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Exploring Eversden Wood by Louise Bacon and Vince Lea |
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 Most
of us are familiar with the ancient boulder clay woodlands of the
heaviest of heavy soils in the area of South Cambridgeshire, North
Essex, N W Suffolk and adjacent parts of Bedfordshire. They have a
long and interesting history, much studied by Cambridge academics,
most notably Oliver Rackham, who has developed the discipline of
historical ecology through studies of these woods.
The main reason for
their survival in what is now predominantly an arable landscape is
that the soils were too heavy and wet to be ploughed; they then
became vital as sources of timber and wood for construction, crafts
and as fuel. Old maps show us that most had the same boundaries as
they do today. They were recognised for their unique assemblages of
plants in the earliest days of botany and were among the first sites
to receive protection under the new era of nature conservation in
the 1960s; Hayley Wood, for instance, was an early site purchased by
the county Wildlife Trust (CAMBIENT as it was then). Other woods in
the area are not always as well studied, and throughout these woods,
the fauna is less well documented than the flora; this is especially
true of the invertebrate fauna. Over the past two or three years we
have made several visits to Eversden Wood, initially to study the
birds and then to begin to get an insight into the insect fauna of
the site. This paper outlines our findings and speculates on why
this woodland is interesting.We first visited Eversden Wood (TL3453) during preliminary fieldwork for a British Trust for Ornithology Woodcock survey in 2003. Winter visits to the site showed lots of evidence of the past coppice practices, such as old multi-stemmed trees. The three main features of this woodland are very heavy, wet soils with lots of standing water – much wetter than the other woods in the area; a very diverse and natural mixture of tree species – no one species dominating overall but patches of different tree communities; and a network of wide, grassy rides and a couple of reasonable-sized glades. The boulder clay woodlands of southern Cambridgeshire are normally dominated by Ash and Field Maple, with Hazel, Hawthorn, Small-leaved Elm, willows and Blackthorn also being present in varying densities. The other main species present in them is Pedunculate Oak, which has often been planted a very long time ago as timber, but not at high density as would be found with modern forestry. However, the difference with Eversden Wood is the addition of significant quantities of Silver Birch and Aspen, fewer oaks than some nearby woods, and a noticeable mosaic of species through the wood. This mosaic of tree types may be in part due to its history – it is in three parishes, and there could have been differences in the management of woodland in historic times in the different parishes resulting in differences today. Our surveys have shown that there is a broad mixture of birds present during the breeding season in this wood, including Marsh Tit, Coal Tit, Nuthatch (all scarce breeders in Cambridgeshire), Treecreeper, Blackcap, Chiffchaff, Willow Warbler, all three Woodpeckers (although we have no evidence for breeding of Lesser Spotted Woodpecker) alongside the more ubiquitous Blue and Great Tits, Chaffinch, Blackbird, Robin, Dunnock, Wren, Song Thrush, etc. Buzzards are also seen with increasing frequency around the area, especially in winter. Our bird survey visits gave several sightings of interesting, initially unknown insects. On one May visit with friends, a strange “wasplike” insect landed on a fore-arm, and its large size (that of a wasp) and black and yellow colouration made it striking and interesting – something we had never seen before. John Dawson, vc29 moth recorder identified this as the Birch Sawfly (Cimbex femoratus). This is not a common insect, but once seen, always remembered. The observation which really clinched our interest in the site was actually of day-flying lepidoptera in late March. About a year after the initial observation of what we had decided were day-flying moths, a chance discussion with John Dawson, hinted at the identity of these moths as either Orange Underwing (Archiearis parthenias) or Light Orange Underwing (Archiearis notha), both day-flying spring species of geometer moths. Neither had been recorded in Cambridgeshire (vc29) for many decades; the last record of Light Orange Underwing was from Eversden in 1934 (Victoria County History). Orange Underwing is a birch feeder in its larval stage, and Light Orange Underwing an Aspen feeder, so both could potentially have been observed by us in Eversden. Several days of determined observation in 2004 by both the authors and by John Dawson led to sightings in several locations within the wood, around stands of both aspens and birches. JD managed to net a couple of individuals and confirmed Light Orange Underwing, Nationally Scarce Nb (recorded in 30-100 10km squares). Presumably the species had continued to exist there un-recorded since the 1930s. In 2005 and 2006 we again looked for these species, and again saw moths flying very early in the year around Birch trees, these probably being Orange Underwing, but unfortunately all were at a great height and none was caught for verification. The number of interesting insect sightings led us to seek permission to take John Dawson and several moth traps into the wood. The landowner has been very co-operative in granting us access with a vehicle to this wood, parts of which are served by two public rights of way, but it is a substantial walk from the nearest parking-spot. The wood has a series of grassy rides, two of which are these public rights of way, the others are not. We ran five Mercury Vapour (MV) light traps and one or two actinic light traps on a number of occasions from June 2005 to May 2006. Other field trips during summer were made by either the authors or others to look for beetles and day-flying moths. One of the moth team also made a visit in November 2006 to record leaf-miner moths, which can be identified by their distinctive patterns left in leaves. We used the same locations for each light-trapping session, covering a broad range of tree species, but only around a quarter of the woodland. We have recorded 314 species in total, of which 6 are beetles, 3 hymenoptera, one groundhopper and one fly. All others are lepidoptera (303 moths). The number of interesting species recorded was unprecedented at the time, and to get species unrecorded for several decades and also species new to the vice county in a short survey period was a real highlight. A summary of the most interesting insect finds is given in the table below alongside numbers of species recorded:
Notes: Orange Moth first record since 1974; Poplar Lutestring first since 1991, Euzophera pinguis – ash specialist, rare; Orange Footman, becoming more frequent, woodland specialist; Maple Pug – rare, woodland specialist, Square-spotted Clay – Nationally scarce (Nb), ex UKBAP species; this area is a national hot-spot for this latter species. No attempt was made to count individuals on these occasions, but the ideal conditions prevailing on our second visit led to the most amazing abundance of moths that the two authors have ever seen, along with swarms of other insects such as midges, craneflies, beetles, ichneumons, sawflies, and a couple of Hornets. We also had a bat detector running during the evening and heard Barbastelle bats flying overhead. The abundant moths in the wood are a vitally important food source for this species. The other insects include the longhorn beetles Leiopus nebulosus, Phymatodes testaceus, Stenocorus meridianus, sawflies tentatively identified as Tenthredo mesomelas and T. maculata, and the cranefly Tipula maxima. The use of light-traps to investigate the diversity of these species groups is poorly documented, but we have had other successes with luring longhorn beetles to MV light. This is notable, as at the time, we had spent warm mid-day hours looking for longhorns on flowers and vegetation, but had seen none, so to then observe species coming to light was a bonus. Research on the effectiveness of MV and actinic light traps for monitoring non-moth insect populations is lacking, but a potential worthwhile course of investigation. Carabid (Ground), Staphylinid (Rove) and Elaterid (Click) beetles have also been noted by the authors at light with regularity, but our lack of knowledge of these groups precludes further discussion of them here. None of the ‘Interesting species’ listed in the table is nationally rare – most are classified as Nationally Notable or ‘Local’ species with a widespread but thin distribution across Britain. They are, however, scarce within vc29. Orange Moth, in particular, has no other known current sites in the county, the previous record being in 1974 from a completely different part of the county, but the following year (2006) was found in one other wood. Most of these species we found are woodland specialists and their local scarcity is a result of the lack of woodland in the area. The ancient woodland sites like Eversden Wood offer the best chance of finding these specialists, since the continuous cover of trees has allowed the populations to persist. Hayley Wood was another well-studied site in 2005/6 and was found to have several of these species as well. Many of these species are rather sedentary and unlikely to colonise new plantations unless very close to existing woods. Also, they have specialised requirements in terms of foodplants (the Light Orange Underwing being a good example, feeding only on the catkins of Aspen). Some species require a number of different components in the same habitat; flowering plants for nectar and specific growth stages of trees for larval feeding, leaf litter for pupation etc.; those species which, like the fritillary butterflies, depended upon lots of vigorous early stage growth following coppice operations, have probably mostly been lost, as there have only been a few intermittent attempts at coppicing in the last 50 years or so. Recent revival in the interest of coppice produce has not been sufficient to reverse this situation in Eversden Wood. Some coppicing has been done, but there are so many Fallow Deer in the area that the new shoots of the coppiced tree stumps are eaten to the ground as soon as they appear, leading to the death of the trees rather than the desirable regrowth. This deer population also influences the flora – it is not a woodland with carpets of spring flowers – fallow grazing sees to that. It is clear from the invertebrates we have found so far that several factors are important in influencing the invertebrates of the wood. We consider these to be the following: • Aspen allowed to grow to a fair size, in larger populations than in other woods in the area, and scattered throughout several parts of the wood • Birch scattered throughout the wood, rather than in small pockets of sandy soils • Cessation of coppicing • Dead wood of all tree species, both standing and fallen, found throughout the wood; especially important for the beetles we have found so far. Much remains to be discovered in this woodland, and we hope to revisit other parts in the coming years to continue our work. Acknowledgments We would like to thank the landowner for his co-operation in allowing access to this valuable ancient woodland away from the public rights of way, and John Dawson and Ian Barton, amongst others, for all their knowledge, identifications of difficult species and invaluable hours spent in this woodland.Reprinted from Nature in Cambridgeshire No 50, pages 44 - 48 |