within it telling an interesting story of the vegetational history (Girling & Greig,
1977). Alluvial gley soils occupying well defined floodplains are to be found
mainly in the larger streams and rivers delimiting the wider Forest area, but
narrow tracts of similar soils line most of the V-shaped tributary valley bottoms.
Brown soils
This major group is comparatively poorly represented in the Forest. It is
mainly associated with Bagshot Beds outcrops, locally well drained parts of the
Pebble Gravel and parts of the Glacial and River Terrace Gravels. In the for-
mer, stagnogleyic argillic brown earths of the Bursledon series consist of leached
strongly acid yellowish brown fine sandy loams below a mor humus surface, and
usually a brownish slightly mottled fine sandy clay loam subsoil. The similar
freely drained fine sandy Shedfield series is more youthful, occuring on slightly
steeper, probably eroded, facets of the slope, and has no argillic horizon.
On Pebble Gravel, typical paleoargillic brown earths resembling soils
described by Sturdy (1971) as the St Albans series are found sporadically in
deep loamy or pebbly sandy areas, whilst loamy and silty more or less gravelly
gleyic argillic brown earths occur on River Terrace gravels on Wanstead Flats
and elsewhere, interspersed by ground-water gley soils where water tables are
locally higher.
These freely or moderately well drained coarse textured gravelly soils, and
to an extent the imperfectly drained Essendon and Bolderwood series, are prone
to summer drought, as the available soil water they can hold is not sufficient to
meet the transpiration demands made by the forest vegetation (soil moisture
deficit). In established Forest trees this is probably only noticed as an overall
slow growth rate with perhaps some premature leaf drop, but in grassy areas
with shallow rooted vegetation, the symptoms of moisture stress may be very
severe. The large fine sand content of the Bursledon and Shedfield series
enhances their ability to retain available water, and so the soils are not
noticeably droughty.
ACKNOWLEDGEMENTS
Judy Fox of the Polytechnic of Central London is thanked for supplying
analytical data for one soil profile in Great Monk Wood, and Ellis Thomson at
Rothamsted Experimental Station for drawing the diagrams.
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