Canopy Depth Research Articles

Rainfall interception modelling: Is the wet bulb approach adequate to estimate mean evaporation rate from wet/saturated canopies in all forest types?

The Penman–Monteith equation has been widely used to estimate the maximum evaporation rate (E) from wet/saturated forest canopies, regardless of canopy cover fraction. Forests are then represented as a big leaf and interception loss considered essentially as a one-dimensional process. With increasing forest sparseness the assumptions behind this big leaf approach become questionable. In sparse forests it might be better to model E and interception loss at the tree level assuming that the individual tree crowns behave as wet bulbs (‘‘wet bulb approach”). In this study, and for five different forest types and climate conditions, interception loss measurements were compared to modelled values (Gash’s interception model) based on estimates of E by the Penman–Monteith and the wet bulb approaches. Results show that the wet bulb approach is a good, and less data demanding, alternative to estimate E when the forest canopy is fully ventilated (very sparse forests with a narrow canopy depth). When the canopy is not fully ventilated, the wet bulb approach requires a reduction of leaf area index to the upper, more ventilated parts of the canopy, needing data on the vertical leaf area distribution, which is seldom-available. In such cases, the Penman–Monteith approach seems preferable. Our data also show that canopy cover does not per se allow us to identify if a forest canopy is fully ventilated or not. New methodologies of sensitivity analyses applied to Gash’s model showed that a correct estimate of E is critical for the proper modelling of interception loss.

Tectonic subsidence provides insight into possible coral reef futures under rapid sea-level rise

Sea-level rise will change environmental conditions on coral reef flats, which comprise extensive habitats in shallow tropical seas and support a wealth of ecosystem services. Rapid relative sea-level rise of 0.6 m over a relatively pristine coral reef in Solomon Islands, caused by a subduction earthquake in April 2007, generated a unique opportunity to examine in situ coral reef response to relative sea-level rise of the magnitude (but not the rate) anticipated by 2100. Extent of live coral was measured from satellite imagery in 2003, 2006, 2009 and 2012. Ecological data were obtained from microatolls and ecological surveys in May 2013. The reef was sampled at 12 locations where dense live hard coral remained absent, remained present or changed from absent to present following subsidence. Ecological data (substratum depth, live coral canopy depth, coral canopy height, substratum suitability, recruitment, diversity and Acropora presence) were measured at each location to identify factors associated with coral response to relative sea-level rise. Vertical and horizontal proliferation of coral occurred following subsidence. Lateral expansion of live coral, accomplished primarily by branching Acropora spp., resulted in lower diversity in regions which changed composition from pavement to dense live coral following subsidence. Of the ecological factors measured, biotic factors were more influential than abiotic factors; species identity was the most important factor in determining which regions of the reef responded to rapid sea-level rise. On relatively pristine reef flats under present climatic conditions, rapid relative sea-level rise generated an opportunity for hard coral to proliferate. However, the species assemblage of the existing reef was important in determining response to sea-level change, by providing previously bare substrate with a source of new coral colonies. Degraded reefs with altered species composition and slower coral growth rates may be less able to respond to climate change-induced sea-level changes.

Forest-atmosphere BVOC exchange in diverse and structurally complex canopies: 1-D modeling of a mid-successional forest in northern Michigan

Foliar emissions of biogenic volatile organic compounds (BVOC)—important precursors of tropospheric ozone and secondary organic aerosols—vary widely by vegetation type. Modeling studies to date typically represent the canopy as a single dominant tree type or a blend of tree types, yet many forests are diverse with trees of varying height. To assess the sensitivity of biogenic emissions to tree height variation, we compare two 1-D canopy model simulations in which BVOC emission potentials are homogeneous or heterogeneous with canopy depth. The heterogeneous canopy emulates the mid-successional forest at the University of Michigan Biological Station (UMBS). In this case, high-isoprene-emitting foliage (e.g., aspen and oak) is constrained to the upper canopy, where higher sunlight availability increases the light-dependent isoprene emission, leading to 34% more isoprene and its oxidation products as compared to the homogeneous simulation. Isoprene declines from aspen mortality are 10% larger when heterogeneity is considered. Overall, our results highlight the importance of adequately representing complexities of forest canopy structure when simulating light-dependent BVOC emissions and chemistry.

Understanding turbulent kinetic energy (TKE) stationarity within a forest canopy

Year round measurements of turbulence were taken at heights, above, below, and in the live crown in an old-growth forest in Howland, ME. A technique to determine the stationarity of turbulence kinetic energy (TKE) is presented and used as a classifier of the turbulence intermittency in the nocturnal boundary layer. The results show that both the length of a stationary TKE signal and the scale of intermittency vary with canopy depth. TKE remains stationary for longer periods above the canopy, and shorter periods are observed in the open space below the live crown. Neutral stability conditions exhibit the highest intermittency at all heights. Additionally a new intermittency factor is introduced which allows for characterizing turbulent regimes. The results have broader implications for understanding and identifying turbulent statistics in the stable boundary layer.

Seasonal and within-canopy variation in shoot-scale resource-use efficiency trade-offs in a Norway spruce stand.

Previous leaf-scale studies of carbon assimilation describe short-term resource-use efficiency (RUE) trade-offs where high use efficiency of one resource requires low RUE of another. However, varying resource availabilities may cause long-term RUE trade-offs to differ from the short-term patterns. This may have important implications for understanding canopy-scale resource use and allocation. We used continuous gas exchange measurements collected at five levels within a Norway spruce, Picea abies (L.) karst., canopy over 3 years to assess seasonal differences in the interactions between shoot-scale resource availability (light, water and nitrogen), net photosynthesis (An ) and the use efficiencies of light (LUE), water (WUE) and nitrogen (NUE) for carbon assimilation. The continuous data set was used to develop and evaluate multiple regression models for predicting monthly shoot-scale An . These models showed that shoot-scale An was strongly dependent on light availability and was generally well described with simple one- or two-parameter models. WUE peaked in spring, NUE in summer and LUE in autumn. However, the relative importance of LUE for carbon assimilation increased with canopy depth at all times. Our results suggest that accounting for seasonal and within-canopy trade-offs may be important for RUE-based modelling of canopy carbon uptake.

Woodland habitat structures are affected by both agricultural land management and abiotic conditions

The identification of habitat structures with biologically meaningful links to habitat quality has enabled an increased understanding of wildlife distributions in fragmented landscapes. However, knowledge is lacking of where these structures occur in the landscape. For a broad-scale agricultural landscape, we investigated how the occurrence and abundance of wildlife habitat structures is related to abiotic conditions and land management practices, and whether this differed between old growth and regrowth woodland. We used generalised linear mixed models to investigate the distribution of eight habitat structures in the South-West Slopes bioregion of south-eastern Australia. Only one habitat structure, canopy depth, was related to abiotic conditions alone, whereas only leaf litter cover was related to land management practices only. Each of the other structures (abundance of logs, large trees, hollow-bearing trees, mid-sized trees and dead trees, and amount of native grass cover) was related to a combination and/or interaction of abiotic conditions and land management practices. Old growth woodland had higher log, large tree and hollow-bearing tree abundance, whereas regrowth woodland had higher mid-sized tree and dead tree abundance. Our findings inform key management prescriptions that can be used to improve conservation efforts so they have strong, quantifiable effects on wildlife habitat in temperate agricultural landscapes. Our case study shows that by understanding how management actions in specific abiotic conditions lead to the increased occurrence or abundance of particular habitat structures, management can be spatially targeted to alternative conservation strategies relevant to the landscape of interest.

Characterization of Air Profiles Impeded by Plant Canopies for a Variable-Rate Air-Assisted Sprayer

<abstract> <bold><sc>Abstract.</sc></bold> The preferential design for variable-rate orchard and nursery sprayers requires that the sprayers are able to control the liquid and air flow rates based on the canopy structure in real time. Demand for this advanced feature has increased rapidly with the public demand for reductions in pesticide use. A variable-rate, air-assisted, five-port sprayer had been in development to achieve variable discharge rates of both liquid and air. To verify the capability of varying the airflow rate by changing the fan inlet diameter of the sprayer, air jet velocities impeded by plant canopies were measured at various locations inside tree canopies of three different sizes and foliage densities. Air jet velocities were adjusted by changing the sprayer fan inlet diameter with an airflow regulator and measured with a constant-temperature anemometer coupled with hot-wire probes. Peak air velocity and airflow pressure decreased with foliage density and canopy depth. For the 0.34 m fan inlet diameter, the airflow pressure ratio of the front portion to the back portion of the canopies was 2.45 for a 1.65 m tall and 13.4 leaf area index (LAI) Tsuga canadensis (Tree 1), 1.43 for a 2.35 m tall and 2.5 LAI Ficus benjamina (Tree 2), and 1.64 for a 3.0 m tall and 1.5 LAI Acer rubrum (Tree 3). Similarly, the front-to-back peak air velocity ratios were 8.55, 1.59, and 1.89 for Tree 1, Tree 2, and Tree 3, respectively. Variations were significant for peak air velocities and airflow pressures among the three different tree volumes and foliage densities. Increasing the fan inlet diameter from 0.13 to 0.34 m increased average airflow pressure from 2.84 to 4.01 kg m^-2, from 3.88 to 5.82 kg m^-2, and from 2.46 to 3.75 kg m^-2 inside the canopies of Tree 1, Tree 2, and Tree 3, respectively, while it also increased average peak air velocity from 2.6 to 4.5 m s^-1, from 5.5 to 9.1 m s^-1, and from 3.0 to 5.2 m s^-1 inside the three tree canopies. Therefore, the new sprayer design with an airflow regulator to alter the fan inlet diameter was able to provide variable airflow for different canopy sizes and foliage densities and offered a potentially effective approach to discharge uniform airflow profiles to carry droplets with efficient spray penetration into plant canopies.

Can plasticity make spatial structure irrelevant in individual-tree models?

Distance-dependent individual-tree models have commonly been found to add little predictive power to that of distance-independent ones. One possible reason is plasticity, the ability of trees to lean and to alter crown and root development to better occupy available growing space. Being able to redeploy foliage (and roots) into canopy gaps and less contested areas can diminish the importance of stem ground locations. Plasticity was simulated for 3 intensively measured forest stands, to see to what extent and under what conditions the allocation of resources (e.g., light) to the individual trees depended on their ground coordinates. The data came from 50 × 60 m stem-mapped plots in natural monospecific stands of jack pine, trembling aspen and black spruce from central Canada. Explicit perfect-plasticity equations were derived for tessellation-type models. Qualitatively similar simulation results were obtained under a variety of modelling assumptions. The effects of plasticity varied somewhat with stand uniformity and with assumed plasticity limits and other factors. Stand-level implications for canopy depth, distribution modelling and total productivity were examined. Generally, under what seem like conservative maximum plasticity constraints, spatial structure accounted for less than 10% of the variance in resource allocation. The perfect-plasticity equations approximated well the simulation results from tessellation models, but not those from models with less extreme competition asymmetry. Whole-stand perfect plasticity approximations seem an attractive alternative to individual-tree models.

English

The experiment was conducted by combining two factors namely; irrigation scheduling with three levels and nutrient management with five levels. The two factors were crossed factorially; irrigation treatments were arranged in vertical strips and integrated nutrient management arranged in horizontal&ndash;strip with strip plot design replicated three times. Field soil was sampled for physical and chemical property determinations. Equal amount of irrigation water were applied before the initiation of irrigation treatments. Once the drip system was installed, irrigation was done on the basis of daily evapotranspiration (ETo) value of the previous day. Growth and canopy characteristics such as plant height, stem diameter, lateral branch length, canopy width and canopy depth were measured and canopy cover was estimated. Additionally yield and yield components at harvest were measured from sample fruits. Physiological data such as chlorophyll content, quantum yield, and Ft were assessed. Data were subjected to analysis of variance as per the design using the SAS Software. Among irrigation levels tested, highest total yield 82.14 t ha-1, was recorded from full irrigation treatment followed by 57.30 t ha-1 from 80% ETc irrigation levels and lowest total yield 49.30 t ha-1 from 60% of full irrigation depth. This finding indicated that tomato should be irrigated at full water requirement to get maximum fruit yield. From this investigation, the total fruit yield was recorded from N 185 kg ha-1 P 60 kg ha-1 combination and N 75 kg ha-1 P 50 kg ha-1 treatment combination with 67.483 and 67.31 t ha-1 respectively. Application of N 185 kg ha-1 P 60 kg ha-1 combination (grower&#39;s check) did not contribute to much yield difference but would encourage luxury consumption and environmental pollution. Thus combinations of full irrigation treatment with N 75 kg ha-1 P 50 kg ha -1 nutrient application would be recommended for verification for tomato production around Melkassa. &nbsp; Key words: Drip irrigation, N and P nutrient, evapotranspiration (ETo), ETc, tomato.

Comprehensive ecosystem model‐data synthesis using multiple data sets at two temperate forest free‐air CO2 enrichment experiments: Model performance at ambient CO2 concentration

AbstractFree‐air CO2 enrichment (FACE) experiments provide a remarkable wealth of data which can be used to evaluate and improve terrestrial ecosystem models (TEMs). In the FACE model‐data synthesis project, 11 TEMs were applied to two decadelong FACE experiments in temperate forests of the southeastern U.S.—the evergreen Duke Forest and the deciduous Oak Ridge Forest. In this baseline paper, we demonstrate our approach to model‐data synthesis by evaluating the models' ability to reproduce observed net primary productivity (NPP), transpiration, and leaf area index (LAI) in ambient CO2 treatments. Model outputs were compared against observations using a range of goodness‐of‐fit statistics. Many models simulated annual NPP and transpiration within observed uncertainty. We demonstrate, however, that high goodness‐of‐fit values do not necessarily indicate a successful model, because simulation accuracy may be achieved through compensating biases in component variables. For example, transpiration accuracy was sometimes achieved with compensating biases in leaf area index and transpiration per unit leaf area. Our approach to model‐data synthesis therefore goes beyond goodness‐of‐fit to investigate the success of alternative representations of component processes. Here we demonstrate this approach by comparing competing model hypotheses determining peak LAI. Of three alternative hypotheses—(1) optimization to maximize carbon export, (2) increasing specific leaf area with canopy depth, and (3) the pipe model—the pipe model produced peak LAI closest to the observations. This example illustrates how data sets from intensive field experiments such as FACE can be used to reduce model uncertainty despite compensating biases by evaluating individual model assumptions.

Reducing Ionospheric Effects in InSAR Data Using Accurate Coregistration

Interferometric synthetic aperture radar (InSAR) is a valuable tool for the study of geophysical phenomena such as crustal deformation, ice motion and structure, and vegetation canopy depths, but it is adversely affected by uncharacterized inhomogeneities in ionospheric propagation delay. Ionospheric disturbances distort both InSAR phase and correlation maps. Here, we present a method to compensate ionospheric propagation variations using accurate image coregistration. This significantly improves both the interferometric coherence and phase accuracy. An azimuth gradient in the total electron content (TEC) from a spatially variable ionosphere results in a range-dependent azimuth phase gradient being added to the phase histories of the pixels being imaged. These phase gradients are equivalent to Doppler shifts, and thus they cause azimuth offsets between the actual and imaged positions of the pixels. Measuring these offsets accurately permits estimation of the gradient and correction of the interferograms for much of the phase distortion, resulting in more accurate estimates of coherence. We show an example over Greenland where the TEC variation causes the correlation to drop from about 0.7 to about 0.2 in one region if spatially varying offsets are not accounted for; it also adds an estimated 4.4 radians of interferometric phase over an 80 km InSAR scene. After applying our algorithm, we find that the correlation in regions affected by the ionospheric inhomogeneity becomes comparable to correlation in the rest of the image. In a more challenging example over Iceland, we show that our method improves the correlation from 0.15 to 0.25 in some areas.

Spray Deposition inside Tree Canopies from a Newly Developed Variable-Rate Air-Assisted Sprayer

Abstract. Conventional spray applications in orchards and ornamental nurseries are not target-oriented, resulting in significant waste of pesticides and contamination of the environment. To address this problem, a variable-rate air-assisted sprayer implementing laser scanning technology was developed to apply appropriate amounts of pesticides based on tree canopy characteristics including tree height, width, volume, foliage density, and occurrence. The new sprayer performance was evaluated in an apple orchard by quantifying spray deposition inside canopies at three different growth stages (leafing, half-foliage, and full-foliage) with three sprayer treatments: the new variable-rate sprayer (S 1 ), the same sprayer without the variable-rate function (S 2 ), and a conventional air-blast sprayer (S 3 ). Their spray coverage and deposits inside canopies were measured and compared with water-sensitive papers and nylon screens. The three sprayer treatments provided fairly consistent spray coverage and deposits in the spray direction (or canopy depth direction) at the leafing stage. The variations in spray coverage and deposits in the spray direction increased considerably for S 2 and S 3 at the half-foliage and full-foliage stages. S 1 produced better uniformity in spray coverage and deposits across the tree height direction than S 2 and S 3 at all growth stages. Compared to constant-rate sprayers, the new variable-rate sprayer only consumed 27% to 53% of the spray mixture while still achieving adequate spray coverage inside the canopies. In addition, the spray deposition from the new sprayer was very consistent regardless of the canopy growth stage. Therefore, the new sprayer increased spray efficiency and improved spray accuracy by greatly lowering the possibility of overspray, resulting in reduced spray costs and potential reduction of environmental pollution.

Contrasting effects of sampling scale on insect herbivores distribution in response to canopy structure

Species diversity of insect herbivores associated to canopy may vary local and geographically responding to distinct factors at different spatial scales. The aim of this study was to investigate how forest canopy structure affects insect herbivore species richness and abundance depending on feeding guilds' specificities. We tested the hypothesis that habitat structure affects insect herbivore species richness and abundance differently to sap-sucking and chewing herbivore guilds. Two spatial scales were evaluated: inside tree crowns (fine spatial cale) and canopy regions (coarse spatial scale). In three sampling sites we measured 120 tree crowns, grouped n five points with four contiguous tree crowns. Insects were sampled by beating method from each crown and data were summed up for analyzing each canopy region. In crowns (fine spatial scale) we measured habitat tructure: trunk circumference, tree height, canopy depth, number of ramifications and maximum ramification level. In each point, defined as a canopy region (coarse spatial scale), we measured habitat structure using a vertical cylindrical transect: tree species richness, leaf area, sum of strata heights and maximum canopy height. A principal component analysis based on the measured variables for each spatial scale was run to estimate habitat structure parameters. To test the effects of habitat structure upon herbivores, different general linear models were adjusted using the first two principal components as explanatory variables. Sap-sucking insect species richness and all herbivore abundances increased with size of crown at fine spatial scale. On the other hand, chewer species richness and abundance increased with resource quantity at coarse scale. Feeding specialization, resources availability, and agility are discussed as ecological causes of the found pattern.

Association of elevation error with surface type, vegetation class and data origin in discrete-returns airborne LiDAR

Airborne LiDAR (light detection and ranging) data are now commonly regarded as the most accurate source of elevation data for medium-scale topographical modelling applications. However, quoted LiDAR elevation error may not necessarily represent the actual errors occurring across all surfaces, potentially impacting the reliability of derived predictions in Geographical Information Systems (GIS). The extent to which LiDAR elevation error varies in association with land cover, vegetation class and LiDAR data source is quantified relative to dual-frequency global positioning system survey data captured in a 400-ha area in Ireland, where four separate classes of LiDAR point data overlap. Quoted elevation errors are found to correspond closely with the minimum requirement recommended by the American Society of Photogrammetry and Remote Sensing for the definition of 95% error in urban areas only. Global elevation errors are found to be up to 5 times the quoted error, and errors within vegetation areas are found to be even larger, with errors in individual vegetation classes reaching up to 15 times the quoted error. Furthermore, a strong skew is noted in vegetated areas within all the LiDAR data sets tested, pushing errors in some cases to more than 25 times the quoted error. The skew observed suggests that an assumption of a normal error distribution is inappropriate in vegetated areas. The physical parameters that were found to affect elevation error most fundamentally were canopy depth, canopy density and granularity. Other factors observed to affect the degree to which actual errors deviate from quoted error included the primary use for which the data were acquired and the processing applied by data suppliers to meet these requirements.

Simulation of oil productivity and quality of N–S oriented olive hedgerow orchards in response to structure and interception of radiation

Simulations of oil yield and quality are presented for N–S oriented, hedgerow olive orchards of a range of structures (viz. canopy depth, canopy width, canopy slope and row spacing) using responses of yield and quality parameters to solar irradiance on canopy walls measured in a range of orchards, cv. Arbequina, in Spain. Results reveal that orchard yield of hedgerows of rectangular shape reaches a maximum when canopy depth equals alley width (row spacing−canopy width) and decreases at wider spacing, and/or with wider canopies, as the length of productive row decreases per unit area. Maximum yields for 4-m deep canopies were 2885kgha−1 at 1-m width and 5-m row spacing, 2400kgha−1 at 2-m width and 6-m spacing, and 2050kgha−1 at 3-m width and 7-m spacing. Illumination of canopies can be increased by applying slopes to form rhomboidal hedgerows. Substantial yield advantage can be achieved, especially for wide hedgerows, partly by closer row spacing that increases row length per unit area. By comparison, responses to latitude in the range 30–40° are small and do not warrant different row spacing. Oil quality parameters also respond to orchard structure. Responses are presented for oleic and palmitic acid, stability, and maturity index. Oleic acid content declines as alley spacing increases and is smaller, shallow than in wide, deep canopies. Palmitic acid content, stability, and maturity index increase with row alley spacing and are greater in narrow, shallow than in wide, deep canopies.

Photosynthetic traits in Australian wheat varieties released between 1958 and 2007

We investigated crop and leaf photosynthetic traits in a set of Australian wheats released between 1958 and 2007. Environmental variation generated a range in pre-anthesis radiation use efficiency between 1.54 and 2.68gMJ−1. For these contrasting conditions, radiation use efficiency increased linearly with year of cultivar release at a rate of 0.012gMJ−1 per year.The fraction of incident radiation at different depths in the canopy profile increased linearly with year of cultivar release. Leaf greenness increased with year of cultivar release but the magnitude of this effect varied in the canopy profile; SPAD increased 0.24unitsyr−1 between 0 and 0.2m, 0.44unitsyr−1 between 0.2 and 0.3m, 0.22unitsyr−1 between 0.3 and flag leaf, and 0.11unitsyr−1 for the flag leaf. There was a sharp extinction of nitrogen concentration with canopy depth relative to the extinction of radiation in older varieties that shifted to a flatter nitrogen-radiation extinction in newer varieties. Increased radiation use efficiency in newer varieties was associated with the relaxation in the coupling between the extinction of nitrogen and radiation in the profile which was in turn partially related to the improved nitrogen status of modern varieties, as quantified with the nitrogen nutrition index.Stomata density (range: 38–56mm−2), stomata length (0.043–0.055μm), stomata width (0.024–0.032μm), light-saturated photosynthesis (9.3–19.6μmolm−2s−1) and respiration (1.6–7.3μmolm−2s−1) measured in the flag leaf at anthesis were unrelated to year of cultivar release.Shifts in crop-level traits associated with breeding and selection for yield were a likely source of improvement in pre-anthesis radiation use efficiency.

Throughfall deposition and canopy exchange processes along a vertical gradient within the canopy of beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst)

To assess the impact of air pollution on forest ecosystems, the canopy is usually considered as a constant single layer in interaction with the atmosphere and incident rain, which could influence the measurement accuracy. In this study the variation of througfall deposition and derived dry deposition and canopy exchange were studied along a vertical gradient in the canopy of one European beech (Fagus sylvatica L.) tree and two Norway spruce (Picea abies (L.) Karst) trees. Throughfall and net throughfall deposition of all ions other than H+ increased significantly with canopy depth in the middle and lower canopy of the beech tree and in the whole canopy of the spruce trees. Moreover, throughfall and net throughfall of all ions in the spruce canopy decreased with increasing distance to the trunk. Dry deposition occurred mainly in the upper canopy and was highest during the growing season for H+, NH4+, NO3− and highest during the dormant season for Na+, Cl−, SO42− (beech and spruce) and K+, Ca2+ and Mg2+ (spruce only). Canopy leaching of K+, Ca2+ and Mg2+ was observed at all canopy levels and was higher for the beech tree compared to the spruce trees. Canopy uptake of inorganic nitrogen and H+ occurred mainly in the upper canopy, although significant canopy uptake was found in the middle canopy as well. Canopy exchange was always higher during the growing season compared to the dormant season. This spatial and temporal variation indicates that biogeochemical deposition models would benefit from a multilayer approach for shade-tolerant tree species such as beech and spruce.

Model to Predict Spray Deposition in Citrus Airblast Sprayer Applications: Part 2. Spray Deposition

A model was developed to simulate spray dispersion and predict pesticide deposition in citrus trees when using an air-carrier sprayer. The model can be split into two parts: (1) dispersion, which focuses on spray transport and droplet dispersion in open space, and (2) deposition, which focuses on spray transport and deposition inside a canopy. The dispersion part of the model and its validation were presented in the first part of this article. This second part presents details of the deposition component of the model and validation with data from a field experiment. The experiment involved spray application of a fluorescent dye solution to orange trees using a conventional airblast sprayer, and sampling leaves at two heights and four canopy depths. The spray treatments, consisting of combinations of two nozzles (Albuz ATR Lilac and Blue) and two forward speeds (2.4 and 4.8 km h-1), were applied in a randomized complete block design with five replications. Samples were analyzed by fluorometry, and leaf area was measured with an area meter. The results showed good agreements between the model output and the experimental data for canopy deposition, with the best predictions yielding a modeling efficiency and correlation coefficient of 61.3% and 0.92, respectively. However, the ground deposition data were overly underpredicted by more than three orders of magnitude and were not considered appropriate. This shortcoming notwithstanding, the model has potential for meeting the set objectives, and it has been implemented in an expert system to assist spray applicators in making decisions critical for efficient spray operations.

Canopy radiation transmission for an energy balance snowmelt model

To better estimate the radiation energy within and beneath the forest canopy for energy balance snowmelt models, a two stream radiation transfer model that explicitly accounts for canopy scattering, absorption and reflection was developed. Upward and downward radiation streams represented by two differential equations using a single path assumption were solved analytically to approximate the radiation transmitted through or reflected by the canopy with multiple scattering. This approximation results in an exponential decrease of radiation intensity with canopy depth, similar to Beer's law for a deep canopy. The solution for a finite canopy is obtained by applying recursive superposition of this two stream single path deep canopy solution. This solution enhances capability for modeling energy balance processes of the snowpack in forested environments, which is important when quantifying the sensitivity of hydrologic response to input changes using physically based modeling. The radiation model was included in a distributed energy balance snowmelt model and results compared with observations made in three different vegetation classes (open, coniferous forest, deciduous forest) at a forest study area in the Rocky Mountains in Utah, USA. The model was able to capture the sensitivity of beneath canopy net radiation and snowmelt to vegetation class consistent with observations and achieve satisfactory predictions of snowmelt from forested areas from parsimonious practically available information. The model is simple enough to be applied in a spatially distributed way, but still relatively rigorously and explicitly represent variability in canopy properties in the simulation of snowmelt over a watershed.

Yield characteristics of N–S oriented olive hedgerow orchards, cv. Arbequina

Profiles of yield (g oil m −2) and yield components, fruit density (m −2), size as dry weight (DW) (g), and oil% DW were measured in 11 N–S oriented hedgerow orchards, cv. Arbequina, of various height and alley width combinations in Spain. Profiles of daily shortwave solar radiation incident vertically on the canopy walls (MJ m −2) calculated by a canopy illumination model were weakly exponential, revealing the importance of alley width in determining the diurnal persistence of sunlit canopy wall to depth. Strong positive linear relationships were established between radiation incident on canopy walls and fruit size and oil% over the entire canopy depth in all orchards. In contrast, fruit density was closely related to incident radiation on canopy walls only in the lower profile where incident daily solar radiation was <6 MJ m −2 during oil production in October. The consequence was a weaker relationship between yield (g oil m −2) and incident radiation on canopy walls than between the size and oil% components. Explanation is found in the impact of pruning applied to maintain hedgerow height that removes fruit in the current year. Results emphasize the importance of alley width:height relationships in determining complete illumination of canopy walls in hedgerow orchards giving guidance to questions of optimal orchard structure for maximum yield. They also demonstrate importance and need for work on canopy management to maintain yield in upper canopies of hedgerows where fruit are large and also have high oil%.