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| Titel |
Experimental warming delays autumn senescence in a boreal spruce bog: Initial results from the SPRUCE experiment |
| VerfasserIn |
Andrew Richardson, Morgan Furze, Donald Aubrecht, Thomas Milliman, Robert Nettles, Misha Krassovski, Paul Hanson |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250125161
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| Publikation (Nr.) |
 EGU/EGU2016-4700.pdf |
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| Zusammenfassung |
| Phenology is considered one of the most robust indicators of the biological impacts of global
change. In temperate and boreal regions, long-term data show that rising temperatures are
advancing spring onset (e.g. budburst and flowering) and delaying autumn senescence (e.g.
leaf coloration and leaf fall) in a wide range of ecosystems. While warm and cold
temperatures, day length and insolation, precipitation and water availability, and other factors,
have all been shown to influence plant phenology, the future response of phenology to rising
temperatures and elevated CO2 still remains highly uncertain because of the challenges
associated with conducting realistic manipulative experiments to simulate future
environmental conditions.
At the SPRUCE (Spruce and Peatland Responses Under Climatic and Environmental
Change) experiment in the north-central United States, experimental temperature (0 to +9˚ C
above ambient) and CO2 (ambient and elevated) treatments are being applied to mature,
and intact, Picea mariana-Sphagnum spp. bog communities in their native habitat
through the use of ten large (approximately 12 m wide, 10 m high) open-topped
enclosures.
We are tracking vegetation green-up and senescence in these chambers, at both the
individual and whole-community level, using repeat digital photography. Within each
chamber, digital camera images are recorded every 30 minutes and uploaded to the
PhenoCam (http://phenocam.sr.unh.edu) project web page, where they are displayed
in near-real-time. Image processing is conducted nightly to extract quantitative
measures of canopy color, which we characterize using Gcc, the green chromatic
coordinate.
Data from a camera mounted outside the chambers (since November 2014) indicate
strong seasonal variation in Gcc for both evergreen shrubs and trees. Shrub Gcc rises steeply
in May and June, and declines steeply in September and October. By comparison, tree Gcc
rises gradually from March through June, and declines gradually from August through
December. These patterns can also be seen in other daily images recorded at the site since
January 2012.
Air warming treatments at SPRUCE began in August 2015, and had a substantial
influence on autumn senescence of the plant community, as a whole, within each chamber.
Generally, vegetation in the warmed chambers stayed green longer than that in the unwarmed
chambers. We characterized the seasonality by fitting a sigmoid curve to the Gcc
time series data, and we used the autumn half-maximum date of the sigmoid as an
indicator of the timing of senescence. We found a strong linear relationship between
senescence date and temperature treatment (r2 = 0.71,n = 10). Overall, senescence was
delayed by 3.5 ± 0.7 days per 1˚ C of warming. Thus, although photoperiod is
widely believed to be the key trigger for autumn senescence, our results do not
indicate that the autumn response to warming is in any way constrained by day
length.
The SPRUCE experiment is planned to running through 2025. Looking forward, we
anticipate that different results may be obtained in year 2 of the SPRUCE experiment if
warming treatments result in earlier spring onset, and increased evapotranspiration
during spring and early summer, leading to drought conditions by late summer. |
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