Bt production is also very important. Trees engineered with Bt have the toxic product of the bacteria in all cells. Ingestion of the toxin by soil micro-organisms has been shown to kill these life forms as well as the insects that eat leaves and twigs. Low lignin content is a high research priority because one third of the dry weight of wood is lignin, which cannot be used by the pulp industry. Of course lignin gives trees their rigid structure.
Rapid growth is another desirable trait for obvious reasons.
Some eucalypti are ready for harvest in as little as 4-5 years. But these trees deplete soil nutrients very rapidly, and they can even negatively impact local hydrological regimes. Bioremediation is another research focus, to develop trees that will remove toxic metals and other pollutants from the soil. Some studies have indicated that these trees may simply move the metals from the soil into the air through trees' leaves. Sterilization techniques have been sought to calm down the public about concerns that the above traits will move into wild species through horizontal gene transfer.