Evidence of periodicities related to climate and planetary behaviors in ring-width chronologies of Atlas cedar (Cedrusatlantica) in Morocco

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Abstract
Mean standardized 120-year ring-width chronologies of Cedrusatlantica (Endl.) Carrière (Atlas cedar) computed for four geographical regions of Morocco (Rif, Central Middle Atlas, Eastern Middle Atlas, High Atlas) and mean annual 49-year precipitation series computed for four bioclimatic strata that overlay the geographical regions were analyzed in the frequency domain. Their predominant frequency components were estimated at the end of a stepwise procedure that involved the analysis of a modified periodogram. A 7-year periodicity has been detected in all the precipitation series and in some of the tree-ring series. These ring-width indices also show periodicities of about 11 and 18.6 years, which have been assigned aposteriori to the planetary system dynamics, i.e., to sunspot activity and lunar nodal tide, respectively. Among-region differences in the year to year fluctuations of C. atlantica radial growth were statistically assessed using analysis of variance of the finite Fourier transform of the mean standardized ring-width chronologies for 39 sites located in the four geographical regions. In particular, they were assessed at frequencies corresponding to the detected periodicities related to climate and planetary behaviors. Low to high concordance levels have been observed among tree-ring series from different geographical regions, and these concordance levels were related to the sensitivity of Catlantica to limiting factors.

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