Exploration of long-term growth changes using the tree-ring detrending program “Spotty”

Abstract

A new tree-ring detrending program (Spotty) performs analyses of changing growth trends and environmental signals with tree age. Spotty is particularly useful in understanding the nature of long-term, centennial scale trends in tree-ring data but has a variety of dendrochronological applications. The program permits the user to define up to fifty age classes from a file of increments data. Age classes can be defined as ranges (e.g., 25–50, 100–150 years) or as single years (e.g., 25, 40, 55 years). The program will select the data corresponding to these classes and fit spline functions to the respective age class, data clouds. The user is allowed to choose a certain spline bandwidth, and can decide to fit splines to either the raw or Regional Curve Standardization (RCS) detrended data – with the RCS routine being included in Spotty – thus permitting the analysis of different underlying frequencies for each selected age class. The individual, age class splines may also be compared for common (or deviating) variance. Spotty facilitates color graphics and allows saving results for further use in other programs. PC and Mac versions of the program are available at the WSL Dendro Sciences ( www.wsl.ch/forschung/forschungsunits/dendro) and LDEO Tree-Ring Lab ( www.ldeo.columbia.edu/res/fac/trl/public/publicSoftware.html) web pages.