Coastal forests in the Mid-Atlantic region are threatened by sea level rise through chronic and episodic salinization and hydrologic alterations, leading to inland marsh migration and the occurrence of ghost forests. This study uses dendrochronology to explore the impact of rising sea level on the annual growth of Juniperus virginiana (the Eastern red cedar) at the St. Jones component of the Delaware National Estuarine Research Reserve in Dover, DE. Chronologies from low and high elevations were developed, and a difference chronology (high–low) was generated. A rapid field assessment of tree stress indicated greater stress in low elevation trees, and low elevation soil tests showed higher soil moisture and salt content compared to samples from high elevation. Ring width indices were analyzed in relation to water level, precipitation, the Standardized Precipitation Evapotranspiration Index, and temperature, with Pearson’s correlation analysis. Trees growing at low elevation showed greater climate sensitivity and responded favorably to cool, wet summers. Over time, correlations between growth and climate variables decreased, while negative correlations with tidal water level increased—a pattern that presented nearly a decade earlier in the low elevation system. Given the widespread distribution of the Eastern red cedar and its sensitivity to changes in sea level, this species may be particularly useful as a sentinel of change in coastal landscapes as sea levels rise.
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Yellow-cedar blue intensity tree-ring chronologies as records of climate in Juneau, Alaska, USA
This is the first study to generate and analyze the climate signal in blue intensity (BI) tree-ring chronologies from Alaska yellow-cedar (Callitropsis nootkatensis (D. Don) Oerst. ex D.P. Little). The latewood BI chronology shows a much stronger temperature sensitivity than ring width and can thus provide information on past climate. The well-replicated BI chronology exhibits a positive January–August mean maximum temperature signal for 1900–1975, after which it loses temperature sensitivity following the 1976–1977 shift in northeastern Pacific climate. The positive temperature response appears to recover and remains strong for the most recent decades, but the coming years will continue to test this observation. This temporary loss of temperature sensitivity from about 1976 to 1999 is not evident in ring width or in a change in forest health but is consistent with prior work linking cedar decline to warming. A confounding factor is the uncertain influence of a shift in color variation from the heartwood–sapwood boundary. Future expansion of the yellow-cedar BI network and further investigation of the influence of the heartwood–sapwood transitions in the BI signal will lead to a better understanding of the utility of this species as a climate proxy.
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- Award ID(s):
- 1659322
- NSF-PAR ID:
- 10147329
- Date Published:
- Journal Name:
- Canadian Journal of Forest Research
- Volume:
- 49
- Issue:
- 12
- ISSN:
- 0045-5067
- Page Range / eLocation ID:
- 1483 to 1492
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The Arctic is rapidly warming, and tundra vegetation community composition is changing from small, prostrate shrubs to taller, erect shrubs in some locations. Across much of the Arctic, the sensitivity of shrub secondary growth, as measured by growth ring width, to climate has changed with increased warming, but it is not fully understood how shrub age contributes to shifts in climate sensitivity.
We studied Siberian alder,
Alnus viridis ssp.fruticosa , a large nitrogen‐fixing shrub that has responded to climate warming with northward range expansion over the last 50 years. We used serial sectioning of 26 individual shrubs and 94 cross‐sections to generate a 98‐year growth ring chronology, including one 142‐year‐old, Siberian alder in Northern Alaska. We tested how secondary growth sensitivity to climate has changed over the past century (1920–2017) and how shrub age affects climate sensitivity of alder growth through time.We found that over time, alder growth as expressed by the stand chronology became more sensitive to July mean monthly air temperature. Older shrubs displayed higher sensitivity to June and July temperature than younger alders. However, during the first 30 years of growth of any shrub, temperature sensitivity did not differ among individuals. In addition, the June temperature sensitivity of growth series from individual cross‐sections depended on the age of the attached shrub.
Our results suggest that age contributes to climate sensitivity, likely through modifying internal shrub carbon budgets by changing size and reducing alder's dependence on N‐fixation over time. Older, more sensitive alder may enhance C and N‐cycling while having greater recruitment potential. Linking alder age to climate sensitivity, recruitment and total N‐inputs will enable us to better predict ecosystem carbon and nitrogen cycling in a warmer Arctic.
Read the free
Plain Language Summary for this article on the Journal blog. -
The science of tropical dendrochronology is now emerging in regions where tree-ring dating had previously not been considered possible. Here, we combine wood anatomical microsectioning techniques and radiocarbon analysis to produce the first tree-ring chronology with verified annual periodicity for a new dendrochronological species, Neltuma alba (commonly known as “algarrobo blanco”) in the tropical Andes of Bolivia. First, we generated a preliminary chronology composed of six trees using traditional dendrochronological methods (i.e., cross-dating). We then measured the 14 C content on nine selected tree rings from two samples and compared them with the Southern Hemisphere (SH) atmospheric 14 C curves, covering the period of the bomb 14 C peak. We find consistent offsets of 5 and 12 years, respectively, in the calendar dates initially assigned, indicating that several tree rings were missing in the sequence. In order to identify the tree-ring boundaries of the unidentified rings we investigated further by analyzing stem wood microsections to examine anatomical characteristics. These anatomical microsections revealed the presence of very narrow terminal parenchyma defining several tree-ring boundaries within the sapwood, which was not visible in sanded samples under a stereomicroscope. Such newly identified tree rings were consistent with the offsets shown by the radiocarbon analysis and allowed us to correct the calendar dates of the initial chronology. Additional radiocarbon measurements over a new batch of rings of the corrected dated samples resulted in a perfect match between the dendrochronological calendar years and the 14 C dating, which is based on good agreement between the tree-ring 14 C content and the SH 14 C curves. Correlations with prior season precipitation and temperature reveal a strong legacy effect of climate conditions prior to the current Neltuma alba growing season. Overall, our study highlights much potential to complement traditional dendrochronology in tree species with challenging tree-ring boundaries with wood anatomical methods and 14 C analyses. Taken together, these approaches confirm that Neltuma alba can be accurately dated and thereby used in climatic and ecological studies in tropical and subtropical South America.more » « less
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Abstract. We evaluate a range of blue intensity (BI) tree-ringparameters in eight conifer species (12 sites) from Tasmania and New Zealandfor their dendroclimatic potential, and as surrogate wood anatomicalproxies. Using a dataset of ca. 10–15 trees per site, we measured earlywoodmaximum blue intensity (EWB), latewood minimum blue intensity (LWB), and theassociated delta blue intensity (DB) parameter for dendrochronologicalanalysis. No resin extraction was performed, impacting low-frequency trends.Therefore, we focused only on the high-frequency signal by detrending alltree-ring and climate data using a 20-year cubic smoothing spline. All BIparameters express low relative variance and weak signal strength comparedto ring width. Correlation analysis and principal component regressionexperiments identified a weak and variable climate response for mostring-width chronologies. However, for most sites, the EWB data, despite weaksignal strength, expressed strong coherence with summer temperatures.Significant correlations for LWB were also noted, but the sign of therelationship for most species is opposite to that reported for all coniferspecies in the Northern Hemisphere. DB results were mixed but performedbetter for the Tasmanian sites when combined through principal componentregression methods than for New Zealand. Using the fullmulti-species/parameter network, excellent summer temperature calibrationwas identified for both Tasmania and New Zealand ranging from 52 % to78 % explained variance for split periods (1901–1950/1951–1995), withequally robust independent validation (coefficient of efficiency = 0.41 to0.77). Comparison of the Tasmanian BI reconstruction with a quantitativewood anatomical (QWA) reconstruction shows that these parameters recordessentially the same strong high-frequency summer temperature signal.Despite these excellent results, a substantial challenge exists with thecapture of potential secular-scale climate trends. Although DB, band-pass,and other signal processing methods may help with this issue, substantiallymore experimentation is needed in conjunction with comparative analysis withring density and QWA measurements.more » « less
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Abstract Reconstructing how biota have responded to fast‐paced warming events in the past can help predict their responses to rapid climate changes in the future. Here we suggest that natural communities located near glaciers are useful laboratories for this purpose as they experienced climate changes accentuated by past ice‐margin fluctuations. By reconstructing an Alaskan glacier's position over a 166‐year period and measuring the periglacial air temperatures over the last 3 years, we estimate that the adjacent temperate rainforest episodically cooled and warmed by 0.5–0.7°C/decade. These rates of change exceed most historical warming trends measured elsewhere on Earth and are comparable to the rates of climate warming predicted for the next century. The ring‐width responses of yellow‐cedar trees growing at varying distances from the ice edge illustrate the potential for using periglacial ecosystems to predict how forests may respond to rapid warming in the future.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1139/cjfr-2018-0525
