Shaded Positions Research Articles

Grazing impacts on Auchenorrhyncha diversity and abundance on a Scottish upland estate

Abstract. 1. Livestock grazing impacts on insect populations in a variety of ways. For phytophagous insects the impact is primarily a result of altering the structure and species assemblage of vegetation. However not all species react in similar ways and even within an order there may be winners and losers from different grazing regimes.2. A long‐term, replicated, controlled experiment, comprising four grazing treatments, was established within an upland acid grassland area in Scotland. Auchenorrhyncha were sampled by suction sampling and sweep‐netting in the fifth year following the start of the treatments.3. A significant treatment effect was apparent in the suction samples with Auchenorrhyncha abundance being three to four times higher in the ungrazed plots compared to the other treatments. Abundance was also highest from the ungrazed plots in the sweep net samples, but this effect was not statistically significant. Redundancy analysis (RDA) showed that a suite of species which are typical of shaded positions responded with increased abundance in the ungrazed plots.4. The findings demonstrate that the assemblages found in ungrazed areas can be vastly different to those found in even lightly grazed areas and therefore, underline the benefits of varied grazing regimes in maximising diversity. Furthermore, the work underlines the benefit of employing multiple sampling methods.

Daylighting performance evaluation of a bottom-up motorized roller shade

This paper presents an experimental and simulation study for quantifying the daylighting performance of bottom-up roller shades installed in office spaces. The bottom-up shade is a motorized roller shade that opens from top to bottom operating in the opposite direction of a conventional roller shade, so as to cover the bottom part of the window, while allowing daylight to enter from the top part of the window, reaching deeper into the room. A daylighting simulation model, validated with full-scale experiments, was developed in order to establish correlations between the shade position, outdoor illuminance and work plane illuminance for different outdoor conditions. Then, a shading control algorithm was developed for application in any location and orientation. The validated model was employed for a sensitivity analysis of the impact of shade optical properties and control on the potential energy savings due to the use of daylighting. The results showed that Daylight Autonomy for the bottom-up shade is 8–58% higher compared to a conventional roller shade, with a difference of 46% further away from the façade, where the use of electric lighting is needed most of the time. The potential reduction in energy consumption for lighting is 21–41%.

Is nitrogen stress more apparent in shaded, fruiting almond spurs than in exposed, non-fruiting spurs?

SummaryLeaf abscission rates and nitrogen concentrations in persistent leaves were tracked on non-fruiting and fruiting almond [Prunus dulcis (Mill.) D.A.Webb] spurs located in either well-exposed or shaded canopy positions. Fruiting spurs, especially in shaded positions, had higher mid-season leaf abscission rates than did non-fruiting spurs, and the difference in abscission rates between shaded, fruiting spurs and other spur sub-populations increased with tree nitrogen deficiency. Nitrogen concentrations and contents of persistent leaves were lower on fruiting spurs than on non-fruiting spurs. Nitrogen contents of persistent leaves did not decline substantially over the period of kernel development (a period of high nitrogen demand by the fruit) regardless of spur shading and fruiting status, or tree nitrogen status. This indicates that little net nitrogen remobilisation from persistent leaves occurred during this period, even on fruiting spurs on nitrogen-deficient trees. Nitrogen deficiency accentuated nitrogen stress in shaded and fruiting spurs, as indicated by early leaf abscission. However, such differential stress was not reflected by the nitrogen concentration or content of persistent leaves during kernel development. Thus, sampling of persistent leaves from the shaded, fruiting spur sub-population for nitrogen analyses did not provide a practical, more sensitive diagnostic indicator of tree nitrogen status than did conventional leaf sampling from non-fruiting spurs.

Simple tool to evaluate the impact of daylight on building energy consumption

This paper presents a simple building simulation tool for integrated daylight and thermal analysis. The tool is capable of importing the thermal and visual properties for different glazings and shading positions from the Window Information System (WIS) program. A coupled ray-tracing and radiosity methodology is used to derive the daylight levels for different sky conditions. Both detailed daylight distribution for a particular day and time and hourly discrete values on a yearly basis may be obtained. For an integrated simulation the hourly daylight levels are fed into an existing simple thermal simulation program capable of calculating energy demand and the indoor environment. Straightforward control systems for general and task lighting systems have been implemented together with a shading control strategy that adjusts the shading according to the indoor operative temperature, the risk of glare and the profile angle of the sun. The implemented daylight calculation method allows for shades from the window recess and overhang, and for distant shades blocking the sky vault. Comparisons with the ray-tracing program Radiance show that the accuracy of this approach is adequate for predicting the energy implications of photoresponsive lighting control. The amount of input is small, which makes the tool useful for integrated daylight optimisation in the early design process.

Mollusc grazing limits growth and early development of the old forest lichen Lobaria pulmonaria in broadleaved deciduous forests

THIS STUDY AIMS: (1) to quantify mollusc grazing on juvenile and mature thalli of the foliose epiphytic lichen Lobaria pulmonaria, and (2) to test the hypothesis inferring a herbivore defensive role of lichen depsidones in forests with indigenous populations of lichen-feeding molluscs. Lichens were transplanted in shaded and less shaded positions in each of two calcareous broadleaved deciduous forests, one poor in lichens, one with a rich Lobarion community. Preventing the access of molluscs significantly reduced the loss of juvenile L. pulmonaria, particularly in the naturally lichen-poor forest. Molluscs also severely grazed mature thalli in the lichen-poor forest, especially thalli placed under the more shading canopies. Furthermore, reducing the natural concentration of depsidones by pre-rinsing with acetone increased subsequent grazing significantly, showing that lichen depsidones function as herbivore defence in natural habitats. Our results suggest that mollusc grazing may play important roles in shaping the epiphytic vegetation in calcareous deciduous forests, and that recently established juvenile L. pulmonaria thalli seem to be particularly vulnerable.

Sustainable Management of Nutrients in Forage-Based Pasture Soils: Effect of Animal Congregation Sites (5 pp)

Background, Aim and Scope Grazing animals have a dominant effect on the movement and utilization of nutrients through the soil and plant system, and thus on the fertility of pasture soils. Grazing can accelerate and alter the timing of nutrient transfers, and increase the amount of nutrients cycled from plant to soil. Long periods, position of shade, and water resources for grazing cattle can influence the spatial distribution of soil biochemical properties including soil organic carbon (C), total extractable inorganic nitrogen (TEIN), and Melich 1 extractable total phosphorus (TP). The objective of this study is to test whether cattle congregation sites typical on most Florida ranches, such as mineral feeders, water troughs, and shade areas are more nutrient-rich and may contribute more nutrients to surface and groundwater supply than in other pasture locations under Florida conditions. Materials and Methods: Baseline soil samples around and beneath three congregations sites in established (>10 yr) grazed beef cattle pastures at the United States Department of Agriculture (USDA), Agricultural Research Service (ARS), Subtropical Agricultural Research Station (STARS), Brooksville, FL, were collected in 2003, 2004, and 2005. Results: The levels of soil TEIN and TP were significantly (p ≤ 0.001) affected by the interaction of congregation sites and distance away from the center of the sites. Mineral feeders had the highest concentration of TP followed by shades and water troughs. The concentrations of soil TP decreased almost linearly with distance (x = meter) away from the center of the mineral feeders (-5.24x + 55.10; R2 = 0.92; p ≤ 0.001) and the shades (-6.25x + 57.21; R2 = 0.85; p ≤ 0.001). However, the level of TP around the water troughs (-0.25x + 16.91; R2 = 0.09) does not appear to change significantly with distance, staying close to about 13-18 mg kg-1. The levels of TEIN decreased linearly with distance away from the mineral feeders from the center of the shades. A linear model can describe the relationship between TEIN and distance away from the center of shades: -11.3x + 78.2; R2 = 0.95; p ≤ 0.001. The shaded sites (34.25 ± 1.7 mg kg-1) had higher levels than the mineral feeders (7.22 ± 0.60 mg kg-1) or water troughs (10.06 ± 0.8 mg kg-1) sites. Discussion: The higher soil TP near and around the mineral feeders can be attributed to the presence of phosphorus in the supplemental feeds. The average level of soil TP in the mineral feeders of 34.05 ± 0.44 mg kg-1 was not high enough to be of environmental concern. Losses of soil phosphorus by overland flow are becoming a big concern when the concentrations for soil phosphorus exceeded 150 mg kg-1 in the upper 20 cm of soils. With TN, the shaded sites (34.25 ± 1.7 mg kg-1) had either higher levels than the mineral feeders (7.22 ± 0.60 mg kg-1) or water trough (10.06 ± 0.80 mg kg-1) sites. Higher TEIN content at the shade sites may have been more likely due to frequent urination of animals and lack of vegetation immediately adjacent to shades. The lack of vegetation within and/or near the shades then had no uptake mechanism for removal of inorganic nitrogen, unlike the heavy demand for inorganic nitrogen by bahiagrass in other areas of the pasture. An accumulation of TEIN immediately adjacent to shades could lead to a potential point source that would be susceptible to leaching or gaseous losses to the environment. Conclusions: Early results of the study are suggesting that cattle congregation sites in beef cattle operations in Florida are not nutrient-rich, therefore may not contribute more nutrients to surface and groundwater supply under Florida conditions. Recommendations and Perspectives: Since there is no apparent vertical build up or horizontal movement of TEIN and TP in the landscape, we can then surmise that cattle congregation sites may be considered not a potential source of nutrients at the watershed level, at least on the sand ridge soils in Florida. Further research is continuing, including sampling at cattle congregation sites at other locations in north and south Florida, which started in July 2004.

High-density orchards improve the quality of ‘Songold’ plums from lower, more shaded canopy positions

Gel breakdown is a major postharvest problem in ‘Songold’ plums (Prunus salicina Lindl.) that is exacerbated in fruit harvested from lower canopy positions in large trees. Modern high-density orchards with small trees aggressively address this problem through improved light distribution. Fruit quality was observed over two years from different canopy positions in modern plum orchards trained to high-density V- and spindle systems to determine if the incidence of gel breakdown reported in the lower canopy of large, widely spaced plum trees is reduced. There was no significant difference in incidence of gel breakdown in the top or base of the canopy in any of the experiments. Fruit shaded with 80% shade netting, showed an increased tendency of gel breakdown compared to the exposed control. Effective light management in an orchard can improve plum fruit quality.

Synthesis of Integral Photography Images Using Shade™

This paper proposes a new technique to produce high quality integral photography (IP) images. IP is an ideal 3D image display system in which viewers can see realistic 3D images from arbitrary directions without wearing special glasses. In addition, IP is excellent with printing technologies since both pinhole arrays and IP images can be printed on transparent sheets by high resolution printers. Up to now IP images were produced by using CG or photography, but the quality of the CG images was not always satisfactory, since only simple objects such as cones or spheres were used. Shade™ is a commercial three dimensional CG application with abundant powers of expression, and is very popular among professional CG artists especially in Japan, since it is suitable for expressing complex shapes such as human bodies with delicacy. By controlling the camera position of Shade by a script language, and synthesizing an IP image from resultant still images according to our algorithm, the authors achieved the 3D display of realistic scenes created with Shade.

Natural selection and the distribution of shell colour morphs in three species of Littoraria (Gastropoda: Littorinidae) in Moreton Bay, Queensland

The distribution of yellow, brown and red morphs of sympatric species of Littoraria were recorded on mangrove trees of the genus Avicennia within Moreton Bay, Queensland. The roles of background mimicry (leaf vs. bark, dark vs. light), niche selection and thermal tolerance (sunny vs. shaded positions and height above ground) were examined. The yellow advantage found previously in the area was tested. Total yellow morph frequency adjusted to a reduction in leaf background on pruned trees. Morph frequencies in Littoraria species reflect differences in habitat use. L. filosa (high yellow frequency) was more frequently found on leaves at the highest tree levels, while L. luteola (high brown frequency) was more frequently found on branches at lower levels. It is therefore argued that morphs mimic background elements. Previously reported niche selection by yellow and brown morphs of leaf and bark backgrounds is shown to be a result of the distribution of L. luteola on branches and L. filosa on leaves. At warmer times of the year, yellow L. filosa were more common in sunny positions; this is thought to be a result of thermal tolerance. There appears to be some advantage to particular morphs on particular tree types, but this relationship needs to be examined further. Mangrove-dwelling Littoraria are a promising model to investigate molluscan polymorphism. In the past, erroneous identification of sympatric species may have influenced the accuracy of reported patterns. We used allozyme electrophoretic markers as a precise identification technique.

Floral sex ratios and gynomonoecy in Aster (Asteraceae)

Gynomonoecy is the sexual system in which female and bisexual flowers occur on the same plant. This system has received little attention despite the considerable work on other plant sexual systems in the past few decades. Our study examines one hypothesized advantage of having two flower types on a plant, namely that this arrangement permits flexibility in allocation of resources to male and female reproductive functions. We examined 16 species of Aster (Asteraceae), a genus of gynomonoecious, perennial herbs. Plants in this genus produce heads consisting of a whorl of female flowers around a cluster of bisexual flowers. Among field-grown plants we found no evidence that plant size, date, position of heads, rainfall, or shade influenced the proportion of female flowers. A series of greenhouse experiments likewise revealed no large or consistent effects of light, nutrients, or position of heads on the proportion of ray flowers. While floral ratios proved very stable in the face of environmental and physiological variables, they exhibited significant variation among plants and among sibships in most species. We conclude that the presence of two flower types in gynomonoecious asters is not advantageous in permitting flexibility in allocation of resources to male and female functions. We believe that the advantage of the female flowers in aster heads lies either in reducing pollen-pistil interference or in attracting pollinators.

Does Shading Behavior of Incubating Shorebirds in Hot Environments Cool the Eggs or the Adults?

-Birds that nest on the ground in hot environments employ behavioral and physiological mechanisms to prevent the overheating of their eggs and themselves (e.g. egg covering, belly soaking, orientation on the nest, ptiloerection, panting, and gular fluttering). One of the least energetically expensive behaviors employed during incubation at high temperatures is nest shading. During shading, the birds raise themselves onto their tibiotarsi so that the incubation patch is about 2 to 3 cm above the eggs. It has frequently been assumed that birds adopt shading behavior to allow for direct convective cooling of the eggs. However, an alternative hypothesis is that birds rise up onto their tibiotarsi in order to place themselves out of the boundary layer. In doing so, adult birds cool themselves directly by convection. The lowering of the adult's body temperature during nest shading may, of course, cool the eggs indirectly when the bird resumes incubation. We tested these hypotheses using a taxidermic model of a Crowned Plover (Vanellus coronatus), which nests in hot environments in South Africa. Field observations have shown that this species spends 20 to 50% of its time shading when incubating at high environmental temperatures. When we alternated the bird between incubating and shading positions, we found that bird temperature, but not egg temperature, was lowered by shading behavior. Furthermore, wind speed had a significant negative effect on bird temperature but not egg temperature. Therefore, our results support the hypothesis that shading behavior functions to lower the temperature of incubating adults rather than of the eggs. Received 24 September 1996, accepted 14 May 1997. INCUBATION IN BIRDS usually is considered to be a warming process (e.g. Vleck 1981, Whittow 1986). However, bird species that nest on the ground in environments characterized by high daytime temperatures have to employ behavioral and physiological mechanisms to prevent the overheating of their eggs and themselves (Schmidt-Nielsen 1965, Grant 1982, Ward 1990). These mechanisms include egg covering (Maclean 1972), belly soaking (Jayakar and Spurway 1965, Howell 1979, Maclean 1975, Grant 1982, Ward 1988), orientation on the nest, ptiloerection, panting, and gular fluttering (Maclean 1967, 1975, 1976; Grant 1982; Ward 1989a,b). Eggshells of birds nesting in semiarid to arid regions also have reduced water-vapor conductance, increased thickness, and reduced effective pore area (Ar et al. 1974, Vleck et al. 1979, Ward 1987, Arad et al. 1988). Attentive behavior at the nest is thought to be important for maintenance of egg tempera1 E-mail: downs@zoology.unp.ac.za 2 Present address: Mitrani Center for Desert Ecology and Ramon Science Center, Blaustein Institute for Desert Research, Ben Gurion University of the Negev, Sede Boqer 84990, Israel. tures below lethal levels in harsh, hot environments (Grant 1982, Ward 1989a,b). During the heat of the day, incubating shorebirds nesting near the Salton Sea in California spent most of their time shading or loosely sitting over their eggs (Grant 1982). Nest relief occurred about every 10 to 15 min during the heat of the day (Grant 1982). Indeed, many shorebirds that nest in areas of high ambient temperatures shade their eggs at moderate to high temperatures (Maclean 1976, Ward 1989a,b). The Crowned Plover (Vanellus coronatus) is a medium-sized shorebird (average body mass = 167 g; Maclean 1993) that commonly occurs in open grasslands and lightly wooded savannas in sub-Saharan Africa (Ward and Maclean 1989). The nest is a shallow scrape (1 to 2 cm deep) in the ground (Ward 1987). These ground nests may get cold at night, requiring the parent to incubate the eggs to keep them warm. A more stressful period for the incubating birds occurs during the main breeding season, when daytime surface temperatures usually exceed 50?C. During these periods, the eggs require cooling (Ward 1990). Typical egg temperatures in birds vary between 30 and 35?C, and hyperthermia evidently is more injurious to the de-

Intracanopy variation in nitrogen cycling through leaves is influenced by irradiance and proximity to developing fruit in mature walnut trees

Intracanopy variation in net leaf nitrogen (N) resorption and N cycling through leaves in mature walnut (Juglans regia L. cv Hartley) trees were monitored in 3 different years. Differential irradiance among the spurs sampled was inferred from differences among leaves in dry weight per unit area (LW/LA) which varied from 4.0 mg · cm−2 to 7.0 mg · cm−2 in shaded (S) and exposed (E) canopy positions, respectively. Our results, using 15N-depleted (NH4)2SO4 validated the concept that N influx and efflux through fully expanded leaves occurred concurrently during the period of embryo growth. Additionally, it also suggested that N influx into leaves was substantially greater in exposed as compared with shaded canopy positions. Because of its well documented phloem immobility, leaf Ca accumulation was used to better estimate the relative influx of N into exposed and shaded leaves. N cycling varied locally within the tree canopy, i. e. Ca (and presumably N) influx was 100% greater in exposed than shaded tree canopy positions, but influx was not influenced significantly by the proximity of developing fruit. In contrast, both the amount and percentage N efflux was significantly greater during embryo growth in fruit-bearing than defruited spurs. Net leaf N resorption averaged 2–4 times greater (25–30%) in fruit-bearing spurs than the 5–10% decrease in the leaf N content in defruited spurs. Since about 90% of leaf N content reportedly occurs as protein, fruit N demand apparently influenced protein turnover and catalysis in associated spur leaves. The amount of leaf N resorption was greater in exposed than shaded positions in the tree canopy in 2 of the 3 years of data collection. Our data show that like leaf N content, N influx, N efflux and net leaf N resorption vary throughout mature walnut tree canopies under the combined local influences of fruiting and irradiance.

Influence of light exposure on characteristics and storage life of kiwifruit

Abstract Quality and storage life of kiwifruit were investigated on fruits from shaded and exposed positions of the canopy and on fruits artificially shaded and grown in absence of light. At harvest the fruits grown in high light intensity have a high quality and can be stored for a long time; after 25 weeks of cool storage they have a soluble solids concentration > 14° Brix and a flesh firmness of c. 10 N. Fruits from shaded positions of the canopy showed significantly lower mean fresh weight and chlorophyll content (‐35%); at harvest and during storage they were slightly but consistently less firm and had lower soluble solids concentration than exposed fruits. Artificial shading of individual fruit for most of the growing season significantly reduced chlorophyll content in the mesocarp (‐77%), starch and alcohol‐soluble sugars concentration, flesh firmness, soluble content and dry matter, whereas the titratable acidity was significantly increased. The storage life of artificially shaded fruits was significantly reduced in comparison with exposed fruits, with significant increase in weight loss and fruit disease.

DISTRIBUTION OF EGGS OF WESTERN BLACKHEADED BUDWORM, ACLERIS GLOVERANA (WALSINGHAM) (LEPIDOPTERA: TORTRICIDAE), AND OF FOLIAGE OVER THE CROWNS OF WESTERN HEMLOCK, TSUGA HETEROPHYLLA (RAF.) SARG.

AbstractEggs of western blackheaded budworm, Acleris gloverana (Walsingham), were found on the underside of needles of western hemlock, Tsuga heterophylla (Raf.) Sarg., with higher densities in the mid-crown area toward the outer tips of branches. Fringe and dominant trees were preferred oviposition sites over trees in lower crown classes or shaded positions. Vertical differences in needle density were considerable and led to high variability in insect densities when expressed on a per branch basis. When densities of eggs were based on a fresh branch weight basis there was a significant decrease in sample bias caused by the uneven distribution of foliage over the crowns.

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.

The understanding of industrial melanism in the peppered moth (Biston betularia) (Lepidoptera: Geometridae)

Melanic polymorphism in B. betularia has been extensively studied. Correlations between high melanic frequency and high levels of air pollution have been demonstrated. Kettlewell and others have shown that differential bird predation has an important effect on the maintenance of the polymorphism, and coefficients of visual selection have been obtained on the assumption that the moth habitually rests on tree trunks. Computer models based on these selective coefficients show that they are not sufficient accurately to explain observed melanic frequencies. Other non-visual selective factors and weak frequency-dependent selection have been invoked to improve fits. Analysis of the resting positions of moths recorded in the wild demonstrates that B. betularia does not usually rest in exposed positions on tree trunks, but rather rests on the underside of branches, on trunks in shaded positions just below major branch joints or on foliate twigs. The results of a pilot selection experiment, while agreeing qualitatively with Kettlewell's results, suggest that fitness estimates that assume trunk-resting are quantitively incorrect. The error is greatest for melanic moths in rural areas. It is suggested that visual selective coefficients based on a true assessment of the resting behaviour of the moths may considerably improve the fit between computer predictions and observed phenotype frequency distributions.

Factors affecting levels of some phenolic compounds, digestibility, and nitrogen content of the mature leaves ofBarteria fistulosa (Passifloraceae)

Levels of total phenolics, condensed tannins, acid detergent fiber, pepsin/cellulase digestibility, and nitrogen in mature leaves of 26 individuals of the ant-plant,Barteria fistulosa, have been determined. Analysis of the results in terms of the presence or absence of ants and the position of the branch from which the leaves were collected showed no relationship with concentrations of phenolics or fiber and only a weak relationship with digestibility and nitrogen. By contrast, light intensity strongly influenced levels of phenolics, notably condensed tannins, so that mature leaves of individuals growing in direct sunlight were less digestible and appeared to be of lower quality as food for herbivores than did mature leaves of individuals in shaded positions. Possible reasons for the variation in condensed tannin levels are discussed.

Some Effects of Grapefruit Tree Canopy Position on Microclimate, Water Relations, Fruit Yield, and Juice Quality1

Abstract Positional differences among leaf and fruit surface temperatures and water relations of ‘Ruby’ grapefruit (Citrus paradisi Macf.) were related to fruit load and juice quality. Southern top canopy positions experienced the highest temperatures and lower water potentials and yielded more fruit with more soluble solids than other canopy positions. Canopy depth was also an important determinant of fruit yield and early season juice quality. Based on data from 3 trees during 2 seasons, there were greater fruit loads with higher °Brix and lower acidity in the outside canopy positions than in the inside positions. Upper canopy positions tended to have lower acidity and consequently higher °Brix/acid ratios than the lower positions. Abaxial fruit hemispheres were smaller and had a lower percent juice than their paired adaxial fruit hemispheres. Grapefruit from sunlit canopy positions mature earlier than fruit from shaded positions. Since there were more fruit with higher soluble solids in the most exposed canopy positions, daily heat stress and leaf and fruit water stress were not limiting factors in grapefruit yield and juice quality with respect to different tree canopy positions.

Leaf Angle: An Adaptive Feature of Sun and Shade Leaves

Ten woody deciduous dicot species, ranging from obligate sun plants to facultative sun/shade plants, were grown in full sun and approximately 17% of full sun. Observations of leaf orientation showed that the leaves of most species are slanted, some to nearly vertical, in full sun and are more nearly horizontal in the shade. Although no preferential orientation for compass direction was observed, these responses may be useful. The sun position should enhance photosynthetic capacity and efficiency and promote leaf cooling during high solar radiation. The shade position should maximize the individual leaf photosynthetic input.

Transpiration of Abies Concolor

The transpiration rate of Abies concolor (Gord. & Glend.) Lindl. differed considerably between top and bottom sun branches for trees 28 m high or more. This difference changed with the time of day, tree height, time of year, and exposure to sun and shade. The transpiration of 1966 (new) needles was more rapid than for 1-year-old needles and differed according to sun and shade exposure and position on the tree. By mid-August of two different years, the transpiration rate of young and old sun needles of A. concolor was reduced drastically even though air temperatures remained above 18 C and relative humidity dropped to low levels by midday.