The numerous ponds on the acid gravels provide a further bryophyte habitat. In the marshy shallows
Drepanoclados exannulatus. D. fluitans , and Calliergon cordifolium are widespread, though rare
elsewhere in Essex. In a few ponds Fontinalis antipyretica grows on submerged tree roots, and less
reliably, the floating liverworts Riccia fluitans and Ricciocarpos natans. The latter, a very local plant
nationally, that has been on the Forest since the 1920s. occurred in Earl's Path Pond until it was dredged
after the 1976 drought, and subsequently in Goldings Hill Upper Pond (dredged in 1988 and 1991),
and is probably therefore now extinct. The alien Riccia rhenana appeared floating in the marshy
shallows of the Warren Pond in 1984. but these shallows have now also been dredged.
In the numerous Forest bogs the most obvious bryophytes are the sphagnum mosses. Nowhere else
in Essex are they to be found in such profusion. They occur in several different types of location. In
spring-head bogs and springline seepages, as at Rat's Lane and the Long Bog, High Beach; Dulsmead
Hollow near the Wake Arms and Oak Hill, Debden; in bogs ponded back by what are now roads, but
what must once have been ancient trackways, as at Lodge Road North and South Bogs, and Jacks Hill
North; or simply by logs falling across streams forming temporary dams; in damp hollows where the
Pebbly Clay Drift deposits maintain a perched water table, as on Sunshine Plain; and finally, in some
of the numerous shallow gravel workings cut into Pebbly Clay Drift and Glacial Gravel deposits.
In all cases however they occur in acid habitats on the Bagshot Sands, the Glacial Gravel or the
Pebbly Clay Drift, where these overlie the less permeable Claygate Beds, the acid nature of the water
preventing decay, and promoting the accumulation of acid peat. Originally these hilltop sites were
probably covered by thin, patchy. Boulder Clay deposits and the stream rises were probably vegetated
by alder carr, associated with such plants as Golden Saxifrage and Narrow Buckler Fern. Following
deforestation of the hill tops by early man. erosion of the Boulder Clay and subsequent development
of heathland, followed by leaching and podzolisation of soils overlaying sands and gravels, resulted
in sphagnum bogs replacing alder carr. Typical alder carr still exists in similar situations along the
Bagshot Hill ridges fanning out across Essex to the east of the Forest, and the pollen record from the
Lodge Road and Jack's Hill bogs shows the presence of alder pollen in the area up to about 30cm
from the present surface.
Probably the most abundant species of sphagnum in terms of quantity is Sphagnum palustre, which
occupies the outer margins of the sphagnum bogs, but in terms of distribution, S. auriculatum var.
auriculatum is the most widespread, its ability to remain desiccated for much of the summer, enabling
it to flourish as tiny patches in seasonally damp hollows all over the higher parts of the Forest, bursting
into growth in the autumn and winter.
Three other species are also widespread. S. squarrosum, characteristic of bogs shaded by birch
encroachment, as in the eastern bay of Strawberry Hill Pond, and S. recurvum together with S.
fimbriatum, both abundant in the permanently wet centres of several of the larger bogs and wet gravel
working hollows. These two are a deep green, and rather delicate, compared with S. palustre and S.
squarrosum.
Seven other sphagnum species have been recorded for the Forest. Of these S. papillosum, S. tenellum
and S. subnitens are no longer present, possibly due to their intolerance of acid rain during the worst
phase of pollution during the 1960 s and early 1970 s. S. capillaceum has turned up on the Forest on
several occasions in recent years, and S. compactum appeared on Sunshine plain in 1988, the first
time on the Forest (as far as we are aware) since 1906, but has since been destroyed by fire. The other
two species, S. cuspidatum and S. auriculatum var. inundatum are now very scarce, as few open bog
pools remain on the Forest.
Sphagnum bogs, like most other habitats, change with time. Starting out as open pools with
submerged forms of S. cuspidatum, and both the S. auriculatum varieties; S. palustre and S.
auriculatum var. auriculatum colonise the outer margins, which fluctuate in wetness with the seasons,
while S. recurvum and S. fimbriatum occupy the permanently wet inner margins of the pools.
Eventually, aided by growth of the giant Polytrichum commune and Aulacomnium palustre, they close
over the open pools and form sphagnum hummocks. Finally, as birch trees encroach and shade the
sites, S. squarrosum moves in and becomes the dominant species.
Unless a bog is cleared out artificially, or the water table responds to climatic changes, so that springs
move up or down the valleys creating extended bogs; or a log falls across a stream causing a sudden
ponding back of extra water, the bogs are eventually colonised by higher plants. Horsetails in the case
of Dulsmead Hollow, and Molinia tussocks in the case of Jacks hill Bog North.
Tragically, the attitude towards conservation of the sphagnum bogs has not always been favourable.
A certain young lady having ridden her horse into the Snaresbrook bog allegedly kicked up such a
fuss that the bog was infilled! - leading to the loss of a rich sphagnum bog flora including Star sedge
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