Showing papers on "Leaf area index published in 1992"
TL;DR: In this article, the projection coefficients of several objects including spheres, cylinders, hemicircular cylinders, and triangular and square bars are investigated through mathematical derivation and numerical calculation for a range of ellipsoidal angular distributions.
Abstract: To eliminate the confusion in the definition of leaf area index (L) for non-flat leaves, the projection coefficients of several objects including spheres, cylinders, hemicircular cylinders, and triangular and square bars are investigated through mathematical derivation and numerical calculation for a range of ellipsoidal angular distributions. It is shown that the projection coefficient calculated based on half the total intercepting area is close to a constant of 0.5 when the inclination angle of the objects is randomly (spherically) distributed, whereas the calculated results based on the object's largest projected area are strongly dependent on the shape of the objects. Therefore, it is suggested that the leaf area index of non-flat leaves be defined as half the total intercepting area per unit ground surface area and that the definition of L based on the projected leaf area be abandoned.
1,171 citations
TL;DR: This study points at the inadequacy of scaling-up from physiological baselines to ecosystems without accounting for interactions among components, and it emphasizes the urgent need for whole-system experimental approaches in global-change research.
Abstract: Carbon, nutrient, and water balance as well as key plant and soil processes were simultaneously monitored for humid tropical plant communities treated with CO2-enriched atmospheres. Despite vigorous growth, no significant differences in stand biomass (of both the understory and overstory), leaf area index, nitrogen or water consumption, or leaf stomatal behavior were detected between ambient and elevated CO2 treatments. Major responses under elevated CO2 included massive starch accumulation in the tops of canopies, increased fine-root production, and a doubling of CO2 evolution from the soil. Stimulated rhizosphere activity was accompanied by increased loss of soil carbon and increased mineral nutrient leaching. This study points at the inadequacy of scaling-up from physiological baselines to ecosystems without accounting for interactions among components, and it emphasizes the urgent need for whole-system experimental approaches in global-change research.
468 citations
TL;DR: In this paper, the relationship between the normalized difference vegetation index (NDVI) and absorbed photosynthetically active radiation (APAR) in a vegetation canopy was studied and the results indicated that instantaneous observations can be used to characterize the diurnally integrated APAR in vegetation canopies.
447 citations
TL;DR: Many of the physiological relations between water or nutrient availability and production and carbon allocation reported in this study are consistent with results from studies on lowland Douglas-fir and other conifer forests in the Pacific Northwest.
Abstract: Changes in biomass distribution, canopy dynamics, and above- and be- lowground net primary production were examined in a Rocky Mountain Douglas-fir (Pseu- dotsuga menziesii var. glauca forest in New Mexico. Nutrient and water availability were experimentally altered by: fertilization (F), irrigation (I), carbon in the form of wood chips (WC), carbon + irrigation (WC/I), and control (C). Prior to treatment, aboveground tree biomass ranged from 238 to 369 000 kg/ha, projected leaf area index (LAI) ranged from 5.4 to 8.7 m2/m2 and aboveground net primary production (ANPP) ranged from 9200 to 11 900 kg* ha-I yr-i. Aboveground NPP was correlated positively (R2 = 0.85) with LAI before the treatments. Canopy dynamics were strongly influenced by water and nutrient availability. For trees of similar diameter, irrigated and fertilized trees supported a signif- icantly greater biomass of new twig and new foliage than control trees. During the 2-yr study leaf area index (LAI) increased by 5, 12, 18, and 24% in the C, I, WC/I, and F plots, respectively, and decreased by 3% in the WC plots. Stand level biomass distribution and production patterns were also affected by the availability of nutrients and water. Two years after the treatments were initiated, new foliage masses were 2400 (F), 2300 (WC/I), 2000 (I), 1900 (C), and 1800 (WC) kg/ha. In 1986, aboveground NPP was 33% greater in the F than WC treatment. Irrigation also increased ANPP. Fine root net primary production ranged from 1540 to 4200 kg ha-i yr-i and was significantly greater (P < .1) in the control than in the four treatments. BNPP comprised 46 (C), 32 (WC), 31 (I), 23 (WC/I), and 23 (F) % of total NPP. Total NPP was correlated positively with LAI (R2 = 0.66) and ranged from 15 360 kg ha- Iyr-I in the WC treatment to 21 140 kg ha-l yr-I in the F treatment. Many of the physiological relations between water or nutrient availability and production and carbon allocation reported in this study are consistent with results from studies on lowland Douglas-fir and other conifer forests in the Pacific Northwest. Collectively, these studies provide a mechanistic understanding of how water and nutrient availability govern production and carbon allocation of conifer forests in the western United States.
400 citations
TL;DR: The effects of interactions between the canopy and the atmosphere on forest water use dynamics are shown by a fourfold variation in coupling of the tree canopy air saturation deficit to that of the overhead atmosphere on a typical fine day due to changes in stomatal conductance.
Abstract: Tree transpiration was determined by xylem sap flow and eddy correlation measurements in a temperate broad-leaved forest of Nothofagus in New Zealand (tree height: up to 36 m, one-sided leaf area index: 7). Measurements were carried out on a plot which had similar stem circumference and basal area per ground area as the stand. Plot sap flux density agreed with tree canopy transpiration rate determined by the difference between above-canopy eddy correlation and forest floor lysimeter evaporation measurements. Daily sap flux varied by an order of magnitude among trees (2 to 87 kg day-1 tree-1). Over 50% of plot sap flux density originated from 3 of 14 trees which emerged 2 to 5 m above the canopy. Maximum tree transpiration rate was significantly correlated with tree height, stem sapwood area, and stem circumference. Use of water stored in the trees was minimal. It is estimated that during growth and crown development, Nothofagus allocates about 0.06 m of circumference of main tree trunk or 0.01 m2 of sapwood per kg of water transpired over one hour.Maximum total conductance for water vapour transfer (including canopy and aerodynamic conductance) of emergent trees, calculated from sap flux density and humidity measurements, was 9.5 mm s-1 that is equivalent to 112 mmol m-2 s-1 at the scale of the leaf. Artificially illuminated shoots measured in the stand with gas exchange chambers had maximum stomatal conductances of 280 mmol m-2 s-1 at the top and 150 mmol m-2 s-1 at the bottom of the canopy. The difference between canopy and leaf-level measurements is discussed with respect to effects of transpiration on humidity within the canopy. Maximum total conductance was significantly correlated with leaf nitrogen content. Mean carbon isotope ratio was -27.76±0.27‰ (average ±s.e.) indicating a moist environment. The effects of interactions between the canopy and the atmosphere on forest water use dynamics are shown by a fourfold variation in coupling of the tree canopy air saturation deficit to that of the overhead atmosphere on a typical fine day due to changes in stomatal conductance.
281 citations
TL;DR: In this paper, a linear relation between cumulative APAR and cumulative aboveground phytomass production was found for both corn and soybeans, and the rate of accumulation per unit APAR was more than twice as great for corn as for soybean.
274 citations
TL;DR: In this paper, a 3D radiative transfer model was used to investigate the relationship between spectral indices and fraction of absorbed photosynthetically active radiation (PAR) in horizontally heterogeneous vegetation canopies.
258 citations
TL;DR: In this paper, the authors compared field measurements of LAI to normalized difference vegetation index (NDVI) values derived using Lnandsat Thematic Mapper (TM) data, for 16 fertilized and control slash pine plots on three dates.
189 citations
TL;DR: In this article, a Poisson model is developed to describe sunfleck or gap size distributions under clumped plant canopies, based on the assumption that foliage clumps are randomly distributed in space and foliage elements are within each clump.
181 citations
TL;DR: In this article, the authors consider the inference of vegetation status from measurements in the visible and near infrared, in the presence of variable soil reflectance, and propose a leaf vegetation index VL, having limits 0 nd 1, for the field case.
121 citations
TL;DR: The characteristic pattern of stand growth, with culmination at about the time of canopy closure, is associated with declines in both the amount and efficiency of leaf area.
TL;DR: It is argued that long-term multidisciplinary research, such as the BFG study, is necessary for advancing understanding of the links between site conditions and forest productivity.
TL;DR: In this article, the relationship between microwave vegetation indexes and plant biophysical parameters is discussed, using a simple slab model that considers vegetation as a uniform absorbing and scattering medium upon the soil surface.
TL;DR: With elevated CO2 a new equilibrium in transpiration is established in which leaf area increases offset decreases in stomatal conductance and the addition of nitrogen increases transpiration without any indication of a newilibrium being reached during the simulated period.
Abstract: A spatially explicit hydroecological landscape model of water, carbon and energy balances (Topog- IRM) is described The landscape is envisaged as a catchment forested with a single stratum comprising Eucalyptus maculata trees The model was used to simulate the direct effects of a 2× elevation in atmospheric carbon dioxide at two levels of nitrogen on catchment water yield, soil moisture status and tree growth Experimental results used to parameterise the model are detailed Key features of the model are (1) an ability to scale hydrological processes at the catchment scale in three dimensions, and (2) a means to integrate multiple factors/ stresses on plant growth The effects of CO2 on catchment hydrology (water yield or soil moisture content) and forest growth (expressed as leaf area index, LAI) were modelled for a 2-year period, and contrasted with the effects of added nitrogen Results were expressed as totals for the catchment or spatially distributed across the catchment For the total catchment, water yield increased in the order: high CO2 with low N, high CO2 with high N, ambient CO2 with low N, ambient Co2 with high N LAI increased from 33 to 57 in the order: ambient CO2 with low N, ambient CO2 with high N, high CO2 with low N, high Co2 with high N These results agree with previous data New findings are: (1) with elevated CO2 a new equilibrium in transpiration is established in which leaf area increases offset decreases in stomatal conductance; (2) the addition of nitrogen increases transpiration without any indication of a new equilibrium being reached during the simulated period; (3) the spatial distribution of soil moisture changes, presenting a new resource base for spatial changes to species composition and growth rates The major hydroecological responses to elevated CO2 are seen as increased maximum upper canopy leaf area, increased litter inputs, especially at times of drought (hence changed fire regimes), changes in the composition of the understorey (hence litter composition, soil microfauna, and the spatial expression of biological diversity) and a slight increase in water yield
TL;DR: Foliage analyses indicate that thinning improved nitrogen, potassium, and magnesium nutrition and increased the translocation of potassium from 1-year-old foliage to support new growth in young Douglas-fir plantations.
Abstract: The effect of thinning and cultural practices (multinutrient fertilization, pruning) on total aboveground biomass increment and growth efficiency was studied over three consecutive 2-year periods (1981–1987) in young Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) plantations. Net aboveground biomass increment over the 6-year period averaged 14.5, 7.8, and 5.5 Mg•ha−1•year−1 for the high-, medium-, and low-density plots, respectively. Growth efficiency, after dropping sharply between leaf area indexes of 1 and 6 m2/m2, remained relatively constant up to a leaf area index of 17, the highest measured. Consequently, aboveground biomass increment continued to increase at leaf area indexes well above that at which the Beer–Lambert law predicts maximum light should be absorbed. Foliage analyses indicate that thinning improved nitrogen, potassium, and magnesium nutrition and increased the translocation of potassium from 1-year-old foliage to support new growth. However, fertilization increased foliar nitrogen ...
TL;DR: In this paper, a third-order polynomial accurately described the relationship between leaf area index (LAI) and plant height (both normalized with respect to their maxima) for a range of normal and leaf licensed and experimental plant lines during the late vegetative and early grain filling stages.
Abstract: Leaf area distribution determines the interception of radiation for photosynthesis. A method of analysis was developed to quantify differences in vertical leaf area distribution in a corn (Zea Mays L.) canopy. A third-order polynomial accurately described the relationship between leaf area index (LAI) and plant height (both normalized with respect to their maxima) for a range of normal and leaf licensed and experimental plant lines during the late vegetative and early grainfilling stages (r 2 ≥0.85). The shape of the polynomial reflected the bell shape of individual leaf area versus leaf number curves, with the densest leaf area in the mid-portion of the canopy (...)
TL;DR: It is argued that a reflectance measurement ( WDVI ) itself may be more appropriate than ground cover or LAI to quantify interception of solar radiation by a crop canopy.
TL;DR: It is shown that in dense stands of growing herbaceous plants the vertical pattern of leaf nitrogen distribution resembles the pattern of mean light attenuation in the stand and hence tends to maximize total daily photosynthetic carbon gain of the whole stand.
Abstract: Using a combination of mathematical modeling and field studies we showed that in dense stands of growing herbaceous plants the vertical pattern of leaf nitrogen distribution resembles the pattern of mean light attenuation in the stand and hence tends to maximize total daily photosynthetic carbon gain of the whole stand. Flowering represents a strong sink of nitrogen away from the photosynthetic apparatus and in herbs like Solidago altissima it induces leaf shedding. We studied both the effect of nitrogen reallocation and leaf shedding on the whole canopy photosynthesis and changes in leaf nitrogen distributions in stands moving from the growing to the flowering stage. Despite a decrease in leaf area index and total nitrogen available for photosynthesis in the flowering stand, the leaf nitrogen distribution here also leads to an almost maximum canopy photosynthesis. In both the growing and the flowering stands the leaf area index was higher than calculated optimum values. It is pointed out that this should not necessarily be interpreted as ‘non-adaptive’.
TL;DR: Light interception and leaf area distribution were measured on four planting systems of cultivars ‘Golden Delicious’ and cultivar ‘Karmijn de Sonnaville’ on M.9 rootstock at tree densities ranging from 2000 to 8333 trees ha−1 and leaf dry weight per unit area was closely related to irradiance within the canopy.
TL;DR: It is shown that the model is able to reproduce the surface energy flux components over both dense and partial canopies, and that the partition between soil evaporation and foliage transpiration can be made, leading to the monitoring of global vegetation stomatal resistance through the growing season.
TL;DR: The authors present field measurements and the results of a three-dimensional canopy model inversion for sand shinnery oak and estimate oak leaf area index (LAI) and canopy density, expressed as percentage of cover, from the bidirectional reflectance data.
Abstract: The authors present field measurements and the results of a three-dimensional canopy model inversion for sand shinnery oak. Spectral bidirectional radiance measurements in three spectral channels, 0.65-0.67 mu m, 0.81-0.84 mu m, and 1.62-1.69 mu m, encompassing both the complete land surface and sky hemispheres, were acquired for a sand shinnery oak plant community in west Texas. The changes in canopy reflectance that occur with variations in solar zenith angle and view direction and for two seasons of the year were evaluated. A three-dimensional radiation interaction model (TRIM) was then inverted to estimate oak leaf area index (LAI) and canopy density, expressed as percentage of cover, from the bidirectional reflectance data. >
TL;DR: In this article, the authors used a hand-held infrared thermometer to measure the foliage temperature of strawberries in a simple semicircular greenhouse to assess the water stress in a very mild and mild water stress regime.
TL;DR: The canopy radiation model EXTRAD was used to quantify the accuracy of leaf area index (LAI) estimations from vegetation indices (Vis), derived from green and infra-red crop reflectance as mentioned in this paper.
Abstract: The canopy radiation model EXTRAD was used to quantify the accuracy of leaf area index (LAI) estimations from vegetation indices (Vis), derived from green and infra-red crop reflectance. The Vis we...
TL;DR: It is concluded that late-season foliar N application can improve yields of tropical semidwarf rices, particularly for direct-seeded culture.
TL;DR: In this paper, the authors measured the reflectance of six maize genotypes on 16 dates in 1984 at the Nebraska Sandhills Laboratory using a modular multiband radiometer, and the results indicated that the 1D SAIL model underestimated red and overestimated NIR reflectance at partial canopies because it did not account for exposed bare soil.
TL;DR: In this paper, the root zone water storage between 0 and 1 m depth was monitored at 14-day intervals under contrasting canopies of Eucalyptus nitens (a gum) and Eucaliaptus delegatensis (an ash) during their fourth and fifth years of growth and periods of non-limiting and limiting water availability, respectively.
Journal Article•
01 Jul 1992
TL;DR: The results of a NASA field experiment conducted in the Superior National Forest near Ely, Minnesota, during the summers of 1983 and 1984 are described in this paper, where the authors examined the use of remote sensing to provide measurements of biophysical parameters in the boreal forests.
Abstract: Described here are the results of a NASA field experiment conducted in the Superior National Forest near Ely, Minnesota, during the summers of 1983 and 1984. The purpose of the experiment was to examine the use of remote sensing to provide measurements of biophysical parameters in the boreal forests. Leaf area index, biomass, net primary productivity, canopy coverage, overstory and understory species composition data are reported for about 60 sites, representing a range of stand density and age for aspen and spruce. Leaf, needle, and bark high-resolution spectral reflectance and transmittance data are reported for the major boreal forest species. Canopy bidirectional reflectance measurements are provided from a helicopter-mounted Barnes Multiband Modular Radiometer (MMR) and the Thematic Mapper Simulator (TMS) on the NASA C-130 aircraft.
TL;DR: In this article, the amount of water loss due to plant transpiration was partitioned from total evapotranspiration by covering the water surface of the lysimeters with styrofoam beads.
Abstract: Field experiments were completed to determine patterns of evapotranspirative water loss from salt and tidal freshwater marshes in Virginia. Water losses from “Mariotte systems” attached to open-water lysimeters and lysimeters vegetated by dominant marsh macrophytes were used to calculate hourly rates of open-water evaporation (Eo) and evapotranspiration (ET), respectively, during low tide. In the tidal freshwater marsh, ET was significantly greater than Eo (p=0.002, n=6); in the salt marsh, there were no differences between mean rates of ET and Eo (p=0.200, n=3). The ratio ET:Eo was highly correlated with leaf area index (LAI) (r2=0.82). In the tidal freshwater marsh, the amount of water loss due to plant transpiration was partitioned from total evapotranspiration by covering the water surface of the lysimeters with styrofoam beads. Measured transpiration rates in the tidal freshwater marsh were strongly correlated with leaf area index according to the following linear regression equation: T=0.355(LAI)−0.084 (r2=0.797, n=10). Because LAI was shown to be a good predictor of the relative increase in ET over Eo, it is likely that in vegetated tidal freshwater marshes with high leaf densities most atmospheric water loss comes from plants, not from the surface of the marsh. In salt marshes, low plant densities do not contribute substantially to atmospheric water loss, suggesting that paths of water transport and patterns of solute concentration in the subsurface environment are different compard to the tidal freshwater marsh.
TL;DR: It is concluded that the general nonlinear model (LA =0.0234 ✕ LDW) can accurately estimate leaf area of peanut canopies across a wide range of cultivars and growth stages.
Abstract: Leaf area index (LAI) is important for light interception, radiation-use efficiency (RUE), and plant growth; however, determination LAI requires substantial capital investment, often not available in developing countries. On the assumption that there is a sufficiently close relationship between leaf area (LA) and leaf dry weight (LDW) and possibly total biomass (TBM), it should be possible to estimate LA from these parameters. Therefore, eight peanut (L.) cultivars varying widely in growth habit were harvested at 10-d intervals, starting from 30 days after planting (DAP) until harvest maturity in 1989 and used to determine LA from both LDW and aboveground TBM. The relationship between LA and LDW and LA and TBM were determined by two statistical models: linear and nonlinear. The general nonlinear model (LA = 0.0234 × LDW) derived from LDW gave the best fit (= 0.98) and standard error (SE = 0.71), compared with the TBM model (LA = 0.0205 × TBM; = 0.95; SE = 0.83). Both LA-LDW and LA-TBM models were validated using data from an experiment conducted in 1985, which showed a good agreement between the estimated and measured LA. The LA-LDW nonlinear model produced estimations close to 1:1 (= 0.98). Although cultivars exhibited disparate morphology and growth habit, specific cultivar models differed only slightly from one another. Therefore, we concluded that the general nonlinear model (LA =0.0234 ✕ LDW) can accurately estimate leaf area of peanut canopies across a wide range of cultivars and growth stages.