The Biod­iversity and Man­age­ment of Aspen Woodlands

The Biod­iversity and Man­age­ment of Aspen Woodlands:

Pro­ceed­ings of a one-day con­fer­ence held in Kin­gussie, Scot­land, on 25^th May 2001

Edited by Peter Cos­grove and Andy Amph­lett 2002

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The Biod­iversity and Man­age­ment of Aspen Woodlands

The Biod­iversity and Man­age­ment of Aspen wood­lands: Pro­ceed­ings of a one-day con­fer­ence held in Kin­gussie, Scot­land, on 25^th May 2001

CON­TENTS: Fore­word and over­view Peter Cos­grove and Andy Amph­lett 4

The eco­logy and his­tory of Aspen wood­lands Peter Quelch 8

Fungi and Aspens: Pro­mot­ing biod­iversity, Aspen friends and foes Ern­est and Valer­ie Emmett 12

The import­ance of Aspens for lichen Les and Sheila Street 16

Bry­ophytes on Aspens Gor­don Rothero 23

Aspen, a vital resource for saproxyl­ic flies Gra­ham Rotheray 29

The Large Pop­lar Long­horn Beetle, Saperda carchari­us in the Scot­tish High­lands Tracey Begg and lain MacGow­an 32

Byc­tiscus pop­uli, a leaf rolling weevil depend­ent on Aspen Jon Mellings and Steve Compton 33

The import­ance of Aspen for Lepid­op­tera Mark Young 37

Beavers: Aspen heav­en or hell? Dave Batty 41

Col­our pho­to­graphs insert i — viii

Vari­ation in Aspen in Scot­land: genet­ics and sil­vi­cul­ture Bill Mason, Eric East­on and Richard Ennos 45

Improv­ing the avail­ab­il­ity of nat­ive Aspen for use in north­ern Scot­land Mark Ban­ham and Paul Young 56

Wood­land man­age­ment meas­ures for Aspen wood­lands Denis Tor­ley 59

Agri-envir­on­ment man­age­ment meas­ures for Aspen wood­lands Alis­on McK­night 63

Deliv­er­ing action: how Aspen fits into the UK Biod­iversity Action Plan­ning pro­cess Peter Cos­grove 68

The Trees for Life Aspen Pro­ject Alan Wat­son Feath­er­stone 69

The man­age­ment of Inver­tromie wood, Scotland’s fourth largest stand of Aspen Tom Prescott 74

Hab­it­at frag­ment­a­tion lain McGow­an 79

Aspen in myth and cul­ture Anne Elli­ott 81

Del­eg­ate dis­cus­sion 84 Del­eg­ates list 85

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The Biod­iversity and Man­age­ment of Aspen Woodlands

Fore­word

Peter Cos­grove Cairngorms Biod­iversity Officer, Cairngorms Part­ner­ship, 14 The Square, Grant­own-on-Spey, Moray­shire, PH26 3HG. 

Andy Amph­lett The Roy­al Soci­ety for the Pro­tec­tion of Birds (RSPB), Aber­nethy Forest Nature Reserve, Forest Lodge, Nethy­bridge, Inverness-shire, PH25 3EF.

These pro­ceed­ings are the res­ult of hard work and enthu­si­asm of many indi­vidu­als and organi- sations involved in action and research into the biod­iversity and man­age­ment of Aspen wood- lands in the UK. This interest and effort cul­min­ated in a one-day con­fer­ence held at The Duke of Gor­don Hotel, Kin­gussie in the heart of Aspen coun­try on Fri­day the 25^th May 2001. Over 120 people inter­ested in the biod­iversity and man­age­ment of Aspen wood­lands atten­ded the con- ference.

The qual­ity of both the present­a­tions and the poster ses­sions con­vinced the organ­isers of the need to pub­lish this mater­i­al as a fit­ting per­man­ent record of the con­fer­ence. Most of the papers in these pro­ceed­ings were presen­ted in one form or anoth­er at the con­fer­ence, with a small num- ber of addi­tion­al import­ant papers invited from oth­er con­trib­ut­ors. It is hoped that these pro- ceed­ings have cap­tured the expert­ise and interest of the vari­ous spe­cial­ists and enthu­si­asts that was so evid­ent on the 25^th May 2001. In par­tic­u­lar, it is hoped that these papers will stim­u­late fur­ther pos­it­ive action and research into the biod­iversity and man­age­ment of Aspen wood­lands in the UK.

As a focus for future action, Trees for Life have offered to estab­lish and host a web-site and cen- tral inform­a­tion resource on Aspen that is eas­ily access­ible to land man­agers, research­ers and the gen­er­al pub­lic. If you would like to become more involved in Aspen action please vis­it Trees for Life’s web­site: http://​www​.trees​forlife​.org​.uk

Finally, we would like to thank the spon­sors and part­ners; Aber­deen­shire Coun­cil, But­ter­fly Con­ser­va­tion, Cairngorms Loc­al Biod­iversity Action Plan, Cairngorms Part­ner­ship, Forest of Spey Pro­ject, Forestry Com­mis­sion, High­land Coun­cil and the High­land Loc­al Biod­iversity Action Plan Part­ner­ship, RSPB, Scot­tish Nat­ur­al Her­it­age (SNH), and Wood­land Trust Scot­land, who came togeth­er to make this con­fer­ence hap­pen. We are very grate­ful to the pro­ceed­ings authors and pho­to­graph­ers who con­trib­uted their time and efforts so freely. In par­tic­u­lar, spe­cial thanks are due to Tom Prescott of the RSPB, and to Anne Elli­ott and Peter Beat­tie of SNH for organis- ing such a suc­cess­ful and enjoy­able event.

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The Biod­iversity and Man­age­ment of Aspen Woodlands

Over­view

As a wood­land type, or as a sig­ni­fic­ant com­pon­ent of oth­er wood­lands, Aspen is restric­ted, in the Scot­tish High­lands, to a very lim­ited num­ber of sites mainly in the North-east. Here its loc­al abund­ance, in parts of Badenoch and Strath­spey espe­cially, mak­ing a strik­ing con­tri­bu­tion to the land­scape, seems at odds with its lack of form­al recog­ni­tion in cur­rent nation­al veget­a­tion clas- sifications.

With one excep­tion, the papers in these pro­ceed­ings con­cen­trate on Aspen in the North east High­lands, where the con­fer­ence and fieldtrip were held. Links could and should be made with Scand­inavi­an eco­lo­gists, who view Aspen, espe­cially old indi­vidu­al trees, as key­stone compo- nents in pre­serving biod­iversity in boreal forests. There, Aspen is a focus of cur­rent research, e.g. as part of the Uni­ver­sity of Helsinki’s Biod­iversity in Boreal Forests pro­ject (http://​www​.hel​sinki​.fi/​s​c​i​e​n​c​e​/​b​i​obof/).

In the Scot­tish High­lands, Aspen is par­tic­u­larly asso­ci­ated with well drained, often moist, miner- al soils. Here it was a very early post-gla­cial col­on­ist (before Scots pine) and has per­sisted in mixed woods with Birch, Hazel, Wil­low and Row­an, which are prob­ably of great antiquity. It also occurs more rarely, as stands with­in the nat­ive pinewoods.

As a tree spe­cies, Aspen is wide­spread across the Brit­ish Isles appear­ing to be espe­cially fre- quent in South-east Eng­land (Per­ring and Wal­ters 1962). Exam­in­a­tion of a selec­tion of recent county Flor­as from Eng­land which map Aspen at the tet­rad scale reveals Aspen to be very fre- quent in some areas, ran­ging from just 8% of tet­rads in Devon (Ivimey-Cook 1984) to 35% in Kent (Philp 1982) and a remark­able 41% in Sus­sex (Hall 1980). Do large Aspen stands occur out­side the High­lands? The scant descrip­tions in these Flor­as make it hard to place Aspen into an eco­lo­gic­al con­text, but the resource seems to be very large else­where, war­rant­ing more attention.

Rare spe­cies con­fined to, or with nation­ally import­ant pop­u­la­tions on Aspen include flies, moths, beetles, fungi, lichens and mosses, as described in sub­sequent papers. In terms of prac­tic­al nature con­ser­va­tion, a num­ber of these spe­cies are in need of emer­gency ​“first aid”. The inver- teb­rates, as is so often the case, are in the greatest need of tar­geted (and mon­itored) man­age- ment. They include a num­ber of spe­cies with crit­ic­ally low pop­u­la­tions which util­ise rel­at­ively eph­em­er­al com­pon­ents of the total Aspen resource, e.g. the decay­ing cam­bi­al lay­ers under the bark of large dia­met­er logs on the ground, or the foliage of Aspen suck­ers less than 1m high. A num­ber of lichens and one moss are sim­il­arly restric­ted to just a few indi­vidu­al Aspen trees, though in the medi­um term they may be able to per­sist on these trees.

In a turn around from usu­al situ­ations, these pro­ceed­ings lack inform­a­tion (with one not­able excep­tion — European beaver) on the ver­teb­rate fauna asso­ci­ated with Aspen. For example, we appear to know next to noth­ing about the bird spe­cies and com­munit­ies asso­ci­ated with Aspen in this coun­try. Else­where in Europe, Aspen wood­land and its dead wood resources attract sev- eral spe­cies of hole nest­ing birds, includ­ing vari­ous spe­cies of wood­peck­ers, some of which are absent from the UK. Aspens are also used by oth­er, per­haps unex­pec­ted, spe­cies such as Caper­cail­lie (Tet­rao urogal­lus). The ​‘Bird spe­cies of UK Aspen wood­lands’ paper has yet to be writ­ten, but breed­ing records of Buz­zard (Buteo buteo), Great spot­ted wood­peck­er (Dendro­copus major) Red­start (Phoen­i­cur­us phoen­i­cur­us) and Red­wing (Turdus ili­acus) from the after­noon fieldtrip sug­gests it is an area worthy of fur­ther investigation.

For all of these ​‘Aspen depend­ent’ spe­cies, chance events or unin­formed man­age­ment could be dev­ast­at­ing for loc­al pop­u­la­tions. All require reg­u­lar pop­u­la­tion and dis­tri­bu­tion mon­it­or­ing and hab­it­at man­age­ment tri­als aimed at secur­ing pop­u­la­tions. It is behold­en on spe­cial­ists, advisors and site man­agers to con­sider the implic­a­tions of any pro­posed actions (or inac­tion) on oth­er taxo­nom­ic groups or hab­it­ats. Mellings and Compton report the appar­ent loss of the BAP wee- 5

The Biod­iversity and Man­age­ment of Aspen Woodlands

vil, Byc­tiscus pop­uli, at one site due to the remov­al (for unspe­cified con­ser­va­tion reas­ons) of Aspen scrub. Though stat­ist­ic­ally unlikely, cre­ation of dead wood to increase poten­tial breed­ing sites for threatened Dip­tera could lead to a loss of a sim­il­arly threatened lichen or moss. Prac­tic­ally, we either accept that risk (not recom­men­ded!) or we ensure that adequate baseline sur­veys are car­ried out pri­or to man­age­ment, and that site man­agers know the exact loc­a­tion of import­ant trees. Unfor­tu­nately, the cur­rent lack of skilled field lichen­o­lo­gists and bry­olo­gists is a crit­ic­al prob­lem for facil­it­at­ing informed man­age­ment decisions.

Peter Quelch’s goal of pro­tect­ing, regen­er­at­ing and expand­ing all exist­ing Aspen woods, stands and trees, as well as plant­ing into new areas deserves sup­port. How­ever, it has to be remem- bered that it will be dec­ades before some com­pon­ents of the over­all Aspen hab­it­at will have increased, e.g. large dia­met­er trees and snags. Clonal vari­ation is almost cer­tainly a sig­ni­fic­ant determ­in­ing factor for the epi­phyte com­munit­ies of Aspen and quite plaus­ibly for oth­er groups e.g. Dip­tera. New plant­ings of Aspens should fol­low the pro­tocol adop­ted by Trees for Life (Wat­son) and include mater­i­al from as wide a range of loc­ally occur­ring clones as possible.

Much atten­tion has centred on the import­ance of the largest Aspen stands, as being the only instances whereby nat­ur­al pro­cesses can main­tain a con­tinu­ity of sup­ply of key micro-hab­it­ats. Rothero high­lights the pos­sible sig­ni­fic­ance of smal­ler stands and way­side Aspens for bry­ophytes, and Cop­pins et al. (2001) have demon­strated the out­stand­ing import­ance of some small Aspen stands for lichens. Such examples should be tar­geted for sur­vey and conservation.

Giv­en that Aspen will suck­er so freely, it is obvi­ous that exclu­sion or oth­er con­trol of graz­ing ani- mals will be an import­ant tool to expand exist­ing stands. Com­plete exclu­sion of browsers may not be desir­able, as the main­ten­ance of suc­ces­sion­al hab­it­ats with asso­ci­ated pol­len and nec- tar sources may be of value to for­aging adult inver­teb­rates. Aspen stands occur in a wide vari- ety of con­texts and import­ant hab­it­ats may occur with­in the bounds of a pro­jec­ted Aspen expan- sion zone. Com­plete exclu­sion of graz­ing from such areas may be dam­aging to oth­er interests. Again, adequate sur­vey pri­or to for­mu­lat­ing man­age­ment plans is required.

Sev­er­al con­trib­ut­ors dis­cussed and high­lighted the grants and fin­an­cial assist­ance avail­able to land man­agers to pro­gress prac­tic­al action for Aspen and its depend­ent spe­cies. Spe­cif­ic exam- ples of the prac­tic­al work car­ried out to date are presen­ted, includ­ing the chal­lenges of recon- nec­t­ing isol­ated Aspen stands to facil­it­ate import­ant eco­lo­gic­al pro­cesses, such as spe­cies dis- persal or gene flow. As a num­ber of authors point out, we are only just begin­ning to identi­fy and under­stand the com­plex biod­iversity asso­ci­ated with Aspen in the UK, and clearly much is still wait­ing to be discovered.

Finally, Anne Elliott’s paper illus­trates that interest in Aspen is not just the domain of eco­lo­gists and spe­cial­ist research­ers. Aspen has strong cul­tur­al links for the people of the Scot­tish High­lands and their sup­port will be cru­cial if any action for Aspen is to be suc­cess­ful. We should not lose sight of the fact that Aspen wood­lands are a beau­ti­ful and strik­ing fea­ture of the High­land land­scape, and worthy of con­serving for that reas­on. Indeed it can be argued that Aspen helps improve the qual­ity of life for loc­al res­id­ents and helps make the High­land area spe- cial for vis­it­ors and tourists.

Aspen seems to have sur­vived as an ancient rem­nant up to now largely by default, rather than by design. These pro­ceed­ings provide com­pel­ling evid­ence of why this situ­ation should change and how Aspen con­ser­va­tion and man­age­ment should move up the UK con­ser­va­tion agenda in the future.

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The Biod­iversity and Man­age­ment of Aspen Woodlands

Ref­er­ences

Cop­pins, B., Street, S. and Street, L. 2001. Lichens of Aspen woods in Strath­spey. Report to Brit­ish Lichen Soci­ety and SNH.

Hall, P.C. 1980. Sus­sex Plant Atlas. An Atlas of the dis­tri­bu­tion of wild plants in Sus­sex. Booth Museum of Nat­ur­al History.

Per­ring, F.H. and Wal­ters, S.M. 1962. Atlas of the Brit­ish Flora. 2^nd. Edi­tion (1976). EP Publishing.

Philp, E.G. 1982. Atlas of the Kent Flora. Kent Field Club.

Ivimey-Cook, R.B. 198). Atlas of the Devon Flora. The Devon­shire Association.

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The Biod­iversity and Man­age­ment of Aspen Woodlands

The eco­logy and his­tory of Aspen woodlands

Peter Quelch Nat­ive Wood­land Adviser, Forestry Com­mis­sion, Whiteg­ates, Loch­gil­p­head, Argyll, PA31 8RS. Email: peter.​quelch@​forestry.​gov.​uk

Intro­duc­tion

This paper gives a quick over­view of Aspen, both as a tree spe­cies and as a rare wood­land type in Scot­land. The eco­logy of Aspen is well covered by Rick Wor­rell, along with oth­er selec­ted papers and book­lets. Much has been writ­ten about the folk­lore of Aspen (Elli­ott, this volume) and why it is such an enig­mat­ic and well loved tree.

This paper will exam­ine where Aspen occurs nat­ur­ally in today’s land­scape, and then to ask if we are sat­is­fied with the status quo. If we are not, what great­er part could Aspen play in Scotland’s woods and forests, and what actions should be con­sidered on its behalf? At present, Aspen is a well liked but ​‘Cinder­ella’ spe­cies, some­what neg­lected, and yet with an unreal­ised poten­tial. Recog­ni­tion of its val­ues for biod­iversity have emphas­ised Aspen’s import­ance, and this gives the con­text for this paper.

Aspen in the Biod­iversity Action Plan (BAP) process

Simple wood­land clas­si­fic­a­tions tend to label wood­land types by their dom­in­ant tree spe­cies, i.e. Oak­woods, Birch­woods, Pine­woods and so on. We can there­fore recog­nise ​‘Aspen woods’ where loc­ally Aspen pre­dom­in­ates in cer­tain stands of semi-nat­ur­al broadleaves in Badenoch and Strath­spey, along­side Birch, Row­an, Hazel, Sal­low and Alder.

The UK BAP pro­cess uses such a clas­si­fic­a­tion in select­ing the main nat­ive wood­land types and alloc­at­ing tar­gets for action (for an over­view of wood­land clas­si­fic­a­tions see Hall and Kirby, 1998). But what is the status of those nat­ive wood­land types which are not giv­en BAP plans?

• Birch­woods after many years of dis­cus­sion it has now been agreed that upland Birch­woods should have their own Hab­it­at Action Plan (HAP).

• Hazel is not covered sep­ar­ately in the BAP pro­cess, des­pite some lob­by­ing on behalf of the west­ern coastal hazel­woods, which are excep­tion­ally rich hab­it­ats for ocean­ic bry­ophytes and lichens. Cer­tain rare lichens char­ac­ter­ist­ic of this hab­it­at, (e.g. Arthothe­li­um macounii, or Pseudo­cyphel­laria norve­gica) then become sur­rog­ates in the BAP pro­cess for the hab­it­at they depend on, since they have been giv­en Spe­cies Action Plans (SAP).

• Juni­per — this nat­ive shrub spe­cies is covered by hav­ing its own SAP, but no HAP.

• Aspen is men­tioned in the SAPs for three inver­teb­rate spe­cies which depend on it as a hab­it­at, (Ham­mer­schmid­tia fer­ru­ginea, Byc­tiscus pop­uli and Epi­one par­al­lelaria), and two bry­ophytes (Ortho­trichi­um sp.), but Aspen has neither its own HAP or SAP. Aspen wood- lands are how­ever recog­nised as import­ant hab­it­ats in some Loc­al Biod­iversity Action Plans (LBAP), e.g. the Cairngorms LBAP.

Aspen in wood­land classifications

In the Nation­al Veget­a­tion Clas­si­fic­a­tion (NVC) (Rod­well 1991), Aspen is described as a compo- nent of upland Ash­wood (W9b), but even then only occur­ring rarely. Aspen is also men­tioned as an infre­quent com­pon­ent in sev­er­al low­land wood­land types: W5, W6, W8, W10, and W16.

Aspen wood­lands are not recog­nised as a dis­tinct wood­land type in either NVC, or in the Peter­ken Stand Type clas­si­fic­a­tion (Peter­ken 1993), where Aspen is asso­ci­ated with the Rowan/​Birch stands of Type 12A. Rack­ham (1986) recog­nises Aspen wood­lands as a sub­set of Peterken’s Birch/​Hazel woods, at least for East Eng­land. In their clas­sic sur­vey of native

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The Biod­iversity and Man­age­ment of Aspen Woodlands

pine­woods, Steven and Carl­isle (1959) record Aspen as rare or occa­sion­al in most of the pine­woods they sur­veyed, but nev­er abund­ant. Inter­est­ingly they record more than usu­al Aspen in Glen Strath­far­rar pine­woods, which appear to be one of the most nat­ur­al wood­land rem­nants in the coun­try today.

Aspects of Aspen ecology

Like Birch and oth­er suc­cess­ful col­on­isers, Aspen can tol­er­ate a wide range of soil types, from lime-rich sites to acid­ic heaths (for example, Aspen suck­ers are spread­ing onto acid­ic heath at Cran­nach pine­wood, Bridge of Orchy). Like Oak and Ash, Aspen actu­ally prefers good well drained min­er­al soils, a site type that it finds in great­er areas in Badenoch, Strath­spey and Deeside. While sites that it occu­pies are often moist, it is not a wet wood­land spe­cies in the same way as Alder or the Wil­lows, or even Bird cherry. Aspen grows at a wide range of alti­tudes, from sea level (coastal Aspen at Assynt and on Rum) to high alti­tude gul­lies almost to the tree-line.

Aspen his­tory

Aspen has an ancient his­tory in Scot­tish wood­lands, being a very early col­on­iser, arriv­ing with Birch, Sal­low and Row­an dur­ing the pre-Boreal peri­od 10,000 years ago, earli­er than Hazel, and before Scots pine began to dom­in­ate. All this happened well before Oak, Alder, Ash, Elm and Holly joined the flora. I see Aspen not so much as a rare and neg­lected wood­land type, but more as a tree spe­cies which is now under-rep­res­en­ted as a com­pon­ent of nat­ur­al wood­land types in Scot­land, des­pite its ancient lin­eage. I also find it sig­ni­fic­ant that Aspen is host to so many spe- cial­ist spe­cies, des­pite the fact that the tree itself is not now very com­mon or in extens­ive stands. To me this depend­ency indic­ates a very long eco­lo­gic­al asso­ci­ation, and this is backed up by the his­tory of Aspen in Scotland.

Aspen and ancient woodlands

Aspen seems to be strongly linked to ancient wood­land sites, both in Scot­land and in Eng­land where it is also a some­what rare com­pon­ent of usu­ally ancient wood­lands (Rack­ham 1986, 1990). Indeed, I would go fur­ther and sug­gest that Aspen in Scot­land is actu­ally an ancient wood­land indic­at­or spe­cies. Most examples that I find are linked to ancient wood­lands, large or small. For example, I recently came across Aspen in the Ryvoan Pass (Glen­more Forest) in a very mixed old-growth stand at high elev­a­tion, along­side vet­er­an Scots pine, Juni­per and Row­an, as well as very old grey Sal­low and Alder. Aspen has strong con­nec­tions, not only with ancient wood­land patches, but some­times to the tiny wood­land refu­gia of the most nat­ur­al origins.

Aspen in Europe

In Europe and Scand­inavia, where Aspen is more abund­ant, it is usu­ally as a com­pon­ent spe­cies of the north­ern sub-boreal tem­per­ate forest zone (Wor­rell 1996), rather than as a wood­land dom- inant on cer­tain soil types (com­pared to say, Oak or Beech). Its nat­ur­al place seems to be in the small group of broadleaved asso­ci­ates in north­ern con­i­fer­ous forests, along with Birch, Row­an, Sal­low, and Alder, where togeth­er they typ­ic­ally occupy about 15 – 20% of the forest, along­side the Pine and Spruce (Peter­ken 1996).

Reas­ons for cur­rent dis­tri­bu­tion of Aspen

Why has Aspen sur­vived where it is to be found today even some­times after all oth­er tree spe­cies have gone? The reas­ons for Aspen’s abil­ity to sur­vive, albeit in low num­bers, include:

• Aspen is actu­ally a poor col­on­iser (in mod­ern times at least), for while it can pro­duce viable seed this is a rare occurrence.

• Aspen trees are dioecious, so indi­vidu­al trees and even whole clones are either male or female. As indi­vidu­als become sep­ar­ated from the oppos­ite sex, it is not sur­pris­ing that Aspen does not repro­duce well in its cur­rently frag­men­ted con­di­tion. 9

The Biod­iversity and Man­age­ment of Aspen Woodlands

• Nev­er­the­less, Aspen is very good at self-per­petu­ation on a loc­al scale by pro­du­cing mass- es of suck­ers in response to felling, wind­throw, fire or oth­er dis­turb­ance. It seems that veg- etat­ive repro­duc­tion keeps Aspen going in the same loc­al­ity almost indefinitely.

• While graz­ing anim­als do eat the suck­ers (it is more pal­at­able than Alder, but less so than Ash and Elm), suf­fi­cient sur­vive to grow into new trees, unless graz­ing pres­sure is kept at very high levels.

• Aspen is not an inher­ently rare spe­cies like the vari­ous White­beams for example, partly because it has wide soil and alti­tude tolerance.

• Aspen has not tra­di­tion­ally been a valu­able spe­cies for its tim­ber, bark, or cop­pice shoots (unlike Oak and Hazel) and so has not been delib­er­ately pro­tec­ted or cultivated.

• Aspen has prob­ably been reduced in status partly through poor seed­ing abil­ity (com­pared to Birch and Sal­low), com­bined with sus­cept­ib­il­ity to graz­ing, but also an inab­il­ity to form vet­er­an trees (unlike Oak, Holly, Ash, Pine and Alder, which can all sur­vive as stems of many cen­tur­ies age). Long-lived trees have more time in which to set viable seed and pro- duce new gen­er­a­tions dur­ing lulls in graz­ing pres­sure. The reas­on why Aspen can­not live a long time and form a huge hol­low and ancient stem must surely be that the soft white wood is not dur­able against rot fungi (unlike Oak and Pine for example).

• If it were not for its suck­er­ing abil­ity, Aspen may well have been lost entirely from Scotland.

Are we happy with Aspen’s cur­rent distribution?

So, apart from the rel­at­ively small num­ber of Aspen dom­in­ated woods in Badenoch, Strath­spey and Deeside, Aspen is a sur­viv­or in small patches over most of Scot­land. It is found on the sea cliffs of the west coast, in ancient grazed pine­woods in the cent­ral High­lands, in remote refu­gia like the loch­side screes of Loch Muick, in the Bor­der cleugh wood­land rem­nants, and in the for- got­ten corners of many an ancient woodland.

Should Aspen be left alone to inhab­it these sparse niches — the remote and craggy wood­land refu­gia? Should Aspen con­tin­ue to be treated as a some­what enig­mat­ic tree rar­ity, a minor spe­cies, mainly of interest to wood­land his­tor­i­ans and romantics as a ghost of the once great nat­ur­al wood­lands? Or does Aspen have a wider role in Scot­tish woods and forests?

A pos­sible new scen­ario for Aspen?

Lets look again at the role Aspen plays in, for example, cent­ral Swedish forests, where Aspen forms a con­stitu­ent of the broadleaved com­pon­ent of the mixed pine/​spruce forests, along with Birch, Sal­low and Alder.

Why could we not encour­age both Birch and Aspen as a nor­mal com­pon­ent of Scot­tish upland forests, up to a pro­por­tion of say 25%, rather than the cur­rent five or 10% nor­mal max­im­um? The biod­iversity and land­scape bene­fits would be high, and Aspen tim­ber grown in forest con- ditions is (like oth­er Pop­lars) straight and util­is­able, though not of high value (less than Birch, sim- ilar to Alder?). Birch and Sal­low regen­er­ate pro­fusely, Alder read­ily cop­pices even in the face of mod­er­ate deer num­bers, while Aspen suck­ers after felling. So the spe­cies in this group can per- petu­ate them­selves at low cost, and all are rel­at­ively fast growing.

Con­clu­sion

I think that Aspen would be sold short if we con­tin­ued to con­fine it to wood­land refu­gia and regard it as a rar­ity. There is evid­ence that it was once a great com­pon­ent of Scot­tish nat­ur­al wood­lands, and there seems to be no good reas­on why, with help, it could not be so again. It is time for a ​‘Comeback Code’ for Aspen!

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The Biod­iversity and Man­age­ment of Aspen Woodlands

Actions needed to bring Aspen back into its right­ful place could include the following:

• Pro­tect­ing, regen­er­at­ing, and expand­ing where pos­sible, all exist­ing Aspen woods, stands and trees.

• Care­ful plant­ing of Aspen (of both sexes) into some degraded semi-nat­ur­al wood­lands where it is missing

• Plant­ing Aspen into forestry restock areas in suf­fi­cient num­bers, that Aspen becomes a self-per­petu­at­ing com­pon­ent of a group of mixed broadleaves which between them would cov­er 15 – 25% of the gross area of many upland and low­land con­ifer forests.

Ref­er­ences

Ennos R, Wor­rell R, Arkle P, Mal­colm D, 2000. Genet­ic vari­ation and con­ser­va­tion of Brit­ish nat­ive trees and shrubs, Tech­nic­al Paper 31, Forestry Com­mis­sion, Edinburgh.

Hall JE, Kirby KJ, 1998. The rela­tion­ship between Biod­iversity Action Plan Pri­or­ity and Broad Wood­land Hab­it­at Types, and oth­er wood­land clas­si­fic­a­tions, JNCC Report 288, Joint Nature Con­ser­va­tion Com­mit­tee, Peterborough.

Peter­ken G, 1993. Wood­land con­ser­va­tion and man­age­ment, Chap­man and Hall, London.

Peter­ken G, 1996. Nat­ur­al wood­land, Cam­bridge Uni­ver­sity Press, Cambridge.

Rack­ham O, 1986. The his­tory of the coun­tryside, Dent, London.

Rack­ham O, 1990. Trees and wood­land in the Brit­ish land­scape, Dent, London.

Ratcliffe P, 1999. Aspen wood­lands: a case for con­ser­va­tion, paper to the Nat­ive Wood­lands Advis­ory Pan­el for Scot­land, Forestry Com­mis­sion, Edinburgh.

Rod­well J, 1991. Brit­ish Plant Com­munit­ies, Vol I, Wood­lands and Scrub, Cam­bridge Uni­ver­sity Press, Cambridge.

Steven and Carl­isle, 1959. The nat­ive pine­woods of Scot­land, Uni­ver­sity of Aberdeen.

Trees for Life, 2001, Aspen inform­a­tion and papers, on www​.trees​forlife​.org​.uk

Wor­rell R, 1995. European Aspen (Pop­u­lus trem­ula L.): a review with par­tic­u­lar ref­er­ence to Scot­land, I Dis­tri­bu­tion, eco­logy and genet­ic vari­ation, Forestry 68(2), pp 93 – 105; II Val­ues, sil­vi­cul­ture and util­isa­tion, Forestry 68(3): 231 – 243

Wor­rell R, 1996. The Boreal Forests of Scot­land, Tech­nic­al Paper 14, Forestry Com­mis­sion, Edinburgh.

Wor­rell R, Gor­don AG, Lee RS, McIn­roy A, 1999. Flower­ing and seed pro­duc­tion of Aspen in Scot­land dur­ing a heavy seed year, Forestry 72(1): 27 – 34

11

The Biod­iversity and Man­age­ment of Aspen Woodlands

Fungi and Aspens: Pro­mot­ing Biod­iversity Aspen friends and foes

Ern­est and Valer­ie Emmett Drum­lins, New­ton­more Road, Kin­gussie, Inverness-shire, PH21 1HD. E‑mail: E‑[email protected]

It has been estim­ated that about 80% of all the organ­ic energy on the Earth is locked up in wood of vari­ous kinds. This enorm­ous store of energy is under con­stant attack, both when the trees are alive and more so when they are dead: from fungi, bac­teria, insects and smal­ler anim­als. (Ryvarden 2001).

Fore­most in the rela­tion­ships with trees are the fungi and these play sev­er­al dif­fer­ent roles, not all of them det­ri­ment­al to the health of the tree and some also provide food – for insects and oth­er inver­teb­rates, as well as mammals.

The fungi can be clas­si­fied under three main headings:

Cat­egory	Func­tion
Mycor­rhiz­al Endo- Ecto-	Import­ant for most (all?) plants Import­ant for most trees, e.g. Aspen
Sap­ro­phytes or Detrivores	Lit­ter decomposers
Pathogenic/​parasitic	Prin­cip­al causes of tree death

The Mycor­rhiz­al spe­cies are essen­tial for the healthy growth of the tree. These fungi are of two sorts: endo-mycor­rhiz­al and ecto-mycor­rhiz­al. The hyphae of the lat­ter sheath the tree’s roots and, by break­ing down mater­i­al in the forest soil, they provide the tree with nitroge- nous and oth­er nutri­ents, includ­ing min­er­al trace ele­ments. In exchange, the fungus receives car­bo­hydrates man­u­fac­tured by the tree dur­ing pho­to­syn­thes­is. Endo­my­cor­rhiz­al spe­cies are the most wide­spread, but their pres­ence is not revealed by the form­a­tion of fruit­bod­ies on the soil sur­face. These fungi enter the plant root cells form­ing spe­cial­ised inclu­sion bod­ies, where exchange of nutri­ents occurs.

With Aspens, the ecto­my­cor­rhiz­al fungi are more import­ant, and fairly spe­cif­ic asso­ci­ates in this cat­egory include famil­i­ar toad­stool shaped fungi such as Lec­cin­um aur­antiacum, Lec­cin­um durius­cu­lum and Lactari­us con­tro­versus. These are the friends of the Aspen, help­ing it to grow.

The second group of fungi are the Sap­ro­phytes and these include both host spe­cif­ic and cos- mopol­it­an spe­cies. They are the lit­ter decom­posers, redu­cing fallen leaves, twigs and oth­er already dead woody mater­i­al to humus, a prin­cip­al part of forest soils. These fungi include some that look like famil­i­ar toad­stools with lamel­lae (“gills”). Oth­ers are poroid fungi (the Poly­pores), releas­ing their spores from pores instead of lamellae.

Some oth­ers that help to decay the woody mater­i­al look rather like paint splashes and sheets of fungal tis­sue adher­ing to the sur­face but loose at the edges; and yet oth­ers form hard warty growths on twigs and branches. These are the Cor­ti­cioid fungi. They do not have lamel­lae or pores; instead, they form amorph­ous sheets of spore bear­ing tis­sue cov­er­ing the sur­face of logs and twigs.

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The Biod­iversity and Man­age­ment of Aspen Woodlands

Examples of det­ri­vores spe­cif­ic to Aspen are the Poly­pores: Ceri­poriopsis anaer­ina, Antro­dia malic­ola and mel­l­ita, and the Cor­ti­cioid: Penio­phora poly­go­nia. The two Antro­di­as men­tioned have not yet been found in Bri­tain, but it is hoped that they will be found in Scotland.

The cos­mo­pol­it­an spe­cies are legion; for example, many Mycena spe­cies. One that was found in an Aspen grove on The Roy­al Soci­ety for the Pro­tec­tion of Birds’ (RSPB) Insh Marshes Reserve last Novem­ber may be a new spe­cies for sci­ence requir­ing description.

The Poroid and Cor­ti­cioid fungi are among the dom­in­at­ing spe­cies in the decay of Aspens. In two Nor­we­gi­an stud­ies of the spe­cies occur­ring on cut and fallen logs, it was found that most of them were Poly­pores and Cor­ti­cioids (Table 1).

Table 1. Taxo­nom­ic diversity of wood decay­ing fungi on Aspen

Loc­al­ity	Num­ber of species
	Hetero- basi­dio- Poly­pores Cor­ti­cioids Agar­ics mycetes Oth­er Total
South Nor­way (Ander­sen 1995) 123 Logs	21 (14.2%) 64 (42.6%) 43 (29%) 16 (10.3%) 6 (3.9%) 155
South Nor­way (Her­mansen 1974 – 76)	31 (27.7%) 81 (72.3%) 112

Note that in one of these stud­ies, the Aspen logs yiel­ded 155 spe­cies of fungi, an indic­a­tion of the value of lying tim­ber for biodiversity.

The diversity of the fungal spe­cies increases as the wood decay pro­ceeds: in the early stages of decay rel­at­ively few fungi col­on­ise the wood, but as defens­ive sub­stances are removed by early col­on­isers, a suc­ces­sion of spe­cies become involved. By the last stage, when the trunk is los- ing its shape com­pletely, a great num­ber of spe­cies have inhab­ited the former tree, dur­ing its decay cycle.

Some of the rarer fungi fruit only sporad­ic­ally, with long gaps of many years between appear- ances of the sporo­carps, although they are pre­sum­ably present through­out in the veget­at­ive state. In sev­er­al long-term stud­ies, while some spe­cies fruited reg­u­larly, oth­ers were only record- ed once. It has also been found that some fungi can only invade decay­ing wood after a pion­eer spe­cies has over­come the wood’s armoury of defens­ive chem­ic­als and star­ted the par­tial decay. (Niemelä et al. 1995).

So far, nearly 100 spe­cies of fungi have been recor­ded on or with Aspen in Bri­tain (Table 2), by mem­bers of the Brit­ish Myco­lo­gic­al Soci­ety – mostly in Eng­land, reflect­ing where most mycolo- gists live or col­lect and where Aspen is not con­sidered a com­mon tree. The authors anti­cip­ate increas­ing the num­ber of spe­cies recor­ded from Aspen in the com­ing years.

The third group, the Patho­gen­ic fungi, are espe­cially inter­est­ing, and include sev­er­al spe­cies that are spe­cif­ic to Aspen. They are not friends of the Aspen but do great things for biod­iversity. They include the group known as Rusts, as well as lar­ger poroid fungi, the Poly­pores, often referred to as Brack­et fungi.

Aspen is the host for sev­er­al spe­cies of Rust (Melampsora spp.), which cause decay spots on the leaves and some will black­en and kill the grow­ing tips of new shoots. Heavy infest­a­tion can res­ult in defo­li­ation of the Aspen. These fungi thus reduce the growth rate of the tree and obvi- ously are det­ri­ment­al to the life cycle of insects that feed on the young leaves and grow­ing shoot

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The Biod­iversity and Man­age­ment of Aspen Woodlands

tips, such as the Dark-bordered beauty moth (Epi­one vespertaria).

A spec­tac­u­lar flower para­site is Taphrina johan­sonii, and this obvi­ously inter­feres with seed pro- duc­tion where it occurs. It is prob­ably of lim­ited sig­ni­fic­ance in Badenoch and Strath­spey, where flower­ing is rare – although in 2001 the trees were flower­ing and the Taphrina was found loc­ally in Strathspey.

Anoth­er small para­site is the Asco­my­cete, Encoelia fas­cicu­lar­is, which can be found erupt­ing like small brown­ish black cups from the bark of liv­ing trees and on fallen branches on the ground. This fungus causes car­bon­ising rots.

The wood decay­ing para­sites include a sig­ni­fic­ant Poly­pore, Phellinus trem­u­lae, which is respon- sible for the death of most Aspens. It is a ​“white rot” type fungus, decom­pos­ing both the lignin and the cel­lu­lose. The wood from decayed trees has little eco­nom­ic value. Sporo­carps can be found erupt­ing as wedge shaped brack­ets from the trunks of Aspens, or else as a coat­ing on the under­side of branches at the point where they emerge from the main trunk – the ​“branch creepers”.

This fungus, which is the most ser­i­ous patho­gen of Aspen, was pre­vi­ously not recor­ded from Bri­tain until last year, when it was found for the first time on the RSPB Insh Marshes Reserve (Emmett and Emmett 2001) – and so it is not even on the Red Data List for fungi. It was thought that Bri­tain did not have any Aspen trees large enough to sup­port it. In Fen­no­scan­dia, where Aspen is much more com­mon, it usu­ally occurs on large and old trees. In Badenoch, how­ever, it has been found on com­par­at­ively young trees – the dia­met­er at breast height of the smal­lest of the infec­ted trees meas­ured so far, is under 20cm and the largest is about 50cm.

Since the first record­ing of Phellinus on the Insh reserve, it has been found at many sites in the Badenoch and Strath­spey area: at three places in Kin­gussie, at Kin­craig, at Loch an Eilein on the Rothiemurchus estate, Gran­ish near Aviemore, at two sites near Grant­own on Spey and west- wards towards Lag­gan, and it has also been found on the RSPB Aber­nethy Forest reserve and across the Cairngorm mas­sif near to Bal­mor­al. It is likely to be found at oth­er Aspen sites and this has been con­firmed from oth­er areas; for example, recent records from Glen Affric (Wat­son-Feath­er­stone this volume).

The Aspens that grow on the poorer soils, for example on stony moraines, seem to pro­duce sporo­carps more read­ily than those that grow on the rich­er, damper sites closer to water bod- ies. These find­ings con­firm sim­il­ar ones made by myco­lo­gists in Fin­land and Norway.

The prob­lem in record­ing fungi is that most of them are eph­em­er­al and there may not be a friend- ly myco­lo­gist on hand when a fungus fruits! For­tu­nately, Phellinus trem­u­lae is per­en­ni­al, the fruit bod­ies are per­sist­ent and one can see the annu­al growth phases on the fruit bod­ies. They are not easy to spot in the early stages of their growth though, often look­ing like a thumb­nail on the trunk. The fungus is typ­ic­ally a para­site of liv­ing trees, but fruit bod­ies remain alive for a few years after the death of the host tree. It is said not to form new fruit bod­ies on dead trunks (Bal­aban and Kot­laba 1970). The cur­rent authors, how­ever, have observed fruit bod­ies that have appar- ently formed after trees have fallen.

Ento­mo­lo­gists hunt­ing rare saproxyl­ic insects in decay­ing Aspens, record a sweet smell in the soft decay mater­i­al that the lar­vae feed on. Cul­tures of the Phellinus are unusu­ally inter­est­ing in that they emit a sweet smell like Oil of Win­ter­green, due to the pres­ence of methyl ben­zoate, methyl sali­cyl­ate, ben­zyl alco­hol, lin­alool and ethyl ben­zoate (Collins and Halim 1972). It is likely that myceli­um of the Phellinus is present in the decom­pos­ing sap­wood which is home to the lar- vae of these inver­teb­rates, and con­trib­utes these com­pounds to the mix­ture of smells.

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The Biod­iversity and Man­age­ment of Aspen Woodlands

Ref­er­ences: Ballaban, K. and Kot­laba, F. 1970. Atlas drevok