Bringing together leaf trait data spanning 2,548 species and 175 sites we describe, for the first time at global scale, a universal spectrum of leaf economics consisting of key chemical, structural and physiological properties. The spectrum runs from quick to slow return on investments of nutrients and dry mass in leaves, and operates largely independently of growth form, plant functional type or biome. Categories along the spectrum would, in general, describe leaf economic variation at the global scale better than plant functional types, because functional types overlap substantially in their leaf traits. Overall, modulation of leaf traits and trait relationships by climate is surprisingly modest, although some striking and significant patterns can be seen. Reliable quantification of the leaf economics spectrum and its interaction with climate will prove valuable for modelling nutrient fluxes and vegetation boundaries under changing land-use and climate.

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The worldwide leaf economics spectrum

The topography of a catchment has a major impact on the hydrological, geomorphological. and biological processes active in the landscape. The spatial distribution of topographic attributes can often be used as an indirect measure of the spatial variability of these processes and allows them to be mapped using relatively simple techniques. Many geographic information systems are being developed that store topographic information as the primary data for analysing water resource and biological problems. Furthermore, topography can be used to develop more physically realistic structures for hydrologic and water quality models that directly account for the impact of topography on the hydrology. Digital elevation models are the primary data used in the analysis of catchment topography. We describe elevation data sources, digital elevation model structures, and the analysis of digital elevation data for hydrological, geomorphological, and biological applications. Some hydrologic models that make use of digital representations of topography are also considered.

Digital terrain modelling: A review of hydrological, geomorphological, and biological applications

The soil-water characteristic curve can be used to estimate various parameters used to describe unsaturated soil behaviour. A general equation for the soil-water characteristic curve is proposed. A nonlinear, least-squares computer program is used to determine the best-fit parameters for experimental data presented in the literature. The equation is based on the assumption that the shape of the soil-water characteristic curve is dependent upon the pore-size distribution of the soil (i.e., the desaturation is a function of the pore-size distribution). The equation has the form of an integrated frequency distribution curve. The equation provides a good fit for sand, silt, and clay soils over the entire suction range from 0 to 106 kPa. Key words : soil-water characteristic curve, pore-size distribution, nonlinear curve fitting, soil suction, water content.

Equations for the soil-water characteristic curve

This paper presents a modeling approach aimed at seasonal resolution of global climatic and edaphic controls on patterns of terrestrial ecosystem production and soil microbial respiration. We use satellite imagery (Advanced Very High Resolution Radiometer and International Satellite Cloud Climatology Project solar radiation), along with historical climate (monthly temperature and precipitation) and soil attributes (texture, C and N contents) from global (1°) data sets as model inputs. The Carnegie-Ames-Stanford approach (CASA) Biosphere model runs on a monthly time interval to simulate seasonal patterns in net plant carbon fixation, biomass and nutrient allocation, litterfall, soil nitrogen mineralization, and microbial CO2 production. The model estimate of global terrestrial net primary production is 48 Pg C yr−1 with a maximum light use efficiency of 0.39 g C MJ−1PAR. Over 70% of terrestrial net production takes place between 30°N and 30°S latitude. Steady state pools of standing litter represent global storage of around 174 Pg C (94 and 80 Pg C in nonwoody and woody pools, respectively), whereas the pool of soil C in the top 0.3 m that is turning over on decadal time scales comprises 300 Pg C. Seasonal variations in atmospheric CO2 concentrations from three stations in the Geophysical Monitoring for Climate Change Flask Sampling Network correlate significantly with estimated net ecosystem production values averaged over 50°–80° N, 10°–30° N, and 0°–10° N.

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Terrestrial ecosystem production: A process model based on global satellite and surface data

The soil moisture characteristic may be modeled as a power curve combined with a short parabolic section near saturation to represent gradual air entry. This two-part function—together with a power function relating soil moisture and hydraulic conductivity—is used to derive a formula for the wetting front suction required by the Green-Ampt equation. Representative parameters for the moisture characteristic, the wetting front suction, and the sorptivity, a parameter in the infiltration equation derived by Philip (1957), are computed by using the desorption data of Holtan et al. (1968). Average values of the parameters, and associated standard deviations, are calculated for 11 soil textural classes. The results of this study indicate that the exponent of the moisture characteristic power curve can be predicted reasonably well from soil texture and that gradual air entry may have a considerable effect on a soil's wetting front suction.

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Empirical equations for some soil hydraulic properties

1. Introduction 2. Temperature 3. Water Vapor and Other Gases 4. Liquid Water in Organisms and their Environment 5. Wind 6. Heat and Mass Transport 7. Conductances for Heat and Mass Transport 8. Heat Flow in the Soil 9. Water Flow in Soil 10. Radiation Basics 11. Radiation Fluxes in Natural Environments 12. Animals and Their Environment 13. Humans and Their Environment 14. Plants and Plant Communities 15. The Light Environment of Plant Canopies Appendix

An Introduction to Environmental Biophysics

The unsaturated hydraulic conductivity function for soil can be calculated directly from a moisture retention function and a single measurement of hydraulic conductivity at some water content. If the moisture retention function can be represented by Y = Y,(0/0,)-b, where Y is the air entry water potential, 9, is the saturated water content, and 6 is an emperically determined constant, then the hydraulic conductivity is given by k = k,(O/O,)2b+8, where k. is the saturated hydraulic conductivity. Agreement of k calculated using this procedure with experimentally determined conductivities for five soil samples was found to be at least as good as with other calculation procedures

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A simple method for determining unsaturated conductivity from moisture retention data

On the relationship between incoming solar radiation and daily maximum and minimum temperature

1. Introduction. 2. Physical Properties of Soil. 3. Gas Diffusion in Soil. 4. Soil Temperature and Heat Flow. 5. Water Potential. 6. Hydraulic Conductivity and Water Transport Equations. 7. Variation in Soil Properties. 8. Infiltration and Redistribution. 9. Evaporation. 10. Solute Transport in Soils. 11. Transpiration and Plant- Water Relations. 12. Atmospheric Boundary Conditions. Appendix. Index. No responsibility is assumed by the author or publisher for any errors, mistakes, or misrepresentations that may occur from the use of these programs.

Gaylon S. Campbell

Papers

An Introduction to Environmental Biophysics

A simple method for determining unsaturated conductivity from moisture retention data

On the relationship between incoming solar radiation and daily maximum and minimum temperature

Soil physics with BASIC :transport models for soil-plant systems

Soil physics with BASIC