Imagine walking into your favorite local forest one day only to discover that it was now just a massive pile of dirt. Thanks to a nearby construction spot, an incredible amount of dirt had been dumped: Ten feet high and taking up the area of a soccer field. Trees encased and surrounded. No way they will survive. Can the forest regrow and adapt? Will new trees grow on the graveyard of old trees?
A very strange hypothetical! But exactly this happened in Pacific Spirit Park in the early 1970s when the fill from constructing a new underground library building at UBC was dumped just east of what is now Camosun Bog.
Take a look at this aerial photo from 1971, where you can see the big white spots in the forest where the trees are covered with dirt.
This underground library, previously called the Sedgewick Library, now makes up the massive basement of UBC’s main library, the Walter C. Koerner Library. Walking around the basement of Koerner Library you really get the sense of the how much soil had to be dug up and dumped.
Luckily the full amount of the soil didn’t end up getting dumped as the UBC community convinced the University Administration to stop the dumping. They also successfully pushed back on plans to clear-cut most of the park and turn it into housing.
The history of the Camosun Bog and forest – and how incredibly lucky we are to still have it – is a fascinating one. I highly recommend reading this article from UBC Professors Sally Hermansen and Graeme Wynn – Reflections on the Nature of an Urban Bog
A few weeks ago I went on a walk around Camosun Bog and forest with Ian Clague. Ian lives nearby the blog and is a long time volunteer with Pacific Spirit Park Society and Nature Vancouver. He has done a lot of work to help preserve and restore the park. I had heard before about the library fill being dumped nearby Camosun, but never had grasped just how much of it was dumped till I talked to Ian. There is a stairway to the east of the blog where you go up more then 10 feet / 3 meters. I had always though this was a natural part of the landscape. I didn’t realize climbing up this staircase is climbing up the top of the library fill!
On the top of Library Fill Hill you can see the immediate change in forest tree composition. Where the fill has been dumped deciduous broad-leaf trees and invasive species are everywhere. The ground is dense, hard, and lacking any source of real organic matter. Compare that to the bottom of the hill, where the forest is more natural with spongy, fungus-filled soil and tall native evergreen western hemlock trees. The ground full of native species like huckleberry and salal.
This difference between deciduous trees on top of the hill and evergreen trees at the bottom can be seen in looking at a 2020 satellite photo taken during the winter. Notice how the area of deciduous trees (which lose leaves during winter) perfectly matches the area covered by the library fill.
Library Fill Hill was quickly dominated by our native Red Alder after the dumping stopped. Red Alder is a pioneer tree that establishes in disturbed areas with bare soil. Alder is one of the few trees that can do this because most trees are reliant on organic matter in the soil and the nutrients it provides. Alder however, has an incredible evolutionary strategy that makes bare dirt hills the perfect spot for it. It has a symbiosis with Bacteria, that it allows to live inside it’s roots, in little structures called ‘nodules’. This Bacteria ‘fixes’ nutrients for the Alder. That means it obtains nutrients from the air, especially the all-important nitrogen that makes plants green. It’s a trade! Alder gets previously unobtainable nutrients and Bacteria gets a safe place to live.
Under normal BC forest succession, areas of disturbance – like landslides and fires – are quickly colonized by Alders which put organic material back into the soil when they die. Allowing our massive coniferous trees to grow. However, this is not what is happening on Library Fill Hill. Growing underneath the Alders, ready to take their spots when they die, are a ton of non-native tree species: Norway Maple, Sycamore Maple, Horsechestnut, English Oak, and European Wild Cherry.
It’s a perfect case study of just how hard it is to grow back a native forest near a city. There are just too many invasive species planted in people’s lawns that quickly out-compete our native ones. A forest of non-native trees quickly causes havoc on the ecosystem as native birds, insects, and mammals lose their food and habitat sources.
Ian and the Pacific Spirit Park Society (especially the rambunctious bog preservation team known as the ‘crazy boggers‘), have been working hard to do what they can to keep invasive species from taking over Library Fill Hill. Planting native species and removing invasive ones.
One particular project I was fascinated by was Ian telling me about removing young hemlocks growing in the bog and planting them on Library Fill Hill instead. These ‘Camosun Hemlocks’ have been removed from the bog because hemlocks will take over the bog and dry it out as they grow bigger. At one point, before the Crazy Boggers saved bog, it was completely covered with hemlocks. The hemlocks were logged by helicopter so they could be removed without destroying the forest in the process of dragging out the big trees!
Wait, you might say, why do hemlocks need to be removed from the bog if they are native species to the area? If the hemlocks are drying out the Bog and turning it into a forest, isn’t that the natural course of events and why should we stop it? The removal of hemlocks growing is a fascinating illustration of an issue at the core of urban natural areas. How do we handle areas that have seen so much disturbance that corrective human action is needed to return them to a natural state?
Hemlocks are only able to overrun the Bog because the Bog has been artificially drained of water during the construction of surrounding neighborhoods. The Bog has existed since the last retreat of the glaciers that covered Vancouver. The eternal nature of the Bog can be seen in the Musqueam stories about it. The very origin story of their name, Musqueam, is attached to the Bog and flowering plant they are named after (and a two-headed serpent that used to live in the Bog!). Camosun Bog is a living ark; containing preserved plant and animal matter deep in its lower levels that reveals the long history of environmental change in Vancouver.
Even now, the Bog is an ecosystem that you would be hard-pressed to find anywhere else in Vancouver or even BC for that matter. It is truly a wonder!
The ‘Camosun Hemlocks’ which Ian removed and replanted on Library Fill Hill will be interesting to watch as they grow. Unlikely the other native plants also planted near them (Cedar, Douglas-Fir), they are short and shrubby. Reaching sideways instead of stretching upwards under the Alder like the other planted plants. Growing in acidic Bog for even a couple years means you change your growing strategy to slow and steady. It’ll be interesting to see these Hemlocks – who were an invader but now a potential savior – will fair over the years. If you walk around Library Hill Fill they are quite recognizable.
As Ian was showing me these Camosun Hemlocks. I saw something move in the top of my vision. Just above his head was a Barred Owl, almost perfectly camouflaged. Barred Owls are invasive owls to the West Coast despite being native to North America. Just like the Camosun Hemlocks they are creature in the wrong place thanks to humans. Barred Owls come from eastern North America and are only believed to have made it over here because of human disturbance in the prairies. Where we have suppressed fires and dammed rivers which has allow forests to grow in area that was once treeless.
Barred Owls hunt and take the habitat of native owl species, radically changing ecosystems and threatening food chains. It’s a big enough problem that US Government was recently considering mass exterminating them.
It wasn’t surprising to see a Barred Owl on Library Fill Hill. They are now common in other heavily disturbed forests in Vancouver, where non-native plant species have led to booming invasive rat, squirrel, and bunny populations. It was fitting to see one right near a Camosun Hemlock, resting in a non-native Horsechestnut tree, the perfect reminder of the all the paradoxes, pain, and beauty in Urban Nature Areas.
