Craig Macfarlane

Photographic exposure affects indirect estimation of leaf area in plantations of Eucalyptus globulus Labill

Calibrations of indirect methods for estimating leaf area are usually based on small data sets and are often species-specific and may even be stand-specific. We used the Licor LAI-2000 plant canopy analyser (PCA) as a reference to calibrate leaf area measurements based on hemispherical photography. Ten stands of 6‐8 year-old, plantation grown Tasmanian bluegum (Eucalyptus globulus Labill.) in Western Australia were used to investigate the effects of variations in sampling position, photographic exposure and image processing on leaf area (or leaf area index, L) estimated using hemispherical photography. We also compared our photographic estimates of L with those obtained via destructive sampling (allometry) in both evenly spaced and highly clumped stands of E. globulus. Varying exposure by one stop affected estimated L by approximately 13% but we confirmed that correct exposure can be approximately predicted by metering exposure outside the canopy. In situations where metering exposure outside the canopy is impractical, we recommend the use of empirically derived relationships between L estimated from photographic images made at a constant exposure and actual L derived from other means. Mean tilt angle obtained for E. globulusfrom the photographic method (68.7 2.5 s.e.) agreed well with estimates for Eucalyptusspecies from other studies. Owing to the non-random arrangement of crowns within plantations, sampling position significantly affected mean tilt angle. In highly clumped stands with closely spaced double rows and wide inter-double row gaps, underestimation of L by 16‐30% with the photographic method was probably the result of greater foliage clumping at the crown level. We concluded that, in stands of E. globulus and probably other broadleaf species with evenly distributed crowns, foliage clumping at the shoot or branch level is unlikely to be a significant source of error in indirect estimates of L. Scattering of blue light may result in large underestimates of L when using the PCA. In stands with ‘extreme’ architecture, indirect, light interception-based methods are likely to greatly underestimate L, although, positioning the sensor so as remove large gaps from view may allow accurate estimates of L even in these stands. ©2000 Published by Elsevier Science B.V. All rights reserved.

Measurement of Crown Cover and Leaf Area Index Using Digital Cover Photography and Its Application to Remote Sensing

Digital cover photography (DCP) is a high resolution, vertical field-of-view method for ground-based estimation of forest metrics, and has advantages over fisheye sensors owing to its ease of application and high accuracy. We conducted the first thorough technical appraisal of DCP using both single-lens-reflex (DSLR) and point-and-shoot cameras and concluded that differences result primarily from the better quality optics available for the DSLR camera. File compression, image size and ISO equivalence had little or no effect on estimates of forest metrics. We discuss the application of DCP for ground truthing of remotely sensed canopy metrics, and highlight its strengths over fisheye photography for testing and calibration of vertical field-of-view remote sensing.

Phloem sap and leaf δ13C, carbohydrates and amino acid concentrations in Eucalyptus globulus change systematically according to flooding and water deficit treatment

Phloem is a central conduit for the distribution of photoassimilate, nutrients, and signals among plant organs. A revised technique was used to collect phloem sap from small woody plants in order to assess changes in composition induced by water deficit and flooding. Bled phloem sap δ13C and sugar concentrations were compared to δ13C of bulk material, soluble carbon extracts, and the neutral sugar fraction from leaves. Amino acid composition and inorganic ions of the phloem sap was also analysed. Quantitative, systematic changes were detected in phloem sap composition and δ13C in response to altered water availability. Phloem sap δ13C was more sensitive to changes of water availability than the δ13C of bulk leaf, the soluble carbon fraction, and the neutral soluble fraction of leaves. Changes in water availability also resulted in significant changes in phloem sugar (sucrose and raffinose), inorganic nutrient (potassium), and amino acid (phenylalanine) concentrations with important implications for the maintenance of phloem function and biomass partitioning. The differences in carbohydrate and amino acid composition as well as the δ13C in the phloem, along with a new model system for phloem research, offer an improved understanding of the phloem-mediated signal, nutrient, and photoassimilate transduction in relation to water availability.

Climate determines vascular traits in the ecologically diverse genus Eucalyptus

Current theory presumes that natural selection on vascular traits is controlled by a trade-off between efficiency and safety of hydraulic architecture. Hence, traits linked to efficiency, such as vessel diameter, should show biogeographic patterns; but critical tests of these predictions are rare, largely owing to confounding effects of environment, tree size and phylogeny. Using wood sampled from a phylogenetically constrained set of 28 Eucalyptus species, collected from a wide gradient of aridity across Australia, we show that hydraulic architecture reflects adaptive radiation of this genus in response to variation in climate. With increasing aridity, vessel diameters narrow, their frequency increases with a distribution that becomes gradually positively skewed and sapwood density increases while the theoretical hydraulic conductivity declines. Differences in these hydraulic traits appear largely genotypic in origin rather than environmentally plastic. Data reported here reflect long-term adaptation of hydraulic architecture to water availability. Rapidly changing climates, on the other hand, present significant challenges to the ability of eucalypts to adapt their vasculature.

Application of an enthalpy balance model of the relation between growth and respiration to temperature acclimation of Eucalyptus globulus seedlings.

The enthalpy balance model of growth uses measurements of the rates of heat and CO2 production to quantify rates of decarboxylation, oxidative phosphorylation and net anabolism. Enthalpy conversion efficiency (ηH) and the net rate of conservation of enthalpy in reduced biosynthetic products (RSGΔHB) can be calculated from metabolic heat rate (q) and CO2 rate (RCO2). ηH is closely related to carbon conversion efficiency and the efficiency of conservation of available electrons in biosynthetic products. RSGΔHB and η can be used, together with biomass composition, to describe the rate and efficiency of growth of plant tissues. q is directly related to the rate of O2 consumption and the ratio q:RCO2 is inversely related to the respiratory quotient. We grew seedlings of Eucalyptus globulus at 16 and 28°C for four to six weeks, then measured q and RCO2 using isothermal calorimetry. Respiratory rate at a given temperature was increased by a lower growth temperature but ηH was unaffected. Enthalpy conversion efficiency—and, therefore, carbon conversion efficiency—decreased with increasing temperature from 15 to 35°C. The ratio of oxidative phosphorylation to oxygen consumption (P/O ratio) was inferred in vivo from ηH and by assuming a constant ratio of growth to maintenance respiration with changing temperature. The P/O ratio decreased from 2.1 at 10-15°C to less than 0.3 at 35°C, suggesting that decreased efficiency was not only due to activity of the alternative oxidase pathway. In agreement with predictions from non-equilibrium thermodynamics, growth rate was maximal near 25°C, where the calculated P/O ratio was about half maximum. We propose that less efficient pathways, such as the alternative oxidase pathway, are necessary to satisfy the condition of conductance matching whilst maintaining a near constant phosphorylation potential. These conditions minimize entropy production and maximize the efficiency of mitochondrial energy conversions as growing conditions change, while maintaining adequate finite rates of energy processing.

Plant mitochondria electron partitioning is independent of short-term temperature changes

We tested the hypotheses that relative activity of the less efficient alternative oxidase (AOX) path changes with diurnal temperature changes, and thus changes carbon use efficiency with temperature. The activities of the alternative and cytochrome oxidase (COX) paths in plant tissues of three species were determined by measuring 18O/16O discrimination and total respiration from 17 to 36 degrees C. A new, more accurate method for calculating oxygen uptake rate from the mass spectrometry data was developed. Total carbon use efficiency was calculated from the ratio of respiratory heat and CO2 rates measured from 10 to 35 degrees C. Oxygen isotope discrimination (22.9 +/- 0.4 per thousand) and AOX participation were invariant with temperature in leaf tissue of Cucurbita pepo, Nicotiana sativa and Vicia faba, thus falsifying the first part of the hypothesis. Stress responses of respiration at the temperature extremes limited the range for which carbon use efficiency could be accurately measured to 15-30 degrees C in N. sativa, to 10-25 degrees C in C. pepo and to 20-30 degrees C in V. faba. Carbon-use efficiency was invariant at these temperatures in these species, demonstrating that changes in other pathways that would vary carbon-use efficiency were also invariant with temperature.

Estimation of foliage clumping from the LAI-2000 Plant Canopy Analyzer: effect of view caps

Key messageFoliage clumping can be estimated from logarithm averaging method in LAI-2000. The spatial scaling of clumping effects considered by the instrument is dependent on the sensor’s azimuthal view.AbstractAccurate estimates of foliage clumping index (Ω) are required to improve the retrieval of leaf area index (L) from optical instruments like LAI-2000/2200 Plant Canopy Analyzer (PCA) and digital hemispherical photography (DHP). The logarithm averaging method is often used to approximate L because clumping effects are considered at scales larger than the sensor’s field of view. However, the spatial scaling considered for logarithm averaging typically differs between PCA and DHP, resulting in different estimates of foliage clumping. Based on simulation, we demonstrated that applying restricting azimuth view caps (e.g., 45° or 10°) allows reliable estimation of Ω and more accurate estimation of L from PCA. Simulated Ω and L values were comparable to those measured using the PCA, DHP and litter traps. Linear averaging of the gap fractions across readings at a plot or site yields a concurrent estimate of effective leaf area index (Le), thus enabling the calculation of Le, L, and Ω from a single instrument fitted with view caps. Users need to be aware that the method they use for averaging gap fractions determines whether they are measuring Le or L, and PCA users need to be aware that they are applying increasingly large corrections for foliage clumping as they use more restrictive view caps, a fact that they can use to their advantage to improve estimates of L.

The SMAP Level 4 Carbon Product for Monitoring Ecosystem Land–Atmosphere CO 2 Exchange

The National Aeronautics and Space Administration’s Soil Moisture Active Passive (SMAP) mission Level 4 Carbon (L4C) product provides model estimates of the Net Ecosystem CO2 exchange (NEE) incorporating SMAP soil moisture information. The L4C product includes NEE, computed as total ecosystem respiration less gross photosynthesis, at a daily time step posted to a 9-km global grid by plant functional type. Component carbon fluxes, surface soil organic carbon stocks, underlying environmental constraints, and detailed uncertainty metrics are also included. The L4C model is driven by the SMAP Level 4 Soil Moisture data assimilation product, with additional inputs from the Goddard Earth Observing System, Version 5 weather analysis, and Moderate Resolution Imaging Spectroradiometer satellite vegetation data. The L4C data record extends from March 31, 2015 to present with ongoing production and 8–12 day latency. Comparisons against concurrent global CO2 eddy flux tower measurements, satellite solar-induced canopy florescence, and other independent observation benchmarks show favorable L4C performance and accuracy, capturing the dynamic biosphere response to recent weather anomalies. Model experiments and L4C spatiotemporal variability were analyzed to understand the independent value of soil moisture and SMAP observations relative to other sources of input information. This analysis highlights the potential for microwave observations to inform models where soil moisture strongly controls land CO2 flux variability; however, skill improvement relative to flux towers is not yet discernable within the relatively short validation period. These results indicate that SMAP provides a unique and promising capability for monitoring the linked global terrestrial water and carbon cycles.

The Australian SuperSite Network: A continental, long-term terrestrial ecosystem observatory

Ecosystem monitoring networks aim to collect data on physical, chemical and biological systems and their interactions that shape the biosphere. Here we introduce the Australian SuperSite Network that, along with complementary facilities of Australias Terrestrial Ecosystem Research Network (TERN), delivers field infrastructure and diverse, ecosystem-related datasets for use by researchers, educators and policy makers. The SuperSite Network uses infrastructure replicated across research sites in different biomes, to allow comparisons across ecosystems and improve scalability of findings to regional, continental and global scales. This conforms with the approaches of other ecosystem monitoring networks such as Critical Zone Observatories, the U.S. National Ecological Observatory Network; Analysis and Experimentation on Ecosystems, Europe; Chinese Ecosystem Research Network; International Long Term Ecological Research network and the United States Long Term Ecological Research Network. The Australian SuperSite Network currently involves 10 SuperSites across a diverse range of biomes, including tropical rainforest, grassland and savanna; wet and dry sclerophyll forest and woodland; and semi-arid grassland, woodland and savanna. The focus of the SuperSite Network is on using vegetation, faunal and biophysical monitoring to develop a process-based understanding of ecosystem function and change in Australian biomes; and to link this with data streams provided by the series of flux towers across the network. The Australian SuperSite Network is also intended to support a range of auxiliary researchers who contribute to the growing body of knowledge within and across the SuperSite Network, public outreach and education to promote environmental awareness and the role of ecosystem monitoring in the management of Australian environments.

Image Analysis of Hemispherical Photographs, Algorithms and Calculations

This chapter is a logical continuation of the chapter on acquisition of hemispherical photographs (HP) in forest environments (Fournier et al. in Hemispherical photography in forest science: theory, methods, applications, Springer, Berlin, 2017), and describes the analysis of hemispherical or ‘fisheye’ canopy photographs, including the calculation of canopy solar radiation and structure. The workflow for digital images proceeds through several steps, from image input to the calculation of canopy structure and solar radiation variables: Image input includes image selection and quality control, while image processing consists of editing and contrast enhancement, registration with coordinate systems, and the creation of configuration or parameter files. Image classification is a critical step in the HP workflow . In the past, pixels were classified as either canopy or sky using manual selection of a threshold grayscale value. More recently, automated methods have become available for classifying pixels and have greatly increased the efficiency and productivity of HP workflow. We discuss some of these new methods for producing a binary data set from the grayscale information in HP. Calculations and output of results from HP requires the definition of sampling grids or circular transects , along which gap fractions and gap sizes are measured as a function of zenith and azimuth directions. Quantitative solar and canopy structure indices, such as site factors and leaf area index (LAI), are output to spreadsheets or text files. Conclusions. This final step includes the interpretation of the results, which are generally output to spreadsheets, databases and models.