Fine root biomass and morphology in an age-sequence of post-agricultural Pinus sylvestris L. stands

The purpose of this study was to examine how stand age affects fine root biomass and morphology in different stages of first generation Scots pine forest development in post-agricultural fields. Stands of different ages (6-, 10-, 16-, 28-, and 47-yr-old) were studied at the same time to provide data on biometrical fine root features, i.e. biomass, length, surface area, volume, number of tips, root tip density, specific root tip density, specific root area, specific root length and fine root tissue density. Soil cores from the upper 20 cm of soil were used for the study. The results of the study show that fine root characteristics did significantly differ among stands of different age. Fine root biomass ranged from 0.9 Mg ha–1 (6-yr-old stand) to 2.3 Mg ha–1 (47-yr-old stand), whereas coarse root biomass ranged from 0.2 Mg ha–1 to 3.2 Mg ha–1, respectively. Fine root biomass in the older stands (10–47-yr-old) remains constant and is ca. 4 times higher than in the youngest stand (6-yrs-old). This shows that the fine root biomass of Scots pine in the upper soil horizons reached a constant biomass at a younger stand age than found in previously published papers, although at the same stage of stand development, i.e. canopy closure. Fine root length, surface area and volume expressed on per stand area basis were significantly different among stands; the highest values were found in the 10-yr-old stand, during the time of canopy closure. This means that stand age (i.e. age of trees in pure even-aged monocultures) is not a major factor influencing the fine root dynamics, instead stage of development and other stand and habitat characteristics may play an important role. Moreover, we found significant linear relationships among stand age and fine root length, surface area and number of fine root tips expressed on a per tree basis. Our study showed that stand age affects both fine root biomass and morphology in Scots pine forests when growing on post-agricultural fields. The differences revealed in our study indicate high plasticity of Scots pine fine roots in response to stand changes over age.