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Small Plots (small + plot)
Selected AbstractsPhysically based modelling of sediment generation and transport under a large rainfall simulatorHYDROLOGICAL PROCESSES, Issue 11 2006Russell Adams Abstract A series of large rainfall simulator experiments was conducted in 2002 and 2003 on a small plot located in an experimental catchment in the North Island of New Zealand. These experiments measured both runoff and sediment transport under carefully controlled conditions. A physically based hydrological modelling system (SHETRAN) was then applied to reproduce the observed hydrographs and sedigraphs. SHETRAN uses physically based equations to represent flow and sediment transport, and two erodibility coefficients to model detachment of soil particles by raindrop erosion and overland flow erosion. The rate of raindrop erosion also depended on the amount of bare ground under the simulator; this was estimated before each experiment. These erodibility coefficients were calibrated systematically for summer and winter experiments separately, and lower values were obtained for the summer experiments. Earlier studies using small rainfall simulators in the vicinity of the plot also found the soil to be less erodible in summer and autumn. Limited validation of model parameters was carried out using results from a series of autumn experiments. The modelled suspended sediment load was also sensitive to parameters controlling the generation of runoff from the rainfall simulator plot; therefore, we found that accurate runoff predictions were important for the sediment predictions, especially from the experiments where the pasture cover was good and overland flow erosion was the dominant mechanism. The rainfall simulator experiments showed that the mass of suspended sediment increased post-grazing, and according to the model this was due to raindrop detachment. The results indicated that grazing cattle or sheep on steeply sloping hill-country paddocks should be carefully managed, especially in winter, to limit the transport of suspended sediment into watercourses. Copyright © 2006 John Wiley & Sons, Ltd. [source] Struggling to Save Cash: Seasonal Migration and Vulnerability in West Bengal, IndiaDEVELOPMENT AND CHANGE, Issue 4 2003Ben Rogaly This article concerns an important but overlooked means by which able-bodied poor people get hold of lump sums of cash in rural West Bengal: seasonal migration for agricultural wage work. Drawing on a regional study of four migration streams, our main focus here is on the struggle to secure this cash by landless households in just one of those streams, originating in Murshidabad District. Case studies are used to illustrate the importance for women in nuclear families of maintaining supportive networks of kin for periods when men are absent. A parallel analysis is made of the negotiations between male migrant workers and their employers, at labour markets, during the period of work, and afterwards. The article then briefly discusses some of the contrasting ways in which remittances are used by landless households and owners of very small plots of land, in the context of rapid ecological change, demographic pressure and growing inequality. [source] Infiltration, runoff and sediment production in blanket peat catchments: implications of field rainfall simulation experimentsHYDROLOGICAL PROCESSES, Issue 13 2002J. Holden Abstract Blanket peat covers the headwaters of many major European rivers. Runoff production in upland blanket peat catchments is flashy with large flood peaks and short lag times; there is minimal baseflow. Little is known about the exact processes of infiltration and runoff generation within these upland headwaters. This paper presents results from a set of rainfall simulation experiments performed on the blanket peat moorland of the North Pennines, UK. Rainfall was simulated at low intensities (3,12 mm h,1), typical of natural rainfall, on bare and vegetated peat surfaces. Runoff response shows that infiltration rate increases with rainfall intensity; the use of low-intensity rainfall therefore allows a more realistic evaluation of infiltration rates and flow processes than previous studies. Overland flow is shown to be common on both vegetated and bare peat surfaces although surface cover does exert some control. Most runoff is produced within the top few centimetres of the peat and runoff response decreases rapidly with depth. Little vertical percolation takes place to depths greater than 10 cm owing to the saturation of the peat mass. This study provides evidence that the quickflow response of upland blanket peat catchments is a result of saturation-excess overland flow generation. Rainfall,runoff response from small plots varies with season. Following warm, dry weather, rainfall tends to infiltrate more readily into blanket peat, not just initially but to the extent that steady-state surface runoff rates are reduced and more flow takes place within the peat, albeit at shallow depth. Sediment erosion from bare peat plots tends to be supply limited. Seasonal weather conditions may affect this in that after a warm, dry spell, surface desiccation allows sediment erosion to become transport limited. Copyright © 2002 John Wiley & Sons, Ltd. [source] Geostatistical characterization of the spatial distribution of Grapholita molesta and Anarsia lineatella males in an agricultural landscapeJOURNAL OF APPLIED ENTOMOLOGY, Issue 2 2006A. Sciarretta Abstract:, The results obtained in spatial analysis of pheromone trap catches of oriental fruit moth, Grapholita molesta (Busck) and Peach twig borer, Anarsia lineatella (Zeller), are reported. The studies were performed in the Molise region, central Italy, during 2002 and 2003. Local distributions of oriental fruit moth and peach twig borer males were considered in a heterogeneous landscape. The aim of the study was to determine the temporal and spatial variation in distribution and abundance of the insect pests inside small plots of fruit orchards (apple, kiwi, peach, pear and plum fruits) and outside (in field crops, irrigation channels, hedgerows and a river), and to evaluate the importance of the host plants in relation to the adult distributions. Results showed that the main ,hot spot' for both lepidopterous pests was in a stone fruit orchard in the northern zone of the study area; other infested areas were in stone orchards and, in the case of A. lineatella, also in plum orchards. The river seems to act as a barrier rather than an ecological corridor. The observed spatio-temporal distributions of G. molesta and A. lineatella differed and were determined mainly by the location of the most important host plants and by the tendency of males to move in the environment, i.e. inside and outside the breeding and mating sites. Adequate knowledge of these spatial processes should be considered as an essential prerequisite for integrated pest management programmes in a precision farming approach. [source] Colonization of an island volcano, Long Island, Papua New Guinea, and an emergent island, Motmot, in its caldera lake.JOURNAL OF BIOGEOGRAPHY, Issue 11-12 2001Abstract Aim Long Island erupted catastrophically in c. 1645 with the probable destruction of its entire biota. While several expeditions have visited the island since, no survey of its flora has been published. In 1968 a small island, Motmot, emerged from its caldera lake. Motmot has been surveyed several times but not since 1988. The aim of this study was to investigate the colonization by vascular plants of this interesting nested pair of islands. Location Long Island is 55 km off the northeast coast of Papua New Guinea (PNG) and Motmot lies in its fresh water caldera lake, Lake Wisdom, c. 4 km from the rim of the surrounding volcano. Methods We conducted a complete survey of the vascular plants on Motmot and made ad hoc collections on Long Island, including surveying three small plots, over 15 days in 1999. In addition, we incorporated data from several collections lodged at the regional herbarium in Lae. Data on seed dispersal syndromes and plant habit were obtained from the literature. Results We recorded 305 species of vascular plants from Long Island, but most trees were small and the species diversity was low. Motmot was still very sparsely vegetated and only forty-five species of vascular plants were found. Communities on Motmot were unspecialized and common species widespread. The flora of Motmot was not significantly different from that on Long Island in terms of the number of species amongst higher taxa, seed dispersal syndromes or plant habits. Main conclusions Low rainfall combined with very porous soils may be responsible for the small stature and low diversity of the forest on Long Island's caldera rim. The absence of specialist littoral species on Motmot, as a result of its landlocked situation, is probably responsible for the very slow species recruitment on the island. This community appears to be functionally important for colonization by comparison with other small volcanic islands in a marine situation. [source] Double exposure in Mozambique's Limpopo River BasinTHE GEOGRAPHICAL JOURNAL, Issue 1 2010JULIE A SILVA This paper examines how double exposure to economic and environmental stressors , and the interaction between the two , affect smallholder farmers in Mozambique's Limpopo River Basin. Studying two case study villages we find that people, in general, are resilient to environmental stressors. However, most households show less resilience to the socioeconomic stressors and shocks that have been introduced or intensified by economic globalisation. Our findings indicate that economic change brought about by structural adjustment policies pressures rural people to alter their approach to farming, which makes it more difficult for them to respond to environmental change. For example, smallholder farmers find it difficult to make a transition to commercial farming within the Limpopo Basin, in part because farming techniques that are well adapted to managing environmental variability in the region , such as seeding many small plots , are not well suited to the economies of scale needed for profitable commercial agriculture. People use a variety of strategies to cope with interactive environmental and economic stressors and shocks, but many face considerable constraints to profitably exploiting market-based opportunities. We conclude that economic stressors and shocks may now be causing small-scale agriculture to be less well adapted to ecological and climate variability, making smallholders more vulnerable to future climate change. Some local level policy interventions, including those that support and build on local environmental knowledge, could assist rural agricultural societies in adapting to future environmental change in the context of economic globalisation. [source] The interrelationship between productivity, plant species richness and livestock diet: a question of scale?APPLIED VEGETATION SCIENCE, Issue 2 2007Karin Süss Wisskirchen & Haeupler (1998) Abstract Question: What relationship exists between productivity, plant species richness and livestock diet? Are the results dependent on scale? Location: A sheep-grazed Koelerio-Corynephoretea sandy habitat of the northern upper Rhine (Germany) as a low productivity model system. Methods: The investigation was carried out for three years at a fine scale (2 m2) and for two years at a broad scale (79 m2). Productivity was measured by means of weighed above-ground phytomass for fine scale and colour-infrared (CIR) aerial photographs of the same system for fine and broad scales. For both scales, total numbers of vascular plant species and numbers of endangered vascular plant species were extracted from current vegetation relevés. Additionally, we obtained data on livestock diet (grazed phytomass, crude protein content). Results: Statistical analyses show an influence of the year on all variables; relationships between variables are not significant in every year. Species richness and number of endangered species are negatively related to productivity at fine scale while crude protein content and grazed phytomass are positively related to productivity. At the broad scale the diversity-productivity relationship shows a ,hump' with highest species numbers in middle pioneer stages; numbers of endangered species are highest in all pioneer stages. Conclusions: We found a strong impact of scale and year on the diversity-productivity relationship. It is inappropriate to analyse only small plots (2 m2), and it is necessary to study different years. This vegetation complex is dependent on grazing impact; thus there is an inversely proportional relationship between nature conservation value (high diversity) and livestock nutrition. [source] | ||||||||||