Appendix 1 – Assessment of the potential for Eurasian beavers to naturally colonise the Cairngorms National Park

An assess­ment of the poten­tial for Euras­i­an beavers to nat­ur­ally col­on­ise the Cairngorms Nation­al Park

Risks and oppor­tun­it­ies asso­ci­ated with their presence

Pre­pared for Cairngorms Nation­al Park Feb­ru­ary 2022

Dr Róisín Camp­bell-Palmer¹, Prof Richard Bra­zi­er and Dr Alan Put­tock Cov­er photo: River Luineag in Cairngorms Nation­al park © Alan Put­tock ¹Lead Con­tact: Dr Róisín Camp­bell-Palmer Email: rcampbellpalmer@​gmail.​com

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Con­tents Over­view and Scope. ………………………………………………………………………………………………………………………………………….4 Status of Beavers in Scot­land.. ………………………………………………………………………………………………………………………….4 The Beaver and its Recovery…………………………………………………………………………………………………………………………….5 Review of Beaver Envir­on­ment­al and Socio-Eco­nom­ic Impacts.. ………………………………………………………………………6 Desktop Ana­lys­is of Beaver Hab­it­at and Dam Capa­city in Cairngorms Nation­al Park.. ……………………………………8 Sum­mary. ……………………………………………………………………………………………………………………………………………………….8 Mod­el­ling of beaver hab­it­at suitability…………………………………………………………………………………………………………….9 Beaver Hab­it­at Suit­ab­il­ity Mod­el­ling. ……………………………………………………………………………………………………………..9 Beaver Veget­a­tion Index (BVI –pre­requis­ite for BHI mod­el­ling) ………………………………………………………………………9 2.3. Beaver Hab­it­at Index mod­el (BHI) …………………………………………………………………………………………………………….10 Beaver Hab­it­at Index maps and sum­mary stat­ist­ics for study area. ……………………………………………………………….11 Beaver Dam Capa­city mod­el­ling. …………………………………………………………………………………………………………………….14 Beaver Dam Capa­city (BDC) mod­el sum­mary. ………………………………………………………………………………………………..14 Beaver Dam Capa­city Mod­el maps for the study area. ……………………………………………………………………………………16 Beaver hab­it­at and dam capa­city mod­el con­clu­sions and next steps. ……………………………………………………………19 Sum­mary of Field Based Assess­ment.. ………………………………………………………………………………………………………….20 Desk and Field Based Assess­ment of the Abil­ity of Beavers to Nat­ur­ally Spread from Exist­ing Areas. ……..20 Sum­mary of 2021 beaver activ­ity in Tay­side and Forth catch­ments.. …………………………………………………………….20 Main poten­tial access routes into Cairngorms con­sidered. ………………………………………………………………………..22

1. Via head­wa­ters of River Spey. ……………………………………………………………………………………………………………………22
2. Via Loch Lag­gan…. …………………………………………………………………………………………………………………………………….24
3. Via Loch Ericht, Loch Ran­noch and Loch Tummel……………………………………………………………………………………….25
4. River Tilt. ……………………………………………………………………………………………………………………………………………………28
5. River Isla and Neigh­bour­ing Channels/​Burns.. ………………………………………………………………………………………….29 Desk and Field Assess­ment of Beaver Suit­ab­il­ity of Sites with­in Cairngorms Nation­al Park.. ……………………….30 River Spey. ……………………………………………………………………………………………………………………………………………………30 Main River Spey. …………………………………………………………………………………………………………………………………………….30 RSPB Insh Marshes.. ………………………………………………………………………………………………………………………………………31 River Luineag to Above Loch Mor­lich.. …………………………………………………………………………………………………………..32 Loch Garten. …………………………………………………………………………………………………………………………………………………..34 River Avon.. ……………………………………………………………………………………………………………………………………………………34 River Don…. …………………………………………………………………………………………………………………………………………………..35 River Dee… ……………………………………………………………………………………………………………………………………………………37 Loch Kinord. ………………………………………………………………………………………………………………………………………………….40 Man­age­ment and Mit­ig­a­tion Oppor­tun­it­ies. ……………………………………………………………………………………………….42

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Sum­mary of Risks and Oppor­tun­it­ies with­in Cairngorms Nation­al Park. ………………………………………………………45 Desk and Field Assess­ment of poten­tial con­flict with agri­cul­tur­al land and fish­ing beats with­in Cairngorms Nation­al Park. ……………………………………………………………………………………………………………………………46 Recom­mend­a­tions for ​‘pre­par­a­tion for arrival’…………………………………………………………………………………………….51 Con­clu­sion. …………………………………………………………………………………………………………………………………………………….51 Ref­er­ences. …………………………………………………………………………………………………………………………………………………….52 Appen­dices.. …………………………………………………………………………………………………………………………………………………….57 Appendix 1: Review of Impacts of beaver return (Adap­ted from Bra­zi­er et al., 2021).. ………………………………….57

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Over­view and Scope The scope of this pro­ject was designed in col­lab­or­a­tion with Cairngorms Nation­al Park (CNP) to assess the poten­tial for Euras­i­an beavers (Castor fiber) to recol­on­ise the CNP from exist­ing pop­u­la­tions, in the catch­ments of the River Tay and Forth. This doc­u­ment also reviews the pre­dict­able impacts this spe­cies is likely to have on the land­scape, eco­logy and land use prac­tices with­in the CNP. It is based on extens­ive field exper­i­ence of beavers in Scot­land gained by Dr Roisin Camp­bell-Palmer, includ­ing inform­a­tion gained from the most recent sur­vey of beaver ter­rit­or­ies with­in Tay­side. This inform­a­tion has been com­bined with mod­el­ling sys­tems developed by the Uni­ver­sity of Exeter to define both hab­it­at suit­ab­il­ity and beaver dam capacity.

This assess­ment invest­ig­ates how beaver activ­ity could enhance and com­ple­ment exist­ing hab­it­at, land use, eco­lo­gic­al, socio-eco­nom­ic and spe­cies-spe­cif­ic man­age­ment con­sid­er­a­tions. It assesses the poten­tial routes of nat­ur­al col­on­isa­tion and makes recom­mend­a­tions regard­ing the for­ward plan­ning require­ments for beavers.

Status of Beavers in Scot­land Bri­tain rep­res­ents the very west­ern extent of the Euras­i­an beaver range. Archae­olo­gic­al evid­ence of their former pres­ence such as gnawed tim­ber and bones in com­bin­a­tions with trade records, illus­tra­tions and oth­er his­tor­ic ref­er­ences, test­i­fies to their former wide­spread occur­rence through­out Bri­tain (Coles, 2006; Man­ning et al., 2014). By the 15^th cen­tury, the trade in Scot­tish beaver furs was no longer eco­nom­ic­ally viable due to over-exploit­a­tion. While oral tra­di­tion recalls their pres­ence in and around Lochaber until the late 1700’s, there is no fur­ther men­tion of their pres­ence after this time (Coles, 2006). The Euras­i­an beaver is there­fore believed to have become gen­er­ally extinct in Scot­land, by the 16^th cen­tury (Kit­chen­er & Con­roy, 1997).

The case for rein­tro­du­cing the Euras­i­an beaver to Scot­land has been debated for over 20 years. Beavers and beaver rein­tro­duc­tion issues are sum­mar­ised in the Scot­tish Nat­ur­al Her­it­age (SNH) ​‘Beavers in Scot­land’ report (Gay­wood, 2015). In May 2009 five Nor­we­gi­an beaver fam­il­ies were released into the Knap­dale Forest of Argyll, as part of the offi­cially sanc­tioned Scot­tish Beaver Tri­al (SBT). Although this offi­cial beaver tri­al con­cluded in 2014 by then beavers res­ult­ing from fur­ther unau­thor­ised releases or escapes in the east of Scot­land had extens­ively col­on­ised the River Tay. In 2016, the Scot­tish Gov­ern­ment stated that they were minded to allow both pop­u­la­tions to remain. In 2019, European Pro­tec­ted Spe­cies (EPS) was accor­ded to beaver pop­u­la­tions in Knap­dale, Argyll and the Tay­side and Forth catch­ments which exten­ded to any pop­u­la­tions nat­ur­ally col­on­ising oth­er areas from these core zones. The Scot­tish Gov­ern­ment made it clear at that time that no fur­ther unau­thor­ised releases would be tol­er­ated or per­mit­ted and a NatureScot Beaver Mit­ig­a­tion Scheme was estab­lished to provide prac­tic­al advice and sup­port to landown­ers and interest groups. A man­age­ment frame­work has been developed in which a range of beaver mit­ig­a­tion tools and inter­ven­tions can be pro­vi­sioned includ­ing tree pro­tec­tion and dam man­age­ment. Under spe­cif­ic cri­ter­ia landown­ers may apply for a licence for leth­al con­trol. In the first year of pro­tec­tion, 39 leth­al con­trol licences were issued and a repor­ted 87 beavers were culled as a res­ult. A cull of a fur­ther 115 was recor­ded in the second year of this schemes oper­a­tion (NatureScot 2020, 2021). While gov­ern­ment policy cur­rently allows the trans­lo­ca­tion of beavers in Scot­land with­in their cur­rent range the only recent applic­a­tions to do so occurred as part of the pop­u­la­tion aug­ment­a­tion exer­cise for the Knap­dale pop­u­la­tion and more recently to move a fam­ily into a series of pool sys­tems at the Argaty Red Kite Centre, near Doune. This last pro­ject rep­res­ents the 4

first suc­cess­fully per­mit­ted trans­lo­ca­tion of beavers with­in a catch­ment where the spe­cies is oth­er­wise free-liv­ing. Oth­er unau­thor­ised releases of beavers have also res­ul­ted in the estab­lish­ment of pop­u­la­tions in oth­er parts of Scot­land, Eng­land and Wales. While this wider res­tor­a­tion has gen­er­ated much excite­ment in the nature con­ser­va­tion com­munity (Bra­zi­er et al., 2020; Law et al., 2016, 2017; Stringer & Gay­wood, 2016) cer­tain land interest groups have expressed strong con­cerns regard­ing the spe­cies abil­ity to modi­fy land­scapes in a man­ner unfa­vour­able to their interests. NatueScot are host­ing a work­shop to devel­op the Nation­al Beaver Strategy which may be in place and help steer decision mak­ing later this year.

The SBT, Tay­side Beaver Study Group, Beaver-Sal­monid Work­ing Groups have all pub­lished their find­ings, and along with ongo­ing data col­lec­tion, landown­er and interest group engage­ment through the Scot­tish Beaver For­um and the NatureScot Beaver Mit­ig­a­tion Scheme sig­ni­fic­ant data and exper­i­ence informed the decision-mak­ing pro­cess regard­ing beaver pres­ence and man­age­ment in Scot­land. In 2019, the Scot­tish Gov­ern­ment gave European Pro­tec­ted Spe­cies (EPS) to beaver pop­u­la­tions in Knap­dale, Argyll and the Tay­side and Forth catch­ments (referred to as Tay­side beavers in this report) which exten­ded to anim­als nat­ur­ally col­on­ising from these zones, but that fur­ther unau­thor­ised releases would be an offence and not per­mit­ted at present. The NatureScot Beaver Mit­ig­a­tion Scheme was estab­lished to provide mit­ig­a­tion advice and sup­port to vari­ous landown­ers and interest groups. A man­age­ment frame­work has been developed in which a range of beaver mit­ig­a­tion tools and inter­ven­tions can be pro­vi­sioned includ­ing tree pro­tec­tion and dam man­age­ment. Under spe­cif­ic cri­ter­ia landown­ers may apply for a licence for leth­al con­trol. In the first year of pro­tec­tion, 39 leth­al con­trol licences were issued and a repor­ted 87 anim­als dis­patched, and a fur­ther 115 in the second year (NatureScot 2020, 2021). Note that gov­ern­ment policy cur­rently allows the trans­lo­ca­tion of beavers in Scot­land with­in their cur­rent range, this has only occurred as part of the pop­u­la­tion aug­ment­a­tion of Knap­dale beaver pop­u­la­tion and most recently a fam­ily to the Argaty Red Kite Centre, near Doune. This rep­res­en­ted the first suc­cess­fully applied and per­mit­ted with­in catch­ment trans­lo­ca­tion of beavers in Scot­land. Beavers col­on­ising the Tay­side and Forth catch­ments form the largest pop­u­la­tion cur­rently in Bri­tain, with oth­er wild breed­ing pop­u­la­tions ori­gin­at­ing from unau­thor­ised releases exist­ing in Kent, Devon and Avon areas. DEFRA/ NE have recently held a con­sulta­tion pro­cess to devel­op future beaver strategies in Eng­land. An announce­ment on the future leg­al status of beavers in Eng­land is expec­ted this year.

As the bulk of the beaver pop­u­la­tion which now inhab­its Bri­tain developed from unau­thor­ised sources its pre­cise ini­tial com­pos­i­tion (e.g. num­bers and sex ratios) is unknown. This paucity of inform­a­tion also applies to a broad range of oth­er issues impact­ing its status such sur­viv­al data and the impact of ran­dom cull­ing. In Scot­land the SBT, Tay­side Beaver Study Group and Beaver-Sal­monid Work­ing Group have all pub­lished their find­ings. These stud­ies in com­bin­a­tion with ongo­ing research pro­jects, stake­hold­er involve­ment and wider engage­ment through the Scot­tish Beaver For­um and the NatureScot Beaver Mit­ig­a­tion Scheme are all assist­ing the decision-mak­ing pro­cess regard­ing beavers in Scotland.

The Beaver and its Recov­ery Mod­ern beavers exist only in the north­ern hemi­sphere and are rep­res­en­ted by two extant spe­cies; the Euras­i­an C. fiber and the North American/​Cana­dian C. canaden­sis. Though highly sim­il­ar in appear­ance, beha­viour, eco­logy and bio­logy, they diverged from a com­mon ancest­or ~7.5 mil­lion years ago and pos­sess dif­fer­ent chro­mo­some num­bers and can­not hybrid­ise (Horn et al., 2014). Both are large, semi- aquat­ic highly ter­rit­ori­al rodents which live in fam­ily units, and exhib­it spe­cial­ised beha­viours such as 5

tree felling and dam­ming. They are a highly adapt­able spe­cies and can modi­fy many types of nat­ur­al, cul­tiv­ated and urb­an hab­it­ats to suit their needs (Camp­bell-Palmer et al., 2016; Pachinger & Hulik, 1999).

Over­hunt­ing for its castoreum glands, fur and meat in his­tor­ic times meant that Euras­i­an beaver by the end of the 19^th cen­tury was on the verge of extinc­tion with an estim­ated ~1,200 indi­vidu­als remain­ing in a scat­ter­ing of isol­ated pop­u­la­tions (Nolet & Rosell, 1998). While the spe­cies has recovered its exist­ence in part through­out much of its former range due to hunt­ing reg­u­la­tion, pro­tect­ive legis­la­tion, nat­ur­al expan­sion and pro­act­ive trans­lo­ca­tions and is now believed to num­ber in excess of 1.5 mil­lion, a frac­tion of its former status (Hal­ley et al., 2020). The first known beaver trans­lo­ca­tions, from Nor­way to Sweden, occurred in 1922, and since then, there have been more than 205 recor­ded trans­lo­ca­tions which have restored beavers to 25 nations where they were formerly extinct (Hal­ley et al., 2012). Over­time this pro­cess incor­por­ated a mix of offi­cial and more unortho­dox returns such as that under­taken in Bel­gi­um (Ver­beylen, 2003). Large viable pop­u­la­tions of North Amer­ic­an beavers are also now well estab­lished on a Euras­i­an scale as a his­tor­ic lack of ini­tial know­ledge that the two spe­cies were not the same. In more recent times fur­ther escapes of this form from zoos or game parks have also occurred. Though both spe­cies func­tion the same eco­lo­gic­ally, as a non-nat­ive remov­al and ster­il­isa­tion pro­grammes exist par­tic­u­larly in Fin­land and parts of Ger­many, they are thought to have been suc­cess­fully removed from parts of France and Lux­en­berg (Hal­ley et al., 2020).

Review of Beaver Envir­on­ment­al and Socio-Eco­nom­ic Impacts Beavers have the abil­ity to modi­fy eco­sys­tems pro­foundly to meet their eco­lo­gic­al needs, with sig­ni­fic­ant asso­ci­ated hydro­lo­gic­al, geo­mor­pho­lo­gic­al, eco­lo­gic­al and soci­et­al impacts. While this report prin­cip­ally reviews cur­rent state-of-the-art sci­entif­ic under­stand­ing of the beavers role as a quint­es­sen­tial eco­sys­tem engin­eer from a European per­spect­ive it also incor­por­ates North Amer­ic­an research.

Appendix 1 adapts and updates a recent com­pre­hens­ive and peer reviewed lit­er­at­ure review (Bra­zi­er et al., 2021) which sum­mar­ises how beaver impact: • Eco­sys­tem struc­ture and geo­mor­pho­logy • Hydro­logy and water resources • Water qual­ity • Fresh­wa­ter eco­logy • Humans and society

It con­cludes by examin­ing future con­sid­er­a­tions that may need to be resolved as beavers fur­ther expand in the north­ern hemi­sphere with an emphas­is upon the eco­sys­tem ser­vices that they can provide and the asso­ci­ated man­age­ment that will be neces­sary to max­im­ise the bene­fits and min­im­ise the con­flicts arising from their beha­vi­our­al activities.

In addi­tion to the inform­a­tion presen­ted in the appendix, since its pub­lic­a­tion addi­tion­al beaver and fish inter­ac­tion­al work has been pub­lished. Glob­ally, fresh­wa­ters are the most degraded and threatened of all eco­sys­tems. In north­ern tem­per­ate regions, beaver (Castor spp.) rein­tro­duc­tions are increas­ingly being used as a low-cost and self-sus­tain­ing means to restore river cor­ridors. River modi­fic­a­tion by beavers has been well doc­u­mented to increase avail­ab­il­ity of suit­able hab­it­at for fish, 6

includ­ing sal­monids. The key bene­fits of beaver activ­ity for sal­monids that are com­monly cited include increased hab­it­at het­ero­gen­eity and qual­ity. Ponds cre­ated upstream of beaver dams provide juven­ile over­win­ter­ing and rear­ing hab­it­at and can be a crit­ic­al refuge for lar­ger fish. The bene­fi­cial response from a fish­er­ies per­spect­ive is usu­ally quan­ti­fied in terms of increased fish abund­ance, con­di­tion and growth, and over­all pro­ductiv­ity. Con­versely, the prin­cip­al neg­at­ive con­sequence of beaver activ­ity often cited is the poten­tial for dams to impede or delay sal­monid migra­tion, par­tic­u­larly for upstream mov­ing adults dur­ing their migra­tion to the spawn­ing grounds.

The modi­fic­a­tion of flu­vi­al hab­it­ats due to beaver activ­ity may influ­ence the avail­ab­il­ity of suit­able hab­it­at for fish, includ­ing Atlantic sal­mon (Salmo salar) and brown trout (Salmo trutta), which in Scot­land are spe­cies of high eco­nom­ic value. Increases in the size and geo­graph­ic­al extent of Scot­tish beaver pop­u­la­tions as a res­ult of suc­cess­ful recruit­ment, fur­ther rein­tro­duc­tions, escapes, and illeg­al releases has caused con­cern in rela­tion to their poten­tial impact on sal­monid fish­er­ies. A recent study by Need­ham et al., (2021) invest­ig­ated the response of young brown trout to hab­it­at modi­fic­a­tion by beavers. By modi­fy­ing flu­vi­al hab­it­at, beavers had pro­found effects on a loc­al brown trout pop­u­la­tion through the cre­ation of impoun­ded reaches that pro­moted a high­er abund­ance of lar­ger size classes. Inver­teb­rate abund­ance was high­er in the mod­i­fied stream and com­munity com­pos­i­tion differed between the mod­i­fied and con­trol streams. This study provides import­ant insight into the pos­sible future effect of beavers on Brit­ish fresh­wa­ter eco­sys­tems. Beaver: Nature’s Eco­sys­tem Engin­eers Geo­morph­ic Impacts • Beaver dam­ming lim­ited to small streams • Drives trans­ition in sed­i­ment dynam­ics from erosion­al net depos­ition­al • Changes in chan­nel plan­form, lon­git­ud­in­al pro­files, slope, increased sinu­os­ity. Water Qual­ity Impacts • Sus­pen­ded sed­i­ment and nutri­ents are depos­ited • Ponds become large sed­i­ment and nutri­ent stores. • Increased water avail­ab­il­ity, raised water tables and increased inter­ac­tion with aquat­ic and ripari­an veget­a­tion all shown to impact upon biogeo­chem­ic­al cyc­ling and nutri­ent fluxes. Hydro­lo­gic­al Impacts • Can reduce lon­git­ud­in­al (down­stream) con­nectiv­ity, whilst sim­ul­tan­eously increas­ing lat­er­al flood­plain con­nectiv­ity. • Increased sur­face water stor­age and elev­ated water table. • beaver dam sequences and wet­lands can atten­u­ate flow dur­ing high and low flow peri­ods. Aquat­ic Eco­logy Impacts • Extend­ing wet­lands aids aquat­ic plant recruit­ment, abund­ance and diversity. • Nutri­ent rich beaver mead­ows sup­port diverse plant life. • Mul­ti­tude of bene­fits for fish, inver­teb­rates and amphi­bi­ans. • Sal­monid spe­cies can nav­ig­ate beaver dams. • Upstream fish move­ment may be reduced in low gradi­ent, low energy sys­tems. Human-Beaver Impacts • Real oppor­tun­it­ies for humans provided by beavers, as well as real poten­tial con­flicts • oppor­tun­it­ies may be obtained by dif­fer­ent people to those who incur the costs in cer­tain con­texts. • Effect­ive man­age­ment strategies should con­sider bene­fi­ciar­ies and cost-bear­ers in a hol­ist­ic man­ner, bridging the dis­tinc­tions with­in a closed loop man­age­ment sys­tem. • Man­age­ment strategies require clear com­mu­nic­a­tion. Fig­ure 1. A visu­al sum­mary of beavers impacts as eco­sys­tem engin­eers. 7

Desktop Ana­lys­is of Beaver Hab­it­at and Dam Capa­city in Cairngorms Nation­al Park Desktop ana­lys­is pre­pared by Dr Alan Put­tock to provide under­stand­ing of beaver hab­it­at and dam capa­city pri­or to field visits.

Sum­mary The hab­it­at suit­ab­il­ity and the capa­city for beavers to dam chan­nels with­in the study areas was assessed using beaver mod­el­ling tools developed by research­ers at the Uni­ver­sity of Exeter (Gra­ham et al., 2020). These mod­el­ling tools con­sist of a Beaver Hab­it­at Index (BHI) mod­el and a Beaver Dam capa­city (BDC) model.

There is a require­ment to com­plete an ana­lys­is of rivers catch­ments to assess their suit­ab­il­ity for sup­port­ing pop­u­la­tions of beaver. Beaver hab­it­at suit­ab­il­ity is determ­ined primar­ily by veget­a­tion suit­ab­il­ity which has been clas­si­fied nation­ally using a Beaver Veget­a­tion Index (BVI) as well as access to water bod­ies. Togeth­er these two factors have been incor­por­ated into a Beaver hab­it­at Index mod­el (BHI). BHI has been run nation­ally to devel­op a high res­ol­u­tion (5m) con­tinu­ous ras­ter product that can inform loc­al decision mak­ing with regard to beaver rein­tro­duc­tion. BHI clas­si­fies hab­it­at suit­ab­il­ity from 0 (No access to veget­a­tion — not suit­able) to 5 (Highly Suitable)

Beavers are also well known as eco­sys­tem engin­eers, hav­ing the capa­city to change envir­on­ments to suit their needs. The beaver engin­eer­ing activ­ity that has the greatest capa­city to modi­fy eco­sys­tems is dam build­ing. Dam build­ing and the cre­ation of pon­ded sur­face water has the abil­ity to bring bene­fits (i.e. for biod­iversity, water stor­age, flow atten­u­ation) but also poten­tially man­age­ment and con­flict (i.e. loc­al­ised inund­a­tion of land, block­ing of crit­ic­al infra­struc­ture). BDC clas­si­fies reaches from no capa­city for dam build­ing to a per­vas­ive capa­city for dam­ming. Cairngorms Nation­al Park A 0 10 20 km Fig­ure 2. Cairngorms Nation­al Park bound­ary. Basemap data ©Map­Tiler Open­Street­Map Con­trib­ut­ors Google. Beaver Net­work Gra­ham et al., 2021 and con­tains fea­tures based on digit­al spa­tial data from the Centre for Eco­logy and Hydro­logy NERC (CEH). Con­tains OS data Crown copy­right [and data­base right] 8

NAME Cairngorms Catch­ment Dee Don Oth­er Spey Tay Miss­ing Fig­ure 3. Main river sys­tems in Cairngorms Nation­al Park Mod­el­ling of beaver hab­it­at suit­ab­il­ity Beaver Hab­it­at Suit­ab­il­ity Mod­el­ling Sum­mary Descrip­tion: Pro­duc­tion of a con­tinu­ous descrip­tion of hab­it­at suit­ab­il­ity for beaver. First a veget­a­tion suit­ab­il­ity index is cre­ated using mul­tiple high-res­ol­u­tion spa­tial data­sets from Ord­nance Sur­vey, CEH and Coper­ni­cus will be com­bined to provide detailed land cover/​vegetation inform­a­tion which is clas­si­fied based on empir­ic­al field obser­va­tion of beaver hab­it­at and pref­er­ence. Veget­a­tion suit­ab­il­ity is com­bined with addi­tion­al para­met­ers describ­ing stream net­works and water bod­ies. Whilst beaver hab­it­at suit­ab­il­ity is primar­ily defined by veget­a­tion suit­ab­il­ity, beavers also require water for secur­ity and move­ment. There­fore, access­ib­il­ity to water bod­ies (i.e. chan­nels, ponds, and lakes) will also determ­ine the viab­il­ity of beaver occu­pancy and there­fore are required to clas­si­fy hab­it­at accurately.

Out­puts: This product provides a high-res­ol­u­tion (5m cell size) resource (ras­ter Tiff format) for describ­ing hab­it­at suit­ab­il­ity for beaver. This data­set can allow the user to explore which land­scapes were most (or least) suite to beaver rein­tro­duc­tion and also to under­stand where hab­it­at enhance­ment might be use­ful to sup­port future reintroduction.

Beaver Veget­a­tion Index (BVI –pre­requis­ite for BHI mod­el­ling) Veget­a­tion is import­ant for clas­si­fy­ing beaver hab­it­at (Hart­man, 1996; John et al., 2010; Pinto et al., 2009; St-Pierre et al., 2017). It was there­fore crit­ic­al to estab­lish a reli­able Beaver Veget­a­tion Index (BVI) using nation­ally-avail­able spa­tial data­sets. No single data­set con­tained the detail required to depict all key veget­a­tion types. There­fore, a com­pos­ite data­set was cre­ated from: OS Vec­torMap data (Ord­nance Sur­vey, 2018), The Centre for Eco­logy and Hydro­logy (CEH) 2015 land cov­er map (LCM) (Row­land et al., 2017), Coper­ni­cus 2015 20 m tree cov­er dens­ity (TCD) (Coper­ni­cus, 2017) and the CEH woody lin­ear fea­tures frame­work (Schol­e­field et al., 2016).

Veget­a­tion data­sets were assigned suit­ab­il­ity val­ues (zero to five). Zero val­ues were assigned to areas of no veget­a­tion i.e. build­ings and val­ues of five were assigned to favour­able hab­it­at i.e. decidu­ous 9

wood­land. Val­ues were assigned based on a review of rel­ev­ant lit­er­at­ure (Haarberg & Rosell, 2006; Jen­kins, 1979; Nolet et al., 1994; O’Connell et al., 2008), field obser­va­tion and com­par­is­on with satel­lite imagery. Vec­tor data were con­ver­ted to ras­ter format (res­ol­u­tion of 5 m). TCD data were res­ampled to 5m and aligned with con­ver­ted vec­tor lay­ers. An infer­ence sys­tem was used to com­bine these four ras­ter data­sets to cre­ate the BVI. The work­flow pri­or­it­ises the reli­ab­il­ity fol­lowed by the highest value data.

Examples of highly suit­able land (graded 5) include broad-leaf wood­land, mixed wood­land and shrub; examples of suit­able veget­a­tion (graded 4) include shrub and marsh; examples of mod­er­ately suit­able (graded 3) include con­i­fer­ous wood­land, marsh, shrub and unim­proved grass­land; examples of barely suit­able (graded 2) include reeds, shrub and heath­land and boulders, neut­ral grass­land; examples of unsuit­able (graded 1) include heath­er, acid grass­land, unim­proved grass and boulders, bog; examples of no access­ible veget­a­tion (graded 0) include shingle and sand, build­ings, rock, urb­an, fresh­wa­ter and saltwater.

2.3. Beaver Hab­it­at Index mod­el (BHI) Whilst veget­a­tion is a dom­in­ant factor in determ­in­ing hab­it­at suit­ab­il­ity for beaver, so is prox­im­ity to a water body (Gurnell et al., 2008), with beavers being strong swim­mers, using water bod­ies both to provide secur­ity, as a means of escap­ing pred­at­ors and to access for­aging areas. It is thought that most for­aging occurs 10 m of a watercourse/​body (Haarberg & Rosell, 2006), and rarely above 50 m (Stringer et al., 2018). How­ever, great­er for­aging dis­tances have on occa­sion been observed and as in Mac­far­lane et al., 2015 it has been accep­ted as a max­im­um dis­tance in which the vast major­ity of for­aging occurs. There­fore, to determ­ine suit­able hab­it­at for beaver incor­por­at­ing both BVI veget­a­tion suit­ab­il­ity and water access­ib­il­ity a 100m buf­fer was applied to water bod­ies. To do this the OS mas­termap river net­work and OS vec­tor in land water bod­ies were com­bined to get the best read­ily avail­able nation­al water­body and water course coverage.

Whilst BVI was run nation­ally on a 5m scale it is best viewed as a pre­par­at­ory step for BHI (and later BDC) mod­el­ling and is super­seded in use­ful­ness by the BHI data­set. It is strongly recom­men­ded that most ana­lys­is and man­age­ment applic­a­tions use BHI i.e. if there is an area of pre­ferred veget­a­tion such as wil­low wood­land, more than 100m from a water­body it is thought inac­cess­ible to beaver and there­fore does not form suit­able habitat.

Both BVI and BHI use a scor­ing sys­tem of zero to five (Table 1). Scores of five rep­res­ent veget­a­tion that is highly suit­able or pre­ferred by beavers and that also lies with­in 100 m of a water­body. Zero scores are giv­en to areas that con­tain no veget­a­tion or are great­er than 100 m from a water­body. It is import­ant to note that the hab­it­at mod­el con­siders ter­restri­al hab­it­at where for­aging primar­ily occurs and that water­courses them­selves are also scored zero. It is also import­ant to note that all scores above 1 con­tain suit­able veget­a­tion. 10

Table 1. BVI and BHI value defin­i­tions. It is crit­ic­al to note that all val­ues above 1 are suit­able for beaver. BVI and BHI Val­ues 0 1 2 3 4 5 Defin­i­tion Not suit­able (no access­ible veget­a­tion) Not suit­able (unsuit­able veget­a­tion) Barely Suit­able Mod­er­ately Suit­able Suit­able Highly Suit­able Beaver Hab­it­at Index maps and sum­mary stat­ist­ics for study area Caimgorms_​NP_​BHI Band 1: lyr.1 (Gray)

1. Likely Unsuit­able
2. Barely Suit­able
3. Mod­er­ately Suitable
4. Suit­able
5. Highly Suit­able Cairngorms Nation­al Park 0 20 km Basemap data ©Map­Tiler Open­Street­Map Con­trib­ut­ors Google. Beaver Net­work Gra­ham et al., 2021 and con­tains fea­tures based on digit­al spa­tial data from the Centre for Eco­logy and Hydro­logy NERC (CEH). Con­tains OS data Crown copy­right [and data­base right] Fig­ure 4. Beaver Hab­it­at Index at a 5m res­ol­u­tion across entire Nation­al Park. Con­tains Ord­nance Sur­vey data Crown Copy­right 2007 and some fea­tures of this map are based on digit­al spa­tial data licensed from the Centre for Eco­logy & Hydro­logy, NERC (CEH). Aer­i­al imagery: Open-Source Google imagery © Open­Street­map (and) con­trib­ut­ors CC-BY-SA. 11

Cairngorms_​NP_​BHI Band 1: lyr.1 (Gray)

1. Likely Unsuit­able
2. Barely Suit­able
3. Mod­er­ately Suitable
4. Suit­able
5. Highly Suit­able Cairngorms Nation­al Park Catchments_​Boundaries & Hydro­logy, © NERC (CEH). Aer­i­al imagery: Open-Source Google imagery © Open­Street­map (and) con­trib­ut­ors CC-BY-SA. Crown Copy­right 2007 and some fea­tures of this map are based on digit­al spa­tial data licensed from the Centre for Eco­logy Fig­ure 5. Beaver Hab­it­at Index for Nation­al Park with SEPA catch­ment bound­ar­ies High­lighted. Con­tains Ord­nance Sur­vey data 12 10- 20 km Basemap data ©Map­Tiler Open­Street­Map Con­trib­ut­ors Google. Beaver Net­work Gra­ham et al., 2021 and con­tains fea­tures based on digit­al spa­tial data from the Centre for Eco­logy and Hydro­logy NERC (CEH). Con­tains OS data Crown copy­right [and data­base right]

Table 2. Beaver Hab­it­at Index sum­mary stat­ist­ics for ripari­an veget­a­tion along chan­nels in Cairngorms Nation­al Park. Beaver Hab­it­at Index Cat­egory Total (km) Per­cent­age (%) Highly Suit­able 1053.5 10.7 Suit­able 952.9 9.7 Mod­er­ately Suit­able 789.7 8.0 Barely Suit­able 1158.1 11.8 Likely Unsuit­able 5858.7 59.7 Per­cent­age of Chan­nels in CNP with ​‘Pre­ferred’ BHI 4 to 6 6 to 8 8 to 10 10 to 12 12 to 14 14 to 16 16 to 18 10 15 20 25 30 km Fig­ure 6. Per­cent­age of chan­nels ineach of the main catch­ments, with ​‘pref­ferred’ beaver hab­it­at along their banks. Illus­trates hab­it­at is most suit­able in the Spey fol­lowed by the Dee. N 13

Table 3. Beaver Hab­it­at Index sum­mary stat­ist­ics for ripari­an veget­a­tion along chan­nels in Cairngorms Nation­al Park sep­ar­ated by catch­ment. Catch­ment Beaver Hab­it­at Index Total (km) Per­cent­age (%) Dee Highly Suit­able 261.9 11.7 Dee Suit­able 188.9 8.4 Dee Mod­er­ately Suit­able 127.5 5.7 Dee Barely Suit­able 171.0 7.6 Dee Likely Unsuit­able 1488.0 66.5 Don Highly Suit­able 21.8 3.7 Don Suit­able 107.6 18.1 Don Mod­er­ately Suit­able 93.3 15.7 Don Barely Suit­able 125.0 21.1 Don Likely Unsuit­able 245.4 41.4 Spey Highly Suit­able 670.6 14.8 Spey Suit­able 539.2 11.9 Spey Mod­er­ately Suit­able 439.7 9.7 Spey Barely Suit­able 650.6 14.3 Spey Likely Unsuit­able 2245.6 49.4 Tay Highly Suit­able 91.8 3.8 Tay Suit­able 107.0 4.5 Tay Mod­er­ately Suit­able 120.2 5.0 Tay Barely Suit­able 206.6 8.6 Tay Likely Unsuit­able 1870.5 78.1 Oth­er Highly Suit­able 7.3 17.9 Oth­er Suit­able 10.2 24.8 Oth­er Mod­er­ately Suit­able 8.9 21.8 Oth­er Barely Suit­able 4.7 11.4 Oth­er Likely Unsuit­able 9.9 24.1 Beaver Dam Capa­city mod­el­ling Beaver Dam Capa­city (BDC) mod­el sum­mary The Beaver res­tor­a­tion assess­ment tool (BRAT) was developed in North Amer­ica (Mac­far­lane et al., 2014, 2015) to determ­ine the capa­city for river sys­tems to sup­port Beaver dams. The BRAT mod­el has been fur­ther deployed in a range of dif­fer­ent river sys­tems to aid both Beaver recol­on­isa­tion and beaver dam ana­logue led res­tor­a­tion. The BRAT mod­el not only provides an invalu­able tool for design­ing effect­ive, empir­ic­ally based, res­tor­a­tion strategies but it also indic­ates where Beaver dams might be con­struc­ted and there­fore where they may cause poten­tial management/​conflict issues. The BRAT mod­el struc­tures the frame­work of the mod­el around the river net­work itself and using a fuzzy logic approach which builds in the con­sid­er­able uncer­tainty that is asso­ci­ated with beaver habitat/​dammable reaches. Fur­ther­more, it provides a range of out­put val­ues to pre­dict the dam capa­city which has implic­a­tions for beaver pref­er­ence towards a giv­en loc­a­tion. We have there­fore used the BRAT frame­work to devel­op an optim­ised beaver dam capa­city (BDC) mod­el for Great Britain.

The BDC mod­el estim­ates the capa­city of river sys­tems to sup­port dams at the reach-scale (c.a. 150m). The mod­el also high­lights reaches that are more likely to be dammed by beaver and estim­ates the num­ber of beaver dams that could occur for a catch­ment at pop­u­la­tion car­ry­ing capa­city. As such, this 14

highly detailed tool would provide under­stand­ing of where dams are most likely to occur and in what dens­it­ies, sup­port­ing future work on the con­flicts and oppor­tun­it­ies that might accrue from beaver reintroduction.

The mod­el infers the dens­ity of dams that can be sup­por­ted by stream reaches (111.1m ± 52.5) across a catch­ment. Using low-cost and open-source data­sets, the fol­low­ing attrib­utes are cal­cu­lated for each reach: (i) stream gradi­ent, (ii) low (Q80) and high flow (Q2) stream power, (iii) bank­full width, (iv) stream order, and (v) the suit­ab­il­ity of veget­a­tion, with­in 10m and 40m of the bank, for beaver dam con­struc­tion. These con­trolling vari­ables are com­bined using a sequence of infer­ence and fuzzy infer­ence sys­tems which fol­low an expert-defined rules sys­tem that allows for the con­sid­er­able uncer­tainty often asso­ci­ated with these types of com­plex eco­lo­gic­al processes.

Each reach was clas­si­fied for dam­ming capa­city using five cat­egor­ies from none, defined as no capa­city for dam­ming to per­vas­ive where a max­im­um capa­city of 16 – 30 dams could the­or­et­ic­ally be con­struc­ted in a km of chan­nel. It is import­ant to note that the mod­el assumes both reach and catch­ment pop­u­la­tion car­ry­ing capa­city for beaver. There­fore, in real­ity the max­im­um num­ber of dams indic­ated in a cat­egory class is unlikely to occur. A full list of BDC clas­si­fic­a­tions is included in Table 3.

Table 4. BDC clas­si­fic­a­tions and defin­i­tions. BDC Clas­si­fic­a­tion None Rare Occa­sion­al Fre­quent Per­vas­ive Defin­i­tion No capa­city for dam­ming Max capa­city for 0 – 1 dams/​km Max capa­city for 1 – 4 dams/​km Max capa­city for 5 – 15 dams/​km Max capa­city for 16 – 30dams/​km 15

Beaver Dam Capa­city Mod­el maps for the study area Cairngorms Nation­al Park Cairngorms_​Beaver Net­work None Rare Occa­sion­al Fre­quent Per­vas­ive 0 20 km Basemap data ©Map­Tiler Open­Street­Map Con­trib­ut­ors Google. Beaver Net­work Gra­ham et al., 2021 and con­tains fea­tures based on digit­al spa­tial data from the Centre for Eco­logy and Hydro­logy NERC (CEH). Con­tains OS data Crown copy­right [and data­base right] Fig­ure 6. Beaver Dam Capa­city mod­el res­ults for Nation­al Park. Con­tains Ord­nance Sur­vey data Crown Copy­right 2007, and some fea­tures of this map are based on digit­al spa­tial data licensed from the Centre for Eco­logy & Hydro­logy, © NERC (CEH). Aer­i­al imagery: Open-Source Google imagery © Open­Street­map (and) con­trib­ut­ors CC-BY-SA. 16

Cairngorms Nation­al Park Catchments_​Boundaries Cairngorms_​BeaverNetwork None Rare Occa­sion­al Fre­quent Per­vas­ive Fig­ure 7. Beaver Dam Capa­city mod­el res­ults and catch­ment bound­ar­ies. Con­tains Ord­nance Sur­vey data © Crown Copy­right 2007, Licence num­ber 100017572 and some fea­tures of this map are based on digit­al spa­tial data licensed from the Centre for Eco­logy & Hydro­logy, © NERC (CEH). Aer­i­al imagery: Open-Source Google imagery © Open­Street­map (and) con­trib­ut­ors CC- BY-SA. 17 20 km Basemap data ©Map­Tiler Open­Street­Map Con­trib­ut­ors Google. Beaver Net­work Gra­ham et al., 2021 and con­tains fea­tures based on digit­al spa­tial data from the Centre for Eco­logy and Hydro­logy NERC (CEH). Con­tains OS data Crown copy­right [and data­base right]

0 5 10 15 20 km 15 20 25 km Dee Spey Per­cent­age of Chan­nels with ​‘Per­vas­ive’ BDC 0 to 2 2 to 4 4 to 6 6 to 8 8 to 10 30 km N 0 km 0 5 10 15 20 25 km Don Tay N BDC_​cat Fre­quent None Occa­sion­al Per­vas­ive Rare N Fig­ure 8. Sum­mary BDC fig­ures. Top BDC for each of the main river catch­ments, bot­tom % of chan­nels in each catch­ment with ​‘Per­vas­ive’ dam capa­city. Illus­trat­ing this is highest in Spey. 18

Table 5. Beaver Dam Capa­city Sum­mary Stat­ist­ics for Cairngorms Nation­al Park. BDC Cat­egory Total (km) Per­cent­age (%) None 1695.4 17