The significance of forest cover, topographic position and some meteorological variables for throughfall of rain under a balsam fir forest in western Newfoundland

Van Kesteren, Alfred Rein (2004) The significance of forest cover, topographic position and some meteorological variables for throughfall of rain under a balsam fir forest in western Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

Throughfall, the process of rainfall passage through a tree canopy to the forest floor, is a major water flux in the forest hydrological cycle. Balsam fir has not been studied for this flux in western Newfoundland where it is the predominant tree species. -- Data were collected from June 7 to October 7 1998 to describe throughfall magnitudes and variability. An analysis of variance model was applied to investigate balsam fir forest cover, topographic position and interaction of these factors on throughfall receipt. A sample size of 36 plots for incident rainfall and 36 for throughfall was monitored during the study. Correlative relationships with meteorological variables recorded by a on-site data logger system were also investigated. -- Balsam fir forest cover was found to be the predominant variable influencing throughfall flux on a seasonal basis, with the throughfall percentage averaging 85% of incident rainfall over 28 discrete rainfall events. High inter-event variability in throughfall flux was found and is attributed to differences in the character of the rainfall events over the study duration. Topographic position was not significant on a seasonal basis. Significant meteorological influence amongst collections was detected. Air temperature, relative humidity and wind speed were not correlated with the throughfall magnitudes. Weighting of rainfall amounts and intensities did exhibit significant correlation. Analyses of wind direction at the plot level demonstrated significant windward and leeward effects on throughfall magnitudes. The throughfall process was dominated by canopy saturation and a steady state drip, although minor occult precipitation influences were observed. An exceedance of throughfall over incident rainfall was also observed, indicating the presence of non steady state throughfall regimes for balsam fir forest cover.

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