TORONTO - The Ontario government is using flawed data to determine how many trees should be chopped down in public forests, says a study released Thursday by a leading conservation group.

The study by the Wildlands League, a chapter of the Canadian Parks and Wilderness Society, found that many "unsubstantiated'' assumptions are being fed into the Strategic Forest Management Model which determines the province's logging practices.

The assumptions are critical because Ontario predicts the amount of allowable logging using the computer model, said forest conservation analyst Dave Pearce.

Pearce said an analysis of some eight forest management units covering more than five million hectares of provincial forests currently open for logging found harvesting levels are based on an inaccurate assessment of the forest resource inventory -- namely, how many trees and what species actually exist in Ontario forests.

Industry experts, however, say it's folly to suggest Ontario is being excessively or irresponsibly logged.

The study suggests the province has also overestimated how fast forests will grow back and underestimated how much forest land is lost to roads, landings, slash piles and poor regeneration, and also the amount of damage forests suffer from fire, wind and insects.

The province has also failed to properly account for wildlife habitat, said Pearce.

"The whole model is really premised on how valid those assumptions are going into the model,'' he said. "If it's not based on real world data, then your results are likely going to be skewed.''

As a result, he said, Ontario could be harvesting more wood than the province's forests can sustain, despite a recent downturn in the forestry industry.

"Theoretically, there should be reduced pressure on the forest because the model says we can have this much, but over the last couple of years, we haven't been cutting that much,'' he said.

The study also recommends the Ministry of Natural Resources receive more funding for its stewardship branch so staff can properly assess forest inventories and better supervise the industry.

Ministry officials refused Thursday to comment on the report until they have fully reviewed it. Those within the industry, however, said Ontario and Canada have some of the most sustainable forestry management practices in the world.

"If you look at the entire forested land base in Ontario, it's over 69 million hectares,'' said Scott Jackson of the Ontario Forest Industries Association, which represents some 30 small and large timber companies including giants Domtar and Abitibi-Consolidated.

"We on average harvest about 200,000 (hectares). That is less than one-third of one per cent of the total forested area in the province of Ontario.''

When it comes time to harvest, Jackson said companies can't just cut down whatever they like. The development of a forest management plan, he said, can take more than two years and involves public consultation and stakeholder meetings.

He said there are upwards of 30 guidelines aimed at protecting wildlife, natural land features and cultural heritage that must be followed and that companies are getting far more use out of every log now than ever before.

"We're making products out of what a decade ago would be considered a wasteful byproduct. To suggest there's no innovation in the forestry industry is completely misguided,'' Jackson said.

The growing environmental movement has given rise to opportunities for cogeneration and the development of the bio-fibre industry, he added.

"That is something that typically will not be accomplished if, as many groups are saying right now, (the government) significantly reduces the allowable harvest area.''