Morphology of the Structural Root System of Sitka Spruce 1. Analysis and Quantitative Description

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Abstract
Root systems of 16-year-old, plantation grown, Sitka spruce of a range of sizes were excavated by hand from a peaty gley soil. The length of each root segment and position of each branching point, bend, fork and proliferation was measured for four root systems using a plumb-bob after placing them in a rigid, metal framework. On three root systems measurements were made by tape and protractor of numbers of roots, branching points, bends, root lengths, branching angles and distribution of root origins around the bole. Statistical analysis of these measurements revealed the root branching process as inherently regular. First-order roots tended to be regularly distributed around the main stem. The orientation of roots was determined by their initial direction either from the mainstem or where they were formed as laterals, and by changes in direction either from the mainstem or where they were formed as laterals, and by changes in direction at bends or branching points which tended to be alternately clockwise and anticlockwise. Lateral branches subtended larger angles from their parent roots than the angles between the two arms of a root fork and, irrespective of the length of a root segment, the laterals arising from it were evenly distributed along its length. The angles of lateral roots were generally more steeply downward than those of their parents. Root angles and directions changed where changes in soil structure or ditches were encountered. We suggest that the root growth of Sitka spruce is inherently regular in that the species may possess mechanisms which ensure that its structural root system is more extended and more evenly spread than would result if growth was at random. However, root growth takes place in a heterogenous environment and it is this which causes the variability in final root pattern.
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