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Studying tree hydraulics and electronics on the ground and in the canopy

Friday, July 2, 2010, by Lisa Chen and Sarah Fouzia Choudhury
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We are studying tree hydraulics; specifically, we’re measuring sap flow in trees to understand at a fundamental level how trees get water from their roots to their canopy. A large component of this project is to understand the methodology used to assess sap flow, which includes the granier and the pulse system. Furthermore, we are also interested in evaluating the effectiveness of the method and the best way to calibrate the data. We are currently collecting and analyzing the data that is coming in from the granier and the pulse system that we have installed. There is some de-bugging we have been doing with the systems, and we are also in the process of inserting more probes into trees to get more data points.

On a day-to-day basis, we have largely been setting up the granier system and preparing for data analysis by taking tree measurements. To set up a good granier system, we have been spending a lot of time making probes, which are very expensive to purchase. Making probes involves a lot of sawing, wire cutting, and soldering. We work with many power tools, thermal couple wires, and super glue. It is very hardcore! We also do a lot of wiring, screwing, and labeling in the field to get the relevant trees connected to the right systems. In addition, we sometimes drive and ride on the “Buckey,” which is a truck similar to a cherry picker that can take us up to the canopy of the forest.

(By Lisa Chen): I have learned a lot about tree physiology and electronics. With the right materials, I can now make $500 granier probes. (A skill which could provide an interesting career alternative if my future plans don’t work out!) In addition, I can now identify a number of different trees such as maples, oaks, and hemlocks, which I wasn’t able to do before this summer. Jim Wheeler (one of our mentors), Sarah, and I spent a long time trying to identify the first chestnut tree we came across, and I am proud to say that I can now identify chestnut trees by sight. In addition, I can operate the “Buckey,” and I think that is an incredibly cool skill.

(By Sarah Fouzia Choudhury): We spent most of the first few weeks making probes, which were surprisingly time consuming to make, but it was useful for learning how they work. We have only processed data for a short while, and have had to wade through a lot of junk data since some of the probes get “creative” with the data they collect. But it would only make it so much more worthwhile when a probe was reading properly and providing interesting results. One of the patterns we have noticed is that the bole of the tree (the part of the tree nearest the ground) often shows a lag of some time. One hypothesis (assuming this is not an artifact of the granier heat dissipation method) is that the tree is acting as a sponge, so the crown of the tree starts to draw water before the roots pull water out of the soil, and it then recharges through the day. We used photosynthetically active radiation (PAR) as a proxy for the amount of solar radiation reaching the trees and stimulating stomatal opening and sap flow.

This Wednesday, we put more probes in the crown of a maple and a pine. For this, we had to raise the jib, and move ourselves into position with the finesse of a parking expert. However, our attempts at doing so were a little less than par, and involved a few broken branches. This delicate maneuver was followed by drilling into the tree, pushing in the probes, and making the required electrical connections. 

From here, we hope to continue analyzing the sap flow data and finding meaningful results. We are also interested in measuring photosynthesis rates and the amount of water that is present in the sun leaves of several species to understand tree hydraulics better.