Blue gum trees - an important koala habitat - were harvested from the plantation in December, leaving only a few isolated stands of trees.
Some koalas had starved to death in the remaining trees. Others were apparently killed by bulldozers.
About 80 surviving koalas have been removed and are being cared for.
The deaths come after tens of thousands of koalas were killed in the bushfires that have ravaged Australia. The marsupial is listed as "vulnerable" by Australia's Environment Ministry.