Registering your forest with the Emissions Trading Scheme (ETS) is a voluntary but does enable owners to generate and sell some excess carbon credits for responsible foresting.
Registering for, and claiming, carbon credits (NZU’s) does not result in a liability other than the need to surrender the credits if the forest or woodlot suffers a carbon loss due to the likes of fire, wind or harvest.
In the event of harvest, or if the forest burns down, the carbon credits (NZU’s) lost would have to surrendered but can never exceed the total claimed.
If the NZU’s are sold to a willing buyer, there is a liability. That liability is the need to have enough credits in the account equal to the number of credits lost by harvest or fire. If there are not enough credits then you have to go on the open market and buy sufficient credits to equal to your liability.
Quite clearly carbon trading is about being able generate and sell some excess carbon credits.