Rehabilitation of Degraded Tropical 1 Forest Ecosystems Project S. Kobayashi1 , J.W. Turnbull2 and C. Cossalter3 Abstract 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. BACKGROUND AND JUSTIFICATION Agency and ITTO 1991). Tropical forest loss and degradation affect not only timber production but There are 4.5 billion hectares of forests of which also local and global environments and are causes 3% are in the tropics. Tropical forests have been of flooding, erosion, landslides, desertification and affected severely by human activities resulting in other natural disasters. their rapid reduction in size and quality. Apart from 1 the estimated 16.9 million hectares lost annually Center for International Forestry Research, Bogor, Indonesia. mainly through conversion for agriculture and Present address: Forestry and Forest Products Research Institute, Matsunosato 1, Kukizaki, Inashiki, Ibaraki 305-8687, shifting cultivation, more than 5 million hectares Japan. Tel: +81-298-733781/733211 ext. 246, Fax: +81-298- have become secondary forests after harvesting. 731541, E-mail: [email protected] 2 These secondary forests lack adequate CSIRO Forestry and Forest Products, Canberra, Australia. 3 management and silvicultural treatments (Forestry Center for International Forestry Research, Bogor, Indonesia. 2 S. Kobayashi , J.W. Turnbull and C. Cossalter The potential loss of biological diversity, success rate of rehabilitation and reforestation which could be as high as one quarter of all activities. species of plants, animals, fungi and micro- In the Asia Pacific region rainforests organisms on the earth over the next 25 years, decreased from 325 million ha in 1980 to about threatens the sustainable and harmonised half this value by the mid 1990s and are projected development of the global ecosystem. Reduction to decline to 30-35 million ha in another decade of the tropical forest is also related to global (Tiarks et al. 1998). At the same time population warming through acceleration of the greenhouse growth and rapid economic expansion in the region gas emissions such as carbon dioxide, methane has escalated demand for industrial wood products and nitrogen oxide and accumulated decrease of and fuelwood. Increased supply of wood from carbon dioxide through photosynthesis by tropical plantation forests has the potential to reduce trees (Kira 1991, Uchijima 1991). pressure on natural forest resources as well as The harvesting of timber affects forest contributing to environmental care and economic ecosystems in various ways which include site advancement for landholders in the tropics. degradation, reduced forest water supply, soil loss Many soils of tropical forest ecosystems are and greenhouse gas emission. Selective and clear poor in nutrients. Nevertheless, undisturbed natural cutting, fire and burning are major causes of land forests do not usually display symptoms of nutrient degradation, and forest harvesting becomes a disorders because nutrient cycles are in a state of dynamic equilibrium where inputs and outputs of trigger for other forms of land utilisation nutrients are in balance and plant demand for (Kobayashi 1988, 1994). While forest harvesting nutrients is met by efficient recycling systems. affects changes in ecosystems, subsequent land Where natural forests are replaced by short- utilisation may cause more severe impacts on rotation plantations there will be changes in natural ecosystems (Fig.1). nutrient storage and cycling processes due to The effects of forest harvesting and fire factors such as harvesting wood, changed organic have not fully been understood, especially in matter quality, fertilisation, erosion, leaching, and tropical rainforests (Lamb 1990). Information on modified patterns of organic matter turnover. the long-term impacts of tree harvesting and fire These factors can affect storage and supply of soil on forest ecosystems especially with regard to nutrients for tree growth and ultimately the changes in vegetation, soil and productivity, is sustainability of plantations. Studies on the effects lacking. Rehabilitation of degraded forests and of monoculture plantations on organic matter lands is a most urgent matter requiring enrichment dynamics and nutrient cycling have usually found of ecosystems and sustainable use of degraded changed patterns of organic matter and nutrient areas at regional and global scales. In a logged- storage (Evans 1992, Jordan 1985, Kobayashi over forests, where former ecosystems more or less 1994). There is concern that short rotations of some remain, the development of methods to accelerate species in plantations will not be sustainable in natural regeneration is needed (Forest Agency and the long-term. Long-term sustainable production ITTO 1991). Where little or none of the natural will rely on management practices which maintain ecosystem remains, plantations, site management soil organic matter, conserve nutrient stores and and productivity must be considered. Successful minimise direct nutrient loss. There is critical need regeneration and reforestation depends on the for designed experiments which evaluate accurate evaluation of site conditions created by silvicultural options, especially at the phase harvesting, e.g. the success of natural regeneration between harvesting and control of the site by the by commercial tree species is strongly influenced replacement trees. In particular, the research must by the intensity of harvesting. Studies of biological focus on ecosystem variables and functional and physiological characteristics of regenerated processes which will allow quantitative assessment trees or newly planted trees and of the processes of plantation management and its likely long-term influencing productivity are necessary improve the impacts. Figure 1. Rehabilitation of Degraded Tropical Forestry Ecosystem Natural Forest Forest Plantation Degraded Land Logged-over Forest Forest Harvesting *(1) Evaluating of forest harvesting impacts on forest ecosystem ForestEcosystemsProject RehabilitationofDegradedTropical Selective Cutting (Thinning) Clear - cutting Seedling No Seedling Distribution Distribution *(3) Development of silvicultural techniques on degraded forest lands Accelerating Enrichment Forest Plantation Natural Regeneration Planting *(2) Development of rehabilitation methods on logged-over forests Improved Forest Ecosystem** Improved Productivity** Rehabilitated Forest Sustained Forest Plantation * Actual target is development of adequate techniques. ** Final target is conservation of biodiversity and environment of forest. 3 4 S. Kobayashi , J.W. Turnbull and C. Cossalter Pulpwood in particular is a low value, high which could be developed to assist their volume product and the industry is characterised rehabilitation. Although a number of reforestation by large areas under short rotation with high volume trials have recently been started for the purpose of tree crops. It is this type of plantation management regeneration of useful tree species, plantation and that is most likely to exert excessive demands on even recovery of former forest ecosystems, many the site, and hence it is highly appropriate for studies of them are empirical “trial and error” type of addressing issues of sustainability. The challenge activities. Few are sufficiently systematic and for researchers is to provide the scientific scientific. information that enables managers to devise Assembly and analysis of data in relation silvicultural systems for plantations which enhance to harvesting impacts which significantly influence soil properties important to sustainable production