In Iran, we are selling harvested trees based on their volume. But volume measurements is not so precise. Instead, if we could sell the logs based on their weight, it can be simply done by loading a truck and weighting it.
Here is the problem, roughly speaking, about a half of wood weight is water and wood moisture depends on the time that a contractor may leave the logs in cutting area. So, if a contractor postpone transporting the logs, he will pay less. It should be mentioned that because of so many problems of transportation, we can not easily force the contractors to deplete cutting fields.
How do you sell logs in your country?
http://en.wikipedia.org/wiki/Caspian_Hyrcanian_mixed_forests
Viewing from methdology, you need to develop the relationship between volume, weight and time after cutting. In generel, wood weight W=d*V, where d is wood density and V is wood volume. Or in another equation, V=f*W, where f is a conversion factor. If a contractor postpone transporting the logs, W will become less, but f should become more to keep V contant. So you are necessary to measure the volumes of 30-50 sample logs, and weigh the weight of each log day by day for a period (7-10 days, depending on the time contractors postpone transporting the logs). Using the measuration data of sample logs, you can develop a equation like V=(a+b*D)*W. The sample size should be large enough, at least more than 30 or 50. Normally, the work should be done by an authoritative insitution. If not, your contractors might not trust you.
Dear Zeng
Thank you for your suggestion. I don't know if you sell your products in your country based on this method or not, but deriving this W is difficult. It depends on a large variety of factors like: tree species, location of the logs under canopy or directly being exposure to sun light, diameter of the logs, weather condition and ... . So we can expect different W for alto of different situation which we could deal with in practice. Suppose that it is possible to derive such a species-weather-location -...- specific constants. When we are loading a truck with different logs of different species that were exposed to different light condition and etc, how this constant should be applied to the total weight of a truck. Your suggestion looks very nice theoretically, but I think in practice, the problem still remains unsolved.
In my country of Croatia we sell logs exclusively by volume.. I agree the weight question is far too complicated to be solved quickly and easily.. maybe the question should not be if we can use weight as a unit of measurement for lumber sale but whether we can develop more accurate methods of measuring timber volume.. Best regards, I.Bulka
The evaluation unit for timber sales should be related to the product that it will be obtained. If the product is also evaluated by volume, eg wood for timber, the product volume will be sawn volume, regardless of whether board, rafters, etc. and then can be sold in dozen. However, wood species which produce essential oils and the product to be obtained is the essential oil, the timber may be evaluated by weight, as the amount of product (essential oil) has a proportional relationship to the weight yield of wood of that species (eg 1 ton of wood, with yield of 2% in oil, are obtained 20 kg of oil and then can be sold in volume - liter).
Of course, the moisture changes along the year, but in the same site. When collecting wood from different sites, average moisture has no trends. Then, you may use a volume equation and a fresh density estimation for the species.
The best option implies two things:
1) To sign a condition in contracts for a maximum time to weight the truck. This has to be considered by both parts of market (sellers and buyers).
2) For each species, experiments about biomass and moisture loss are needed, within the maximum period signed in contract (recommendable of 2 days)
Weight = Fresh volume x Fresh density x (100 - % lost moisture)
With volume equations from regional level research, my experience so far indicates a very low difference between real weight and predicted weight.
An example: final cut of 25 hectares in Galicia for E. globulus, 5.871 ton predicted vs 5842 ton obtained.
A great deal of work has been done on weight-scaling southern pine in the US. With a good library service accessing subscriptions you may be able to find much of this; probably there are USFS Research Bulletins as well out of the Southern Forest Experiment Station.
Switching to weight usually involves a lot of stress between landowners, loggers, and the mills. Here in US people usually (with some reason) mistrust the mills for "beating them on the scale". A change to weight can be tumultuous and stressful. People forget that "stick-scaling" can be variable and dishonest too. In the longrun it can be better for everyone, mostly for the lower value items. But for low value sawlogs, in many parts of US logs and stumpage are priced by the ton.
Assuming a suitable government oversight of honesty of the scales, it can be done. Just takes time and preparation.
LCI
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