The Earthworms of Wistman’s Wood, Dartmoor
A Report to English Nature: August 2001
Kevin R. Butt1 and Joanna Kostecka2
Introduction
Wistman’s Wood, covering 3 - 4 ha, is located at approximately 400 m on the west-facing
slope of the West Dart river (Nat. grid ref. SX 613 770) It is a National Nature Reserve with
SSSI status, known widely for the stunted, gnarled oak trees (Quercus rober) that are covered
with epiphytes. Much has been written of the pedunculate oaks themselves and their
associated flora. However the fauna, which is sparse, is poorly recorded with the exception of
birds, mammals and selected insect groups (Page, 1995).
Very little has been recorded of the soil fauna associated with this woodland and the
surrounding area. This report addresses only a part of this enormous community by
concentrating on the earthworms (Lumbricidae) and builds upon a preliminary survey (Butt,
1998).
[For a full description of Wistman’s Wood, refer to the most recent management plan.]
Methods
Due to the relatively sensitive nature of the soils within Wistman’s Wood, sampling was kept
to a minimum during the two survey periods. Each was conducted during a single day only
(April 4 1998 and 26 May 1999).
1998 Survey
This employed digging and hand sorting of soil. Prior to this, a brief reconnaissance of the
area for surface casting by earthworms was undertaken. Randomly selected areas of 0.1 m 2
were dug to a depth of 0.1 m. Although in practice, this was usually impossible due to the
presence of large rocks below the soil surface. The soil, once removed, was placed on plastic
sheeting and hand sorted for earthworms (other soil macro-invertebrates were also noted; see
Butt 1998). After removal of the soil, a suspension of mustard powder, (10 g l -1) acting as a
vermifuge, was applied to the sample areas, an adaptation of the method proposed by Gunn
(1992) and successfully used by Butt (2000). All soil was returned to the hole after sorting
was complete. All earthworms located were preserved in 4 % formaldehyde for later
identification, following the convention of Sims & Gerard (1999). Six sites were selected,
with 4 replicas per site
The sites were:
i) North Grove
ii) Middle Grove
iii) Between (i) and (ii)
iv) Between (ii) and South Grove
v) Moorland to East of (ii) (Moor ‘A’)
vi) Moorland to East of (iv) (Moor ‘B’)
The largest block of woodland (South Grove) was not sampled, as it is the section first
encountered by most members of the public via the footpath from Two Bridges. It was
thought that to be seen within this section might have encouraged others to venture into the
wood. [In reality very few people were seen during the visit, as heavy rain showers appeared
to dissuade all but committed visitors.]
1999 Survey
To supplement the sampling of 1998, the authors returned the following year with additional
equipment. This comprised an Octet apparatus, as described by Thielemann (1986), a device
for extracting earthworms from the soil without recourse to digging. It works by delivering an
electrical current from a 12 v battery, into the soil in a controlled manner, such that
earthworms are driven to the surface. By way of comparison a more standard vermifuge
extraction method using a dilute (0.4 %) solution of formaldehyde (Raw, 1959) was also
employed. The standard area sampled for each method was 0.2 m2 and 5 replicates were
employed for each. Sampling took place in 2 areas only, South Grove (not sampled in 1998)
and in the area between South and Middle Groves. Once again sampling was kept to a
minimum, whilst permitting the collection of representative data. All earthworms collected
were preserved in 4 % formaldehyde for later identification, following the convention of
Sims & Gerard (1999).
During sampling soil depth measurements were taken from points in each quadrat and soil
temperatures recorded. Soil samples were not removed from site.
Walking towards Wistman’s wood along the path from Two Bridges, earthworm casting was
observed on the soil surface. Casting was also seen on the path below the woodland adjacent
to the fence beside the West Dart River. In both cases, earthworms were extracted from
below these casts using a few drops of dilute formaldehyde, and preserved for identification.
Results
1998 Survey
There were no obvious outward signs of earthworm presence (surface casting) within the
woodland areas. Three species of earthworm were located. These were Dendrodrilus rubidus
(Savigny, 1826), Lumbricus eiseni (Levinsen, 1884) and Lumbricus rubellus (Hoffmeister,
1843). Details relating to distribution, abundance and biomass are recorded in Appendix 2.
Woodland sites, those between the woodlands and moorland sites produced, 15, 2.5 and 13.8
animals m-1 respectively with respective biomasses of 2.51, 1.2 and 9.3 g m-1. All three
species were located within the woodland sites, with D. rubidus representing 75 % by number
but only 39 % by mass. No worms were recovered from 3 of the eight quadrats sampled
within the woodland.
The lowest number of earthworms was found within samples taken from the sites located
between the Woodland Groves. Only two specimens, one each of L. eiseni and L. rubellus,
were located. The moorland sites produced eleven specimens all of L. rubellus, the largest
mature individual having a mass of 1.36 g.
Numbers of earthworms found within the woodland sites and on the moorland were very
similar but the total biomass recovered from the latter was in excess of three times that from
the former. This was due to the species composition and not a function of age structure. (D.
rubidus may be mature at as little as 0.14 g.)
Within the area between North and Middle Grove, a small earthworm was collected from
beneath sheep dung. This was probably D. rubidus, but was too small for identification to
species level.
WISTMAN'S WOOD (DARTMOOR)
Sampling from 4/4/98
(0.1 m2 handsorted samples)
MOORLAND SITES
Moorland "A"
Number
Sample
1
2
3
4
Tot
Mass (g)
D.rub.
0
0
0
0
0
L.eis.
0
0
0
0
0
L.rub.
2
3
0
0
5
Tot
Sample
1
0
3
4
Tot
2
3
0
0
5
D.rub.
0
0
0
0
0
L.eis.
0
0
0
0
0
L.rub.
2.11
2.81
0
0
4.92
Tot
2.11
2.81
0
0
4.92
D.rub.
0
0
0
0
0
L.eis.
0
0
0
0
0
L.rub.
1.1
0.24
0.65
0.53
2.52
Tot
1.1
0.24
0.65
0.53
2.52
0
0
7.44
7, 44
D.rub.
0
0
0
0
0
L.eis.
0
0.18
0
0
0.18
L.rub.
0
0
0
0
0
Tot
0
0.18
0
0
0.18
D.rub.
0
0
0
0
0
L.eis.
0
0
0
0
0
L.rub.
0
0
0
0.76
0.76
Tot
0
0
0
0.76
0.76
0
0.18
0.76
0, 94
D.rub.
0.08
0
0
0.09
0.17
L.eis.
0
0
0
0
0
L.rub.
0
0
0
0.95
0.95
Tot
0.08
0
0
1.04
1.12
D.rub.
0.54
0.05
0.02
0
0.61
L.eis.
0
0.28
0
0
0.28
L.rub.
0
0
0
0
0
Tot
0.54
0.33
0.02
0
0.89
0.78
0.28
0.95
2, 01
Moorlan
d "B"
Number
Sample
1
2
3
4
Tot
Mass (g)
D.rub.
0
0
0
0
0
L.eis.
0
0
0
0
0
L.rub.
1
1
2
2
6
Tot
1
1
2
2
6
11
11
Sample
1
2
3
4
Tot
Grand Moorland Totals (0.8 m2)
0
0
BETWEEN WOODLAND SITES
North - Middle Grove
Number
Sample
1
2
3
4
Tot
Mass (g)
D.rub.
0
0
0
0
0
L.eis.
0
1
0
0
0
L.rub.
0
0
0
1
1
Tot
0
1
0
1
1
Sample
1
0
3
4
Tot
Middle - South
Grove
Number
Sample
1
2
3
4
Tot
Mass (g)
D.rub.
0
0
0
0
0
L.eis.
0
0
0
0
0
L.rub.
0
0
0
1
1
Tot
0
0
0
1
1
2
2
Sample
1
2
3
4
Tot
Grand Between Woodland
Totals (0.8 m-2)
0
0
WOODLAND SITES
North Grove
Number
Sample
1
2
3
4
Tot
Mass (g)
D.rub.
2
0
0
1
3
L.eis.
0
0
0
0
0
L.rub.
0
0
0
2
2
Tot
Sample
1
0
3
4
Tot
2
0
0
3
5
Middle
Grove
Number
Sample
1
2
3
4
Tot
Mass (g)
D.rub.
4
1
1
0
6
L.eis.
0
1
0
0
1
L.rub.
0
0
0
0
0
Tot
4
2
1
0
7
2
12
Sample
1
2
3
4
Tot
Grand Woodland Totals (0.8 m2)
9
1
1999 Survey
The three species located in 1998 were found and in addition Dendrobaena octaedra
(Savigny, 1826) was located within South Grove. Details of numbers and biomasses for the 2
areas sampled are shown in Appendix 3. Combining results from the 2 methods used,
densities of 32.5 and 4.5 earthworms m-1 with biomasses of 8.84 and 3.4 g m-1 were recorded,
for South Grove and the area between South and Middle Groves, respectively. In both areas a
high proportion of the animals collected were immature and could only classified as
Lumbricus. spp.
In South Grove all 4 species were recorded whereas only L. rubellus was found in the site
located between the Woodland Groves.
Use of the 2 extraction methodologies did not produce significantly different numbers of
specimens from South Grove (p > 0.05). However, significantly more earthworms were
extracted with formalin than with the electrical method between South and Middle Grove.
The latter only producing a single specimen from 5 x 0.2 m2. (Mean soil temperature, which
can affect this technique, was recorded as 10.4 oC.)
High soil moisture content (not measured) and large rocks below the soil surface may have
also inhibited the electrical technique. Measurements revealed soil depths ranging from 0.02
to 0.18 m at sampling sites. Further analysis of these measurements is not presented as the
sites were selected to permit insertion of the electrical probes and were not therefore
randomly chosen.
Earthworms collected from below casting, on the paths from Two Bridges and below the
woodland adjacent to the river, were all L. rubellus.
Discussion
The combination of sampling techniques revealed the presence of 4 earthworm species and it
is likely that this represents the full community of this site. All of the species located are acid
tolerant and prefer soil pH in the range 3.5- 7.0 (Satchell, 1955). Both L. eiseni and L.
rubellus are associated with moorland habitats whilst D. rubidus is a woodland species, often
found under moss and under bark of old trees (Sims & Gerard, 1999).
The number and biomass of earthworms found within the woodland are lower than figures
reported for lowland oak woodland of 106 - 122 individuals m-2, with a biomass of 61 - 122 g
m-2 (Edwards & Bohlen, 1996). Such figures are also at the lower end of the scale compared
with woodlands dominated by other tree species, due to the poor nutritional quality of oak
litter (e.g. Muys et al., 1992). The acidic nature of the soils (not measured here) and high
precipitation, leading to very wet soils are probably the major factors influencing earthworm
distribution and abundance at this site.
Surface casting by Lumbricus rubellus has been recorded before, e.g. in the compacted soils
of landfill caps (Butt et al, 1999) but would not be expected in agricultural or forest soils.
This behaviour is more common amongst deep burrowing earthworms (not represented at this
site).
The number of earthworms and other soil macro-invertebrates was much greater within the
woodland groves compared with the other sampling areas. This greater abundance and
diversity is almost certainly a function of greater niche availability.
Recommendations
It is recommended that a more detailed assessment of all soil invertebrates, possibly at the
scale employed here, would prove useful to obtain a more complete picture of the
biodiversity of upland oak woodlands.
Also a regular (every 5 or 10 years) monitoring programme for earthworms might be valuable
to detail any major changes which could occur. This would however be usefully undertaken
in conjunction with the above.
With respect to upland oak woodland in general, this type of monitoring need not apply
specifically to Wistman’s Wood but could encompass a range of appropriate sites,
determined by local Biodiversity Action Plans.
References
Butt, K. R. (1998) The Earthworm Fauna of Wistman’s Wood, Dartmoor (A preliminary
survey). Unpublished Report to English Nature, University of Central Lancashire.
Butt, K. R. (2000) Earthworms of the Malham Tarn Estate (Yorkshire Dales National Park)
Field Studies 9, 701-710.
Butt, K. R., Frederickson, J. and Lowe, C. N. (1999) Colonisation and spread of
earthworms on a partially restored landfill site. Pedobiologia 43, 684-690.
Edwards, C. A. and Bohlen, P. J. (1996) Biology and Ecology of Earthworms
(3rd Edition). Chapman & Hall, London.
Gunn, A. (1992) The use of mustard to estimate earthworm populations. Pedobiologia 36,
65-67.
Muys, B., Lust, N. and Granval, Ph. (1992) Effects of grassland afforestation with
different tree species on earthworm communities, litter decomposition and
nutrient status. Soil Biology and Biochemistry 24, 1459-1466.
Page, P. A. (1995) Wistman’s Wood Forest Nature Reserve: Second Management Plan
(1994-1999). English Nature, Unpublished.
Raw, F. (1959) estimating earthworm populations by using formalin. Nature 184, 1661-2.
Satchell, J. E. (1955) Some aspects of earthworm ecology. In Soil Zoology, (Ed. D. K.
Mc
E. Kevan), Butterworths, London. pp 180-201.
Sims, R. W. and Gerard, B. M. (1999) Synopses of the British Fauna (New Series)
31-Earthworms. The Linnean Society, London.
Thielemann, U. (1986) Elektrischer Regenwurmfang mit der Oktett-Methode.
Pedobiologia, 29, 296-302.
1
Department of Environmental Management, University of Central Lancashire,
Preston PR1 2HE UK
2
Institute of the Natural Bases of the Agricultural Production, Agricultural University
in Krakow, Economy Department in Rzeszów, ul. Cwikliñskiej 2,
35-959 Rzeszów, Poland