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1.
New features in the dendroTools R package : bootstrapped and partial correlation coefficients for monthly and daily climate data
Jernej Jevšenak, 2020, izvirni znanstveni članek

Povzetek: Climate-growth relationships are usually analysed using monthly climate data. The dendroTools R package also provides methodological approaches that enable climate-growth analysis for daily climate data. Such analysis reveals more complete climate signal patterns. In this article, new functions of the dendroTools R package are presented. Partial correlation coefficients are now implemented and can be used to calculate the strength of a linear relationship between two variables, while controlling for a third variable. Bootstrapped correlations can then be used to provide insights into the confidence intervals of statistical estimates. The calculation of partial and bootstrapped correlations is available for daily and monthly data. Finally, data transformation, S3 generic plotting and summary functions are also presented here.
Ključne besede: dendroTools, daily climate data, partial correlations, bootstrap, dendroclimatology
Objavljeno v DiRROS: 24.09.2020; Ogledov: 775; Prenosov: 259
.pdf Celotno besedilo (604,66 KB)
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2.
Daily climate data reveal stronger climate-growth relationships for an extended European tree-ring network
Jernej Jevšenak, 2019, izvirni znanstveni članek

Povzetek: An extended European tree-ring network was compiled from various sources of tree-ring data from Europe, northern Africa and western Asia. A total of 1860 tree-ring chronologies were used to compare correlation coefficients calculated with aggregated day-wise and month-wise mean temperature, sums of precipitation and standardised precipitation-evapotranspiration index (SPEI). For the daily approach, climate data were aggregated over periods ranging from 21 to 365 days. Absolute correlations calculated with day-wise aggregated climate data were on average higher by 0.060 (temperature data), 0.076 (precipitation data) and 0.075 (SPEI data). Bootstrapped correlations are computationally expensive and were therefore calculated on a 69.4% subset of the data. Bootstrapped correlations indicated statistically significant differences between the daily and monthly approach in approximately 1% of examples. A comparison of time windows used for calculations of correlations revealed slightly later onset and earlier ending day of the year for the daily approach, while the largest differences between the two approaches arise from window lengths: Correlations calculated with day-wise aggregated climate data were calculated using fewer days than the monthly approach. Differences in the onset and ending dates of periods for the daily and monthly approaches were greater for precipitation and SPEI data than for temperature data.
Ključne besede: tree rings, dendroclimatology, tree-ring network, daily climate data, climate-growth relationships, dendroTools
Objavljeno v DiRROS: 21.08.2019; Ogledov: 1767; Prenosov: 682
.pdf Celotno besedilo (889,22 KB)
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3.
DendroTools : R package for studying linear and nonlinear responses between tree-rings and daily environmental data
Jernej Jevšenak, Tom Levanič, izvirni znanstveni članek

Povzetek: We introduce in this paper the dendroTools R package for studying the statistical relationships between tree-ring parameters and daily environmental data. The core function of the package is daily_response(), which works by sliding a moving window through daily environmental data and calculating statistical metrics with one or more tree ring proxies. Possible metrics are correlation coefficient, coefficient of determination and adjusted coeffi- cient of determination. In addition to linear regression, it is possible to use a nonlinear artificial neural network with the Bayesian regularization training algorithm (brnn). dendroTools provides the opportunity to use daily climate data and robust nonlinear functions for the analysis of climate-growth relationships. Models should thus be better adapted to the real (continuous) growth of trees and should gain in predictive capabilities. The dendroTools R package is freely available in the CRAN repository. The functionality of the package is demonstrated on two examples, one using a mean vessel area (MVA) chronology and one a traditional tree-ring width (TRW).
Ključne besede: dendroclimatology, daily climate data, running window, nonlinear modelling, tree-ring proxies, climate reconstruction
Objavljeno v DiRROS: 16.04.2018; Ogledov: 2481; Prenosov: 1272
.pdf Celotno besedilo (1,19 MB)
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