ABSTRACT
Bioenergy at its most fundamental level is about burning the accumulated proceeds of photosynthesis. Fossil bioenergy, in the form of coal, fueled the early industrial revolution and today, along with oil, sustains contemporary human civilization. In the early 20th century, these concentrated and conveniently packaged fossil fuels largely replaced wood, tallow, and dung as sources of heat
6.1 Introduction ............................................................................................................................99 6.1.1 The Mirage of a Bioenergy Panacea......................................................................... 100
6.2 Dening Ecological Sustainability ....................................................................................... 102 6.2.1 Key Terms and Processes ......................................................................................... 103
6.2.1.1 Nutrient Cycling ......................................................................................... 103 6.2.1.2 Biomass and Trophic Structure .................................................................. 103 6.2.1.3 Vegetation Diversity and Structure ............................................................ 103 6.2.1.4 Species-Area Relationships........................................................................ 104
6.3 Bioenergy Cropping Systems and Species Selection ............................................................ 104 6.3.1 Residues .................................................................................................................... 104 6.3.2 Bioenergy Plantations and Dedicated Crops/Trees .................................................. 106
6.3.2.1 Implications of Changing Crop Rotation Lengths ..................................... 106 6.3.2.2 System Stability and Landscape Considerations ....................................... 108
6.3.3 Native versus Exotic Species .................................................................................... 109 6.3.3.1 Case Study: Exotic Conifers as Biofuel Crops and Invasive Weed Risks ......... 110
6.3.4 Perennial Polycultures .............................................................................................. 111 6.4 Other Considerations ............................................................................................................ 111 6.5 Toward a Diverse Bioenergy Portfolio ................................................................................. 112 References ...................................................................................................................................... 112
and animal traction as a source of power; 200 years ago, 20% of U.S. agricultural land was devoted to growing “fuel” to feed livestock (Sexton et al. 2007). Today, many in the world recognize the many environmental, geopolitical, and economic costs of fossil fuel dependence, and the growing immediacy of the exhaustion of our fossil fuel reserves. As a result of this recognition, we nd ourselves reconsidering bioenergy, primarily from living plants, as a partial solution to these problems. Despite the recent attention paid to liquid biofuels, all biomass allocated to energy worldwide currently represents only approximately 10% of the total of 11,410 million tons of oil equivalent used per annum (IEA 2007).
