Organic farming and biodiversity

The level of biodiversity that can be yielded from organic farming provides a natural capital to humans. Species found in most organic farms provides a means of agricultural sustainability by reducing amount of human input (e.g. fertilizers, pesticides).[8] Farmers that produce with organic methods reduce risk of poor yields by promoting biodiversity. Common game birds such as the ring-necked pheasant and the northern bobwhite often reside in agriculture landscapes, and are a natural capital yielded from high demands of recreational hunting. Because bird species richness and population are typically higher on organic farm systems, promoting biodiversity can be seen as logical and economical.

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.[9] Hole et al. (2005) summarized a study conducted by Brown (1999) and found nearly double the population and diversity when comparing farming methods.

Organic farms are said to be beneficial to birds while remaining economical. Bird species are one of the most prominent animal groups that benefit from organic farming methods. Many species rely on farmland for foraging, feeding, and migration phases. With such, bird populations often relate directly to the natural quality of farmland. The more natural diversity of organic farms provides better habitats to bird species, and is especially beneficial when the farmland is located within a migration zone.[10] In 5 recent studies almost all bird species including locally declining species, both population and variation increased on organic farmland,.[3][11] Making a switch from conventional farming methods to organic practices also seems to directly improve bird species in the area.[12] While organic farming improves bird populations and diversity, species populations receive the largest boost when organic groups are varied within a landscape. Bird populations are increased further with optimal habitat for biodiversity, rather than organic alone, with systems such as Conservation Grade.[13]

A specific study done in the UK in 2006 found substantially more butterflies on organic farms versus standard farming methods except for two pest species. The study also observed higher populations in uncropped field margins compared with cropland edges regardless of farm practice.[2] Conversely, Weibull et al. (2000) found no significant differences in species diversity or population.

Ten studies have been conducted involving spider species and abundance on farm systems. All but three of the studies indicated that there was a higher diversity of spider species on organic farms, in addition to populations of species. Two of the studies indicated higher species diversity, but statistically insignificant populations between organic and standard farming methods.

Out of 13 studies comparing bacteria and fungus communities between organic and standard farming, 8 of the studies showed heightened level of growth on organic farm systems. One study concluded that the use of “green” fertilizers and manures was the primary cause of higher bacterial levels on organic farms. On the other hand, nematode population/diversity depended on what their primary food intake was. Bacteria-feeding nematodes showed preference towards organic systems whereas fungus-feeding nematodes showed preference for standard farm systems. The heightened level of bacteria-feeding nematodes makes sense due to higher levels of bacteria in organic soils, but the fungus-feeding populations being higher on standard farms seems to contradict the data since more fungi are generally found on organic farms.[3]

According to Hole et al. (2005), beetle species are among the most commonly studied animal species on farming systems. Twelve studies have found a higher population and species richness of carabids on organic systems. The overall conclusion of significantly higher carabid population species and diversity is that organic farms have a higher level of weed species where they can thrive. Staphylinid populations and diversity have seemed to show no specific preference with some studies showing higher population and diversity, some with lower population and diversity, and one study showed no statistical significance between the organic and conventional farming systems.

Two comparative studies have been conducted involving mammal populations and diversity among farm practices. A study done by Brown (1999) found that small mammal population density and diversity did not depend on farming practices, however overall activity was higher on organic farms. It was concluded that more food resources were available to small mammals on organic farms because of the reduction or lack of herbicides and pesticides. Another study conducted by Wickramasinghe et al. (2003) compared bat species and activity. Species activity and foraging were both more than double on organic farms compared to conventional farms. Species richness was also higher on organic farms, and 2 of the sixteen species sighted were found only on organic farms.[14]

Approximately ten studies have been conducted to compare non-crop vegetation between organic and conventional farming practices. Hedgerow, inner-crop and grassland observations were made within these studies and all but one showed a higher weed preference and diversity in or around organic farms. Most of these studies showed significant overall preference for organic farming preferences especially for broad-leafed species, but many grass species showed far less on conventional farms likely because pesticide interaction was low or non-existent. Organic farm weed population and richness was believed to be lower in mid-crop land because of weed-removal methods such as under sowing.[3] Switching from conventional to organic farming often results in a “boom” of weed speciation due to intense chemical change of soil composition from the lack of herbicides and pesticides. Natural plant species can also vary on organic farms from year-to-year because crop rotation creates new competition based on the chemical needs of each crop.[15]

Biological research on soil and soil organisms has proven beneficial to the system of organic farming. Varieties of bacteria and fungi break down chemicals, plant matter and animal waste into productive soil nutrients. In turn, the producer benefits by healthier yields and more arable soil for future crops.[16] Furthermore, a 21-year study was conducted testing the effects of organic soil matter and its relationship to soil quality and yield. Controls included actively managed soil with varying levels of manure, compared to a plot with no manure input. After the study commenced, there was significantly lower yields on the control plot when compared to the fields with manure. The concluded reason was an increased soil microbe community in the manure fields, providing a healthier, more arable soil system.[7]

Organic farming practices still require active participation from the farmer to effectively boost biodiversity. Making a switch to organic farming methods does not automatically or guarantee improved biodiversity. Pro-conservation ethics are required to create arable farm land that generates biodiversity. Conservationist ideals are commonly overlooked because they require additional physical and economical efforts from the producer.[6] Common weed-removal processes like undercutting and controlled burning provides little opportunity for species survival, and often leads to comparable populations and richness to conventionally managed landscapes when performed in excess. Another common process is the addition of biotopes in the form of hedgerows and ponds to further improve species richness. Farmers commonly make the mistake of over-using these resources for more intense crop production because organic yields are typically lower. Another error comes from the over-stratification of biotopes. A series of small clusters does not provide adequate land area for high biodiversity potential.[6]