Comparing riparian and non-riparian boreal black spruces for their responses to climate: a dendroisotopic analysis
The objective of this study is to verify if stable isotopes (C, O) and growth series retrieved from black spruce trees (Picea mariana) growing on boreal lakeshores (riparians trees) show similar variations to those growing away from the shores (non-riparian trees). In NE Canada, riparian trees are particularly interesting because they eventually become lake subfossils, which form the main archives of hydro-climate conditions. However, the extent to which those riparian trees, growing in old-growth, humid environments, bear signals that are representative of regional growing / fractionation conditions, remains unclear.
We studied 25 riparian and 15 non riparian trees. The sampling method permitted the construction of annually resolved δ18O and δ13C series with a replication of five trees per year between 1950 and 2015 for the two populations of trees. Our analysis of the linkages between selected climate variables and chronologies of ring widths and δ13C values shows a similar response and a strong correlation between riparian and non-riparian trees. The trends in ci (intracellular concentration of CO2), and ci/ca ratios are similar between both populations. Also, both δ18O and δ13C present the same correlation with climatic variables, such as growing season maximum temperature. These results suggest that black spruce trees found in lakes are representative of the mechanisms of response to climate that predominate in boreal forests. Therefore, the proxy series from ancient riparian trees (now on lake floors or buried in sediments) should yield climate reconstructions that are illustrative of regional phenomena.