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The creosote bush (Larrea tridentata) is a common desert perennial with bifoliate, amphistomatic, divaricate leaves. The leaves can vertically close their folioles and vary their profile with respect to direct solar radiation. Field data from different Mexican deserts showed a significant correlation between foliole aperture and mean foliole inclination: in plants in which folioles were more open, the foliole surfaces were less vertical. In a series of field experiments in the Chihuahuan Desert, foliole aperture varied significantly with the water-status of the plant and the hour of the day. In moist plants, folioles opened in the early morning and closed in the afternoon. Water-stressed plants showed significantly lower foliole apertures. A simulation of the light interception patterns of the plants showed that foliole closure in water-stressed individuals reduces direct radiation interception by around 24%. Most (64%) of the reduction in interception was due to the vertical inclination of the photosynthetic surfaces induced by foliole closure in the water-stressed plants. The rest (36%) of the reduction in interception was due to differential self-shading between foliole pairs, which was higher in the closed folioles of the water-stressed plants, but operated more towards the early hours of the day.

It is regrettable, but not surprising, that phenology has received relatively little attention from ecologists. Phenological data are hard won, accumulating only slowly through careful, daily observations not well suited to the demands of a thesis project or a grant cycle. Organizing coordinated and standardized observations over many sites and many years is a daunting task not much in keeping with the priorities of most granting agencies. Until very recently, it was impractical to simulate realistic diurnal and seasonal climate regimes as a basis for controlled phenological experiments (Wang et al. 1994). Despite these difficulties work on the phenology of woody plants has continued and invites incorporation into a variety of ecological analyses. We convened a symposium at the XVth International Botanical Congress to highlight contemporary work on the phenology of woody species in the hope that this topic would gain wider recognition and support. The papers that follow include most of those presented at the symposium. Helmut Lieth, who has long appreciated the importance of phenological studies (1974), provided an excellent introduction to the symposium. He reported on the long tradition of phenological observation, including contemporary efforts like the International Phenological Gardens that include clonal plantings at sites throughout Europe (Polte-Rudolf 1993). He emphasized the availability of long-term historical records of phenological observations (Lieth 1974; Polte-Rudolf 1993), which provide a basis and reference for current work. Martin Lechowicz drew on some of these historical records to explore the interrelationships among reproductive events and foliar phenology in eastern North American deciduous trees. Kihachiro Kikuzawa presented an overview of his models for foliar phenology, including an outline of their recent extension to questions of coordination between canopy architecture, leaf physiology, and leaf phenology. Takayoshi Koike reports an experimental study that followed the phenological as well as physiological responses of tree seedlings to ele

A canopy of the traditional morphotype of Triticosecale Wittmarck and the new one were analysed in two consecutive years under different climatic conditions. On the basis of dry matter and assimilatory surface of the plant organs during the vegetation period, the following growth indices were determined: RGR, CGR, ULR, ULRc, LAI, LAD, LADc and HI. Radiation use efficiency was also calculated. The two possible strategies of yield formation by analysed triticale plants were discussed.

Diurnal measurements of alfalfa leaf distribution and crop canopy reflectance were made in stressed and unstressed alfalfa plots in Phoenix, AZ. Measurements were made on three dates in January, May, and November. Results showed that heliotropic leaf movements were directly affected by crop water status. Under well-watered conditions, alfalfa leaves tended to track the sun throughout the day, in both the azimuthal and zenithal directions. In the stressed plots, diurnal tracking ability diminished as the day progressed and the canopy assumed a more vertical profile due to leaflet cupping. The stressed canopy then had a lower spectral reflectance (measured at nadir) than the unstressed canopy, in both the red and near-IR wavebands. The Perpendicular Vegetation Index (PVI) decreased with the stress-induced change in architecture while the near-IR/red ratio remained relatively constant. As a result, the near-IR / red ratio was more successful in estimating alfalfa biomass than was the PVI. These results emphasize the need to account for stress-induced architectural differences in plant canopies when using remotely sensed spectral data.

We examined the relationship between stand density and stem quality characteristics for lodgepole pine (Pinuscontorta). The influence of initial stand density on end of rotation log quality was inferred by analyzing data from unmanaged, rotation-age stands. Quality characteristics examined included first log branch diameters, taper, wood density, and the proportion of sapwood. After differences in diameter at breast height were accounted for, only branch size was strongly influenced by stand density. A strong negative exponential relationship was found between the mean of the five largest branches per first log and number of trees per hectare.

The influence of canopy architecture on the irradiance distribution on leaf surfaces in horizontally heterogeneous canopies was investigated using a procedural radiative transfer model. Four model canopies were abstracted as plant stands of 10 rows and 20 plants per row, and the procedural model was executed in conjunction with these digitized canopies. From the resulting distribution of the penetration function, the energy incident on leaf surfaces along the normal was calculated. The irradiance distribution was characterized by formally defining three kinds of irradiance — normal, diminished and null. Gross and net photosynthetic efficiencies due to irradiance in each energy class are presented. Canopy architecture was found to significantly influence the efficiency of energy use by affecting the interception pattern of solar radiation.

Spectral reflectances of Produra wheat were measured at 13 different times of the day at Phoenix, Arizona, on April 14, 1979 using a nadir-oriented hand-held 4-band radiometer which had bandpass characteristics similar to those on current LANDSAT satellites. Different sun altitude and azimuth angles caused significant diurnal changes in radiant return in both visible and near-IR regions of the spectrum and in several vegetation indices derived from them. The magnitude of these changes were related to different canopy architecture, percent cover, and green leaf area conditions. Spectral measurements taken at each time period were well correlated with green leaf area index but the nature of the relationship changed significantly with time of day. Thus a significant bias in the estimation of green leaf area index (GLAI) from remotely sensed spectral data could occur if sun angles are not properly accounted for.

Several studies have shown that little movement of carbohydrate occurs in soybean ( Glycine max (L.) Merr.) from a leaf at one node to nodes more than two removed from the source node. Most light is intercepted in the upper periphery of the soybean canopy, but most of the seed yield occurs on the lower central nodes of the soybean plant. Thus, this study was designed to examine leaf area display and light interception patterns in the crop canopy in relation to yield production sites of two varieties of short-season indeterminate soybeans. Altona and Evans soybeans were planted in South Deerfield, MA on 19 May 1982 in rows 25 cm and 75 cm apart. Plots were overseeded by 50% into a fine sandy loam (Typic Udifluvents) and later thinned to populations of 25, 50 and 75 plants per m 2 . Light readings, taken weekly when weather permitted, were integrated over 1 m across and parallel to soybean rows, with the sensor placed on the ground, 25 and 50 cm above the ground and above the canopy dependent on plant height. Growth samples were taken biweekly with samples for leaf area determination divided into five strata, separated on the basis of point of attachment and display of the leaves. Soybean plants grown in narrow rows (25 cm) had a greater leaf area index, intercepted more light and yielded 23% more than soybeans grown in wide rows. For seed yield there was a variety-row width-density interaction, with Evans requiring a lower density for maximum yield than Altona in the 25-cm row width. Seed yield averaging 346.3 g m −2 for Evans was 32% greater than the average for Altona. Although most light interception, and therefore photosynthate production occurred in the upper regions of the plant canopy, many of the leaves displayed there were attached to nodes lower in the plant. Thus carbohydrates were suppled to lower regions of the plant, from these leaves, where most of the yield was found to occur. However leaves attached low in the canopy were still somewhat shaded by upper leaves, thus it is probable that greater efficiency of production could be obtained by concentrating breeding effects for improved canopy architecture with deeper light penetration into the canopy.

A model for radiative transfer in heterogeneous three-dimensional canopies such as those found in forests is proposed. Its use in estimating important biophysical variables such as leaf area index and canopy architecture from bidirectional canopy reflectance data is discussed. The model and its use in estimating canopy parameters through its inversion are validated with measured canopy reflectance data for corn canopies.

Distributions of assimilates at different times after assimilation of 14CO2 shortly after ear emergence of semidwarf spring wheat differing in leaf angle and row width were similar. The differences in leaf angle were obtained with a normal droopy cultivar and a mutant derived from it and characterized by erect upper leaves. Shortly after emergence, flag leaf laminae and spikes (especially glumes, paleas and lemmas) were the main photosynthesizing parts. Their position in the upper levels accounted for the little effect of canopy architecture on their relative importance for photosynthesis. Leaf sheaths and particularly flag leaf sheaths photo-synthesized as much as about one third of their corresponding lamina. Most of the residual radioactivity at maturity was in the grains., Ledent Jean-François. Assimilation et translocation du 14CO2 chez le froment (Triticum aestivum L.) en fonction de la densité et de la structure du couvert aérien. In: Bulletin de la Classe des sciences, tome 60, 1974. pp. 790-798.

The three-dimensional spatial distribution of leaf areas, leaf angles and leaf azimuths were measured in the experimental stand. Point drops were used to indicate sample leaves. Inclination and azimuth angles were measured by hand. The effect of the forest edge on the canopy architecture extends about one tree height into the stand. The leaf density is twice as large at the edge as in the interior of the stand due to a vertical side at the edge. The leaves in the upper crown and those exposed at the edge are inclined from the horizontal over a wide range of angles. Shade leaves are essentially horizontal. Those exposed to solar radiation at the edge are inclined and oriented with their dorsal surface facing the edge.

Boreal peatlands play a major role in carbon and water cycling and other global environmental processes but understanding this role is constrained by inconsistent representation of peatlands on, or omission from, many global land cover maps. The comparison of several widely used global and continental-scale databases on peatland distribution with a detailed map for the St. Petersburg region of Russia showed significant under-reporting of peatland area, or even total omission. Analysis of the spatial agreement and disagreement with the detailed regional map indicated that the error of comission (overestimation) was significantly lower than the error of omission (underestimation) which means, that overall, peatlands were correctly classified as such in coarse resolution datasets but a large proportion (74–99%) was overlooked. The coarse map resolution alone caused significant omission of peatlands in the study region. In comparison to categorical maps, continuous field mapping approach utilizing MODIS sensor data showed potential for a greatly improved representation of peatlands on coarse resolution maps. Analysis of spectral signatures of peatlands with different types of surface vegetation suggested that improved mapping of boreal peatlands on categorical maps is feasible. The lower reflectance of treeless peatlands in the near- and shortwave-infrared parts of the electromagnetic spectrum is consistent with the spectral signature of sphagnum mosses. However, when trees are present, the canopy architecture appears to be more important in defining the overall spectral reflectance of peatlands. A research focus on developing remote sensing methods for boreal peatlands is needed for adequate characterization of their global distribution.

Observations on crop efficiency and fruit quality of peach trees of ‘Rich May’ grafted onto ‘GF677’ (peach x almond) and ‘Penta’ (Prunus domestica L.) rootstocks are reported. Results were related to canopy architecture parameters, particularly to scaffold branches, shoot and leaf blade inclination angles, to the pattern of light distribution, and to the area of sunflecks projected at midday on the ground. Trees grafted onto ‘GF677’ were more vigorous, in terms of trunk cross-sectional area, summer pruning weight and leaf area. Within canopy light distribution profiles were in agreement with foliage density, with a higher light interception observed in trees grafted on ‘GF677’. Within canopy variation of fruit quality was higher on trees grafted onto ‘GF677’ than on those grafted onto ‘Penta’. Fruit red skin colour and soluble solids content were consistently higher on trees grafted onto ‘Penta’

Leaf area and its spatial distribution are key canopy parameters needed to model the radiation regime within a forest and to compute the mass and energy exchange between a forest and the atmosphere. A much larger proportion of available net radiation is received at the forest floor in open-canopy forests than in closed-canopy forests. The proportion of ecosystem water vapor exchange (lambda E) and sensible heat exchange from the forest floor is therefore expected to be larger in open-canopy forests than in closed-canopy forests. We used a combination of optical and canopy geometry measurements, and robust one- and three-dimensional models to evaluate the influence of canopy architecture and radiative transfer on estimates of carbon, water and energy exchange of a ponderosa pine (Pinus ponderosa Dougl. ex Laws.) forest. Three-dimensional model simulations showed that the average probability of diffuse and direct radiation transmittance to the forest floor was greater than if a random distribution of foliage had been assumed. Direct and diffuse radiation transmittance to the forest floor was 28 and 39%, respectively, in the three-dimensional model simulations versus 23 and 31%, respectively, in the one-dimensional model simulations. The assumption of randomly distributed foliage versus inclusion of clumping factors in a one-dimensional, multi-layer biosphere-atmosphere gas exchange model (CANVEG) had the greatest effect on simulated annual net ecosystem exchange (NEE) and soil evaporation. Assuming random distribution, NEE was 41% lower, net photosynthesis 3% lower, total lambda E 10% lower, and soil evaporation 40% lower. The same comparisons at LAI 5 showed a similar effect on annual NEE estimates (37%) and lambda E (12%), but a much larger effect on net photosynthesis (20%), suggesting that, at low LAI, canopies are mostly sunlit, so that redistribution of light has little effect on net photosynthesis, whereas the effect on net photosynthesis is much greater at high LAIs.

Summary Competitive crop cultivars offer a potentially cheap option to include in integrated weed management strategies (IWM). Although cultivars with high competitive potential have been identified amongst cereal crops, competitiveness has not traditionally been considered a priority for breeding or farmer cultivar choice. The challenge of managing herbicide‐resistant weed populations has, however, renewed interest in cultural weed control options, including competitive cultivars. We evaluated the current understanding of the traits that explain variability in competitive ability between cultivars, the relationship between suppression of weed neighbours and tolerance of their presence and the existence of trade‐offs between competitive ability and yield in weed‐free scenarios. A large number of relationships between competitive ability and plant traits have been reported in the literature, including plant height, speed of development, canopy architecture and partitioning of resources. There is uncertainty over the relationship between suppressive ability and tolerance, although tolerance is a less stable trait over seasons and locations. To realise the potential of competitive crop cultivars as a tool in IWM, a quick and simple‐to‐use protocol for assessing the competitive potential of new cultivars is required; it is likely that this will not be based on a single trait, but will need to capture the combined effect of multiple traits. A way needs to be found to make this information accessible to farmers, so that competitive cultivars can be better integrated into their weed control programmes.

The spatial heterogeneity of tropical forest epiphytes has rarely been quantified in terms of biomass. In particular, the effect of topographic variation on epiphyte biomass is poorly known, although forests on ridges and ravines can differ drastically in stature and exposure. In an Ecuadorian lower montane forest we quantified epiphytic biomass along two gradients: (1) the twig-branch-trunk trajectory, and (2) the ridge-ravine gradient. Twenty-one trees were sampled in each of three forest types (ridge, slope, ravine positions). Their epiphytic biomass was extrapolated to stand level based on basal area-epiphyte load relationships, with tree basal areas taken from six plots of 400 m 2 each per forest type. Our results document the successional addition and partial replacement of lichens by bryophytes, angiosperms and finally dead organic matter along the twig-branch-trunk trajectory. Despite having the highest tree basal area, total epiphytic biomass (mean ± SD) of ravine forest was significantly lower (2.6 ± 0.7 Mg ha -1) than in mid-slope forest (6.3 ± 1.1 Mg ha -1) and ridge forest (4.4 ± 1.6 Mg ha -1), whereas maximum bryophyte water storage capacity was significantly higher. We attribute this pattern to differences in forest dynamics, stand structure and microclimate. Although our study could not differentiate between direct effects of slope position (nutrient availability, mesoclimate) and indirect effects (stand structure and dynamics), it provides evidence that fine-scale topography needs to be taken into account when extrapolating epiphytic biomass and related matter fluxes from stand-level data to the regional scale. © Copyright Cambridge University Press 2011.

Improvement of light penetration within tree canopies has been a constant objective of fruit tree architecture manipulation through the setting up of training systems. Recently, centrifugal training, i.e. the removal of fruiting shoots in the tree centre and on the underside of branches, has been proposed to improve fruit size and colour as well as return-bloom as compared to conventional solaxe-trained trees with equivalent crop loads. The present study was conducted to quantify the benefits of centrifugal training on light interception by the fruiting shoots via computer-assisted three-dimensional representations of foliage geometry. Data were collected on six 5-year-old apple trees cv.Galaxy, trained either with solaxe or centrifugal training systems, using an electromagnetic 3D digitiser. The 3D distribution of the foliage in the tree canopy was recreated by combining both the spatial locations of shoots (as measured from 3D digitising) and foliage reconstruction. Light interception efficiency properties of the trees were characterised by silhouette to total area ratio (STAR) values computed from images of the 3D mock-ups. Compared to the solaxe system, centrifugal training significantly improved the STAR of the whole tree by 20%. It also increased both leaf area and STAR of the fruiting shoots by approximately 15%, regardless of their position in the canopy. In this paper, we discuss the role of this enhanced light interception by the canopy in increasing the autonomy of the fruiting shoot, i.e. improved fruit size and colour, and return-bloom.

Measurements of the area of individual leaves in crops are useful in the analysis of canopy architecture as they allow determination of the structure of leaf area index in a vertical profile. This information may be of use in modelling leaf growth and the assessment of photosynthetic potential of different strata of the canopy with ontogeny (cf. Firman & Allen, 1988).

Two aspects of the heliotropic responses of leaflets of V. unguiculata cv. California Blackeye No. 5 were studied: the environmental conditions responsible for the responses, and the significance of the leaflet orientation responses for adaptation. In the field under drought conditions, leaflets were observed to sun-track (diaheliotropism) in the morning and sun-avoid (paraheliotropism) by becoming more vertical in the afternoon. Overnight irrigation of droughted plants in the field resulted in leaflet movements on the day after irrigation similar to those of the well watered plants. Leaflets of well watered plants were diaheliotropic during the morning and evening, and essentially horizontal during the late morning and afternoon. Controlled-environment studies confirmed field observations of drought effects on leaflet movement and showed that leaflet orientation responses are reversible within 3 h after irrigating droughted plants. Temperature variations similar to those experienced in the field had only small effects on leaflet orientation. Vertical leaflet movement affected canopy architecture and significantly reduced percentage cover at midday. Manually moving the vertical leaflets of droughted plants caused substantial changes in leaflet temperatures, indicating that leaflet movement could substantially reduce heat load, water use, and water deficits in cowpeas.