Am I harvesting wood sustainably or will I eventually run out?

If I want to be a responsible steward of the land, one of the most important things to consider to to ensure that my use of wood does not deplete the resources that I'm managing.  I want to make sure that the trees will be available for at least 7 generations and any harvesting that jeopardizes that means that I'm not stewarding them properly.

I did some conservative calculations last year to make sure our fire wood harvest can be supported by the 67 acres of bush that we have.  The first question I had to answer is:

How many trees do we steward?

I did some research on tree density for aspen forest and found numbers between 500 to 2000 trees per acre.  I decided that I would be very conservative, so I took the lowest number and multiplied it by 67 acres, the amount of bush on the land we steward.  That means we have at least 33,500 trees.  Next question I had to answer:

How much do the trees grow each year?

Again, I did some research and found the average aspen tree weighs about 225kg (green) and they gain about 1.85% (ave) per year (4.2kg per tree).  Since we have 33,500 trees here, that means we have approximately 7.5 million kg of wood growing on this land.  We have other types of trees here too, so if I wanted to be even more accurate, I would have to accommodate them as well.  But this is just an estimate and is why I went on the very conservative side of the calculations.  At 1.85% growth rate, they gain about 140,000kg of weight in a given year.  Again, that is a conservative number as a good, wet growing season could see double or even triple that growth rate.  But I wanted to make sure we never jeopardize the forest by over harvesting.  

Free wood when we do our duty to clear county roads from storm damage.

140,000 kg of wood may seem like a lot, but when an average tree weighs 225kg, that means the forest produces the equivalent of 622 new average trees a year on our 67 acre wood lot.  So the trick now is to ensure that our wood harvesting does not exceed 140,000 kg per year as we don't want to draw upon the base 7.5 million kg that produces this extra wood each year.  This is like living off the interest in your bank account without touching the principle.

We are not the only ones living here.  We must share this land with others!  All life is sacred.

How much wood do we burn each year?

A cord of wood stacked tightly measures 4 feet by 4 feet by 8 feet.  We harvest about 20 cords per year and the average tree that we harvest is about 8 inches.  It takes about 8 of those trees to make a cord of wood, which means we need to collect at least 160 trees per year.  

Are we over harvesting?

160 trees weigh about 36,000kg.  If the forest produces 140,000 kg each year, that means we are only harvesting 25.7% of what it produces each year.  In a really good productive year it may only be 10 - 15%!  I think we are doing okay! 

Shelter for critters

Because we only harvest dead or sick trees, we are not cutting into the productive trees on the land.  If we harvested green trees we would not need as much wood as cured green trees have much more heat in them which then requires less wood, but we would then start cutting into the productive base used to make these calculations.  Dead trees lose BTU's as they decompose so I need to harvest more of them to burn the fires that we have.  Howevever, they are also lighter so that I'm not hauling a lot of weight through the bush.  As a result, we go through about 20 cords per year as we have 3 homes to heat, the shop and the goat water trough.  

It is my observation that we cannot keep up with all the dead fall in the bush.  We have been harvesting dead fall for over 10 years and have yet to come close to catching up.  I've removed 200+ cords of wood from the bush and most people would be hard pressed to notice as it looks dense and healthy.  I leave lots of stumps for the ants, wood peckers, mice and other critters as many of them depend on dead wood.  I also leave a lot of trees laying on the ground for the rabbits, grouse and other ground critters that need shelter and food.  When I limb the trees, I pile them up to help build habitat which mimics a fallen tree.  

Corporate / government clear cutting.  Breaks my heart!

By going through this exercise, I am confident that despite our use of wood, this little piece of heaven will be here for thousands of years.  Our great-great-great-great-great-grand children will have access to this land and it will be as I found it.  

The dead feeds the living!  So we cannot take it all!

The reason I don't clear cut it is because there are hundreds of plants here, not just trees.  There is all kinds of food and medicine spread out between the trees.  I want to ensure that I protect those plants as well.  I've seen clear cutting that wipes out everything and the land is barren.  This is not sustainable at all.  I help control disease by taking the sick, dying and dead.  I also reduce the heat of the fire should a forest fire run through this land.  I do that by removing the dry fuel that the fires need to burn.  We prepare ourselves for fire as it is a natural and rejuvenating process within the northern boreal forest.  So we need to be prepared for fire as well.

Storms provide most of our fire wood.  I clean this up for safety as well.

The University of New Hampshire wrote a simple document to help estimate tree size and density so that you can make these kinds of calculations yourself.