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Giving Bees the Edge

Provide protection for bees in your buffer zone.

By Stuart McMillan


Buffers, the strips of land separating organic from non-organic land, are an integral part of organic production. They are required by all certification bodies to prevent contamination through genetic and pesticide drift. Many people think of buffers as a barrier to “bad” outside products from adjoining conventional land, but if properly designed, they can serve as a tremendous source of “good” elements for the field, farm, and region as a whole.

The agricultural landscape has become increasingly simplified; abandoned farmsteads cleared away, old field edges removed. This land has been put into production and field size increased. In many intensive agricultural regions, these rapidly disappearing areas are the only semi-natural habitat remaining. They contain a mix of introduced plants and the last existing native flora and fauna. This biodiversity is increasingly recognized as critical for maintaining threatened animal and insect populations.

Habitat

While the cause of the recent decline of honey bees continues to be debated, it has long been known that habitat loss and modifications to the farm landscape have been negatively affecting native bee pollinators. Various methods of preserving and promoting field boundaries have been studied and proposed academically, but adoption in the field has sometimes lagged behind. Organic agriculture has a fantastic opportunity to apply some of these strategies in the buffer to enhance overall sustainability.

There is much evidence that vegetation surrounding the cultivated field has various influences on the crops, and the diversity of all the life in and around it. The importance of having a wide range of plants for pollinating insects is well known. Some experiments have found that the abundance of many crop pests is lower, and the abundance of pest predators is higher at the edges of a field as compared to the middle. Other studies have shown that as the plant diversity of the field edge increased, the diversity of the beneficial insects rose. There are a number of reasons why this may be.

The mixture of plants that can occur in a mature field edge produces essential food resources for beneficial insects. Pollen is a rich protein source, while nectar provides energy rich carbohydrates, both of which only come from flowering plants. Pollen also contains essential amino acids. Both plant nectars and pollen are needed by native bees in order to prosper. Plants produce pollen of differing protein contents and nutritional qualities for insects and, of course, at different times of the year when they flower. Throughout a growing season, the lifecycles of beneficial insects demand different resources. When a female insect is reproducing, she needs different food than when preparing to overwinter. Lady beetles feed on pollen when insect prey are not available. Hover flies need to consume pollen for proper egg development, along with nectar for energy while adults. Plant nectars from flowers are essential for predators like lacewings and parasitic wasps. The beneficial insects that may occur on crop edges all have different needs, so encouraging a diversity of plants is your best chance of meeting their needs.

Plants surrounding fields frequently support neutral non-pest insects that are alternate food sources for beneficials. One of the parasitic flies important in the control of the European Corn Borer was promoted by the occurrence of giant ragweed. It was found that there was a ragweed specific caterpillar that was preyed upon before the arrival of the corn borers later in the season. Similarly, ladybeetle control of crop aphids is promoted by a diversity of early and late season plants around the field. In Washington State, the USDA recently examined the relationship between a group of important parasitic wasps Anagrus spp. that attack grape leafhoppers. Researchers consistently found that wild rose and blackberry plants in the areas next to grape vineyards supported higher populations of the parasitic wasps that used both leafhoppers living on the rose, and blackberry and leafhoppers on grape. Having these other plants in the field edge led to better control of the pest leafhopper. In all of these cases, the insects occurring on the weeds or native plants would never pose a threat to the crop, but promote the beneficial insect populations leading to increased pest control for the intended crop.

The vegetation also provides a moderated micro-climate that influences development, reproduction, egg laying or overwintering success. In this role, maintaining structural diversity is as important as species diversity. Different plants will serve various functions throughout the season. Tufted bunch grasses promote the survival of ground dwelling predatory insects such as ground beetles, rove beetles and wolf spiders. Certain bees burrow into these grasses to overwinter. The thick litter layer that builds up in complex, minimally managed, perennial vegetation is very helpful for beneficial insect survival through the winter. Also, the absence of tillage and other agricultural disturbances increases the abundance and diversity of most insects dramatically. This applies not only to the beneficial predatory insects previously discussed, but to pollinating insects, decomposers, weed seed eating insects, and the countless neutral insects that may not serve a direct agronomic role, but are important in their own right.

While insects were used as an example, many of these principles apply to other wildlife such as reptiles, birds and mammals. Field margins can strongly influence the nesting and survival of birds, particularly ground birds. A wide range of animals can use field boundaries as wildlife corridors, either for relocation within the farm or for regional migrations.

By creating a more diverse and permanent buffer strip, other agronomic benefits are realized. Depending on the vegetation present, the buffer may reduce wind velocity and associated crop damage. The reduction of wind may increase snow catch, which is a benefit in drier agricultural areas. It can serve to reduce erosion caused by wind and overland flow of water. It can act as a barrier to nutrient run-off as well. A buffer made up of a mixture of plants will also be a more effective barrier to chemical drift, especially if one includes a mix of shrubs and trees into the buffer area.

The creation of a diverse permanent buffer does not have to be expensive. Although frequently many native species are superior, sometimes easily available cultivated forage varieties will function just fine. Also, the spontaneous growth of introduced weeds and native seeds still in the seed bank will also diversify a simple species mix over time. The judicious gathering of seeds from suitable plants occurring along roads, railways, cemeteries and semi-natural habitats close to the fields provides affordable and regionally adapted varieties.

One reason producers may be reluctant to create a diverse buffer is the loss of cropping land. Some producers need to maintain some form of revenue from the buffer zone. Obviously, with smaller fields the proportion of area used by the buffer increases, but the benefits created from a diverse buffer zone may well offset the loses in cropping area. Do the benefits from this area outweigh the income generated from it? This is a question that must be answered by each producer on a case-by-case situation.

What is appropriate on one farm may not work on the next. In the Great Plains region the best buffer would mimic the original prairie with roughly 75 percent grasses and 25 percent flowering plants. In areas that were traditionally wooded, having a higher percentage of woody shrubs and trees would be more appropriate.  It is a good idea to maintain a species mixture, and not have a totally forested buffer since a fully wooded buffer promotes forest specialist insects that are reluctant to leave the buffer into the arable fields.

If one is producing orchard crops then it would be advantageous to have a buffer that is predominantly trees and shrubs. Look to the original ecosystem for models to follow in creating an appropriate buffer. It is essential to avoid having plants in the buffers that would serve as alternate hosts of diseases and pests or become weeds in your main crops. Some initial research and planning can go a long way in avoiding future difficulties.

Each farm is different and requires a unique solution. What is universal is that a well-designed buffer must provide multiple benefits on an environmental, agronomic, and economic level. Buffers should promote biodiversity, which is as much a part of organic certification as is creating a buffer to exclude prohibited substances.

Further Information:

Xerces Society, www.xerces.org
Wild Farm Alliance, www.wildfarmalliance.org/index.htm.

Stuart McMillan works as an organic inspector in Canada.
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