Now, now, let's not rush to conclusions. It is quite possible that this will be beneficial.
Returning Madagascar to its former glory is not going to happen anytime soon, but is there reason to believe that the Korean investment will result in widespread destruction of habitat? The article says they are leasing an area half the size of Belgium- so, about 15,000 square miles, or 3% of Madagascar's total land area.
Also, agriculture is not entirely incompatible with biodiversity. Hopefully the South Koreans will encourage an ecologically enlightened approach to farming in Madagascar.
Additionally, if the deal is economically beneficial to Madagascar and the Malagasy people, it will lessen the need for Malagasy people to pursue logging and wildlife export jobs. Too, an economically healthy population is more likely to consider the benefits of long-term land-use sustainability, ecological health, and other long-term goals that are hard to see when you are desperately poor.