Building roads, farm fields and other development in the Northern Alberta boreal forest can encourage a wider variety of plants to grow — but there's a breaking point, University of Alberta researchers say.

The study, published in the journal Nature Communications on Tuesday, found that the more human intrusions on the land, the greater diversity of plant species there.

Even compared with pristine areas such as northern Alberta's Wood Buffalo National Park, these altered swathes of land saw a wider variety of plants flourish, said lead researcher Stephen Mayor, a graduate student at the University of Alberta.

'Our research findings mean that the variety of plant life in the boreal forest can tolerate farms, forestry, even oil and gas extraction, but only in moderation.'— Lead researcher Stephen Mayor

But there are limits — when more than half the area was disturbed, the number of native plants began to drop off, he said.

"Our research findings mean that the variety of plant life in the boreal forest can tolerate farms, forestry, even oil and gas extraction, but only in moderation," Mayor said in statement.

As part of the study, researchers counted plant species in areas across all of Northern Alberta, including the oilsands, an area larger than Germany. The study also used satellite and aerial photos to compare the number of plant species.

"We found that when more than half of an area was visibly changed by human use, the number of native boreal plant species began to decrease," Mayor said.

The research also indicated that human development of the land tipped the odds of survival towards certain types of plants. Human intrusions in the forest tended to allow foreign species, such as invasive weeds from Europe, to replace native plants that had lived there for thousands of years, the study showed.

The results can help scientists better understand the full impact of development in Canada's boreal forest, and may aid land-planners in their decisions, researchers said.