Heat Pulse Technique Research Articles

EVAPORATIVE COOLING EFFECTS ON TREE TRANSPIRATION

Overhead sprinklers or micro-sprays are used in apple orchards in Australia to reduce the incidence of sunburn. Evaporative cooling occurs while the fruit surface remains wet and this is an effective way to lower fruit temperatures on hot days. The aim of the evaporative cooling is to apply the water at the right time, and at the right amount to achieve effective cooling of fruit and at the same time avoid excess runoff to the understory. The impact of evaporative cooling on irrigation requirements is unknown. The objective of this study was to undertake some preliminary observations of the effects on fruit temperature and tree transpiration (T). The heat-pulse technique was used to determine T in a commercial 'Royal Gala' apple (Malus domestica) orchard where overhead micro-sprays were already being used for evaporative cooling. The application rate of the micro-sprays was fixed at 2.4 mm/h. Evaporative cooling commenced when air temperature exceeded approximately 34°C and water was predominantly applied in cycles of 15 min on and 30 min off. Six trees were instrumented with sap flow sensors. Three trees (treatment) received evaporative cooling while the other three trees (control) did not. A leaf wetness sensor was placed under the micro-sprays to deduce the surface wetness of the apples. T declined by approximately 50% when the overhead micro-sprays were applying water for evaporative cooling. In the control trees, T decreased by approximately 5% in response to changes in air temperature and relative humidity. T recovered rapidly soon after the water was cut off. These results suggest that EC reduces root-zone irrigation requirements.

An Approach to Make More Technical Thermal Properties Measure in Porous Media

There are three variables measured for the characterization of the thermal properties in porous media and soft rocks. These are the specific variables: heat capacity, thermal conductivity and their relationship with the thermal diffusivity. Recently, Decagon Devices has developed the KD2-Pro meter. This instrument is a useful device, which permits storing more than 4000 thermal data. This company has also improved the design of sensors for their specific use. KD2-Pro uses the infinite line heat pulse technique based on current standard ASTM D 5334. Nevertheless, it is not clear how to obtain the required reliability and accuracy in the measurements since neither the standard nor manufacturer’s user manual include any method or recommendation to develop a measuring set up. Therefore, a strong methodology is required to achieve the maximum efficiency when KD2-Pro is used. This work presents ThermalHyd as the first stadium towards the development of a laboratory and field methodology to obtain reliability, accuracy and rapidity in the analytical dataset of thermal properties in porous media and soft rocks. To carry out the objective several soils from Llobregat river delta plain were used to obtain very acceptable results such as the wetting up samples, being the static method more accurate than dynamic one. Other results were based on the mineralogy of the samples in terms to transferring the heat pulse. Eventually, the microwave oven as a technique to obtain reliable water content dataset was a robust method, especially for its accuracy and faster performance.

Evaluating the potential of a novel dual heat-pulse sensor to measure volumetric water use in grapevines under a range of flow conditions.

The aim of this study was to validate a novel, dual sap-flow sensor that combines two heat-pulse techniques in a single set of sensor probes to measure volumetric water use over the full range of sap flows found in grapevines. The heat ratio method (HRM), which works well at measuring low and reverse flows, was combined with the compensation heat-pulse method (CHPM) that captures moderate to high flows. Sap-flow measurements were performed on Vitis vinifera L. (cvv. Thompson seedless, Chardonnay and Cabernet Sauvignon) grapevines growing in a greenhouse and in three different vineyards, one of which contained a field weighing lysimeter. The combined heat-pulse techniques closely tracked diurnal grapevine water use determined through lysimetry in two growing seasons, and this was true even at very high flow rates (>6L vine-1h-1 for Thompson seedless vines in the weighing lysimeter). Measurements made with the HRM technique under low flow conditions were highly correlated (R2 ~ 0.90) with those calculated using the compensated average gradient method that is used to resolve low flow with the CHPM method. Volumetric water use determined with the dual heat-pulse sensors was highly correlated with hourly lysimeter water use in both years (R2=0.92 and 0.94 in 2008 and 2009 respectively), but the nature of the relationship was inconsistent among replicate sensors. Similar results were obtained when comparing grapevine water use determined from sap-flow sensors to miniaturised weighing lysimetry of 2-year-old potted vines and to meteorological estimates for field-grown vines in two additional vineyards. The robust nature of all of the correlations demonstrates that the dual heat-pulse sensors can be used to effectively track relative changes in plant water use, but variability of flow around stems makes it difficult to accurately convert to sap-flow volumes.

Radial pattern of sap flow and response to microclimate and soil moisture in Qinghai spruce (Picea crassifolia) in the upper Heihe River Basin of arid northwestern China

In order to accurately estimate whole-tree water use and individual tree transpiration, it is important to have reliable information on radial patterns of sap velocity and responses of sap flow to local environmental conditions. Therefore, variation in sap flow and environmental conditions was investigated in a mature Qinghai spruce (Picea crassifolia) stands during the growing season of 2011 at the Pailougou watershed, in Qilianshan Mountain, located in the upper Heihe River Basin, in the arid region of Northwest China. Daily sap flow was measured by the heat-pulse technique on nine trees during the growing season. It was found that the highest daily sap flow velocity in sap flow radial distribution was at 20mm sapwood depth, and that from 10mm to 20mm sapwood depth, the daily sap flow velocity gradually increased, whereas from 20mm to 40mm sapwood depth, sap flow velocity gradually diminished. A simple Gaussian regression model for the radial distribution of sap flux velocity was formulated, which explained 92% of the radial profile variation of sap flow velocity. Sap flow velocity was heightened by increasing the global short-wave radiation (R, Wm−2), vapour pressure deficit (D, kPa), and air temperature (T, °C) when R<800Wm−2, D<1.4kPa, and T<18.0°C. It is, however, inherently difficult to establish firm relationships between sap flow velocity and R, D, and T because of the complex crown environment. The correlation of daily sap flow velocity to soil moisture content on a clear day was fitted by a logistic regression. We conclude that measurement of radial flow pattern provides a reliable method of integrating sap flow from individual measuring points to the whole tree. And D, R, T and soil moisture had varying influences on sap flow velocity in the Qinghai Spruce.

Carbon balance and energy fluxes of a Mediterranean crop

This paper is based on the analysis of a long-term mass (carbon dioxide, water vapour) and energy (solar radiation) balance monitoring programme carried out during years 2010 and 2012 in an irrigated orange orchard in Sicily, using the Eddy Covariance (EC) method. Orange (Citrus sinensis L.) is one of the main fruit crops worldwide and its evergreen orchard may have a great potential for carbon sequestration, but few data are currently available. In the study, the role of the orchard system in sequestering atmospheric CO2 was analyzed, thus contributing to assess the carbon balance of the specie in the specific environment.Vertical energy fluxes of net radiation, soil heat, sensible heat and latent heat fluxes were measured at orchard scale by EC. Evapotranspiration (ET) values were compared with upscaled transpiration data determined by the sap flow heat pulse technique, evidencing the degree of correspondence between instantaneous transpirational flux at tree level and the micrometeorological measurement of ET at orchard level.

Carbon balance and energy fluxes of a Mediterranean crop

This paper is based on the analysis of a long-term mass (carbon dioxide, water vapour) and energy (solar radiation) balance monitoring programme carried out during years 2010 and 2012 in an irrigated orange orchard in Sicily, using the Eddy Covariance (EC) method. Orange (Citrus sinensis L.) is one of the main fruit crops worldwide and its evergreen orchard may have a great potential for carbon sequestration, but few data are currently available. In the study, the role of the orchard system in sequestering atmospheric CO2 was analyzed, thus contributing to assess the carbon balance of the specie in the specific environment.Vertical energy fluxes of net radiation, soil heat, sensible heat and latent heat fluxes were measured at orchard scale by EC. Evapotranspiration (ET) values were compared with upscaled transpiration data determined by the sap flow heat pulse technique, evidencing the degree of correspondence between instantaneous transpirational flux at tree level and the micrometeorological measurement of ET at orchard level.

Transpiration of table grape (Vitis vinifera L.) trained on an overhead trellis system under netting

The quantification of transpiration and corresponding basal crop coefficients is crucial for appropriate irrigation scheduling of drip-irrigated crops. Besides basal crop coefficients already published, there is the announcing need for setting values for the new growing practices such as cropping under netting. In this paper, measurements of unstressed table grape transpiration and basal crop coefficients under netting have been taken. Vineyards of two seedless cultivars (Crimson and Autumn Royal) were trained on an overhead trellis system which permitted the ground cover to reach values up to 90 %. Two campaigns of mid-season measurements were performed using one of the heat pulse techniques available (that known as the T max approach). Obtained values for average seasonal daily transpiration ranged between 3.9 and 4.4 mm day−1, for both cultivars, depending on the period considered. Weekly averages of the basal crop coefficients, from mid-May to end-September, ranged from 0.47 to 0.87. A polynomial equation was fit to the measured basal crop coefficients as a function of fraction of thermal units. After further validation for other cultivars with different cumulative thermal requirements, this equation could be considered helpful for farmers as a practical estimate of the table grape basal crop coefficient under the netting.

Using the compensated heat pulse method to monitor trends in stem water content in standing trees

Studying the dynamics of stem water content (θ) in living trees has an outstanding physiological interest but all the available techniques to measure θ exhibit major drawbacks. In this work, we present a new methodology to estimate variations in θ along with sap velocity using the compensated heat pulse (CHP) technique. One lab experiment was performed on several wooden blocks obtained from three different tree species. Samples were slowly dried and their moisture loss was monitored by both gravimetric approaches and time-domain reflectometry (TDR) or CHP probes in order to contrast the validity of our methodology (volumetric specific heat (VSH)-CHP) over a range of water contents. In addition, a field experiment was conducted to monitor θ fluctuations in standing olive trees (Olea europaea L. cv. 'Arbequina') growing under three different irrigation regimes. In the lab test, the actual θ values deduced gravimetrically differed from the estimates yielded by the VSH-CHP method. However, it could successfully track relative changes in the water stored for the range of θ expected in living wood. Furthermore, the field experiment showed a seasonal change in θ, which was similar in shape and magnitude to those reported in the literature for olive and other Mediterranean tree species. On the other hand, differences in the seasonal patterns of θ between irrigation treatments strongly corresponded with those of sap flow and some leaf water potential measurements. The results of this work suggest that the CHP technique could be employed to monitor the dynamics of both θ and sap flow simultaneously in standing trees and evidence that seasonal changes in θ might be used as a long-term water status indicator.

Corrected surface energy balance to measure and model the evapotranspiration of irrigated orange orchards in semi-arid Mediterranean conditions

In this paper, based on the analysis of a long-term energy balance monitoring programme, a Bowen ratio-based method (BR) was proposed to resolve the lack of closure of the eddy covariance technique to obtain reliable sensible (H) and latent heat fluxes (λE). Evapotranspiration (ET) values determined from the BR method (ETc,corr) were compared with the upscaled transpiration data determined by the sap flow heat pulse (HP) technique, evidencing the degree of correspondence between instantaneous transpirational flux at tree level and the micrometeorological measurement of ET at orchard level. Using the BR-corrected λE fluxes, a crop ET model implementing the Penman–Monteith approach, where the canopy surface resistance was determined from standard microclimatic variables, was applied to determine the crop coefficient values. The performance of the model was evaluated by comparing it with the sap flow HP data. The results of the comparison were satisfactory, and therefore, the proposed methodology may be considered valid for characterizing the ET process for orange orchards grown in a Mediterranean climate. By contrast to reports in the FAO 56 paper, the crop growth coefficient of the orange orchard being studied was not constant throughout the growing season.

IMPROVING HEAT-PULSE METHODS TO EXTEND THE MEASUREMENT RANGE INCLUDING REVERSE FLOWS

Traditional heat-pulse methods are not well suited to measuring either very high or very low sap flows and few methods can measure reverse flow. We have analysed two new methods that potentially extend the measurement range. Both methods can be used by modifying the analysis algorithm and adjusting the probe positions of common heat-pulse methods, with no change to existing equipment. The first method we will refer to as the Symmetrical Gradient method (HPSG). It consists of averaging the temperature difference signal of two probes (ΔT) that are equidistant from the heater. The second method we will refer to as the Symmetrical Derivative method (HPSD). It uses the same symmetrical probe configuration. However, the analysis is based on the maximum rate of change of the temperature difference curve (i.e. the derivative, ΔT’). We use computer modelling to show that these two indicators (ΔT and ΔT’max) are proportional to the heat-pulse velocity across a wide range of positive and negative flows. Hence, both metrics can be used to determine the actual sap flux density with acceptable measurement errors and good measurement sensitivity. We present results from field experiments on a willow tree (Salix alba L.) that was set up to compare our new methods against other heat-pulse techniques. We show that HPSG and HPSD both provide reliable data across a very wide range of flows. We are currently working on other field experiments to further refine our use of HPSG and HPSD to estimate tree transpiration and even to observe sap flow in roots.

Thermal Inertia Modeling for Soil Surface Water Content Estimation: A Laboratory Experiment

We are proposing a new method for estimating soil surface water content from thermal inertia distributions retrieved from visible–near infrared (VIS‐NIR) and thermal infrared (TIR) images. A drying experiment was conducted on three fine‐textured soils while acquiring multispectral VIS‐NIR and TIR images. Simultaneous measurements of soil water content and thermal inertia were conducted by the thermogravimetric method and the heat pulse technique, respectively. Direct measurements were used to test the thermal inertia approach proposed by Murray and Verhoef that requires only knowledge of soil porosity and can be easily inverted to derive soil water content from thermal inertia. For the three considered soils, the performance of the Murray and Verhoef model was practically equal to that of the traditional approach based on the direct estimation of thermal conductivity and heat capacity, which requires more detailed information about soil properties. With the aim of simplifying the estimation of thermal inertia from remotely sensed images, a modified Kersten function was proposed in which the normalized thermal inertia is substituted by the normalized apparent thermal inertia. Comparison between the two modified Kersten functions was satisfactory. The proposed approach allowed predictions of the surface soil moisture from apparent thermal inertia distributions with an acceptable level of accuracy for practical purposes (0.028 ≤ RMSE ≤ 0.043 m3 m−3) and therefore it can be considered a simple and effective tool for estimating the spatial and temporal distribution of surface soil moisture from VIS‐NIR and TIR remotely sensed data.

A model of heat transfer in sapwood and implications for sap flux density measurements using thermal dissipation probes

A variety of thermal approaches are used to estimate sap flux density in stems of woody plants. Models have proved valuable tools for interpreting the behavior of heat pulse, heat balance and heat field deformation techniques, but have seldom been used to describe heat transfer dynamics for the heat dissipation method. Therefore, to better understand the behavior of heat dissipation probes, a model was developed that takes into account the thermal properties of wood, the physical dimensions and thermal characteristics of the probes, and the conductive and convective heat transfer that occurs due to water flow in the sapwood. Probes were simulated as aluminum tubes 20 mm in length and 2 mm in diameter, whereas sapwood, heartwood and bark each had a density and water fraction that determined their thermal properties. Base simulations assumed a constant sap flux density with sapwood depth and no wounding or physical disruption of xylem beyond the 2 mm diameter hole drilled for probe installation. Simulations across a range of sap flux densities showed that the dimensionless quantity k [defined as (ΔT(m) -ΔT)/ΔT, where ΔT(m) is the temperature differential (ΔT) between the heated and unheated probe under zero-flow conditions] was dependent on the thermal conductivity of the sapwood. The relationship between sap flux density and k was also sensitive to radial gradients in sap flux density and to xylem disruption near the probe. Monte Carlo analysis in which 1000 simulations were conducted while simultaneously varying thermal conductivity and wound diameter revealed that sap flux density and k showed considerable departure from the original calibration equation used with this technique. The departure was greatest for variation in sap flux density typical of ring-porous species. Depending on the specific combination of thermal conductivity and wound diameter, use of the original calibration equation resulted in an 81% under- to 48% overestimation of sap flux density at modest flux rates. Future studies should verify these simulations and assess their utility in estimating sap flux density for this widely used technique.

Hydraulic responses of whole vines and individual roots of kiwifruit (Actinidia chinensis) following root severance

Whole vine (K(plant)) and individual root (K(root)) hydraulic conductances were measured in kiwifruit (Actinidia chinensis Planch. var. chinensis 'Hort16A') vines to observe hydraulic responses following partial root system excision. Heat dissipation and compensation heat pulse techniques were used to measure sap flow in trunks and individual roots, respectively. Sap flux and measurements of xylem pressure potential (Ψ) were used to calculate K(plant) and K(root) in vines with zero and ∼80% of roots severed. Whole vine transpiration (E), Ψ and K(plant) were significantly reduced within 24 h of root pruning, and did not recover within 6 weeks. Sap flux in intact roots increased within 24 h of root pruning, driven by an increase in the pressure gradient between the soil and canopy and without any change in root hydraulic conductance. Photosynthesis (A) and stomatal conductance (g(s)) were reduced, without significant effects on leaf internal CO(2) concentration (c(i)). Shoot growth rates were maintained; fruit growth and dry matter content were increased following pruning. The woody roots of kiwifruit did not demonstrate a rapid dynamic response to root system damage as has been observed previously in monocot seedlings. Increased sap flux in intact roots with no change in K(root) and only a moderate decline in shoot A suggests that under normal growing conditions root hydraulic conductance greatly exceeds requirements for adequate shoot hydration.

Sap flow of irrigated Populus alba var. pyramidalis and its relationship with environmental factors and leaf area index in an arid region of Northwest China

Populus alba L. var. pyramidalis Bge. (Populus) is a main tree of the farmland shelter-belt system in the arid region of Northwest China. However, soil moisture cannot satisfy the water requirements of normal Populus growth under local natural conditions, thus studying the transpiration characteristics of irrigated Populus and its relationship with the environmental factors and growth parameters is very important to the growth of the trees in this region. In this study, the sap flow of two irrigated Populus trees was measured during May to September from 2005 to 2008 using the heat-pulse technique. The results show that the maximum and minimum daily sap fluxes in Populus were 15.7–24.0 and 3.0–4.0 L day−1, respectively. And the sum of sap fluxes from June to August accounted for approximately 63–69% of the total sap flux during May to September (almost the whole growing season). The order of the meteorological factors affecting the daily sap flux of Populus was: vapor pressure deficit > solar radiation > mean air temperature > wind speed. Furthermore, a highly linear relationship between the ratio of daily sap flux to the reference evapotranspiration (SF/ET0) and the amount of soil water in the 0–2.0 m layer was found, indicating that the amount of soil water at this layer was quite important to the growth of Populus in this region. Especially, the amount of soil water in the 0.5–1.0 m soil layer contributed to most of the plant transpiration as the highest coefficient of determination at this layer. Based on the environmental factors and leaf area index influencing sap flux, an empirical transpiration model was constructed to estimate daily transpiration.

A heat pulse technique for the determination of small‐scale flow directions and flow velocities in the streambed of sand‐bed streams

AbstractThe hyporheic zone (HZ) has the capability to eliminate and attenuate nutrients and contaminants in riverine systems. Biogeochemical reactions and the potential elimination of contaminants are strongly controlled by the flow paths and dynamics in the HZ. Nevertheless, an easily applicable method for the field determination of flow patterns in the HZ is still lacking. Therefore, a heat pulse technique, which traces the movement of a short heat pulse in the upper part of the HZ and other sand beds, was developed. Five rods are vertically driven into the sediment of the streambed; one rod with a heater as point source located in about 10‐cm sediment depth and four rods with four temperature sensors in 3 cm distance, arranged concentrically with 7 cm diameter around the heating rod. Subsequently, a heat pulse is applied and the resulting breakthrough curves are indicative of flow velocities and flow directions in the streambed. A rough data analysis procedure is also suggested. In addition, laboratory experiments were performed to test the heat pulse technique. These experiments were validated based on coupled numerical modelling of flow and heat transport. First field tests of the method prove that the method is easily applicable under field conditions. These first field tests showed highly complex flow patterns with flow velocities from 1·8 to 4·9 cm min−1and flow directions from parallel to surface flow to opposite to surface flow. This suggests the need for a robust method to quantify hyporheic flow patternsin situ. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Evaluation of the Heat-Pulse Technique for Measuring Soil Water Content with Thermo-TDR Sensor

Abstract The heat-pulse technique is emerging as a useful technique for measuring soil water content, (with the advantages of automated, rapid, and minimal destructive. The purpose of this study is to evaluate the performance of the Liu et al. (2008) thermo-TDR (time domain reflectometry) sensor for measuring soil water content using the heat-pulse technique. For this sensor, the root mean square errors (RMSE) of heat-pulse soil water content HP) estimates compared with gravimetric measures in laboratory evaluations was 0.011 m3 m-3 and was 0.018 m3 m-3 in a field evaluation. The results indicated that the sensor with a needle diameter of 2 mm, needle length of 40 mm, and needle-to-needle spacing of 8 mm can provide accurate, nondestructive, repeated estimates of soil

Responses of transpiration and canopy conductance to partial defoliation of Eucalyptus globulus trees

Partial defoliation has been shown to affect the water relations and transpiration (gas exchange) of plants. Over one growing season, the water relations in response to partial (∼45%) defoliation were examined in four-year-old Eucalyptus globulus trees in southern Australia. Daily maximum transpiration rates ( E max), maximum canopy conductance ( G C max ), and diurnal patterns of tree water-use were measured over a period of 215 days using the heat-pulse technique in adjacent control (non-defoliated) and defoliated trees. Sap-flux measurements were used to estimate canopy conductance and soil-to-leaf hydraulic conductance ( K P); leaf water potential ( Ψ) and climate data were also collected. Following the removal of the upper canopy layer, defoliated trees exhibited compensatory responses in transpiration rate and canopy conductance of the remaining foliage. Defoliated E. globulus had similar predawn but higher midday Ψ l, transpiration rates ( E), canopy conductance ( G C) and K P compared to the non-defoliated controls, possibly in response to increased water supply per unit leaf area demonstrated by higher midday Ψ l. Higher E in defoliated E. globulus trees was the result of higher G C in the morning and early afternoon. This paper also incorporates the cumulative effect of defoliation, in a phenomenological model of maximum canopy conductance of E. globulus. These results contribute to a mechanistic understanding of plant responses to defoliation, in particular the often observed up-regulation of photosynthesis that also occurs in response to defoliation.

Probing of the multilayer Si/SiGe structure with a flux of nonequilibrium acoustic phonons

The Si/Si0.8Ge0.2/Si double quantum wells grown on a silicon substrate were probed in the reflection geometry with a flux of terahertz nonequilibrium acoustic phonons produced by the heat pulse technique. A comparison of the detected phonon arrival signals with those obtained under similar conditions from a silicon sample without a quantum well structure permits one to isolate the component due to the phonon reflection from quantum wells. This reflected signal was found to be strongly anisotropic.

Enhanced water use efficiency in a mixed Eucalyptus globulus and Acacia mearnsii plantation

Significant increases in aboveground biomass production have been observed when Eucalyptus is planted with a nitrogen-fixing species due to increased nutrient availability and more efficient use of light. Eucalyptus and Acacia are among the most popular globally planted genera with the area of Eucalyptus plantations alone expanding to over 19 Mha over the past two decades. Despite this, little is known about how nutrition and light availability in mixed-species tree plantations influence water use and water use efficiency (WUE). This study examined to what extent water use and WUE have been influenced by increased resource availability and growth in mixed-species plantations. Monocultures of Eucalyptus globulus Labill. and Acacia mearnsii de Wildeman and 1:1 mixtures of these species were planted. Growth and transpiration were measured between ages 14 and 15 years. Aboveground biomass increment (Mg ha −1) was significantly higher in mixtures ( E. globulus; 4.8 + A. mearnsii; 0.9) than E. globulus (3.3) or A. mearnsii monocultures (1.6). Annual transpiration (mm) measured using the heat pulse technique was also higher in mixtures ( E. globulus; 285 + A. mearnsii; 134) than in E. globulus (358) and A. mearnsii (217) monocultures. Mixtures exhibited higher WUE than monocultures due to significant increases in the WUE of E. globulus in mixtures (1.69 kg aboveground biomass per cubic metre water transpired) compared to monocultures (0.94). The differences in WUE appear to result from increases in canopy photosynthetic capacity and above- to belowground carbon allocation in mixtures compared to monocultures. Although further studies are required and operational issues need to be resolved, the results of this study suggest that mixed eucalypt–acacia plantations may be used in water-limited environments to produce a given amount of wood with less water than eucalypt monocultures. Alternatively, because mixtures can be more productive and use more water per unit land area (but use it more efficiently), they could be utilized in recharge zones where rising water tables and salinity result from the replacement of vegetation (fast growing trees) that uses higher quantities of water with vegetation (shallow rooted annual crops) that use lower quantities of water.

Transpiration along an age series of Eucalyptus globulus plantations in southeastern Australia

Many of the world's Eucalyptus plantations are grown on short rotations of 15 years or less, which often covers the most rapid phase of stand development and peaks in growth rates and leaf areas. Since transpiration is related to stand leaf area these short rotations that make use of rapid early growth rates, may also maximise plantation water use, which has implications for predicting their water requirements and impacts on catchment hydrology. This study examined the transpiration, leaf area and growth rates of Eucalyptus globulus Labill. plantations aged 2–8 years. Transpiration ( E), estimated using the heat pulse technique, increased from 0.4 mm day −1 at age 2 years to a peak of about 1.6–1.9 mm day −1 in stands aged 5–7 years. This was associated with similar trends for stand leaf area index (LAI) and periodic annual increments of aboveground biomass, which both peaked at about age 4–6 years resulting in a linear relationship between E and LAI. While stand sapwood areas were continuing to increase at age 8 years, E was already declining due to reductions in sap velocity, from 13.5 cm h −1 at age 2 years to 6.3 cm h −1 at age 8 years and reduced sapwood area growth rates. Trees compensated for this reduction in sap velocity with declines in the leaf area ( A L) to sapwood area ( A S) relationship ( A L :A S) with age. There was also a reduction in growth efficiency (aboveground biomass increment per LAI) with age. However, reductions in WUE were small after age 4 years, which explained the linear relationship between E and LAI. If E continues to decline successive short rotation lengths may not only make use of rapid early growth rates but could also increase plantation water use compared to longer rotations over the same period of time.