Not on my island they don't, all the pine is stripped to the nearest deposit, it has ran as a negative since the start of the year. If i do not run my Yards on coal now and again the closer deposits become full and they go to further away deposits, yet they always read a negative.Its not a bug, The foresters timers jumps around, they can be from a + to a - in a matter of minutes, it just depends on where they have to walk to to replant, If you watch them in real time, You will see that they can and do sometimes walk great distances... It would be at that point Aththemanic that you happened to have checked and seen the - numbers, But other occasions they will be replanting right outside their forester huts, That would equal the + number and is why you never run out of trees, the balance of the long/short walks is right.