John Gamon | University of Alberta (original) (raw)

Papers by John Gamon

Monitoring the ongoing declines in biodiversity and ecosystem health is essential for formulating... more Monitoring the ongoing declines in biodiversity and ecosystem health is essential for formulating societal responses. The Group on Earth Observations Biodiversity Observation Network (GEO BON) was created in 2008 to develop a global monitoring network, but that is a huge task with much remaining work. Fortunately, satellite remote sensing can help by providing periodic, global data that is not otherwise available. Continued advances – many of which are discussed in this book’s 19 chapters – in science as well as sensor and computational technology have an increasingly important role. However, taking advantage of these requires bringing together a variety of elements and disciplines, and it is with this in mind that a conceptual system architecture is here suggested. Key elements of this cloud-based architecture include: explicit support for collaboration, particularly across disciplines, to facilitate development of new algorithms; access to a wide variety of data, including satelli...

Remote Sensing of Environment, 2000

Spectral imaging data acquired with Advanced Visible tion bands and in those based on water thick... more Spectral imaging data acquired with Advanced Visible tion bands and in those based on water thickness. The relationship between WI and the canopy RWC signifi-Infrared Imaging Spectrometer over Point Dume (Los cantly improved when only data from plots with green Angeles County, CA, USA) were used to assess the ability vegetation cover Ͼ70% were considered (r 2 ϭ0.88, pϽ of hyperspectral reflectance data to estimate canopy Rel-0.001). All the indices studied had an important strucative Water Content (RWC) at the landscape level. The tural component (as indicated by the strong correlation study was performed on 23 vegetation stands comprised with NDVI), yet only the indices WI and NDWI addiof three characteristic chaparral plant communities, with tionally responded to water content. These results indicontrasting phenological stages and canopy cover. Sevcate that the WI and NDWI are sensitive to variations eral estimates of water content based on the near-infrain canopy relative water content at the landscape scale. red (NIR; reflectance indices and water thickness derived ©Elsevier Science Inc., 2000 from reflectance and radiance data) and shortwave infrared (SWIR) water absorption bands were compared to measurements of vegetation structure and water content

Remote Sensing, 2019

Remotely sensed vegetation indices (RSVIs) can be used to efficiently estimate terrestrial primar... more Remotely sensed vegetation indices (RSVIs) can be used to efficiently estimate terrestrial primary productivity across space and time. Terrestrial productivity, however, has many facets (e.g., spatial and temporal variability, including seasonality, interannual variability, and trends), and different vegetation indices may not be equally good at predicting them. Their accuracy in monitoring productivity has been mostly tested in single-ecosystem studies, but their performance in different ecosystems distributed over large areas still needs to be fully explored. To fill this gap, we identified the facets of terrestrial gross primary production (GPP) that could be monitored using RSVIs. We compared the temporal and spatial patterns of four vegetation indices (NDVI, EVI, NIRV, and CCI), derived from the MODIS MAIAC data set and of GPP derived from data from 58 eddy-flux towers in eight ecosystems with different plant functional types (evergreen needle-leaved forest, evergreen broad-lea...

Nature ecology & evolution, 2018

Biodiversity promotes ecosystem function as a consequence of functional differences among organis... more Biodiversity promotes ecosystem function as a consequence of functional differences among organisms that enable resource partitioning and facilitation. As the need for biodiversity assessments increases in the face of accelerated global change, novel approaches that are rapid, repeatable and scalable are critical, especially in ecosystems for which information about species identity and the number of species is difficult to acquire. Here, we present 'spectral diversity'-a spectroscopic index of the variability of electromagnetic radiation reflected from plants measured in the visible, near-infrared and short-wave infrared regions (400-2,400 nm). Using data collected from the Cedar Creek biodiversity experiment (Minnesota, USA), we provide evidence that the dissimilarity of species' leaf spectra increases with functional dissimilarity and evolutionary divergence time. Spectral diversity at the leaf level explains 51% of total variation in productivity-a proportion compara...

Remote Sensing, 2016

Remote sensing is often used to assess rangeland condition and biophysical parameters across larg... more Remote sensing is often used to assess rangeland condition and biophysical parameters across large areas. In particular, the relationship between the Normalized Difference Vegetation Index (NDVI) and above-ground biomass can be used to assess rangeland primary productivity (seasonal carbon gain or above-ground biomass "yield"). We evaluated the NDVI-yield relationship for a southern Alberta prairie rangeland, using seasonal trends in NDVI and biomass during the 2009 and 2010 growing seasons, two years with contrasting rainfall regimes. The study compared harvested biomass and NDVI from field spectrometry to NDVI from three satellite platforms: the Aqua and Terra Moderate Resolution Imaging Spectroradiometer (MODIS) and Système Pour l'Observation de la Terre (SPOT 4 and 5). Correlations between ground spectrometry and harvested biomass were also examined for each growing season. The contrasting precipitation patterns were easily captured with satellite NDVI, field NDVI and green biomass measurements. NDVI provided a proxy measure for green plant biomass, and was linearly related to the log of standing green biomass. NDVI phenology clearly detected the green biomass increase at the beginning of each growing season and the subsequent decrease in green biomass at the end of each growing season due to senescence. NDVI-biomass regressions evolved over each growing season due to end-of-season senescence and carryover of dead biomass to the following year. Consequently, midsummer measurements yielded the strongest correlation (R 2 = 0.97) between NDVI and green biomass, particularly when the data were spatially aggregated to better match the satellite sampling scale. Of the three satellite platforms (MODIS Aqua, MODIS Terra, and SPOT), Terra yielded the best agreement with ground-measured NDVI, and SPOT yielded the weakest relationship. When used properly, NDVI from satellite remote sensing can accurately estimate peak-season productivity and detect interannual variation in standing green biomass, and field spectrometry can provide useful validation for satellite data in a biomass monitoring program in this prairie ecosystem. Together, these methods can be used to identify the effects of year-to-year precipitation variability on above-ground biomass in a dry mixed-grass prairie. These findings have clear applications in monitoring yield and productivity, and could be used to support a rangeland carbon monitoring program.

Remote Sensing, 2016

This study evaluated the seasonal productivity of a prairie grassland (Mattheis Ranch, in Alberta... more This study evaluated the seasonal productivity of a prairie grassland (Mattheis Ranch, in Alberta, Canada) using a combination of remote sensing, eddy covariance, and field sampling collected in 2012-2013. A primary objective was to evaluate different ways of parameterizing the light-use efficiency (LUE) model for assessing net ecosystem fluxes at two sites with contrasting productivity. Three variations on the NDVI (Normalized Difference Vegetation Index), differing by formula and footprint, were derived: (1) a narrow-band NDVI (NDVI 680,800 , derived from mobile field spectrometer readings); (2) a broad-band proxy NDVI (derived from an automated optical phenology station consisting of broad-band radiometers); and (3) a satellite NDVI (derived from MODIS AQUA and TERRA sensors). Harvested biomass, net CO 2 flux, and NDVI values were compared to provide a basis for assessing seasonal ecosystem productivity and gap filling of tower flux data. All three NDVIs provided good estimates of dry green biomass and were able to clearly show seasonal changes in vegetation growth and senescence, confirming their utility as metrics of productivity. When relating fluxes and optical measurements, temporal aggregation periods were considered to determine the impact of aggregation on model accuracy. NDVI values from the different methods were also calibrated against f APAR green (the fraction of photosynthetically active radiation absorbed by green vegetation) values to parameterize the APAR green (absorbed PAR) term of the LUE (light use efficiency) model for comparison with measured fluxes. While efficiency was assumed to be constant in the model, this analysis revealed hysteresis in the seasonal relationships between fluxes and optical measurements, suggesting a slight change in efficiency between the first and second half of the growing season. Consequently, the best results were obtained by splitting the data into two stages, a greening phase and a senescence phase, and applying separate fits to these two periods. By incorporating the dynamic irradiance regime, the model based on APAR green rather than NDVI best captured the high variability of the fluxes and provided a more realistic depiction of missing fluxes. The strong correlations between these optical measurements and independently measured fluxes demonstrate the utility of integrating optical with flux measurements for gap filling, and provide a foundation for using remote sensing to extrapolate from the flux tower to larger regions (upscaling) for regional analysis of net carbon uptake by grassland ecosystems.

Remote Sensing of Environment, 1994

We followed diurnal and seasonal changes in physiology and spectral reflectance of leaves through... more We followed diurnal and seasonal changes in physiology and spectral reflectance of leaves throughout the canopies of sunflower plants grown in control, nitrogen (N)-limited, and water-stressed plots. Leaves from control sunflower plants had significantly higher levels of nitrogen, chlorophyll (chl), ribulose bis phosphate carboxylase/oxygenase (RuBPCase) activity and photosynthetic rates and lower starch content and leaf thickness than N-limited plants. Water-stressed plants had the highest N and chl contents (on an area basis). They also had the lowest water potential and photosynthetic rates, in spite of maintaining high RuBPCase activities. Leaves from stressed plants (especially N-limited) had significantly higher reflectances in the visible wavelengths and lower in the near IR than leaves from control plants. The only clear trend across canopy levels was the higher reflectance at all wavelengths but especially in the visible of the lower (oldest) leaves. ND VI-like parameters were useful in distinguishing stress and control leaves over the growing season. However, several narrow-band indices provided better physiological information than NDVI. The physiological reflectance index (PRI) (R55o-R53o/ Rs~o + R53o) followed diurnal changes in xanthophyU pigments and photosynthetic rates of control and N-limited leaves. The

ORNL Distributed Active Archive Center Datasets, 1999

Public reporting burden for this collectionof information is estimated to average 1 hour per resp... more Public reporting burden for this collectionof information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send commentsregardingthis burden estimate or any other aspect of this collectionof information,including suggestions for reducing this burden,to Washington Headquarters Services, Directoratefor _nformatlonOperationsand Reports,

2013 IEEE International Geoscience and Remote Sensing Symposium - IGARSS, 2013

Remote Sensing, 2018

The quantification of isoprene and monoterpene emissions at the ecosystem level with available mo... more The quantification of isoprene and monoterpene emissions at the ecosystem level with available models and field measurements is not entirely satisfactory. Remote-sensing techniques can extend the spatial and temporal assessment of isoprenoid fluxes. Detecting the exchange of biogenic volatile organic compounds (BVOCs) using these techniques is, however, a very challenging goal. Recent evidence suggests that a simple remotely sensed index, the photochemical reflectance index (PRI), which is indicative of light-use efficiency, relative pigment levels and excess reducing power, is a good indirect estimator of foliar isoprenoid emissions. We tested the ability of PRI to assess isoprenoid fluxes in a temperate deciduous forest in central USA throughout the entire growing season and under moderate and extreme drought conditions. We compared PRI time series calculated with MODIS bands to isoprene emissions measured with eddy covariance. MODIS PRI was correlated with isoprene emissions for most of the season, until emissions peaked. MODIS PRI was also able to detect the timing of the annual peak of emissions, even when it was advanced in response to drought conditions. PRI is thus a promising index to estimate isoprene emissions when it is complemented by information on potential emission. It may also be used to further improve models of isoprene emission under drought and other stress conditions. Direct estimation of isoprene emission by PRI is, however, limited, because PRI estimates LUE, and the relationship between LUE and isoprene emissions can be modified by severe stress conditions.

ORNL Distributed Active Archive Center Datasets

The BOREAS TE-4 team collected continuous records of gas exchange under ambient conditions from i... more The BOREAS TE-4 team collected continuous records of gas exchange under ambient conditions from intact boreal forest trees in the BOREAS NSA from 23-Jul-1996 until 14-Aug-1996. These measurements can be used to test models of photosynthesis, stomatal conductance, and leaf respiration, such as SiB2 (Sellers et al., 1996) or the leaf model (Collatz et al., 1991), and programs can be obtained from the investigators. The data are stored in tabular ASCII files.

Ecophysiology of Photosynthesis, 1995

Most photosynthesis measurements involve remote determinations. In gas-exchange systems, includin... more Most photosynthesis measurements involve remote determinations. In gas-exchange systems, including those based on chambers, atmospheric gradients, and eddy correlation, photosynthesis determinations are remote in the sense that the measurements are based on effects of leaves, plants, or canopies on the gaseous environment. In radiation-based remote sensing, the subject of this chapter, photosynthesis determinations are based on interactions between leaves, plants, or canopies and the radiation environment. The wavelength bands potentially useful for measurements related to photosynthesis range from the visible through the thermal and microwave regions. While remote sensing generally connotes large-scale satellite measurements, radiation-based remote sensing can be effectively utilized to address questions in photosynthesis research ranging in spatial scale from the chloroplast to the globe.

Plant, Cell and Environment, 1991

ABSTRACT . Sunflower plants (Helianthus annuus L., cv. CGL 208) were field-grown in adjacent plot... more ABSTRACT . Sunflower plants (Helianthus annuus L., cv. CGL 208) were field-grown in adjacent plots of varying resource availability. Control plants received irrigation (on a 4–5 d interval) and high levels of fertilizer nitrogen. Nutrient-stress (N-stress) plants received control levels of irrigation but no nutrient amendments and were determined to be nitrogen-limited. Water-stress (H2O-stress) plants received control levels of fertilizer nitrogen, but no irrigation after approximately 6 weeks of plant growth. Both stress treatments reduced maximum and diurnal net photosynthesis (A) but resulted in different physiological or biochemical adjustments that tended to maintain or increase A per unit of resource (nitrogen or water) in shortest supply while decreasing the ratio of A per unit of abundant resource. Nutrient-stress reduced total foliar nitrogen, foliar chlorophyll, and initial and total RuBPCase activities, thereby enhancing or preserving photosynthetic nitrogen-use efficiency (NUE), defined as the maximum A observed per unit of leaf nitrogen, relative to the control and H2O-stress treatments. In addition, N-stress reduced photosynthetic water-use efficiency (WUE), defined as the ratio of A to stomatal conductance to water vapour (g). The slope of A versus g increased with H2O-stress. In addition, sunflower plants responded to H2O-stress by accumulating foliar glucose and sucrose and by exhibiting diurnal leaf wilting, which presumably provided additional improvements in photosynthetic WUE through osmoregulation and reduction of midday radiation interception respectively. Photosynthetic NUE was decreased by H2O-stress in that control levels of total nitrogen, foliar chlorophyll, and RuBPCase activities were maintained even after mean diurnal levels of A had fallen to less than 50% of the control level. We conclude that field-grown sunflower manages a trade-off between photosynthetic WUE and NUE, increasing use efficiency of the scarce resource while decreasing use efficiency of the abundant resource.

New Phytologist, 1995

summary Reflectance changes at 531 nm, associated with the zeaxanthin-antheraxanthin-violaxanthin... more summary Reflectance changes at 531 nm, associated with the zeaxanthin-antheraxanthin-violaxanthin interconversion and the related thylakoid energization, are widespread among plant species. We evaluated an index based on 531 nm reflectance ('PRI', Photochemical ...

Aquatic Botany, 1997

We studied the reflectance spectra of the emergent aquatic vegetation of Searsville Lake in coast... more We studied the reflectance spectra of the emergent aquatic vegetation of Searsville Lake in coastal central California using a high spectral resolution hand-held spectroradiometer with the aim of assessing spectral indices as indicators of photosynthetic radiation-use efficiency. The photochemical reflectance index (PRI), defined as (R,,,-Rs7a)/(RS3r + R,,), was strongly correlated with the ratio of secondary and protective pigments to chlorophyll a and with epoxidation state (EPS) of the xanthophyll cycle pigments (violaxanthin + 0.5 antheraxanthin)/(violaxanthin + antheraxanthin + zeaxanthin), and therefore, with photosynthetic radiation-use efficiency (PRUE) (measured as mol CO, mol-' photons). This reflectance-based measure seems to be useful as a remote index of aquatic vegetation photosynthetic function and physiological status. These results extend and reinforce previous studies conducted in terrestrial vegetation that indicate a functional relationship between PRI, EPS, and PRUE at leaf and canopy scales. 0 1997 Elsevier Science B.V.

Ecology, 2000

Spectral transmittance signatures (expressed as absorbances) were studied as a potential indicato... more Spectral transmittance signatures (expressed as absorbances) were studied as a potential indicator of photosynthetic and nonphotosynthetic contributions to the canopyabsorbed photosynthetically active radiation (PAR). An analytical approach was made under laboratory conditions using synthetic canopies in an integrating sphere. This approach provided the basis for identifying spectral (absorbance-based) features and indices to estimate green (photosynthetic) and nongreen (structural and dead materials) contributions to canopy absorbance. A strong relationship was found between the amplitude of the first derivative of the absorbance (A RE) and green area, while the integrated absorbance in the PAR region (A PAR) mainly responded to variations in total area. The ratio A RE /A PAR was closely correlated to the fraction of photosynthetic area to total area (i.e., the canopy green fraction). Similarly, the ratio and normalized difference of the absorbances at 680 and 900 nm (A SR and A NDVI) closely tracked variations in the canopy green fraction. Subsequently, these indices were tested in field plots with contrasting structural characteristics. Under field conditions, A RE was a good indicator of green biomass. The indices A SR and A NDVI were also reliable indicators of green biomass but were affected by changes in sampling conditions. As in the lab study, A RE /A PAR was a good indicator of canopy green fraction. Thus, ground-based measurements of canopy spectral transmittance provided a tool for determining the photosynthetic contribution to canopy-absorbed PAR by correcting for nonphotosynthetic canopy components. Moreover, A RE showed a strong correlation with conventional vegetation indices derived from spectral reflectance measurements. This technique could be a useful tool for plant ecophysiology studies and a field-validation method for remote-sensing studies.

IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium

In advance of the FLEX mission, experimental studies are needed to better understand the factors ... more In advance of the FLEX mission, experimental studies are needed to better understand the factors driving Solar-Induced Fluorescence (SIF) emission from vegetation across different temporal and spatial scales. Here, we present findings from boreal (evergreen and deciduous) forest trees and Midwestern (annual) crops, illustrating effects of seasonal downregulation and drought on the fluorescence signals. Further work is needed to develop defensible, quantitative fluorescence measurements, and to partition the drivers of the fluorescence signals into effects of structure and physiology.

Thanks for the positive comments and useful suggestions. In the revisions, I have argued for a mo... more Thanks for the positive comments and useful suggestions. In the revisions, I have argued for a more integrated approach to optical sampling that includes SIF along with reflectance-based indices and other approaches. The influence of both APAR and downregulation on fluorescence signals have been mentioned, and additional references on SIF have been added. However, given the length of the review, a full discussion of all the SIF literature seemed beyond the scope of the current paper, particularly since most of that literature has not yet been fully integrated with reflectance-based approaches. Also, there remain practical and theoretical challenges to doing so (given the parallel history of the approaches and the ongoing need for more robust instrumentation). I leave integrated SIF-reflectance studies as a recommendation for future work, particularly in the context of radiative transfer modeling, with the flux tower network as an ideal testbed for advancing our understanding of the ...

New Phytologist

Leaf reflectance spectra have been increasingly used to assess plant diversity. However, we do no... more Leaf reflectance spectra have been increasingly used to assess plant diversity. However, we do not yet understand how spectra vary across the tree of life or how the evolution of leaf traits affects the differentiation of spectra among species and lineages. Here we describe a framework that integrates spectra with phylogenies and apply it to a global dataset of over 16 000 leaf-level spectra (400-2400 nm) for 544 seed plant species. We test for phylogenetic signal in spectra, evaluate their ability to classify lineages, and characterize their evolutionary dynamics. We show that phylogenetic signal is present in leaf spectra but that the spectral regions most strongly associated with the phylogeny vary among lineages. Despite among-lineage heterogeneity, broad plant groups, orders, and families can be identified from reflectance spectra. Evolutionary models also reveal that different spectral regions evolve at different rates and under different constraint levels, mirroring the evolution of their underlying traits. Leaf spectra capture the phylogenetic history of seed plants and the evolutionary dynamics of leaf chemistry and structure. Consequently, spectra have the potential to provide breakthrough assessments of leaf evolution and plant phylogenetic diversity at global scales.

Remote Sensing of Environment, 2000

Remote Sensing, 2019

Nature ecology & evolution, 2018

Remote Sensing, 2016

Remote Sensing of Environment, 1994

ORNL Distributed Active Archive Center Datasets, 1999

2013 IEEE International Geoscience and Remote Sensing Symposium - IGARSS, 2013

Remote Sensing, 2018

ORNL Distributed Active Archive Center Datasets

Ecophysiology of Photosynthesis, 1995

Plant, Cell and Environment, 1991

New Phytologist, 1995

Aquatic Botany, 1997

Ecology, 2000

IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium

New Phytologist