Abstract
Age-related trends are present in tree-ring widths (TRW), but their presence in tree rings isotope is debated. It is unclear how cambial age influences the relationships between TRW and isotopes. Tree-ring isotopes of alpine larch and cembran-pine trees showed only trends in the juvenile period (>100 years), which might mask the inter-relations between tree-ring proxies during cambial age. This work tries to unmask the age-trend influences by examining the correlations in TRW—stable isotopes with and without age-trend correction. The non-detrended and linear-detrended values of TRW, of δD and δ18O showed significant correlations for ages up to 100 years, but not afterward. However, the correlation values, after spline or first-difference time-series detrending, were not age-related. Thus, detrending methods affect the correlations in the juvenile phase and may affect climate-related interpretations. The correlations between TRW and δ13C were not age-related, while those among the isotopes were significant throughout the ages. The correlation between δ13C and δD was the exception, as it became significant only after age > 100 years, suggesting a different use of reserves in the juvenile phase. In conclusion, the relationships among the tree-ring parameters are stable in all the different detrend scenarios after the juvenile phase, and they can be used together in multi-proxy paleoclimatic studies. The data of the juvenile phase can be used after spline-detrending or first-difference time-series calculation, depending on the purpose of the analysis to remove age-related trends. The work also provides clues on the possible causes of juvenile age trends.
Highlights
Tree ring widths (TRW) are widely used for paleoclimatic study due to having the great advantage of annual resolution and accurate dating on the calendar timescale [1,2,3]
TRW and δ18 O show positive and significant correlations in the first 50 years followed by a loss of significant correlation after approximately 100 years (Figure 2b,e)
In both cases the correlations TRW-δD and TRW-δ18 O of the two youngest age classes present absolute r values that are much higher than those using the values of all ages shown in the blue box
Summary
Tree ring widths (TRW) are widely used for paleoclimatic study due to having the great advantage of annual resolution and accurate dating on the calendar timescale [1,2,3].The cellulose of such tree-ring samples and its stable isotopes can provide complementary proxies for paleoclimate and tree physiology [4,5]. The normal procedure for detecting such trends is to align the data on the cambial age (ring number from the pith) to verify if there are consistent modifications with age [10] This procedure is efficient, but does not give clues for the interpretation of the presence or absence of the trends. They may be caused by factors external to the trees, such as canopy effect, precipitation, water source, or internal factors linked to changes in metabolic activity. Our recent work on the samples of this database detected age-related trends of the values of hydrogen, oxygen and carbon isotopes only in the first
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