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  • 11
    Electronic Resource
    Electronic Resource
    The contribution of abiotic processes to buried litter decomposition in the northern Chihuahuan desert (1989)
    Springer
    Oecologia 79 (1989), S. 133-135 
    Details
    ISSN: 1432-1939
    Keywords: Decomposition ; Buried Litter ; Abiotic ; Deserts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Creosobebush (Larrea tridentata) fine litter was treated with either the general biocide HgCl2 and CuSO4 or water (controls) and buried 5 cm beneath the soil surface in the northern Chihuahuan Desert. The treated litter showed significantly less mass loss than controls during the three month summer-autumn field study; controls lost about 20% of the original mass while treated litter lost less than 2%. In addition, the total nitrogen content of the control litter increased from an initial concentration of about 14.08 g kg-1 to 17.62 g kg-1 dry weight by the end of the study, while treated litter nitrogen content decreased to 13.30 g kg-1. Results suggest abiotic processes other than leaching have little effect on the decomposition of buried litter in this environment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00378250
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  • 12
    Electronic Resource
    Electronic Resource
    Validation of a primary production model of the desert shrub Larrea tridentata using soil-moisture augmentation experiments (1981)
    Springer
    Oecologia 51 (1981), S. 357-363 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In previous papers we have described and verified a primary production model of the desert shrub Larrea tridentata. Here we address the validation phase of the evaluation of this model. Two versions of the model which differ in the priority scheme used for allocating carbon to reproductive or vegetative organs were compared on the basis of their usefulness and reliability over a range of soil-moisture conditions. Over an entire growing season when soil-moisture conditions were near “normal” both versions of the model were adequate predictors of total above-ground vegetative growth and one was an adequate predictor of reproductive growth as well. A more detailed analysis revealed that the versions varied in the range of soil-moisture conditions over which they were adequate and that neither was adequate when soil-moisture had remained high for extended periods. The validation process has revealed some likely areas for model improvement to increase adequacy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00540906
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  • 13
    Electronic Resource
    Electronic Resource
    A new contagion index to quantify spatial patterns of landscapes (1993)
    Springer
    Landscape ecology 8 (1993), S. 155-162 
    Details
    ISSN: 1572-9761
    Keywords: Contagion index ; spatial pattern ; probability ; information index ; landscape ecology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A contagion index was proposed by O'Neill et al. (1988) to quantify spatial patterns of landscapes. However, this index is insensitive to changes in spatial pattern. We present a new contagion index that corrects an error in the mathematical formulation of the original contagion index. The error is identified mathematically. The contagion indices (both original and new) are then evaluated against simulated landscapes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00125347
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  • 14
    Electronic Resource
    Electronic Resource
    Relationships between a terrain-based hydrologic model and patch-scale vegetation patterns in an arctic tundra landscape (1993)
    Springer
    Landscape ecology 8 (1993), S. 229-237 
    Details
    ISSN: 1572-9761
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Implicit in the relationship between vegetation patterns and landforms is the influence of topography on the water regime at the patch scale. Hence, based on the numerous process-based studies linking plant structure and function to water in the arctic, we hypothesize that the general pattern of arctic landscapes can be explained by a mesotopographic variable such as water drainage. In this paper, we test this hypothesis by examining the spatial relationship between patterns of vegetation and the water regime in a small watershed in northern Alaska. Using gridded elevation data, we develop a model (T-HYDRO) to generate a 2-dimensional water flow field for the watershed and compare this to vegetation patterns as given by 1) a vegetation map developed from aerial photographs in conjunction with extensive field sampling; and 2) a normalized difference vegetation index (NDVI). Our results show that it is possible to account for about 43% of the spatial variance in NDVI, which supports our hypothesis. In spite of its limitations, the correspondence of patterns presented in this paper provides encouraging evidence that we can find simple approaches to stratify landscapes and that it is possible to overcome the frequently made assumption of spatial homogeneity in ecosystems modeling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00125130
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  • 15
    Electronic Resource
    Electronic Resource
    A model of arctic tundra vegetation derived from topographic gradients (1998)
    Springer
    Landscape ecology 13 (1998), S. 187-201 
    Details
    ISSN: 1572-9761
    Keywords: vegetation pattern ; tussock tundra ; landscapes ; topography ; water drainage ; scaling up
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We present a topographically-derived vegetation model (TVM) that predicts the landscape patterns of arctic vegetation types in the foothills of the Brooks Range in northern Alaska. In the Arctic there is a strong relationship between water and plant structure and function and TVM is based on the relationships between vegetation types and slope (tan β) and discharge (δ), two independent variables that can be easily derived from digital terrain data. Both slope and discharge relate to hydrological similarity within a landscape: slope determines the gravitational hydrological gradient and hence influences flow velocity, whereas discharge patterns are computed based on upslope area and quantify lateral flow amount. TVM was developed and parameterized based on vegetation data from a small 2.2 km2 watershed and its application was tested in a larger 22km2 region. For the watershed, TVM performed quite well, having a high spatial resolution and a goodness-of-fit ranging from 71–78%, depending on the functions used. For the larger region, the strength of the vegetation types predictions drops somewhat to between 56–59%. We discuss the various sources of error and limitations of the model for purposes of extrapolation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007986410048
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  • 16
    Electronic Resource
    Electronic Resource
    Policy science: A conceptual and methodological analysis (1975)
    Springer
    Policy sciences 6 (1975), S. 1-27 
    Details
    ISSN: 1573-0891
    Source: Springer Online Journal Archives 1860-2000
    Topics: Political Science , Economics
    Notes: Abstract In the first section policy science is differentiated from policy analysis, the notion of policy is defined, and an analysis of the concept of policy science is offered which gives emphasis to what is unique in this intellectual endeavor when it is conceived as a general method of problem solving. Section II provides a discussion of the criteria of rationality for the conduct of policy science. Attention is focused upon the methodological differences between science and policy science and upon certain methodological difficulties which are peculiar to policy science. The third section gives consideration to one important relationship between facts and values in the policy science process. While it is generally well recognized that values enter into policy science in a way they do not enter into science, it is also widely held that they do not operate in such a way as to frustrate the central objective of the policy scientist (i.e., the solution or alleviation of a policy problem). It is argued that the relation between values and facts in policy science is frequently such as to have this undesired frustrative effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00186752
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  • 17
    Electronic Resource
    Electronic Resource
    Effects of elevated CO2 and nitrogen fertilization pretreatments on decomposition on tallgrass prairie leaf litter (1994)
    Springer
    Plant and soil 165 (1994), S. 115-127 
    Details
    ISSN: 1573-5036
    Keywords: Andropogon gerardii ; carbon chemistry ; carbon dioxide ; litter quality ; Poa pratensis ; Sorghastrum nutans
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Standing dead and green foliage litter was collected in early November 1990 from Andropogon gerardii (C4), Sorghastrum nutans (C4), and Poa pratensis (C3) plants that were grown in large open-top chambers under ambient or twice ambient CO2 and with or without nitrogen fertilization (45 kg N ha−1). The litter was placed in mesh bags on the soil surface of pristine prairie adjacent to the growth treatment plots and allowed to decay under natural conditions. Litter bags were retrieved at fixed intervals and litter was analyzed for mass loss, carbon chemistry, and total Kjeldahl nitrogen and phosphorus. The results indicate that growth treatments had a relatively minor effect on the initial chemical composition of the litter and its subsequent rate of decay or chemical composition. This suggests that a large indirect effect of CO2 on surface litter decomposition in the tallgrass prairie would not occur by way of changes in chemistry of leaf litter. However, there was a large difference in characteristics of leaf litter decomposition among the species. Poa leaf litter had a different initial chemistry and decayed more rapidly than C4 grasses. We conclude that an indirect effect of CO2 on decomposition and nutrient cycling could occur if CO2 induces changes in the relative aboveground biomass of the prairie species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00009968
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  • 18
    Electronic Resource
    Electronic Resource
    Modelling whole-plant allocation in relation to carbon and nitrogen supply: Coordination versus optimization: Opinion (1996)
    Springer
    Plant and soil 185 (1996), S. 65-74 
    Details
    ISSN: 1573-5036
    Keywords: balanced activity ; optimal control theory ; plant growth ; root-shoot ratio
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract One of the few integrating theories related to allocation is the hypothesis of optimization. While optimization theory has great heuristic appeal and has been used to describe a range of physiological and ecological phenomena, it has major limitations. Optimization is necessarily based on a definite time integral and an optimal control strategy must be specific to the same patterns exhibited by the driving variables over this same period of time. Optimization tends to employ the use of oversimplifications in order to facilitate analytical solutions to the optimal control strategy, i.e. the mechanism governing the response of plants, which is the critical issue of interest. It is difficult to define objective criteria that can account for the natural variability in plants and testing the quantitative predictions of optimality models is also difficult. Thus, we suggest that optimization theory is too limited for practical use in modelling whole plant allocation. In this paper, we introduce the use of coordination theory as a practical alternative. We develop a simple plant growth allocation model using both coordination and optimization approaches and show that coordination theory is easily applied, produces results that are quantitatively similar to optimization, and overcomes the inherent limitations of optimization theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02257565
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  • 19
    Electronic Resource
    Electronic Resource
    Changes in root NH 4 + and NO 3 − absorption rates of loblolly and ponderosa pine in response to CO2 enrichment (1997)
    Springer
    Plant and soil 190 (1997), S. 1-9 
    Details
    ISSN: 1573-5036
    Keywords: elevated CO2 ; loblolly pine ; ponderosa pine ; root nitrogen uptake rate ; root respiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Root growth and physiological uptake capacity for NH 4 + and NO 3 − were examined for seedlings of loblolly and ponderosa pine grown for 160 days under two CO2 levels, ambient (35 Pa) and ambient plus 35 Pa (70 Pa). Fraction of biomass allocated to active fine roots as well as total N (NH 4 + + NO 3 − ) absorption per unit root dry mass were unaffected by CO2. On a whole-plant basis, elevated CO2 led to a significant increase in N acquisition in loblolly but not in ponderosa pine. However, even in loblolly pine where CO2 significantly increased plant N acquisition, the relative increase, in biomass far exceeded the gain in N, i.e. a 60% increase in total dry weight was accompanied by only a 30% increase in N gain in response to high CO2. We suggest that the commonly reported decline in tissue N concentration of these and other species at high CO2 is largely caused by inability of the root systems to sufficiently compensate for increased N demand. Elevated CO2 significantly altered root uptake capacity of the different N forms, i.e., high CO2 significantly increased NO 3 − absorption rates, but decreased NH 4 + absorption rates in both species though the decrease in loblolly was insignificant. However, elevated CO2 increased root respiration rate in loblolly pine while significantly decreasing it in ponderosa pine. This indicates that CO2-induced changes in plant preference for inorganic N forms is not simply regulated by root energy status. If changes in plant preference for inorganic N forms represent typical responses to elevated CO2, the results could have important implications for N dynamics in managed and natural plant communities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004206624311
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  • 20
    Electronic Resource
    Electronic Resource
    Soil aeration in relation to soil physical properties, nitrogen availability, and root characteristics within an arctic watershed (1996)
    Springer
    Plant and soil 178 (1996), S. 37-48 
    Details
    ISSN: 1573-5036
    Keywords: anaerobic ; N availability ; permafrost ; tundra ; tussock
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The seasonal change in soil oxygen availability was determined in several habitats along a topographic moisture gradient in an arctic watershed. The effect of changes in soil aeration on soil chemical and plant properties was examined by comparison of the driest (tussocks) and wettest (wet sedge tundra) sites along this gradient. Spatial variability and seasonal change in soil oxygen availability was closely linked to the hydrologic regime and the thickness of the organic soil horizon. The greatest extension of the aerobic soil layer was found beneath well-drained tussocks, while less than 10% of the unfrozen soil layer is aerated in flooded wet sedge tundra. Intertussock areas and watertracks (channels of water drainage) have intermediate levels of aeration. In tussock tundra, soil oxygen diffusion is restricted in the mineral soil layer below the organic horizon due to reduced pore space. Organic matter constituents and their change with depth were similar beneath tussocks and in wet sedge tundra, indicating that factors other than soil aeration (e.g. low soil temperatures, short growing season) are the primary controls on decomposition in these two arctic tundra systems. NH4 +, the dominant form of inorganic N, was more available in wet sedge tundra than in tussock tundra. At both sites, extractable and soil solution NO3 - concentrations increased 4 to 8 fold in the second part of the growing season, indicating increased nitrifier activity with improved soil oxygen availability. Although soils thawed as deep as 60 cm, approx. 90% of the root biomass was concentrated within 20 cm of the surface. Despite the anaerobic soil environment in wet sedge tundra, the dominant species there, Eriophorum angustifolium, reached slightly greater rooting depths than E. vaginatum, whose roots grow in the elevated, aerobic portion of tussocks. E. angustifolium had a root porosity of 31%, within the range found for wetland species, while roots of E. vaginatum had a porosity close to 12%. Rhizome porosity were low in both species (11%).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00011161
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