Mixed Plantations Of Eucalyptus And Leguminous Trees Enhance Biomass Production

Two Eucalyptus species-E. saligna Sm. and E. grandis Hill-are especially favored in Hawaii for wood, fiber, and fuel production because of their quick growth and high yields. Their growth is limited, however, on many sites by low levels of available nitrogen. Supplemental nitrogen can be provided by nitrogen-fixing plants, such as legumes. A test was conducted to determine whether planting two leguminous species-Acacia melaxylon R. Br. and Albizia facataria (L.) Fosberg-could increase biomass production. Results after 65 months suggest that Eucalyptus growth can be increased substantially by planting the species in mixture with leguminous trees. Total biomass production was much greater in the mixed species plantations than in the pure Eucalyptus plantation.

The aim of this book is to present, in depth, updated information on soil and microbial processes involved in mixed plantations of Eucalyptus and N2-fixing species, especially Acacia mangium, focusing on Forestry, Soils, Biology, Ecosystem Services and Sustainability. The potential of substituting chemical N fertilizer by a consortium of leguminous species that fix atmospheric nitrogen is an interesting solution for a more sustainable, economically and environmentally sound forest system. Among the main topics, we present reference topics on soil microbiology, as biological nitrogen fixation, the role of mycorrhiza in mixed plantations, bio-indicators of soil quality, and plantgrowth promoting bacteria with biotechnological potential. Here we discuss Ecosystem services and ecological benefits of these systems, the invasive potential of A.mangium, as well as the regulations and perspectives of land use policies for mixed forests and their role in the sustainability of the system.

Large areas of the warm, humid tropics in Southeast Asia, the Pacific, Latin America, the Caribbean, and Africa are hilly or mountainous. Jackson and Scherr (1995) estimate that these tropical hillside areas are inhabited by 500 million people, or one-tenth of the current world population, many of whom practice subsistence agriculture. The region most affected is Asia which has the lowest area of arable land per capita. Aside from limited areas of irrigated terraces, most of the sloping land, which constitutes 60% to 90% of the land resources in many Southeast Asian countries, has been by-passed in the economic development of the region (Maglinao and Hashim, 1993). Poverty in these areas is often high, in contrast to the relative wealth of irri gated rice farms in lowland areas that benefited from the green revolution. Rapid population growth in some countries is also exacerbating the problems of hillside areas. Increasingly, people are migrating from high-potential lowland areas where land is scarce to more remote hillside areas. Such migra tion, together with inherent high population growth, is forcing a transforma tion in land use from subsistence to permanent agriculture on fragile slopes, and is creating a new suite of social, economic, and environmental problems (Garrity, 1993; Maglinao and Hashim, 1993).

Regression equations to predict total and stemonly above-ground dry biomass for six species (Acacia melanoxylon, Albizio falcataria, Eucalyptus globulus, E. grandis, E. robusta, and E. urophylla) were developed by felling and measuring 2- to 6-year-old plantation trees on the island of Hawaii. Logarithmic transformations of the equations using diameter and height are recommended for estimating Albizia falcataria and E. grandis biomass, whereas logarithmic equations using diameter only are recommended for the other four species that have fewer sample trees collected from a single location.

Much of the world's forested land is dominated by mixed-species stands. Understanding the complex structure and dynamics of these mixtures is a necessary step in the process of formulating appropriate silvicultural systems for their management. David M. Smith, Professor Emeritus of Silviculture at Yale University, has devoted much of his career to the study of the structure, development, and silvicultural treatment of these kinds of stands. This volume is presented by Professor Smith's collegues to honor the contributions he has made to the field. It contains both reviews of past work and results of current studies of mixed stands: topics range from analysis of forest dynamics in unmanaged stands to studies of silvicultural systems applied to mixtures, with examples drawn from boreal, temperate, and tropical regions. Much of the work stresses the importance of understanding the characteristic growth patterns of individual species within mixed stands, and how species interactions shape developmental patterns.