Biomass Stock and Productivity of Primeval and Production Beech Forests: Greater Canopy Structural Diversity Promotes Productivity

Abstract

Our knowledge of temperate broadleaf forest ecology is based mostly on the study of production forests, which lack the terminal stage of forest development and have a simpler stand structure than old-growth and primeval forests. How primeval and production forests differ in net primary production (NPP) is not well known. In three primeval and three nearby production forests of European beech (Fagus sylvatica) in the Slovakian Carpathians, we measured aboveground biomass stocks (live and dead), aboveground NPP (ANPP) and parameters characterizing canopy structural diversity (leaf area index and its spatial variation). Our study aims were (1) to explore the role of canopy structural diversity for ANPP and (2) to assess evidence of a productivity decline in the terminal stage. While aboveground live biomass stocks were on average 20% greater in the primeval forests (386 vs. 320 Mg ha⁻¹; insignificant difference at two sites), deadwood mass stocks were on average four times larger than in the production forests (86 vs. 19 Mg ha⁻¹). ANPP was similarly high in the primeval and production forests (10.0 vs. 9.9 Mg ha⁻¹ y⁻¹) and did not decrease towards the terminal stage. Production models indicate that, in the primeval forests, about 10% of ANPP (ca. 1 Mg ha⁻¹ y⁻¹) was generated by effects related to leaf area heterogeneity, evidencing a positive effect of structural diversity on forest productivity, even though species diversity was low. This study helps to better understand the impact of forest management on the productivity and carbon storage in temperate woodlands.