THIS REPORT FROM 2004 shows that the ministry was optimistically predicting much higher growth in its plantations than has turned out to be the case. At the time the report was written, it was well known in the ministry what the implications of the Mountain Pine Beetle would likely be (the loss turned out to be not as bad as was believed would be the case at the time). So the MPB can't be blamed for the miscalculation of timber supply around this time.
The report predicted timber supply would be about 74 million cubic metres per year by 2020. The actual harvest in that year, which followed the closure of dozens of mills in BC's Interior due to a shortage of timber supply, was around 50 million cubic metres.
In other words, BC's Chief Forester Jim Snetsinger signed off on a timber supply analysis that predicted there would be 50 percent more timber available in 2020 than there actually was. The result was many years of over-cutting of healthy forests.