Allelopathy in forested ecosystems

In the context of forestry, the concept of allelopathy has recently been expanded from a plant to plant interference phenomenon to an ecosystem-level phenomenon that is influenced by ecosystem disturbance. This chapter reviews the latest development in our understanding of forest allelopathy and the ways in which this new knowledge can be used in sustainable forest management. Allelopathic effects of certain canopy trees on tree seedlings and understory plants have direct effects on forest renewal. Likewise some understory plants with allelopathic property can have controlling effects on tree regeneration and species composition. In fire adapted boreal forests, particularly natural fires, the level and distribution of fire severity plays a critical role in the manifestation of forest allelopathy. The high severity fires break down allelochemicals by thermal decomposition, create favorable seedbed by consuming forest floor humus and releasing nutrients and removing competing plants by killing underground regenerating organs. Clearcut harvesting and low-severity fires on the other hand, may promote vegetative regeneration of understory plants with competitive and allelopathic properties as their underground perennating structures remain unharmed. This may cause retrogressive succession by resisting tree colonization and inducing long-term habitat degradation. Research in the last two decades has increased our understanding on the mechanism of forest allelopathy in fire adapted boreal forests, but our knowledge in forest allelopathy in tropical forest is very limited. Control of competing and allelopathic plants after forest harvesting is a serious issue in forestry and public opinion is not favorable in using chemical herbicides. Alternative methods such as use of allelopathic straw mulch, herbicides of biological origin (bialaphose), planting tree seedling pre-inoculated with mycorrhiza, and scarification and spot fertilization at planting have produced good results. It is possible to develop alternative methods of weed control in forestry by using allelopathy principle. However, substantial infusion of research and development funds is necessary to make significant progress in this area.