Hydrologic variation of stemflow yield across co- occurring dominant canopy trees of varying mortality

Concern over forest dieback due to environmental change and the long residence times of standing dead trees necessitates understanding the impact of forest health on the redistribution of precipitation by forest canopies. Stemflow represents a critical point source input of water and nutrients to forest ecosystems. We investigate the variation in water storage capacity, stemflow volume and stemflow funnelling ratios from two co-occurring dominant canopy species, Fagus grandifolia Ehrh. (American beech) and Liriodendron tulipifera L. (yellow poplar), across three different mortality classes: live, stressed (girdled) and standing dead. Over 25 rainfall events, interspecific differences in stemflow volume distributions were significant over all (U=45881, p<00001), leaf-off (U=11285, p<00001) and leaf-on (U=11582, p<00001) events. Stemflow funnelling ratios were greater in F.grandifolia (260+/- 12) compared with L.tulipifera (49+/- 04). Minimum precipitation threshold amounts required to initiate stemflow were lower for F.grandifolia compared with L.tulipifera, and lower for live and stressed compared with dead. Mean stemflow volume from both species was 15+/- 02lstem(-1)event(-1) from dead stems, 892+/- 77lstem(-1)event(-1) from stressed stems and 913+/- 89lstem(-1)event(-1) from live stems. The results of this study improve our understanding of the influence of mortality on rainfall partitioning and stemflow fluxes and may give insight into how mortality generating factors such as pest defoliation and climate change may alter stemflow relationships in forested ecosystems. Copyright (c) 2013 John Wiley & Sons, Ltd.