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| Titel |
Climate- and disturbance-driven changes in vegetation composition and structure limit future potential carbon storage in the Greater Yellowstone Ecosystem, USA |
| VerfasserIn |
Paul D. Henne, Todd J. Hawbaker, Feng Zhao, Chengquan Huang, Erin M. Berryman, Zhiliang Zhu |
| 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 |
250129401
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| Publikation (Nr.) |
 EGU/EGU2016-9509.pdf |
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| Zusammenfassung |
| The Greater Yellowstone Ecosystem (GYE) provides unique opportunities to understand how
changing climate, land use, and disturbance affect ecosystem carbon balance. The GYE is
one of the largest, most intact ecosystems in the United States. However, distinct management
histories on National Park, National Forest, and private lands, elevational climate gradients,
and variable fire activity, have created a mosaic of stand ages and forest types. It is uncertain
how greenhouse forcing may alter the carbon balance of the GYE. Whereas increasing
temperatures may enhance productivity and perpetuate the GYE as a carbon sink,
climate-driven increases in fire frequency may offset productivity gains by limiting
biomass accumulation. We investigated how changes in fire frequency and size
may affect vegetation dynamics and carbon sequestration potential in the GYE
using the LANDIS-II dynamic landscape vegetation model. LANDIS-II provides
sufficient spatial resolution to capture landscape-level variation in forest biomass
and forest types (i.e. 90 × 90 m grid cells), but can integrate disturbance regimes
and vegetation dynamics across the entire GYE (92,000 km2). We initiated our
simulations with biomass and stand conditions that preceded the exceptional 1988
fire, when 16% of the GYE burned. We inferred the biomass, species abundances,
and stand demographics of each model cell by combining satellite imagery with
forest inventory data, and developed two fire regime scenarios from historical fire
records. We developed a historic wildfire scenario with infrequent fires by excluding
1988 from our calibration of fire sizes and frequencies, and a future scenario with
more frequent and larger fires by including 1988 in our calibrations. Fire frequency
increased in all forest types in our future scenario, with a 152% increase in the
annual forest area burned relative to observed area burned during recent decades.
However, the changes in fire frequency varied among forest types, with the largest
increases in lodgepole pine (Pinus contorta; 332% increase) and spruce/fir (Picea
engelmannii, Abies lasiocarpa; 243% increase) stands. In model runs with the historic fire
regime, average stand age and live biomass remained consistent with pre-1988
values during the 200-year simulation period; biomass increased significantly only in
recently-logged areas. In contrast, a marked shift to younger stands with lower biomass
occurred in the future fire scenario. Average stand age declined from 112 years to 31
years in lodgepole pine stands, and from 191 years to 65 years in spruce/fir stands,
with consequent reductions in living biomass. A smaller shift in stand age was
simulated for douglas-fir (Pseudotsuga menziesii) stands (i.e. 121 to 92 years). These
fire-driven changes in stand age and biomass coincided with important shifts in species
abundances. Specifically, lodgepole pine stands replaced large areas previously
dominated by spruce and fir. Our results suggest that the potential for increasing the
amount of fossil fuel emissions offset by carbon sequestration on public lands in the
American West is limited by ongoing changes in disturbance regimes. Instead,
land managers may need to consider strategies to adapt to climate change impacts. |
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