Sunday, December 14, 2014

The Complex and Capable Western Red Cedar

Life is challenging - just ask the venerable "tree of life," the title that many Pacific Northwest Native Americans give to the species we also call, western red cedar (Thuja plicata).

Fragrant and fast-growing, these massive trees once provided the raw materials for a complex assortment of life-sustaining goods. From dug-out canoes to chewing gum and medicines, to soft and fibrous bark useful for everything from diapers to ropes, baskets and fishing nets. Red cedar would eventually become the official tree of British Columbia in February, 1988.

Cedar tree retrofitted as the Tilikum
Seventy-seven years earlier, a mariner from Victoria, British Columbia, purchased an old, 38' cedar dugout canoe from a Nootka Indian woman for $80 in silver. After a major retrofit, including the addition of three masts and a cabin, Captian J.C. Voss named the former cedar tree, Tilikum ("friend"), and attempted to sail around the world.

From Victoria, the seaworthy tree set sail in 1901 for Australia, New Zealand, South Africa and South America before coming to port in England in 1904. In three years and three months, the tree called "friend" safely crossed three major oceans. After laying derilect for years, the Tilikum was eventually returned to Victoria where it now resides in the Maritime Museum of B.C.

This famous cedar tree somehow survived a dangerous journey across disparate cultures and technologies when it sailed into waters dominated by steamships. An analogous journey is now underway, this time into the unseen shoals of climate change.

"Flagging" on a western red cedar branch
Last summer a concerned park visitor asked me why all of the cedar trees bore brown limbs. I assured her that "flagging," as it's called, is perfectly normal. While deciduous trees drop all of their leaves at the same time, evergreens drop only their oldest needles each year. Typically - I said in my comforting, know-it-all voice - the brown cedar flags on our trees are clumps of three-year-old needles located closest to the trunk. Younger, green needles fill out the rest of each branch and keep the tree looking mostly green year round.

That was the simple answer, and it calmed her concerns about the cedars growing in Glacier Park. Evergreen needle lifespans typically average 2-17 years, depending on the tree species. But just like the venerable cedar tree, reality is far more complex.

In reality, evergreen tree needle longevity can vary quite a bit, within one species and even within one tree. A study in northern Idaho found that cedar needles from mature trees averaged 8.9 years old. But the needles averaged 6.8 years in the upper third of the tree and 10.6 years in the lower third. Location within the tree affected the amount of shading, as well as the average needle age.

Location, as in elevation and latitude, also affects the lifespans of evergreen needles. In a report from 1939, ponderosa pine (Pinus ponderosa) needles from California averaged 3 years on the coast and 5-8 years at higher elevations. Lodgepole pine (P. contorta) needles growing in Wyoming averaged from 9.5 to 13.1 years between low and high elevations (2,800 m to 3,200 m). In Europe, Scots pine (P. sylvestris) needle longevity tripled, from 4 to 12 years, along a 3,000 m elevational transect.

But when various evergreen tree species from different elevations and latitudes are grown together in common gardens, the needle age differences fade within each species. Genetics provides the ability, but not the impetus.

What's the common theme here? Environmental stress. Needles grow faster and and die younger in sunny, warm and wet environments. Needles grow slower and older in relatively shady, dry, cold, high, and nutrient-poor environments.

And stress is where climate change rears its ugly head, but not just stress on trees. I'm thinking of the stress on concerned scientists, trying their level best to model the future effects of an unknown climate on our boreal forests. A rapid increase in atmospheric carbon, as carbon dioxide, over the past 300 years has shipped us all headfirst into uncharted waters.

During the day, trees use carbon dioxide and release oxygen. Carbon is sequestered from the environment and stowed away into plant parts - needles, etc. - to be released only very slowly during decomposition. So while climate change provides trees with extra warmth and carbon, carbon sequestration in all plants helps to buffer the rate of climate change - a very fortunate thing for us animal types. Unfortunately, natural variations in needle growth and carbon sequestration are proving rather difficult to model.

Until recently, almost all climate change models used a constant for needle growth in boreal forests. More sophisticated models are starting to incorporate a nuanced approach to predicting how our northern trees will respond to increasing carbon levels, and thus a more accurate picture of what lies ahead.

But as good as our science is - and it's amazingly detailed already - we don't know our destination, and there are no known ports on the horizon. Sort of like the Tilikum, some among us are clinging to obsolete, carbon-based technology with a dated mindset, merely hoping for the best. We are capable of so much more, and our best climate scientists are working hard to produce accurate maps for what will surely be a challenging journey.