title: Greenness indices from digital cameras predict the timing and seasonal dynamics of canopy-scale photosynthesis.
abstract: The proliferation of digital cameras co-located with eddy covariance instrumentation provides new opportunities to better understand the relationship between canopy phenology and the seasonality of canopy photosynthesis. In this paper we analyze the abilities and limitations of canopy color metrics measured by digital repeat photography to track seasonal canopy development and photosynthesis, determine phenological transition dates, and estimate intra-annual and interannual variability in canopy photosynthesis. We used 59 site-years of camera imagery and net ecosystem exchange measurements from 17 towers spanning three plant functional types (deciduous broadleaf forest, evergreen needleleaf forest, and grassland/crops) to derive color indices and estimate gross primary productivity (GPP). GPP was strongly correlated with greenness derived from camera imagery in all three plant functional types. Specifically, the beginning of the photosynthetic period in deciduous broadleaf forest and grassland/crops and the end of the photosynthetic period in grassland/crops were both correlated with changes in greenness; changes in redness were correlated with the end of the photosynthetic period in deciduous broadleaf forest. However, it was not possible to accurately identify the beginning or ending of the photosynthetic period using camera greenness in evergreen needleleaf forest. At deciduous broadleaf sites, anomalies in integrated greenness and total GPP were significantly correlated up to 60 days after the mean onset date for the start of spring. More generally, results from this work demonstrate that digital repeat photography can be used to quantify both the duration of the photosynthetically active period as well as total GPP in deciduous broadleaf forest and grassland/crops, but that new and different approaches are required before comparable results can be achieved in evergreen needleleaf forest.
authors.forename: Michael
authors.initials: M
authors.lastname: Toomey
authors.forename: Mark A
authors.initials: MA
authors.lastname: Friedl
authors.forename: Steve
authors.initials: S
authors.lastname: Frolking
authors.forename: Koen
authors.initials: K
authors.lastname: Hufkens
authors.forename: Stephen
authors.initials: S
authors.lastname: Klosterman
authors.forename: Oliver
authors.initials: O
authors.lastname: Sonnentag
authors.forename: Dennis D
authors.initials: DD
authors.lastname: Baldocchi
authors.forename: Carl J
authors.initials: CJ
authors.lastname: Bernacchi
authors.forename: Sebastien C
authors.initials: SC
authors.lastname: Biraud
authors.forename: Gil
authors.initials: G
authors.lastname: Bohrer
authors.forename: Edward
authors.initials: E
authors.lastname: Brzostek
authors.forename: Sean P
authors.initials: SP
authors.lastname: Burns
authors.forename: Carole
authors.initials: C
authors.lastname: Coursolle
authors.forename: David Y
authors.initials: DY
authors.lastname: Hollinger
authors.forename: Hank A
authors.initials: HA
authors.lastname: Margolis
authors.forename: Harry
authors.initials: H
authors.lastname: Mccaughey
authors.forename: Russell K
authors.initials: RK
authors.lastname: Monson
authors.forename: J William
authors.initials: JW
authors.lastname: Munger
authors.forename: Stephen
authors.initials: S
authors.lastname: Pallardy
authors.forename: Richard P
authors.initials: RP
authors.lastname: Phillips
authors.forename: Margaret S
authors.initials: MS
authors.lastname: Torn
authors.forename: Sonia
authors.initials: S
authors.lastname: Wharton
authors.forename: Marcelo
authors.initials: M
authors.lastname: Zeri
authors.forename: Andrew D
authors.initials: AD
authors.lastname: And
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Richardson
mesh_terms: D065928:Forests; D010781:Photography / Q000295:instrumentation* / Q000379:methods*; D010788:Photosynthesis / Q000502:physiology*; D010860:Pigments, Biological; D010944:Plants / Q000145:classification / Q000378:metabolism*; D012621:Seasons; D013997:Time Factors
chemical_list: D010860:Pigments, Biological