S. Gaskin et R. Gardner, The role of cryptogams in runoff and erosion control on bariland in the Nepal Middle Hills of the southern Himalaya, EARTH SURF, 26(12), 2001, pp. 1303-1315
Cryptogams are communities of non-vascular plants that live on the soil sur
face. Numerous functions have been attributed to these crusts, including ch
anges in soil fertility and nutrient status, soil hydrology and soil erosio
n. Most significant for this paper is the reported benefit of cryptogams in
reducing soil erosion by water in semi-arid areas. However, to date there
have been few attempts to understand the soil conservation value of cryptog
ams in subsistence agricultural systems or in humid mountain environments.
This paper investigates the potential of cryptogams in soil erosion by wate
r on agricultural hillslope terraces (bariland) in the Nepal Middle Hills o
f the southern monsoonal Himalaya. The research is significant because the
loss of fertile topsoil is considered by some to be the biggest threat to t
he livelihoods of subsistence farmers in the area in the medium and long te
rm.
The current study was conducted in the field between two of the weeding eve
nts that take place under maize cover, grown in the traditional manner. Thr
ee groundcover types which represented (i) maize only (types A), (ii) maize
and weed cover (types B), and (iii) maize and cryptogam cover (types C) we
re monitored utilizing multiple microerosion plots. Measurements of runoff
and soil loss data were collected sequentially on a storm-by-storm basis th
roughout the monitored period from 24 July 1997 to 29 August 1997. Measurem
ents of infiltration rates were also taken on each of the groundcover types
at selected times.
Results collected from the erosion plots demonstrate that runoff and soil l
osses over distances of <2 m can be significantly reduced by up to 50 per c
ent with cryptogam cover, compared to maize-only canopies. Mean runoff for
all storm events sampled from plot types A, B and C were 3.4 1 m(-2), 1.6 1
m(-2) and 1.5 1 m(-2) respectively. For soil loss, the results were 21.7 g
m(-2), 11.3 g m(-2) and 10.2 g m(-2) respectively. Therefore, cryptogams w
ould appear to offer a similar degree of protection to the soil surface fro
m runoff and raindrop erosion, to that afforded by weed cover. Weed and cry
ptogam covers protect the soil surface from rainfall kinetic energies and w
ork to preserve surface microtopographies, depressional storage and surface
water detention. Terminal infiltration rates taken at the end of the monit
ored period showed that well developed maize- and cryptogam-covered soil su
rfaces (types C) have a mean terminal infiltration rate of 35.0 mm h(-1) co
mpared to 44.5 mm h(-1) for comparable maize- and weed-covered soil surface
s (types B), and 15.5 mm h(-1) for maize-only soil surfaces (types A). Thes
e results show that cryptogams and weeds also have relatively higher infilt
ration rates than comparable maize-only covered plots, devoid of groundcove
r.
The findings in this study may have implications for traditional weed manag
ement practices used by local hill farmers, which often destroy cryptogam s
oil coatings two to three times during the maize growing period. However, f
urther work needs to be done to ascertain farmers' understandings of crypto
gams. It is hoped that conservationists will benefit from incorporating cry
ptogams into the design of future soil erosion studies relating to developm
ent programmes. Copyright (C) 2001 John Wiley & Sons, Ltd.