Part Of Canopy Research Articles

Factors controlling transpiration of mature field-grown tea and its relationship with yield

The objective of this experiment was to determine the factors influencing the transpiration rates of mature, clonal tea ( Camellia sinensis L.) and estimate its transpiration efficiency. The heat pulse technique was used to measure transpiration rates of tea plants growing in the field as part of extensive canopies at Talawakelle, Sri Lanka during the period between 1 January and 19 February 1997. Irrigation and shading treatments were used to determine the influence of soil water content ( S) and irradiance on transpiration rate. The transpiration rate declined only slightly when S decreased from field capacity (44%) to 33%. However, when S declined below 33%, the transpiration rate showed a rapid decline from 1.6 to 0.7 l per plant per day at 15% S. When S was near field capacity, maximum transpiration rates of 0.53–0.93 l plant −1 h −1 occurred between 1000 and 1500 h. The corresponding maxima when the S was near permanent wilting point (i.e. at −1.5 MPa matric potential) were 0.27–0.53 l plant −1 h −1. Transpiration decreased linearly with decreasing irradiance throughout the range of radiation levels tested (i.e. from 100 to 15% of full sunlight) at a rate of 0.031 l per plant per day per % reduction in solar irradiance. The daily transpiration rates of tea plants (0.42–1.07 l per plant per day) under the natural shade of Grevillea robusta were considerably lower than the value of tea plants in the open, 3.511 l per plant per day. Spraying of an antitranspirant, Kaolin, decreased canopy temperature by 2–4°C and especially around mid-day. Kaolin also decreased transpiration slightly during the period between 1000 and 1500 h. Transpiration efficiency ( T E) was 9.637 kg ha −1 (made tea) mm −1 of water transpired. The relationship between total dry matter yield and the ratio between transpiration and mean saturation vapour pressure deficit also was linear with a proportionality constant of 6.9 g kg −1 kPa.

Role of canopy height in the resistance of Lycopersicon hirsutum f. glabratum to Tuta absoluta (Lep., Gelechiidae)

The objective of this work was to study the effect of plant canopy height on the resistance of the tomato species Lycopersicon hirsutum to the tomato leafminer Tuta absoluta. Determination of the levels of tridecan‐2‐one (2‐TD) and undecan‐2‐one (2‐UD) in L. hirsutum, as well as the leaf area, density and types of trichomes present in L. hirsutum and L. esculentum were made on apical, medium and basal parts of plant canopy. Correlation of these data were made with the following biological characteristics of T. absoluta: rates of oviposition and egg hatching; length of egg, larval and pupal stages; mortality of the larval and pupal stages; pupal weight; and sex ratio. Levels of 2‐TD on leaves of L. hirsutum increased from bottom to top of canopy. Tuta absoluta had higher oviposition and egg hatching, as well as lower mortalities and smaller larval and pupal periods in L. esculentum than in L. hirsutum. Longer pupal period and greater number of small and large mines of T. absoluta were verified in the apical and medium parts of L. hirsutum plants. On the other hand, higher pupal mortality and longer larval periods were obtained in the apical and basal parts of the L. hirsutum plants. Larval mortality was higher in the basal part of those plants. In L. esculentum, leaves from the apical part of the plant promoted lower mortality, longer larval period and greater number of large mines of T. absoluta. However, a shorter pupal period was verified on leaves of the basal part. It appears that an increase in glandular trichome density in L. hirsutum leads to an increase in the levels of 2‐TD, which, in turn slows down larval development.

A mechanism to explain the preservation of leaf litter lenses in coals derived from raised mires

Leaves and other non-woody canopy parts are rarely preserved in coals. Although the pH of pore waters within peat swamps is usually relatively low (≤3.5), providing geochemical conditions that would promote preservation after burial, shed canopy parts may remain at the air–soil interface for periods of up to several months prior to burial by additional organic detritus. Leaf half-life in tropical forests has been reported to range from several weeks to months, depending upon species histology. During this time of exposure on the forest floor, catabolic (internal enzymatic), fungal, bacterial and root degradation, as well as saprophagous scavenging, act upon the least resistant parts to promote decay into hemic and sapric macerals. It is unusual, then, to find well-preserved leaves in peats or coals. When such accumulations are encountered, either permineralized in coal balls or duripartically preserved in lignites, the bedded leaves generally are spatially isolated. Several explanations have been proposed to account for such fossil Lagerstätten that require temporal changes in accumulation or degradation rates. Neither of these mechanisms is required to account for such accumulations. Bedded leaves, showing minimal evidence of subaerial exposure and degradation, have been recovered at depth from a vibracore taken 1 km into the interior of a peat swamp in the Rajang River delta, Sarawak, East Malaysia. Evidence is provided to indicate that such accumulations form within peat substrate depressions resulting from the displacement of rootstocks as trees either die and fall over, or are blown down in severe storms. These localized, acidic water-filled pools act as a natural buffer to the degradation of fallen canopy parts that accumulate therein.

FRUIT CANOPY POSITION EFFECTS ON QUALITY AND STORAGE RESPONSE OF 'TAROCCO' ORANGES

Quality characteristics of mature 'Tarocco' oranges harvested from the northern, southern and interior part of tree canopy was investigated over 10 weeks of storage at 9°C plus 1 week of simulated marketing period at 21°C. No significant differences in fruit mass loss and decay percentage were observed after 5 or 10 weeks of cold storage. After simulated marketing period (SMP) mass loss was significantly higher in fruit from northern part of tree canopy. Differences in mass loss between fruit from interior and southern parts were insignificant. Decay percentage was significantly lower in southern fruit with minimal differences between northern and interior fruit. h * colour values were significantly higher in fruit from interior canopy. After SMP differences in h * colour were insignificant. Fruit canopy position did not affect endogenous ethylene concentration. At harvest and after 10 weeks of cold storage respiration rate was higher in northern fruit, lower in southern fruit and intermediate in fruit from the interior part of canopy. After SMP differences in respiration rates were not significant. Freshly harvested fruit from the external southern side of the tree had higher soluble solids concentration (SSC) and lower acid levels, resulting in higher SSC: acid ratio and improved taste in comparison to fruit from northern and interior parts of canopy. By the end of SMP these differences tended to level out. At harvest ethanol level in the juice was significantly higher in fruit from southern part of canopy. By the end of cold storage and after SMP a sharp increase in ethanol concentration was detected in all samples, with no significant differences in relation to canopy position. SMP resulted in off-flavour development, presumably due to the high levels of ethanol in the juice.

ORCHARD FACTORS AFFECTING FRUIT STORAGE QUALITY AND PREDICTION OF HARVEST DATE OF APPLES

Numerous and well-recognised factors may affect the quality of pome fruits at harvest and following storage. Generally, fruit quality is associated with climatic and soil conditions, tree characteristics and cultural practices. The apple fruit is especially sensitive to low calcium concentration and susceptible to a number of physiological disorders during storage. Many environmental and cultural factors influence calcium content of apple fruits at maturity. When dormancy has been broken and bloom period begins, many important factors come into play that can affect ultimate fruit quality. These are related to fertilisation, pollination, seed number and fruit set. Number of seeds may influence the rate of calcium transport to the apples, probably by production and transport of auxins. On the other hand. fruits, which develop from terminal flowers, are richer in calcium than those developing from lateral ones. The location of fruits in the tree crown is also influencing calcium concentration, and incidence of physiological disorders; more fruits are affected in the upper parts of canopy. This is probably due to a poorer calcium input to these fruits. Cropping level of the tree is also a factor. Fruits from trees with light crops show generally a lower calcium concentration and they are more prone to bitter pit and internal breakdown. It seems that fruits compete in some manner with vegetative tissues for calcium transported from the root system. Summer pruning can have a strong positive effect on fruit quality, which at least in part is associated with increased Ca levels. Calcium treatments have also been shown to reduce the occurrence of physiological disorders. Wide variability of individual fruits within a tree as well as of trees within an orchard block, in respect to fruit maturation and subsequent storability was found to be associated with fruit calcium levels and differences in bloom time. Apples low in calcium show an earlier onset of the endogenous ethylene climacteric as fruits mature on the tree. On the other hand, fruits developed from late blooming flowers were considerably smaller than those from early blooming ones. Fruits from late blooming flowers produced less ethylene, exhibited a lower starch index and developed superficial scald during storage. This indicates that apple cultivars with a prolonged bloom period should be harvested at least twice. The date of harvest plays an important role in the quality of stored apple Ethylene is regarded as a more reliable indicator of physiological maturity than starch hydrolysis. In addition to this information, we attempted to predict the onset of the ethylene climacteric. The rapidity of the development of the ethylene climacteric is related to fruit maturity and we used this developmental phenomenon to predict the optimal harvest date.

Food resource matching by foraging tits Parus spp. during spring‐summer in a Mediterranean mixed forest; evidence for an ideal free distribution

We analysed whether patterns of microhabitat use by Blue Tits Parus caeruleus, Great Tits Parus major and Crested Tits Parus cristatus inhabiting a mixed forest consistently matched the patterns of food availability experienced by foraging birds during spring‐summer. The use of five microhabitats by each bird species (the foliage of three tree species, shrubs and ground) and the availability of food in trees during the prebreeding, breeding and post‐breeding periods of the birds' annual cycle were measured. All three tit species foraged mainly in the outer part of tree canopies (small branches and leaves or needles). Tit distributions between tree species matched food resource distributions irrespective of overall food resource levels, which varied four‐fold between the study periods, and tit species. Tits also exploited secondary microhabitats (shrubs and ground) in periods of low food availability; Blue Tits tended to use shrubs, whereas Great and Crested Tits foraged on the ground. Between‐trees distributions fitted that expected from an ideal free distribution, suggesting that food availability and intraspecific exploitative competition were the main factors governing tree use by tits. In contrast, patterns of use of secondary microhabitats (shrubs and ground) seemed to indicate a role for the species‐specific morphological configurations of each tit species since Blue Tits are better adapted to hang and tended to forage in shubs, whereas Great and Crested Tits are better adapted to feed on horizontal surfaces and tended to forage on the ground. No evidence of interspecific interactions was observed. Overall, the results pointed to an independent exploitation of Mediterranean mixed forest by each bird species, food availability and food accessibility being the main factors affecting microhabitat use by foraging tits.

Estimating the contribution of canopy components to direct light interception of apple trees using a laser-assisted scanning device

To estimate the amount of direct sunlight intercepted by any part of an apple tree canopy, a modified point quadrat method was developed. The relative direct light interception by different components within apple tree canopies was estimated by a laser scanning method, based on moving a laser beam above the canopy in set patterns. The percent of contacts of the laser-simulated ‘sunbeam’ on leaves on different shoot types or other parts of the canopy was determined in several different tree forms. The laser was positioned by two different methods: a two-axis laser positioner and a solar arc positioning device. Two two-axis laser positioner allowed an above-canopy laser to be rotated accurately in both vertical and horizontal planes to provide a grid of positions surrounding the canopy surface. The solar arc positioning device was designed to move the pole-mounted laser along an artificial solar track to simulate the movement of the sun throughout a day. Various sampling schemes were examined to develop efficient sampling procedures for evaluating the proportion of relative direct light interception by different components of the tree canopy. No particular patterns of light interception by different shoot types were found in three tree forms. From these analyses, to overcome the natural variations in tree canopy characteristics, general recommendations are to use a solar are positioning device to provide an angular range over which measurements can be taken, to use 75–100 laser samples per tree and to distribute the sampling points over the whole canopy with 3–4 are heights per tree.

張掖のオアシスのコムギ畑における乱流輸送量の測定とモデル計算

Simultaneous measurements of water vapor, sensible heat, carbon dioxide and momentum fluxes were made above and within plant canopies of a wheat field at Zhangye oasis in June, 1992, using the eddy correlation method. The diurnal variations of energy and carbon dioxide budget components and related meteorological parameters were obtained. Vertical fluxes of water vapor, sensible heat and carbon dioxide above plant canopies were predominant, compared with the fluxes at the middle layer of the plant canopy. This implies that, in the daytime, the upper part of dense plant canopies (LAI = 5) was an active source region of water vapor as well as an active sink region of carbon dioxide. A moderate and steady wind from the surrounding warmer desert and Gobi areas increased an upward water vapor flux and caused a significant downward sensible heat flux above plant canopies ; these phenomena are the so-called oasis effects peculiar to the arid region. The diurnal variations of turbulent fluxes and related quantities observed in a wheat field were compared with the results of Goudriaan's simulation model. The model simulates well some primary characteristics of wheat crop micrometeorology ; large loss of latent heat in upper parts of plant canopies, and a significant downward sensible heat flux under moderate wind speed conditions.

Detection of turbulent coherent motions in a forest canopy part II: Time-scales and conditional averages

Turbulent exchanges between plant canopies and the atmosphere are known to be strongly affected by intermittent coherent motions, which appear on time traces of turbulent variables as periodic, large-amplitude excursions from the mean. Detecting these features requires objective and powerful signal analysis techniques. We investigate here the possibilities offered by the recently developedwavelet transform, presented in a companion paper. For this purpose, a set of data acquired in a 13.5 m high pine forest in southwestern France was used, which provided time series of wind velocities and air temperature recorded at two levels simultaneously, under moderately unstable conditions. Firstly, a duration scale of the active part of coherent motions was estimated from the wavelet variance. Then, we focused on the detection itself of large-scale features; several wavelet functions were tested, and the results compared with those obtained from more classical conditional sampling methods such as VITA and WAG. A mean time interval Δ=1.8h/u* (h being the canopy height andu* the friction velocity) between contiguous coherent motions was obtained. The features extracted from the various traces and ensemble-averaged over 30 min periods appeared very similar throughout the four hours of data studied. They provided a dynamic description of the ejection-sweep process, readily observable at both levels. An alternate Reynolds decomposition of the instantaneous turbulent fields, using the conditionally averaged signals, allowed the relative importance of large- and small-scale contributions to momentum and heat fluxes to be estimated. The results were found to be in good agreement with comparable studies.

Detection of turbulent coherent motions in a forest canopy part I: Wavelet analysis

Turbulence measurements performed at high frequencies yield data revealing intermittent and multi-scale processes. Analysing time series of turbulent variables thus requires extensive numerical treatment capable, for instance, of performing pattern recognition. This is particularly important in the case of the atmospheric surface layer and specifically in the vicinity of plant canopies, where largescale coherent motions play a major role in the dynamics of turbulent transport processes. In this paper, we examine the ability of the recently developedwavelet transform to extract information on turbulence structure from time series of wind velocities and scalars. It is introduced as a local transform performing a time-frequency representation of a given signal by a specific wavelet function; unlike the Fourier transform, it is well adapted to studying non-stationary signals. After the principles and the most relevant mathematical properties of wavelet functions and transform are given, we present various applications of relevance for our purpose: determination of time-scales, data reconstruction and filtering, and jump detection. Several wavelet functions are inter-compared, using simple artificially generated data presenting large-scale features similar to those observed over plant canopies. Their respective behaviour in the time-frequency domain leads us to assign a specific range of applications for each.

Energy Budget in a Paddy Field

Characteristics of diurnal variations of sensible and latent heat fluxes above and within plant canopies were presented, using the data obtained by the eddy correlation method. The results show that the latent heat fluxes above plant canopies are much larger than those within plant canopies and that they are also much larger than sensible heat fluxes above plant canopies. The upper part of plant canopies contributes as a sink for sensible heat and a source of water vapor. The downward sensible heat fluxes could be readily observed in a paddy field. Model calculation shows that this may be caused by combinations of several factors such as lower insolation, higher air temperature, and higher wind speed.

Sediment Facies, Depositional Environments, and Distribution of Phytoclasts in the Recent Mahakam River Delta, Kalimantan, Indonesia

The Mahakam River delta is a tide- and wave-dominated delta located on the edge of the Kutei basin, eastern Kalimantan, Borneo. It is a coastal deltaic sequence, Neogene to Holocene in age, from which all recoverable hydrocarbons (crude oil and natural gas) are considered to be derived from kerogen III predecessors. However, a complete understanding of the types of sediments sourcing the hydrocarbons has not yet been achieved. A vibracoring program sampled the principal fine-grained depositional environments in two transects; one within the fluvially-dominated regime, one within the tidally-dominated regime. Ten sedimentary facies are distinguished and phytoclasts have been recovered from all environments of deposition. Canopy parts from the mixed tropical forest community are preserved throughout the delta, whereas dicotyledonous angiosperm mangroves are restricted to the subtidal zone and delta front. Nypa parts are preserved in most depositional environments. In sites where there appears to be an absence of macrodetritus, dispersed cuticle is recoverable. Identifiable plant parts include wood and fibrous tissues, Nypa petioles and leaf laminae, dicotyledonous angiosperm leaves and isolated cuticles, fruits and seeds, roots and rootlets, and moss. Dammar is found either as dispersed resin ducts or amorphous clasts. Additional biotic components found in bedded plant littersmore » include insects, gastropods, bivalves, sand dollars, ostracods, and crabs. Fluvial channels and depositional sites associated with these systems in the delta front can be differentiated from Nypa swamps and mixed tropical hardwood-palm swamps based on their phytological components and accessory biotic elements. 39 refs., 10 figs., 3 tabs.« less

Assessment of production and dispersal of inoculum ofAlternaria Macrospora in various parts of the cotton canopy

Morning and evening counts of spores ofAlternaria macrospora in a cotton (Gossypium barbadense) field were assessed for the number of spores (a) produced on the last night, (b) dispersed during the day, and (c) retained in the spore reserve on leaves. Throughout the season, 1 m2 of the field produced (P) and dispersed (D) approximately 163 x 106 and 137 x 106 spores, respectively. The 16% discrepancy between P and D values reflects experimental errors. Most spores were produced on shed leaves on the ground, fewer on leaves in the lower part of the canopy, and least on leaves in the upper canopy. The contribution to total D decreased from leaves in the lower part of the canopy, to shed leaves, and to leaves in the upper canopy. In tests with potted plants with spore-bearing lesions attached to various heights of the canopy under various conditions of weather, dispersal of spores at these heights was conditioned mainly by wind velocity, which decreased from the upper to the lower part of the canopy. In leaves close to the ground, approximately 29% of the released spores were removed by sedimentation to the ground. On any one day, the daily rate of D differed from the daily rate of P. On days in which D was higher than P, the difference was due to a reserve of spores remaining on lesions after dispersal during the previous days. In weather adverse for production of new spores, the reserve was depleted within 4 and 6 days in the top and bottom leaves, respectively, but remained relatively high in the shed leaves on the ground; a similar number of days was needed to restore the depleted reserve in sporulation-favorable weather.

Comparison of boom and airblast sprayers on T-trellis apples

SUMMARYT-trellis apple trees treated with combinations of fungicides and insecticides applied with a boom sprayer had a lower percentage of fruit damage from diseases and insects than those treated with an airblast sprayer. With the boom sprayer, chemical deposit was uniform in distribution between outer and inner parts of the tree canopy, but with the airblast sprayer there was more than a threefold difference in deposit between parts of the canopy. The boom sprayer was inferior to the airblast sprayer in the control of apple aphids (Aphis pomi) when vertical top growth (watersprouts) had grown to 0·7–1 m. Management of aphids with a boom sprayer would probably require the control or periodic removal of watersprout growth, or the use of systemic insecticides.

Mediterranean Fruit Fly (Diptera: Tephritidae) in Nature: Location and Diel Pattern of Feeding and Other Activities on Fruiting and Nonfruiting Hosts and Nonhosts

Systematic quantitative observations of locations and diel patterns of activities of adult Mediterranean fruit flies, Ceratitis capitata (Wiedemann), were made in a semiisolated mixed orchard and surroundings in southern Egypt during 4 wk in early autumn 1984. Flies were regularly sighted on all fruiting and nonfruiting hosts, whereas on nonhost vegetation they were observed occasionally. At dawn, both sexes were at rest in upper sunlit parts of tree canopies, where females began primarily feeding and males released pheromone and began calling activities. With increasing temperature and light, flies moved progressively to lower, more shaded positions. Most feeding events occurred on juice oozing from ripe guava and wounds on orange fruit. Bird droppings and leaf surfaces (probably providing bacteria as nitrogen sources) were additional important feeding sites. Male feeding on fruit peaked in the late afternoon; most ovipositions (on orange and guava) also occurred then. The high level of predation on fruit is proposed as an explanation of the origin of lek behavior on foliage. We, as observers, could detect leks by the odor of the male pheromone. Preferred sites for lek formation were the illuminated areas of tree canopies that were on or near fruiting host trees and that were protected by dense foliage from intense predation by Odonata and wasps. The greatest number of calling males, bouts of male-male competition, leks, and mating pairs were found on fruiting citrus trees. Attraction of females to calling males and formation of mating pairs peaked in midmorning and again following hot midday temperatures.

Remote detection of physiological depression in crop plants with infrared thermal imagery.

The infrared thermal imagery was measured concurrently with physiological status in stressed and non-stressed corn and wheat canopies. Thermal images were obtained with an infrared thermography system from a distance of 5 to 20 m. Each thermal image, composed of 512 (H) × 240 (V) pixels with a sensitivity of 0.05°C, was recorded in a video tape every 8 seconds in the field, and analyzed in a laboratory later. A root-reducing treatment was used for simulating environmental stresses, which treatment was carried out by cutting a root system with a thin metal plate at the depth of 20 cm, but brought little apparent change in plant stands. Photosynthesis, transpiration and stomatal conductance in the stressed canopy were depressed, which were accompanied with an inverse change in the canopy surface temperature. The maximum difference in mean surface temperatures of the stressed and non-stressed parts of the canopy was no less than 4.2°C in corn and 3.1°C in wheat. Gaussian distribution of spatial temperature frequency in the stressed part shifted toward higher temperature from that of non-stressed part of the canopy, which was visualized clearly on the pseudo-color thermal image while no visible changes were observed directly from the distance. The infrared imagery was effective, especially, for detecting phisiological depression or for comparing various canopies in their physiological status on a remote and real-time basis.

Biostratinomy of a holocene oxbow lake: A backswamp to mid-channel transect

A study in a Holocene oxbow lake system of the Alabama River, southeastern Gulf Coastal Plain, has provided some insights into potentially preservable macrodetritus and its distribution. A backswamp to mid-channel transect evaluated abandoned channel geomorphology, standing vegetation, forest floor litter, and potential for preservation in the subsurface. Distribution of living taxa is controlled by soil moisture. Plants tolerant of infrequent water stress occur in the backswamp. Higher species diversity characterizes the subaerially exposed levee. Forest floor litter reflects the overall patterns of standing vegetation, yet there is a general trend towards transport of canopy parts towards the backswamp. Leaf litter degrades rapidly and little macrodetritus is recoverable from subaerial levees. Bedded leaf litter occurs in the channel forebank. Backswamp cores are dominated by woody branches, although roots occur in the uppermost sediments. Cores recovered from the oxbow lake preserve leaves as impressions in the muds, in addition to canopy woods, bark, and fructifications. To assess lateral diversity trends, recovered macrodetritus was indexed using the Shannon-Wiener index. Diversity of backswamp and channel cores is lower than that of the surficial forest floor litter. Comparison between indexed backswamp surface litter samples and recovered macrodetritus from backswamp subsurface cores indicates that subsurface diversity is lower. This difference is the result of a variety of factors. Where abandoned channel systems can be traced laterally in the stratigraphic record, the nuances of preserved biofacies may provide a means to distinguish various parts of the system and allow for a more refined interpretation of terrestrial alluvial plain sediments.

Preliminary observations on phytotaphonomic assemblages in a subtropical/temperate Holocene bayhead Delta: Mobile delta, Gulf Coastal Plain, Alabama

Studies conducted in the Holocene bayhead Mobile Delta, southeastern Gulf Coastal Plain, have begun to aid in elucidating the relationships between vegetational communities and macrodetrital litter recovered in various sedimentary environments. The bayhead delta is the result of the Mobile-Tensaw River progradation through a drowned Pleistocene river valley. Geomorphic sites sampled in the upper delta plain include channel forebank, levee, swamp, and abandoned channel (bayou). Channel forebanks are littered with parallel to subparallel oriented logs and branches, but subsurface accumulations of plant organs have not been identified, to date. Although levees are sites in which forest floor litter accumulates, bioturbation by rooting and fluctuating water conditions degrade plant parts. Alluvial and Deep Alluvial Swamps are sites in which prostrate logs and erect tree bases are more prone to being preserved by suspension load sedimentation. Forest floor litter beds of these swamps rarely may be preserved by event deposition (i.e. anomalous flooding). Recovered subsurface plant parts include fragmented woody detritus, bark, and seeds. The site most prone to preserving bedded leaf litter is the abandoned channel. Vegetation surrounding the bayou contributes canopy parts resulting in organic-rich muds. The lower delta plain is the area where passive and active sediment accumulation occurs in open water distributary bays and flanking subaerial levee/marshes. Marshes are inhabited by a herbaceous community in which rooting mats predominate the subsurface samples. Most aerial plant litters degrade or are consumed on the surface of the marsh. Root: shoot ratios have not been assessed, to date. Interdistributary bays infilled by passive sedimentation (flooding) preserve an extensively degraded assemblage of plant parts in a high-organic mud. Interdistributary bays infilled by active sedimentation (crevasse splay) preserve (1) bedded leaf litter horizons in distributary mouth bar sands and adjacent estuarine silty-muds and (2) transported detrital peats in shallows near crevasse channel distributary mouth bars. These litter horizons are composed of plant parts transported from distal Levee and Swamp communities of the transitional and upper delta. Proposed hypotheses to reconstruct plants (organic connection) through the repeated associations of parts found in clastic sedimentary environments must be reevaluated with respect to the taphonomic processes occurring in specific depositional environments.

Experiments on scalar dispersion within a model plant canopy part I: The turbulence structure

This is the first of a series of three papers describing experiments on the dispersion of trace heat from elevated line and plane sources within a model plant canopy in a wind tunnel. Here we consider the wind field and turbulence structure. The model canopy consisted of bluff elements 60 mm high and 10 mm wide in a diamond array with frontal area index 0.23; streamwise and vertical velocity components were measured with a special three-hot-wire anemometer designed for optimum performance in flows of high turbulence intensity. We found that: (i) The momentum flux due to spatial correlations between time-averaged streamwise and vertical velocity components (the dispersive flux) was negligible, at heights near and above the top of the canopy. (ii) In the turbulent energy budget, turbulent transport was a major loss (of about one-third of local production) near the top of the canopy, and was the principal gain mechanism lower down. Wake production was greater than shear production throughout the canopy. Pressure transport just above the canopy, inferred by difference, appeared to be a gain in approximate balance with the turbulent transport loss. (iii) In the shear stress budget, wake production was negligible. The role of turbulent transport was equivalent to that in the turbulent energy budget, though smaller. (iv) Velocity spectra above and within the canopy showed the dominance of large eddies occupying much of the boundary layer and moving downstream with a height-independent convection velocity. Within the canopy, much of the vertical but relatively little of the streamwise variance occurred at frequencies characteristic of wake turbulence. (v) Quadrant analysis of the shear stress showed only a slight excess of sweeps over ejections near the top of the canopy, in contrast with previous studies. This is a result of improved measurement techniques; it suggests some reappraisal of inferences previously drawn from quadrant analysis.

Experiments on scalar dispersion within a model plant canopy part II: An elevated plane source

An experiment is reported in which heat was released as a passive tracer from an elevated lateral line source within a model plant canopy, with hs = 0.85 hc (hs and hc being the source and canopy heights, respectively). A sensor assembly consisting of three coplanar hot wires and one cold wire was used to measure profiles of mean temperature % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaiikamaana% aabaGaeqiUdehaaiaacMcaaaa!390C!\[(\overline \theta )\], temperature variance (Σθ2), vertical and streamwise turbulent heat fluxes, and third moments of wind and temperature fluctuations. Conclusions were: (i) Despite the very heterogeneous flow within the canopy, the observed dispersive heat flux (due to spatial correlation between time-averaged temperature and vertical velocity) was small. However, there is evidence from the plume centroid (which was lower than hs at the source) of systematic recirculating motions within the canopy. (ii) The ratio % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeq4Wdm3aaS% baaSqaaiabeI7aXjaab2gacaqGHbGaaeiEaaqabaGccaGGVaWaa0aa% aeaacqaH4oqCaaWaaSbaaSqaaiaab2gacaqGHbGaaeiEaaqabaaaaa!41DF!\[\sigma _{\theta {\text{max}}} /\overline \theta _{{\text{max}}} \] (of maximum values on vertical profiles) decreased from 1 near the source to an asymptotic value of 0.4 far downstream, in good agreement with previous experimental and theoretical work for concentration fluctuations in the surface layer well above the canopy. (iii) The eddy diffusivity for heat from the line source (KHL) increased, downstream of the source, to a nearly constant ‘far-field’ vertical profile. Within the canopy, the far-field KHL was an order of magnitude larger than KHP, the equivalent diffusivity for a plane source; well above the canopy, the two were equal. The time scale defined by (far-field KHL)/(vertical velocity variance) was independent of height within the canopy. (iv) Budgets for temperature variance, vertical heat flux and streamwise heat flux are remarkably similar to the equivalent budgets for an elevated line source in the surface layer well above the canopy, except in the lower part of the canopy in the far field, where vertical transport is much more important than in the surface layer. (v) A random flight simulation of the mean height and depth of the temperature plume was generally in good agreement with experiment. However, details of the temperature and streamwise turbulent heat flux profiles were not correct, suggesting that the model formulation needs to be improved.