Rehabilitation of degraded tropical forest ecosystems project

Tropical forests are being cleared at a rate of 16.9 million hectares per year and timber harvesting results in over 5 million hectares becoming secondary forests annually without adequate management. This decrease and degradation affect both timber production and many environmental values. Selective and clear cutting, and burning are major causes of land degradation. An assessment is needed of harvesting impacts that influence rehabilitation methods. The harvesting impacts on ecosystems vary with time and methods of logging, timber transporting methods, logged tree species, soil characteristics, topographies, local rainfall patterns etc., and must be assessed in a range of conditions with long term monitoring. Increased supply of wood from plantation forests has the potential to reduce pressure on natural forest resources as well as contributing to environmental care and economic advancement for landholders. Short-rotation plantations can result in changes in nutrient storage and cycling processes due to factors such as harvesting wood, fertilisation, erosion, leaching, and modified patterns of organic matter turnover. These factors can affect storage and supply of soil nutrients for tree growth and consequently the sustainability of plantation systems. Opportunities exist to manipulate soil organic matter through silvicultural practices but these must be technically feasible, economically viable and socially acceptable. The following research objectives are proposed: (1). evaluation of forest harvesting and fire impacts on the forest ecosystems, (2). development of methods to rehabilitate logged-over forests, secondary forests and degraded forest lands, (3). development of silvicultural techniques on plantation and degraded lands, (4). network on the rehabilitation of degraded tropical forest ecosystems. It is anticipated that the results of these studies will contribute to the sustainable use of forest resources and environmental conservation. 1 Center for International Forestry Research, Bogor, Indonesia. Present address: Forestry and Forest Products Research Institute, Matsunosato 1, Kukizaki, Inashiki, Ibaraki 305-8687, Japan. Tel: +81-298-733781/733211 ext. 246, Fax: +81-298731541, E-mail: ksige@ffpri.affrc.go.jp 2 CSIRO Forestry and Forest Products, Canberra, Australia. 3 Center for International Forestry Research, Bogor, Indonesia. BACKGROUND AND JUSTIFICATION There are 4.5 billion hectares of forests of which 3% are in the tropics. Tropical forests have been affected severely by human activities resulting in their rapid reduction in size and quality. Apart from the estimated 16.9 million hectares lost annually mainly through conversion for agriculture and shifting cultivation, more than 5 million hectares have become secondary forests after harvesting. These secondary forests lack adequate management and silvicultural treatments (Forestry 1 2 S. Kobayashi , J.W. Turnbull and C. Cossalter The potential loss of biological diversity, which could be as high as one quarter of all species of plants, animals, fungi and microorganisms on the earth over the next 25 years, threatens the sustainable and harmonised development of the global ecosystem. Reduction of the tropical forest is also related to global warming through acceleration of the greenhouse gas emissions such as carbon dioxide, methane and nitrogen oxide and accumulated decrease of carbon dioxide through photosynthesis by tropical trees (Kira 1991, Uchijima 1991). The harvesting of timber affects forest ecosystems in various ways which include site degradation, reduced forest water supply, soil loss and greenhouse gas emission. Selective and clear cutting, fire and burning are major causes of land degradation, and forest harvesting becomes a trigger for other forms of land utilisation (Kobayashi 1988, 1994). While forest harvesting affects changes in ecosystems, subsequent land utilisation may cause more severe impacts on natural ecosystems (Fig.1). The effects of forest harvesting and fire have not fully been understood, especially in tropical rainforests (Lamb 1990). Information on the long-term impacts of tree harvesting and fire on forest ecosystems especially with regard to changes in vegetation, soil and productivity, is lacking. Rehabilitation of degraded forests and lands is a most urgent matter requiring enrichment of ecosystems and sustainable use of degraded areas at regional and global scales. In a loggedover forests, where former ecosystems more or less remain, the development of methods to accelerate natural regeneration is needed (Forest Agency and ITTO 1991). Where little or none of the natural ecosystem remains, plantations, site management and productivity must be considered. Successful regeneration and reforestation depends on the accurate evaluation of site conditions created by harvesting, e.g. the success of natural regeneration by commercial tree species is strongly influenced by the intensity of harvesting. Studies of biological and physiological characteristics of regenerated trees or newly planted trees and of the processes influencing productivity are necessary improve the success rate of rehabilitation and reforestation activities. In the Asia Pacific region rainforests decreased from 325 million ha in 1980 to about half this value by the mid 1990s and are projected to decline to 30-35 million ha in another decade (Tiarks et al. 1998). At the same time population growth and rapid economic expansion in the region has escalated demand for industrial wood products and fuelwood. Increased supply of wood from plantation forests has the potential to reduce pressure on natural forest resources as well as contributing to environmental care and economic advancement for landholders in the tropics. Many soils of tropical forest ecosystems are poor in nutrients. Nevertheless, undisturbed natural forests do not usually display symptoms of nutrient disorders because nutrient cycles are in a state of dynamic equilibrium where inputs and outputs of nutrients are in balance and plant demand for nutrients is met by efficient recycling systems. Where natural forests are replaced by shortrotation plantations there will be changes in nutrient storage and cycling processes due to factors such as harvesting wood, changed organic matter quality, fertilisation, erosion, leaching, and modified patterns of organic matter turnover. These factors can affect storage and supply of soil nutrients for tree growth and ultimately the sustainability of plantations. Studies on the effects of monoculture plantations on organic matter dynamics and nutrient cycling have usually found changed patterns of organic matter and nutrient storage (Evans 1992, Jordan 1985, Kobayashi 1994). There is concern that short rotations of some species in plantations will not be sustainable in the long-term. Long-term sustainable production will rely on management practices which maintain soil organic matter, conserve nutrient stores and minimise direct nutrient loss. There is critical need for designed experiments which evaluate silvicultural options, especially at the phase between harvesting and control of the site by the replacement trees. In particular, the research must focus on ecosystem variables and functional processes which will allow quantitative assessment of plantation management and its likely long-term impacts. 3 Rehabilitation of Degraded Tropical Forest Ecosystems Project N at ur al F or es t Lo gg ed -o ve r Fo re st Fo re st P la nt at io n Fo re st H ar ve st in g S el ec tiv e C ut tin g