How Many Recycled Newspapers Does It Take to Save a Tree?
Bruce G. Marcot, Ph.D. Ecologist
USDA Forest Service, PNW Research Station, Portland OR
How
many recycled newspapers does it take to save a tree? This simple
question was posed by a grade school teacher in southern California,
and I have played ecological detective  consulting with US Forest
Service silviculturists  to find them an answer.
Here is my reply to the teacher (who also happens to be my sister
Vivian Crowe):
The bottom line 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 you average out the weight. Call this average weight
W.
1) 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)
or
N = 26,553.6 / W (if you measure in OUNCES,
which is far more accurate)
2) 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.
3) 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!
OK, here are the details of calculations underlying
this:
I assumed that a "tree" in this calculation is an "average"
Douglasfir (Pseudotsuga menzeisii) that is 12" d.b.h.
(diameter at breast height) and 90 feet tall. This is an average
size of a tree grown on private or public lands for harvest as timber.
Such a tree would produce two 40foot logs, one averaging 81/2"
smallend diameter and the other 2" smallend diameter. It
also assumes a "2inch top" which means the top two inches
of the tree, on average, is nonmerchantable 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 (cm^{3}); this comes from standard
formulae used by silviculturists for a tree of this average size
and species (Douglasfir). The mean density of the wood of such
a tree (younggrowth Douglasfir) is 0.45 g/cm^{3}, so the
total merchantable mass of such a tree is the merchantable volume
times this density, or = 1,858,718 cm^{3} x 0.45 = 836,423
grams (g). About ninetenths of such wood is usable as pulp, such
as for newsprint. So 836,423 g x 0.90 = 752,780.8 g of pulpusable
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.
Many thanks to Glenn Christensen and Jamie Barbour at Portland
Forestry Sciences Lab, PNW Research Station, for their help in tracking
down the numbers used in these calculations.
