Forest land buyers need to be aware of undisclosed carbon liability. Buying land that had forests on it prior to 1990, can lead to an unforeseen large carbon liability bill. Our recent experience with such properties has led us to discover there could be 160,000 ha of land where owners may not know they have a significant liability. That could be over 5000 woodlots nationally. These are previously forested areas that did not receive an allocation of carbon units, nor given an exemption from the ETS; hence there is no reason for a legal record, or entry on the land title. For trees harvested after the title transfer the liability is with the new owner. As there is a period of 20 years grace to re-establish native forest (30% over 5m tall), this liability can emerge much later and often a complete surprise. If there is an existing forest on the property, we advise careful due diligence on when it was planted. This means expert examination of aerial photography and satellite imagery.