Total Pageviews

Sunday, January 3, 2010

Fine furniture and Global Cooling

Jungles and Global Warming
It is often stated cutting down tropical jungles is contributing to global warming; that jungle logging is destroying the lungs of the world which we need for turning atmospheric carbon dioxide back into oxygen. Sadly, a mature tropical forest doesn't produce any net oxygen and doesn't sequester any carbon. A mature forest, by one definition at least, is one which has reached equilibrium between photosynthesis and oxidation of waste materials. If biomass is being oxidized by rotting as fast as it is being produced by  photosynthesis, there is no net oxygen production and no net conversion of carbon dioxide into biomass.  The correct sort of logging could convert mature tropical jungles into very effective carbon sinks, enrichen tropical soils and displace/replace fossil fuels.Italic

In temperate forests, by contrast, you may have a build up of dead organic material on the forest floor that goes on and on and the final product of the break down of this forest litter is humus which contains sequestered carbon in a fairly refractory form. In the limited sense in which we are defining 'mature', such a temperate forest is not mature and can stay immature for a very long time. Similarly up in the tundra, some of each year's growth of organic material may be frozen into the permafrost and so over the years accumulate more and more organic material. The layer of organic material in the tundra can be very deep. In the limited sense we are talking about, this ecosystem is also not mature. However in the continuously wet warm conditions of a tropical forest, and with its huge diversity of life, any organic material that falls on a tropical forest floor is soon mineralized and incorporated back into the biomass of the forest. Humus oxidises (breaks down) above about 25 degrees so there is no accumulation of carbon in the soils. A major reason that tropical forests exist is because of their ability to recycle nutrients with very little loss from the system. When decay balances photosynthesis, no net biomass is accumulating and no net oxygen is produced.

In the present type of jungle logging, the land is clear felled, removing anything of value and burning the remainder. Then either grass for cattle or oil palms are planted. The logs are sent to make furniture etc. and the waste from the saw mills and from the furniture factories is burnt. In so far as you produce fine, high quality, long lasting furniture, houses and so forth, you are sequestering some carbon although only a small proportion of the original amount which was logged. The land is left nutrient poor and most of the original biomass is returned to the atmosphere as carbon dioxide. This type of logging is clearly detrimental in terms of increasing the amount of carbon dioxide in the atmosphere not to mention the destruction of an environment of great beauty.

If you really wanted to use the forests only to sequester carbon dioxide, you would selectively cut down large trees and bury them in a swamp. Under anaerobic conditions, wood is very refractory (doesn't break down). As long as the swamp stays flooded, the sequestered carbon remains sequestered. Let's be realistic though. Such a plan would have all of the expenses of logging and then some, but none of the profit. It would be an non starter economically. To make a system work, there has to be profit. So what sort of system could work.

First of all, let's keep the idea of selective logging. We take out selected prime trees for wood and turn them into fine furniture etc. Manufacturing is done in the country where the trees are logged and preferably close to where the logging occurs. Why ship prime wood overseas and allow someone else make most of the profit. Quality is important. Cheap furniture which is not properly engineered will break down and will be burnt, releasing its carbon and new wood will have to be cut to make new furniture. It is important to build fine products that will last many many generations. In addition if you produce very long lasting furniture, as the markets are saturated the need for new logging will decrease

Back in the jungle, masses of seedlings are just waiting for a ray of sun to reach them, many of them from the felled tree itself. Following the fall of a jungle giant, growth activity is insane. Seedling reach up at phenomenal speed in a race to find their place in the sun. Of course, as they do this they are sucking Carbon dioxide from the air. This part of the jungle is now 'immature'. Even when they reach the canopy, they continue to increase in diameter, sequestering more and more carbon. Now the question is what to do with all the waste wood in the form of branches cut off the tree during logging, offcuts and sawdust produced during the production of lumber and offcuts produced during furniture manufacture. All this material can be burnt just to get rid of it but it can also be burnt to produce energy which can run, for instance, the saw mill. Vertical integration can ensure that milling and furniture production are all in the same location and close to the area being logged.

The use of offcuts for energy was once done when the saws of saw mills were run directly from steam driven belts using the waste wood from the mill. The waste wood, however, can also be used to generate electricity which is more convenient energy form to transmit to the saws. Electricity has the added benefit that the excess can be fed into the grid to earn profit. The grid forms the energy storage unit for the mill and any energy produced reduces the amount of new carbon (coal) that must be burnt somewhere else.

Another intriguing solution is to char the wood. Heating wood in the absence of oxygen produces a mix of gas and tar, similar to what comes out of an oil well and leaves behind charcoal. In traditional charcoal production, all the volatiles are used in a wasteful system to produce the heat to pyrolyze the wood and the carbon contained in the volatiles goes back into the air. The charcoal, which is light to transport and burns without smoke is sold, mainly to private users, to cook their food. In an efficient industrial process, there should be a considerable quantity of volatiles left over to either be used for electricity production or as raw materials for industry. Pyrolysis needs high temperature but doesn't take much heat energy*. The amount of volatiles left over for the production of electricity or as an industrial feed stock depends to a large extent on how well the pyrolysis vessel is insulated and how efficiently you introduce heat energy into the vessel. An interesting possibility is to use electricity to heat the pyrolysis vessel. And what about the charcoal produced.

As mentioned you can sell charcoal for home cooking and it will replace the use of fossil fuel. A special benefit of charcoal is that it doesn't produce smoke pollution and hence can be used in crowded conditions. It also isn't dangerous in the way that kerosene is. Every year thousands of women in India, for instance, are burnt and maimed by exploding kerosene burners. (Indian divorce) One danger of charcoal burners, though, is their use in confined areas, especially for heating at night. As the oxygen is exhausted, carbon monoxide is produced which is deadly. Charcoal can also be used for soil enhancement.Link
Charcoal itself doesn't contain much in the way of nutrients. However, just like humus in cooler climates, charcoal can hold nutrients and release them to plants. Very rich soils have been found along the Amazon river where Milena of people have charred their organic wastes and incorporated them into the soil. The soils are called Terra Preta. Humus breaks down in tropical temperatures charcoal does not. By using charcoal this way we strike three blows against carbon dioxide. First and most obvious, the carbon contained in the charcoal is sequestered for a very long time in the soil. Charcoal even in warm tropical soils is very refractory. Secondly, by holding nutrients that might otherwise wash out of the soil, it produces a nutrient store for tropical agriculture. Charcoal will have a market with farmers and hence the charcoal makers can sell it at a profit. During charcoal manufacture there are big chunks, idea for selling for fuel and lots of small to tiny charcoal which is ideal as a soil conditioner. Thirdly, If your fields are more productive because of nutrient retention, you don't need to cut down more jungle to maintain your production.

Farmers won't gain any nutrients by applying charcoal to their fields but if they practice good farm management by, for instance, returning manure from their cow sheds to their fields, the charcoal will hold the nutrients on the land. Without humus (only available in cool climates) or charcoal, the nutrients are washed down into the water table. This is especially so in high rainfall areas typical of jungle areas. In this way, charcoal in soils also helps to protect water quality.

The correct logging systems and subsequent handling of wood waste could turn the jungles in tropical parts of the world into valuable carbon sinks while displacing some fossil fuels and enriching tropical soils. Properly managed it could also preserve the most amazing environment on earth.

No comments: