How Many Recycled Newspapers Does It Take to Save A Tree?
Bruce G. Marcot, Ph.D. Research Ecologist
USDA Forest Service, PNW Research Station, Portland ORWithin a few months, the tree that took four centuries to grow was transformed into newspapers, read by commuters on afternoon trains, and then tossed away.How many recycled newspapers does it take to save a tree? This simple question was posed by a grade school teacher and her students in southern California, and I have played ecological detective -- consulting with US Forest Service silviculturists -- to find them an answer.
- Nelson, Richard (1992) The island within. Pp. 33-38 in: Left Bank #2: Extinction, Blue Heron Publishing, Inc., Hillsboro, Oregon. 149 pp. [p. 37]
Here is my reply to the teacher (who also happens to be my wonderful sister Vivian Crowe):
The bottom line is that the answer depends on the average weight of a newspaper. What you need to do as part of this is to have your students each bring in one newspaper (get them from different days of the week, and maybe from different newspaper subscriptions), have them weigh each paper, and then average out the weight. Call this average weight W.
Then, the answer to the question of "How many newspapers come from an average tree?" (call this N) is:
N = 1,660.0 / W (if you measure in POUNDS)
N = 26,553.6 / W (if you measure in OUNCES, which is far more accurate)
So ... then, as you track the number of newspapers you have your students recycle, you can find out how many trees they save by dividing the number of newspapers by N.
For example, let's say that an average newspaper weighs 2.2 pounds (my complete guess!) or 35.2 ounces, then N = 26,553.6 / 35.2 = 754.4 newspapers per tree. Then, over a year's time, if one family recycles 365 newspapers, they save 365 / 754.4 = 0.48 trees, or about half a tree. If the families of all 30 students recycle, then you're saving about 15 trees per year, which is enough habitat for two colonies of Acorn Woodpeckers, or half a dozen nests of Brown Creepers, or lots of other things!
How Did I Do This?
OK, here are the details of calculations underlying this:
I assumed that a "tree" in this calculation is an "average" Douglas-fir (Pseudotsuga menzeisii) that is 12" dbh (diameter at breast height) and 90 feet tall. (Douglas-firs are common in my neck of the woods and sometimes used for pulp.) This is an average size of a tree, as grown on private or public lands, for harvest as timber. Such a tree would produce two 40-foot logs, one averaging 8-1/2" small-end diameter and the other 2" small-end diameter. It also assumes a "2-inch top" which means the top two inches of the tree, on average, is non-merchantable because of the taper of the tree to a tip.
The total merchantable volume of such a tree is 65.64 cubic feet, or 1,858,718 cubic centimeters (cm3); this comes from standard formulae used by silviculturists for a tree of this average size and species (Douglas-fir). The mean density of the wood of such a tree (young-growth Douglas-fir) is 0.45 g/cm3, so the total merchantable mass of such a tree is the merchantable volume times this density, or = 1,858,718 cm3 x 0.45 g/cm3 = 836,423 grams (g). About nine-tenths of such wood is useable as pulp, such as for newsprint. So 836,423 g x 0.90 = 752,780.8 g of pulp-usable wood. This equals 1,660.0 pounds or 26,553.6 ounces, the values I used in the formulae at the top of this note.
QED. (Math-talk for the Latin Quod Erat Demonstrandum, Thus It Has Been Proven.)
What I Ignored
The calculation also assumes that newspapers are 100% recyclable, which is not particularly true. You can vary the degree of "recyclability" and determine what it would take to save trees accordingly.
I also ignored the energy and economic costs associated with growing, cutting, and processing live trees to make pulp and newspapers, as compared with costs for recycling (it ain't free, folks).
Including such factors would be a nice student project as well. Gotta leave something for you to do!
So ... how many trees do YOU save a year by recycling?
Many thanks to silviculturist Glenn Christensen and wood products specialist Dr. Jamie Barbour at Portland Forestry Sciences Lab, for their help in tracking down the numbers I used in these calculations.