October 09, 2011

The colours of the mast

The hot weather last week dried the acorns in their cups and sent them thudding to the ground. Now, beneath several of the big oaks on Tooting Common, there is a carpet of brown oak-nuts.

Oak trees begin producing acorns when they are about 40-50 years old, and in a good year (a 'mast year') a mature oak will produce up to 50,000 acorns – although very few will go on to become mature oaks themselves.

High in fat, protein and carbohydrate, acorns are an excellent food source for animals like squirrels and jays, which sometimes aid in their dispersal and germination by caching them for future use; a spell underground can also help to leach bitter tannins from the acorns by allowing rain and groundwater to soak into them. Although an oak seedling will get more light if it germinates away from its parent's canopy, oaks are known to co-operate by sharing water supplies through their root system in dry years; there is some advantage in the acorn not falling too far from the tree!

Pigs are another animal that loves acorns, but large amounts can be poisonous to sheep, cattle and horses. In the New Forest the ancient right of pannage is still extended to commoners; this is the right to graze pigs on the common land, so that they can eat the acorns, for sixty days.

Beech nuts (pictured above) are another type of mast, less bitter than acorns. In beechwoods the mast and shells create a dry mulch on the forest floor which, along with beeches' dense summer canopy and slow-rotting, non-nutritious leaves, make it very difficult for other species to colonise the undergrowth layer, reducing competition for the trees, but opening up the forest floor to spring species such as anemones, oxslips, wild garlic and bluebells, which are most often found in our beechwoods.