Biodiverse shelterbelts benefit to farm crops, researchers find

Native bees and insects can help honey bees with pollination duties, according to Dr Melanie Davidson. Photo / Plant & Food Research

Native tree plantings buzzing with helpful insects are being researched as a potential replacement for traditional shelterbelts and hedgerows to boost horticulture and crops.

Plant & Food Research scientists involved in the work, Dr Melanie Davidson and Dr Brad Howlett, have recently published initial findings based on a five-year trial in Canterbury that showed the "designer" plantings were effective.

Dr Davidson said the research so far has been concentrated around arable land but the researchers would be putting in another bid for funding to expand the research into other types of farmland.

"Bees are not the only insects that are pollinators.

"There are a lot of other insects that do some great work,'' she said.

While many farmers are planting native trees in riparian margins, few so far had thought to carry through the plantings to other parts of the farm and the benefits that might be possible.

New Zealand's native insect pollinators include beetles, moths and flies as well as native bees.

"We've got 28 species of native bees and they love flowers.

"My favourite insect is probably the hoverfly which has neat markings and is wonderful to watch because it hovers like a hummingbird.

"The hoverfly larvae loves to eat aphids and the adults like flowers so they are beneficial insects in several ways,'' she said.

Bumble bees are well known to be useful pollinators as well.

Assessing native insect pollinators has to take into account the complex local environment and the network of relationships between insects and plants.

Dr Davidson said the research has widespread relevance.

"It's not just farmers. These types of plantings can be done by community groups, councils and lifestyle block owners.

"Plantings can be put in to link up fragmented pockets of bush.

"The angle we are taking with beneficial insects is that they have a direct economic value,'' she said.

Biodiversity in shelterbelts can benefit crops, researchers find. Photo / Plant & Food Research

In the study, scientists from Plant & Food Research demonstrated the concept of designing native plantings using a mixture of species to optimise bee and non-bee crop pollinators in an intensively managed agricultural landscape.

The plantings on three farms were designed using existing literature to identify and anticipate interactions between native plants and crops with pests and pollinators.

Dr Davidson said she was mindful during the research that insect pests could also move into the plantings and cause problems for farmers.

"We didn't want to create problems by creating habitats that might not only fail to improve crop pollination but create pest reservoirs.

"We were able to identify at least a dozen species of native plants that encouraged beneficial insects. Some are specific to regions but there are many that will grow anywhere in New Zealand.''

These include cabbage trees, flaxes, hebe and coprosma.

The scientists found that five years after planting, 20 pollinating species were supported by the designed plantings out of the 21 anticipated.

While the expected bee-plant species interactions were confirmed by the study, the networks of non-bee pollinators were bigger and more complex than predicted. This indicates that the plantings were highly effective in supporting these interactions.

Immature life stages of non-bee pollinators, however, were not supported by plantings suggesting that alternative strategies should be sought for larval requirements.

Davidson said the native plantings offered a food source for birds as well.

"One of the farmers reported hearing bellbirds for the first time after establishing native plants on their farm. We're hoping that over time we will see tui come back to the plains with more native plants established in Canterbury,'' she said.

"We have really just scratched the surface. There is so much more to learn and we are hoping to be able to extend our research, which has already created a lot of interest.''

The findings are being shared with industry to support the development of designed habitats on farms.