Stem Area Index Research Articles

Potato growth, nitrogen balance, quality, and productivity response to water-nitrogen regulation in a cold and arid environment.

The pervasively imprudent practices of irrigation and nitrogen (N) application within Oasis Cool Irrigation zones have led to significant soil nitrogen loss and a marked decrease in water and nitrogen use efficiency. To address this concern, a comprehensive field experiment was conducted from April to September in 2023 to investigate the impact of varying degrees of water and fertilization regulation strategies on pivotal parameters including potato yield, quality, nitrogen balance, and water-nitrogen use efficiency. The experimental design incorporated two water deficit degrees at potato seedling (W1, 55%-65% of Field Capacity (FC); W2, 45%-55% of FC), and four distinct nitrogen application gradients (N0, 0 kg ha-1 of N; N1, 130 kg ha-1 of N; N2, 185 kg ha-1 of N; N3, 240 kg ha-1 of N). A control was also included, comprising N0 nitrogen application and full irrigation (W0, 65%-75% of FC), totally eight treatments and one check. The results indicated that the tuber yield, plant dry matter accumulation, plant height, plant stem, and leaf area index increased with higher nitrogen fertilizer application and irrigation volume. However, tuber starch content, vitamin C, and protein content initially increased and then decreased, while reducing sugar content consistently decreased. Except for W1N2 treatment, the irrigation water use efficiency increased as the N application rate rose, while the nitrogen partial factor productivity, crop nitrogen use efficiency and soil nitrogen use efficiency decreased with an increase in N fertilizer application. The W1N2 treatment resulted in a higher yield (43.16 t ha-1), highest crop nitrogen use efficiency (0.95) and systematic nitrogen use efficiency (0.72),while maintaining moderate levels of soil nitrate and ammonium nitrogen. Therefore, through the construction of an integrated evaluation index (IEI), the W1N2 treatment of mild water deficit (55%-65% of FC) at potato seedling combined with the medium nitrogen application (185 kg ha-1 of N) has the highest IEI (0.978), it was recommended as the optimal water-nitrogen regulation and management strategies to facilitate high-yield, high-efficiency, and environmentally sustainable potato production in the cold and arid oasis areas of northwest China.

Winter Wheat Experiments to Optimize Sowing Dates and Densities in a High-Yielding Environment in New Zealand: Field Experiments and AgMIP-Wheat Multi-Model Simulations

This paper describes the data set that was used to test the accuracy of twenty-nine crop models in simulating the effect of changing sowing dates and sowing densities on wheat productivity for a high-yielding environment in New Zealand. The data includes one winter wheat cultivar (Wakanui) grown during six consecutive years, from 2012-2013 to 2017-2018, at two farms located in Leeston and Wakanui in Canterbury, New Zealand. The simulations were carried out in the framework of the Agricultural Model Intercomparison and Improvement Project for wheat (AgMIP-Wheat). Data include local daily weather data, soil profile characteristics and initial conditions, crop measurements at maturity (grain, stem, chaff and leaf dry weight, ear number and grain number, grain unit dry weight), and at stem elongation and anthesis (total above ground dry biomass, leaf number per stem and leaf area index). Several in-season measurements of the normalized difference vegetation index (NDVI) and the fraction of intercepted photosynthetically active radiation (FIPAR) are also available. The crop model simulations include both daily in-season and end-of-season results from twenty-nine wheat models.

An improved vegetation emissivity scheme for land surface modeling and its impact on snow cover simulations

This study developed an improved vegetation emissivity scheme for the Community Land Model (CLM) version 4.5 to more accurately simulate the effects of vegetation emissivity on snow processes in the Northern Hemisphere over winter and spring. The original scheme of vegetation emissivity in CLM produced an unreasonably low vegetation emissivity with a minimum value of around 0.70 in the cold season. Thus, we developed a new vegetation emissivity scheme based on maximum emissivity and leaf and stem area indices of vegetation, which can simulate vegetation emissivity more realistically than the original scheme. Our simulations were driven by the Climatic Research Unit-National Centers for Environmental Prediction (CRU-NCEP) reanalysis data. Results show that CLM with the new scheme produces stronger longwave radiation to the ground surface and generates more solid water drips off vegetation over winter and spring than with the original scheme. Such changes improve snow cover fraction (SCF) simulations for the middle and high latitudes in North America, central Eurasia, and the eastern Tibetan Plateau. About 200 and 350 thousand km2 with the SCF changes show a better SCF simulation with the new scheme over winter and spring, respectively. However, increased errors were found in SCF simulations with the new scheme, and further analysis indicates that such errors may be related to biases in the CLM forcing variables from the CRU-NCEP reanalysis data as compared with those from in situ observations. Moreover, the new emissivity scheme decreases total upward longwave radiation and increases surface net radiation and turbulent fluxes. Overall, the improved vegetation emissivity scheme in this study provides an effective tool to generate better understanding of the effects of vegetation on snow at regional scales and gives strong insight into improved land surface process modeling.

An experiment to improve the capability of the regional climate model RegCM4.5 to simulate the land surface climate in dense vegetation areas

The capability of the regional climate model RegCM4.5 to simulate land surface climate in dense vegetation areas is improved by changing the empirical parameter \( \alpha \) in the canopy interception coefficient in the Community Land Model, version 4.5 (CLM4.5). It is found that \( \alpha \) is a very important and sensitive parameter. After increasing the value of \( \alpha \), the simulation biases of latent and sensible heat flux in the wet season as well as the evaporation of intercepted water from the vegetation canopy (Ec) and vegetation transpiration (Et) are significantly reduced. In addition, the simulated 2 m air temperature and surface run-off in the wet season are improved obviously. However, surface soil moisture and temperature are not sensitive to the change of \( \alpha \). When regional climate simulation is conducted by RegCM4.5, the value of \( \alpha \) can be increased to 0.5 if the annual average sum of the leaf area index and the stem area index is more than 2.5, which could enhance the capability of the model, to a certain extent, to simulate the land surface climate.

Growth of Sugar Cane Under Cultivation Flooded at Different Speeds Lowering of the Water Table

In order to study the effect of downgrade rate of water table in the growth of sugar cane (Saccharum spp, cultivate 867515), an experiment in was carried under randomized block design with factorial arrangement (3 × 5 + 1) and 4 replications, applying the flood irrigation system in 3 stages of development (67, 210 and 300 days after planting - DAP) with 5 downgrade rate of water table (3, 6, 9, 12 and 15 days) and the control (no flood). The plants were grown in soil columns of 240 liters, filled with Yellow Oxisol by 300 days after planting and monitored as the height of the stem, number of leaves, stem diameter, number of internodes, number of tillers, leaf area, growth increment, rate relative growth, leaf area index, leaf area ratio and specific leaf area. The stages of development that the flooding was applied at a rate of lowering of the groundwater level variables influenced the growth of cane sugar. The plants drenched at 210 days after planting for 12 days had higher growth of stem, leaf number, leaf area and leaf area index. Plants exposed to water logging after 67 and 210 days after planting obtain better physiological indices that the witness and those who received the 305 DAP waterlogging. It is recommended that the spacing between drains is estimated to be able to lower the water table, after a reloading project to 30 cm deep in 15 days.

Biophysical drivers of seasonal variability in Sphagnum gross primary production in a northern temperate bog

AbstractSphagnum mosses are the keystone species of peatland ecosystems. With rapid rates of climate change occurring in high latitudes, vast reservoirs of carbon accumulated over millennia in peatland ecosystems are potentially vulnerable to rising temperature and changing precipitation. We investigate the seasonal drivers of Sphagnum gross primary production (GPP)—the entry point of carbon into wetland ecosystems. Continuous flux measurements and flux partitioning show a seasonal cycle of Sphagnum GPP that peaked in the late summer, well after the peak in photosynthetically active radiation. Wavelet analysis showed that water table height was the key driver of weekly variation in Sphagnum GPP in the early summer and that temperature was the primary driver of GPP in the late summer and autumn. Flux partitioning and a process‐based model of Sphagnum photosynthesis demonstrated the likelihood of seasonally dynamic maximum rates of photosynthesis and a logistic relationship between the water table and photosynthesizing tissue area when the water table was at the Sphagnum surface. The model also suggested that variability in internal resistance to CO2 transport, a function of Sphagnum water content, had minimal effect on GPP. To accurately model Sphagnum GPP, we recommend the following: (1) understanding seasonal photosynthetic trait variation and its triggers in Sphagnum; (2) characterizing the interaction of Sphagnum photosynthesizing tissue area with water table height; (3) modeling Sphagnum as a “soil” layer for consistent simulation of water dynamics; and (4) measurement of Sphagnum “canopy” properties: extinction coefficient (k), clumping (Ω), and maximum stem area index (SAI).

Evapotranspiration and Land Surface Process Responses to Afforestation in Western Taiwan: A Comparison between Dry and Wet Weather Conditions

Abstract. An afforestation project was initiated in the western plain of Taiwan to convert abandoned farming lands into forests to improve the ecological and environmental conditions. This study was conducted to understand the potential impacts of this land cover change on evapotranspiration (ET) and other land surface processes and the differences in the impacts under clear and rainy weather conditions. Numerical simulations with the land surface covered with crops and forests were conducted using an atmosphere-land coupled model during a summer monsoon season. Sensitivity experiments were conducted to understand the possible impacts of the convection and atmospheric planetary boundary layer parameterization schemes used in this study on the simulation results. The results of the entire simulation period indicate that, although the maximum solar radiation is increased by 30 W m -2 from about 800 W m -2 due to smaller albedo after afforestation, the maximum ET near noon time is decreased by about 3 mm h -1 from about 17 mm h -1 on clear days, mainly due to increased stem area index and reduced wind speed within the forest canopies. Meanwhile, the maximum sensible heat flux is increased by about 100 W m -2 from 200 W m -2 due to larger total vegetation area (the sum of leaf and stem area index) in forests. Similar responses in ET and other land surface processes to the afforestation are obtained for clear weather conditions. In contrast, ET is increased and sensible heat flux is decreased under rainy conditions. The changes in ET are more important on clear days than on rainy days in determining the responses over the entire simulation period. The sensitivity experiments confirmed the simulated responses of ET and other land surface processes. The results suggest that afforestation would modulate hydrological cycles by reducing ET on clear days and elevating ET on rainy days, thereby reducing the risks of hydrological extremes.

Parameterization of the snow-covered surface albedo in the Noah-MP Version 1.0 by implementing vegetation effects

Abstract. Snow-covered surface albedo varies depending on many factors, including snow grain size, snow cover thickness, snow age, forest shading factor, etc., and its parameterization is still under great uncertainty. For the snow-covered surface condition, albedo of forest is typically lower than that of short vegetation; thus snow albedo is dependent on the spatial distributions of characteristic land cover and on the canopy density and structure. In the Noah land surface model with multiple physics options (Noah-MP), almost all vegetation types in East Asia during winter have the minimum values of leaf area index (LAI) and stem area index (SAI), which are too low and do not consider the vegetation types. Because LAI and SAI are represented in terms of photosynthetic activeness, stem and trunk in winter are not well represented with only these parameters. We found that such inadequate representation of the vegetation effect is mainly responsible for the large positive bias in calculating the winter surface albedo in the Noah-MP. In this study, we investigated the vegetation effect on the snow-covered surface albedo from observations and improved the model performance by implementing a new parameterization scheme. We developed new parameters, called leaf index (LI) and stem index (SI), which properly manage the effect of vegetation structure on the snow-covered surface albedo. As a result, the Noah-MP's performance in the winter surface albedo has significantly improved – the root mean square error is reduced by approximately 69 %.

MODIS Consistent Vegetation Parameter Specifications and Their Impacts on Regional Climate Simulations

Abstract A consistent set of Moderate Resolution Imaging Spectroradiometer (MODIS) vegetation parameters, including leaf and stem area index (LAI and SAI, respectively), land-cover category (LCC), fractional vegetation cover (FVC), and albedo parameterization are developed, and their impacts on North American regional climate are evaluated based on 10-yr Climate–Weather and Research Forecasting Model (CWRF) simulations. As compared with the previous Advanced Very High Resolution Radiometer (AVHRR) set, MODIS LCC increases grassland and cropland fractions in the central Great Plains and Midwest, respectively. Evergreen needleleaf forest converts to mixed forest in the Southeast, and mixed forest converts to evergreen needleleaf in Canada. FVC decreases by 0.05–0.3 over the central Great Plains but increases by 0.1–0.35 over the northern Rocky Mountains, Canada, and the U.S. Southeast. MODIS LAI is less than AVHRR by 2–6, except in the central Great Plains, eastern Rocky Mountains, and central Mexico. LCC and FVC changes over the central Great Plains reduce CWRF warm biases by 0.71°C and wet biases by 0.36 mm day−1. Large LAI reductions cause latent and sensible heat fluxes to decrease by 0.78–5.81 and 0.91–6.54 W m−2, respectively. They also lessen cold biases over the Gulf States and Southeast and wet biases over the North American monsoon region and Canada during summer. In densely vegetated regions including eastern Canada, the Ohio Valley, and the mid-Atlantic region, spring and summer precipitation decreases and temperature increases result from LAI reductions that cause positive evapotranspiration–precipitation–soil moisture feedbacks. Conversely, precipitation and temperature decreases in sparely vegetated regions, such as the Great Plains, result from FVC reductions that cause negative albedo–evapotranspiration–precipitation–soil moisture feedbacks.

Comparison of Measured and Simulated Friction Velocity and Threshold Friction Velocity Using SWEEP

Adequately simulating the occurrence and magnitude of erosion using the Wind Erosion Prediction System is critical for resource conservation and improving environmental quality in the United States and other regions of the world. Past observations indicate an insensitivity of the Wind Erosion Prediction System erosion submodel (Single-event Wind Erosion Evaluation Program (SWEEP)) to simulate the occurrence of wind erosion from loess soils during intensifying winds in the Pacific Northwest United States. This insensitivity is attributed to either underestimation of friction velocity (u*) or overestimation of threshold friction velocity (u*t), but no definitive work has been conducted to validate u* and u*t in the SWEEP. The objective of this study was to compare measured u* and u*t with those simulated by the SWEEP. The SWEEP begins to simulate erosion when u* exceeds u*t, thus we compared measured and simulated u* and u*t of agricultural fields during wind erosion events in eastern Washington. No evidence indicated that the SWEEP consistently overestimated or underestimated u*. The SWEEP was very sensitive to the stem area index, and estimation of u* was better when the SWEEP was used at field sites characterized by a lower rather than a higher stem area index. Our results, however, indicate that the SWEEP overestimated u*t during all observed erosion events. Therefore, simulating the occurrence of wind erosion of loess soils in the Pacific Northwest and other arid and semiarid regions of the world may be improved through better estimation of u*t in the SWEEP.

Dry matter accumulation and seasonal partitioning in mature Opuntia ficus-indica (L.) Mill. fruiting trees

Aim of this study was to understand the allocation of biomass into different canopy and root components and to measure the stem area index and its partitioning by cladode functionality (age), for fruiting Opuntia ficus-indica (OFI) Gialla trees, spaced 6x5 m apart and trained to a globe. The net primary productivity (NPP), calculated taking into account dry weight gain for above-ground vegetative components of OFI trees was 3.6 t C ha–1. Including the fruit component and 1st flush current-year cladodes, NPP of above-ground components becomes 12 t ha–1, equivalent to 5.4 t C ha–1. Current-year cladodes were the highest C sink (49% of total annual C fixed in the canopy), secondary growth accounted for 22% of C fixation and the fruit component for 29%. This study demonstrated that OFI trees, grown in a commercial fruit orchard, couple high productivity, in terms of fruit yield and harvest index, with relevant C fixed in the canopy.

Fruit productivity and carbon gain of Opuntia ficus-indica (L.) Mill. trees

Opuntia ficus-indica (OFI) tree and orchards efficiency has been poorly studied, in terms of relation between orchard lay out, light interception, and cropping efficiency. Apparently, there is no other way to increase orchard production than increasing the number either of trees ha-1 or fertile shoots tree-1, considering that a fruit count higher than 6-7 cladode-1 reduces fruit harvest size. The first option requires a reduction of unit tree size and canopy volume. The second option implies the use of large trees that often reduce their efficiency 12-15 years after planting. In 15-year-old OFI trees spaced 6 5 m apart trained to a globe and 2.5-3.0 m high, stem area index (SAI) calculated on the ground surface area covered by the tree was 2.9 and 6.5, respectively, for most active 1- and 2-year-old cladodes and whole canopy surface area. SAI orchard (cladode surface area/ground surface area allotted to the tree) values were slightly lower: 1.8 and 3.9. The proportion of annual dry matter allocated to the...

Development of high resolution land surface parameters for the Community Land Model

Abstract. There is a growing need for high-resolution land surface parameters as land surface models are being applied at increasingly higher spatial resolution offline as well as in regional and global models. The default land surface parameters for the most recent version of the Community Land Model (i.e. CLM 4.0) are at 0.5° or coarser resolutions, released with the Community Earth System Model (CESM). Plant Functional Types (PFTs), vegetation properties such as Leaf Area Index (LAI), Stem Area Index (SAI), and non-vegetated land covers were developed using remotely sensed datasets retrieved in late 1990's and the beginning of this century. In this study, we developed new land surface parameters for CLM 4.0, specifically PFTs, LAI, SAI and non-vegetated land cover composition, at 0.05° resolution globally based on the most recent MODIS land cover and improved MODIS LAI products. Compared to the current CLM 4.0 parameters, the new parameters produced a decreased coverage by bare soil and trees, but an increased coverage by shrub, grass, and cropland. The new parameters result in a decrease in global seasonal LAI, with the biggest decrease in boreal forests; however, the new parameters also show a large increase in LAI in tropical forest. Differences between the new and the current parameters are mainly caused by changes in the sources of remotely sensed data and the representation of land cover in the source data. Advantages and disadvantages of each dataset were discussed in order to provide guidance on the use of the data. The new high-resolution land surface parameters have been used in a coupled land-atmosphere model (WRF-CLM) applied to the western US to demonstrate their use in high-resolution modeling. A remapping method from the latitude/longitude grid of the CLM data to the WRF grids with map projection was also demonstrated. Future work will include global offline CLM simulations to examine the impacts of source data resolution and subsequent land parameter changes on simulated land surface processes.

Measuring Harvestable Biomass in Short-Rotation Willow Bioenergy Plantations Using Light Attenuation

Routine monitoring of above ground biomass within purpose-grown willow biomass energy production systems is important for timing harvest and other operations to maximize profit and increase plantation productivity. The objective of this study was to assess the efficacy of an elegant nondestructive mensurative technique for providing reliable estimates of harvestable biomass for six willow varieties during a 3-year rotation. The LAI-2000 Plant Canopy Analyser was used to measure the stem area index of growing willow and relate it to harvestable biomass at four locations within Saskatchewan, Canada over a 3-year period. Given the highly significant relationship (R2 = 0.95; P < 0.0001) between measured stem area index and harvestable willow biomass, independent of variety, age, or location, this simple mensurative technique is a promising alternative for estimating above ground biomass in short-rotation willow plantations.

Coeficiente de repetibilidade e parâmetros genéticos em capim-elefante

O objetivo deste trabalho foi determinar os coeficientes de repetibilidade de caracteres morfofisiológicos em genótipos de capim-elefante (Pennisetum spp.), a partir de dados obtidos durante seis ciclos de avaliação. Foram estimados: número mínimo de medições e parâmetros genéticos. Utilizou-se o delineamento experimental de blocos ao acaso, em arranjo de parcelas subdivididas, com quatro níveis de N (controle, 30, 60 e 90 kg ha‑1 por corte) e 16 genótipos de Pennisetum (11 híbridos interespecíficos e cinco cultivares). Os ciclos consistiram de avaliações em 2010 (21/4, 19/7 e 28/9) e 2011 (6/1, 7/4 e 3/8). Os coeficientes de repetibilidade foram de média‑alta magnitude para todas as variáveis, o que indica que houve regularidade entre as medidas repetidas. Para as variáveis massa de forragem, altura da planta, comprimento e largura da folha, diâmetro do colmo, clorose e índice de área foliar, três ciclos de avaliação são suficientes para obter R² de 90%, pela análise de componentes principais. Para o comprimento do entrenó, o mínimo de sete avaliações é necessário para predizer o valor real dos genótipos. Os parâmetros genéticos das variáveis massa de forragem, comprimento e largura da folha, diâmetro do colmo e clorose foliar são de alta magnitude, o que favorece a seleção de genótipos superiores de Pennisetum.

A simple technique for estimating above-ground biomass in short-rotation willow plantations

Successful purpose-grown willow production systems require regular monitoring of willow growth to apply timely management techniques for increased productivity and timing of harvest for maximizing profit. The objective of this study was to assess the efficacy of a novel method of estimating above-ground willow biomass, involving measuring light attenuation through the willow canopy, to calculate a ‘stem area index’ for relating to harvested willow biomass. Two different willow clones, with contrasting growth form, were used: single stem (Charlie) and multi-stem (SV1). Given the strong correlations (r2 > 0.97; p < 0.05) between the measured stem area index and harvested willow biomass, regardless of growth form, it appears that this simple mensurative technique is a promising alternative for estimating above-ground biomass in short-rotation willow plantations.

Stem respiration in tropical forests along an elevation gradient in the Amazon and Andes

AbstractAutotrophic respiration involves the use of fixed carbon by plants for their own metabolism, resulting in the release of carbon dioxide as a by‐product. Little is known of how autotrophic respiration components vary across environmental gradients, particularly in tropical ecosystems. Here, we present stem CO2 efflux data measured across an elevation transect spanning ca. 2800 m in the Peruvian Amazon and Andes. Forest plots from five elevations were studied: 194, 210, 1000, 1500, and 3025 m asl Stem CO2 efflux (Rs) values from each plot were extrapolated to the 1‐ha plot level. Mean Rs per unit stem surface area declined significantly with elevation, from 1.14±0.12 at 210 m elevation to 0.62±0.09 μmol C m−2 s−1 at 3025 m elevation. When adjusted for changing forest structure with elevation, this is equivalent to 6.45±1.12 Mg C ha−1 yr−1 at 210 m elevation to 2.94±0.19 Mg C ha−1 yr−1 at 3025 m elevation. We attempted to partition stem respiration into growth and maintenance respiration components for each site. Both growth and maintenance respiration rates per unit stem showed similar, moderately significant absolute declines with elevation, but the proportional decline in growth respiration rates was much greater. Stem area index (SAI) showed little trend along the transect, with declining tree stature at higher elevations being offset by an increased number of small trees. This trend in SAI is sensitive to changes in forest stature or size structure. In the context of rapid regional warming over the 21st century, such indirect, ecosystem‐level temperature responses are likely to be as important as the direct effects of temperature on maintenance respiration rates.

Observations and modeling of turbulent fluxes during melt at the shrub-tundra transition zone 1: point scale variations

Vegetation has a significant influence on snow accumulation and energy availability for snowmelt. This is particularly true in the vicinity of the arctic treeline, characterized by the alternation of shrub-tundra and open-tundra, with the former expected to spread more and more. This work considers the time variation in turbulent fluxes over two open-tundra and shrub-tundra sites, where measurements of sensible and latent heat fluxes over the canopy are available. An improved version of the GEOtop hydrological model with a dual-layer surface scheme has been used to interpret and reproduce the measurements. The model allows us to separate the contribution of the vegetation and the surface to the turbulent fluxes measured above the canopy and, despite some issues related to the parameterization of the turbulence in the canopy, is able to reasonably reproduce the turbulent fluxes measured above the vegetation and the snowmelt acceleration observed in the shrub-tundra. The maximum energy contribution to the surface during snowmelt is found to occur for values of the leaf and stem area index around 1.0. The model proves to be a valuable platform to be applied in a distributed model to predict the spatial variability of snowmelt and surface energy balance.

Allometric constraints on sources of variability in multi-angle reflectance measurements

Bidirectional reflectance signatures of vegetation are strongly shaped by the shadows cast between objects in a scene, such as tree crowns or leaves. Differences in the shape and spatial density of these objects result in distinct bidirectional reflectance distribution functions (BRDFs) in different biomes. We examined how allometry may constrain the variability of canopy architectural parameters in BRDF models, and consequently alter the attribution of variation in the simulated bidirectional reflectance factor (BRF). Allometry is the covariation between the size or number of organisms and their component parts. To test the importance of realistic variation and covariation of canopy architecture on BRDF, we incorporated the 3-D radiative transfer model DISORD (which uses the geometric optics (GO) model of Li and Strahler) into a Monte Carlo (MC) algorithm. The MC algorithm generated an ensemble of tree canopies whose parameters fulfilled the allometry of a set of measured forest plots from Russian forest inventory. The role of view geometry was directly considered using perturbations of the parameters to evaluate the sensitivity of the BRF itself, evaluated at different view angles, and the difference in BRF (ΔBRF) as measured at two view angles representing paired satellite observations. The allometrically constrained forest plots had reduced variation in ΔBRF compared to the uncorrelated plots, but the variation of the BRF itself is dramatically increased by allometry. The variation of the BRF is relatively constant among the view angles examined, whereas the variation in ΔBRF increases dramatically with larger phase angles. The BRF was most sensitive to canopy attributes that were important in radiative transfer, such as LAI and stem area index (SAI), but there were also large (∼ 40% of variance) contributions of geometric components such as tree number, crown size, and ground cover. By contrast, sensitivity of ΔBRF was dominated by ground cover, crown size and tree number, which all play a role in the GO calculations. The mix of sensitive parameters was not dramatically different between gymnosperms and angiosperms, nor between allometric and correlated runs. Together these results indicate that forest structure and leaf area could be usefully inverted together using paired observations with different viewing geometries. Ideal pairs of observations are those with large difference in phase angle, and along the gradient of the BRF peak, which most commonly occur with sequential MODIS/Terra overpasses.

Consistent Parameterization of Roughness Length and Displacement Height for Sparse and Dense Canopies in Land Models

Abstract While progress has been made in the treatment of turbulence below, within, and above canopy in land models, not much attention has been paid to the convergence of canopy roughness length and displacement height to bare soil values as the above-ground biomass, or the sum of leaf and stem area indices, becomes zero. Preliminary formulations have been developed to ensure this convergence for the Community Land Model version 3 (CLM3) and are found to significantly improve the wintertime simulation of sensible heat flux (SH) compared with observational data over the Cabauw site in the Netherlands. The simulation of latent heat flux (LH) is also moderately improved. For global offline CLM3 simulations, the new formulations change SH by more than 5 W m−2 over many regions, while the change of LH is less than 1 W m−2 over most of the regions.