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What is Growing in the Canopies of the Tallest Trees in the World?

Lichen, Bryophyte and Vascular Plant Biodiversity Study

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The canopy can seem out of reach, hundreds of feet overhead, a mystery just waiting to be discovered. The coast redwood canopy ecosystem remained virtually unexplored and undocumented for most of the last century. It was not until the late 1990s that we first learned about the abundant and rich canopy life hundreds of feet above the ground. These first discoveries came from the pioneering research of Professor Stephen Sillett at Humboldt State University in Northern California. Dr. Sillett made the coast redwood canopy accessible to the scientific community with arborist rope techniques and revealed the lush treetop habitat that few individuals have seen firsthand, even today.

A multitude of mosses and lichen cling to the bark of redwoods, but they are dwarfed in size by the ferns, shrubs, and even other trees that can reside aloft. They are all called epiphytes – plants growing non-parasitically on the branches and trunks of large host trees. Coast redwood epiphytes are a diverse bunch, but what they have in common is a respectable ability to tolerate tough treetop weather and a dependence on old redwood trees. Sustained by winter rain and summer fog, epiphytes thrive in these majestic giants that have been shaped by the centuries into architectural vertical habitats – trees with divided trunks, thick limbs, fire cavities, and other nooks and crannies.

Recent League-supported research by Rikke Reese Naesborg looked at the epiphyte community in three coast redwood parks in the southern redwood range. Age, crown structure, and climate can all play a role in the diversity and abundance of the epiphytic community in these trees. In the southern part of the redwood range there is less rainfall and generally smaller, younger and possibly less complex trees. This raises an interesting question as to whether the epiphytes found there are different than those found in the northern part of the coast redwood range.

Rikke’s research looked at some of the tallest trees at Armstrong Redwoods State Natural Reserve in Sonoma County, Big Basin Redwoods State Park in the Santa Cruz Mountains and Pfeiffer Big Sur State Park in Monterey. Results show that initial thoughts that epiphyte diversity might be lower in the southern coast redwood range does not hold true. Yet the abundance of epiphyte type changed. There was actually an increase in lichen diversity at Big Basin RSP and Armstrong RSNR compared to some northern parks (comparison study is Williams & Sillett 2007). But there were fewer bryophytes (mosses) and vascular plants in the southern parks compared to the northern trees. The number of epiphytes at Pfeiffer Big Sur SP was extremely low compared to the other sites, possibly due to the location of the study trees within the park.

Below is a table of total species richness for the study parks.

PARK LICHEN BRYOPHYTES VASCULAR PLANTS TOTAL
Armstrong Redwoods SNR 165 20 32 217
Big Basin Redwoods SP 178 28 24 230
Pfeiffer Big Sur SP 34 4 7 45
Total 220 30 44 294

This epiphyte research helps paint a better picture of what is going on in the canopies of these tall trees. If we hope to restore younger, cut-over forests to the rich, diverse old-growth of the future we need to first find out what species are present in these old forests.


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