IMPORTANCE OF BIODIVERSITY IN FARM LANDSCAPES
Biodiversity is a key component of organic farming systems. Organic farms rely on healthy functioning landscapes that can provide the ecosystem services required to grow healthy crops. Supporting diverse functioning ecosystems on farms can be challenging, especially in the largescale grain cropping systems of the prairies. This is where Organic Science Cluster (OSC) researchers from the University of Manitoba have been experimenting with adding flowering habitat to the margins of grain fields, with the goal of increasing both sustainability and farm productivity.
Many of the practices commonly used on organic farms (e.g., higher crop diversity, cover crops, reduced pesticide use) are likely to support higher biodiversity compared to conventional practices. However, with overall farm landscapes becoming increasingly simplified, increasing pesticide use, and insect and bird populations declining, it is clear that we need to do more to provide habitat and increase biodiversity across these landscapes. Features that protect and promote biodiversity are, in fact, mandated in the Canadian organic standards (section 5.2.4). The standards state that:
“Management practices shall include measures to promote and protect ecosystem health on the operation and incorporate one or more of the following features:
- pollinator habitat;
- insectary areas;
- wildlife habitat;
- maintenance or restoration of riparian areas or wetlands; or
- other measures which promote biodiversity
NOTE: Existing native prairie, parkland, or wetland habitats should be maintained and enhanced whenever possible”
How can organic farmers increase biodiversity and the related benefits, including pollination and biocontrol, on their farms?
Habitat can be increased both in crop fields, and in surrounding non-crop areas. One intervention that has gained attention is seeding patches of non-crop plants along field margins or within the field itself. Within the field, this could be in the form of strips of native prairie plants through a field at regular intervals (for example the Iowa STRIPs project), or it could be patches of perennials in marginal low-producing areas of the field. Often the types of non-crop plants are chosen to match the local ecology. For example, in a forested ecoregion you might incorporate shrubs and trees, while in the prairies you might include wildflowers, grasses, and forbs.
These strips of non-crop plants provide habitat, particularly for insects—which can provide food for insectivorous birds, and benefit nearby crops through the provision of ecosystem services, such as pollination and pest control. Patches of perennial plants also serve to cover the soil, potentially reducing soil erosion and nutrient runoff, while impacting the soil microbial community and carbon storage.
SPECIES SEEDED IN FLORAL STRIPS
Annuals: Phacelia, buckwheat, sunflower, sainfoin, crimson clover, Persian clover
Tame perennials: Intermediate wheatgrass, chicory, alfalfa, alsike clover, red clover
Native perennials: Blue grama, purple prairie clover, white prairie clover, little bluestem, green needlegrass, showy sunflower, stiff sunflower, heartleaf golden alexanders, old field goldenrod and gray goldenrod
FLORAL STRIPS PROJECT IN MANITOBA
OSC3 researcher Dr. Jason Gibbs and his team at the University of Manitoba have been studying the impacts of floral strips on organic and conventional farms in southern Manitoba. The project is titled ‘Increasing pollination, biological control, and beneficial insect diversity on farms using flowering habitats.’
The researchers worked with producers to establish floral strips of approximately one acre in size along the edges of grain fields. The floral strips contained nineteen species of flowering plants and grasses including native and introduced plants, both annuals and perennials. They wanted to determine the effect of the strips on insects, particularly insects that can be beneficial to crops such as pollinators, weed seed herbivores, and biocontrol or “natural enemy” insects that prey on plant pests. To compare the invertebrate communities, insects were collected from the floral strips and adjacent crop fields, as well as from control fields with no floral strips and nearby semi-natural areas.
The study is ongoing and final results will be forthcoming, but first-year results showed that the wildflower plantings next to the fields attracted a greater abundance of beneficial insects compared to the control field edges. Wild bees were much more abundant in the wildflower plantings, which was expected because the flowers attract bees from the surrounding landscape. Interestingly, there also tended to be more bees in the flower strips compared to nearby undisturbed semi-natural areas. This is likely because the natural areas were not as diverse and had less abundant floral resources than the floral strips themselves. Pitfall traps were used to collect another group of beneficial insects: ground-dwelling beetles in the family Carabidae. In the first year, there was a dramatic increase in the abundance of these beetles, which act as predators (of insects), as well as weed seed herbivores.
The researchers attribute these preliminary increases in insect numbers to the floral strips providing an attractive resource and a refuge for beneficial insects. The strips could not have led to an increase in the local populations in such a short time frame, instead, they must have attracted insects from different parts of the landscape. In subsequent years, the researchers continued to find high levels of insects maintained in the plantings, which supports the idea that the floral strips are sustaining insect populations in the area. The researchers are still in the process of analyzing the thousands of samples that have been collected; it remains to be seen whether the floral strips will result in a build-up of the populations over time.
Another group of beneficial insects, hover flies, showed slightly different patterns. Hover fly larvae tend to be predators of plant pests and the adults are pollinators. Some of these flies, also known as syrphid flies, were more abundant in the unmodified grassy areas compared to the floral strips, and it remains to be seen how the diversity of hover flies varies between the grassy strips and floral areas.
In addition to the impact on insect diversity and abundance, producers want to know how the floral strips will impact their crops. Will the floral strips increase crop pollination, and will this affect yield? Or will they harbour weeds and invertebrate pests? The researchers in Manitoba are determining the impact of the strips on pollination and the yield of the crops in adjacent fields; these results are not yet available. They also assessed the weed community in the crops beside the strips to see if they were causing weed problems, although it is possible that the floral strips could help reduce weed pressure by acting as a buffer to stop weeds from invading the field margins. So far, the researchers have not found any evidence that floral strips had a negative effect on pollination, nor increased weed pressure.
An important objective of this research was to develop a set of best management practices to help producers establish habitat enhancement strips on their own farms. Dr. Gibbs advised that preparation is key to successfully establishing perennial floral plantings. He recommends that producers carefully consider the context of their fields (for example, assess weed pressure and moisture availability) and start slowly with a small area using a high seeding density. Gibbs also suggests using an annual cover crop or nurse crop to help control weeds while the perennials establish, and to not be afraid to mow the floral strips to remove the seed heads of fast-growing weeds. The hope is that once perennials are established, they should be quite low maintenance. Future research aims to determine which plant species are most reliable in terms of germination and establishment.
Dr. Gibbs’ team will be producing summaries of the best management practices developed during their study to help producers establish floral strips. As the third Organic Science Cluster wraps up this winter, we are looking forward to the final results from this study. Stay tuned!
(OSC3) Originally published in Organic Science Canada magazine, Issue #5, Spring 2023
