Doing Canopy Science
Scientific exploration of tall forests has blossomed with the development of rope techniques to access tree crowns. Here is a brief description of these techniques and illustrations of their applications in canopy research at Humboldt State University.
The climbing equipment required for the study of old-growth redwood forests is cumbersome and must be manually hauled to the trees. Sometimes, the trees are located across raging creeks, and it is necessary to tow the gear on Tyrolean traverse.
Once a tree is rigged, a dangerous process not described here, a climber (red arrow) ascends the main rope which is over a pulley near the treetop.
The first climber up a rigged tree takes the rope off the pulley and uses a loop near the midpoint to anchor both ends of the rope hanging to the ground.
The next climbers ascend in pairs and measure the main trunk’s diameter at regular height intervals. They can also easily explore cavities in the trunk such as this fire cave in a Sequoiadendron giganteum.
Within the crown, climbers measure diameters and XYZ coordinates of all woody structures, including branches, limbs, and reiterated trunks.
Motion lanyards, which are used by arborists as well as canopy scientists, enable climbers to reach nearly all parts of large tree crowns. Here Jim Spickler measures a branch diameter far out in the crown of an 281-foot-tall Eucalyptus regnans.
One climber typically remains on the fixed rope next to the main trunk and records data being collected by other climbers moving around the crown with motion lanyards.
Sometimes it is easier to rely on old-fashioned primate skills to reach parts of tree crowns. Here Marie Antoine scampers along the underside of a redwood branch to get a distal diameter.
When huge tree crowns are being mapped, motion lanyards alone are insufficient; longer ropes are also required. To get leaf samples from the outer crown of this Sequoiadendron giganteum, I (red arrow) swung out from higher in the crown using a rope looped through a ART Rope Guide that was anchored to an overhanging limb, looped my motion lanyard over a sturdy branch in the outer crown, and then lowered from both rope systems to reach the leaves.
The outermost leaves of trees are sometimes inaccessible from within the crown, and it is necessary to rig a Tyrolean traverse between adjacent trees. Moving from the crown of one tree to another on ropes is sometimes safer and more efficient than climbing the second tree from the ground. Here Cameron Williams crosses between two Sequoiadendron giganteum.
Infrared survey lasers (Impulse 200LR, Laser Technology Inc.) are an essential tool for mapping tree crowns. Here Bryan Kotwica measures the horizontal extension of a Sequoiadendron giganteum branch with a laser.
Accurately measuring the total height of a tall tree often requires a climber to stand very close to the treetop so that a tape can be extended to its highest leaf. Since the tops of trees are fragile, I protect the tree’s cambium by anchoring myself to an ART Rope Guide. This friction-saving device is placed as high up in the tree as can be reached by hand and trusted with one’s life in the event of a fall. A personal climbing line is then looped through the device and slacked out enough to permit free-climbing a bit higher in the tree to reach its highest leaf. If necessary, an extendable pole is used to lift the tape to the exact height of the tree’s highest leaf.
To better understand the forces affecting trees, we install sensors in the crown. Here the measuring tape (orange), is hung from a sling wrapped around the trunk just above sensors mounted near the top of a 299-foot-tall Sequoia sempervirens.
The treetop sensors we use include instruments (ICT International Pty. Ltd.) that quantify light, air temperature, air humidity, leaf wetness, wind speed, precipitation, and xylem sap flow.
In the old-growth redwood forest canopy, our sensor arrays are solar-powered. Each tree receives a 50-watt solar panel that maintains a 12-volt battery, which powers the sensors and a datalogger controlling and storing their measurements. Here is a view of the array near the top of a 366-foot-tall Sequoia sempervirens.
The battery and datalogger are housed inside a waterproof enclosure (red arrow) hung from the trunk with a sling. Here is a view of the array near the top of a 361-foot-tall Sequoia sempervirens.
Instruments installed in old-growth redwood forest canopies have been collecting data since 2000 when the first array was deployed in Atlas Tree. The light, temperature, humidity, wind, and precipitation sensors shown here (Campbell Scientific Inc.) functioned for over 5 years before they were removed from the canopy.
Wireless sensors hold promise for future deployments, but good old-fashioned wiring still does the job in the redwood canopy. Here Anthony Ambrose and I solder replacement sensors onto the array measuring sap flow through a reiterated trunk in the lower crown of a 332-foot-tall Sequoia sempervirens.
Canopy sensors need to be serviced periodically. Here I am clearing debris from a sensor measuring precipitation in the middle crown of a 367-foot-tall Sequoia sempervirens.
Several sensors must be installed around a large trunk’s circumference to adequately quantify sap flow through the entire crown. Here Anthony Ambrose and I install sensors in the lower trunk of a 371-foot-tall Sequoia sempervirens. These sensors revealed that the tree can lose over 1000 liters of water during a single day via evapotranspiration.
Installing sap flow sensors requires drilling 1-mm-diameter, 25-mm-deep holes in the outermost layers of a tree’s wood, the sapwood. Sequoia sempervirens is incredibly resistant to attack by wood decay fungi, so these small injuries have no effect on tree health. Here Anthony Ambrose drills a hole for a sap flow sensor in the main trunk of a redwood.
A wide variety of scientific instruments can be used to study tall trees. Here Marie Antoine patiently waits while a LiCor 6400 Portable Photosynthesis System quantifies leaf gas exchange in an 266-foot-tall Eucalyptus regnans.
George Koch long ago convinced me that there were few limits to the questions we could ask about tall trees. Here he is perched on a Metolius port-a-ledge near the top of a 298-foot-tall Sequoiadendron giganteum getting ready to deploy instruments.
Quantification of light availability throughout tree crowns is made easy with a digital camera on a self-leveling mount (Régents Instruments Inc.). Here I am measuring light availability of leaves in the inner crown of a 356-foot-tall Sequoia sempervirens.
Trees record their growth history in annual rings laid down by the cambium as it produces wood. This information can be accessed only by studying the wood itself. Here Marie Antoine extracts a small cylinder of wood from a redwood limb. The study of dendrochronology is becoming increasingly important in my laboratory, which uses WinDENDRO (Régents Instruments Inc.).
Scientific understanding of tall trees requires accurate quantification of whole-tree dimensions that can be attained by non-destructive crown mapping coupled with a small amount of destructive sampling. In 2006, we removed all the leaves from 50 randomly selected branches spanning the full range of heights and diameters observed in 15 crown-mapped Sequoia sempervirens up to 371 feet tall. This represented just 1% of the total leaves. Here Bob Van Pelt and Marie Antoine remove the leaves from a branch and put them in a large bag hung from slings.
Once removed from the tree, a branch and its leaves are transported to the ground, where they are weighed. A sub-sample is then weighed, taken to the laboratory, dissected further, scanned, dried, and re-weighed. Our hierarchical approach to mapping and sampling tall trees is generating accurate whole-tree estimates of leaf biomass, leaf area, cambium surface area, bark, sapwood, and heartwood for the first time.
