Harvesting and Using Wood Crops
Ideally, trees should be harvested when their growth rates are no longer
optimal. This point will vary with the original spacing, subsequent thinning,
and growing conditions during the life of the plantation. A woody biomass
plantation grown at the highest density should be harvested between the
third and seventh years. A cottonwood fuelwood plantation where trees have
been well spaced (10 feet by 10 feet) and thinned may show maximum growth
for twenty years.
You can determine a decrease in growth rate by keeping records of the diameter
or circumference of a few selected (marked) trees over the years. Be sure
to measure each tree during the dormant season and at the same height each
year. Record the diameter for each tree and discuss these figures with your
district forester. The forester can advise you when the trees are past their
peak growth or when the tree crop is mature and ready for harvest.
Large-diameter fuelwood can be cut with a chain saw. Smaller-diameter
material can be cut with a backpack brush cutter or cleaning saw equipped with a circular
saw blade. Usually another person must hold down the tree to the right side
of the person operating the brush cutter. Material less than 2 inches in
diameter can be manually cut with long-handled lopping shears.
If you have planted at the smallest spacing for woody biomass (30 inches
by 18 inches), your trees may be ready for harvest after only three years.
When cutting the biomass, leave a stump at least 6 inches tall if you will
be cultivating the sprout growth. Naturally, coppice growth will not do
well if it must compete for light with established trees. For this reason,
extension foresters in Iowa (see Sources) recommend
taking out entire blocks of trees when harvesting biomass.
Soon after it is cut, biomass should be chipped and large diameter fuelwood
should be split to fit your stove. Wood is easier to split when it is green.
If you will be burning chipped biofuel in a modified grain drier or space
heater, run the wood through a standard drum chipper. Hydraulic chippers
are considerably more expensive but produce a more uniform chip than other
chippers. Large leasing companies have chippers available for rent.
While wood is drying, it should be stored outdoors under a raised cover
that sheds precipitation but allows for plenty of air circulation. Fuelwood
may take six to nine months to air-dry to the desired 20 to 25 percent moisture
content. The drying time can be shortened if the wood is stacked in a solar
fuel drier. Dry logs will have a lighter, greyish color and will have seasoning
checks. Chips will dry faster than logs if there is good air circulation
through the pile. You can hasten the drying process by rerouting heat from
your biofuel furnace back through the chip pile. Some biofuel burners will
burn green material, in which case drying would be unnecessary; keep in
mind, though, that dry wood always generates more heat than green wood.
If your plantation produces more wood than you can use, you can sell the
excess wood or put it to other uses. Large-diameter, fine-quality cottonwoods
can be sold as sawlogs (even veneer), and saplings can be sold for pulpwood.
Cut, split firewood can be sold to others who would like to heat with wood.
Information on all these options is presented in Selling Trees: A Guide
for Illinois Landowners (see Sources). Wood chips can be
used as bedding for cattle or poultry, as mulch for
orchards and other crops (generally with the addition of a side-dressing
of nitrogen fertilizer), and as filler for roadbeds and pathways.
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