Max. wood from natural areas harvested at replacement rate.
Effect of previous land cover on wood yield only lasts for one timestep.
No wood harvest from agricultural expansion.
Added variable tree logging cost (fixes oscillating export issue).
Timber and carbon production now serialized during calibration.

Added NATURAL_REGROWTH_TIME parameter.

Further forest work on GAMS code.

Fix for land allocation error in allocAreas method. Unprotected natural area was being calculated on more that one occasion within a timestep resulting in changing proportions of 'other natural' and 'forest' that should be protected. Area(s) of natural land that should be protected now updated at the start of each timestep and remain constant throughout the timestep.