Answer:

eucalyptus

Answer	Crossword Clue
EUCALYPTUS	Koala's diet source
EUCALYPTUS	Undergrowth?
EUCALYPTUS	Tree favored by koalas

EUCALYPTUS	Tree common in California.
EUCALYPTUS	Gum tree.
EUCALYPTUS	Source of heavy timber wood
EUCALYPTUS	Giant timber tree from down under