Two things, for one there are many uses for wood, as long as it's not burnt why not make use of what you can rather than just burying.
And secondly the rate of pine growth varies greatly, see: http://www.forestenterprises.co.nz/new/afi/nzplantation.htm So location is key, as is choosing a very fast growing tree. Also Corella and other micro seaweeds are incredibly good as a natural supplement. So a bit of both, also the micro seaweed can be used to fertilize the land as discussed.
