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

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Above-ground net primary production (ANPP=change in biomass litter fall) 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 over story 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. Litter fall from all vegetation combined represented the largest share of ANPP; increases in over story biomass represented the next largest share. Soil CO2 flux was also higher on the north aspect. Despite higher over story 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

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