Keston Common owned by the London Borough of Bromley is situated in the north of the area, about 2 miles from Down House, at the southern edge of the London Basin. The lowland heath and acid grassland habitats here provided Charles Darwin with quite different plants and animals to study from those of the chalk and clay-with-flints nearer to his home. The soils of the Common are acid and nutrient poor, being derived from the free draining sands and gravels of the underlying Blackheath Beds. In Darwin’s time Keston Common was grazed and more open but since grazing stopped in the 1930s some of the heathland has been colonised by trees. Initial colonisers included the fast-growing silver birch but now oak woodland is developing in places. Work is in progress to restore some of the heathland because this is a threatened habitat in the UK, especially in south-east England. Darwin used the area in his earthworm researches, investigating their presence/absence in different parts of the heath. The following extract, dated 15th October 1880, is from Darwin’s papers kept at Cambridge University Library (CUL: DAR 64.1:51).
"On Keston Common in the triangle between the Hayes & Keston-Mark roads, & north of the path that runs across from the Holwood wicket is a high bit of land covered with heath the ground amonst the heath being quite covered with lichen; I walked carefully over this place & pulled up the heath & looked among the roots, saw no trace of worms. The Holwood path divides the lower part of this bit of common into two regions, the S being chiefly gone (gorse) & fern with grass & having worm castings, the north (region) being the pure heath & lichen region. There is gras[s] on both borders of the path & worm castings on both borders. But higher up the heath vegetation is on both sides of the path & here there are no worms on the grass edging. In another place there is gorse-fern-grass vegetation in the damp bottom of the valley, & heath on the sides of the valley, & a little <> 20-25 yards 3 words illeg del> <> went <> into the heath; this glade had grass, <> broom, gorse <> a few flowers & very little heath & was about a yard wide. It was a little tongue of <> running up into the worm-less vegetation. I hunted it carefully & found no castings but found them directly <> bottom of the valley <>"
"On Hayes Common where it was burnt the heath is a good deal mixed with gorse & there is much moss but not lichen; there were no worms <>. As you walk over towards Barton (Baston) it gets more grassy & ferny, & at last I found one casting on the grass border of the path."
Note: <...> = deletion <<...>> = addition
Darwin’s earthworm studies culminated in the book, ‘The Formation of Vegetable Mould, through the Action of Worms’ published in 1881, which can be read on line at www.darwinonline.org.uk
Darwin also spent much time observing round-leaved sundew at Keston Bog. This small area of valley mire habitat retains water due to the presence of impermeable Eocene clay about 1 metre below the soil surface. It still supports plants rare in the south-east such as cotton sedge and bog asphodel. Round-leaved sundew has been lost due to increased shading, falling water table and increased eutrophication (enrichment of the soil by plant foods nitrogen and phosphates, here mainly derived from leaf litter). Darwin first noticed how insects became stuck to the leaves of sundew whilst on a visit to Hartfield in 1860. This led him to investigate how it trapped and digested insects, pioneering work which led to the publication of ‘Insectivorous Plants’ in 1875. His major source for sundew was Keston Bog where it was then common. Darwin explained how insects supplied the plants with nitrogen making it possible for them to survive in poor soil The plants also needed plenty of water because to digest the insects it was necessary to secrete an acid fluid from,
"glands, sometimes as many as 260, exposed during the whole day to a glaring sun."
Darwin’s son, Francis, wrote in ‘Life and Letters’ (1887) that his father,
"used to ask doubtfully whether he might have a horse and cart to send to Keston for Drosera".
William Baxter, the son of Bromley’s pharmacist, who supplied Darwin with chemicals for his experiments with sundew, recalled meeting Darwin whilst collecting sundew at Keston Bog in1879 (see Nomination Document).
A project is currently in place at Keston Bog to restore this fragile habitat and it is hoped that round-leaved sundew may return.
The three main ponds at Keston support many dragonfly species and Caesar’s Well, the site of one of a series of springs at the source of the River Ravensbourne, was well known to Victorian microscopists as a very interesting source of freshwater algae. Keston Ponds were the most likely source of the mud from which Darwin germinated plants from samples of mud in one of a sequence of experiments into the geographical distribution of freshwater plants.
From this experiment, he wrote in the Origin of Species (1859),
"I do not believe that botanists are aware how charged the mud of ponds is with seeds: I have tried several little experiments, but will here give only the most striking case: I took in February three table-spoonfuls of mud from three different points, beneath water, on the edge of a little pond; this mud when dry weighed only 6 ¾ ounces; I kept it covered up in my study for six months, pulling up and counting each plant as it grew; the plants were of many kinds, and were altogether 537 in number; and yet the viscid mud was all contained in a breakfast cup! Considering these facts, I think it would be an inexplicable circumstance if water-birds did not transport the seeds of fresh-water plants to vast distances, and if consequently the range of these plants was not very great."
The top two ponds acted as reservoirs of fresh water for the new Holwood House built for John Ward in 1820s. This was supplied via an hydraulic ram from the north-east corner of the middle pond.
Ravensbourne Open Space
To the north of Keston Common is an area of wet meadows along the River Ravensbourne which was once part of the land belonging to Ravensbourne Lodge, home of the Bonham-Carter family from 1853-1862. Friends of the Darwins, surviving letters include some from Elinor Bonham-Carter to the Darwins in which she describes the expressions of her dog and newborn niece/nephew, presumably associated with the publication of, ‘The Expression of Emotion in Man and Animals’ by Darwin in 1872 . The wet meadows support species not found elsewhere within the nominated World Heritage Site including ragged robin, kingcup, purple loosestrife and greater birdsfoot trefoil. Darwin studied the flower structure of purple loosestrife and remarked how the leaves of greater birdsfoot trefoil move at night, their leaflets rising up against the stem due to the presence of small cells at the base of their stalks which through the intake and loss of water act as a hinge.
North of Ravensbourne Open Space, Padmall Wood is mainly sweet chestnut coppice with some very large ancient coppice stools. A recent historic landscape assessment showed ancient charcoal hearths here. The woodland would have been a familiar part of the landscape to Darwin and contains species he studied, including wood sorrel and wild angelica.