A 1991 study (FRDA Report #165) found that managing competing vegetation with herbicides can seriously affect the availability of grizzly bear forage over both the short and long term.
Over the short term, the bears' local food supply can be significantly reduced, even though some forage species do recover a few years after the herbicide treatments have been completed.
More importantly, managing competing vegetation can contribute to shortages in grizzly bear forage over the long term by helping to create dense stands of regenerated trees which can deprive berry-producing shrubs and other vegetation of the sun they need to survive. As dense stands grow, the forest canopy gradually begins to close, and after 15 to 25 years, the sunlight can no longer reach the forest floor. Most of the plant species important to grizzly bears cannot tolerate these low-light conditions, and they either die out or fail to produce fruit. Since many of B.C.'s second-growth forests are on rotation periods of between 80 and 100 years (length of time between harvests), this can result in a critical shortfall in grizzly forage over an extended period of time.
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