Full Canopy Research Articles

A multistep approach to classify full canopy and leafless trees in bottomland hardwoods using very high-resolution imagery

ABSTRACTThe distribution of leafless and full-canopy trees in fall is essential in understanding the phenological and morphological characteristics of forests and those are critical baseline information for several scientific questions and management scenarios. The rapid progress of very high-resolution satellite-borne sensors provides a feasible solution to fast and accurately map tree coverage during the growing season. However, less attention has been paid to the leaf-off seasons. One biggest challenge with classification on fall imagery is the potential confusion among different land features, as evidenced by the no significant difference between bare land and leafless trees from t-test and transformed divergence (TD) analysis results. We proposed an integrative approach to classifying leafless and full-canopy trees on fall imagery of 0.46-m WorldView-2 (WV-2). We adopted a two-step classification approach by first removing the non-forest area from the WV-2 imagery with the mask layer generated from the publicly available summer imagery of 1-m National Agriculture Imagery Program imagery via object-based image analysis. Two classification methods, namely decision tree (DT) and nearest neighborhood (NN), were employed to classify full canopy and leafless trees in the masked WV-2 imagery. DT performed slightly better than NN regarding higher overall accuracy and fewer feature requirements.

Performance of the METRIC model in estimating evapotranspiration fluxes over an irrigated field in Saudi Arabia using Landsat-8 images

Abstract. Accurate estimation of evapotranspiration (ET) is essential for hydrological modeling and efficient crop water management in hyper-arid climates. In this study, we applied the METRIC algorithm on Landsat-8 images, acquired from June to October 2013, for the mapping of ET of a 50 ha center-pivot irrigated alfalfa field in the eastern region of Saudi Arabia. The METRIC-estimated energy balance components and ET were evaluated against the data provided by an eddy covariance (EC) flux tower installed in the field. Results indicated that the METRIC algorithm provided accurate ET estimates over the study area, with RMSE values of 0.13 and 4.15 mm d−1. The METRIC algorithm was observed to perform better in full canopy conditions compared to partial canopy conditions. On average, the METRIC algorithm overestimated the hourly ET by 6.6 % in comparison to the EC measurements; however, the daily ET was underestimated by 4.2 %.

Early drought effect on canopy development and tuber growth of potato cultivars with different maturities

The morphological growth characteristics of shoots, stolons, and tubers were measured on potatoes (Solanum tuberosum L.) grown in irrigation and drought from plant emergence. Three cultivars with a wide range of seasonal maturing patterns, Chubaek (very early), Superior (medium-early), and Jayoung (late), were used. The drought was maintained up to the tuberization stage in the year 2015, and it was extended to early tuber bulking in the year 2016. The drought delayed the time to full canopy development by 2–6days and decreased the growths of shoots in terms of stem length, stem thickness, number of stems, and fresh weight of the shoots. The harvest index was increased in all cultivars due to the decreased shoot growth. The early drought also increased the length of underground stolons. However, the decreases in stem thickness and stem number and the increases in harvest index and stolon length were only significant in the year 2016. Even though the drought did not affect tuberization in early and medium-early cultivars, it decreased early tuber growth by suppressing the longitudinal growth expressed by the ratio of length to width of the tubers. The decrease of tuber growth was observed until the end of the season with the exception of Superior in 2016. In late maturing cultivar, tuber initiation and tuber yield were dependent on the season or length (severity) of the drought. In 2016 when late cultivar, Jayoung, experienced a long drought starting from the emergence of the plants to early tuber bulking, the drought induced earlier tuberization than irrigation treatment, and showed a higher harvest index than in 2015. The early tuberization and tuber bulking due to the long drought induced increased tuber yields. The occurrence of second growth tubers was highly attributed to the maturity of cultivars in both years and the drought in 2016.

Estimation of air temperature and reference evapotranspiration using MODIS land surface temperature over Greece

ABSTRACTModerate Resolution Imaging Spectroradiometer (MODIS), land surface temperature data, during daytime (LSTday) or night-time (LSTnight), were employed for predicting maximum (Tmax) or minimum (Tmin) air temperature measured at ground stations, respectively, in order to be used as alternative inputs in minimum data-based reference evapotranspiration (ET) models in 28 stations in Greece during the growing season (May–October). The deviations between daily LSTnight and Tmin were found to be small, but they were greater between LSTday and Tmax. Furthermore, the temperature vegetation index (TVX) method was employed for achieving more accurate Tmax values from LSTday, after determining the normalized difference vegetation index of a full canopy (NDVImax). The TVX method was validated on ‘temporal’ basis, but when the method was tested spatially, the improvement on the Tmax estimates from LSTday was not encouraging, for being used operationally over Greece. Thus, LSTday or LSTnight MODIS data were used as inputs in three ET models [Hargreaves–Samani, Droogers–Allen, and Reference Evapotranspiration Model for Complex Terrains (REMCT)] and their estimations, as compared with ground-based Penman–Monteith estimates, indicated that the REMCT model achieved the most accurate ET predictions (r = 0.93, mean bias error = 0.44 mm day–1 and root mean square error = 0.74 mm day–1), which can allow the spatial analysis of ET at higher spatial resolutions in areas with lack of ground temperature data.

Below-canopy contributions to ecosystem CO2 fluxes in a temperate mixed forest in Switzerland

Forests are structurally complex ecosystems with several canopy layers, each with distinct functional properties contributing differently to the net ecosystem CO2 exchange. A large number of studies have addressed ecosystem-scale net CO2 fluxes in forests, but only few studies have investigated the role of the forest understory. The goal of this study was to quantify the below-canopy contribution to ecosystem CO2 fluxes of a mixed deciduous forest in Switzerland. Below- and above-canopy eddy-covariance (EC) measurements were made continuously over two years, complemented by within canopy wind and CO2 concentration profile measurements.On an annual basis, the below-canopy fluxes indicated a net carbon source dominated by soil respiration, while the above-canopy fluxes were dominated by tree photosynthesis leading to a net carbon sink. Below-canopy fluxes showed a net carbon sink only in spring, with the early emergence of understory plants before overstory canopy leaf-out. Below-canopy respiration partitioned from the EC measurements agreed well with previous chamber-based soil respiration measurements. However, below- and above-canopy fluxes became decoupled under full canopy closure, thus leading to unaccounted below-canopy fluxes when measured only above the canopy. Wind and CO2 concentration profile measurements supported this finding. Decoupling was independent of low turbulence conditions and decoupled periods could be identified using the relationship between the below- and above-canopy standard deviation in vertical wind velocity. A decoupling correction was applied to the above-canopy measurements during decoupled periods and corrected annual net ecosystem production (NEP) agreed well with independent estimates from biomass inventory combined with models. Overall, the below-canopy fluxes contributed 79% to annual ecosystem respiration, but only 9% to annual ecosystem photosynthesis. The decoupling correction reduced annual NEP for the site from about 760 to 330gCm−2yr−1. Our results showed that below-canopy EC measurements are essential in this mixed deciduous forest, and likely in many other forests, to fully understand the carbon dynamics within structurally complex ecosystems.

Performance of Precision Mobile Drip Irrigation in the Texas High Plains Region

Mobile drip irrigation (MDI) technology adapts driplines to the drop hoses of moving sprinkler systems to apply water as the drip lines are pulled across the field. There is interest in this technology among farmers in the Texas High Plains region to help sustain irrigated agriculture. However, information on the performance of this system and its benefits relative to common sprinkler application technologies in the region are limited. A two-year study was conducted in 2015 and 2016 to compare grain yields, crop water use (ETc) and water use efficiency (WUE) of corn (Zea Mays L.) irrigated with MDI, low elevation spray application (LESA) and low energy precision application (LEPA) methods. Irrigation amounts for each application method were based on weekly neutron probe readings. In both years, grain yield and yield components were similar among application treatment methods. Although WUE was similar for the MDI treatment plots compared with LEPA and LESA during the wet growing season (2015), MDI demonstrated improved WUE during the drier year of 2016. Additional studies using crops with less than full canopy cover at maturity (sorghum and cotton) are needed to document the performance of MDI in the Texas High Plains region.

Flow adjustment inside homogeneous canopies after a leading edge – An analytical approach backed by LES

A two-dimensional analytical model for describing the mean flow behavior inside a vegetation canopy after a leading edge in neutral conditions was developed and tested by means of large eddy simulations (LES) employing the LES code PALM. The analytical model is developed for the region directly after the canopy edge, the adjustment region, where one-dimensional canopy models fail due to the sharp change in roughness. The derivation of this adjustment region model is based on an analytic solution of the two-dimensional Reynolds averaged Navier–Stokes equation in neutral conditions for a canopy with constant plant area density (PAD). The main assumptions for solving the governing equations are separability of the velocity components concerning the spatial variables and the neglection of the Reynolds stress gradients. These two assumptions are verified by means of LES. To determine the emerging model parameters, a simultaneous fitting scheme was applied to the velocity and pressure data of a reference LES simulation. Furthermore a sensitivity analysis of the adjustment region model, equipped with the previously calculated parameters, was performed varying the three relevant length, the canopy height (h), the canopy length and the adjustment length (Lc), in additional LES. Even if the model parameters are, in general, functions of h/Lc, it was found out that the model is capable of predicting the flow quantities in various cases, when using constant parameters. Subsequently the adjustment region model is combined with the one-dimensional model of Massman [Bound. Layer Meteorol., 83(3):407–421, 1997], which is applicable for the interior of the canopy, to attain an analytical model capable of describing the mean flow for the full canopy domain. Finally the model is tested against an analytical model based on a linearization approach.

Assessing Fractional Cover in the Alpine Treeline Ecotone Using the WSL Monoplotting Tool and Airborne Lidar

ABSTRACTAs forest cover in mountain areas impacts headwater properties like habitat extent and downstream water resources, it is important to assess and understand the changes that occur across forest transition zones like the alpine treeline ecotone (ATE). Such changes occur slowly and manifest at decadal to century time scales; however, the present benchmark spatial resolution for land cover analysis from oblique repeat photographs, 100 m, is insufficient to analyze anticipated changes in ATE over a century-scale. In this research note, fractional cover classification of the ATE is achieved through oblique photography analysis with the WSL Monoplotting Tool. Seven oblique photographs of the West Castle Watershed (Alberta, Canada), collected by the Mountain Legacy Project, were gridded to a 20-m resolution and assigned canopy cover classes by manual interpretation. Four canopy cover classes (i.e., no cover, low vegetation, partial canopy, full canopy) were compared to lidar-derived fractional cover. The extraction of canopy cover information from oblique photography at a resolution of 20 m introduces the ability to assess and quantify changes in the ATE using century-scale oblique photographic records.

Impact of Repeated Yearly Applications of Prohexadione-Calcium On Vegetative and Reproductive Growth of ‘Golden Delicious’/M.9 Apple Trees

Abstract Growth retardants have great potential to balance between vegetative and reproductive growth. To assess the effects of prohexadione-calcium (Pro-Ca, Regalis) on reproductive and vegetative growth, return bloom, fruit set, and also fruit quality in ‘Golden Delicious’ apple grafted on M.9 rootstock, an experiment was performed during 2010-2012. The applications of 125 mg dm-3 Pro-Ca on the same trees in each year resulted in a 40-43% shoot length reducing. Internodes length decreased with Pro-Ca at about 30%, while total node number was unaffected. Results indicate that Pro-Ca applications have no effects on tree trunk growth, flowering, yield, fruit set and development. Pro-Ca also didn’t have any negative impact on fruit quality during the three consecutive years. Moreover, Pro-Ca resulted in higher fruit size compared to control in the third year of trial. The results of this experiment clearly suggest that fruit growers can use Pro- Ca for the control of vegetative growth without having any negative effects on fruit quality and yield parameters. Once a full canopy has been achieved, annual shoot growth can be suppressed in the range of 20 to 30 cm with 125 mg dm-3 Pro-Ca treatment in ‘Golden Delicious’ apple trees.

Ground-truthing of remotely sensed within-field variability in a cv. Barbera plot for improving vineyard management

Background and Aims Precision viticulture encompasses a series of techniques from remote to proximal sensing for describing and exploiting within-vineyard variability. Our aim was to assess how vigour mapping associated with detailed ground-truthing can provide guidelines for more sustainable vineyard management. Methods and Results A satellite image taken with a 5 m-pixel resolution on a mature, small-sized (0.6 ha) cv. Barbera vineyard at full canopy made it possible to build a vigour map on the assessment of normalised difference vegetation index (NDVI) distinguishing low-vigour (LV), medium-vigour (MV) and high-vigour (HV) areas of equal surface. Detailed single-vine records for vegetative growth (shoot length, leaf area and pruning mass), yield components (bud fruitfulness, yield per vine and bunch and berry mass) and grape composition were recorded within each vigour class at harvest; leaf nutritional status and ripening curves were monitored for the same classes. While NDVI showed a close correlation to several vegetative, yield and grape composition parameters, LV vines exhibited excellent performance for remunerative yield (3.2 kg/vine, or a potential yield of 13.3 t/ha) and full ripening with maintenance of adequate TA. Both MV and HV showed excessive vigour and cropping leading towards incomplete ripening. Conclusions The combination of NDVI mapping and detailed ground-truthing allows the identification of the vigour level for the greatest vineyard efficiency and the definition of an appropriate strategy either to exploit current variability through selective harvesting or to correct variability through variable rate application of nitrogen. Significance of the Study The NDVI mapping via low-resolution satellite images associated with ground-truthing appears to be a straightforward protocol to increase sustainable vineyard management.

In situ measurement of Scots pine needle PRI

BackgroundThe Photochemical Reflectance Index (PRI) calculated from narrow-band spectral reflectance data is a vegetation index which is increasingly used as an indicator of photosynthetic activity. The leaf-level link between the status of photosynthetic apparatus and PRI has been robustly established under controlled light conditions. However, when a whole canopy is measured instantaneously, the PRI signal is heavily modified by vegetation structure and local variations in incident light conditions. To apply PRI for monitoring the photosynthesis of whole canopies under natural conditions, these large-scale measurements need to be validated against simultaneous leaf PRI. Unfortunately, PRI changes dynamically with incident light and has a large natural variation. No generally accepted procedure exists today for determining the PRI of canopy elements in situ.ResultsWe present a successful procedure for in situ measurements of needle PRI. We describe, characterize and test an optical measurement protocol and demonstrate its applicability in field conditions. The measurement apparatus consisted of a light source, needle clip, spectroradiometer and a controlling computer. The light level inside the clip was approximately two-thirds of that on sunlit needle surfaces at midday. During each measurement the needle was inserted into the clip for approximately 5 s. We found no near-instantaneous changes (sub-second scale jumps) in PRI during the measurements. The time constants for PRI variation in light to full shade acclimations were approximately 10 s. The procedure was successfully applied to monitor the greening-up of Scots pine trees. We detected both facultative (diurnal) PRI changes of 0.02 (unitless) and constitutive (seasonal) variations of 0.1. In order to reliably detect the facultative PRI change of 0.02, 20 needles need to be sampled from both sunlit and shaded locations.ConclusionsWe established a robust procedure for irradiance-dependent leaf (needle) PRI measurements, facilitating empirical scaling of PRI from leaf (needle) to full canopy level and the application of PRI to monitoring the changes in highly structured vegetation. The measured time constants, and facultative and constitutive PRI variations support the use of an artificial light for in situ PRI measurements at leaf (needle) level.

Multiangular Observation of Canopy Sun-Induced Chlorophyll Fluorescence by Combining Imaging Spectroscopy and Stereoscopy

The effect that the canopy structure and the viewing geometry have on the intensity and the spatial distribution of passively measured sun-induced chlorophyll fluorescence at canopy scale is still not well understood. These uncertainties constrain the potential use of fluorescence to quantify photosynthesis at this level. Using a novel technique, we evaluated the diurnal changes in the spatial distribution of sun-induced fluorescence at 760 nm (F760) within the canopy as a consequence of the spatial disposition of the leaves and the viewing angle of the sensor. High resolution spectral and stereo images of a full sugar beet canopy were recorded simultaneously in the field to estimate maps of F760 and the surface angle distribution, respectively. A dedicated algorithm was used to align both maps in the post-processing and its accuracy was evaluated using a sensitivity test. The relative angle between sun and the leaf surfaces primarily determined the amount of incident Photosynthetic Active Radiation (PAR), which in turn was reflected in different values of F760, with the highest values occurring in leaf surfaces that are perpendicularly oriented to the sun. The viewing angle of the sensor also had an impact in the intensity of the recorded F760. Higher viewing angles generally resulted in higher values of F760. We attribute these changes to a direct effect of the vegetation directional reflectance response on fluorescence retrieval. Consequently, at leaf surface level, the spatio-temporal variations of F760 were mainly explained by the sun–leaf–sensor geometry rather than directionality of the fluorescence emission. At canopy scale, the diurnal patterns of F760 observed on the top-of-canopy were attributed to the complex interplay between the light penetration into the canopy as a function of the display of the various leaves and the fluorescence emission of each leaf which is modulated by the exposure of the individual leaf patch to the incoming light and the functional status of photosynthesis. We expect that forward modeling can help derive analytical simplified skeleton assumptions to scale canopy measurements to the leaf functional properties.

Effects of deer on woodland structure revealed through terrestrial laser scanning

Summary Terrestrial laser scanning (TLS) captures the three‐dimensional structure of habitats. Compared to traditional methods of forest mensuration, it allows quantification of structure at increased resolution, and the derivation of novel metrics with which to inform ecological studies and habitat management. Lowland woodlands in the UK have altered in structure over the last century due to increased abundance of deer and a decline in management. We compared whole‐canopy profiles between woodlands with high (>10 deer km−2) and low deer density (c. 1 deer km−2), and in stands with and without records of management interventions in the last 20 years, providing a test case for the application of TLS in habitat assessment for conservation and management. Forty closed‐canopy lowland woodlands (height range 16·5–29·4 m) were surveyed using TLS in two regions of the UK, divided into areas of high‐ and low‐deer abundance, and between plots which had been recently managed or were unmanaged. Three‐dimensional reconstructions of the woodlands were created to document the density of foliage and stem material across the entire vertical span of the canopy. There was a 68% lower density of understorey foliage (0·5–2 m above‐ground) in high‐deer woodlands, consistent in both regions. Despite this, total amounts of foliage detected across the full canopy did not differ between deer density levels. High‐deer sites were 5 m taller overall and differed in the distribution of foliage across their vertical profile. Managed woodlands, in contrast, exhibited relatively minor differences from controls, including a lower quantity of stem material at heights from 2 to 5 m, but no difference in foliage density. All main effects were replicated equally in both regions despite notable differences in stand structures between them. Synthesis and applications. Terrestrial laser scanning allows ecologists to move beyond two‐dimensional measures of vegetation structure and quantify patterns across complex, heterogeneous, three‐dimensional habitats. Our findings suggest that reduction of deer populations is likely to have a strong impact on woodland structures and aid in restoring the complex understorey habitats required by many birds, whereas management interventions as currently practiced have limited and inconsistent effects.

Stimulation affecting latex physiology and yield under low frequency tapping of rubber (Hevea brasiliensis) clone RRIM 600 in southern Thailand

Tapping and ethylene stimulation induce s the dynamic change of latex cell metabolism. Those changes under the implement of low frequency tapping systems with ethylene stimulation were investigated during the both periods ( low yield and the high yield) of the year of production. The experiment was established at Thepa Research Station, Songk hla province by using 9 - year - old rubber trees (clone RRIM 600). An experiment was arranged as One Tree Plot design, there were five treatments following T1: S/3 d1 2d/3, T 2: S/2 d2, T3: S/2 d3 ET 2.5% Pa1(1) 8/y (m), T4: S/3 d2 ET 2.5% Pa1(1) 4/y (m) and T 5: S/3 d3 ET 2.5% Pa1(1) 12/y (m). There were three replicates in each treatment. It was found that ethylene stimulation affected the responses of initial flow rate (IFR), plugging index (PI), average latex yield (AY) and sucrose content (Suc). There was a significant difference among the treatments in the both periods. After ethylene stimulation, IFR of the T3 and T5 were superior in the low yield period and showed inferior in the high yield period compared with the T1. PI rapidly decreased in the ethylene application treatments in the both periods. AY of the T3 was the highest in the low yield period and AY of the ethylene stimulation treatments was higher than non - stimulated treatments in the high yield period. Suc of the T3 only increased on the first ta pping day after stimulation in the both periods. Expression to the ethylene stimulation in the low yield period was higher than the high yield period. It was remarkable that the stimulation was effecti vely expressed during a full canopy stage. With the pos itive impact of stimulation on latex physiological parameters, latex yield under low frequency tapping could be compe nsated by ethylene application. (Resume d'auteur)

Investigating sources of measured forest-atmosphere ammonia fluxes using two-layer bi-directional modelling

Understanding and predicting the ammonia (NH3) exchange between the biosphere and the atmosphere is important due to the environmental consequences of the presence of reactive nitrogen (Nr) in the environment. The dynamics of the natural sources are, however, not well understood, especially not for forest ecosystems due to the complex nature of this soil-vegetation-atmosphere system. Furthermore, the high reactivity of NH3 makes it technically complex and expensive to measure and understand the forest-atmospheric NH3 exchange. The aim of this study is to investigate the NH3 flux partitioning between the ground layer, cuticle and stomata compartments for two temperate deciduous forest ecosystems located in Midwestern, USA (MMSF) and in Denmark (DK-Sor). This study is based on measurements and simulations of the surface energy balance, fluxes of CO2 and NH3 during two contrasted periods of the forest ecosystems, a period with full developed canopy (MMSF) and a senescent period for the DK-Sor site, with leaf fall and leaf litter build-up. Both datasets indicate emissions of NH3 from the forest to the atmosphere. The two-layer NH3 compensation point model SURFATM-NH3 was used in combination with a coupled photosynthesis-stomatal conductance model to represent seasonal variation in canopy physiological activity for simulating both net ecosystem CO2 exchange rates (R2=0.77 for MMSF and R2=0.84 for DK-Sor) and atmospheric NH3 fluxes (R2=0.43 for MMSF and R2=0.60 for DK-Sor). A scaling of the ground layer NH3 emission potential (Гg) was successfully applied using the plant area index (PAI) to represent the build-up of a litter layer in the leaf fall period. For a closed green forest canopy (MMSF), unaffected by agricultural NH3 sources, NH3 was emitted with daytime fluxes up to 50ng NH3-N m−2s−1 and nighttime fluxes up to 30ng NH3-N m−2s−1. For a senescing forest (DK-Sor), located in an agricultural region, deposition rates of 250ng NH3-N m−2s−1 were measured prior to leaf fall, and emission rates up to 670ng NH3-N m−2s−1 were measured following leaf fall. For MMSF, simulated stomatal NH3 emissions explain the daytime flux observations well, and it is hypothesized that cuticular desorption is responsible for the observed NH3 emissions at night. During leaf fall in DK-Sor, ground fluxes dominate the NH3 flux with a mean emission rate of 150ng NH3-N m−2s−1. This study shows that forests potentially comprise a natural source of NH3 to the atmosphere, and that it is crucial to take into account the bi-directional exchange processes related to both the stomatal, cuticular and ground layer pathways in order to realistically simulate forest–atmosphere fluxes of NH3.

Real time canopy density validation using ultrasonic envelope signals and point quadrat analysis

An important goal for orchard and vineyard spraying systems is real-time adjustment of the operating parameters according to the target density, with the aim of keeping the droplets in the canopy, thus improving spray deposition and reducing spray drift. One apple orchard and two vineyards were scanned weekly using an ultrasonic system, the data provided by the sensors was correlated with the data obtained performing Point Quadrat Analysis. Results show the system has to be calibrated for each plant or variety and proved that the ultrasonic system is capable of sensing density within an average error of 4.76% during early, mid-season and full canopy, up to harvest date.

Growth decline assessment in Pinus sylvestris L. and Pinus nigra Arnold. forest by using 3-PG model.

Aim of the study: We assessed the ability of the 3-PG process-based model to accurately predict growth of Pinus sylvestris and P. nigra plantations across a range of sites, showing declining growth trends, in southern Spain.Area of study: The study area is located in “Sierra de Los Filabres” (Almería).Material and methods: The model was modified in fifteen parameters to predict diameter (DBH, cm), basal area increment (BAI, cm2 yr-1) and leaf area index (LAI, m2 m-2) in healthy trees and trees showing declining growth. We assumed that a set of specific physiological parameters (stem partitioning ratio-pFS20, maximum litterfall rate-γFx, maximum canopy conductance-gCx, specific leaf area for mature aged stands-σ1, age at which specific leaf area = ½ (σ0 + σ1), age at full canopy cover-tc, and canopy boundary layer conductance-gB) included in 3-PG would be suitable for predicting growth decline related to climate conditions. The calibrated model was evaluated using dendrochronological and LAI data obtained from plots.Main results: Observed and simulated DBH showed a high correlation (R2 > 0.99) between modelled and measured values for both species. In contrast, modelled and observed BAI showed lower correlation (R2 < 0.68). Sensitivity analysis on 3-PG outputs showed that the foliage parameters - maximum litterfall rate, maximum canopy conductance, specific leaf area for mature aged stands, age at which specific leaf area, and age at full canopy cover - were important for DBH and BAI predictions under drought stress.Research highlights: Our overall results indicated that the 3-PG model could predict growth response of pine plantations to climatic stress with desirable accuracy in southern Spain by using readily available soil and climatic data with physiological parameters derived from experiments.Keywords: Hybrid process model; forest management models; growth prediction; Pinus spp, Parameterization; forest decline.

Artificial spur extinction alters light interception by ‘Royal Gala’ apple trees

Total dry matter production by apple orchards is positively related to light interception. Consequently, maximising light interception is important in commercial apple orchards, as it directly affects tree growth and yield. Artificial spur extinction (ASE) is a method of crop load control that reduces the density and alters distribution of floral buds in whole trees. Because ASE reduces total bud numbers on the tree, total light interception may be affected. The objective of this study was to investigate the impact of ASE treatments on canopy light interception. In a mature 'Royal Gala'/M9 orchard in Hawke's Bay, New Zealand, we compared unmodified trees with trees managed using ASE. Bud densities in ASE trees were set to 2, 4 and 6 buds cm -2 branch cross-sectional area (BCA) in late winter, while unmodified trees were not altered. On both ASE and unmodified trees, crop loads were set after final fruit drop by hand thinning to 2 fruit bud -1 on 2 buds cm -2 BCA or single fruit on 4 and 6 buds cm -2 BCA. Over one season, fractional light interception by the canopies was calculated from the difference between the mean of irradiance readings above the canopy and the mean of irradiance readings below the canopy. Light interception of unmodified trees increased from ∼30% at 2.5 weeks after budbreak (WABB) to ∼60% at 8 WABB and thereafter did not change until leaf-fall. Prior to 8 WABB, light interception by trees set at ASE 6 did not differ from that by the unmodified trees. In trees set at ASE 4 and 2, light interception was initially lower (25.7 and 22.7% respectively) than other treatments and this effect lasted until 5 WABB in ASE 4 and 8 WABB in ASE 2. At full canopy, trees managed with ASE intercepted ∼4% more light than unmodified trees. Higher light interception of ASE trees is probably because ASE stimulates a higher proportion of fruiting spurs to produce short- to medium-length annual bourse shoots with greater leaf area than spur bourse buds.

Transpiration and evaporation of grapevine, two components related to irrigation strategy

The quantification of evaporation is crucial for the appropriate use of water, especially in arid areas where rainfall is scarce. An experiment was carried out in a semiarid area of Spain (Albacete) with the objective of quantifying the evaporation and transpiration of grapevine cv. Tempranillo and the effects of irrigation frequency on the evaporation. Measurements of transpiration and crop evapotranspiration of grapevine cv. Tempranillo without soil water limitations were conducted in a weighing lysimeter covered with a waterproof canvas during different periods from 2011 to 2014. The transpiration rates measured on the days after irrigation were higher than those measured when irrigation was not applied or when there were no precipitation events. Evaporation, calculated as the difference between the days on which the lysimeter surface was covered or not covered, ranged from 81% of evapotranspiration in the first phenological stages to 30% close to the time of full canopy cover. Under similar canopy cover and reference evapotranspiration, transpiration measured on the days when irrigation was applied was greater than transpiration measured on the days when the vines were not irrigated. Different irrigation strategies were applied to determine the effect of the quantity of water applied on the evaporation, and the results showed that the greater the amount of irrigation applied, the higher the efficiency, when the irrigation frequency is reduced; in fact, three times more water was applied during each irrigation event and the evaporation percentage was 7% lower. Therefore, a high irrigation frequency should be questioned in semiarid areas.

Rapid Leaf Deployment Strategies in a Deciduous Savanna.

Deciduous plants avoid the costs of maintaining leaves in the unfavourable season, but carry the costs of constructing new leaves every year. Deciduousness is therefore expected in ecological situations with pronounced seasonality and low costs of leaf construction. In our study system, a seasonally dry tropical savanna, many trees are deciduous, suggesting that leaf construction costs must be low. Previous studies have, however, shown that nitrogen is limiting in this system, suggesting that leaf construction costs are high. Here we examine this conundrum using a time series of soil moisture availability, leaf phenology and nitrogen distribution in the tree canopy to illustrate how trees resorb nitrogen before leaf abscission and use stored reserves of nitrogen and carbon to construct new leaves at the onset of the growing season. Our results show that trees deployed leaves shortly before and in anticipation of the first rains with its associated pulse of nitrogen mineralisation. Our results also show that trees rapidly constructed a full canopy of leaves within two weeks of the first rains. We detected an increase in leaf nitrogen content that corresponded with the first rains and with the movement of nitrogen to more distal branches, suggesting that stored nitrogen reserves are used to construct leaves. Furthermore the stable carbon isotope ratios (δ13C) of these leaves suggest the use of stored carbon for leaf construction. Our findings suggest that the early deployment of leaves using stored nitrogen and carbon reserves is a strategy that is integrally linked with the onset of the first rains. This strategy may confer a competitive advantage over species that deploy leaves at or after the onset of the rains.