The effects of burning strength in shifting cultivation on the early stage of secondary succession in tropical rain forest was investigated at four sites (Sabal, Balai Ringin, Niah, and Bakam) in Sarawak, Malaysia. The number and growth (diameter, height, and biomass) of germinated seedlings were measured in experimental shifting cultivation plots in which the burning strength varied between 0, 100, 200, and 300 t/ha at Sabal, Balai Ringin, and Niah and 0, 20, and 100 t/ha at Bakam. Species composition of germinated tree and herbaceous seedlings was surveyed, and a germination test of buried seed was conducted at Niah and Bakam. The number of germinated seedlings decreased with increasing burning strength, whereas seedling growth was promoted by burning. During the first year, growth was best in the intermediate burning strength plots, whereas during the second year, growth was best in the most strongly burned plots. Species composition differed between unburned and burned sites. Site-specific factors such as original stand biomass, soil properties, and invasion of exotic species also affected germination and growth. Buried seeds in the Ao layer were killed by burning, and nearly all seeds in the 0-5 cm layer were killed in the plots with the highest burning strength (> 100 t/ha). On the basis of our findings, we conclude that in shifting cultivation systems burning promotes vegetation recovery when the burning strength is properly managed.

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We conducted a comparative study of nitrogen (N) dynamics in soil by examining a dry dipterocarp forest (DDF) and a dry evergreen forest (DEF), under similar climatic conditions, in northeastern Thailand. The soil N dynamics were described by measuring seasonal N mineralization and nitrification rates, soil microbial biomass, and the size of inorganic N pools and extractable organic N and C pools. We estimated the fluxes and production of inorganic N in soil using the ion exchange resin core and buried bag methods. Carbon and N accumulations were higher in the DEF than in DDF; DEF had likely been protected from fire for a longer time than DDF. We also found temporal and vertical differences in soil N dynamics between DDF and DEF. The greatest inorganic N flux in the soil occurred at the onset of the wet season in DDF, whereas inorganic N was produced throughout the wet season in DEF. N uptake occurred in the uppermost soil horizon in DDF, whereas N uptake in DEF occurred in the deeper soil horizon. The mean residence time of inorganic N was greater in DEF than in DDF. These results suggest that N cycles were faster in DDF than in DEF. During long-term incubation experiments, the dominant inorganic N form changed from NH₄⁺ to NO₃^-, coinciding with declining extractable organic C (EOC) concentrations at both sites. Shortages of EOC occurred earlier in DDF than in DEF. This finding indicates that EOC may be a useful index of C availability for soil N dynamics.

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An optimal spore extraction procedure is deduced for collecting spores of arbuscular mycorrhizal fungi (AMF spores) from clayey soil. The key to efficient spore collection is how to diffuse gathered clayey particles, since significant numbers of spores are coated with clayey particles. A sucrose-centrifuge spore extraction method was used for AMF spore collection. The effect on collected spore numbers of the soil-suspension shaking time and the ultrasonic processing time was tested using a clayey soil taken from a natural tropical forest. The number of AMF spores increased gradually with shaking-time up to approximately 20 minutes, suggesting that the AMF spores were effectively released from clayey soil by shaking. Ultrasonic processing for longer than 30s reduced the extracted spore numbers. It is concluded that 40 minutes soil-suspension shaking-time and 30 seconds ultrasonic processing gives a suitable extraction procedure for collecting AMF spores for clayey soil. This extraction procedure for AMF spores from clayey soil is set out step by step in an Appendix.

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An investigation was conducted to determine the extent of diversity and relationships among 36 aromatic rice cultivars collected from Asia. Characterization for 22 morphological characters with 101 morphometric descriptors was carried out. High and comparative levels of phenotypic variation using phenotypic frequency distribution and Shannon-Weaver diversity index were found between countries of origin. Most traits were polymorphic except to ligule color. Grain size, grain shape, culm strength, plant height and secondary branching contributed the highest mean diversity indices (H' = 0.91, 0.88, 0.87, 0.82 and 0.83, respectively). For trait groups, highest diversity was found in grain and culm traits (H' = 1.00 and 0.96, respectively). Populations from Vietnam were more diverse than others (H' = 0.92) whereas populations from India and Thailand displayed lower diversity indices (H' = 0.46 and 0.49, respectively). No clear association was detected between phenotypic diversity and countries of origin. Five clusters of 36 genotypes based on Euclidean distance were observed with 1 to 22 cultivars per group. The results of the character distribution and phenotypic diversity analysis permitted some broad generalization about collection and conservation of aromatic rice cultivars. This also indicated the presence of important genes for future aromatic rice breeding purposes. Despite the limitation in estimating total genetic variation, the present study indicated that morphological traits were useful for preliminary evaluation and can be used as a general approach for assessing genetic diversity among morphologically distinguishable aromatic rice cultivars.

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Site selection methods for shifting cultivation of the Iban were studied at five longhouses in the Mujong River area of Sarawak, Malaysia with special reference to their knowledge of secondary vegetation. Shifting cultivation practices in the area were more intense than reported in previous studies and were conducted with one-time cropping of upland rice followed by about a 2-10 year fallow period. In all, 42 sites of secondary forests were selected for the vegetation survey. They were classified into 25 suitable sites and 17 unsuitable sites for shifting cultivation by landowners, based on their perception through knowledge of vegetation. Interviews of farmers were also conducted to discover and assess indicator plants from plants encountered during the vegetation survey. In the first stage of decision-making for site selection, old secondary forests, especially with difficult access, were excluded. Secondly, the farmers took into consideration the composition and growth of secondary vegetation and, to a lesser extent, other environmental factors. During the early fallow period, less than about three years, some species such as Lalang (Imperata cylindrica) and Kemunting (Melastoma polyanthum) dominated. The farmers perceived such sites as unsuitable for shifting cultivation. Left fallow for several years (more than three years), tree species replaced small plants, e.g., grasses, ferns and shrubs, through vegetation succession. Farmers perceived the presence of many tree species as indicating fertile land, but some of them occurred more frequently or with higher density at unsuitable sites than at suitable sites. Nevertheless, tree size as measured by stem diameter at breast height was greater at suitable sites than at unsuitable sites, indicating that the farmers comprehensively grasp the growth condition of these plants for land fertility evaluation and site selection. Judging from the rice yield survey, the Iban farmers' site selection was appropriate for achieving sufficient rice production for their subsistence.

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The Ministry of Forestry and Estate Crops and Japan International Cooperation Agency initiated a participatory forest fire prevention program at two site villages in Jambi Province, Indonesia in 1997, aiming to prevent wild fires around protected forests by intensifying communities' land use with tree crops. This article analyzes farmers' performances in the program and its effects on fire prevention until 2000. Critical issues to fire prevention were inflammable undergrowth spreading fast on farmers' land after discontinuation of their cultivation by wild boars' crop raiding as well as their careless land burning in community consultations. Based on their proposal, an integrated green belt (IGB) was developed with a wire fence, a ditch, and perennial or annual crops on their land around forests to solve these problems. Farmers participated actively in fencing, ditching and tree planting, helped by safeguard of their farming against pests and favorable marketing of cash crops. Their improved land use with increased crops contributed to reducing inflammable vegetation and free land burning. Farmers were motivated to prevent wild fires, given tree crops. However, farmers' self-reliance was limited in land management and tree planting that they proposed for shortage of their skills, capital or labor, which resulted in considerable material and financial provisions under the IGB program. Communities can hardly achieve extensive tree planting and internalization of introduced activities simultaneously at their villages. The IGB was more advantageous to settler farmers adept in land cultivation and cropping than local farmers relying on surrounding natural resources. Effects of participatory fire prevention models depend on farmers' self-help abilities of land management and cropping to minimize fire-prone vegetation and land burning by meeting their farming needs, availability of capital, labor and information to improve the abilities, and crop markets as well as model simplicity. A single model is not equally effective among communities with different resource use, requiring diversification.

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Soil properties under secondary forests were studied in relation to vegetation conditions to clarify the site selection method for shifting cultivation of the Iban in Sarawak, Malaysia. Soils and vegetation were surveyed at 25 suitable sites and 17 unsuitable sites for shifting cultivation, classified by the landowners based on their perceptions through knowledge of vegetation condition. Principal component analysis classified soil properties into three principal components. The first was soil texture and organic matter with high factor loadings of clay content, cation exchange capacity, total C, and total N, and, to a lesser extent, exchangeable K. These properties were little affected by the fallow duration and site suitability. Clay content was regarded as one of important factors related to the levels of organic matter and nutrient retention capacity of the soils. The second component reflected soil acidity and exchangeable bases with high factor loadings of pH, exchangeable Ca and Mg, exchangeable Al, and Al saturation. These properties reflected the remnant effects of ash addition and fallow duration. However, no clear differences were apparent in these properties in terms of site suitability. The third component was linked to N availability, including the C/N ratio and exchangeable NH₄. The N availability was higher at suitable sites than at unsuitable sites. At suitable sites, N availability tended to be higher with increasing fallow age. The N availability showed a statistically significant correlation with the site score of the first axis obtained from correspondence analysis of plant density, suggesting a strong relationship between N availability and vegetation condition. That relationship was attributable to depletion of the available N of the soils during cropping and at the initial fallow stage, as well as to improvement of N availability of soils with increasing length of the fallow period. This finding related to N availability was consistent with farmers' criteria for fertile land: leaves of trees in fertile land should be dark green. The presence of some specific plant species might be correlated with levels of available P and soil hardness. Results of this study show that the Iban farmers' vegetation-based site-selection method might reflect the ability of secondary forest ecosystems to supply nutrients for rice plants through burning practices.

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