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| Titel |
Water limitations on forest carbon cycling and conifer traits along a steep climatic gradient in the Cascade Mountains, Oregon |
| VerfasserIn |
L. T. Berner, B. E. Law |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 22 ; Nr. 12, no. 22 (2015-11-19), S.6617-6635 |
| Datensatznummer |
250118171
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| Publikation (Nr.) |
 copernicus.org/bg-12-6617-2015.pdf |
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| Zusammenfassung |
| Severe droughts occurred in the western
United States during recent decades, and continued human greenhouse gas
emissions are expected to exacerbate warming and drying in this region. We
investigated the role of water availability in shaping forest carbon cycling
and morphological traits in the eastern Cascade Mountains, Oregon, focusing
on the transition from low-elevation, dry western juniper (Juniperus
occidentalis) woodlands to higher-elevation, wetter ponderosa pine
(Pinus ponderosa) and grand fir (Abies grandis) forests. We
examined 12 sites in mature forests that spanned a 1300 mm yr−1
gradient in mean growing-year climate moisture index
(CMIgy
), computed annually (1964 to 2013) as
monthly precipitation minus reference evapotranspiration and summed October
to September. Maximum leaf area, annual aboveground productivity, and
aboveground live tree biomass increased with CMIgy
(r2 = 0.67–0.88, P < 0.05), approximately 50-, 30-, and 10-fold
along this drier to wetter gradient. Interannual fluctuations in CMI
affected the annual radial growth of 91 % of juniper, 51 % of pine,
and 12 % of fir individuals from 1964 to 2013. The magnitude of the
site-average growth–CMI correlations decreased with increased
CMIgy
(r2 = 0.53, P < 0.05). All three
species, particularly fir, experienced pronounced declines in radial growth
from c. 1985 to 1994, coinciding with a period of sustained below-average
CMIgy
and extensive insect outbreak. Traits of
stress-tolerant juniper included short stature, high wood density for
cavitation resistance, and high investment in water transport relative to
leaf area. Species occupying wetter areas invested more resources in height
growth in response to competition for light relative to investment in
hydraulic architecture. Consequently, maximum tree height, leaf
area : sapwood area ratio, and stem wood density were all correlated with
CMIgy
. The tight coupling of forest carbon
cycling and species traits with water availability suggests that warmer and
drier conditions projected for the 21st century could have significant
biogeochemical, ecological, and social consequences in the Pacific Northwest. |
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