Silvicultural systems and biological nitrogen fixation

Abstract

Biological nitrogen fixation occurs in most, probably all, forest ecosystems (Chap. 2), and thus is a factor in all silvicultural systems. Silvicultural systems are defined here as purposeful attempts to derive benefits for humans from forested (or afforested) lands. Such attempts vary from minimal efforts to protect wild ecosystems from catastrophic fire to the establishment of artificial stands of exotic trees which are then vigorously managed for specific products. Although ‘forest products’ are commonly thought of as wood in its various fuelwood and manufactured forms, of equal or greater importance in many places are clean water, stabilized soil, enhanced wildlife populations, improved grazing for domestic livestock, and enhanced recreational opportunities. Thus, this discussion of nitrogen fixation as a silvicultural tool will emphasize, but will not be limited to, silvicultural systems with wood production as their objective. Also, since all silvicultural systems probably contain some nitrogen-fixing organisms, this discussion is limited to 1) those in which naturally-occurring fixation is recognized as particularly important and is a factor in silvicultural decisions (passive systems) and 2) those in which fixation is enhanced through species introduction or silvicultural practices, or both (active systems).