A World Above Our Heads Samuel Hargrove Science, Science & Medicine Four years ago, I was hit with the sudden need to get into the redwood forest canopy and find out what was up there. From various sources, including the book The Wild Trees by Richard Preston, I had heard tell of a sky world held aloft hundreds of feet in the air and hardly explored—a poorly understood ecosystem awaiting exploration. The canopy is so much more than trees. Branches and limbs make up the substrate, but the real stars of the show are all the organisms that fill unique roles in the treetops. Unfortunately, the world’s forest canopy ecosystems are being destroyed before humans can begin to appreciate their complexity and understand the intricate workings of these sky habitats. How to Climb a Redwood With this in mind, I began trying to figure out how to access the treetops as soon as I began college. The University of California, Santa Cruz campus has several hundred acres of forests and other natural habitats, and I began scouting tall trees to test out my canopy access methods. The first challenge to overcome when you want to climb up into the redwood canopy is that the lowest branch of any given tree can be more than a hundred feet off the ground. I knew that canopy researchers used a crossbow to shoot an arrow trailing a fishing line over a high branch, then used that fishing line to pull over a rope. One end of this rope would then be tied to a point near the ground, making the other end of the rope taut and ready to climb. It took me several months to get it right. Some of the gear I used was appallingly unsafe—like a 20-year-old, overly stretchy rock climbing rope. Trial-and-error is not a good method when expertise is needed and danger is constant. Luckily, neither my friends nor I ever got seriously hurt in this experimental period. Eventually, I was able to break into the redwood forest canopy. Life in the Canopy I found lichens caked in thick, crusty layers; huge limbs in the uppermost reaches of tree crowns; and, most significantly, distinct patterns in how epiphytic species (organisms that live on plants, such as lichens) were distributed throughout the canopy. I saw that certain leafy, lettuce-like lichens were barely present in the lower parts of redwood crowns, and grew ever more dominant as I moved higher through the crown. Not only that, but their reproductive output changed dramatically from tree bottom to top. Down in the lower reaches of the tree, where this species begins to show up, it is virtually sterile. Toward the upper crown, it gradually increases the numbers of cup-like reproductive structures (called apothecia) it puts out. It also produces different numbers of soredia, or asexual propagules, at different heights. The lichen tapers out in the uppermost parts of the canopy. This lichen, which I later found is called Flavoparmelia caperata, is not unique in this stratified growth pattern. Every other lichen seems to have a specific layer of the canopy that it prefers or requires. Lichens seem to be exquisitely sensitive to the changes in light, temperature and moisture that occur along a vertical gradient in a tree. But how dramatic are these changes? And how do they interact to control not only which lichens grow where, but how they grow? From my initial explorations, my interest in canopies and canopy organisms only increased. I became fascinated with epiphytes. In some parts of the world, like the tropics and some very well-developed rainforests in northwestern California, the forest canopies support epiphytic ferns, shrubs, and even trees. In drier forests, lichens dominate. Lichens are fascinating organisms. Actually, they’re really not individual organisms at all. Each lichen is an intimate association between a fungus and either a green alga (like the kind that land plants evolved from) or a cyanobacterium (like those that gave our atmosphere its oxygen). Lichens don’t show up in the press often, but they occasionally make headlines for their ability to withstand extreme conditions. Scientists have exposed lichens to the vacuum of space, where they are subjected to extreme cold, radiation, and lack of air. After months in these conditions, the lichens have been brought back to Earth, where they continue to grow (see also Sánchez et al. 2014). Going Higher (and Deeper) When I decided to work on a senior thesis, I knew I would be studying the redwood forest canopy, and the dynamics that govern the species therein. The question I am asking in this study is about how lichens are controlled by environmental factors and how this affects their dispersal throughout the redwood canopy. Why does Flavoparmelia act so different at different heights in any given redwood tree? Which microclimatic factors are most important to it, and how do these factors work together to determine where Flavoparmelia grows and how it reproduces? Furthermore, do these environmental constraints lead to a stratification of the lichen’s spores? In other words, because Flavoparmelia seems to put out more spores at certain heights, do certain layers in the canopy have more airborne spores than others? How might this, in turn, lead to even more sharply defined boundaries for where the lichen grows? In eight large redwood trees in the Santa Cruz Mountains, I will map out Flavoparmelia’s distribution and reproductive state—how much it is reproducing, both sexually and asexually—at each part of the canopy. To determine the effects of microclimatic factors, I will install iButtons© at different heights in each tree. These little devices continuously record temperature and moisture data. I will use a canopy camera to see how much light is reaching each point in the canopy. I will also use a vacuum air trap to find out which sorts of spore are where throughout the canopy and how abundant they are. I will synthesize this information to tease apart which factors are important in controlling where this lichen can grow, and how environmental factors determine how it spreads throughout the redwood canopy. Canaries in the Canopy I mentioned that the canopy ecosystems of the world are disappearing. This is true everywhere. Even where logging does not take place, changing weather patterns are beginning to impact the biology of the forests. Since lichens are so finely attuned to their environment, they might be at the highest risk of being pushed beyond what they can handle in a warming climate. In a sense, lichens are the canaries in the canopy. If we know what they require in terms of temperature, sunlight, and moisture, we can predict where they will be able to survive in the future, and we can know which areas we need to preserve. This project is about the fundamental unknowns of the redwood forest canopy. It’s an unfamiliar environment up there, and one that we have a hard time understanding. One reason for this is that it’s so difficult to access. Another is that the canopy is a three-dimensional space where organisms can move up, down, and laterally. This is very different from what can happen on the ground. But we have the chance to gain insights into how this system works, so that we can protect what is left of this fascinating world in the sky. If you’d like to help fund Samuel’s research, please visit his fundraising page on Experiment.com. Further Reading Brandt, A., J. de Vera, O. Silvano, and O. Sieglinde 2014. Viability of the lichen Xanthoria elegans and its symbionts after 18 months of space exposure and simulated Mars conditions on the ISS. International Journal of Astrobiology. Published online 23 July 2014. Sánchez, F. J., J. Meeßen, M. del Carmen Ruiz, L. G. Sancho, S. Ott, C. Vílchez, G.Horneck, A. Sadowsky, and R. de la Torre 2014. UV-C tolerance of symbiotic Trebouxia sp. in the space-tested lichen species Rhizocarpon geographicum and Circinaria gyrosa: role of the hydration state and cortex/screening substances. International Journal of Astrobiology 13:1-18. Hilmo, O., Y. Gauslaa, L. Rocha, S. Lindmo, and H. Holien 2013. Vertical gradients in population characteristics of canopy lichens in boreal rainforests of Norway. Botany 91:814-821. MacDonald, A., and D. Coxson 2013. A comparison of Lobaria pulmonaria population structure between subalpine fir (Abies lasiocarpa) and mountain alder (Alnus incana) host-tree species in British Columbia’s inland temperate rainforest. Botany 91:535-544. Martínez, I., T. Flores, M. A. G. Otálora, R. Belinchón, M. Prieto, G. Aragón, and A.Escudero 2012. Multiple-scale environmental modulation of lichen reproduction.Fungal Biology 116:1192-1201. Sillett, S. C., and T. R. Rambo 2000. Vertical distribution of dominant epiphytes in Douglas-fir forests of the central Oregon Cascades. Northwest Science 74:44-49. Sillett, S. C., B. McCune, J. E. Peck, T. R. Rambo, and A. Ruchty 2000. Dispersal limitations of epiphytic lichens result in species dependent on old-growth forests. Ecological Applications 10:789-799. Williams, C. B., and S. C. Sillett 2007. Epiphyte communities on redwood (Sequoia sempervirens) in northwestern California. The Bryologist 110:420-452.