Rooting patterns and fine root biomass of Pinus pinaster assessed by trench wall and core methods

Variability of fine root (diameter < 2 mm) distribution was investigated in four 55 to 56-year-old Maritime pine (Pinus pinaster) stands using a combination of trench wall observations and destructive sampling. Our objectives were to assess patterns of fine root distribution, to estimate tree fine root biomass and to explore interactions with understorey vegetation in a gradient of relevant site conditions. Results showed that root density decreased with soil depth in all stands, and variability appeared to be highest in litter and subsoil layers especially where compacted soil layers occurred. Roots were clustered in patches in the top 0-50 cm of the soil or were present as root channels at greater depths. Cluster number, cluster size and number of root channels were comparable in all four stands. Overall fine root biomass at depths of 0-120 cm ranged from 2.7 to 7.2 Mg ha(-1) and was highest for the two driest stands. The use of trench wall records made it possible to reduce the variability of these estimates. Understorey species represented as much as 90% of the total number of fine roots in the upper layers, and the understorey formed a considerable proportion of the total ecosystem biomass, suggesting that understorey species are likely competitors for nutrients in this ecosystem. Further studies should focus on the interaction of the understorey and pine roots and the ecological significance of clustered roots and nutrient distributions.