There is a buzz on range-and pasture lands. And we really need to pay attention to native pollinators and the benefits that they provide, says a rangeland ecologist.
“Pollinators are critical to rangelands themselves, and the plants that are there,” said Cameron Carlyle, an assistant professor at the University of Alberta, who is not only studying the benefits pollinators provide, but tracking how well they are doing.
The range of pollinator species is diverse but they roughly fall into two groups, he said.
“Bumblebees are the large fuzzy bees that we commonly think of when we think of bees. Solitary bees tend to be smaller and take many forms. Bees aren’t the only pollinators — moths, butterflies and flies are other insect pollinators — but generally most pollination done by insects in our grasslands is done by bees.”
Pollinators have ‘co-evolved’ with native plant species, said Cary Hamel, conservation science manager of the Nature Conservancy of Canada’s Manitoba region.
“These ecosystems have been evolving for thousands of years,” he said.
Most ranchers think of rangelands in terms of their ability to produce grass for their cattle, but it goes beyond that. Healthy and productive rangelands have a diverse array of species, including native forbs (such as buffalo bean or pea vine) or introduced ones (such as clover or alfalfa).
“The productivity of that grass could be partially dependent upon forb (flowering plant) species that are present,” said Carlyle. “Anything that is flowering is going to be dependent upon pollination and a lot of that is dependent upon insect pollinators.”
So if pollinators disappear out of the rangeland ecosystem, then some plants, such as nitrogen-fixing legumes, will, too.
“If we start to lose (legumes) then we would see declines in productivity,” said Carlyle. “Not to mention the loss in diversity in forage types on the landscape.”
In much of Western Canada, we don’t know if native pollinators are on the decline. But Carlyle said other research indicates bumblebee numbers are falling. The exact cause isn’t known but there are indications that their ranges are shifting and that a changing climate is a factor.
“Climate change is likely going to impact these native bees,” said Carlyle. “They are getting ‘squished’ as the climate changes because southern areas will become too warm for them but their populations can’t move north fast enough.”
Helping them out
So what can grazers do to sustain a diverse and abundant pollinator community?
Keeping your range in good health tops the list.
“Our research has found a fairly strong positive relationship between range health and bee diversity and bee abundance,” Carlyle said. “In general, a lack of invasive species, a diversity of plants, and the maintenance of structure is more conducive to a healthy pollinator community,” added Hamel. “If you have land with flowers or flowering plants, that’s a great start. Continue to maintain those habitats.”
Diversity is also a good thing as shrubs and forest, grassland, and wetlands provide a variety of habitat for different pollinators. However, in the Aspen Parkland zone, keeping open meadows and prairie areas intact and free from shrub and tree encroachment benefits pollinators.
Having different types of grasses also helps.
“Bunchgrasses can be really important in terms of where they nest,” said Hamel, noting butterflies complete their lifecycle on the rangeland and the caterpillars will use grass as a source of food.
“Many native species are tied to native grasses.”
Having nearby tame pastures can also be a plus as they provide an additional food source for pollinators, which can travel several hundred metres or even, for some species, a few kilometres.
“Tame pastures usually have a significant floral component and they can play a role in conservation,” said Hamel, adding having different food sources at different times in the growing season “makes the landscape stronger.”
Both Hamel and Carlyle have seen different pollinator communities use different stages of rangelands at different times throughout the year.
“On recently grazed rangeland, the grazing resulted in a reduced litter layer, we suspect,” said Hamel. “It meant the site warmed up early in the spring and it had a greater abundance of pollinators in the springtime and a greater diversity.”
Large ranches, for example, that have a diversity of land uses and grazing approaches typically have a greater diversity of pollinators. And when rangeland borders cropland, particularly canola fields, both landscapes benefit.
“When we look at Alberta, or anywhere on the Prairies, there is this mosaic of different land uses — cropland and rangeland,” said Carlyle. “What we are also seeing is areas that have more rangeland, whether you’re in a canola field or in rangeland, if a piece of land is surrounded by more rangeland, you’re going to have more bees and a more diverse bee community.”
However, canola and other flowering crops only provide their abundance of pollen and nectar for a brief period, so rangelands are the key provider — and not only for food.
“Many bees nest in the ground or amongst dead plant material, so rangelands and other areas with undisturbed soils are important nesting grounds for bees,” said Carlyle. “Areas such as cropland where soils and the soil surface are regularly disturbed are less suitable nesting grounds.”
Both Hamel and Carlyle said there is little research on native pollinators — but both are working on changing that.
‘As we learn more, I suspect there are going to be some surprises,” Hamel said.