Zwu, this is an interesting point you make.
However you are forgetting the flip side of the equation. The trees produce cash at least twice a rotation, once during trimming and once when they are felled.
Here's some positive news on the sector.
Chinese demand raises log prices
http://www.stuff.co.nz/business/3546879/Chinese-demand-raises-log-prices
Had myself singing "Extension to the Suspension" the other day. tralalala