Expert: Dana Krempels, Ph.D. - 9/27/2007

Question
How long does it take for a water molecule to go from the root of a coastal or
inland redwood tree to the leaves? thanks

Answer
Dear Sharon,

Unfortunately, there isn't a single, simple answer to your question.  The rate of transpiration (i.e., the movement of water from the roots through the stem and out through the gas exchange pores on the leaves of a plant) varies tremendously not only with environmental conditions, but also can vary among the parts of the plant itself (for example, transpiration rate can proceed about twice as fast in smaller twigs than in the trunk).

Temperature, humidity, sunlight, soil moisture content, time of day, and many other factors can profoundly affect transpiration rate, making range anywhere from ZERO to whatever the maximum rate is for the particular species or individual tree.

A large tree can move water through its trunk at a rate of about 0.5 - 3.5 meters per hour during daylight hours when the temperature is about 25 Celsius.  But with every 10 degree Celsius increase in temperature, the rate can double.
And the rate can vary from individual to individual.

I am not aware of any studies in which the transpiration rate of a sample of Sequoia trees has been quantified, but it would be interesting to find out.  I suspect that the rate is slower than in a hardwood tree, as not only is much of the xylem in a redwood old and sealed (heartwood), but also the xylem is comprised largely of tracheid cells, rather than vessel elements (as in a hardwood tree).  The latter are able to conduct water much faster than tracheids because of the larger lumen space of the vessels themselves.

I did a literature search to see if I could find any hard numbers, but the only studies I could find reported sap flow as % of maximum, and gave no units!  Amazing!

I hope this is at least somewhat helpful.

Dana