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Steve Sillett is an associate professor of botany in the Department of Biological Sciences at Humboldt State University in Arcata, California, where he teaches courses on lichens, mosses, and forest canopy biology. He takes graduate students with previous climbing experience and trains them one-on-one in the modern techniques needed to study redwoods.

What do these redwoods mean to you?

I鈥檓 totally in love with them. When I leave the ancient forests and I鈥檓 driving through all the cut-over forests back to the university, I鈥檓 going: 鈥淛eez, I just can鈥檛 believe the stuff that I鈥檝e seen.鈥� I come away completely enriched and renewed every single time. You get this sense of prehistory.

You sound as if you鈥檙e describing a spiritual experience.

A part of it is very spiritual. It鈥檚 one of the things that I cherish the most about my job. If you can set aside all the mental chatter that goes on in your head as a scientist, or for me, as an American, and be quiet for a minute, then you get into this space where you are interacting with another organism that functions completely differently. You have these epiphanies when you completely lose sight of yourself and become part of something that is much greater.

What triggers it?

It mostly happens when I鈥檓 on traverses between trees. I鈥檓 out in the middle, hanging on a little rope, and I鈥檓 pulling myself across. I鈥檒l pause to take a breath and all of a sudden there鈥檚 this complete silence of the mind. There鈥檚 this awareness of where you are, 90 metres up, in this breathing, living forest of ancient beings, spinning through space. There are definitely those moments, and they come unbidden. You should be able to cultivate that awareness in your daily life, without having to climb 110 metres up a tree and hang from a rope, but for me, that鈥檚 where it tends to happen.

What came first, your passion for trees or your passion for climbing?

I thought I was going to be an organic chemist for a while. I used to climb trees around Portland, Oregon, to relieve the stress of college. I took a real fancy to it.

Once, I found a 90-metre redwood tree that I could scamper up by jumping onto its lower branches from a smaller, adjacent tree. I climbed to the very top. This was before I knew about ropes or anything. I was 19 years old, and not very cautious.

This particular tree had a rotten top with a bunch of huckleberry bushes growing out of it. When I got up there, exhausted from my first climb up a big redwood, there were all these berries I could eat. I crawled up along some of the branches and hung out up there, marvelling. The thing that strikes you when you see an old-growth redwood canopy from above is how individual each tree looks. It changed my life.

And now you are surrounded by redwoods where you teach at Humboldt State University?

Yes. The university is on the north coast of California, just above Humboldt Bay in the coast redwood belt. Less than 1 per cent of the remaining forest is old-growth. It鈥檚 a pretty big area, though, for the redwoods once went in a broad swathe near the coast from the Oregon border all the way down south of San Francisco. Now there are only four large reserve areas left. Within an hour鈥檚 drive south of Arcata is Humboldt Redwood State Park, and that鈥檚 the place with the really tall redwoods.

How do you climb these 110-metre-tall trees?

You fire a rubber tipped arrow from a powerful hunting bow. The arrow is connected to a fishing reel and must land way up into the crown, over something sturdy, usually a big old branch. The problem with redwoods is that the first branches are above 60 metres. A lot of times you cannot find anything safe below 75 metres. So you really have to launch these arrows. And then, using the fishing line, you pull up ropes, and climb up to the branch you shot over. Of course, that鈥檚 only half the battle, or less. You鈥檝e got to get to the top. You advance ropes over successively higher branches, and you use certain types of friction knots, and you haul yourself up one branch at a time.

Didn鈥檛 you end up with a strange world record?

As far as I know I hold the record for a tree-entry bow-and-arrow shot. It was this big old redwood named Prometheus. From the lower part of the tree I couldn鈥檛 see anything safe that could hold my weight. The only thing I trusted was a branch nearly 90 metres up near the top. I had to get to that branch before I could climb the tree, and eventually I did.

How dangerous is this climbing?

The first step is the most dangerous. From the ground, you can鈥檛 really tell what鈥檚 going on up there. Having climbed so many of these trees, I look for features I know are trustworthy. But when you put your weight on the rope and start climbing, sometimes things can break and come down on you. That鈥檚 when you can get killed. That鈥檚 the part that people really, really need to appreciate. I hope that climbing ancient redwoods doesn鈥檛 become a recreational activity. It would lead to harm to the habitat 鈥� and probably to deaths. I鈥檝e had branches break and hit me a couple of times. Some of these branches can be many hundreds of kilograms, especially if they鈥檝e just broken, say, in a storm and still have a lot of water in them.

Have you ever come across bad weather up there?

Yes. Once, I was up a tree in Redwood National Park in January. I had forgotten to check the satellite forecast. I got up to about 109 metres and all of a sudden there were gale-force winds with horizontal sleet, freezing rain, and lighting. The whole tree, which has 148 trunks and is one of the most complex I鈥檝e ever seen or heard of, started bucking wildly in the wind, and all the trunks were moving independently. I saw lightning striking in the same grove. I got the hell out of there.

Do you have to train for this?

Tree climbing has become such an all-consuming thing that I鈥檓 always in training. I can only climb the coastal redwoods from about mid-September to February. The rest of the year, either the spotted owl or the marbled murrelet is nesting in the canopy, so we have to stay out. I climb between three and five days a week, every week. In the summer, when I鈥檓 not climbing redwoods, I鈥檓 climbing giant sequoias in the Sierra Nevada Mountains or Douglas firs in Oregon and Washington.

An IMAX crew filmed you climbing the world鈥檚 second-largest tree, a giant sequoia, and then descending into a cave in the heart of the tree.

It was incredible! You go into the darkness, and the temperature starts dropping. The deeper you go, the cooler and darker it is. You get about 25 metres down and turn on your headlamp, and you look around at the walls of this chamber, and all the wood is rotten and covered with fungal mycelia. It鈥檚 cool and dank and scary 鈥� who knows what鈥檚 down there! Maybe there is a big old colony of bats that would fly up and freak you out. You never know what could break off and fall from above. It鈥檚 this crumbling tube that goes down. When you first set foot on the bottom of the chamber, it鈥檚 so spongy and rotten.

How does it smell?

It was awesome. I鈥檓 particularly fond of the smell of rotting wood. And it had a very, very strong, very distinctive odour. Redwood and giant sequoias have wood that鈥檚 chemically protected from decomposition. That鈥檚 why it鈥檚 red. It鈥檚 got all these phenolics in there. So when it decomposes, it has a certain odour to it. Unless you smell it, it鈥檚 hard to describe what it鈥檚 like.

What鈥檚 the crown of a giant redwood like?

There are multiple trunks sprouting from the tree, some of which are as big as full-size trees in other forests, up to 50 metres long. Each of these trunks has its own branch system. And they can also have other trunks coming off trunks coming off trunks. The highest I know is a ninth-order trunk. In an ancient forest, you鈥檝e got trees with a tremendous amount of character. You can鈥檛 go into a forest that has been cut and regrown, and see anything like what I鈥檓 talking about. That鈥檚 been the real eye-opener.

Do crowns have much living in them?

Yes. Sometimes there are enormous branches 2 metres in diameter that might be a thousand years old. And you get massive soil accumulation on these branches. Redwoods shed an enormous amount of older needles every year. They pile up on those huge branches, then the fungi start colonising and decomposing the needles into soil. The ferns then invade, and they really increase the water-holding capacity of the soil, because they have these really fine, tightly woven roots.

How thick is the soil up there?

I鈥檓 not kidding 鈥� you get metre-thick soil mats on these branches. Individual fern fronds could be a metre long and you might have more than a thousand fronds on a branch that might be 5 metres long and 2 metres wide. As a thicket of ferns builds up over time 鈥� and we are talking centuries here 鈥� the soil becomes like peat, very, very spongy, and it holds a lot of water. Organisms that live on the forest floor require pretty moist conditions. If, during a series of rainy days, they can manage to climb up into the tree and find one of these fern mats, then they can live up there. That鈥檚 why we find, amid these fern mats, all kinds of creatures including salamanders, earthworms, slugs, snails and millimetre-long crustaceans that normally live in stream gravel. Apparently they manage to swim up the tree.

What about plants?

We find spruce, hemlock and Douglas fir trees growing off the redwood branches. The seeds blow in and the trees grow right there on the branch, right off the soil. If a hemlock tree growing on the soil mat can send its roots down into the heart of the redwood, it has an almost unlimited supply of water and nutrients. Then you get pretty big hemlock trees, nearly 10 metres tall. And you find huge huckleberry bushes in almost every big redwood tree. I鈥檝e seen some 7 to 8- metre-high bushes, with trunks as big as your leg.

Are you still eating huckleberries up there?

Every fall. It鈥檚 quite a treat. You see a lot of other organisms coming in and feeding on them, including bandtail pigeons and chipmunks.

Given the environmental degradation that鈥檚 going on, do you feel a pressure to study the redwood canopy? Is time running out for them?

Well, the redwood forest has been exploited so heavily that the only remaining old-growth is in state or national parks. The battle has already been fought and lost in the redwood forest. Science can鈥檛 win it any more. What I鈥檓 trying to do is get a handle on how the trees function, and to understand how they might respond to the state of the planet-a state that seems to be getting worse and worse.

The more I鈥檝e looked into them, the more it becomes clear that the biodiversity and character we are seeing in the ancient redwood canopy are not replicable in any type of human time frame. You don鈥檛 see it in managed forests, and it鈥檚 gone from our landscape. The Oregon coast range is almost completely logged. California鈥檚 coast range is a little bit better because we got some of these large reserves. And there are some nice spots in Washington state. But by and large, all the way up to Alaska, this type of habitat has virtually been eliminated.

Will what you鈥檙e learning help us appreciate other old-growth forests?

Yes. There鈥檚 a lot more at stake for the immediate conservation of old-growth forests in British Columbia, with some of the Alaska yellow cedar and the Western red cedar forests, and even in parts of Washington and Oregon and parts of Northern California, where other types of forests are being cut.