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 QUEBEC

Variations in periodicities of the radial growth response of black ash (Fraxinus nigra Marsh.) exposed to yearly spring flooding were studie d in relation to hydrological fluctuations and site ecological factors at Lake Duparquet in northwestern Quebec. Eight mean standardized 188 0-1988 ring-width 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 dendrochronolog ical series were submitted to spectral analysis based on the multi-fre quential periodogram statistic. Monthly mean water discharge records o f the Harricana River, and monthly mean temperature and total precipit ation 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 s eries; the 3.75- and 7.5-year components are harmonics of a 15-year pe riodicity 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 predo minant 6.25-year periodicity was detected in the water discharge of th e Harricana River and, to a lesser extent, in the ring-width chronolog ies of mid and high elevations. After an about 11-year periodicity was detected in several tree-ring and climatic series, peaks in the corre sponding sine waves fitted to the tree-ring series were found to corre spond to maxima in sunspot activity. Effects of geomorphological landf orm 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 r eplicates. Significant landform effects were observed at short to long er periodicities, while an elevation environmental gradient was finely delimited. The low to high concordance levels observed in the periodi cities of tree-ring series from different stands were related to ecolo gical factors.