ROOT SYSTEM EXPOSURE IN A WOODLOT
by David C.C. Fayle, PhD. RPF

For those who have never had an opportunity to view the disposition of tree roots in the soil, the removal of several cubic metres of soil within a wooded area by the Badger Daylighting Soil Removal System and exposure of the roots therein was a valuable learning experience.

It was much easier to understand that 20-25% of the tree's biomass occurs below ground (though still hard to realize that this takes 40-60% of the annual carbon).

For those who have excavated root systems, whether by hand and/or the use of water, there was the thought, "If only I had had this technique available to me". As one of the latter people and a long time researcher of roots, I was impressed by the ease at which the operation was conducted, and the quality of results. Although the sandy soil presented minimal problems, it could be seen how the technique would also work in clay or stony soils.

At the demonstration site in the woodlot, the most obvious feature was the prolific interwoven network of ropelike horizontal roots of various thickness at a depth of about 10 to 30 cm, forming the skeleton or structural framework of the surface root system of many individual trees.

Another feature was the abundance of smaller diameter roots which often grew obliquely upwards from the ropelike roots and branched profusely, forming the fine root system. The washing technique had preserved most of these fine roots, but any fungal hyphae associated with the mycorrhizal component were obviously lost.

The ropelike roots were generally relatively straight or slightly sinuous. Occasionally a root would take a sharper turn in direction, the result of death of the original root tip (for example from physical damage, chewing by soil insects), extension continuing from a lateral close to or further from the old tip, and subsequent secondary thickening obscuring the event.

Because of the limited area exposed, it was not possible to follow individual roots from the stem base to their ends, or the origin of all the roots. However, for the species present, roots could have been from trees 10 metres or more away - well beyond the spread of their crowns in this closed canopy woodlot.

Part of the stem-root bases of maple , oak and pine were exposed, showing the rapid reduction in taper, and the amount of root branching, in this zone near the stem. (Even in large trees, such as found on the West Coast, the same pattern appears.) Although some deeper descending roots could be seen, the vertical component was much less displayed than the horizontal component and any differences in the exploitation of the soil by the different species could not be observed.

In this well drained sandy soil, roots probably descended several metres. Their distribution would be relatively sparse compared to the surface horizontal roots, but could be important contributors of moisture for trees when the surface layers of the soil become dry and competition for moisture at the surface becomes intense.

To demonstrate some of the difference between the seedling root system and that of an older maple, the soil was washed away from the roots of one of the many seedlings present. A distinct primary (tap)root with lesser developed lateral roots was present ( tap root system ) whereas on the older maple the primary root had become 'engulfed' by the secondary thickening of the more dominant oblique and horizontal roots, resulting in the development of the so-call heart root system.

Later, the washing technique was demonstrated at the edge of the roadway by 'cutting' a narrow trench to locate the buried natural gas line. The gravelly backfill was easily removed and roots could be seen which has grown through the backfill.

This demonstration and that in the woodlot showed how the Badger Daylighting System could be used for both practical and research purposes for example, information on the extension of roots beyond a planting hole could be obtained with minimal damage.

All in all, a most useful demonstration.

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