Question: Tree transpiration rate

[Geoff Vanderkooy]

Greetings everyone!

  My wife is trying to discover how much water a tree transpires during a day.
Does anyone know, or can suggest a reference she could look at?
For example, how much water does an average, 100 year-old Douglas fir transpire?
How much does this vary with weather conditions?

  She is trying to design & build an interactive computer presentation for a
non-profit nature sanctuary here.

  Thanks in advance for your help!

Geoff (gvanderk at me.uvic.ca)