The use of saproxylic invertebrates in the selection and evaluation of areas of relic forest in pasture-woodlands

6 Pages·1994·2.1 MB·

by  Paul T Harding

BR.J.ENT.NAT.HIST.,7(SUPPL. 1): 1994 21
THE USE OF SAPROXYLIC INVERTEBRATES IN THE
SELECTION AND EVALUATION OF AREAS OF RELIC
FOREST IN PASTURE-WOODLANDS
PAUL HARDING
T.
Biological Records Centre, Institute ofTerrestrial Ecology, Monks Wood
,
Abbots Ripton, Huntingdon, Cambridgeshire PE172LS.
AND K.N.A. ALEXANDER
The National Trust, 33 Sheep Street, Cirencester, Gloucestershire GL7 JQW.
INTRODUCTION
Types ofwoodlands andforest relics
Traditional woodland management throughout most of Britain has been mainly by
coppicing orby a combination ofcoppicing with maiden or 'standard' trees. Until the
1970s woodland conservation policy in lowland Britain was concentrated towards
coppice/coppice-with-standards woodland, these being the most prevalent and best
documentedtypesofwoodland. Suchwoodswererecognizedasbeingimportantfortheir
distinctive vascular floras and, in some cases, for their butterflies. Almost all the
woodland areas protected by statutory legislation or by the voluntary conservation
movement, up to the 1970s, were ofthis type.
Thesetypesofwoodlandmanagementresultedin littlehabitatforthefaunaandflora
particularly associatedwiththeolderage-classesoftreeswhichwouldhaveoccurredin
natural (unmanaged) forest in these latitudes (see, for example, Warren & Key, 1991).
Evidenceofsub-fossilremainsfromHolocenesitessuggestthatnaturalforestwithmixed
speciesandageclassesoftreessurvivedinsomeareasuntilatleast3000yearsbeforethe
present. Anoticeablefeatureatsomeofthese sitesisthattherewere large,oldtrees. In
thefewcaseswheresub-fossilinsectremainshavebeenstudied,avariedsaproxyliefauna
has been recorded in association with evidence ofabundant, and often large, trees.
Several of the saproxylic species recorded in Holocene deposits no longer occur in
Britain(Girling, 1982). Othershavebeenrecordedinthe 19thand20thcenturiesatasmall
number ofsites characterized by Ratcliffe (1977) in the Nature conservation review as
'mixeddeciduouswoodland: ancientparksandovermaturewoodland'. Theimportance
ofthesesitesasrefugiaforahithertoneglectedcomponentoftheBritishfloraandfauna
was coming to be recognized in the 1970s. At this time, two leading British woodland
ecologists,OliverRackhamandGeorgePeterken,were(largelyindependently)developing
theirknowledge and ideas on the role ofwoodland management history in influencing
present-day woodlandcommunities. The'woodpasture'formofwoodlandmanagement
wasrecognizedbybothRackhamandPeterkenasanimportantanddistinctivewoodland
type. Also, Francis Rose had been developing an index of ecological continuity in
woodlands,usingepiphyticlichens,mainlyinareaswithlargeandoldtreessuchasparks
andotherareas managed as pasture-woodlands.
BR.J.ENT.NAT.HIST..7(SUPPL. I): 1994 22
A survey ofthe 'mature timberhabitat'
In 1975, P.T.H.wascommissionedbythethenNatureConservancyCouncil(NCC)to
examinetheextentofthe 'maturetimberhabitat' inlowlandBritain. Theproject,which
extended over four years, was primarily to identify areas which were known to be of
importance,orwhichmayhavepotential,forsaproxylicinvertebrates. Alaterpartofthe
project looked at the problems ofmanagementofsuch sites.
AninitialinventoryofsiteswascompiledbyP.T.H.in 1975,basedlargelyonpublished
and anecdotal information on the occurrence ofsaproxylic species and on information
aboutsiteswithnumbersoflarge,oldtrees. In 1976and 1977,hevisitedabout 100such
sites to assess the extent and quality ofthe habitat potentially available for saproxylic
fauna. Theprojectdidnotincludeopportunitiesforsystematicsamplingatthesesitesin
the way that thecomplementary surveysoflichens were being madeby Francis Rose.
A listofsaproxylic invertebrates
As part ofthe project, the help ofseveral ofthe most experienced entomologists in
Britainwasenlistedtocompilealistof(mainly)saproxylicspecieswhichwereregarded
as being characteristic ofsites already accepted as being rich in saproxylics. This self-
fulfillingprophecywasdeveloped withreferencetotheworkofPalm(1959)andrelated
workonothergroups,forexampleRose's'indexofecologicalcontinuity' (usinglichens)
(Rose, 1974, 1976), Peterken's 'ancient woodland indicators' (using vascular plants)
(Peterken, 1974) and ancient woodland molluscs (Paul, 1979). The list of beetles,
pfourblsiasphreodxyilniacreCpoolreto(pHtaerrdainognl,y,19w78a)s,wevaesnttueastleldyopvuebrlsiesvheerdalinyeHaarsrdainndga&revRiossedev(e1r9s8i6o)n.,
However,theoriginallistofColeopterawascompiledfromthecombinedknowledgeand
experienceofA.A. Allen, P.M. Hammond, F.A. Hunter, C. Johnsonand P. Skidmore, to
whom full acknowledgement must be given.
Previously, comparative lists ofa few species and a small number ofsites had been
compiled by Allen (1966) and Welch & Harding (1974). After the publication of the
olirsitg(mHaalmlmisotnindH,ar1d9i7n9;g(W1e9l7c8h),&seCvoeoratlera,ut1h9o8r1s;haAvtetyc,o1m9p8a3r;edGaorrleavnadl,ua1t9e8d3)s.itesusingthe
The 196 species included in Annex 2 of Harding & Rose (1986) was regarded as
tentative. They emphasized that the list could only be used to evaluate sites with the
following limitations in mind:
1 it is a listofsaproxylic species believed tobe associated with dead-woodhabitats in
ancient pasture-woodlands; it is not a listofwoodland indicators;
2 itisanationallistforlowlandBritaininwhichregionalvariationscanbeaccommodated
to only a limited extent;
3 theecology and distribution ofmany species is relatively poorly understood.
INDEX OF ECOLOGICALCONTINUITY FOR SAPROXYLIC
COLEOPTERA
In a paper to a regional meeting ofthe Royal Entomological Society at Leicester in
1987, K.N.A.A. proposed the development of an 'index of ecological continuity for
saproxyliccoleoptera' basedonthelistpublishedin Harding&Rose(1986)(Alexander,
1988).
This index complemented thatdeveloped forlichens, butwith the added advantages
thatalargersuiteofspecieswasused(195beetlesasagainst30lichens),thelistwasgraded
enablingmorerefinedusageandthespeciesarenotsosensitivetoatmosphericpollution.
Disadvantages were that, unlike lichens, beetles are seasonal and many species are
difficulttosample. Inarecent paper, Hammond & Harding (1991) described the range
BR.J.ENT.NAT. HIST.,7(SUPPL. 1); 1994 23
of sampling techniques used in conducting qualitative and quantitative surveys of
saproxylicinvertebrates. Moredetailedinformationontechniques(inatropicalcontext)
is given by Hammond (1990).
The 195 saproxylic species (one non-saproxylic was omitted) listed by Harding and
Rose were categorized in three groups according to the extent to which they have been
consistently recorded from areas of ancient woodland with continuity of dead wood
habitats. ForexampleGroup 1 specieswereregardedtobethemostfaithfultosuchsites
and Group 3 those which could occurwidely in wooded land.
K.N.A.A. proposedthatthese threegroupsshouldformthebasisofascoring system,
on apresence/absencebasis, tointerpretlistsofspeciesrecordedatasiteand toprovide
anevaluationofthesitebasedonthespeciesofsaproxylicColeopterarecorded. Thevalue
ofeachofthethreegroups,asrelatedtotheothers,issubjective,butGroup 1 specieswere
regardedtobemoreimportant(forreasonsofscarcityandapparentfaithfulnesstoknown
ancientpasture-woodlands)thanthoseinGroup3andthereforemeritahigherscore. Thus
thepresenceofaGroup 1 speciesscores3,aGroup2speciesscores2andaGroup3species
scores 1.
Adecision was made toexcludehistorical records inthecalculationofthe index and
only records since 1950havebeen used. The index is intended tobe used inevaluation
fornatureconservationandthereforeshouldreflectthecurrentandrecentpastinterestof
thesitesbeingconsidered. Manyoftheanecdotalrecordsavailableforsitesarehistorical.
Including such records would bias the index to select sites which were important in the
early 20th century, but many of which subsequently have been destroyed or severely
degraded as relicsofforestwithold trees. The cut-offdate forrecordstobe used in the
indexwassettledat 1950,followingtheexampleoftheNCC'sInvertebrateSiteRegister.
Thegeneralpaucityofrecordsformanysites,andtheabsenceofanysystematicattempt
tosurveythebeetlesofalargenumberofsites,inevitablymeansthatcomparisonsofone
sitewithothers aresubjecttoconsiderablebias. Theoriginal index valuescalculated in
1987havebeensubjecttoongoingrevisionasnewrecordsforsiteshavebeenincorporated
andascompletelynewsiteshavebeensurveyed. However,itispossibletoplaceasiteon
a scale of importance relative to other sites providing the above caveats are accepted.
Table 1 isalistofthemostimportantpasture-woodlandsitesin lowlandBritainassessed
using the 'index ofecological continuity' (lEC).
Index values of20 or more appear to identify the most important sites ofa national
series, butthis threshold may needtoberaisedas moresurveyresultsbecomeavailable.
The sites listed in Table 1 should be considered as priority areas for conservation
measures to protect and perpetuate the habitat.
GEOGRAPHICAL DISTRIBUTION OF SITES IN BRITAIN
The list ofsites in Table 1 has a clear bias towards the lowlands and the south-east.
Ecologicalconsiderationssuggestthatthisbiasreflectstheprobablerangeofthe largely
thermophilous species included in the assemblage, but recorderbias is almostcertainly
present; few sites in Wales, the south-westand northern Englandhavebeen surveyed in
detail. Basedonpre-1950records,sitessuchasGibside(TyneandWear)andShutePark
(Devon) have lEC values of26 and 31 respectively. However, important sites such as
Moccas Park (HerefordAVorcester) and Duncombe Park (North Yorkshire) are on the
fringes ofthis lowland/south-eastern area.
Regional indices,basedonthenational index,wouldprovidegreatersensitivityinthe
assessment of sites. Garland (1983) proposed such a regional index, based partly on
Harding(1978),butdidnotdistinguishclearlybetweenthespecializedsaproxylicspecies
andgeneralancientwoodlandindicators. Furtherconsiderationshouldbegiventoeither
regionalindicesortoregionalweightingofthenationalindex,butthecollectionofmore
data (new sites, systematic surveys by specialists, resurvey of sites omitted from the
presentlistduetotheageoftherecords,collationofunpublisheddata)areprobablyamore
urgent priority.
.
BR.J.ENT.NAT.HIST.,7(SUPPL. 1): 1994 24
Table 1 The most important national sites forthe saproxylic Coleopteraofancient woodlands, especially
pasture-woodlands,gradedusingtheindexofecologicalcontinuity(lEC)
SiteName Area*
BR.J.ENT.NAT.HIST.,7(SUPPL. 1); 1994 25
A EUROPEAN PERSPECTIVE
In 1980,theCouncilofEuropesetupaConsultants' Grouptoidentifyprojectsrelated
to invertebrate conservation which might be supported by the Council. A project on
saproxylic invertebrates was selected to provide insight into the decomposer sector in
ecosystems. Anadvantageofthisprojectwasthatadditionalinformationontheremnants
ofthe natural forests ofEurope wouldbe acquired.
Theprojectbeganin 1982withtheestablishmentofcriteriaforuseintheselectionof
thesaproxylicstobeusedasbio-indicatorsofsitequality. Thecriteria,listedbySpeight
(1989), resulted in alistof33 insectspecies. This listwas soonabandonedbecausethe
species were already so localized within their European range that only a few forests
wouldbeidentifiedasaresult,althoughthosesiteswouldprobablyhavebeenthecreme
delacreme. NoneofthespecieslistedisknowntohaveoccurredinBritaininrecenttimes.
Based on the original criteria, a revised and considerably expanded list of about 200
speciesofColeoptera,Diptera,HemipteraandHymenopterawasprepared(Speight1989,
Annex 1). Using this list of species and a simple questionnaire, Speight sought
informationonthesitesregardedbynationalspecialiststobethemostimportantforthese
andsimilarspecies. Fourrelicdeciduousforestsiteswereselectedfromtheinformation
collated by Speight: Windsor, New Forest, Epping Forest and Moccas Park. The
Caledonian pineforest atAbernethy was also included.
CONCLUSIONS
The evaluation of sites for wildlife conservation has traditionally been based on
botanical and ornithological assessments. In the case ofrelic woodlands formerly or
currentlymanagedbythewood-pasturesystem,vascularplants(primaryproducers)and
birds(secondaryproducers)areunlikelytoprovidemeaningfulmeasuresoftheimportance
ofsuchsites. Decomposers,suchassaproxylicColeoptera,areespeciallyassociatedwith
suchrelicareasandprovideamorereliablemeasureofthebiodiversityofsites. Asimple
method to assess deciduous pasture-woodlands in lowland Britain has been developed
whichusesavailabledata,oftenderivedfromthebiologicalrecordingactivitiesofasmall
groupofspecialists. Moredataareneededtodevelopandimprovethepresentindexof
ecologicalcontinuityofsaproxylicColeoptera,butthepreliminaryresultsshowthatitis
possible to identify and rank sites at a national level. Hammond & Harding (1991)
discussedwaysinwhichthepresentlistofspeciescouldbeimproved(forexamplebythe
additionofsomespeciesandtheomissionofothers). Theyalsoproposedthatlistsofrare
non-saproxylicwoodlandColeopteracouldbecompiledforuseintheevaluationofsites.
ACKNOWLEDGEMENTS
P.TH. is grateful to the entomologists, mentioned above, who helped to compile the
original list of Coleoptera and to the then NCC which funded his work on pasture-
woodlands. K.N.A.A. isgratefultothe staffattheInvertebrate SiteRegisterofthethen
NCCforaccesstotheirdatabaseinthecompilationofsitelistsforthecalculationofthe
lEC.
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