Measurement and modeling of canopy water partitioning in a reforested landscape: The Ganaraska Forest, southern Ontario, Canada

Abstract

Summary A major hydrologic consequence of reforestation is an increase in canopy interception ( I c ), with consequent effects on such processes as soil and groundwater recharge. This study examines the change in rainfall partitioning between throughfall ( TF ), stemflow ( SF ) and I c in red pine plantations of different ages and in mature mixed hardwood forest stands in the Ganaraska Forest on the crest of the Oak Ridges Moraine in southern Ontario. It also tests the ability of the Liu interception model to predict I c in these stands. Forest characteristics, TF , SF and I c were either measured or estimated during the 2009 and 2010 growing seasons for three red pine stands 36–41 years old (as of 2009), three red pine stands 57–62 years old, and three mixed hardwood stands 74–107 years old. Despite considerable variability in total I c in a given stand type in both years, there was a general increase in I c as a fraction of above-canopy precipitation ( P g ) from younger to older red pine stands and to mixed hardwood stands. This was accompanied by a decrease in SF depth as a fraction of P g from younger to older red pine stands, followed by an increase in SF / P g in mixed hardwoods. The Liu model provided good predictions of I c in 2009 for eight of nine stands with canopy storage capacities optimized using the 2009 data. Model performance was almost as good when tested against the 2010 data using the 2009 model parameters. Adjustment of the parameter representing the ratio of mean evaporation rate to mean rainfall rate to account for greater evaporative demand in 2010 led to a modest improvement in model performance. The increase in growing season I c / P g ratios as red pine plantations in the Ganaraska Forest mature and undergo a managed transition to mature mixed hardwoods may have important implications for soil water and groundwater recharge that require further study. The Liu model is a promising means of estimating I c in forest stands of differing age and type, which in turn will assist in understanding the hydrologic consequences of reforestation in this landscape.