Into the Canopy: The 2014 Muir Woods BioBlitz

In March 2014, Muir Woods National Monument took part in a BioBlitz, an event to find and identify as many species as possible in a short time, to learn what lives in its forest canopy. Four scientists, Stephen Sillett, Marie Antoine, Cameron Williams and Reese Næsborg, became the first people ever to climb trees at Muir Woods. They surveyed life in the canopy and, for the first time, measured a redwood and a Douglas fir there.

The climbers

Sillett, who has long been fascinated by redwoods and other tall trees, and Antoine, a botanist whose first love was lichens, have climbed countless California redwoods and are leading experts in climbing and studying the world's tallest living things. Næsborg has extensive experience studying lichens and epiphytes, organisms that grow on the surface of plants, and Williams has studied forest canopies around the world. Williams and Næsborg, of the University of California, Berkeley, later wrote up the climb in a paper, "What's in the Trees at Muir Woods?"

They were especially interested in lichens. A lichen is a partnership, a symbiosis between fungi and algae: the fungi give it shape and structure, while the algae give it color and feed the fungi through photosynthesis. North America has about 3,600 known lichen species.

The climb

Because no one had climbed trees for research at Muir Woods before, the Park Service was very cautious. When the scientists arrived on a Friday morning, the area around the two study trees had been fenced off and safety officers were controlling access to protect passersby. Climbing the tallest trees takes proper equipment, training and experience.

At noon they began. Sillett and Antoine climbed a 249-foot redwood in Cathedral Grove; Williams and Næsborg climbed a 230-foot Douglas fir. Both trees were among the largest in the grove and probably at least several hundred years old. The teams surveyed from the top down.

Bare bark, then a burst of life

Antoine noticed at once that nothing grew on the redwood's lower trunk: for the first 50 meters it was bare bark. Then, at about 50 meters, the change was abrupt, and suddenly every branch was covered, mostly with lichens. Williams and Næsborg suggested the bare trunk may be explained by the redwood's unfriendly bark chemistry, low light and fairly dry bark, and especially by its microclimate, standing closely surrounded by other tall trees in dense Cathedral Grove. The main trunks of coast redwoods generally carry sparse epiphyte communities, especially below the crown. Redwood bark contains tannic acid, which gives it its red color and helps it resist fire, insects and disease, and makes the trunk less hospitable to epiphytes.

High in an old tree, many microclimates exist side by side: sunny, dry spots and shady, damp ones, and big branches where decaying leaves build up soil in which ferns, huckleberries and other plants take root. Each offers a home for different living things. From about 70 meters up the redwood, Sillett reported finding a fairly high diversity of life on the bark.

What they found

• Epiphytes: more than 40 species on the redwood and more than 50 on the Douglas fir. Williams and Næsborg attributed the difference to the trees' different surfaces and microclimates. The Douglas fir's branches and upper trunk were so thickly coated that the bark was hard to see, while the redwood had nothing below 50 meters, a few moss-covered dead branches around that height, and lichen-covered branches above.
• A salamander: a juvenile arboreal salamander about ten meters up the Douglas fir.
• A healthy forest: Sillett had expected signs of decline from heavy trail use and trampling but found none; the canopy was more vigorous than he expected, and the redwood's growth rate had increased in recent decades.

Although only one redwood and one Douglas fir were surveyed, the scientists noted that it greatly improved knowledge of the monument's canopy life, simply because no one had inventoried epiphytes on its large trees before.

Lichens and clean air

In November 2014, Næsborg and Williams returned for a broader lichen survey and found 103 species at Muir Woods, in their paper "Lichen Diversity in Muir Woods National Monument." The most species grew on California buckeye, followed by tanoak and Douglas fir, and dead redwood foliage and cones that stay on the tree for years also supported many.

Lichens reveal a lot about a forest. They feed animals, give birds nesting material and protect tree bark from harsh weather, and they are indicators of air quality: some tolerate pollution, while others survive only in clean air. At Muir Woods, the forest interior was dominated by lichens sensitive or somewhat sensitive to air pollution. Several pollution-tolerant species grew near the parking area, but they were not abundant, and sensitive species were found there too.

For the climbers, the canopy was a different world of distinct microclimates and species. Næsborg called it a very special and beautiful place, even after climbing many trees.

Sources

• National Park Service, Muir Woods National Monument, "Into the Canopy - The 2014 Muir Woods BioBlitz." https://www.nps.gov/articles/000/into-the-canopy-the-2014-muir-woods-bioblitz.htm
• Cameron Williams and Reese Næsborg, "What's in the Trees at Muir Woods?" https://www.researchgate.net/publication/333092787_What%27s_in_the_trees_at_Muir_Woods, and "Lichen Diversity in Muir Woods National Monument," https://www.researchgate.net/publication/333092921_Lichen_diversity_in_Muir_Woods_National_Monument. Quotations from the scientists are paraphrased here.
• Save the Redwoods League, BioBlitz 2014: https://www.savetheredwoods.org/research/bioblitz-2014-muir-woods-national-monument/
• The Park Service's page spells the botanist's surname both "Antoine" and "Antonie"; this page uses "Antoine," the more frequent spelling. Its photographs, credited to Save the Redwoods League, are not reproduced.
• Words on this page from people and organisations outside the federal government are paraphrased; rewritten in hubnx's own words.