scale would be beneficial: at the farm scale because this is the economic unit of farming, and at the landscape scale because this is the scale at which many organisms respond. This would allow a more balanced and globally relevant assessment of organic farming effects on biodiversity, ecosystem services, food production and agricultural sustainability.


We thank authors who performed the reviewed studies (see Appendix S1 Supporting information) and who corresponded with us during data collection, and FAO for the publication of their data. We also thank Peter Batary and one anonymous reviewer for constructive feedback, and John Stevens for help with calculating residuals. The work was funded by the Swedish Research Council FORMAS and the Ekhaga Foundation. SLT was supported by UK Natural Environment Research Council.

Further Reading

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March 2014

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