Kim Hy Proposed Nature Reserve - Frontier-publications.co.uk

when heavy mists and, sometimes, hoar frost settles in the valleys early in the morning.
At this time of year there tends to be a large difference between diurnal and nocturnal
temperatures (reaching 20.8ºC during Frontier’s survey), and the temperature can fall to
2ºC. Much of the precipitation condenses in the form of mist; during Frontier’s phase 2
work, 26 consecutive days passed without any rain during November. These winter
conditions can seriously damage crops. Average temperature is 21.6ºC (maximum
38.6ºC). Humidity averages 82% but can fall to 10%. Prevailing winds are north-easterly
and south-westerly.
2.2.2 Topography and Hydrology
Much of the landscape of Kim Hy and An Tinh communes, where most of the remaining
forest lies, is strongly characterised by dramatic outcrops of limestone tower karst,
forming a topographical patchwork of sheltered valleys and gorges interspersed with
steep, rocky cliffs. Access over this terrain is extremely difficult, accounting for the
relatively in tact forest block; slope angles on the karst are over 45º and most reach
heights of 650-800m, the highest being Kuoi Coi at 985m. A number of caves, crevasses
and subterranean gorges have formed in or under the limestone from erosion and
chemical weathering, performing some important ecological functions.
To the north and east, mudstone–based hills with slope angles of around 20-25º and
average heights of 400-500m source the tributaries of the Bac Giang river, which flows
through An Tinh and Luong Thuong communes, 5km to the north-east of Na Ri and into
Ngan Son district. Between these hills the landscape is dominated by flooded rice
paddies.
There are virtually no over-ground water bodies within the main limestone area of Kim
Hy and An Tinh as most precipitation percolates through the limestone and collects in or
below the limestone bedrock in deep underground ‘wells’, forming a well-developed
subterranean drainage system marked by seasonal fluctuations in water level and
sometimes spilling over to form small surface streams.
2.2.3 Geology and Soil
Geologically, Kim Hy and An Tinh communes are dominated by Devonian-
Carboniferous limestone of various depth of deposition and which have been influenced
by denudation and karstic processes associated with fluctuations in sea level. The
mudstone hills rest on beds of quartzite, sandstone and schist. No soil surveys were
conducted during the Frontier work phases: the information below is taken from surveys
undertaken by FIPI in 1997. A map summarising distribution of the main soil types is
held at the provincial FPD office.
Frontier Vietnam Forest Research Programme Technical Report No.24. 21