Select Committee on Agriculture Appendices to the Minutes of Evidence

Annex 2



  1.1  This review looks at the published evidence, mostly from the last decade, from studies which have sought to test the hypothesis that organic farming benefits wildlife. None of the studies has looked at the wildlife on a conventionally managed farm and then followed the same farm through conversion (or vice versa). Most of the methodology has relied instead on the researchers pairing existing organic farms with nearby conventional farms which are as similar as possible to the organic farm, except for the organic management system. There are potential problems with such a methodology. The organic farms were not selected at random for conversion as this decision depends on the inclination of individual farm managers. Such farms may have been managed prior to conversion in a way which maintained healthier wildlife populations. In this event larger or more diverse wildlife populations on organic farms will simply have been maintained, rather than recreated, by the organic system. There is also a paucity of research around organic farming in the uplands. This gap needs to be addressed by future research. Annex 1 sets out some of the theoretical reasons for hypothesising that organic farming should be better for wildlife than conventional farming.

  1.2  There are at least three reasons, however, for suspecting that the report results underestimate the scale of the benefit from the organic farming system:

    1.2.1  at least in the UK until very recently organic farms have tended to be smaller family run units. In trying to match these with similar conventional farms there is likely to have been a tendency to avoid the bigger, most intensively managed, conventional units which are usually assumed to support the lowest populations of wildlife;

    1.2.2  it is now accepted that the yields on organic farms dip on conversion from conventional practice and then gradually built over a period of about a decade as the organic system of fertility building gradually recovers from the withdrawal of agro-chemicals . It is likely that there is also a time lag in the response of wildlife populations to the change. In at least some of these studies a general shortage of organic farms led researchers to use recently converted units which may not yet have acquired their full "complement" of organic wildlife;

    1.2.3  most organic units exist in a "sea" of conventionally farmed land. Island biogeography would suggest that if there is a wildlife benefit from organic farming it will be amplified when organic units coalesce and organic farming starts to be practised at a landscape scale.


General Reviews

2.1  MAFF commissioned two studies (Unwin et al 1995 and Gardner and Brown 1998) which reviewed previous work and examined both the direct and indirect evidence for a biodiversity benefit from organic farming systems. Both studies concluded that organic systems, on balance, provide more wildlife benefits than any other available system of farming. Gardner and Brown concluded that:

    2.1.1  organic regimes were shown to have an overall benefit for biodiversity at the farm level, both in terms of the agricultural practices adopted and in the occurrence and management of uncropped areas.


  2.2  Recent studies (Kay and Gregory 1998 and 1999) commissioned by English Nature looked at the arable weed flora of organic and conventionally farmed fields in the Oxfordshire Chilterns. Although some individual species were more common under conventional management regimes there was greater species diversity, greater frequency of scarce and declining species and greater overall abundance of non crop plant species in fields managed organically.

    2.2.1  Out of 23 of the rare or declining "target" species, 18 were more common on the organic farms with 13 of these found only on the organic farms; three species were found only on conventional farms.

    2.2.2  The organic field flora included four species on the UK Biodiversity Action Plan list while the conventional field flora contained only one BAP species.

    2.2.3  One of the BAP species, corn buttercup, an arable plant identified as having experienced the most rapid decline of any British plant, was found on over a quarter of the organic fields in the first year of the study and not found at all on the conventional fields.

    2.2.4  Importantly, many of the plants restricted to the organic farms were known to be sensitive to herbicides.

  2.3  These results are borne out by several other studies. Hald (1999) looked at a total of 38 matched pairs of organically and conventionally managed cereal fields over two years and found that:

    2.3.1  richness of wild plant species was highest in organic fields;

    2.3.2  all the variables tested had highest values—and often several times higher—in organically farmed cereals with four exceptions: total vegetation biomass, crop biomass, proportion of a single broad leaved taxon (dead nettles) and proportion of grasses;

    2.3.3  even in spring, ie before herbicide spraying, the densities of plants and species of the wild flora in conventionally farmed cereals were about half the densities in organically farmed cereals;

    2.3.4  a feature of the conventional system was the marked decrease in pre-herbicide spraying plant and species density from the crop margin (distances <6m) to mid-field (distances >6m). Spraying with herbicide in conventional fields reduced the density of both plants and species even further, resulting in a summer vegetation in conventional mid-fields being very much poorer and with much lower density compared with organic mid-fields;

    2.3.5  the two aspects used to assess the environmental value of conventional and organic cereal fields in relation to the herbivorous arthropod fauna (availability of green parts of preferred taxa and accessibility of food from flowers) showed the highest relative values in organically farmed fields. This higher proportion of suitable arthropod food resources is additional to the fact that the biomass of wild plants in organic fields was five times higher than in conventional fields.

  2.4  Brooks et al (1995) compared the weed flora and stubble seed abundance in 23 pairs of cereal fields over two years and found that:

    2.4.1  the number of weed species present on the organic fields was significantly greater than on the conventionally managed fields;

    2.4.2  overall weed cover was greater on the organic fields;

    2.4.3  there was no overall difference in weed seed abundance between organic and conventional fields on the post-harvest stubble, but grass seeds were more abundant on the conventional fields and the seeds of dicotyledonous species more abundant on organic fields.

  2.5  Moreby et al (1994) looked at 59 pairs of organic and conventional cereal fields over two years in the UK. Sampling was restricted to points 3m in from the field margin which, considering the findings of Hald (1999) and Redderson (1997), was likely to minimise the differences between the two regimes. Despite this the study found that:

    2.5.1  there was a significantly higher total weed cover (including grasses) in the organic fields in one of the two years;

    2.5.2  organic farms had significantly more species per 0.25m2 than conventional ones in both years of the study;

    2.5.3  organic farms had significantly more broad-leaved weed species and a significantly greater percentage cover of broad-leaved weeds than conventional farms;

    2.5.4  of the eight most commonly occurring broadleaved species, all but one, (cleavers) had greater percentage cover scores on the organic farms in both years. These differences were significant in one or both years for the remaining seven species and the category "other broadleaved species".


  2.6  In a study which ran in parallel to the one reported by Hald (1999) looking at flora Redderson (1997) looked at the arthropod fauna in 38 matched pairs of fields in two consecutive years. Key findings include:

    2.6.1  in one year the conventional cereal fields had higher total arthropod abundance than the matching organic ones. However, this was based entirely on aphid abundance. Excluding aphids and collembola, this study revealed a uniform pattern of higher total arthropod abundance and biomass and of species diversity in organic cereal fields;

    2.6.2  a decline in abundance and species diversity from field margin towards midfield was demonstrated and tended to be steeper in conventional fields;

    2.6.3  apart from the unpredictable aphid numbers, arthropods, and particularly the species preferred as bird food items, are a richer resource in organic cereal fields than in conventional ones and this difference is even greater when midfields are compared.

  2.7  Moreby et al (1994) also looked at the arthropod fauna of their fields. Again sampling was restricted to points 3m from the field margin in late June and early July, when migration into the crop from the field margin is likely to have minimised any difference between the two systems. Additionally none of the conventional fields were sprayed with insecticide during the study. Although when all taxa were added no significant differences between farming regimes were observed for the total numbers of invertebrates sampled there were some qualitative differences:

    2.7.1  cereal aphid densities were higher in the conventional crops in both years and increased numbers of parasitised aphids on conventional fields may have reflected the differences in aphid numbers;

    2.7.2  the guild of primarily weed-feeding chick-food insects were most usually found at higher densities in organic fields, although many of the statistical comparisons did not achieve signficance.

  2.8  Dritschilo and Wanner (1980) looked at carabid communities in four pairs of corn fields in Illinois and Iowa. They found that:

    2.8.1  organic fields had both a greater abundance of ground beetles and a larger variety of species in all four field pairs during the June sampling period (when 90 per cent of the specimens were collected). In three of the four pairs of fields the differences in numbers collected per trap per day were statistically significant.

  2.9  Kromp (1989) looked at the carabid beetle communities across adjacent fields of organically and conventionally farmed winter wheat in two consecutive years in Austria. Key findings include:

    2.9.1  in the organically farmed wheat fields higher numbers of carabid species and considerably higher numbers of individuals were collected than in the conventionally farmed fields;

    2.9.2  two species were collected exclusively from the organic fields. Both species are considered rare in Austria and in this location were found in neither the conventional fields nor in adjacent habitats; organically farmed fields possibly providing the only habitat for these species in the region;

  Kromp concluded that the proximate reasons for these results were:

    2.9.3  mainly due to the higher weediness, greater heterogeneity of crop density and absence of pesticides in organic wheat fields.

  2.10  In a further study Kromp (1990) looked at carabid populations in adjacent organic and conventional potato fields over two years. Key findings include:

    2.10.1  in both years the total numbers of carabids and number of carabid species were higher in the organically managed fields;

    2.10.2  of the sixteen dominant species (representing 96 per cent of the catch):

    —  five species showed similar activity densities under both types of management;

    —  two species showed higher activity densities in one or both years under conventional management;

    —  the other nine species occurred exclusively or at higher densities in the organically farmed fields.

  2.11  Pfifner (1990) looked at the epigeal arthropods on 12 plots comparing organic and conventional farming in a long term study which started in 1977. Only the summary of this paper is in English and reviewed here but key findings were:

    2.11.1  the abundance of carabids, staphylinids and spiders was greater in organic than conventional systems;

    2.11.2  there was both greater species richness and more homogeneous distribution of carabids in the organically farmed plots.

  2.12  Hokkanen and Holopainen used pitfall trapping to look at the activity density of carabids in three organic and four conventional cabbage fields over two years. They found that:

    2.12.1  different species of beetle tenderd to be favoured by the different farming systems;

    2.12.2  the biomass of captured carabids was significantly (between two and 20 times) higher on the organic fields;

  2.13  Brooks et al (1995) used a combination of soil cores and vacuum sampling (11 pairs of fields) and pitfall trapping (13 pairs of fields) to look at invertebrate populations on winter cereal fields and found that:

    2.13.1  Earthworms were significantly more abundant on organic than conventional fields;

    2.13.2  Staphylinid beetles occurred at significantly greater densities on the conventional fields (vacuum sampling);

    2.13.3  the weevil Sitona lineatus and the carabid Demetrias atricapillus occurred at significantly greater densities on the organic fields (vacuum sampling);

    2.13.4  of 12 carabid species analysed from the pitfall trap samples five were significantly more abundant on the organic fields while none were significantly more abundant on the conventional fields.

  2.14  Feber et al (1997) surveyed the butterfly populations of 18 pairs of organic and conventional farms over two years in England. They found that:

    2.14.1  there was no significant difference in the abundance of large white and small white (the two species of British butterfly considered to be agricultural pests) between the two farming systems in either year;

    2.14.2  the abundance of non-pest butterflies was significantly higher in organic than in conventional systems in both years;

    2.14.3  the management of the uncropped boundary had a significant effect on non-pest abundance, with organic boundaries attracting higher numbers of butterflies than conventional boundaries;

    2.14.4  the abundance of non-pest butterflies within the surveyed cropped habitats was significantly greater on the organic farms.

  2.15  Feber et al (1998) sampled the spider fauna in nine pairs of conventional and organic winter wheat fields in southern England. They found that:

    2.15.1  both the number of spiders captured and the species richness of spider samples were higher in organic than conventional winter wheat fields;

  They attributed this to the generally greater "weediness" of organic crops concluding:

    2.15.2  our most consistent result was the increased abundance and species richness of spiders in our samples with increasing abundance of understory vegetation within each crop, both overall and within each system, within each sampling session.


  2.16  Farmland birds too have been shown to benefit from organic management. Christensen et al (1996) looked at 124 pairs of organic and conventional farms over four years in Denmark. Of the 145 bird species recorded 92 occurred in sufficient numbers to allow statistical comparison between the two farming systems. Statistically significant differences were found for 34 species with three species (oystercatcher, thrush nightingale and reed warbler) being commoner on conventional farms. The other 30 species, which included kestrel, skylark, swallow, blackbird, song thrush, starling, linnet and corn bunting, were all significantly more abundant on organic farms. Overall the study showed higher bird species diversity and much higher bird densities on organic farms. The authors concluded:

    2.16.1  the results from the point censuses were very clear: all common, characteristic farmland species occurred with higher frequencies in organically farmed areas, the differences between the two types of farmland often being statistically highly significant.

  2.17  Wilson et al (1997) looked specifically at the skylark, a species which nests and feeds within the crop and is sometimes assumed to be disadvantaged by the mechanical weeding practices associated with organic farming and found:

    2.17.1  that skylark pairs must make two to three nesting attempts per season in order for populations to be self-sustaining;

    2.17.2  Skylarks require structurally diverse crop mosaics in order to make multiple nesting attempts without territory enlargement or abandonment;

    2.17.3  organically-cropped fields supported significantly higher skylark densities throughout the breeding season than intensively cropped fields or grazed pasture.

  Using the data collected from this and other studies to construct a simple population model they further say:

    2.17.4  our predictions about the demographic status of skylark populations breeding on lowland farmland suggest that, without structurally diverse crop mosaics which allow breeding pairs to make multiple nesting attempts without recourse to territory shifts or abandonments, skylark populations in arable landscapes in lowland England are likely to be demographic "sinks", unable to sustain their numbers in the absence of immigration. Mixed farms, with mosaics of both winter and spring-sown cereals, and extensively managed pastures and meadows are more likely to support self-sustaining skylark populations, especially if farmed organically, than farms dominated by winter cereals, broad-leaved crops, or intensively grazed or cut grassland.

  2.18  Chamberlain et al (1999) compared bird populations from 22 pairs of organic and conventional farms over three breeding seasons (66 comparisons) and over two autumn/winter seasons (44 comparisons) across England and Wales. Most of the comparisons which they made did not achieve statistical significance however they did find that:

    2.18.1  generally, organic farms held higher densities of breeding birds in the field boundaries than conventional farms, the density on organic farms exceeding that on conventional farms in 43 out of 51 comparisons for individual species:

    2.18.2  in field boundaries outside the breeding season nine comparisons showed a significant result, all showing a higher density on organic farms. Overall the density on organic farms exceeded that on conventional farms in 56 out of 64 individual comparisons;

    2.18.3  in no species was significantly higher bird density detected on conventional farms.

  They concluded that:

    2.18.4  this study has indicated that at the whole farm level, farming practices which are characteristic of organic agriculture would greatly benefit several species of farmland bird.

  2.19  Petersen (1994) reviewed the evidence from a series of Danish studies comparing the abundance and ecology of birds on organically and conventionally farmed areas. The key results were:

    2.19.1  mean breeding season densities of birds calculated from point count data were higher on organically farmed land than on conventionally farmed land for Lapwing, Skylark, Swallow, Whitethroat, Starling, Linnet, Corn Bunting and Yellowhammer. No significant difference was found for White Wagtail and Magpie.

    2.19.2  in a specific study of yellowhammers, densities were higher on transects through organically managed farmland than through conventionally managed farmland during the winder period (January-March).

  2.20  Bradbury et al (in press) in an intensive study of yellowhammers on four organic and five conventional farms found:

    2.20.1  that although yellow hammers nested earlier on organic farms (and so might be able to make more nesting attempts per season) there was no significant difference between the two farming regimes in clutch size, hatching success or fledging success;

  As yet unpublished data from related work has shown that:

    2.20.2  when feeding nestlings, yellowhammers forage most frequently in uncultivated field margins, but also visit cereal crops to collect invertebrate prey. When visiting cereal crops they are significantly more likely to use organic rather than conventional crops.

  2.21  One clear exception to trend is the linnet. Unusually linnets feed their young entirely on seeds and so are not reliant on summer invertebrate food supplies. Detailed autecological study in the 1960s showed linnets feeding their young on a range of broadleaved weed seeds deriving from plants which have now much declined on farms. More recently Moorcroft and Wilson (in press) have shown that linnets have learnt to compensate for this by feeding on the unripe seed of oilseed rape, a crop seldom included in organic rotations. The recent stabilisation of linnet populations is almost certainly due to this adaptation to the conventionally farmed environment. Further unpublished work has shown much lower nesting densities and high rates of chick starvation on conventional farmland in the absence of oil seed rape. This does not mean that linnets will not benefit from an increase in organic farming (Christensen et al 1996), just that they have evolved a strategy which can allow them to survive in some conventionally farmed environments.


  3.1  In making a change in ecosystem management as fundamental as moving from conventional to organic farming there are bound to be species which both benefit and lose out. Additionally the types of study reported here are likely to give rise to some statistical noise giving seemingly anomalous results in both directions. Even allowing for this there are some clear conclusions which can be drawn from the studies reviewed. When you compare the two farming systems then on balance:

    3.1.1  there are higher numbers and greater densities of non crop species (wildlife) on organic farms;

    3.2.2  there is a greater diversity of wildlife on organic farms;

    3.2.3  overwhelmingly, whether it is Birds of Conservation Concern (BOCC), Biodiversity Action Plan arable weeds or non pest butterflies, the wildlife species which have suffered the greatest declines on farmland in the last fifty years do better under an organic farming system;

    3.2.4  species which appear to be unaffected by the farming system or are favoured by conventional management are usually still either common and widespread or, like cereal aphids, cleavers, large white and small white butterflies, regarded as agricultural pests;

    3.2.5  where we have gained an insight into the mechanisms by which organic farming favours wildlife the findings are consistent with the theoretical benefits of organic farming outlined in Annex 1.


  Bradbury, R.B., Kyrkos, A., Morris, A.J., Clark, S.C., Perkins, A.J. & Wilson, J.D. in press. Habitat associations and breeding success of yellowhammers Emberiza citrinella on lowland farmland. Journal of Applied Ecology.

  Brooks D., Bater, J., Jones, H. & Shah, P.A. 1995. The effect of organic farming regimes on breeding and winter bird populations. Part IV. Invertebrate and weed seed food-sources for birds in organic and conventional farming systems. BTO Research Report 154.

  Chamberlain, D.E., Wilson, J.D. & Fuller, R. J. (1999) A Comparison of Bird Populations on Organic and Conventional Farm Systems in Southern Britain. Biological Conservation 88: 307-320.

  Christensen, K.D., Jacobsen, E.N., & Nohr, H. (1996) A Comparative Study of Bird Faunas in Conventionally and Organically Farmed Areas. Dansk Orn. Foren. Tidsskr. 90: 21-28.

  Dritschillo, W, & Wanner, D (1980). Ground beetle abundance in organic and conventional corn fields. Environmental Entomology 9: 629-631.

  Feber, R.E., Bell, J. Johnson, P.J., Firbank, L.G. & Macdonald, D.W., (1998). The Effects of Organic Farming on Surface-Active Spider (Araneae) Assemblages in Wheat in Southern England, UK. The Journal of Arachnology, (1998), 26, 190-202.

  Feber, R.E., Firbank, L.G., Johnson, P.J. & Macdonald, D.W. (1997). The Effects of Organic Farming on Pest and Non-Pest Butterfly Abundance. Agriculture Ecosystems and Environment 64: 133-139.

  Gardner, S.M. & Brown, R.W. (1998). Review of the Comparative Effects of Organic Farming on Biodiversity. MAFF contract OFO 149.

  Hald, A.B. (1999). Weed vegetarian (wild flora) of long established organic versus conventional cereal fields in Denmark. Ann. Appl. Biol 134: 307-314.

  Hokkanen, H & Holopainen, J.K. (1986). Carabid species and activity densities in biologically and conventionally managed cabbage fields. J. Appl. Entmo., 102: 353-363.

  Kay, S. & Gregory, S. (1998). Rare Arable Flora Survey 1998. Northmoor Trust.

  Kay, S. & Gregory, S. (1999). Rare Arable Flora Survey 1999. Northmoor Trust.

  Kromp, B. (1989). Carabid beetle communities (Carabidae, Coleoptera) in biologically and conventionally farmed agroecosystems. Agriculture, Ecosystems and Environment 27: 241-251.

  Kromp, B. (1990). Carabid beetles (Coleoptera, Carabidae) as bioindicators in biological and conventional farming in Austrian potato fields. Biology and Fertility of Soils 9: 182-187.

  Moreby, S.J, Aebischer, N.J., Southway, S.E. & Southerton, N.W. (1994). A comparison of the flora and arthropod fauna of organically and conventionally grown winter wheat in southern England. Ann. Appl. Biol. 125: 13-27.

  Moorcroft, D. & Wilson, J.D. In press. The ecology of linnets (carduelis cannabina) on lowland farmland. In Aebischer. N.J., Evans, A.D., Grice P. & Vickery, J.A. eds. Lowland farmland birds. Proceedings of the 1999 BOU Spring Conference, Southampton. Tring: British Ornithologist's Union.

  Petersen, B.S. 1994. Interactions between birds and agriculture in Denmark: from simple point counts to detailed studies of breeding success and foraging behaviour. In Hagemeijer, E.J.M. & Verstrael, T.J., Bird Numbers 1992. Distribution, monitoring and ecological aspects. 12th International Conference of IBCC and EOAC, pp49-56.

  Pfiffner, L. (1990). Effects of different farming systems on the presence of epigeal arthropods, in particular ground beetles (Col., Carabidae), in winter wheat plots. Bulletin de la Societe Entomologique Suisse 63: 63-67.

(Only the summary of this paper is reproduced in English. The full paper has not been reviewed).

  Reddersen, J. (1997). The arthropod fauna of organic versus conventional cereal fields in Denmark. In Entomological Research in Organic Agriculture, pp. 61-71. Eds B Kromp and P Meindl. Biological Agriculture and Horticulture 15.

  Unwin, R., Bell, B., Shepherd, M., Webb, J., Keatinge, R & Bailey, S (1995). The Effects of Organic Farming Systems on Aspects of the Environment. A review prepared for MAFF

  Wilson, J.D., Evans, J, Browne, S. J & King, J. R. (1997). Territory Distribution and Breeding Success of Skylarks Alaunda arvensis on Organic and Intensive Farmland in Southern England. Journal of Applied Ecology 34, 1462-1478.

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