The Last Stand by Peter E. Kelly

Author:Peter E. Kelly
Language: eng
Format: epub
ISBN: 9781554883325
Publisher: Dundurn

Cliff cedars, especially those along Georgian Bay, bear a remarkable load of ice and snow in the winter.

A slab of rock has fallen off this cliff, leaving only the roots of a cedar killed in the process. Some cedars may precipitate a rockfall by loosening rock as their roots expand.

Surprisingly rock fall from above the cedar is not as important as rock fall from below. Let us explain. When a seed germinates on a ledge or a fissure, the roots begin to penetrate the pre-existing labyrinth of cracks in the rock. The roots establish themselves and take advantage of available pockets in the limestone. Once there, they grow and expand in volume. Roots enter through crevices then spread along vertical planes of rock parallel to the surface. Cedars only a few decades old may penetrate up to thirty centimetres into the cliff. Roots penetrate further into the cliff if the trees are not growing in soil. The roots of cedars less than forty years in age also expand an average of twenty-five vertical centimetres and over sixty horizontal centimetres along these planes. The roots may mould themselves to fit the internal structure of the rock and dense root mats are often found behind loosely attached slabs of rock. If some portion of the cliff’s surface is marginally unstable, then the cracks will expand as the roots expand. Alternatively, freeze-thaw activity will hasten crack expansion. Blocks or sheets of rock separate themselves from the cliff face, the rock is dislodged and the root is exposed to the elements. It becomes dehydrated, dies and initiates a stem-strip by cutting off the water supply to part of the stem.

This process influences more than just the morphology of the tree; it can determine whether it lives or dies. If a seed lands and germinates on an unstable cliff surface with many cracks and crevices,

the roots will have lots of room to expand. The tree will grow faster, the rock will be weakened, the rock falls and subsequent root death will occur with increasing rapidity. Unstable cliff faces support fewer eastern white cedars than stable ones. Cedars are the sixth most common plant on stable quarry walls but only the tenth most common plant on unstable quarry walls.

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