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Grasslands Going To Bush, Aerial Photos Show

SE 21-09-11W -1946

SE 21-09-11W -1994

“Fire was one of nature’s natural elements, and we have controlled it.”

– Bill Gardiner

When Henry Youle Hind led an expedition across the Prairies in 1858, there were apparently very few trees.

“The country west of Souris is a treeless desert, in dry seasons destitute of water, and without a shrub or bush thicker than a willow twig,” according to the Manitoba Historical Society’s website.

That’s not the case any more.

Tree cover has increased tenfold in some areas examined as part of the Native Pasture Improvement Project (NPIP) that began in 2005, according to Bill Gardiner, a MAFRI pasture and rangeland specialist.

“Brush encroachment is a serious problem in a lot of our native pastures in Manitoba and we’re losing a lot of grasslands because of it,” said Gardiner, who gave a presentation on the subject at a recent pasture tour near Sidney.

“We’re losing a lot of it primarily because in the absence of fire, brush tends to move in.”

MOVING IN

Since it began, NPIP has established 50, 40-acre demonstration sites on public and private land to examine the effectiveness of various strategies for beating back the bush, including treatments ranging from spraying to mechanical means such as logging. Cattle grazing was used as a followup at all sites.

During the inventory assessment stage, the Remote Sensing Unit of Manitoba Conservation was used to compare recent and historic aerial photos taken of blocks of land in rural municipalities including Alonsa, Portage la Prairie, and Miniota.

Some of the results were striking.

A 3,840-acre block in the R. M. of Alonsa that is currently PFRA and leased Crown land showed that where there was once just 393 acres of mature trees in 1946, the total area of bush cover had soared to 2,976 acres.

A further example, taken from what is now a wildlife management area in Portage R. M., saw tree cover grow from 188 acres in the 1940s to 2,239 acres within the 3,200-acre block.

In the R. M. of Cameron, a 1,440-acre parcel in a wildlife management area with sandy soil in the province’s southwest corner would surely confound the sensibilities of 19th-century explorer Hind, if he was alive to see it today.

Where in the 1940s there was 632 acres of trees, that figure grew to 975 acres in the mid-1990s.

ABSENCE OF FIRE

The main reason for the burgeoning growth of trees on what was a virtually treeless plain was the absence of Prairie fires. A changing climate may also have played a role, said Gardiner.

“Fire was one of nature’s natural elements, and we have controlled it,” he said. “Who wants to have their fences burnt? Maybe some changes in climate have added to that as well.”

Test sites which compared total biomass yield of grass, forbs and shrubs in one-metre square cages after using various sprays such as Remedy, 2,4-D, Grazon and mechanical clearing methods such as roller chopping, cable drag and bulldozing on bush eight to 10 feet tall, mature standing trees, and pasture invaders such as dogwood and buckbrush.

Yields in the second and third years appeared to be the best for most chemical treatments, but began to drop off after the fourth year as new growth appeared.

“What that tells you is that there is no one-shot treatment that lasts a whole long time,” said Gardiner. “If you can get six to eight years out of a treatment, that’s probably not too bad, but you’re going to have to follow up with another treatment.”

CONTROL SHORT LIVED

All of the control methods cost money and offered only relatively short-lived effects. Grazon, for example, costs roughly $56 per acre, and Remedy $72 per acre, plus aerial application expenses. Mechanical control is the cheapest, especially if a homemade drag such as a large I-beam is used behind large machinery.

The overall economic analysis of all strategies will come out in the final report due this fall, he added.

One thing that he stressed was the importance of grazing livestock as a natural means of keeping brush down, which was used at all sites.

“There’s nothing better than grazing to go in and follow any treatment,” he said. “If you have the means, grazing can do it all, but it’s a costly and very intensive exercise.”

In the R. M. of Alonsa, a chemical-free trial saw 90 cow-calf pairs on a 220-acre site divided into 12 paddocks has shown “pretty good” results so far, he noted, although the data has not been compiled yet.

“The technology is still in its developmental stages. We don’t know everything in terms of best timing or best combination of treatments, said Gardiner. [email protected]

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