The relationship between carbon dioxide uptake and canopy colour from two camera systems in a deciduous forest in southern England

Abstract

Summary1. Carbon dioxide flux measurements using the eddy covariance (EC) methodology have helped researchers to develop models of ecosystem carbon balance. However, making reliable predictions of carbon fluxes is not straightforward due to phenological changes and possible abiotic/biotic stresses that profoundly influence tree functioning. 2. To assess the influence of canopy phenological state on CO 2 flux, we installed two different digital camera systems at different viewing angles (an outdoor webcam with a near-horizontal view and a commercial 'fisheye' digital camera with a downward view) on a flux measurement tower in southern England and tracked the visual change of the canopy in this oak-dominated (Quercus robur L.) forest over two growing seasons. 3. Changes in the setting of the camera's white balance substantially affected the quality of the webcam images. However, the timing of the onset of greening and senescence was, nevertheless, detectable for the individual trees as well as the overall canopy for both years. The greening-up date assessed from the downward images from a hemispherical lens was ∼5 days earlier than from the horizontal-view images, because of ground vegetation development (not visible in the horizontal view). 4. The effects of a late air frost in 2010 were evident in the canopy greenness, and these led to reductions in daily gross primary productivity (GPP). The cameras recorded differences between individual tree crowns, showing their different responses to the late frost. 5. A major new finding from this work is the strong relationship between GPP and Hue, which was stronger than the relationship between GPP and NDVI.

Tracking forest phenology and seasonal physiology using digital repeat photography: a critical assessment

“…A late-summer decline in GEP was evident in most years, which did not closely match either G cc or LAI. In contrast to previous suggestions that hue is more correlated to GEP and LAI than G cc (Mizunuma et al 2013), we found no positive correlation between hue and GEP (R ¼À0.2, P ¼ 0.03) or LAI (R ¼À0.3, P , 0.01) at our site. Indeed the seasonal cycle of hue is critically dependent on the color balance of the camera (Appendix: Fig.…”

Relationship between leaf physiologic traits and canopy color indices during the leaf expansion period in an oak forest

“…The chlorophyll concentration has high relationship with the photosynthesis rate and the gross primary productivity (GPP) (Field andMooney 1986, Morecroft et al 2003). Therefore, the peak GPP may not synchronize with the peak of the greenness indices, such as Gcc and ExG, during the growing season (Richardson et al 2007, Ahrends et al 2009, Mizunuma et al 2013. On the other hand, Richardson et al (2007) evaluated the relationship between broadband normalized difference vegetation index (NDVI) and the greenness index in the canopy scale, and showed that the peak of NDVI and Gcc, ExG have highly time-serial synchronization (Richardson et al 2007).…”

Exploring the Potential for Automatic Extraction of Vegetation Phenological Metrics from Traffic Webcams

“…The images captured by these traffic cameras offer extended analysis possibilities, particularly when coupled with similar resolution observations of precipitation and temperature, carbon flux measurements and soil properties [47]. This will benefit the understanding of budgets of carbon and water exchange (e.g., gross primary productivity (GPP) [50,51]) and moreover shed light on any interannual variability in the growing season caused by weather conditions (e.g., windstorms [52]) and other occasional but often severe biotic stresses that influence the physiological status of trees [45,53]. Beyond this there is scope for the data to be used in the understanding of ecosystem interactions, food chains, pollination, breeding and migration [54,55].…”