Oscillants at Spier's parklands
25 November
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Oscillant empty
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Half-full
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Full oscillant beneath a large sycamore tree
A fascinating and almost hypnotic phenomenon at Spier's is that of oscillants, pools of groundwater at the base of trees that rapidly, cyclically, and mysteriously fill up and then empty again.
Alas, no magic is involved, for the cause is the wind rocking the whole tree back and forth, often almost imperceptibly. This rocking motion of the whole root ball acts like a syringe, sucking such water up on the 'blow' and pushing it back on the 'lull'.
These oscillants eventually create large cavities beneath the trees as the water is really liquified soil that can often squirt out and then drain away, leaving a void beneath the tree concerned. The trees grio on the soil is weakend and may lead to the tree falling, however trees are dynamic and responsive organisms that can grow new or strengthen existing roots to help compensate for this loss of adhesion to the substrate.
Trees with anchor-like tap roots, such as oaks, are less prone to developing oscillants, whilst trees such as lime, willow, and sycamore with wide-spreading root systems and mainly horizontal-growing surface roots are prone to developing them on wet soils.
In summer when it is hopefully dry and severe storms are rare, such oscillants can become the temporary homes or shelters of small mammals for breeding and rearing young or simply escaping predators.
Fascinating to watch, oscillants are best located after a period of heavy rainfall and during moderate storms, certainly not, for safety sake, in truly stormy weather!
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