Abstract: This paper develops concepts of grapevine canopy microclimate by considering how the canopy presence can alter the climate. Solar radiation levels are particularly affected due to high absorption by leaves. The radiation environment of canopy exteriors is shown to depend on vineyard geometry and ambient radiation levels. The number of leaf layers within grapevine canopies determines the degree of shading, and an optimal canopy density of about three leaf layers is advocated. Three means of altering canopy microclimate are discussed: shoot number control, vigor control, and use of training systems. The interaction between row spacing, shoot number, vigor, and leaf angle in affecting canopy density is illustrated. Within-canopy shading is promoted by high shoot numbers per hectare, wide row spacing, high vine vigor, and vertical leaves. Examples are given of the effect of reduced vigor on improving canopy microclimate. An analysis of different training systems shows that shading is reduced with narrow rows or by canopy division. The review concludes by considering the effects of canopy microclimate on yield, fruit and wine composition, and offers points for further research.

Abstract: The premise that mature lodgepole pine forests are susceptible to mountain pine beetle attack when physiologically stressed was supported experimentally by manipulating the canopy density and availability of nitrogen in a 120—yr—old forest exposed to a high population of beetles. Where canopy density was reduced, ether by us or by the insects, surviving trees significantly increased their resistance to attack over a 3—yr period. Increased resistance was reflected by changes in wood production per unit of leaf area (tree growth efficiency). Improved nitrogen nutrition hastened tree recovery but did not prevent attacks by beetles until growth efficiencies exceeded 100 g of wood production per square metre of foliage. Growth efficiency, as here defined, is an index of vigor that may reflect the relative ability of susceptible trees to produce defensive compounds following attack.

Abstract: Leaf gas exchange, transpiration, water potential and xylem water flow measurements were used in order to investigate the daily water balance of intact, naturally growing, adult Larix and Picea trees without major injury. The total daily water use of the tree was very similar when measured as xylem water flow at breast height or at the trunk top below the shade branches, or as canopy transpiration by a porometer or gas exchange chamber at different crown positions. The average canopy transpiration is about 12% lower than the transpiration of a single twig in the sun crown of Larix and Picea. Despite the similarity in daily total water flows there are larger differences in the actual daily course. Transpiration started 2 to 3 h earlier than the xylem water flow and decreased at noon before the maximum xylem water flow was reached, and stopped in the evening 2 to 3 h earlier than the water flow though the stem. The daily course of the xylem water flow was very similar at the trunk base and top below the lowest branches with shade needles. The difference in water efflux from the crown via transpiration and the water influx from the trunk is caused by the use of stored water. The specific capacitance of the crown wood was estimated to be 4.7 x 10-8 and 6.3 x 10-8 kg kg-1 Pa-1 and the total amount of available water storage was 17.8 and 8.7 kg, which is 24% and 14% of the total daily transpiration in Larix and Picea respectively. Very little water was used from the main tree trunk. With increasing transpiration and use of stored water from wood in the crown, the water potential in the foliage decreases. Plant water status recovers with the decrease of transpiration and the refilling of the water storage sites. The liquid flow conductance in the trunk was 0.45 x 10-9 and 0.36 x 10-9 mol m-2s-1 Pa-1 in Larix and Picea respectively. The role of stomata and their control by environmental and internal plant factors is discussed.

Abstract: The carbon, phosphorus, and water cycles of a subtropical floodplain forest, and related ecosystem characteristics, were studied. Located at 750 m elevation in Puerto Rico (latitude 18? N) the forest had 27 tree species, 3059 stems/ha, a basal area of 42.4 m2/ha, maximum height of 17 m, and a leaf area index of 3.3. Palm (Prestoea montana) dominated the forest, and, with two other species, accounted for 68% of the dominance. Throughfall, stemflow, interception, runoff, transpiration, and evapotranspiration accounted for 81.6, 9.8, 8.6, 77.7, 13.7, and 22.3% of annual rainfall (3725 mm) respectively. The stand carbon storage was 28.77 kg/M2, distributed as follows: aboveground 35.4%, vegetation 44.2%, soil to 1 m depth 55%, palms 10.9%. Vegetation biomass was partitioned as follows: leaves 9.8% (75% are palm leaves), wood 68%, and roots 21.8%. Net aboveground primary carbon productivity (NPP) was 876 g-m-2 yr-'. Average litterfall was 2.4 g.m-2* d-' (palm leaves 32%, other leaves 39%, and wood 10%). Half-lives of decaying material were 188, 306, 462, and 576 d, respectively, for palm leaves still attached to the parent tree, dicotyledonous leaves, palm leaves on the ground, and palm trunks. Total organic carbon concentrations in stream water increased with increasing stream discharge (from 2 g/m3 to 30 g/m3). Watershed export of carbon was 50 g-m-2 yr-' (including 12 g m-2 yr- I in the form of leaf litter). Mean P concentration in palm leaves (1.18 mg/g) was twice that in dicotyledonous leaves (0.64 mg/g). Compared to a rainfall phosphorus input to the watershed of 63 mg m-2 yr-', leaching from the canopy was high (167 mg.m-2 yr-'), as was the loss of P from the watershed (611 mg m-2 yr-'). Phosphorus-conserving mechanisms included a high rate of retranslocation in palms (504 mg m-2 yr-'). In spite of these mechanisms, there was a net P loss from the watershed that ranged from 136 to 544 mg iM-2 yr-'. Periodic flooding, poor soil aeration, intensive year-round rainfall, and low atmospheric saturation vapor pressure deficits are believed to be the main driving forces of the floodplain forest, which exhibits many characteristics typical of lowland rain forests and floodplain wetlands. Rates of NPP, litterfall, and biomass turnover (residence time of 14-17 yr) are faster than expected for the climatic conditions, whereas rates of wood production and storage of organic matter in the vegetation and soil profile are lower than expected for the climate.

Abstract: CANHAM, C.D. (Institute of Ecosystem Studies, Cary Arboretum, Box AB, Millbrook, New York 12545). Suppression and release during canopy recruitment in Acer saccharum. Bull. Torrey Bot. Club. 112: 134-145. 1985.-Patterns of radial growth were used to reconstruct the history of suppression and release during canopy recruitment of Acer saccharum Marsh. in old-growth northern hardwood forests of the Adirondack Mountains of New York. In a stand that had been selectively logged 60-80 years ago, only 20 per cent of canopy trees between 20-40 cm DBH had undergone periods of suppression prior to canopy recruitment. However, in 2 unlogged stands, all of the sampled trees had undergone from 1 to 5 definable episodes of suppression prior to eventual recruitment at an average age of 110-126 years. The mean lengths of periods of suppression (22-28 years in the two unlogged stands), combined with the mean numbers of periods of suppression in each core (2.9-3.1 per tree) indicate that saplings of Acer saccharum responded to canopy openings cr'eated by the death of neighboring trees before eventually replacing an individual directly overhead. The ability to withstand suppression appears to be an essential trait for a life history that allows Acer saccharum to exploit the relatively short-lived pulses of resources created by small canopy openings.

Abstract: The temperature and atmospheric humidity in a tropical lowland rain forest in Costa Rica were measured in order to assess the microclimate in different forest environments. Two disturbed sites, a single tree fall gap (400 m2) and an 0.5 hectare clearing, were compared for periods up to two years after disturbance. Two locations in primary forest, the canopy and understory, were also monitored. Temperatures were highest in the clearing, intermediate in the canopy and gap which were similar, and lowest in the understory. Vapor pressure deficits (VPD) were highest in the clearing, followed by the canopy, the gap and the understory. With regrowth of the vegetation in the gap and clearing sites, the temperatures and vapor pressure deficits significantly decreased. After 1 year, the microclimate at seedling height in the clearing resembled that of the gap, and after two years the microclimate of the gap was very similar to that of the understory. Seasonal differences in temperature and VPD were small compared to differences caused by changes in the stature of the vegetation.

Abstract: A model is derived for the amount of light specularly reflected and polarized by a plant canopy. The model is based on the morphological and phenological characteristics of the canopy and upon the Fresnel equations of optics. The theory demonstrates that the specular reflectance of the plant canopy is a function of the angle of incidence and potentially contains information to help discriminate between species. The theory relates the specular reflectance to botanical condition of the canopy-to factors such as development stage, plant vigor, and leaf area index (LAI).

Abstract: A major impediment to the understanding and modeling of propagation through and backscattering and emission from vegetation canopies has been the lack of canopy attenuation data as a function of frequency, incidence angle, and polarization configuration. This paper presents the results of attenuation experiments conducted for canopies of winter wheat and soybeans in the late spring and early summer of 1984. Attenuation data were acquired at 1.55, 4.75, and 10.2 GHz for horizontal and vertical polarizations at incidence angles near 20° and 50°. In addition, wheat decapitation and soybean defoliation experiments were conducted to evaluate the relative importance of different canopy constituents (such as heads, leaves, and stalks) to the total canopy attenuation. The measured data were compared to calculations based on a model that treats the stalks as parallel elements of a uniaxial crystal and the leaves and branches as randomly oriented disks and needles, respectively. Very good agreement was obtained between theory and experimental observations for the soybean canopy for both polarizations and for the wheat canopy for vertical polarization; however, the model consistently underestimated wheat attenuation (relative to the data) for horizontal polarization. This deficiency of the model is attributed to the fact that it considers all the stalks to be vertically oriented, whereas in reality the stalks exhibit an orientation distribution, although it is centered around the vertical direction.

Abstract: The algal dominated communities immediately above and below the low-water spring level on a moderately exposed Manx shore were investigated by canopy removal experiments. Fucus serratus, Laminaria digitata and L. hyperborea were removed. Competition was shown to be important in determining the zonation of L. digitata and the distribution along the wave exposure gradient of other species such as Alaria esculenta, Desmarestia aculeata and D. viridis, and L. saccharina. Many species of algal epiphytes were early colonizers of canopy removal areas suggesting that competition from canopy algae usually restricts them to an epiphytic habit. The results indicate that interactions between macrophytes are much more important than grazing in structuring these communities.

Abstract: The carbon dioxide and water vapor exchanges of forest canopies can be calculated from the weather using a portfolio of submodels for the canopy processes This paper considers the submodels necessary to calculate these exchanges on an hourly basis and compares the output of the model with measurements of the canopy exchanges made by the energy balance-Bowen ratio method

Abstract: A model was derived to calculate interception loss from a forest canopy on the basis of thrice daily observations of air temperature and relative humidity, daily means of wind run, daily totals of precipitation and the number of rainy hours and of bright sunshine. The forest canopy was characterized by mean tree height, crown density and water storage capacity. The model was calibrated and tested on four separate data sets obtained during 1964, 1965, 1980 and 1981 in the pine forest of the lysimeter station near Castricum, the Netherlands. Model sensitivity was demonstrated for roughness length, the above canopy wind correction factor and relative humidity during rain. Simulated net precipitation explained at least 92 percent of the observed net precipitation, suggesting a good predictive model.

Abstract: Solar radiative transfer through a coupled system of atmosphere and plant canopy is modeled as a multiple-scattering problem through a layered medium of random scatterers. The radiative transfer equation is solved by the discrete-ordinates finite-element method. Analytic expressions are derived that allow the calculation of scattering and absorption cross sections for any plant canopy layer from measurable biophysical parameters such as the leaf area index, leaf angle distribution, and individual leaf reflectance and transmittance data. An expression for a canopy scattering phase function is also given. Computational results are in good agreement with spectral reflectance measurements directly above a soybean canopy, and the concept of greenness- and brightness-transforms of Landsat MSS data is reconfirmed with our computed results. A sensitivity analysis with the coupled atmosphere/canopy model quantifies how satellite-sensed spectral radiances are affected by increased atmospheric aerosols, by varying leaf area index, by anisotropic leaf scattering, and by non-Lambertian soil boundary conditions. Possible extensions to a 2-D model are also discussed.

Abstract: SOME agricultural research issues require that engineers provide continuous monitoring and treatment control of plant environments over seasonal time frames under field-like conditions. In such a system, complete mass balances of C02 and H20 were maintained on six soybean canopies grown in sunlight at two C02 treatment levels, 330 and 660 pmiol mol '.In each set of C02 treatments, the three canopies were differentially watered to create one non-stressed canopy and two water stressed canopies. Seasonal balances were based on daily integrated values of transpiration, daytime C02 exchange and nighttime C02 exchange. Canopies were completely harvested for total biomass and yield determinations at the end of the growing season. Final biomass and yield were increased by C02 enrichment and decreased by water stress. The water stressed high C02 treatments yielded more than the continuously well watered low C02 treatment. On average, the high C02 canopies transpired about 10% less water over the season than did the low C02 canopies. Cumulative seasonal net CO, exchange rate correlated linearly and positively with seasonal biomass accumulation (R = 0.99) and seed yield (R = 0.95). A simple linear correlation between seasonal transpiration and yield (or biomass accumulation) did not hold across C02 treatments (R = 0.16). However, when C02 treatments were separated, yield showed a strong correlation with seasonal transpiration for low C02 (R — 0.95) and high C02 (R = 0.99) conditions. These whole canopy results are based on the continuous competent operation of the environmental chamber systems throughout the 108 day season and confirm the unique utility of this research tool.

Abstract: (1) Papyrus swamps at Lake Naivasha, Kenya and at Busoro, Rwanda, were investigated. The structure of the papyrus (Cyperus papyrus) canopy is described. (2) Aerial biomass was 3245 g m-2 at Naivasha, and 1384 g m-2 at Busoro while the culm densities were 12.7 m-2 and 17.9 m-2, respectively. Combined data from several sites give a linear relationship between aerial biomass and culm density but it does not follow the thinning rule (-3/2 power law). (3) Papyrus umbels on mature culms were larger at Naivasha than at Busoro and their photosynthetic tissues (rays + bracteoles) had mean surface areas per culm of 6275 cm2 and 5242 cm2, respectively. The area of photosynthetic tissue per unit ground area (umbel area index) was 7-0 at Naivasha and 8. 1 at Busoro. (4) The chlorophyll content of the photosynthetic tissue was similar to that recorded for other emergent macrophytes and light interception by the canopy was virtually complete. There was no evidence that these features of the canopy limit productivity. (5) The annual temperature cycles at the two sites were different with the Naivasha site experiencing daily mean temperatures 3 IC, and mean minimum temperatures 10 IC, lower than at Busoro. This may account for the higher biomass at Naivasha, because lower night temperatures reduce respiratory losses. (6) There were differences in the root environment at the two sites with lower conductivity, redox potential and nitrogen concentration at Busoro. This suggests that growing conditions at Busoro were 'poorer' than at Naivasha.

Abstract: SUMMARY (1) Water use by coniferous plantations can lead to water shortages in regions where water is a scarce resource. If water losses are to be reduced by silvicultural practice with minimal effects on growth, it is essential to know where in the canopy are to be found the main sources of water and sinks for CO2. (2) A null-balance porometer was used to measure the stomatal conductance of current-year shoots from different levels, aspects, trees and age-classes in the canopy of a plantation forest of Scots pine (Pinus sylvestris) in eastern England. Concurrent measurements of photosynthesis were made on adjacent shoots by measuring the uptake of 14CO2 over 30 s. Measurements were made in 1976 in each of the months from March to October. (3) Shoot conductance declined during the day as the water vapour saturation deficit increased, but there was little evidence of stomatal closure as a result of internal water deficits, in spite of the drought conditions experienced during the summer months. Maximum values of conductance (0.5-0.7 cm s-') were obtained in September and October. (4) Photosynthetic rates were closely related to the changing incident quantum flux density except at large saturation deficits when rates became CO2 limited as a result of stomatal closure. Maximum rates of photosynthesis were 055 mg m-2 s-. (5) Rates of photosynthesis and conductances of shoots declined with depth in the canopy and varied diurnally with aspect. There were two age-classes of shoot present but it was not possible to establish consistent ratios of performance between them. The variation of photosynthesis and conductance between trees was considerably less than that within a tree. (6) These results demonstrate that most CO2 assimilation occurs in the upper half of the canopy and suggest that water losses in transpiration could be significantly reduced, with minimal effects on growth, by pruning the lower parts of the tree crowns.

Abstract: Sugar maple is becoming more important in oak-hickory forests near the relatively xeric western margin of the eastern deciduous forest. To identify site characteristics conducive to sugar maple in these forests, vegetation, environmental and disturbance history data were obtained for 115 oak-hickory stands in the Missouri river hills and central Ozark Mountains. Detrended Correspondence Analysis ordination of the data revealed clear vegetational gradients in importance of sugar maple and oak species. Sugar maple was most important on soils with high pH and water-holding capacity, whereas white and black oak and flowering dogwood were more common on drier sites with more acidic soils. Topographic exposure, fire and grazing were negatively correlated with sugar maple importance and positively correlated with importance of several oak species. Sapling data suggested that oak species are regenerating successfully only on exposed dry sites despite the ubiquitous presence of canopy oaks capable of producing large seed crops. Sugar maple reproduction, on the other hand, is abundant in most areas where a source of seed is present.

Abstract: Studies were conducted in the Sacramento Mountains, New Mexico, to determine the intluence of juniper (Juniperus monosperma [Engelm.] Sarg.) canopy on understory vegetation. The basal area of grass species was estimated at 6 locations beneath the canopies of 50 one-seed junipers. Other parameters measured were litter depth, canopy height, canopy cover, canopy closure, tree height, trunk diameter, north-south crown diameter, and east-west crown diameter. Locations adjacent to the trunk had the greatest juniper canopy cover and litter depths, and the lowest height to canopy. Locations at the end of the canopy had the least crown cover and litter depths, and the greatest height to canopy. All but one of the grass species had greater basal areas at the edge locations and the least at the interior locations beneath juniper canopies. Pinyon ricegrass(Piptochuetiumfimbriatum [H.B.K.] Hitch.) was the exception; it was never found at the exterior locations. Regression models indicated that shading influenced the basal areas of most grass species. Litter depth was negatively correlated with grass basal cover in only 4 models and positively correlated in 1. Basal area of pinyon ricegrass was positively correlated with trunk diameter, a reflection of tree age, indicating that the grass requires time to become established. Also, basal area of pinyon ricegrass was positively correlated with canopy cover, indicating that this species requires the modified microenvironment afforded by shading.

Abstract: (1) A point-quadrat method and computed tomography were used to reconstruct two-dimensional foliage density distributions in tree and forest canopies using many photographs taken from various positions in a canopy section. (2) The reconstructed canopy profile (the graphical representation of the foliage density distribution in a canopy section) obtained by computed tomography was similar to the pattern of leaf area density distribution obtained by the clipping method. The calculated foliage density was in direct proportion to the actual leaf area density. (3) Canopy profiles could be reconstructed with photographs taken from the ground level alone. (4) The method was applied to a warm-temperate, evergreen, broad-leaved forest, and a two-dimensional forest canopy structure was obtained quantitatively and nondestructively.

Abstract: The relative importance of aboveground and belowground competition to growth and establishment of understory tree seedlings was examined in the Piedmont region of North Carolina. First-year seedlings of three species-red maple (Acer rubrum L.), flowering dogwood (Cornus florida L.) and sourwood Oxydendrum arboreum (L.) DC]-were grown in trenched and untrenched plots under a forest canopy and within a windthrow. Survival and changes in height and leaf area were recorded. Nearly all maple seedlings survived. Those in windthrow plots were significantly larger than those in forest plots. Trenching had little significant effect on maple. Dogwood mortality was greater in untrenched than in trenched plots. Light (as estimated by canopy photographs) was significantly correlated with dogwood seedling size only in trenched plots. Availability of soil resourses, especially water, moderated the positive effect of decreased aboveground competition. Although all sourwood seedlings eventually died, those within the windthrow survived longer than those within the forest. Seedlings of this species are extremely scarce and apparently require both high light and mineral soil for successful establishment.

Abstract: RATES of detachment of soil particles by raindrop impact were measured in the field under corn and soybean canopies in ten minute simulated rainstorms of 40, 50, 75 and 100 mm/h intensity. The percentage of the rainfall volume reaching the ground surface decreased with increasing canopy cover only slightly until 50% cover was attained, and then more rapidly to reach about 40% of that in open ground with 90% cover. Detachment rates under corn increased with canopy cover and were 1.5 to 2.0 times greater at 90% cover than with no cover at all. A similar increase in detachment occurred under soybean at the lowest rainfall intensity, but detachment rates decreased at the other intensities so that at 90% cover they were 20 to 60% of those for bare soil. Inverse relationships were obtained between detachment and rainfall energy for all intensities under corn and at the lowest intensity under soybean; positive relationships were found for the other intensities under soybean. Existing approaches to modeling soil detachment under plants need to be modified to allow for cases where the volume and energy of the rain do not decrease in direct proportion to increases in effective canopy area and where the transformed raindrops are a more efficient detaching agent than the natural rainfall.