Stable carbon isotopes and drought signal in the tree-rings of northern white-cedar trees from boreal central Canada. (Invited)
Abstract
Despite the demonstrated value of tree-ring δ13C analysis, there have been a limited number of dendroisotopic δ13C studies conducted throughout the North American boreal forest. Dendroisotopic series are generally short and few tree species/habitats have been investigated. We present recent work conducted in the boreal forest of Manitoba, central Canada. Old northern white-cedar (Thuja occidentalis L.) trees were sampled at their northwestern limit of distribution. The objectives of the study were 1) to determine the major climatic factors associated with each of the ring-width and δ13C chronology and 2) to provide a multi-century inference of drought events based on tree-ring δ13C and ring width analyses. We also compared the δ13C chronology developed from Thuja occidentalis trees to that of white spruce (Picea glauca Moench) and jack pine (Pinus banksiana Lamb.) trees developed in northern Manitoba. Fifteen T. occidentalis trees were selected for δ13C analysis and holocellulose was isolated from each tree-ring through standard chemical extraction techniques. The annually resolved δ13C chronology spanned from 1650 to 2006 A.D. and incorporated dead and living T. occidentalis trees selected from two sites. Hydric organic conditions on horizontal topography punctuated by scattered wet depressions prevailed at both sites. A ring-width chronology was also developed from both dead and living T. occidentalis trees from the region. All chronology development followed standardization of each of the δ13C series using a 60-year cubic spline function with a 50% frequency response. Results indicated that ring width was more often associated with climate conditions prevailing in the year prior to ring formation compared to the δ13C values. During the year of ring-formation, ring width was associated with spring and early summer conditions whereas, δ13C was more indicative of overall summer conditions. Conditions conducive to moisture stress were however important for both radial growth and carbon assimilation, particularly during the month of June in the current growing season. During this month, the ring-width index was sensitive to moisture stress (positive and negative association with precipitation and temperature, respectively) whereas the δ13C index showed enrichment with increasing temperature and drought index. Our results also suggested that in T. occidentalis ring width was more responsive to prolonged drought than δ13C since periods of decreased radial growth most often coincided with documented drought intervals. Past experimental studies had indicated that young T. occidentalis trees may adjust stomatal conductance following exposure to water deficit suggesting that trees could develop a tolerance to subsequent water deficit. We speculate that in periods of extended drought, the absence of sustained year-to-year enriched δ13C values in T. occidentalis trees may thus reflect stomatal conditioning. This suggests that tree-ring δ13C in T. occidentalis trees may have limited utility in drought reconstruction. Comparing the T. occidentalis δ13C data with that of other coniferous species from northern Manitoba revealed that T. occidentalis was the most δ13C-enriched species and that it portrayed the lowest δ13C sensitivity. Low correlations also were observed between species chronologies.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMGC24B..03T
- Keywords:
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- 0454 BIOGEOSCIENCES / Isotopic composition and chemistry;
- 1812 HYDROLOGY / Drought;
- 1851 HYDROLOGY / Plant ecology;
- 9350 GEOGRAPHIC LOCATION / North America