ABSTRACT
Mankind has altered and transformed 40–50 per cent of the ice-free terrestrial surface of the Earth and appropriates an estimated 20 per cent of the global net primary production (Imhoff et al, 2004). The world's population is predicted to increase by 34 per cent from today to reach 9.1 billion people in 2050 (FAO, 2009). At the same time, this population will be more urbanized and have higher income levels than today. This larger and richer population will place unprecedented demands on the Earth's natural resources for the production of food and fibre (FAO, 2009). Currently humans appropriate 40–50 per cent of the available fresh water, and this is predicted to increase to 70 per cent by 2050 (Postel et al, 1996). In addition, it has been estimated that humans have doubled the nitrogen inputs from fertilizing agricultural systems and fossil fuel burning into terrestrial ecosystems (Vitousek et al, 1997), and the current atmospheric nitrogen deposition has enhanced the forest carbon sink by some 10–20 per cent (Schulze et al, 2009). These figures indicate that a large proportion of the increase in the production of food and fibre has come through intensification of agricultural and forest management systems, although extensification of agriculture and plantation forestry through land-use change, e.g. forest clearing, has also contributed to this. It is expected that 20 per cent of the required increase in food production in countries with developing economies between now and 2050 will be contributed through the extensification of agriculture. These projections demonstrate that there will be intense competition for land between different land-use options such as food production, production of timber, fibre and biofuels as well as nature conservation, and the development of urban areas and infrastructure. The growing demand for food, fibre, water, etc. is likely to lead to further deteriorations of ecosystem services as has been documented in the Millenium Ecosystem Assessment (2005). The projections also stress that we need to be mindful about the possible consequences of replacing natural ecosystems that provide great benefits to human societies such as clean drinking water, soil protection, etc. Many of the ecosystem services they provide are irreplaceable, or the technology necessary to replace them is prohibitively expensive (Palmer et al, 2004). Thus the role of both natural and replacement, or man-made ecosystems in maintaining these services becomes increasingly important. In the past, tree plantations have had ambivalent roles with regards to ecosystem services. Their production function has served in a very efficient way to meet the growing demand for wood products. However, where tree plantations have replaced native ecosystems (forests or grasslands), many ecosystem services have deteriorated. The expansion of fast-growing industrial plantations for pulp, together with the rapid expansion of oil-palm plantations, has been a major driver of deforestation in the past, for example in Indonesia (Barr, 2002; Uryu et al, 2008). Where plantations were established on degraded or former agricultural land, many ecosystem services improved (see previous chapters and Cossalter and Pye-Smith, 2003). The future development of forest plantations, both in terms of extent as well as quality and management has to be viewed in this context.
