Shade tolerance and suitability of tree species for planting in rubber plantations

The rapid increase in rubber monoculture in Xishuangbanna has resulted in extensive damage to its local ecosystem. To decrease the negative effects, the concept of the ecological-economic rubber plantation (EERP) system was proposed. The EERP entails intercropping rubber plants with other economically significant plants, which would not only decrease the ecological impact of the rubber plantation, but also maintain and potentially increase its profitability compared with rubber monocultures. In order to select the appropriate species and intercropping pattern in the EERP system, we compared the photosynthetic parameters of five economically important trees (Swietenia mahagoni, Coffea arabica, Mesua ferrea, Myristica yunnanensis and Paramichelia baillonii) under four irradiance levels. The optimal irradiance intensity of C. arabica and M. yunnanensis was approximately 40%, and these species can be planted in the understory of an 8- to 15-year-old rubber forest. Adult S. mahagoni, M. ferrea and P. baillonii grow taller than the rubber trees, and their seedlings also show superior performance in 100% irradiance than in other irradiances. Thus, in an EERP, these valuable trees could be planted adjacent to rubber plantations but on sites that are economically and environmentally marginal for rubber production.     

栗茶间作模式下茶树根系的基础特性

对安徽枞阳县周潭镇大山村中国森林生态网络大山试验示范区的栗茶间作茶园和单作茶园茶树根系的特征进行了试验研究。结果表明:栗茶间作促进了茶树根系的生长。间作茶园茶树根系的干重、吸收根比例、比根长和根系生理活性明显大于单作茶树根系;间作茶园茶树根系在土壤中的分布比单作茶树根系更深、更均匀;间作茶园内茶树和栗树根系在土壤空间中各自具有相对不同的生态位。栗茶间作具有较好的生态学基础,是一种可持续发展的茶园经营模式。     

On-farm evaluation of the establishment of clonal rubber in multistrata agroforests in Jambi,Indonesia

Perennial tree crops are often grown in complex multistrata systems that incorporate natural vegetation. These systems contribute simultaneously to sustaining rural livelihoods and to the conservation of biodiversity, but their productivity is usually low. Introduction of high yielding germplasm, usually selected in monocultural plantations, is a potential way to increase productivity, but a critical requirement is that such plants can be established in a competitive multispecies environment. The establishment of clonal planting stock in the jungle rubber agroforests of Indonesia was explored through participatory on-farm research. The trial involved four farmers who grew clonal rubber trees in a total of 20 plots, constituting five replicate experimental blocks spread across four farms. Unexpectedly, vertebrate pest damage by monkeys (Presbytis melalophos nobilis) and wild pigs (Sus scrofa) was the most important influence on establishment, explaining almost 70% of the variation in rubber tree growth. The amount of labour invested in weeding was also positively correlated with rubber tree growth. Farmers generally decided to completely cut back vegetation between rows of rubber trees, including potentially valuable trees, rather than weeding within the rows and selectively pruning trees in the inter-row. Farmers thought that the inter-row vegetation would harbour vertebrate pests and compete with the clonal rubber, and they had access to fruits, firewood and other non-timber forest products from other land. Thus, contrary to expectations, when offered clonal germplasm, farmers opted to use plantation monoculture methods to protect what they considered a valuable asset, rather than maintain the traditional multispecies strategy they use with local germplasm. This revised version was published online in June 2006 with corrections to the Cover Date.     

<Emphasis Type="Italic">Eucalyptus</Emphasis> agroforestry system for small farms: 2-year experiment with rice and beans in Minas Gerais,Brazil

In Minas Gerais, Brazil, Eucalyptus plantation agroforestry techniques for small farms appear to be an adequate alternative to small-scale plantations, and by integrating timber and food production, they can meet local demands for aliment and wood. Intercropping of Eucalyptus camaldulensis with rice and beans was studied to compare yields of intercropping and monocultures over 2 years. In the first year, no differences were found in the productivity between the intercropped and monoculture systems of E. camaldulensis, rice and beans in both seasons. In the second year, E. camaldulensis in monoculture showed the lowest productivity. If compared with E. camaldulensis intercropped with agricultural crops, during the rainy season, beans intercropped with E. camaldulensis showed similar productivity when compared to monoculture. In the dry season, the productivity of beans in monoculture was higher than intercropping. In the second year, rice productivity was very low for both systems due to the lack of precipitation during the fructification phase. The equivalence area index (EAI) confirmed the advantages of the intercropping system over the monoculture system for E. camaldulensis and beans and rice, at least in the first 2 years.     

Plant and bird diversity in rubber agroforests in the lowlands of Sumatra,Indonesia

Plant and bird diversity in the Indonesian jungle rubber agroforestry system was compared to that in primary forest and rubber plantations by integrating new and existing data from a lowland rain forest area in Sumatra. Jungle rubber gardens are low-input rubber (Hevea brasiliensis) agroforests that structurally resemble secondary forest and in which wild species are tolerated by the farmer. As primary forests have almost completely disappeared from the lowlands of the Sumatra peneplain, our aim was to assess the contribution of jungle rubber as a land use type to the conservation of plant and bird species, especially those that are associated with the forest interior of primary and old secondary forest. Species-accumulation curves were compiled for terrestrial and epiphytic pteridophytes, trees and birds, and for subsets of ‘forest species’ of terrestrial pteridophytes and birds. Comparing jungle rubber and primary forest, groups differed in relative species richness patterns. Species richness in jungle rubber was slightly higher (terrestrial pteridophytes), similar (birds) or lower (epiphytic pteridophytes, trees, vascular plants as a whole) than in primary forest. For subsets of ‘forest species’ of terrestrial pteridophytes and birds, species richness in jungle rubber was lower than in primary forest. For all groups, species richness in jungle rubber was generally higher than in rubber plantations. Although species conservation in jungle rubber is limited by management practices and by a slash-and-burn cycle for replanting of about 40 years, this forest-like land use does support species diversity in an impoverished landscape increasingly dominated by monoculture plantations.     

Adoption of intercropping in rubber smallholdings in Kerala, India: a tobit analysis

Natural rubber (Hevea brasiliensis) is one of the major plantation crops of the state of Kerala in India and intercropping is practised during the initial gestation period of the crop. In this paper a to bit model was used to study the decision making behaviour of farmers in adoption and extent of adoption of intercropping in three regions of Kerala. The availability of family labour and the type of intercrops were found significant in explaining the adoption behaviour in all three regions. The perception of profitability of intercropping was also found to influence decision on adoption. The probability of adoption of intercropping was highest for three intercrops, banana (Musa spp.), cassava (Manihot esculenta) and pineapple (Ananas comosus). Targeting extension efforts to groups of farmers with available family labour and popularising selected intercrops may result in higher rates of adoption of intercropping in all three regions of the state.This revised version was published online in November 2005 with corrections to the Cover Date.     

Financial analysis of shaded cocoa in Ghana

The cultivation of cocoa has been an important driver of tropical deforestation globally. Efforts to reverse this trend are focusing on the reintroduction of shade trees to cocoa plantations. Shade trees are valuable in enhancing biophysical conditions on cocoa (Theobroma cacao) fields and contribute to biodiversity and product diversification for smallholder producers. Participatory trials of cocoa agroforests planted with indigenous shade tree species were undertaken with farmers in the Atwima District of the Ashanti Region of Ghana, to increase tree volume on cocoa fields while improving rural livelihoods and enhancing environmental sustainability. An ex ante financial analysis of the technology was undertaken to assess its economic viability. Input–output data were collected from farmer experiments over three seasons and supplemented with data from traditional cocoa fields of varying rotation ages, and secondary data on production in later years of an eighty-year cocoa rotation. A discounted cash flow analysis was carried out to estimate the benefit-cost (B/C) ratio, net present value (NPV), internal rate of return (IRR) and land expectation value (LEV) as well as the sensitivity to a 20% decline in cocoa prices and additional chemical costs for various shade scenarios at a 10% discount rate. It was observed that cocoa production is, in general, profitable. The change from the traditional system to one with hybrid cocoa raised the IRR from 31% to 57% with planted shade and 67% without, although extra agrochemical costs would tend to reduce the profitability of unshaded hybrid cocoa in particular. The age of maximum LEV for the various scenarios suggests that the optimum economic rotation for the hybrid cocoa is between 18 and 29 years, much less than the traditional system.     

Production physiology of three native shrubs intercropped in a young longleaf pine plantation

The objective of this study was to evaluate how competition would affect the physiology, and thus productivity of American beautyberry (Callicarpa americana L.), wax myrtle [Morella cerifera (L.) Small] and inkberry [Ilex glabra (L.) A. Gray] when intercropped in a longleaf pine (Pinus palustris Mill.) plantation in the southeastern United States. The effect of competition was assessed via comparisons of mortality, biomass, light transmittance, gas exchange and soil moisture between intercropping and monoculture (treeless) treatments. Overall, shrubs in the intercropping treatment performed worse than those in the monoculture, with higher mortality, and reductions in biomass of 75.5, 50.6, and 68.7% for C. americana, M. cerifera and I. glabra, respectively. Root–shoot ratios for all species were significantly higher and soil moisture during dry periods was significantly lower in the intercropping treatment. Light transmittance below the pine canopy was high (57.7%) and I. glabra was the only species that exhibited reduced A _max when belowground resources were not limiting. These results suggest that the effect of shading is minimal and belowground competition is likely the most important determinant of productivity in this system.     

Spice crops agroforestry systems in the East Usambara Mountains,Tanzania: growth analysis

A scarcity of cultivation land calls for more intensive and productive land use in the East Usambara Mountains in NE Tanzania. Spice crops could generate cash in higher parts of the mountains, but the present cultivation methods are depleting the valuable forest resources. The trial was established at the end of 2000 to find out how the two popular cash crops, cardamom (Elettaria cardamomum (L.) Maton.) and black pepper (Piper nigrum L.), normally grown under the natural forest, will produce in intensive agroforestry system with two multipurpose farm trees, Grevillea robusta A.Cunn. and nitrogen fixing Gliricidia sepium Jacq. Results from 6 years showed that cardamom produced better with grevillea than in natural forest; 5.5 times more in the fourth year than the average in the area. The Land Equivalent Ratios for black pepper and cardamom showed that pepper intercropped with grevillea produced 3.9 times more than in monoculture whereas cardamom intercropped with grevillea and pepper produced 2.3 times more than in monoculture. Gliricidia improved the nitrogen and organic matter content of the soil over the levels found in natural forest. Soil acidity was, however, preventing the plants from using the available mineral nutrients more effectively.     

Effects of intercropping with Atractylodes lancea and application of bio-organic fertiliser on soil invertebrates,disease control and peanut productivity in continuous peanut cropping field in subtropical China

The consecutive monoculturing of peanut seriously affects its yield and quality in the red soil regions of southern China. Different control measures for consecutively monocultured peanut fields should be explored to ensure the sustainable development of the local peanut industry. In this study, the influence of two different regimes, the intercropping of peanut with Atractylodes lancea and the furrow application of bio-organic fertiliser (BOF), on the community composition of soil invertebrates, the severity of peanut disease and peanut productivity was evaluated in an upland region where peanut had been monocropping for 5 years. We found that intercropping with A. lancea and the furrow application of BOF significantly changed the community composition of soil invertebrates and increased their biodiversity, as estimated by the Shannon and Simpson indices. Intercropping with A. lancea significantly reduced the proportion of Collembola, such as Tullbergia, Onychiurus, Folsomia and Folsomina, while the furrow application of BOF significantly increased the abundance of Collembola, such as Isotomidae compared with conventional monoculture. The intercropping significantly increased the proportion of Acarina, such as Mesostigmata and Oribatida, whereas the furrow application of BOF did not increase this proportion compared to conventional monoculture. The intercropping and application of BOF significantly reduced the damping-off in seedling and root rot disease at the maturation stage and increased peanut yield. The leaf spot disease of peanut was significantly suppressed by the intercropping but not by the application of BOF. The results of the study suggested that the intercropping of peanut with A. lancea and the furrow application of BOF could effectively relieve the problems associated with consecutive monoculture of peanut in the red soil regions of southern China.     

Imperata management strategies used in smallholder rubber-based farming systems

A large proportion of global natural rubber production takes place in Southeast Asia. The majority of this rubber is produced by smallholders. Thailand, Indonesia and Malaysia are the three principal countries involved. In Malaysia and Indonesia the smallholder sector accounts for 72% and 84% of total rubber production respectively. In other countries rubber plays a significant role on a more local basis. Imperata is a serious problem for the smallholder rubber farmer in most of Southeast Asia in three respects: the high cost (labour and/or capital) of opening Imperata-infested land, its competitive effect on rubber and annual intercrops, and the fire hazard that it poses during the dry season as a major source of combustible material. The costs of Imperata to smallholders are substantial in terms of a direct loss through fire and revenue foregone or delayed as a result of competition. Most smallholders intercrop their rubber during the first 1–3 years after planting it, and during this period Imperata is reasonably well controlled. Intercropping is only feasible for a limited period because of limited soil fertility and/or the shading effect of the rubber trees. After intercropping, Imperata tends to establish itself for a few years until it too is shaded out by the rubber. This is the problem period, during which farmers practise only limited weed management, if any.A large amount of research has been done on methods of controlling Imperata, but the recommended methods have been generally spurned by smallholders unless they have been given subsidies to apply them. This paper describes the precise nature of the Imperata problem, with reference to some of the smallholder rubber-based farming systems within Southeast Asia; the different Imperata control strategies currently practised in these farming systems; and some of the constraints on the adoption of currently and recently recommended practices. It then proposes a ten-point agenda for research on Imperata control, including two ways in which current research programmes could be usefully reoriented: first, they need to take greater account of smallholder farming systems and constraints; and second they should shift their emphasis from single-method to integrated control systems.     

Intercropping system of tropical leguminous species and Eucalyptuscamaldulensis, inoculated with rhizobia and/or mycorrhizal fungi in semiarid Brazil

For the purpose of reforestation and wood supply the leguminous tree Anadenanthera peregrina, a native species, was intercropped with Eucalyptus camaldulensis in a degraded semiarid area of Brazil. Single and mixed stands of these species were inoculated with Rhizobium and/or arbuscular mycorrhizal fungi (AMF). The growth of all species in mixed stands did not differ from those cultivated in monoculture and land equivalent ratio (LER) exceeded unity in intercropped plots. Inoculated plants showed greater height and diameter growth and dry matter and nutrient concentration in plants of A. peregrina was higher in inoculated single plots. The distribution, composition and density of AMF species was related to the rhizosphere effect of plant species. The intercropped model where all the plants were inoculated achieved soil AMF diversity patterns similar to those of the preserved area and showed also higher soil organic matter, nutrient content as well as a reduction in soil macroporosity. This model of intercropping may be considered as an efficient system for reforestation under semiarid conditions.     

Economics of species change subject to risk of climate change and increasing information: a (quasi-)option value analysis

Context

In the context of climate change, several forest adaptation options have to be advocated such as a shift to more resistant species.

Aims

We provide an economic analysis of timber species change as a tool for adapting forests to climate change.

Methods

We use the framework of cost–benefit analysis, taking uncertainty into account both exogenously (sensitivity analysis) and endogenously [(quasi-)option value calculations]. We apply the method to assess the economic rationale for converting Norway spruce stands to Douglas-fir in the French Black Mountain.

Results

We find that the Douglas-fir conversion is land expectation value (LEV) maximizing under a wide range of a priori (subjective) probabilities attached to high mortality of Norway spruce under climate change (for probabilities higher than 0.25–0.31). If information about the impacts of climate change is expected to increase over time, and given the large sunk costs attached to conversion, a delay strategy may be preferable to transition and to status quo when the impacts of climate change on Norway spruce mortality are sufficiently ambiguous. In such cases, getting information earlier increases the LEV by €5–60/ha.

Conclusion

Beyond the specifics of the case study, this paper suggests that quasi-option value is a relevant tool to provide insights to forest owners dealing with adaptation decisions in the context of climate change.     

Modelling and economic evaluation of forest biome shifts under climate change in Southwest Germany

We evaluated the economic effects of a predicted shift from Norway spruce (Picea abies (Karst) to European beech (Fagus sylvatica (L) for a forest area of 1.3 million ha in southwest Germany. The shift was modelled with a generalised linear model (GLM) by using presence/absence data from the National Forest Inventory in Baden-Württemberg, a digital elevation model, and regionalised climate parameters from the period 1970 to 2000. Two scenarios from the International Panel on Climate Change (IPCC) (B1, A2) for three different time scales (2030, 2065, and 2100) were investigated. The GLM predicted a decrease of the suitable area for growing Norway spruce between 21% (B1, 2030) and 93% (A2, 2100) in comparison to 2000. This corresponds to a reduction in the potential area of Norway spruce from between 190,000 and 860,000 ha. The financial effect of this reduction in area was then evaluated by using a classical Faustmann approach, namely the land expectation value (LEV) as an economic parameter for forests of Norway spruce versus European beech. Underlying cash flows were derived from a distance dependent, single-tree growth simulator (SILVA) based on data for prices and costs of the year 2004. With an interest rate of r = 2%, the predicted loss in the potential area of Norway spruce is related to a decrease of the LEV between 690 million and 3.1 billion Euro. We discuss the sensitivity of these results to changing interest rates, risk levels, and rotation lengths. Results suggest that managing forestland for profitability will be increasingly difficult under both climate scenarios.     

Trade-offs analysis for possible timber-based agroforestry scenarios using native trees in the Philippines

To assess possible new agroforestry scenarios the tree–soil–crop interaction model in agroforestry systems (WaNuLCAS 3.01) was used based on-site specific data collected from Tabango (Central Philippines). Three native timber trees (Shorea contorta Vid., Pterocarpus indicus Juss., and Vitex parviflora Willd.) and one widely spread exotic specie (Swietenia macrophylla King.) were simulated under different intercrop scenarios with maize (Zea mays L.) and subsequently compared. Model simulation results quantified and explained trade-off between tree and crop. For example, higher tree densities will lead to a loss of crop yield that is approximately proportional to the gain in wood volume. However, beside this trade-off effect, there is considerable scope for tree intercropping advantage under a fertilization scenario, with systems that yield about 50% of the maximum tree biomass still allowing 70% of monoculture maize yield. Maximum tree yield can still be obtained at about 20% of the potential crop yield but intermediate tree population densities (400 trees ha⁻¹) and the resulting larger stem diameters may be preferable over the larger total tree biomass obtained at higher tree densities. Another advantage from intercropping systems is that trees directly benefit from the inputs (i.e., fertilizer) that are applied to the crops. The three native trees species studied have different performance in relation to productivity but are similar to (or even better than) S. macrophylla.     

西双版纳热带雨林国家公园周边社区土地利用方式及发展研究

国家公园和周边社区居民存在着非常紧密的互动关系。文章以西双版纳热带雨林国家公园周边社区为研究对象,于2010年1~12月采用PRA、RRA(乡村快速评估)方法,对周边263个社区开展调查分析。结果显示,社区的土地利用模式已趋向稳定,单一种植粮食的种植业结构正在调整,发展扩大种植了橡胶、茶叶、水果等经济林木和甘蔗等经济作物,原始生产方式正在被固定农田、种植长期经济林木取代。针对存在的问题,对国家公园及社区的进一步管理和发展提出建议。     

Productivity of hedgerow shrubs and maize under alleycropping and block planting systems in semiarid Kenya

A field experiment was conducted for eight cropping seasons from 1988 to 1991 in semiarid Machakos, Kenya, to compare the productivity of shrubs and crops in intercropping (alleycropping) versus block (sole) planting systems. The study, conducted in a split-plot experiment with three replications, consisted of two tree species (Leucaena leucocephala andSenna siamea syn.Cassia siamea) in the main-plots and combinations of two planting systems (alleycropping and block planting of the shrubs and maize) with five different ratios of land allocation for the shrub and crop (1000, 1585, 2080, 2575, and 0100) in sub-plots. Thus, a sole maize and a sole tree were included in the subplot treatments. The spacing between hedgerows of shrubs in intercropping was 6.7, 5, and 4 m, respectively, corresponding to 15, 20, and 25% land allocation to shrubs. The trees were pruned to 0.5 m height four times a year. Intercropped hedgerows of senna and leucaena produced 10% and 24% more biomass than their respective block planting systems. On average, leucaena produced more biomass than senna. Maize alleycropped with leucaena yielded 16% less grain than sole-crop maize, whereas senna intercropping caused hardly any maize-yield reduction. Compared with the respective sole-crop systems, leucaena intercropping did not affect land equivalent ratio (LER), whereas LER increased by 28% with senna intercropping. The different tree:crop land occupancy ratios did not affect the production of either the component species or of the total system, except that LER declined with incrreased spacing between hedgerows. It is concluded that in semiarid highlands of Kenya, leucaena and crops should better be grown in sole blocks, not in alleycropping. In the case of slow-growing species such as senna, intercropping is worthwhile to consider only if the additional labour needed does not pose a serious problem for management, and the species has fodder value.     

Economics of intercropping loblolly pine and switchgrass for bioenergy markets in the southeastern United States

The main objective of this study was to assess the economics of alley cropping of loblolly pine (Pinus taeda L.) and switchgrass (Panicum virgatum) in the southern United States. Assuming a price range of switchgrass between $15 and $50?Mg^?1 and yield of 12?Mg?ha^?1 year^?1, we investigated the effect of switchgrass production on the optimal forest management for loblolly pine stands under different stumpage prices. We considered the following potential scenarios: no competition between species for resources; reduced loblolly pine productivity due to competition with switchgrass; and reduced productivity of both species due to competition for nutrients, water and light. Findings also suggested that the optimal system would depend on the competitive interactions between switchgrass and loblolly pine crops, and the expected prices for each crop. Loblolly pine monoculture would be the most profitable option for landowners compared to intercropping systems with switchgrass below $30?Mg^?1. However, when switchgrass prices are ??$30?Mg^?1, landowners would be financially better off adopting intercropping if competitive interaction between crops were minimal. In order to realize higher economic returns for intercropping system, forest landowners must make some efforts in order to diminish the decline of productivity.     

A financial evaluation of two contrasting silvicultural systems applicable to Pinus taeda grown in north-east Uruguay

The Loblolly pine (Pinus taeda L.) plantation area in north-east Uruguay was 108 000 ha in 2008. Recent industrial capacity developments have resulted in major structural changes. Silvicultural system selection depends on site productivity, costs, timber prices and public policies. This study aimed to assess economic returns for two silvicultural systems in north-east Uruguay, in scenarios with and without a plantation subsidy: System I, with a short, 12-year rotation, primarily for small logs; and System II, with a longer, 24-year rotation. For System I, the underbark volume was 198 m³ ha^?1 (mean annual increment16.5 m³ ha^?1 y?¹) and land expectation value (LEV) at a 9.7% discount rate was US$561 ha^?1 and US$442 ha^?1, with and without subsidy, respectively. System II resulted in 318 m³ ha^?1 underbark volume (13.2 m³ ha^?1 y^?1) and the LEV was US$860 ha^?1 and US$771 ha^?1, with and without subsidy, respectively. System I was more profitable than extensive cattle husbandry only when the distance to mill was equal to or less than 60 km and wood millyard prices were equal to or higher than US$27.8 m^?3 and US$28.8 m^?3 with and without subsidy, respectively. Values for System II, in which the main product was a mix of sawlog diameters, were positive and higher than those for System I, both with and without subsidy. If a company invested in forest plantations without due provision for early silvicultural treatments, such as pruning and precommercial thinning, a high risk of financial loss would ensue. Long-rotation sawtimber regimes similar to System II would be more profitable and offer a lower risk of financial losses. The results suggest subsidy withdrawal in Uruguay should not lead to changes in silvicultural systems; in fact, it rendered regimes designed for low-value wood, such as System I, even less advisable.     

Carbon return and dynamics of litterfall in natural forest and monoculture plantation of Castanopsis kawakamii in subtropical China

The amount of carbon returned through litterfall and its seasonal pattern were studied in a natural forest of Castanopsis kawakamii (NF) and adjacent monoculture plantations of C. kawakamii (CK) and Chinese fir (Cunninghamia lanceolata) (CF) in Sanming, Fujian Province, China. Mean annual carbon return through total litterfall over 3 years (from 1999 to 2001) was 5.097 t·hm⁻² in the NF, 4.337 t·hm⁻² in the CK and 2.502 t·hm⁻² in the CF respectively. Of the total carbon return in the three forests, leaf contribution accounted for 58.96%, 68.53% and 56.12% and twig 24.41%, 22.34% and 26.18%, respectively. The seasonal patterns of carbon return from total litterfall and leaf-litter were quite similar among the three forests. A peak of carbon input from litterfall in the NF and the CK occurred in spring except for the highest annual C return through branch litter of the NF in summer, while the CF showed the maximum C return in summer. The results of this study demonstrate that the natural forest has a greater C return through litterfall than monoculture plantations, which is beneficial to the increase of soil organic matter storage and the maintenance of soil fertility. [Supported by the Teaching and Research Award Program of MOE P.R.C. (TRAPOYT) and the Key Basic Research Project of Fujian Province (2000F004)]