The current infestation is actually causing the BC forests to be nearly a net carbon negative! (edit: to clarify I mean negative as in they're increasing the carbon output of the forests compared to the carbon sink. May be wording it wrong)
I think you got it right, forests are only carbon sinks as long as the trees are alive then they release their sequestered carbon as they rot.
Typical tree dying is sporadic event and can be taken back up by other trees in a normal situation.
Here the tree death is not sporadic and there are not enough growing things to re-uptake the all the released carbon so it enters circulation.
The current infestation is actually causing the BC forests to be nearly a net carbon negative! (edit: to clarify I mean negative as in they're increasing the carbon output of the forests compared to the carbon sink. May be wording it wrong)