A study of a population of birches in Glen Gairn

Summary

A small population of birches was studied with a view to measuring the rangeof morphological variation in Betula pendula Roth, and B. pubescens Ehrh. The general morphological features of crown and bark of trees in the area indicated that both species were present. A more detailed study was made of leaf and fruit characters, accepted by other investigators as being useful in discriminating between the species. It was shown that such characters varied continuously throughout the population and no tree was wholly pubescens- like or pendula-like in all characters.

The implications of these results are discussed in relation to the situation in Glen Gairn and to the general taxonomic situation of the British birches.     

Development of branch,crown, and vertical distribution leaf area models for contrasting hardwood species in Maine,USA

Key message

Branch, crown vertical leaf area distribution models were developed for naturally regenerated hardwood species and planted hybrid poplar clones. Species-specific differences were found at all levels of investigation.

Abstract

Coexistence in mixed-species stands is strongly influenced by species differences in leaf area production and distribution. The majority of leaf area models in the literature are focused on conifer species, which have substantially different crown forms than hardwood species. Therefore, the goal of this investigation was to develop branch, crown, and vertical leaf area distribution models for various hardwood species that accounted for their greater crown complexity. A nonlinear model including branch diameter, branch tip height, and height to the start of the foliage was the best fit for branch leaf area. Branch leaf area ranged from 0.05 to 0.37 m² for Populus grandidentata and Betula populifolia for an averaged sized branch, respectively. The best fit model for crown leaf area was a nonlinear form accounting for stem diameter and crown length. Crown leaf area ranged from 3.26 to 9.85 m² for Populus tremuloides and Betula populifolia for an averaged sized tree, respectively. Vertical leaf area distribution was best fit by a right-truncated Weibull distribution and showed a peak in the middle third of the crown for most of species. In addition, leaf area production varied among four hybrid poplar clones in plantations, suggesting a strong genetic control over crown form. Overall, leaf area varied among species at all levels of investigation, suggesting that coexistence of hardwood saplings in this investigation was strongly influenced both by inherent species-specific leaf area production and vertical distribution.     

冠层位置对5种阔叶树叶片解剖结构与氮含量的影响

不同树冠位置的叶片为了达到功能的最大化,形成了不同的结构与功能的特征。然而,在相同的环境条件下,不同树种之间叶片对环境的反应是否存在一致规律,我们仍然缺乏了解。本研究采用石蜡切片和化学分析方法,对东北林区5个常见阔叶树种（蒙古栎、白桦、水曲柳、胡桃楸和黄波罗）不同树冠位置叶片的形态（叶厚度）、解剖（气孔密度、保卫细胞长度、栅栏和海绵组织厚度）和氮（N）含量特征进行了研究。结果表明：叶片的特征在种间和种内不同树冠位置均存在明显差异,并存在较强的规律性。在种内,5个树种的叶片和栅栏组织厚度均是上层外部最大,而保卫细胞和海绵组织的变化不明显,N含量的变异与树种有关。叶片所处的树冠高度和暴露程度对叶片的结构与N含量变异有重要影响。树种之间,蒙古栎的气孔密度最大,叶片厚度和海绵组织厚度最小,保卫细胞最短,黄波罗恰恰相反。结果表明,为了更好地执行整个树冠的功能,不同树种叶片均出现了与冠层位置有关的结构特征适应。     

Understanding crown shyness from a 3-D perspective

Background and AimsCrown shyness describes the phenomenon whereby tree crowns avoid growing into each other, producing a puzzle-like pattern of complementary tree crowns in the canopy. Previous studies found that tree slenderness plays a role in the development of crown shyness. Attempts to quantify crown shyness have largely been confined to 2-D approaches. This study aimed to expand the current set of metrics for crown shyness by quantifying the characteristic of 3-D surface complementarity between trees displaying crown shyness, using LiDAR-derived tree point clouds. Subsequently, the relationship between crown surface complementarity and slenderness of trees was assessed.MethodsFourteen trees were scanned using a laser scanning device. Individual tree points clouds were extracted semi-automatically and manually corrected where needed. A metric that quantifies the surface complementarity (S_c) of a pair of protein molecules is applied to point clouds of pairs of adjacent trees. Then 3-D tree crown surfaces were generated from point clouds by computing their α shapes.Key ResultsTree pairs that were visually determined to have overlapping crowns scored significantly lower S_c values than pairs that did not overlap (n = 14, P < 0.01). Furthermore, average slenderness of pairs of trees correlated positively with their S_c score (R² = 0.484, P < 0.01), showing agreement with previous studies on crown shyness.ConclusionsThe characteristic of crown surface complementarity present in trees displaying crown shyness was succesfully quantified using a 3-D surface complementarity metric adopted from molecular biology. Crown surface complementarity showed a positive relationship to tree slenderness, similar to other metrics used for measuring crown shyness. The 3-D metric developed in this study revealed how trees adapt the shape of their crowns to those of adjacent trees and how this is linked to the slenderness of the trees.     

不同密度红桦幼苗苗冠结构与竞争对CO2浓度升高的响应

研究了两个种植密度下,红桦 (Betula albosinensis)苗冠结构特征对CO₂浓度的响应,在此基础上探讨了CO₂浓度升高对植物竞争压力的影响。结果表明,冠幅、冠高、苗冠表面积和苗冠体积均受CO₂浓度升高的影响而增加,但是受密度增加的影响而降低。CO₂浓度升高对苗冠的促进效应在低密度条件下大于高密度处理,高密度条件下苗冠基本特征部分地受到CO₂浓度升高的促进作用;升高种植密度的效应则在高CO₂浓度条件下大于现行CO₂浓度处理。高CO₂浓度和高密度条件下,LDcpa（单位苗冠投影面积叶片数）、LDcv（单位苗冠体积叶片数） 和苗冠底部枝条的枝角均低于相应的现行CO₂浓度处理和低密度处理,这主要是由于冠幅和冠高的快速生长所造成的。升高CO₂浓度对枝条长度的影响与枝条在主茎上所处位置有关。总之,升高CO₂浓度有利于降低增加种植密度对苗冠所带来的负效应,而增加种植密度降低了升高CO₂浓度的正效应。LDcpa和LDcv的降低表明,红桦在升高CO₂浓度和种植密度的条件下,会作出积极的响应,从而缓解由于生长的增加所带来的竞争压力的增加。     

Homeostasis in leaf water potentials on leeward and windward sides of desert shrub crowns: water loss control vs. high hydraulic efficiency

Phenotypic plasticity in morphophysiological leaf traits in response to wind was studied in two dominant shrub species of the Patagonian steppe, used as model systems for understanding effects of high wind speed on leaf water relations and hydraulic properties of small woody plants. Morpho-anatomical traits, hydraulic conductance and conductivity and water relations in leaves of wind-exposed and protected crown sides were examined during the summer with nearly continuous high winds. Although exposed sides of the crowns were subjected to higher wind speeds and air saturation deficits than the protected sides, leaves throughout the crown had similar minimum leaf water potential (Ψ_L). The two species were able to maintain homeostasis in minimum Ψ_L using different physiological mechanisms. Berberis microphylla avoided a decrease in the minimum Ψ_L in the exposed side of the crown by reducing water loss by stomatal control, loss of cell turgor and low epidermal conductance. Colliguaja integerrima increased leaf water transport efficiency to maintain transpiration rates without increasing the driving force for water loss in the wind-exposed crown side. Leaf physiological changes within the crown help to prevent the decrease of minimum Ψ_L and thus contribute to the maintenance of homeostasis, assuring the hydraulic integrity of the plant under unfavorable conditions. The responses of leaf traits that contribute to mechanical resistance (leaf mass per area and thickness) differed from those of large physiological traits by exhibiting low phenotypic plasticity. The results of this study help us to understand the unique properties of shrubs which have different hydraulic architecture compared to trees.     

乐昌含笑不同家系的叶形态与生长差异分析

为了解乐昌含笑(Michelia chapensis)叶形态和生长性状的家系变异特征,对15个家系的叶形态性状和生长指标及其相关性进行了分析.结果表明,乐昌含笑叶片形态在家系间和家系内均存在显著差异,不同家系间以帽子峰家系叶形态的平均变异系数最大(23.55％),乐九5家系的最小(12.63％);不同叶形态性状间以干物...     

The expression of light-related leaf functional traits depends on the location of individual leaves within the crown of isolated Olea europaea trees

Background The spatial arrangement and expression of foliar syndromes within tree crowns can reflect the coupling between crown form and function in a given environment. Isolated trees subjected to high irradiance and concomitant stress may adjust leaf phenotypes to cope with environmental gradients that are heterogeneous in space and time within the tree crown. The distinct expression of leaf phenotypes among crown positions could lead to complementary patterns in light interception at the crown scale.Methods We quantified eight light-related leaf traits across 12 crown positions of ten isolated Olea europaea trees in the field. Specifically, we investigated whether the phenotypic expression of foliar traits differed among crown sectors and layers and five periods of the day from sunrise to sunset. We investigated the consequences in terms of the exposed area of the leaves at the tree scale during a single day.Key Results All traits differed among crown positions except the length-to-width ratio of the leaves. We found a strong complementarity in the patterns of the potential exposed area of the leaves among day periods as a result of a non-random distribution of leaf angles across the crown. Leaf exposure at the outer layer was below 60 % of the displayed surface, reaching maximum interception during morning periods. Daily interception increased towards the inner layer, achieving consecutive maximization from east to west positions within the crown, matching the sun’s trajectory.Conclusions The expression of leaf traits within isolated trees of O. europaea varies continuously through the crown in a gradient of leaf morphotypes and leaf angles depending on the exposure and location of individual leaves. The distribution of light-related traits within the crown and the complementarity in the potential exposure patterns of the leaves during the day challenges the assumption of low trait variability within individuals.     

Relationships between foliage and conducting xylem in Picea abies (L.) Karst.

Summary The relationship of leaf biomass and leaf area to the conductive area of stems and branches was investigated in Picea abies. A total of 30 trees were harvested to determine if these relationships were different in different crown zones and in trees growing with and without competition for light. Two methods were compared. In the first, data were accumulated from crown zones situated at the top of trees to the bottom; in the second, data were used from individual crown zones. The results indicated that the latter method is much more sensitive in detecting differences in the relationship of leaf biomass or leaf area to conductive area. The analysis also indicated that ratios such as leaf area/sapwood area are frequently size-dependent. This size-dependency can in some cases result in the differences being abscured, but more often leads to the false impression that the relationship between the variables changes. The relationship between leaf biomass and leaf area and conductive area of stems or branches was different in different crown zones and under different growth conditions. The slopes of these regressions appear to increase with decreasing transpirational demand and decrease with increasing hydraulic conductivity. The intercepts are probably related to the amount of identified sapwood actually involved in water conductance.     

Sapwood hydraulic conductivity and leaf area – sapwood area relationships following thinning of a Eucalyptus nitens plantation

This study tested the hypothesis that the relationship between leaf area (projected, or one‐sided) and sapwood area in Eucalyptus nitens (Deane and Maiden) Maiden is affected by thinning treatment. However, no difference in the relationship between leaf area and sapwood area was found 8 years after thinning. This result suggests that a single regression equation can be used to predict the leaf area of trees in thinned and unthinned stands. The relationship was non‐linear, implying a causal relationship between growth rate and the ratio of leaf area to sapwood area (A_l : A_s). Sapwood hydraulic conductivity increased by approximately 100% from breast height to crown base, whereas sapwood area decreased by 19%. This implies that the efficiency of water transport through the sapwood increased by 60% along this length. This conclusion is supported by the A_l : A_s relationships which showed that the sapwood area at crown base supported, on average, close to 60% more leaf area than a similar amount of sapwood area at breast height. That large trees in this study had greater hydraulic conductivity and higher A_l : A_s lends support to the argument that resource capture, and hence growth rate, influence sapwood hydraulic conductivity.     

光照条件、植株冠层结构和枝条寿命的关系——以桂花和水杉为例

根据衰老理论的代谢率假说,生物寿命与其代谢率有关,个体大小相同的生物体,在质量较好的微生境中通常比较差生境中具有更高的代谢速率。因此,生物体在资源供给较差的生境中通常比资源供给较充足的生境中具有更长的寿命。枝条是木本植物植冠构建的基本单元之一,如果枝条遵循代谢率假说,则可推测在光照较好环境下的植物枝条或小枝将比其在遮荫环境下具有更短的寿命,即枝条寿命与光照条件成反比。以常绿物种桂花(Osmanthus fragrans)和落叶物种水杉(Metasequoiaglyptostroboides)为研究对象,通过测量不同光照环境下,植株大小(株高和胸径)、冠层深度、冠层轮廓(冠层深度/冠层宽度)、相对冠层宽度(冠层宽度/植株高度)以及植株凋落枝条寿命等性状,探讨了光照条件对成年植株冠层形态结构和植株枝条寿命的影响。调查发现:1)枝条的寿命在遮荫条件下显著高于全光照条件下,与理论预测吻合;2)随遮荫程度增加,植株冠层深度和冠层轮廓增加,相对冠层宽度减小;3)枝条的平均寿命与植株冠层深度和冠层轮廓成正比,与植株相对冠层宽度成反比。这表明光照条件可能通过改变植株冠层结构来影响枝条寿命。未来需要进一步研究枝条生物量分配、叶片光合能力和呼吸速率在不同生活型物种之间的差异,以便更全面的理解枝条寿命与生境质量之间的关系。     

不同生境栓皮栎天然更新幼苗植冠构型分析

栓皮栎存在于秦岭南坡的多种林分中,生活在不同生境中的个体往往形成不同的树冠形态和构型特征。为了说明不同生境条件下栓皮栎幼苗的植冠构型变化,采用典型抽样法,对秦岭南坡3种生境中(林冠下、林隙、林缘)的栓皮栎天然更新幼苗的侧枝、叶片特征及其空间分布进行了调查分析,结果表明:3种不同生境中栓皮栎幼苗植冠形态发生了明显的可塑性变化,(1)林冠下的幼苗明显为开阔型树冠,林隙和林缘处的幼苗树冠相对紧密;(2)幼苗的1级侧枝密度与分枝角度在3种生境下均差异显著(P0.05);从Ⅰ到Ⅳ层,林冠下幼苗的分枝角度在冠层内变化幅度不到5°,而林缘处幼苗的分枝角度变化高达40°;发生5个以上1级侧枝的概率以林冠下最大,为0.6;(3)从林缘、林隙到林冠下,幼苗的叶长、叶宽、单叶面积、叶面积指数逐渐降低,数量叶密度和比叶面积则逐渐增大,与其它两种生境相比,林冠下幼苗的叶片逐渐向树冠上层集中,且以更高序的侧枝为主要着生枝条;(4)林隙中栓皮栎幼苗的树高、地径明显优于林缘和林冠下,缩短了苗木进入主林层的时间,林隙对栓皮栎种群更新有利。在今后栓皮栎林的经营中,可以通过适当间伐来增加林隙数量,为森林更新和结构的优化的提供有利条件。     

The genetic resolution of juvenile canopy structure and function in a three-generation pedigree of Populus

 A genetic approach to the understanding of tree architecture is to cross trees of contrasting features and to study their segregating F₂ progenies. For this purpose, members of a 3-generation pedigree, combining Populus trichocarpa, P. deltoides, and their F₁ and F₂ offspring, were grown side by side in a clonally replicated plantation. At 2 and 3 years of growth, tree architecture was analyzed at the stem, branch, and leaf levels. In all generations, proleptic branches were more numerous, longer, and had more and larger leaves than sylleptics initiated in the same year. The analysis of variance revealed significant genotypic effects on growth, branch and leaf biometrics in the F₂ family, with broad-sense heritabilities (H²) ranging from 0.50 to 0.80 for most traits. For branch and leaf traits, the H² values were found to vary among branch types and crown positions. In year 2, the degree of genetic control was stronger for sylleptics than proleptics and for upper than lower crown positions. These patterns were followed in year 3, except that H² values were more a function of position within crown, as a consequence of increased competition among trees. The genetic correlations between branch/leaf morphology and stem growth were also a function of branch type and crown position. Generally, traits on proleptics or at upper positions were more tightly correlated with height growth, whereas those on sylleptics or at lower positions, with basal area growth. By year 3, proleptic traits showed increased genetic correlations with both height and radial growth. The implications of these results for the construction of ideotypes are discussed. Received: 1 December 1995     

Estimating photosynthetic rate and annual carbon gain in conifers from specific leaf weight and leaf biomass

Summary Canopy photosynthesis is difficult to measure directly or to predict with complex models demanding knowledge of seasonal variation in environmental and physiological properties of the canopy. Trees in particular offer a challenge with their large, aerodynamically rough and seasonally-changing canopy properties. In this paper we assess the possibility of using specific leaf weight to predict seasonal and annual net photosynthetic rate in deciduous (Larix sp.) and evergreen (Picea abies) conifers.Annual photosynthetic rate and specific leaf weight of different positions of the crown in both species were highly correlated (r ²=0.930). Annual carbon uptake by different segments in a mature P. abies crown was closely related to leaf biomass. The relationship was improved by adjusting the leaf biomass of each segment in regard to its specific leaf weight relative to the maximum found in the canopy. The adjustment accounted for associated differences in photosynthetic activity. This combined structural index (leaf biomassxrelative specific leaf weight) could, when calibrated, predict the total annual carbon uptake by different parts of the crown. If direct measurements of photosynthesis are not available, the combined structural index may still serve as a comparative estimator of annual carbon uptake.     

Needle-age related variability in nitrogen, mobile carbohydrates, and δ13C within Pinus koraiensis tree crowns

For both ecologists and physiologists, foliar physioecology as a function of spatially and temporally variable environmental factors such as sunlight exposure within a tree crown is important for understanding whole tree physiology and for predicting ecosystem carbon balance and productivity. Hence, we studied concentrations of nitrogen (N), non-structural carbohydrates (NSC = soluble sugars + starch), and δ¹³C in different-aged needles within Pinus koraiensis tree crowns, to understand the needle age- and crown position-related physiology, in order to test the hypothesis that concentrations of N, NSC, and δ¹³C are needle-age and crown position dependent (more light, more photosynthesis affecting N, NSC, and δ¹³C), and to develop an accurate sampling strategy. The present study indicated that the 1-yr-old needles had significantly higher concentration levels of mobile carbohydrates (both on a mass and an area basis) and N_area (on an area basis), as well as NSC-N ratios, but significantly lower levels of N_mass (on a mass basis) concentration and specific leaf area (SLA), compared to the current-year needles. Azimuthal (south-facing vs. north-facing crown side) effects were found to be significant on starch [both on a mass (ST_mass) and an area basis (ST_area)], δ¹³C values, and N_area, with higher levels in needles on the S-facing crown side than the N-facing crown side. Needle N_mass concentrations significantly decreased but needle ST_mass, ST_area, and δ¹³C values significantly increased with increasing vertical crown levels. Our results suggest that the sun-exposed crown position related to photosynthetic activity and water availability affects starch accumulation and carbon isotope discrimination. Needle age associated with physiological activity plays an important role in determining carbon and nitrogen physiology. The present study indicates that across-scale sampling needs to carefully select tissue samples with equal age from a comparable crown position.     

Rice with SUB1 QTL possesses greater initial leaf gas film thickness leading to delayed perception of submergence stress

Background and AimsSubmergence tolerance in rice is primarily attributed to the action of the SUB1 gene, but other associated traits such as leaf gas film (LGF) thickness, leaf hydrophobicity, porosity and leaf density have been known to aid submergence tolerance in rice. However, association of these traits with SUB1 quantitative trait locus (QTL) has not been demonstrated. In this study, we aim to investigate (1) whether the presence of the SUB1 QTL in the genetic background has any influence on the thickness of the LGF and (ii) whether its removal has any impact on stress perception and submergence tolerance in Sub1 and non-Sub1 rice.MethodsWe examined 12 genotypes (including both Sub1 and non-Sub1 types) for different leaf traits such as initial LGF thickness, leaf hydrophobicity, tissue porosity and leaf density in order to work out the relatioship of these traits to the SUB1 QTL in rice. Furthermore, we investigated the changes in the gene expression profile and different metabolic processes in selected genotypes in the presence and absence of their LGF to study its impact on stress perception and adaptation.Key ResultsThe initial thickness of the LGF and hydrophobicity seemed to have a highly positive correlation with the presence of the SUB1 QTL in the genetic background of rice; however, other leaf traits such as porosity and density seemed to be independent of it. Artificial removal of the LGF resulted in partial loss of tolerance, showing increased ethylene production and early induction of anoxia-related genes (SUB1A-1, ACS5, Ramy3D and ADH1) which manifested symptoms such as increased stem elongation, faster chlorophyll and starch breakdown, and partial loss of quiescence in SUB1-containing rice genotypes. Stripping of the LGF resulted in early and enhanced induction of SUB1A-1, indicating a quicker perception of stress.ConclusionsThe presence of SUB1 in the genetic background positively influences surface hydrophobicity and the concomitant LGF thickness of rice. Furthermore, LGF helps in terms of providing better ethylene dissipation and reduced in planta accumulation, owing to the slowing down of ethylene-induced leaf senescence under submergence stress.     

PLANT SIZE AND FORM IN THE UNDERSTORY PALM GENUS GEONOMA: ARE SPECIES VARIATIONS ON A THEME?

This study addressed the hypothesis that phylogenetic changes in plant size at reproductive maturity may have facilitated adaptive radiation of Geonoma species within rain forest understory habitats. Leaf size, leaf form, plant size, and growth form were compared within and among 23 species of Geonoma from lowland and montane rain forest areas of Costa Rica and Colombia. Leaf size was significantly correlated with crown height in 18 of the 21 species examined, and with stem diameter in 17 of the species. In species characterized by a gradual ontogenetic transition from bifid to dissected leaves, shoots with bifid leaves were significantly smaller than shoots with dissected leaves with respect to rachis length, number of plications, and stem diameter. Among species, stem diameter below the crown explained 74% of the variation in leaf size (rachis length). Crown height and stem diameter were positively correlated among clustered species, but not among solitary species or all species combined. Leaf dissection was correlated with crown height among the 17 species with dissected leaves; species with bifid leaves were significantly smaller than species with dissected leaves with respect to leaf size and stem diameter. Solitary species had larger leaves and larger stem diameters than clustered species at the same crown heights. Morphological patterns among species generally followed within-species trends. These patterns suggest that Geonoma species are variants on a generic theme:within and among species, leaf size and complexity of form increase with stem diameter and crown height. Solitary and clustered growth forms appear to be morphologically convergent; within each of these architectural groups, the generic theme still applies. Evolutionary changes in leaf size, leaf form, and plant size, however, have clearly involved other factors in addition to variation in plant size.     

PLASTICITY OF TREE ARCHITECTURE: SPECIFIC AND ECOLOGICAL VARIATIONS FOUND IN AUBREVILLE'S MODEL

The crown form and branching pattern of sapling and adult trees of Terminalia catappa, T. latifolia, and an unidentified species of Manilkara are described. Leaf distribution (leaf positions within the crown) and leaf area index are given for the three species. Although they all exhibit the same architectural model, the two species of Terminalia maintain a tiered canopy in both sapling and large adult trees, while Manilkara has a sapling with poorly defined tiers and an adult with a hollow, hemispherical crown. Thus, the same architectural model (Aubréville's) can give rise to different crown shapes due to quantitative differences in branch geometry, degree of reiteration, and longevity of leaf-bearing branch units. Conversely, similar crown shapes can be produced by trees with different models. Manilkara conforms to the monolayer model of leaf arrangement at maturity, but Terminalia cannot easily be described as a monolayer or a multilayer. Adaptive geometry of a tree and its architectural model are not equivalent nor necessarily comparable.     

The decline of Greek fir (Abies cephalonica Loudon): Relationships with root condition

Abstract

The decline of Greek fir (Abies cephalonica Loudon) has been reported throughout Greece during the last three decades. The symptoms include crown dieback, needle discoloration and loss, death of twigs, branches or whole tree death. A number of causes for the fir decline have been proposed such as drought, climatic change, air pollution and pathogens or insects. Our studies have focused on the relationship between fir decline symptoms and root growth and condition. The crown and root condition of fir trees, at different stages of decline, were assessed and the results showed that root condition was related to needle loss and crown discoloration. Declining trees were characterized by a decreased portion of fine root biomass. No significant differences in total root length and number of roots for each root order were found. In conclusion, our studies showed that the crown condition of Greek firs is reflected on root condition.     

Control of transpiration in three coffee cultivars: the role of hydraulic and crown architecture

Water use and hydraulic architecture were studied in the coffee (Coffea arabica) cultivars San Ramon, Yellow Caturra and Typica growing in the field under similar environmental conditions. The cultivars differed in growth habit, crown architecture, basal sapwood area and total leaf surface area. Transpiration per unit leaf area (E), stomatal conductance (g _s), crown conductance (g _c), total hydraulic conductance of the soil/leaf pathway (G _t) and the stomatal decoupling coefficient, omega (Ω) (Jarvis and McNaughton 1986) were assessed over a range of soil moisture and during partial defoliation treatments. The relationship between sap flow and sapwood area was linear and appeared to be similar for the three cultivars. Variation in g _c, E, and G _t of intact plants and leaf area-specific hydraulic conductivity (k _l) of excised lateral branches was negatively correlated with variation in the ratio of leaf area to sapwood area. Transpiration, g _c, and g _s were positively correlated with G _t. Transpiration and G _t varied with total leaf area and were greatest at intermediate values (10 m²) of leaf area. Omega was greatest in Yellow Caturra, the cultivar with the greatest leaf area and a dense crown, and was smallest in Typica, the cultivar with an open crown. Differences in omega were attributable primarily to differences in leaf boundary layer conductance among the cultivars. Plants of each cultivar that were 40% defoliated maintained sap flows comparable to pretreatment plants, but expected compensatory increases in g _s were not consistently observed. Despite their contrasting crown morphologies and hydraulic architecture, the three cultivars shared common relationships between water use and hydraulic architectural traits. Received: 17 February 1999 / Accepted: 28 July 1999