Above- and below-ground production of trees and other vegetation on contrasting aspects in western Montana: a case study

Abstract

Above-ground net primary production (ANPP=change in biomass+litterfall) and below-ground gross primary production (BGPP) of all vegetation were measured in young (<30 years), paired stands ( n=8) on a north and south aspect in western Montana. Stands of high and low overstory leaf area index were compared. ANPP ranged from 1550 to 4400 kg C ha −1 per year and BGPP ranged from 1360 to 3500 kg C ha −1 per year. ANPP was related to leaf area index and aspect ( p=0.0336 and p=0.0031, respectively), as was BGPP ( p=0.0185 and p=0.0016, respectively). ANPP and BGPP were both greater on the north aspect at any given leaf area index (LAI). Above-ground production of the understory was also higher on the north aspect. Litterfall from all vegetation combined represented the largest share of ANPP; increases in overstory biomass represented the next largest share. Soil CO 2 flux was also higher on the north aspect. Despite higher overstory LAI on the north aspect, understory NPP was higher. These results confirm that all measures of productivity, both above- and below-ground, were higher on the north aspect than on the south aspect. Neither site index nor habitat types reflected the large differences in ANPP and BGPP between aspects.