DendroTools : R package for studying linear and nonlinear responses between tree-rings and daily environmental dataTom Levanič
, Jernej Jevšenak
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
DiRROS - Objavljeno: 16.04.2018; Ogledov: 1305; Prenosov: 458
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Green water reconstructed for Rižana watershed, SW SloveniaTom Levanič
, Urša Vilhar
, Simon Poljanšek
Povzetek: In this case study, set in south-west Slovenia, the feasibility of reconstructing green water (the combined amount of evaporated and transpired water in trees and available in the soil) was investigated. In a simplifed scheme, the amounts of green water were calculated as the diference between precipitation and discharge of the Rižana river. Based on the methods of dendroclimatology, the climate signal was tested on black pine (Pinus nigra Arnold) trees growing in the south-western part of the Rižana watershed near the Slovenian sea coast. Results showed that the measured tree-ring parameters of tree-ring width and density are strongly dependent on the amount of green water. The strongest correlation was between available green water in the period May-August and tree-ring width (r=0.61) and latewood width (r=%0.64) (both n=46, p<0.001). The climate signal is signifcant and stable through time, which enabled the reconstruction of green water data into the period before instrumentally measured data. Green water data from the May-August period were extended from 1966 back to 1937 using tree-ring width, and back to 1940 using latewood width. With additional coring of older trees and the extension of existing chronologies, even longer reconstructions could be developed.
Ključne besede: tree-ring width, tree-ring density, dendrochronology, dendroclimatology, reconstruction
DiRROS - Objavljeno: 18.04.2018; Ogledov: 1133; Prenosov: 465
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Stable isotopes reveal climate signal hidden in tree rings of endemic Balkan PinesTom Levanič
, Jernej Jevšenak
, Polona Hafner
Povzetek: Studies report the good potential of Pinus heldreichii (PIHE) and Pinus peuce (PIPE) for developing long chronologies from living trees and warn that the climate signal is weak in tree-ring widths of PIHE, and particularly PIPE. The goals of the study were to develop long chronologies, and to analyze the climate-growth relationship and potential for long climate reconstructions using tree-ring widths (TRW) and stable carbon isotopes ratios ([delta]13C) in tree rings at the northern edge of species distribution in the eastern part of Montenegro. The PIHE TRW chronology covers the period 1571-2013 (443 years) and the PIPE TRW chronology 1521-2013 (493 years). The temperature signal in PIHE TRW is weak and the precipitation signal is non-existent. PIPE has no climate signal in TRW. Both studied species have very similar [delta]13C chronologies, which allows us to merge isotope chronologies into a single composite [delta]13C Pinus chronology. The composite chronology has a strong signal related to average monthly temperature in June, July, and August and monthly values for cloudiness in July and August, with r > 0.6 and r < -0.6 for individual months, respectively. The climate signal was enhanced when June, July, and August values were merged into seasonal variables. The temporal stability of temperature, precipitation and cloudiness signals is consistent. The spatial extent of the [delta]13C chronology extends over a very large region, including all surrounding countries.
Ključne besede: Pinus heldreichii, Pinus peuce, climate reconstruction, dendrochronology, dendroclimatology, Balkan Peninsula, Bosnian pine, Macedonian pine, Pinus heldreichii H. Christ., Pinus peuce Grisb.
DiRROS - Objavljeno: 20.02.2020; Ogledov: 240; Prenosov: 158
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