To clarify the various functions of the fallow phase in the shifting cultivation system in northern Thailand, the fluctuation of fertility-related properties of soils throughout land-use stages was analyzed and the soil organic matter (SOM) budget was quantitatively evaluated, with special reference to soil microbial activities. The factors that have ensured the long-term sustainability of the shifting cultivation system can be summarized as follows: (1) Some soil properties relating to soil acidity improve when SOM increases in the late stages of fallow. The litter input may be supplying bases that are obtained via tree roots from further down the soil profile to the surface soil. This simultaneous increase in SOM and bases in the surface soil through forest-litter deposition in the late stages of fallow has an increasing effect on nutritional elements. (2) The decline in soil organic C during the cropping phase may be compensated by litter input during 6-7 years of fallow. With regards to overall budget, the organic matter input through incorporation of initial herbaceous biomass into the soil system after establishment of tree vegetation (approximately in the fourth year) was indispensable for maintaining the SOM level. (3) The succession of the soil microbial community from rapid consumers of resources to stable and slow utilizers, along with the establishment of secondary forest, retards further leaching loss of nitrogen (N) and enhances N accumulation in the forest-like ecosystems. It is noteworthy that during the fallow period, nitrifying activity of soil microbes, which was once activated in the cropping phase, is apparently suppressed. As a result, nitrate (NO₃^-) effluent from soil layers was remarkably decreased, even in the initial stages of fallow. The functions of the fallow phase listed above can be considered essential to the maintenance of this forest-fallow system. Agricultural production can therefore be maintained with a fallow period of around 10 years, which is somewhat shorter than widely believed. Traditional shifting cultivation in the study village is shown to be well adapted to its soil-ecological condition.

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Since several decades ago, rural societies in Solomon Islands have experienced rapid socioeconomic changes due to the direct and indirect influences of commercial logging operations by foreign companies on their customary lands. This study aims to explore household level subsistence patterns and their variations within a rural society that was subjected to the logging operation in the recent past, in Roviana, Western Province. Crop yield (MJ) and cash income (SBD: Solomon Islands Dollar) were compared among households and adjusted for the consumer unit (CU) and producer unit (PU), respectively. The results indicated large inter-household variations for both of these variables. Multiple regression analyses showed that the variation in crop yield was primarily explained by the available labor force (PU), while that in cash income was determined by the householders’ participation in SDC, a local enterprise founded using a portion of royalty money, as well as the labor force. It is suggested that an individual’s experience in generating and increasing cash income in local environments increases his/her household’s economic level.

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Rice production has been monitored at 8005 plots of rain-fed paddy field in a village in Northeast Thailand for the period from 1978 to 2002. Rice crop was evaluated and classified into 4 classes, i.e. “good”, “poor”, “crop failure” and “no planting”. Distribution mapping of crop performances showed a large variability among plots, and also extreme changes among years mainly due to flood and drought. All paddy fields were classified into 8 types by cluster analysis. Lower and unstable production was observed in upper paddy fields. Areas with poor yield and no planting paddy fields have decreased in recent years owing to expanding supplementary irrigation and the direct seeding method. Supplementary irrigation is carried out by purchasing water from canals or sucking up river water using engine driving pumps at planting time or severe drought. This indicates that a gradual improvement in rice production is possible with rain-fed rice cultivation. However, large crop failure still occurs frequently especially in areas nearer to rivers.

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Land-use patterns and plant use were recorded at two neighboring villages in central Laos. Bak village is located upland and surrounding land includes an extensive forest area, fallow fields, shifting cultivation fields, grassland, waterside, and paddy fields. During the study period the forest area supplied the largest number of useful plants. Nakhou village is, by contrast, in a lowland area and utilized land included small areas of remnant forest, grassland, waterside, and extensive paddy fields. Paddy fields contained the largest number of useful plants, followed by forest. Villagers compensated for the lack of forest resources in Nakhou village by maintaining and managing a diversity of trees within the paddy field land-use class. In addition, residents of the surrounding villages made the most of locally available plant resources and supplemented each other’s resources through trading. Analysis of local plant use at different geographical scales showed that the relationship between humans and plants at this study site was flexible and influenced mainly by topography and land-use and partly by socio-economic conditions and invasion of naturalized species. Species inventories and descriptions of the external factors influencing plant use at different geographical scales within a spatially heterogeneous landscape, will form an important basis for management and conservation of the plant resources of local communities.

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A pollen and charcoal record from a 153 cm peat swamp forest core in Central Kalimantan provides a picture of environmental change and fire history from 8440 yr BP to 6540 yr BP. The existence of charcoal in all sample layers indicates that fire occurred in the tropical peat swamp forest throughout the period. In the earliest period, from ca. 8440 to 8000 yr BP, there was a Camnosperm comp.-Cratoxylum forest. Palaquium comp. and Sandoricum comp. were also important constituents in this forest. Subsequently, dry climatic conditions prevailed between 7240∼8000 yr BP. These climatic conditions increased the fire frequency and intensity causing vegetation change, i.e. the encroachment of Palaquium comp. and the replacement of the Camnosperma comp.-Cratoxylum forest with a Palaquium comp.-Cratoxylum forest. A Camnosperma comp.-Cratoxylum forest with more prominent representation of Elaeocarpus, Ilex, Randia, Rubiaceae and Sterculiaceae returned to the site when wet climatic conditions prevailed again at ca. 7240-6540 yrs BP. Returning wet climatic conditions reduced fire frequency, prevented intensive fires and allowed for more extensive growth of Camnosperma comp., Elaeocarpus and Ilex, but limited the growth of Palaquium comp. and Sandoricum comp.

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Litter production, accumulation, and decomposition were examined on the seaward and landward sides of a long-term mangrove research site on Pohnpei Island, the Federated States of Micronesia, to estimate the contribution of litter deposited on the mangrove forest floor to carbon accumulation in mangrove forests. The annual litter production in the forest site was relatively high, 15 Mg ha^-1 yr^-1. The litterfall was composed of leaves (55%), reproductive organs such as flowers and seeds (34%), and bark and small branches (11%). The seasonal fluctuation of the litter was small. The amounts of litter deposited on the floor were 0.51 Mg ha^-1 on the seaward side and 0.76 Mg ha^-1 on the landward side. Compared with the mangrove substratum, the litter deposited on the forest floor has an extremely low capacity to act as a carbon sink. During the first year of the leaf decomposition, the mangrove leaves decomposed markedly (k = 7.0 - 18.2) faster than the leaves of the terrestrial mahogany forest (k = 0.3). The mangrove leaves decomposed rapidly, losing more than 60% of their initial weight in the first month. This high rate might result from leaching of labile fraction from the leaves by the high frequency of immersion as well as by the high levels of activity of decomposers on the forest floor at high temperatures and humidity. Moreover, the effect of crab’s feeding on the litter disappearance could not be disregarded. Tidal litter transportation rate was examined by collection of marked leaves along a tide level gradient. The transportation rate was greater as the highest tide level was higher. This study clarified that the disappearance of litter on the mangrove forest floor was strongly influenced by the tide, especially on the seaward side, as well as by the active microbial and faunal decomposability. We concluded that, despite the mangrove forest’s high litter production, litter on the forest floor did not contribute much to carbon accumulation, especially on the seaward side, since litter was disappeared rapidly from forest floor by tidal exportation and strong microbial activity.

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The aim of this study is to clarify the survival and growth performances of six native mangrove species (Avicennia officinalis, Avicennia marina, Bruguiera sexangula, Heritiera fomes, Rhizophora apiculata and Sonneratia apetala) that were replanted on abandoned paddy fields in the Ayeyarwady (AYWD) Delta of Myanmar where natural mangroves once existed. The findings indicate that low survival rate and poor growth of the trees can be attributed to both ground level and biotic disturbances. The growth of trees at low ground was obviously better than that of trees at high ground. At low ground, S. apetala demonstrated the best growth and R. apiculata had the highest survival rate. At high ground, the survival and growth rates of A. officinalis were the best. All the species replanted showed the highest increments of tree height from the middle of rainy season to the beginning of winter.

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Effects of soil water availability on seedling height, dry matter production and allocation were investigated for Khaya anthotheca (a typical species at drier sites in a moist deciduous forest) and Khaya ivorensis (a typical species at wetter sites in a moist deciduous forest). Two-month-old seedlings of the two species were subjected to three soil watering treatments, which were termed wet, moderate and dry treatment, in a glass house for 14 weeks. Seedling height growth was significantly influenced by soil water availability and the pattern of height response was species-specific. K. anthotheca had significantly better growth in the moderate watering treatment than in the wet and dry treatment. As time progressed, plants in the wet treatment of K. ivorensis had greatest height growth than in the moderate and dry treatment. Soil water deficit significantly reduced total dry matter production in K. ivorensis and altered proportional allocation to leaves and roots as a possible strategy for acclimation. Statistically, water deficit did not affect total dry matter production and allocation in K. anthotheca probably due to small sample size used in this study. However, in the moderate and dry treatments, K. anthotheca seedlings had greater total plant dry matter than K. ivorensis seedlings suggesting that the latter is more tolerant to water deficit and that K. anthotheca has considerable potential for plantation forestry in humid tropics of Africa with distinct drought periods.

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Cedrela odorata L. originates from mesic habitats of the Central and South American forest, whereas Khaya senegalensis (Desr.) A. Juss. is native to xeric habitats (hot, dry savanna vegetation) of tropical Africa. In order to estimate drought resistance of C. odorata and K. senegalensis seedlings, transpiration rate (E), stomatal conductance (g_s), chlorophyll fluorescence traits and shoot growth in a progressive mild drought were examined under greenhouse conditions. Withholding watering from container-grown plants resulted in a range of soil water potentials (Ψ_s). As days of drought progressed, E decreased in both species as a result of stomatal limitations. However, K. senegalensis plants generally maintained higher E and g_s than C. odorata plants almost throughout the period of soil drying. Chlorophyll fluorescence measurements before and after drought for both species indicated that photosystem II was negatively influenced by soil drying, with C. odorata being more affected than K. senegalensis. The correlation coefficient for E and Ψ_s; E and F_v ⁄ F_m; g_s and Ψ_s; g_s and F_v ⁄ F_m were higher in K. senegalensis than C. odorata under the same period of drought treatment. Drought restricted shoot growth more in C. odorata than K. senegalensis. These findings suggest that K. senegalensis exhibited stronger drought resistance, whereas C. odorata followed a drought-avoiding strategy (greater leaf shedding) and was more conservative in its water use.

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According to the statistical results of field experiments, banana yield has a strong, positive correlation with the amount of potassium bananas absorb. The correlation coefficient is r=0.915^**. The function of yield (y) with absorbed potassium (x) was y=16351.9+1.01x. For banana grown on medium light soils (sandy loam soils), the critical soil K value was 76.8 mg kg^-1 of available K. The K supply classes established by statistical analysis were: < 76.8 mg kg^-1, 76.8-155 mg kg^-1 and >155 mg kg^-1, corresponding to low, medium and high K supply, respectively. The soil available potassium was lower than 155 mg ⁄ kg in most banana planting regions. After potassium fertilizer was applied, the banana plant yield increased significantly. Banana yield increased 32.38-66.60% when the rate of potassium application was between 477-954 kg ⁄ ha. Application of phosphorus fertilizer also increased the banana yield. It is clear from this study that the application of K fertilizer also markedly increased banana quality.

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