A life in a day for a broom

18th February 2008, Monday

Walking across the false oat-grass dominated shingle yesterday I found a tiny broom plant on the ninth ridge in from the sea, trying to establish itself on relatively bare shingle. Despite its size it will have taken a number of years to get to this big. Some winters the shoots are almost totally blackened and set back to the base of the stem by salt spray, sculpting the prostrate shape of the bushes on Dungeness. This plant was probably at least five years old. 

Young broom

Let us try and imagine how this plant might develop in the future, if it avoids the perils of being trampled to death, driven over by quadbikes, or gravel extraction! The estimates of time are based on some plants I have known, but in my 19 years on Dungeness I have not witnessed anything like the full cycle of an individual plant.

Some years on, and I am not sure how long this takes, it has changed in appearance – it is now a densely vegetated mat of stems, kept close to the ground by rabbit grazing, with the beginnings of a build-up of leaf-litter under the plant. Constant nibbling by rabbits keeps the plant compact, and may well prolong its life as the growing tips are kept young and non-woody.

Young rabbit grazed broom

Skip forward a few more years and rabbit numbers drop, due to Myxomatosis. This gives our broom the opportunity to grow upwards. It is now a mature plant producing  thousands of flowers each spring, helping to paint the shingle a lovely lemon yellow. Each flower will produce 5-10 seeds. Many are eaten by small weevils that live within the seedpods. They in turn are predated by a tiny parasitic wasp, both examples of the chain of invertebrate life dependent on this plant. How many millions of seeds will this plant produce over its life? Yet only a handful will produce viable broom plants due to the rigours of the habitat! If the weevils do not graze the seeds many fall on unwelcoming stony ground, they may have to face severe drought in their early growing seasons, the attention of the Dungeness rabbits, or scorching salty winds.

Flowering broom 

Ten years since the rabbits ceased to influence it’s height and the plant is now in its prime, about 1m across and almost as high. Note the absence of young plants around this specimen – an indication of how much of it’s seed is wasted.

 Mature broom

 Disaster strikes a year or two later though, perhaps a stormy winter with lashings of salt spray, or a dry summer, but our friend is now looking a little the worse for wear. The gaps in its cannopy provide an opportunity for other plants to germinate in its acidic humus, and there are the beginnings of a supply of dead wood. (This particular bush, photographed on Sunday, is one I have been acquainted with since 1993, when it was a low growing rabbit-grazed hummock)

 Old age for our broom

 And now, several decades on we have reached the end of the story for this individual. It has died, leaving branches that will be used by dead-wood eating invertebrates and nesting ants, and a precious deposit of humus, that in this case is being colonised by sorrel. On younger shingle the gap in the cannopy might open up opportunities for more broom plants, but on the older parts of the beach it’s demise  sets the scene for the development of the next stage in the vegetation succession on Dungeness

The end of the story for this broom

Its an amazing plant. It takes the young shingle habitat and totally transforms it by the addition of a deep layer of humus, allowing a greater diversity of species to survive on the shingle.