Development of conifer seedlings roots on soil and fallen logs in boreal and subalpine coniferous forests of Japan

To clarify the process of Abies seedling establishment on soil and fallen logs, we compared the root systems of conifer seedlings on soil and fallen logs in boreal and subalpine old-growth forests in Japan. Eighteen Abies seedlings (nine from soil and nine from fallen logs) were dug up, and for each seedling the diameter and depth of roots, and the length, diameter, and branching of the tap and lateral roots, were assessed. Abies seedlings on soil had well-developed roots. By contrast, those on fallen logs had extensive, shallow roots. Some of the roots on fallen logs were asymmetric, due to the shape of the fallen logs, and some seedlings extended their roots beyond the fallen logs. The root penetration of seedlings on fallen logs was influenced by the depth of the decay of the fallen logs on which they were established. Allocation to coarse roots was increased, and the ratio of the tap root length to total root length was higher in soil than on fallen logs. Although the diameters of the first and second lateral roots did not differ between seedlings growing in soil and those growing in fallen logs, some seedlings on fallen logs had longer or more branching roots, indicating that Abies seedlings show plasticity in root form in response to the microsites where they become established. On fallen logs, the tap roots of seedlings were prevented from penetrating deeper, leaving the seedlings only the decayed surface to utilize. The shallower, more branching root system of seedlings on fallen logs would be effective for becoming established on the logs. (C) 2002 Elsevier Science B.V. All rights reserved.