A belowground perspective of temperate old-growth forests: Fine root system structure in beech primeval and production forests

Abstract

Old-growth forests differ from managed forests by a generally higher biodiversity, larger carbon stores, and greater heterogeneity of aboveground structures. It is not known whether the aboveground structural diversity of old-growth forests is mirrored in root system structure, e.g. by greater root biomass, the occurrence of root gaps, and a different fine root morphology. We studied the fine root system of beech (roots <2 mm in diameter) in three development stages (initial, optimum, terminal) of a primeval beech (Fagus sylvatica) forest in the Slovakian Carpathians and compared it to a nearby beech production forest close to harvest. We conducted root coring to 30 cm depth in 16 plots (84 sampling locations) with subsequent detailed analysis of fine root bio- and necromass, and fine root morphology. Despite lower aboveground wood mass, the production forest had on average about 15% larger beech fine root biomass and necromass totals than the primeval forest, though the differences were not significant. Contrary to expectation, the spatial variation of fine root biomass in the 0–30 cm layer in the structurally diverse primeval forest was not higher than in the more homogeneous production forest. Also, fine root morphology did not differ between primeval and production forest.Across the three primeval forest stages, fine root biomass tended to peak in the optimum stage, but the difference was not significant, and no alteration in fine root morphology across the stages was detected. Fine root necromass increased significantly from the initial to the terminal stage, pointing at higher fine root mortality and/or reduced root decomposition in forest patches with many senescent trees and canopy gaps. Yet, soil fertility did not decrease toward the terminal stage of forest development. From the fine root biomass data, no root gaps could be detected in the terminal stage, perhaps due to rapid gap colonization by beech saplings. We conclude that the structural differences between the fine root systems of beech primeval and production forest were relatively small. Canopy heterogeneity seems to be a less important factor determining root distribution in the primeval forest than soil heterogeneity, which can be high in production forests as well.