Ambience: birds, rope whizzing
Sillett: Here it is probably about 8:30 in the morning. It’s really neat this time of day; trees are just starting to get cranking.
Two-hundred ninety-five feet above the forest floor, ecologist Steve Sillett is near the top of a Redwood, one of the world’s tallest trees. He and his team are trying to learn about the limits of tree height. Can a tree be too tall to sustain its own growth? Welcome to Pulse of the Planet’s Science Diaries, a glimpse of the world of science from the inside.
Sillett: The pores in their leaves are opening up. They’re photosynthesizing with the morning light. And they’re evaporating water because the pores are open to take in CO2. So right now our instruments are showing that the sap is really starting to flow. It hasn’t reached peak velocity yet but it will probably about mid to late morning and then depending on how warm of a day and how much wind there is and if there’s very low humidity, the trees will actually have to shut down to prevent losing too much water. Because if they lose so much water the stress inside their sap wood becomes so much that air bubbles will form and shut the tree down and the top will die. So that’s one of the things we’re looking at is how far the trees can push it before they have to shut down. And ultimately the taller the tree, the earlier in the day it has to do this. So eventually there’s going to be a height beyond which the tree can’t really grow and still have a positive carbon balance, meaning it cannot produce enough sugars through photosynthesis to continue growth.
After collecting his data at the top of the tree, Steve is ready to descend with the help of ropes and a harness.
Sillett: Okay, on the way down, starting at 90 meters. [Whizzing sound of rope] Thirty. Ten
We’ll hear more about Steve Sillett’s work in future programs. Our thanks to SonoPak for the microphones used to make the field recordings in this program.
Pulse of the Planet’s Science Diaries are made possible by the National Science Foundation.