Variations in Periodicities of the Ring Width of Black Ash (Fraxinus nigra Marsh.) in Relation to Flooding and Ecological Site Factors at Lake Duparquet in Northwestern Québec

Variations in periodicities of the radial growth response of black ash ( Fraxinus nigra Marsh.) exposed to yearly spring flooding were studied in relation to hydrological fluctuations and site ecological factors at Lake Duparquet in northwestern Quebec. Eight mean standardized 1880-1988 ringwidth chronologies were constructed from trees growing on the floodplain, for five specific stand geomorphological landforms and three classes of elevation from the lake level. These dendrochronological series were submitted to spectral analysis based on the multi-frequential periodogram statistic. Monthly mean water discharge records of the Harricana River, and monthly mean temperature and total precipitation series collected at the Iroquois Falls weather station, all over the 1915‐1990 period, were analyzed similarly. About 3.5-, 3.75-, and 7.5-year periodicities were detected in all the dendrochronological series; the 3.75- and 7.5-year components are harmonics of a 15-year periodicity that a majority of the series presented. All the ring-width chronologies, with the exceptions of the high elevation class and the stand near a bog, showed a strong biennial periodic component. A predominant 6.25-year periodicity was detected in the water discharge of the Harricana River and, to a lesser extent, in the ring-width chronologies of mid and high elevations. After an about 11-year periodicity was detected in several tree-ring and climatic series, peaks in the corresponding sine waves fitted to the tree-ring series were found to correspond to maxima in sunspot activity. Effects of geomorphological landform and elevation from the lake on the fluctuations from year to year of the radial growth of black ash were assessed by a two-way analysis of variance of the finite Fourier transform of ring-width chronologies from 46 sites, using landform and elevation as factors and sites as replicates. Significant landform effects were observed at short to longer periodicities, while an elevation environmental gradient was finely delimited. The low to high concordance levels observed in the periodicities of tree-ring series from different stands were related to ecological factors.