The need for reductions of greenhouse gas emissions may provide a significant incentive to further develop bioenergy. Biomass can act as a carbon sink and as a substitute for fossil fuels. Its role as a means of reducing C02 in the atmosphere is recognized in the Kyoto Protocol in articles 3.3 and 3.4. The IPCC (1995) estimates that between 60 and 87 GtC could be stored in forests between 1990 and 2050, corresponding to about 12-15 per cent of projected fossil fuel emissions, and without regard to carbon storage in biofuel plantations in currently unforested land.

While the establishment of forest-based carbon sinks may have an important role, they are by no means the solution to climate change. They also remain contentious, a principal concern being related to the permanency of the sink. Hence, there is a view that biomass sinks should be associated with a multifunctional role for biomass, be it for the production of bioenergy or raw materials for other purposes (Schlamadinger et al„ 2001; Read, 1997).

The advantage of using sustainably grown biomass for energy is that it ensures emissions reductions through the substitution of fossil fuels and is not constrained by the saturation limits of managed biomass carbon sinks. Bioenergy for fossil fuel substitution may be complemented with significant carbon sequestration in litter and soils, depending on land-use changes. The levels of carbon substitution and sequestration will depend on the plant species grown and associated management practices, as well as on soil types. Land use and management directed at using biomass for fossil fuel and other raw material substitution could reduce concerns over the temporary nature of land use changes for carbon mitigation as it would be linked to a traded commodity in the form of biomass materials. Associated carbon sinks could also be more secure.

Changes in land use and land management practices associated with energy crops as well as biofuel chain logistics affect the carbon cycle. Consequently, energy crops are not necessarily carbon neutral. The magnitude of carbon released or stored both above and below the ground through the introduction of energy crops may significantly affect the carbon balance of biofuel cycles. This needs to be considered in determining the carbon credits that can be attributed to them. Generally, the introduction of herbaceous and woody perennials on agricultural land or degraded land will lead to an increase in soil carbon. However, many factors, including those external to the land use and management practices, such as local climate, will affect the soil carbon balance and may lead to uncertainties in its assessment. Concerns still remain over the permanence of the carbon sinks.

Following from the Kyoto Protocol, the EU target is a reduction of 8 per cent of greenhouse gas emissions by 2012. Biomass already contributes to avoided C02 emissions by supplying part of the energy demand in the European Union, which would otherwise be mainly met with fossil fuels. Avoided C02 emissions associated with current biomass use are estimated at 2-9 per cent of the 1998 energy-related C02 emissions in the EU (Bauen and Kaltschmitt, 1999).

Increased utilization of biomass could make a substantial additional contribution to reduce C02 emissions and meet the Kyoto Protocol targets. Based on potential estimates and assumptions on its use for heat and power purposes only, it is believed that biomass could reduce 1998 C02 emissions by between 6 and 26 per cent (Bauen and Kaltschmitt, 2001). The consideration of carbon sinks could add further reduc­tions of C02 emissions as a result of biomass utilization (Schlamadinger et al., 2001).

The EU climate policy emphasizes nitrogenous emissions from agricultural activities. Perennial grasses and woody crops have a lower nitrogen fertilization demand and higher nitrogen use efficiency compared to annual crops (including annual biofuel crops), leading to lower nitrogen losses (nitrogen leaching and gaseous nitrogen emissions, mainly N20). Hence, the choice of energy crops will affect greenhouse gas emissions from the agricultural sector and may influence climate change mitigation actions. Nitrogen losses are subject to uncertainties, as they will be affected by soil type.

How such aspects may translate into policy actions that can be integrated with other agricultural, energy and environmental policies deserves further consideration. Although carbon sinks remain contentious and the extent to which they should contribute to the Kyoto commitments unsure, land management for fossil fuel substitution is to some degree likely to be a key issue in meeting stringent greenhouse gas emissions targets. An important issue yet to be addressed is if and how carbon sequestration associated with land management for fossil fuel substitution should be considered.