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RESOURCES: ROOT SYSTEM

EXPOSURE IN A WOODLOT

ROOT SYSTEM EXPOSURE IN A WOODLOTby 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/orthe 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 thesandy 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 orstructural 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 branchedprofusely, 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 ofdeath 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 thickeningobscuring the event.

Because of the limited area exposed, it was not possible to follow

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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 theircrowns 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 asfound 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 couldnot 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 ofmoisture 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 heartroot 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 seenwhich 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.