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Paul C. Stoy Mathew Williams Mathias Disney Ana Prieto-Blanco Brian Huntley Robert Baxter Philip Lewis 《Landscape Ecology》2009,24(7):971-986
Transferring ecological information across scale often involves spatial aggregation, which alters information content and
may bias estimates if the scaling process is nonlinear. Here, a potential solution, the preservation of the information content
of fine-scale measurements, is highlighted using modeled net ecosystem exchange (NEE) of an Arctic tundra landscape as an
example. The variance of aggregated normalized difference vegetation index (NDVI), measured from an airborne platform, decreased
linearly with log(scale), resulting in a linear relationship between log(scale) and the scale-wise modeled NEE estimate. Preserving
three units of information, the mean, variance and skewness of fine-scale NDVI observations, resulted in upscaled NEE estimates
that deviated less than 4% from the fine-scale estimate. Preserving only the mean and variance resulted in nearly 23% NEE
bias, and preserving only the mean resulted in larger error and a change in sign from CO2 sink to source. Compressing NDVI maps by 70–75% using wavelet thresholding with the Haar and Coiflet basis functions resulted
in 13% NEE bias across the study domain. Applying unique scale-dependent transfer functions between NDVI and leaf area index
(LAI) decreased, but did not remove, bias in modeled flux in a smaller expanse using handheld NDVI observations. Quantifying
the parameters of statistical distributions to preserve ecological information reduces bias when upscaling and makes possible
spatial data assimilation to further reduce errors in estimates of ecological processes across scale. 相似文献
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A.K. Guber T.J. Gish Y.A. Pachepsky M.T. van Genuchten C.S.T. Daughtry T.J. Nicholson R.E. Cady 《CATENA》2008
When a field or a small watershed is repeatedly surveyed for soil water content, locations can often be identified where soil water contents are either consistently larger or consistently less than the study area average. This phenomenon has been called temporal stability, time stability, temporal persistence, or rank stability in spatial patterns of soil water contents. Temporal stability is of considerable interest in terms of facilitating upscaling of observed soil water contents to obtain average values across the observation area, improving soil water monitoring strategies, and correcting the monitoring results for missing data. The objective of this work was to contribute to the existing knowledge base on temporal stability in soil water patterns using frequent multi-depth measurements with Multisensor Capacitance Probes (MCPs) installed in a coarse-texture soil under multi-year corn production. Water contents at 10, 30, 50, and 80 cm depths were measured every 10 min for 20 months of continuous observation from May 2001 to December 2002. The MCPs revealed temporal stability in soil water content patterns. Temporal stability was found to increase with depth. The statistical hypothesis could not be rejected (P < 0.0001) that data collected each 10 min, each 2 h, each day, and each week had the same temporal stability. The locations that were best for estimating the average water contents were different for different depths. The best three locations for the whole observation period were the same as the best locations for a month of observations in about 60% of the cases. Temporal stability for a specific location and depth could serve as a good predictor of the utility of this location for estimating the area-average soil water content for that depth. Temporal stability could be efficiently used to correct area-average water contents for missing data. Soil water contents can be upscaled and efficiently monitored using the temporal stability of soil water content patterns. 相似文献
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Nitric oxide (NO) plays a central role in the formation of tropospheric ozone, hydroxyl radicals, as well as nitrous and nitric acids. There are, however, large uncertainties around estimates of global NO emissions due to the paucity of data. In particular, there is little information on the rate of NO emission and its sensitivity to processes such as land use changes in dry environments. Here we report on a two-year study on the influence of afforestation on soil NO fluxes in the semi-arid afforestation system in Southern Israel (Yatir forest, mean annual precipitation ∼280 mm). Laboratory incubations were carried out under seasonally defined conditions of soil moisture and temperature using soils sampled in different seasons from the native shrubland (taken both under shrub canopy and in the inter-shrub areas), and from the adjacent ∼2800 ha, 40-year-old pine afforestation site. Combining laboratory results with field measurements of soil moisture and temperature, we up-scaled soil-atmosphere NO fluxes to the ecosystem level. The different microsites differed in their annual mean NO release rates (0.04, 0.14 and 0.03 mg m−2 d−1 for the shrubland under and between shrubs and for the forest, respectively), and exhibited high inter-seasonal variability in NO emission rates (ranging from zero up to 0.25 mg m−2 d−1 in the wet and dry-rewetting seasons, respectively), as well as in temperature responses. Up-scaling results to annual and ecosystem scales indicated that afforestation of the semi-arid shrubland could reduce soil NO emission by up to 65%. 相似文献
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Regional simulation of maize production in tropical savanna fallow systems as affected by fallow availability 总被引：1，自引：0，他引：1
Upscaling of crop models from the field scale to the national or global scale is being used as a widespread method to make large-scale assessments of global change impacts on crop yields and agricultural production. In spite of the fact that soil fertility restoration and crop performance in many developing countries with low-input agriculture rely strongly on fallow duration and management, there are only few approaches which take into account the effect of fallowing on crop yields at the regional scale. The objectives of this study were to evaluate the sensitivity of maize yield simulations with the Environmental Policy Integrated Climate (EPIC) model to fallow availability at the field and regional scale and (2) to present a novel approach to derive a model-based estimate of the average fallow availability within a typical catchment of the sub-humid savanna zone of West Africa. Therefore, the EPIC model has been validated at the field scale and then incorporated into a spatial database covering a typical catchment within the sub-humid savanna zone of West Africa with 121 sub-basins. Maize-fallow rotations have been simulated within 2556 quasi-homogenous spatial units and then aggregated to the 10 districts within the catchment assuming three different scenarios of fallow availability: 100% of the bush-grass savanna area is available and used in fallow-crop rotations (FU100), 50% of the bush-grass savanna area is available and used in fallow-crop rotations (FU50) and 25% of the bush-grass savanna area is available and used in fallow-crop rotations (FU25). A new aggregation procedure has been developed which is based on changes in the frequency of fallow-cropland classes within the sub-basins to render the simulation results in the spatial database sensitive to changes in fallow availability. Comparison of the average simulated grain yield with the mean yield over the catchment shows that the simulations overestimate maize yields by 62%, 44% and 15% for scenario FU100, FU50 and FU25, respectively. The best agreement between simulated and observed crop yields at the district scale was found when using the assumption that 25% of the savanna is available as fallow land under the present cropping patterns, which corresponds to a fallow-cropland ratio of 0.9. Comparison with farm surveys shows that the combination of remote sensing and dynamic crop modelling with yield observations provides realistic estimates of effective fallow use at the regional scale. 相似文献
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《Arid Land Research and Management》2013,27(4):455-467
Monitoring vast landscapes has, from the beginning of rangeland management, depended on people's judgements. This is no longer tenable, but a more effective method has yet to be devised. The problem is how to do an economical inventory that will detect ecologically important change over extensive land areas with acceptable error rates. The error risk is a function of adequate sample numbers and distribution for each indicator monitored. Of all of the indicators identified for monitoring, ground cover and its inverse, bare ground, may be the most discussed. Ground-cover measurements address soil stability and watershed function which are first-priority ecological concerns; are well adapted to remote sensing frameworks thus allowing extensive, unbiased, economical sampling; and, the measurements, especially when done by computer image analysis, have the potential to reduce or avoid the human-judgement factor. Data collection through remote sensing appears the most logical approach to acquiring appropriately distributed information over large areas in short time periods and on random sites far removed from easy ground access. The value of satellite and high-altitude sensors for landscape-level evaluations, such as plant community distribution, is well established but these tools are inadequate for inventory and measurement of details needed for valid conclusions about range condition. New advances in low-altitude remote sensing may give us the ability to accurately measure bare ground and perhaps other indicators. Combining information from high and low-altitude sensors appears to offer an optimal path for developing a practical system for cost-effective, data-based, rangeland monitoring and management. 相似文献
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YU Pengtao XU Deying WANG YanhuiResearch Institute of Forest Ecology. Environment Protection. Chinese Academy of Forestry Beijing. China 《中国林业科技(英文版)》2002,(3)
The canopy rainfall interception modei linked to environmental conditions and biological features is established on the basis of stationary observation and measurements in China. Upscaling from site observation to regional Ievel estimation of canopy rainfall interception has been made. The potential interception value of forests during the rainfall season in China according to rainfall records of May, July and September in the year 1982, has been simulated and mapped under the GIS software package Idrisi. It coincides well with the spatial and chronological pattern of rainfall in China and can be concluded to reflect the reality. The potential canopy rainfall interception of forests in China based on the potential distribution of forests provides a basis to regional water budget as well as rational use of regional water resources. It is also important to the assessment of forest ecosystem service in China, which is demanded by both scientists and policy makers for the evaluation of afforestation and nat 相似文献
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Carbon concentrations and stocks in forest soils of Europe 总被引：1，自引：0，他引：1
This study presents the results of a series of evaluations of a continent-wide soil database (EU/UN-ECE Level I) with the aim to estimate baseline soil carbon concentrations and stocks. The methodology included the biogeographic stratification of soil carbon measurements throughout Europe using climatic zones derived from the Soil Regions Map of Europe. The presented stock estimates range from 1.3 to 70.8 t C/ha for the O-layer, and from 11.3 to 126.3 t C/ha for the mineral soil 0–20 cm (Germany: 0–30 cm) (5 and 95 percentiles). Histosols were excluded because of methodological differences and data gaps. When looking at the median values of the strata investigated, relationships were found. For example, carbon stocks in the O-layer of sandy soils are distinctly higher than those of fine-textured soils. However, the variability is so high that some of these relationships disappear. For example in western and central Europe, the level of carbon stocks in the mineral soil between shallow soils (Leptosols) and more deeply developed soils (Podzols and Cambisols) do not differ very much. It was also found that just the investigation of topsoils is not sufficient to understand the regional pattern of organic matter in forest soils – unless the subsoil becomes included as well. It is hypothesized that for Europe, the impact of site factors such as climate, texture and relief are difficult to extract from such a database if the data are only stratified according to macro-climatic areas. It has to be considered that the effect of systematic error in the database is quite large (but cannot be identified on the level of the current data availability). In order to receive a first impression of the landscape-level distribution of carbon, a map of carbon concentrations in the topsoil was generated. The results support the relationships found between carbon stocks and site factors, such as climatic zones and soil type. Compared to the much lower carbon concentrations of agricultural soils, the results demonstrate clearly the importance of forest soils for the terrestrial carbon cycling in Europe. 相似文献
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An upscaling approach was developed for simulating soil water flow in horizontal heterogeneous unsaturated zone at field scale under flood irrigation. Based on the assumption of stream tube model and the van Genuchten-Mualem soil hydraulic function with five parameters Ks, α, n, θr and θs, the Richards equation was transformed into a dimensionless form by using the dimensionless forms of temporal and spatial variables, and pressure head. Although a strong dependency of parameters Ks and α on scale does not exist in the transformed Richards equation, the parameter n, which is slightly dependent on scale, still exists in the transformed equation, and the parameter α is introduced in the transformed initial and boundary conditions. Therefore, a power law averaging technique was also included in our upscaling approach. Compared with traditional numerical methods, the distribution of pressure head of each soil column, and the mean and variance of soil water dynamics in all the soil columns can be obtained by numerically solving the transformed Richards equation only one time and by returning to the dimensionless variable expressions, while the traditional Richards equation must be solved once for every soil column. The new approach was calibrated by two numerical experiments, and the soil water content as a function of time and depth was reasonably well simulated for the two experiments which involved different soil textures. Different combinations of α and n were applied for comparing the accuracy of numerical simulations: n had little effect on the simulated results whereas α had some significant effect on the simulated results. To further verify the numerical efficiency of the new approach, we adopted the effective α values corresponding to the exponent p of the power law averaging technique [Eq. (16)] when p approaches 0, p = ± 1 and ± 0.5 to conduct more numerical experiments. It showed that with an initial pressure head profile of equilibrium for Example 1, and with an initial pressure head profile of constant for Example 2, the simulated results of the wetting front at the specific depths were in agreement with that of traditional numerical method, and the errors in simulated pressure heads were small. In summary, the proposed approach can be useful for upscaling unsaturated water flow characteristics in horizontally heterogeneous soils. 相似文献
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