Timber, exploitation

Tropical forests and savannas are the primary source of C emissions that originate from biomass burning (73, 75). However, temperate forests are also sources of atmospheric carbon. Harmon et al. (77) reported that conversion of primary temperate forests to younger, second-growth forests lead to increases in atmospheric CO2 levels, due to losses in long-term carbon storage within these forests. They ascertained that timber exploitation of 5 million hectares of primaiy forests in the Pacific Northwest of North America during the past century has resulted in the addition of 1,500 Tg of C to the atmosphere. 

The availability of different timber species varies considerably with economic and political conditions, and the effects of past exploitation. 

Mineral resources are nonrenewable resources, in contrast to renewable resources such as surface water and timber, which are or can be replenished naturally or artificially. The geological processes by which most mineral deposits form take a very long time. They can, in no way, be thought to replenish deposits extracted from the ground and dispersed by use. However, it is important to recognize that mineral resources are extendable with the help of advancing technology that develops uses for sources that were not readily usable or exploitable before, allows hidden deposits to be discovered, and enhances the efficiency of recovery and of use. 

Nevertheless, cellulose fatty esters with low DS values show other qualities, such as a high hydrophobicity. The development of water-repellent cellulosic materials (i.e., cotton, wood), has led to interesting applications in the textile and wood industries. For instance, the direct esterification of timber with fatty acids (and their derivatives) has resulted in extraordinary outdoor durability and resistance to biological attack (e.g. rotting, termites). Industrial exploitation of this technology has recently been conducted in France [WoodProtect by Lapeyre (Magne et al., 2003)]. In this case, the water-repellence conferred to wood and the lack of recognition from predator enzymes account for these properties. 

MRI is a versatile method and in addition to uses in diagnostic medicine, it is important to note that while MRI is best known as a medical tool, this technique has other useful scientific applications. As an example, geologists have used MRI to examine the composition of geological stmctures, and MRI has also been exploited in assessment of produce and timber quality. However, as noted earlier, MRI scanners cost millions to buy and thousands to run and maintain, so remain a luxury big-budget item. 

Wood is one of the oldest renewable resources exploited by human activity in the form of timber, tools, source of energy and of shelter. Wood is a complex natural material whose stmcture represents the very paradigm of a composite assembly, as briefly outlined in Chapter 1, together with general references to the traditional uses of this multifarious vegetable manifestation. Its main components (see Chapter 1) are cellulose (A), hemicelluloses (B) and lignin (C), accompanied by minor contributions of low molecular weight compounds and mineral salts. This book includes several chapters devoted to the utilization of both the major and some of the minor components of wood considered individually as a source of polymers. 

Most of the recent efforts to develop uses for the condensed tannins have centered on their application in wood adhesives. Reviews by Pizzi (182, 186) and others (15, 78, 87, 93, 208) provide references to several hundred papers and patents on this subject. Despite world-wide research efforts on other sources of tannins, particularly since the 1972-1973 petroleum shortage, the mimosa or wattle tannins extracted from the bark of black wattle Acacia mearnsii) remain the major source of condensed tannins exploited commercially for adhesive manufacture. Of the approximately 100000 tons of wattle tannin produced annually, only about 10000 tons are used in wood adhesives, predominantly in South Africa but also in Australia and New Zealand (186). The extensive use of wattle tannins by the wood products industry of South Africa is impressive indeed, as these tannins have partly replaced phenol and resorcinol usage in adhesives for bonding of particleboard, plywood, and laminated timbers (182, 186, 213). Three factors have contributed to the success in use of wattle tannin-based adhesives, namely the comparatively high costs of phenol and resorcinol in the Southern Hemisphere, their resorcinolic functionality and low molecular weight and, perhaps most importantly, the commitment by the research and industrial communities of these countries to reduce the reliance of the forest products industry on petroleum-based adhesives. 

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