Canopy conductance in a two‐storey Siberian boreal larch forest, Russia

A larch forest in eastern Siberia was characterized by the presence of two distinct storeys, the overstorey with a small leaf area index (LAI) and a dense understorey with a relatively large LAI. To understand the roles of the overstorey and understorey in forest–atmosphere water exchange, canopy conductance ( G c ), a critical parameter used in determining the energy and mass exchange, was calculated on the basis of latent heat flux above the overstorey and understorey, measured separately. Results showed that G c for the overstorey ( G co ) and understorey ( G cu ) experienced different seasonal fluctuations. G co was smaller than G cu during periods of leaf expansion and leaf fall and showed an increasing trend until 1 month after the onset of leaf expansion. In contrast, a sharp decrease in G co was observed immediately before onset of leaf fall. Furthermore, G co was slightly larger than G cu during the fully foliated period. A simple model using solar radiation and vapour pressure deficit ( D ) as inputs successfully reproduced the G c in fully foliated periods with acceptable accuracy. Furthermore, both the understorey and overstorey in this study have a large reference G c ( G c at D  = 1 KPa) than their counterparts of other boreal forests and would not be able to sustain a constant leaf–soil water potential difference as D increases. We speculated that this confers the forest with an advantage allowing it to be able to sustain carbon assimilation during large D days and thus provides for the survival of the ecosystem during the short growing season at this site. Copyright © 2014 John Wiley & Sons, Ltd.