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On the west coast of the US (WA, OR) how many acres of trees would be required to keep a single family home supplied endlessly?

If I and my family plant a tree for everyone tree we cut for fuel, how much property would we need in our tree lot to meet our heating and cooking needs forever? Assuming we begin with established reforest, manage wisely and maintain a steady population of 5 - 7 people.

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OK, one possible setup (and assuming both my math and memory are right, neither of which is certain):

Planting Douglas Fir, which is fairly fast growing (one to two feet a year) and a good wood for lumber and for burning, planted around 16'-18' apart (or half that, and thinned as they grow). They become large enough to be commercially valuable at around 30 years; at that point, they will have a diameter of somewhere between 16" and 21"; I'll be conservative and say they're at the low end, at about 16". That gives you half a cord of wood per tree (18" will get you about 2/3 of a cord, and 21" will get you almost a full cord).

Go to the National Ag Safety Database and look up "Home Heating with Wood" and determine how many cords you need, given the size of your home and the type of stove(s) you are using.

Once you know how many cords you are going to need, multiply that by 2 (2 trees per cord), by 30 (years to grow a tree), then by the feet apart you plant your trees squared (square feet per tree). Divide that by 43560 (square feet in an acre). Add a little more for a safety margin, then add a lot large enough to hold your cutting area plus enough land to hold a year's worth of cut wood for seasoning.

That's how much land you need.

I would suggest you talk to people in the area you plan to move to in order to determine the best woods to grow in the area, how much space they need, how long to harvest and size at harvest, etc. to get an idea of what's reasonable locally. Also, the size of and insulation in your house will make a big difference.

Note: (From Wikipedia) The cord is a unit of measure of dry volume used to measure firewood and pulpwood in the United States and Canada. A cord is the amount of wood that, when "racked and well stowed" (arranged so pieces are aligned, parallel, touching and compact), occupies a volume of 128 cubic feet (3.62 m3)

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I've done this calc for my farm here in Alberta.

  1. I know that it takes 5 cords a year to heat my house.

  2. The average lifespan of trembling aspen is about 40 years. At that point it's about 40 feet tall, and 8" diameter.

  3. The average spacing in my woods is about 10 feet. So 100 ft2 into 40,000 ft2/acre gives me about 400 trees per acre. So with 400 per acre and a 40 year span, I can grow on average 10 trees per acre.

  4. A given tree has about 32 feet of trunk before it gets too small to bother with. The top end is 2" bottom end 8 inches. We will do some crude rounding and say that the first 8 feet is 8" the second 8 feet is 6" the thrird 8 feet is 4" and the last 8 feet is 2" This is overall an underestimate.

  5. A cord is 8 feet x 4 feet x 4 feet. So cord is 36 8" diameter chunks, 64 6" chunks, 144 4"diameter chunks, and we're ignoring the top one, even if we cut it up.

  6. So one tree = 1/36 + 1/64 + 1/144. If we pretend that it's 1/72 instead of 1/64 we get 7/144 cord per tree. So 10 trees is darn close to 1/2 cord.

So for me the answer is 10 acres.

If I managed it more intensely, thinned it, planted hybrids that grew faster, made the spacing more even, I could half the time it takes to grow. If I found a way to use smaller wood, I would have less waste and it would take fewer trees per cord. Also the fastest mass increase is when they are young. 6" apart and 1" diameter at harvest if all you want is fixed carbon.

In Oregon you would have twice the growing season, and a much smaller heating season. (we have 10,000 degree days per year) But people in coastal climates often go light on the insulation.

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