Site classification in the biogeoclimatic ecosystem classification system is based on three differentiating properties: climatic regimes (expressed by biogeoclimatic subzones or variants), soil moisture regimes (SMRs), and soil nutrient regimes (SNRs). A SNR represents a segment of a regional soil nutrient gradient, i.e., soils which provide similar levels of plant-available nutrients over a long period. SNRs are identified in the field using a number of easily observable soil morphological properties and indicator plant species. However, we need to know to what extent soil nutrient properties support these indirect field-estimates. There have been several studies that quantitatively characterize regional soil nutrient gradients in different climatic regions, but no study has yet been done in the subalpine coastal forest (Mountain Hemlock zone). Influenced by a maritime subalpine boreal climate, high-elevation coastal soils differ from low-elevation soils by having a thicker forest floor and a higher organic matter content. In the study summarized here, relationships between soil chemical properties and field-estimated SNRs are examined and soil chemical properties and field-identified SNRs are related to the site index of Pacific silver fir (Abies amabilis (Dougl. ex Loud.) Forbes) - one of the major timber crop species in the Coastal Western Hemlock and Mountain Hemlock zones.

Effect of soil moisture potential (?), temperature (T), genotype, seeding depth (SD) and rate (SR) on seedling emergence (SE), emergence velocity (EV), root yield and grades of cut and peel carrots were studied. SE was reduced at –120 kPa and totally inhibited at -156 kPa. EV was the lowest at – 5 kPa and – 90 kPa. SE was delayed by 33 d at 5°C, reduced at 30°C and totally inhibited at 35 and 40 °C. Heat units 99.75 and 159.60°Cd were the lowest to initiate and complete SE respectively while the optimum was 300 – 350 °Cd. There was no interaction effect between ? and T on SE. Honey snax at 85 seeds/ 30 cm showed the best SE whereas, Triton recorded the highest total yield at 2.54 cm SD and Fancy yield at 85 seeds/ 30 cm implying certain crop ecological and management factors can influence SE, root yield and quality.

No description available.

Irrigation in 1980 accounted for approximately 52 per cent of the water consumed in Southern Africa. The need for planning water resources in the agricultural sector is therefore apparent. Much of Southern Africa's arable farming is carried out on land which, in terms of soil moisture availability to crops, can be described as marginal. Information on soil moisture is therefore valuable to the agriculturalist for planning irrigation schemes and for dryland farming. The objectives of this study were to provide the information mentioned above. This was achieved by producing a detailed delimitation of 712 zones throughout Southern Africa, of more or less homogeneous climate and by providing estimates of crop water requirements under dryland and irrigated conditions in each zone. At the same time the bulk of information which is normally forthcoming from such an analysis involving a large number of combinations of possible input, i.e. crops, soils and planting dates, was reduced, whilst the essential information content was retained. The study provided inter alia an estimate of the frequency of non-exceedance of certain levels of irrigation requirement, based on analyses of soil moisture budgets using long daily rainfall records. The soil moisture budgeting models which were used to estimate the above information were verified inter alia using field measurements of soil moisture. The irrigation analysis was designed such that the results should not became redundant when the inevitable improvement occurs in the estimation of crop factors or soil moisture variables nor if the farming practices change with respect to planting dates. A dryland soil moisture budget analysis for a range of crops and soils was performed in addition to the abovementioned irrigation analysis. The need for this latter study stemmed from the belief that irrigation should not be considered in isolation but rather as one of a range of options, many of them involving dryland farming, facing the agriculturalist. In addition to the dissertation, this study produced a map of Southern Africa on which the 712 homogeneous climate zones are depicted. For each of these zones four pages of computer printout were produced. These pages contain the results of the crop water requirements study for irrigated conditions and the crop water requirement deficit, runoff and an index of stress days for a range of crops, soils and planting dates, under dryland conditions. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1988.

There is no abstract available for this dissertation. / Department of Natural Resources and Environmental Management

A thermo-elastic-plastic model for unsaturated soils has been presented based on the effective stress principle considering the thermo-mechanical and suction coupling effects. The thermo-elastic-plastic constitutive equations for stress-strain relations of the solid skeleton and changes in fluid content and entropy for unsaturated soils have been established. A plasticity model is derived from energy considerations. The model derived covers both associative and non-associative flow behaviours and the modified Cam-Clay is considered as a special case. All model coefficients are identified in terms of measurable parameters. To verify the proposed model, an experimental program has been developed. A series of controlled laboratory tests were carried out on a compacted silt sample using a triaxial equipment modified for testing unsaturated soils at elevated temperatures. Imageprocessing technique was used for measuring the volume change of the samples subjected to mechanical, thermal and hydric loading. It is shown that the effective critical state parameters M, ???? and ???? are independent of temperature and matric suction. Nevertheless, the shape of loading collapse (LC) curve was affected by temperature and suction. Furthermore, the temperature change affected the soil water characteristic curve and an increase in temperature caused a decrease in the air entry suction. The simulations from the proposed model are compared with the experimental results. The model calibration was performed to extract the model parameters from the experimental results. Good agreement between the results predicted using the proposed model and the experimental results was obtained in all cases.

Research Doctorate - Doctor of Philosophy (PhD) / Amidst growing concerns about global warming, efforts to reduce atmospheric CO2 concentrations (i.e. C sequestration) have received widespread attention. One approach to C sequestration is to increase the amount of C stored in terrestrial ecosystems, through improved land management. Terrestrial ecosystems represent a critical element of the C interchange system, however a lack of understanding of the C cycle at regional and sub-regional scales means that they represent a source of primary uncertainty in the overall C budget. This thesis aims to address this deficiency by developing an understanding of catchment-scale processes critical for accurate quantification of C in the landscape. An investigation into the spatial and temporal dynamics of soil organic carbon (SOC) was conducted for a 150ha temperate grassland catchment in the Upper Hunter Valley, New South Wales, Australia. The major factors controlling the movement, storage, and loss of SOC were investigated, including climate, vegetation cover, soil redistribution processes, topography, land use, and soil type. This study falls into four broad areas. In the first part of this study the spatio-temporal dynamics of soil moisture and temperature at the catchment scale are assessed for a range of soil depths. Data recorded from a network of monitoring sites located throughout the study catchment was compared with independently derived soil moisture and temperature data sets. The data indicates that soil moisture and temperature in surface soil layers were highly dynamic, in their response to rainfall and incoming solar radiation, respectively. Deeper soil layers however were less dynamic, with longer lag times observed with increasing soil depth, as topography, soil type, and landscape position were the dominant controlling factors. Climate related variables are important factors affecting plant growth and net primary productivity. The second part of the study quantified spatial and temporal vegetation patterns using both field-based measurements of above-ground biomass and remotely sensed vegetation indices from the MODIS and Landsat TM 5 platforms. A strong and statistically significant relationship was found between climate variables and MODIS derived NDVI, leading to the development of a predictive vegetation cover model using ground-based soil moisture, soil temperature, and sunshine hours data. The ability of remotely sensed data to capture vegetation spatial patterns was found to be limited, while it was found to be a good predictor of temporal above-ground biomass trends, enabling net primary productivity to be quantified over the three-year study period. In the third part of the thesis soil redistribution patterns and erosion rates were quantified using the caesium-137 method and empirical and physically-based modelling approaches. The impact of soil redistribution processes on SOC distribution was investigated, and the amount of erosion derived SOC loss quantified. A significant proportion of SOC stored within the catchment was found below a soil depth of 0.30m, which is the depth of sampling set out in the IPCC and Australian Greenhouse Office guidelines for carbon accounting. Soil depth was identified as a key factor controlling the spatial distribution of SOC, which is in turn determined by position in the landscape (i.e. topography). The fourth and final part of the study describes how data on erosion derived SOC loss were used in conjunction with net primary productivity estimates, to establish a SOC balance. This involved mapping the spatial distribution of SOC using a high resolution digital elevation model of the catchment, in conjunction with soil depth measurements, and quantifying the total SOC store of the catchment. It was observed that temporal changes in SOC were minimal over the limited three-year study period, however, the continuity of catchment management practices over the previous decades suggest that steady-state conditions have perhaps been reached. The study concludes that the key to increasing the amount of SOC and enhancing carbon sequestration in the soil, is to increase the amount of SOC stored at depth within the soil profile, where factors such as soil moisture and temperature, which control decomposition rates, are less dynamic in space and time, and where SOC concentrations will be less vulnerable to changes occurring at the surface in response to global warming and climate change.

Made available in DSpace on 2016-06-02T19:32:14Z (GMT). No. of bitstreams: 1 6709.pdf: 4195083 bytes, checksum: 80992e3623fd375eb0fcff062a4c0f5d (MD5) Previous issue date: 2015-02-05 / Financiadora de Estudos e Projetos / Biological invasion is a threat to biodiversity, due to competition for resources between invaders and native organisms, decreasing the overall biodiversity. So, studies about the invasiveness of the ecossystems and invasion potential of exotic plants several environments must be taken to control this species. Hedychium coronarium, from the Himalayas, is an example of a high invasivisiness plant, taken to different places in the world, mainly due to ornamental uses. This study evaluated the development (height, diameter, birth and ramets mortality and internal rhyzome anatomy) of plants under different moisture contents, in in situ and in vitro experiments. We found the existence of plasticity for both vegetative ramets growth, and the internal rhyzome anatomy, which may contribute to the invasive potential of this plant. / A invasão biológica é uma ameaça à biodiversidade, já que ocorre competição por recursos entre organismos invasores e nativos, diminuindo a biodiversidade global. Assim, estudos sobre a invasão dos ecossistemas e potencial invasão de plantas exóticas em ambientes diversos devem ser realizados para que haja controle das espécies. Hedychium coronarium, proveniente do Himalaia, é um exemplo de planta com alta invasivisidade, levada a diferentes lugares do mundo, sobretudo devido ao potencial ornamental que fornece. O presente estudo avaliou o desenvolvimento (altura, diâmetro, nascimento, mortalidade dos rametas e anatomia interna do rizoma) da planta em ambientes com diferentes umidades, com experimentos in situ e in vitro. Foi encontrado indício de plasticidade, tanto em crescimento vegetativo dos rametas, quanto na anatomia interna dos rizomas, o que pode contribuir para a invasivisidade dessa planta.

abstract: Ponderosa pine forests are a dominant land cover type in semiarid montane areas. Water supplies in major rivers of the southwestern United States depend on ponderosa pine forests since these ecosystems: (1) receive a significant amount of rainfall and snowfall, (2) intercept precipitation and transpire water, and (3) indirectly influence runoff by impacting the infiltration rate. However, the hydrologic patterns in these ecosystems with strong seasonality are poorly understood. In this study, we used a distributed hydrologic model evaluated against field observations to improve our understandings on spatial controls of hydrologic patterns, appropriate model resolution to simulate ponderosa pine ecosystems and hydrologic responses in the context of contrasting winter to summer transitions. Our modeling effort is focused on the hydrologic responses during the North American Monsoon (NAM), winter and spring periods. In Chapter 2, we utilized a distributed model explore the spatial controls on simulated soil moisture and temporal evolution of these spatial controls as a function of seasonal wetness. Our findings indicate that vegetation and topographic curvature are spatial controls. Vegetation controlled patterns during dry summer period switch to fine-scale terrain curvature controlled patterns during persistently wet NAM period. Thus, a climatic threshold involving rainfall and weather conditions during the NAM is identified when high rainfall amount (such as 146 mm rain in August, 1997) activates lateral flux of soil moisture and frequent cloudy cover (such as 42% cloud cover during daytime of August, 1997) lowers evapotranspiration. In Chapter 3, we investigate the impacts of model coarsening on simulated soil moisture patterns during the NAM. Results indicate that model aggregation quickly eradicates curvature features and its spatial control on hydrologic patterns. A threshold resolution of ~10% of the original terrain is identified through analyses of homogeneity indices, correlation coefficients and spatial errors beyond which the fidelity of simulated soil moisture is no longer reliable. Based on spatial error analyses, we detected that the concave areas (~28% of hillslope) are very sensitive to model coarsening and root mean square error (RMSE) is higher than residual soil moisture content (~0.07 m3/m3 soil moisture) for concave areas. Thus, concave areas need to be sampled for capturing appropriate hillslope response for this hillslope. In Chapter 4, we investigate the impacts of contrasting winter to summer transitions on hillslope hydrologic responses. We use a distributed hydrologic model to generate a consistent set of high-resolution hydrologic estimates. Our model is evaluated against the snow depth, soil moisture and runoff observations over two water years yielding reliable spatial distributions during the winter to summer transitions. We find that a wet winter followed by a dry summer promotes evapotranspiration losses (spatial averaged ~193 mm spring ET and ~ 600 mm summer ET) that dry the soil and disconnect lateral fluxes in the forested hillslope, leading to soil moisture patterns resembling vegetation patches. Conversely, a dry winter prior to a wet summer results in soil moisture increases due to high rainfall and low ET during the spring (spatially averaged 78 mm ET and 232 mm rainfall) and summer period (spatially averaged 147 mm ET and 247 mm rainfall) which promote lateral connectivity and soil moisture patterns with the signature of terrain curvature. An opposing temporal switch between infiltration and saturation excess runoff is also identified. These contrasting responses indicate that the inverse relation has significant consequences on hillslope water availability and its spatial distribution with implications on other ecohydrological processes including vegetation phenology, groundwater recharge and geomorphic development. Results from this work have implications on the design of hillslope experiments, the resolution of hillslope scale models, and the prediction of hydrologic conditions in ponderosa pine ecosystems. In addition, our findings can be used to select future hillslope sites for detailed ecohydrological investigations. Further, the proposed methodology can be useful for predicting responses to climate and land cover changes that are anticipated for the southwestern United States. / Dissertation/Thesis / Ph.D. Geological Sciences 2012

Pour améliorer la prévision des crues dans les bassins versants torrentiels, les hydrologues doivent connaître les conditions initiales de l'état hydrique des sols précédant les événements pluvieux. La cartographie de l'humidité des sols, dont les variations sont principalement influencées par la topographie, la couverture végétale et l'hétérogénéité des propriétés des sols, constitue alors un outil précieux pour étudier les processus de formation des écoulements. Ce travail aborde la problématique de la spatialisation des variations spatio-temporelles de l'état hydrique des sols en utilisant la modélisation géostatistique et hydrologique appliquées au bassin versant expérimental marneux du Laval (0.86 km², ORE Draix-Bléone, France). Le suivi in situ des épisodes pluvieux de mai 2015 à novembre 2016 a permis de mettre en évidence une relation significative entre la teneur en eau des sols, la topographie et l'occupation de surface dans les badlands. Il a également permis de mieux appréhender la dynamique spatio-temporelle des variations de teneur en eau des versants à l'échelle saisonnière et événementielle, et de confirmer la majeure contribution aux écoulements de crue des horizons superficiels dénudés. Enfin, la modélisation hydrologique associée au traçage chimique et isotopique des eaux du bassin a apporté une amélioration de la compréhension de l'organisation spatiale de la réponse hydrologique du bassin à l'échelle événementielle. / Hydrologists need to know soil moisture antecedent conditions before rainfall events to improve floodforecasting in torrential catchments. Soil moisture mapping, whose variations are mainly influenced bytopography, vegetation cover, and heterogeneity of soil properties, is therefore a valuable tool to studyhydrological processes. This work adresses the issue of the spatio-temporal variations of soil water statusspatialization using geostatistical and hydrological modeling applied to the Laval marly experimental catchment(0.86 km², ORE Draix-Bléone, France). In situ monitoring of rainfall events from May 2015 to November 2016revealed a significant relationship between soil water content, topography and land cover in the badlands. Italso led to better assess soil water content spatio-temporal dynamics at the hillslope scale and the seasonaland event time scales. It confirmed the major contribution of bare areas to stream flows. Eventually, thehydrological modeling associated to the chemical and isotopic water tracing made it possible to better understand the spatial organization of the catchment hydrological response at the event scale.