AskPablo: How many trees does my office Kill?

trees.jpgThis week I was asked by Craig how many trees his office kills each year. In order to give him an answer I had him collect some basic information, like how many reams of paper they use each week. His office uses around 60 reams per week, an average of 100 sheets per person and 30,000 sheets in total (a ream holds 500 sheets). Over a year the office would use 3000 reams, or 1,500,000 sheets! But how many trees gave their lives to make it possible for old people to print every e-mail they get? Well, let’s find out…

First I need to figure out how big the average tree is. The answer to this question depends highly on how big/old the trees used are. If you raid a Christmas tree farm to make your paper, the answer would be in the millions and if you go into an old-growth redwood forest the answer would be quite small. Does this mean that we should cut down only big trees? No, on the contrary. Younger trees grow much faster, and therefore sequester more carbon from the air. They also grow more densely and it is probably better to support a monoculture tree farm than it would be to raze a biodiverse old-growth ecosystem.
In 2001 the US timber industry harvested 46.6 billion board-feet (one board foot is 12″ x 12″ x 1″, or 144″ cubic inches), which is equivalent to 110 million m^3. At a density of 520 kg/m^3 (for douglas fir) this amounts to an annual harvest of 57.2 million metric tons. Globally 42% of industrial wood harvest devoted to paper production. If this statistic holds true for the US timber industry (does it really matter in a global market?) we are harvesting 24 million metric tons of trees for paper production each year. According to one estimate, the average tree weighs 680 kg, or 0.68 tons. So this means that an estimated 16.32 million trees are harvested for paper production in the US each year.
One of my favorite sources for lifecycle factors are the data sheets that accompany the Wuppertal Institute’s MIPS manual. According to this resource about 2.56 tons of biotic material (trees) are required to make a ton of virgin paper. This is because some parts of the tree are unuseable for paper making, like the branches and bark. If all of my assumptions are correct the US would produce 9.375 million tons of paper each year.
Back to the office paper… A ream of Craig’s paper weighs 3 pounds (1.4 kg). At the lifecycle factor of 2.56 mentioned above, each ream would require 3.6 kg of wood. And at 3000 reams per year his office is using 10,752 kg of wood. Based on the average tree weight above, this amounts to 16 trees per year, or about one every three weeks.
I am happy to report that after I did all these calculations Craig found out that is office recently switched to Aspen 100, a 100% post-consumer recycled content product from Boise Cascade. So the real result of my analysis is that Craig’s office is saving 16 trees per year by using recycled paper. On top of that they have a great recycling program to give their used paper a new life in someone else’s office. Maybe even yours…
With some basic numbers from your procurement person you can use my assumptions above to calculate you own office’s deforestation contribution. This makes a great argument for switching to 100% post-consumer recycled paper in your office too!
Pablo Paster
Sustainability Engineer
For some great paper-related facts see:
10/8, 10:40am: It was pointed out to me that my assumption about the weight of a ream was incorrect. I have adjusted the numbers. Thank you Dave.