Eucalyptus trees were studied to see how they respond to high CO2 levels and drought. Plants grown with more CO2 had better photosynthesis, even when water was limited. Water stress reduced photosynthesis and stomatal conductance, but not the internal CO2 levels. This suggests that both stomatal and non-stomatal factors affect photosynthesis in these trees. The efficiency of photosystem 2 was not affected by the conditions tested.