New Zealand Journal of Forestry (1963) 8(5): 771–785
©New Zealand Institute of Forestry
A study of the Rooting Habits of Rimu and Tawa in Pumice Soils
Rooting systems of seedlings, saplings, and poles were studied by excavating, and that of a mature tree of each species by trenching, through the root profile. Rimu seedlings had weak root systems with no well developed tap root, but tawa seedlings had a strong tap root capable of persisting if the shoot perished for want of light. Pole rimu had a strongly developed system of surface laterals exceeding the crown in radius; in the mature rimu this system extended farther and had more sinkers, and several massive sinkers arose from the tap root. Pole tawa had a dense system of lateral roots lying mainly in the upper layers of mineral soil; in the mature tawa the radius of this system was less than half the crown radius, and the tap root was absent.
Rimu regeneration may fail because the roots of seedlings growing in heavy shade are unable to penetrate the thick layer of raw humus. Removal of all or part of this humus, and reduction of the canopy, should assist regeneration. Tawa seedlings, which have well developed tap roots, are better equipped to establish themselves under rimu.