The effect of organic farming has been a subject of interest for researchers. Theory suggests that organic farming practices, which exclude the use of most synthetic pesticides and fertilizers, may be beneficial for biodiversity. This is generally shown to be true for soils scaled to the area of cultivated land, where species abundance is, on average, 30% richer than that of conventional farms. However, for crop yield-scaled land the effect of organic farming on biodiversity is highly debated due to the significantly lower yields compared to conventional farms. In ancient farming practices, farmers did not possess the technology or manpower to have a significant impact on the destruction of biodiversity even as mass-production agriculture was rising. Nowadays, common farming methods generally rely on pesticides to maintain high yields. With such, most agricultural landscapes favor mono-culture crops with very little flora or fauna co-existence (van Elsen 2000). Modern organic farm practices such as the removal of pesticides and the inclusion of animal manure, crop rotation, and multi-cultural crops provide the chance for biodiversity to thrive.
Impact of organic farming on biodiversity at landscape level
The impact of organic agriculture on biodiversity is not limited to practices within individual plots but is better considered at landscape scale. This broader approach is particularly relevant for reconciling biodiversity conservation while maintaining sufficient agricultural production. In this context, two landscape management strategies are traditionally opposed: land sparing (which combines intensive farming and nature reserves) and land sharing via organic farming. A 2018 literature review of empirical studies indicates that land sparing is generally favored for conserving tropical forest biodiversity (67% of relevant studies). Organic farming supports higher biodiversity than conventional farming, but at the cost of lower yields. A 2022 meta-analysis found that organic farming had on average a 23% increase in biodiversity with a similar reduction in yield. The authors also evaluated whether biodiversity gains outweigh yield losses at the landscape level and concluded that organic farming is advantageous when surrounding unfarmed land is less than 2.4 times as biodiverse as conventional farmland. However, semi-natural habitats and uncropped field margins often exceed this threshold, suggesting that conventional farming combined with land sparing may be preferable in many landscapes. Hodgson et al. found that conventional farming combined with setting aside land as nature reserves is more beneficial for butterfly populations when the yield of organic farming falls below 87% of that of conventional farming. A 2018 review article in the Annual Review of Resource Economics found that widespread upscaling of organic agriculture would cause additional loss of natural habitats because more land is needed due to lower yields in organic farming.
Impact of organic farming on biodiversity at local level
Management practices The conservation of natural resources and biodiversity is a core principle of organic production. Three broad management practices (prohibition/reduced use of chemical pesticides and inorganic fertilizers; sympathetic management of non-cropped habitats; and preservation of mixed farming) that are largely intrinsic (but not exclusive) to organic farming are particularly beneficial for farmland wildlife. Using practices that attract or introduce beneficial insects, provide habitat for birds and mammals, and provide conditions that increase soil biotic diversity serve to supply vital ecological services to organic production systems. Advantages to certified organic operations that implement these types of production practices include: 1) decreased dependence on outside fertility inputs; 2) reduced pest-management costs; 3) more reliable sources of clean water; and 4) better pollination.
Impact on species Nearly all non-crop, naturally occurring species observed in comparative farm land practice studies show a preference in organic farming both by population and richness. Spanning all associated species, there is an average of 30% more on organic farms versus conventional farming methods, however this does not account for possible loss of biodiversity due to decreased yields. Birds, butterflies, soil microbes, beetles, earthworms, spiders, vegetation, and mammals are particularly affected. Some organic farms may use less pesticides and thus biodiversity fitness and population density may benefit. Larger farms however tend to use pesticides more liberally and in some cases to larger extent than conventional farms. Many weed species attract beneficial insects that improve soil qualities and forage on weed pests. Soil-bound organisms often benefit because of increased bacteria populations due to natural fertilizer spread such as manure, while experiencing reduced intake of herbicides and pesticides commonly associated with conventional farming methods. Increased biodiversity, especially from soil microbes such as mycorhizae, have been proposed as an explanation for the high yields experienced by some organic plots, especially in light of the differences seen in a 21-year comparison of organic and control fields.
Earthworms Earthworm population and diversity appears to have the most significant data out of all studies. Out of six studies comparing earthworm biodiversity to organic and conventional farming methods, all six suggested a preference for organic practices including a study at the pioneering Haughley farm in 1980/1981 that compared earthworm populations and soil properties after 40 years. Hole et al. (2005) summarized a study conducted by Brown (1999) and found nearly double the population and diversity when comparing farming methods.
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