Abstract
Abstract. With increasing awareness of the consequences of climate change for global ecosystems, the focus and application of tree ring research have shifted to reconstruction of long-term climate-related trends in tree growth. Contemporary methods for estimating and removing biological growth trends from tree ring series (standardization) are ill-adapted to shade-tolerant species, leading to biases in the resultant chronologies. Further, many methods, including regional curve standardization (RCS), encounter significant limitations for species in which accurate age estimation is difficult. In this study we present and test two tree ring standardization models that integrate tree size in the year of ring formation into the estimation of the biological growth trend. The first method, dubbed size-deterministic standardization (SDS), uses tree diameter as the sole predictor of the growth trend. The second method includes the combined (COMB) effects of age and diameter. We show that both the SDS and COMB methods reproduce long-term trends in simulated tree ring data better than conventional methods; this result is consistent across multiple species. Further, when applied to real tree ring data, the SDS and COMB models reproduce long-term, time-related trends as reliably as traditional RCS and more reliably than other common standardization methods (i.e. C-method, basal area increments, conservative detrending). We recommend the inclusion of tree size in the year of ring formation in future tree ring standardization models, particularly when dealing with shade-tolerant species, as it does not compromise model accuracy and allows for the inclusion of unaged trees.
Highlights
Tree rings have long-served as a record of environmental change in forest ecosystems
We present a variant of the regional curve standardization (RCS) method that uses tree size, measured by diameter at breast height (DBH), in the year of ring formation as the primary determinant of the common biological growth trend
Using simulated tree ring data from the shade-tolerant species sugar maple, we have shown that standardization models that include tree size in the year of ring formation (SDS, COMB) produced chronologies that retain long-term and low-frequency variation better than those produced by models that only included age as a predictor (RCS)
Summary
Tree rings have long-served as a record of environmental change in forest ecosystems. With increasing awareness of the consequences of climate change for global ecosystems, the focus and application of tree ring research have shifted to reconstruction of low-frequency climate-related trends in tree growth (Gedalof and Berg, 2010; Boisvenue and Running, 2006; Jacoby and D’Arrigo, 1997). As it stands, previous optimism regarding the benefits of carbon fertilization for forest growth (Battipaglia et al, 2013; Norby et al, 2005) has been quelled by a lack of consistent evidence in real forests. Central to all of these studies is the assumption that long-term growth trends can be accurately and unbiasedly estimated from tree ring data
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