NatureScot Research Report 1314 - Review of the bryological assessment for hydroelectric schemes scoring system in the light of new data on species status and ecology

Year of publication: 2023

Authors: Averis, A.B.G., Hodgetts, N.G. & Rothero G.P.

Cite as: Averis, A.B.G., Hodgetts, N.G. & Rothero G.P. 2023. Review of the bryological assessment for hydroelectric schemes scoring system in the light of new data on species status and ecology. NatureScot Research Report 1314.

 

Keywords

Hydroelectric schemes; bryological assessment; scoring system; bryophyte; moss; liverwort

Background

The report examines the most recent data on the distribution and status of bryophytes in western Scotland, in order to review and update the scoring system that is part of an online planning tool to help developers explore opportunities for hydro-electric development in Scotland.

Main findings

The report concluded that:

• our online bryophyte planning tool continues to provide accurate information to help developers explore opportunities for hydro-electric developments; and
• some minor updates to the tool were required.

Acknowledgements

Thanks are due to Kenny Taylor of NatureScot for letting and administering this project, and to Des Callaghan for sharing information from the new draft Red List.

Introduction

Potential hydro sites are often potentially rich bryophyte (moss and liverwort) sites. The western Scottish Highlands are of global importance for bryophytes. The temperate, wet climate is ideal for many oceanic species that are globally very rare and restricted climatically to areas with a high rainfall and only moderate temperature fluctuations. Their importance was first recognised by Ratcliffe (1968), who coined the term ‘Atlantic bryophytes’. The document Guidance for applicants on supporting information requirements for hydropower applications (SEPA 2009) recognises the necessity for a full bryophyte survey of potentially rich hydro sites so that green energy production can go ahead without damaging Scotland’s natural heritage. The potential impacts of small hydroelectric schemes on bryophytes and lichens were considered by Demars & Britton (2011).

Averis et al. (2012) produced a scheme for assessing the bryological importance or potential importance of ravines for bryophytes, and made recommendations in relation to small hydroelectric schemes. This uses 29 species of nationally uncommon humidity-demanding bryophytes to classify sites to one of five levels of bryological importance using a scoring system. Un-surveyed or partly surveyed sites are also assessed using maps and aerial photographs. This work assessed 5,629 water courses in western Scotland for their bryological interest.

A 2015 review was undertaken of NatureScot’s guidance on oceanic bryophytes and hydro-electric development by NatureScot’s Scientific Advisory Committee Sub-Group. It was undertaken to validate the above approach or recommend changes to improve it. A number of recommendations were actioned. Recommendation 6 was for NatureScot to review the scoring system in five years to ensure its continuing appropriateness in light of new data on species distributions. This project addresses that recommendation.

Methods

The three authors independently examined the existing guidance and suggested some changes according to new information, notably the discovery of new sites for some species and the under-review Red List of British Bryophytes (Callaghan in prep.). Nomenclatural changes were also made, to bring the list in line with the new British and Irish Checklist (Blockeel et al. 2021). The cut-off date for determining Nationally Rare and Nationally Scarce species has changed from 1950 to 1970 (Pescott 2016), so species status was checked. Proposed changes were discussed via e-mail and a consensus was achieved.

Results

One ‘new’ species has been added to, and none have been removed from, the list of 29 species subjected to assessment. This is Radula holtii, with two populations in Scotland. Table 1 shows the rationale behind the scoring review for each species, with both original and new scores included. Table 2 is the resultant updated version of Table 1 in Averis et al. (2012). The scoring system is almost unchanged, except that Critically Endangered (CE) and Least Concern (LC) (depicting neither Nationally Scarce nor Nationally Rare) categories have been added; however, CR species score the same as EN species. Table 3 is the resultant slightly modified version of Table 2 in Averis et al. (2012).

Discussion

The changes to the scores presented here are fairly minor, but reflect the increasingly complete knowledge we have about the relevant species. For example, it is now even more clear than it was in 2012 that any watercourse with Acrobolbus wilsonii, Hageniella micans or Radula voluta should automatically be in Category A, because these species are so uncommon, and so dependent on water, that they are particularly vulnerable to changes potentially resulting from hydro schemes (please refer to Note 8, Appendix 1). Therefore it would be inappropriate to install a new hydro scheme on a watercourse with any of these species (please see Note 9, Appendix 1). In contrast, Colura calyptrifolia and Daltonia splachnoides, both of which have increased outwith ravine sites, appear to be not so directly dependent on water as was once thought. However, neither of these species has increased within sites likely to be targeted for hydro schemes, so they remain in the list of scored species, albeit with (in the case of Daltonia) a lower score than before.

There was some discussion about Metzgeria leptoneura because it was assigned to Near Threatened in an early version of the new draft Red List (Callaghan in prep.), the perception having been that it has declined (see, for example, Blockeel et al. 2014). However, the latest draft of the new Red List has it as Least Concern, so its score remains as before.

The inclusion of Pseudohygrohypnum (Hygrohypnum) subeugyrium was also considered for this revision. This species is a recent discovery in Britain (Blockeel et al. 2019), many specimens having previously being overlooked as P. eugyrium, but it was decided that we do not yet have sufficient knowledge about its ecology and distribution to include it. It should, however, be considered again in the next revision of this assessment.

We have also reviewed the sites we have collectively surveyed for potential hydro schemes since 2011. Not counting the survey of oceanic bryophytes in the Sunart SAC (Averis & Hodgetts 2013), of a total of 266 sites surveyed, 28 (10.53%) were placed into Category A, and 238 (89.47%) into Category C. This serves to emphasize (a) the importance of Category A sites (see Notes 8 + 9, Appendix 1), and (b) the fact that the vast majority of proposed hydro schemes can safely be allowed without a significant impact on Scotland’s unique oceanic bryophyte flora. It is not known how many of the 28 Category A sites identified now have hydro schemes, but we would expect that allowing a hydro scheme to go ahead at a Category A site would require some kind of special case to be made.

References

Averis, A.B.G., Genney, D.R., Hodgetts, N.G., Rothero, G.P. & Bainbridge, I.P. 2012. Bryological assessment for hydroelectric schemes in the west Highlands – 2^nd edition. Scottish Natural Heritage Commissioned Report No. 449b.

Averis, A.B.G. & Hodgetts, N.G. 2013.  Survey of oceanic bryophytes associated with watercourses in Sunart Special Area of Conservation. Scottish Natural Heritage Commissioned Report No. 595.

Blockeel, T.L., Bell, N.E., Hill, M.O., Hodgetts, N.G., Long, D.G., Pilkington, S.L. & Rothero, G.P. 2021. A new checklist of the bryophytes of Britain and Ireland, 2020. Journal of Bryology 43(1): 1-51.

Blockeel, T.L., Bosanquet, S.D.S., Hill, M.O. & Preston, C.D. (eds.) 2014. Atlas of British and Irish bryophytes. Volume 1. Newbury, Pisces Publications.

Blockeel, T.L., Kiebacher, T. & Long, D.G. 2019. Hygrohypnum subeugyrium (Renauld & Cardot) Borth. (Hypnales), a neglected British moss, with a note on its occurrence in the Himalayas. Journal of Bryology 41(1): 12-20.

Callaghan, D. in prep. Red List of British Bryophytes.

Demars, B.O.L. & Britton, A. 2011. Assessing the impacts of small scale hydroelectric schemes on rare bryophytes and lichens. Scottish Natural Heritage Commissioned Report No. 421.

Pescott, O. 2016. Revised lists of nationally rare and scarce bryophytes for Britain. Field Bryology 115: 22-30.

Ratcliffe, D.A. 1968. An ecological account of Atlantic bryophytes in the British Isles. New Phytologist 67: 365–439.

SEPA 2009. Guidance for applicants on supporting information requirements for hydropower applications. The Water Environment (Controlled Activities) (Scotland) Regulations 2005 (CAR). Aberdeen, Scottish Environment Protection Agency.

Tables

Table 1. Rationale for scores of bryophytes in the watercourse assessment system (Non-bold type = species not recorded in Scotland. Nomenclature according to Blockeel et al. (2021); old names (used in Averis et al. 2012) are in brackets).

Moss species

Moss Species	Original score	New score	Comments	Editors addition: details of score change
Campylopus setifolius	3	3	Least Concern but Nationally Scarce, so no change to the score.	Previously not listed now LC. Still NS
Chionoloma (Paraleptodontium) recurvifolium	3	3	No change.	Previously not listed now LC. Still Nationally Scarce.
Chionoloma (Trichostomum) hibernicum	3	3	Least Concern and Nationally Scarce, so no change to its score.	Previously not listed now LC. Not found in list of NS bryophytes (Pescott 2016). Listed as Oxystegus hibernicus (Prescott 2016)
Cyclodictyon laetevirens	12	12	Critically Endangered, so score stays at 12.	Previously EN. Still Nationally Rare.
Daltonia splachnoides	9	3	Now Least Concern, which takes its score down to 3. All watercourse sites with Daltonia are currently in category A and have a site score of at least 13, so even with Daltonia's species score dropping from 9 to 3, all of these sites remain in category A.	Previously VU. Still Nationally Rare.
Dicranodontium (Campylopus) subporodictyon	6	9	Vulnerable, so score goes up to 9. This doesn't affect the end result because all watercourse sites for this species are in category A anyway.	Previously NT. Still Nationally Rare.
Fissidens polyphyllus	3	3	Least Concern but Nationally Scarce.  Score stays at 3.	Previously not listed now LC. Still NS.
Hageniella micans	3	9	Now Vulnerable, which means the score rises to 9. Most watercourse sites with Hageniella are already in category A, but a very few are in category C, so these few sites move up into category A.	Previously not listed now VU. Still Nationally Scarce.
Heterocladium wulfsbergii	3	3	Least Concern, but still Nationally Scarce, so the score should remain as 3.	Previously not listed now LC. Still NS (although it says it is new to the list).
Isothecium holtii	1	1	No change necessary.	Previously not listed now LC. Not NR or NS.
Platyhypnum (Hygrohypnum) duriusculum*	6	3	Least Concern, so score goes down to 3. There are so few sites with this species that this changes just one site's category from A to C.	Previously NT. Still Nationally Scarce.
Pohlia scotica*	9	9	No change.	VU. NR.
Rhynchostegium alopecuroides (Platyhypnidium lusitanicum)	3	3	Least Concern; no change to its score.	Previously not listed now LC. Still Nationally Scarce.
Schistidium agassizii*	3	3	Least Concern and Nationally Scarce, so no change to its score.	Previously not listed now LC. Still NS.
Sematophyllum demissum	-	-	-	-
Thamnobryum angustifolium	-	-	-	-
Thamnobryum cataractarum	-	-	-	-

 

Liverwort species

Liverwort Species	Original score	New score	Comments	Editors addition: details of score change
Acrobolbus wilsonii	3	9	Vulnerable, so its score increases to 9. This does not change any site categories because there are no Acrobolbus sites in category C.	Previously not listed. Still Nationally Scarce.
Cololejeunea (Aphanolejeunea) microscopica	1	1	No change.	Previously no categories. Now LC
Colura calyptrifolia	1	1	Retained on list after some discussion. Although it has increased overall in Britain, its frequency along watercourses does not seem to have increased in proportion, and it is therefore still similar to the other small Lejeuneaceae scoring 1 point in this respect.	Previously not listed now LC.
Drepanolejeunea hamatifolia	1	1	No change.	Previously no categories. Now LC.
Dumortiera hirsuta	9	9	No change.	Still VU. Still NR.
Harpalejeunea molleri	1	1	No change.	Previously no categories. Now LC.
Jubula hutchinsiae	1	1	No change.	Previously no categories. Now LC.
Lejeunea eckloniana	9	12	Critically Endangered, so the score goes up to 12, but in Scotland possibly not in ravines anyway.	Previously VU. Still NR.
Lejeunea flava	-	-	-	-
Lejeunea hibernica	-	-	-	-
Lejeunea mandonii	12	12	Now Endangered, but no change to its score.	It was previously EN. Still NR.
Lophocolea fragrans	1	1	No change	Previously no categories. Now LC.
Metzgeria leptoneura	1	1	No change.	Previously no categories. Now LC.
Plagiochila exigua	1	1	No change.	Previously no categories. Now LC.
Porella pinnata	-	-	-	-
Radula aquilegia	1	1	No change.	Previously no categories. Now LC.
Radula carringtonii	9	12	Now Endangered, but no change to its score. This does not change any site categories because all Radula carringtonii watercourses are in category A anyway.	Previously VU. Still NR.
Radula holtii	?	12	Critically Endangered = 12 points. Two populations known in Scotland. the W Ross population might be more endangered than the Ardnamurchan population.	Listed as a non-Scottish species in CR 449b (not in bold). CR. NR.
Radula voluta	3	6	Near Threatened, so the score would go up to 6, which shouldn't change any site categories from C to A because there are no Radula voluta sites in category C (all A or B).	Previously not listed. Still NS.

 

* Hygrohypnum duriusculum, Pohlia scotica and Schistidium agassizii do not have oceanic distributions in Europe but are included here because they are so uncommon in Great Britain and Ireland (H. duriusculum and P. scotica are also Red Data Book species) and are riparian with a high dependence on water flow.

 

Table 2. Bryophyte species selected for inclusion in assessment of western Scottish watercourses in relation to proposed hydroelectric scheme (includes additional non-Scottish species (in non-bold type) that are similarly uncommon and hygrophilous, and for which watercourses with hydroelectric potential are an important habitat. Nomenclature according to Blockeel et al. (2021); old names (used in Averis et al. 2012) are in brackets).

Species	Moss of Liverwort	Scotland	England	Wales	Ireland	GB rarity status **	IUCN threat level ***	Score ****
Campylopus setifolius	M	S	E	W	I	NS	LC	3
Chionoloma (Paraleptodontium) recurvifolium	M	S	E	W	I	NS	LC	3
Chionoloma (Trichostomum) hibernicum	M	S	-	-	I	NS	LC	3
Cyclodictyon laetevirens	M	S	E	-	I	NR	CR	12
Daltonia splachnoides	M	S	-	W	I	NR	LC	3
Dicranodontium (Campylopus) subporodictyon	M	S	-	-	-	NR	VU	9
Fissidens polyphyllus	M	S	E	W	I	NS	LC	3
Hageniella micans	M	S	E	W	I	NS	VU	9
Heterocladium wulfsbergii	M	S	E	W	I	NS	LC	3
Isothecium holtii	M	S	E	W	I	-	LC	1
Platyhypnum (Hygrohypnum) duriusculum*	M	S	E	W	I	NS	LC	3
Pohlia scotica*	M	S	-	-	-	NR	VU	9
Rhynchostegium alopecuroides (Platyhypnidium lusitanicum)	M	S	E	W	I	NS	LC	3
Schistidium agassizii*	M	S	E	W	I	NS	LC	3
Sematophyllum demissum	M	-	-	W	I	NR	VU	9
Thamnobryum angustifolium	M	-	E	-	-	NR	DD(TU)	12
Thamnobryum cataractarum	M	-	E	-	-	NR	DD(TU)	12
Acrobolbus wilsonii	L	S	-	-	I	NS	VU	9
Cololejeunea (Aphanolejeunea) microscopica	L	S	E	W	I	-	LC	1
Colura calyptrifolia	L	S	E	W	I	-	LC	1
Drepanolejeunea hamatifolia	L	S	E	W	I	-	LC	1
Dumortiera hirsuta	L	S	E	-	I	NR	VU	9
Harpalejeunea molleri	L	S	E	W	I	-	LC	1
Jubula hutchinsiae	L	S	E	W	I	-	LC	1
Lejeunea eckloniana	L	S	-	-	I	NR	CR	12
Lejeunea flava	L	-	-	-	I	n/a	VU (Ireland)	-
Lejeunea hibernica	L	-	-	-	I	n/a	NT (Ireland)	-
Lejeunea mandonii	L	S	E	-	I	NR	EN	12
Lophocolea fragrans	L	S	E	W	I	-	LC	1
Metzgeria leptoneura	L	S	E	W	I	-	LC	1
Plagiochila exigua	L	S	E	W	I	-	LC	1
Porella pinnata	L	-	E	W	I	NS	LC	3
Radula aquilegia	L	S	E	W	I	-	LC	1
Radula carringtonii	L	S	-	-	I	NR	EN	12
Radula holtii	L	S	-	-	I	NR	CR	12
Radula voluta	L	S	E	W	I	NS	NT	6

 

* Hygrohypnum duriusculum, Pohlia scotica and Schistidium agassizii do not have oceanic distributions in Europe but are included here because they are so uncommon in Great Britain and Ireland (H. duriusculum and P. scotica are also Red Data Book species) and are riparian with a high dependence on water flow

** GB rarity status (for species with 100 or fewer 10km sq. records in GB post-1970): NS = Nationally Scarce (16-100 10km sq. records); NR = Nationally Rare (<16 10km sq. records)

*** IUCN threat categories: LC = Least Concern; DD = Data Deficient (TU = Taxonomically Uncertain); NT = Near-threatened; VU = Vulnerable; EN = Endangered; CR = Critically Endangered

**** Species scoring system: 1 = not NS or NR; 3 = NS; 6 = NT; 9 = VU; 12 = EN & CR

 

Table 3. Species scoring system for Scottish hygrophilous bryophytes (See also Appendix 2: CR 449b, classifying categories).

Species score	NatureScot water course classification system*	IUCN Threat Level	GB Status
1	C or E	Least Concern (LC)	Neither Nationally Scarce nor Nationally Rare
3	C or E		Nationally Scarce
6	A, B or D	Near Threatened (NT)	Nationally Rare or Nationally Scarce
9	A, B or D	Vulnerable (VU)	Nationally Rare or Nationally Scarce
12	A, B or D	Critically Endangered (CR) and Endangered (EN)	Nationally Rare

 

*See Appendix 1 – Note 8 and Appendix 2

Nationally Scarce = 16-100 10km square records in Great Britain post-1970

Nationally Rare = 1-15 10km square records in Great Britain post-1970

Appendix 1. Explanatory Notes and Updates

The additions to the text above come from comments arising from the expert review panel’s scrutiny of this report. The panel consisted of Kathy Dale (Scientific Advisory Committee, NatureScot), Adrian Loening (British Hydro Association), Ian Milne (SEPA).

1. Introduction, Para 2: Averis et al. (2012) surveyed 5,629 waterbodies visible on a 1:250,000 map scale.
2. It is useful to refer to Table 3. ‘Species scoring system for Scottish hygrophilous bryophytes’, before reading through Tables 1 + 2.
3. The ‘New Score’ column in Table 1 refers to the score as per the current draft Red List, and other relevant documents.
4. There are 30 species in bold type in Table 2.
5. Table 2. Column ‘Recorded in’ includes Ireland, which is not included in the current draft Red List.
6. Table 2. The current draft Red List records Chionoloma (Trichostomum) hibernicum and Lejeunea mandonii as present in Wales.
7. Table 2. The current draft Red List records Daltonia splachnoides as present in England.
8. Table 2. (asterix footnote): NatureScot advise that watercourses where the cumulative score of all recorded species is equal to or greater than six points are of national interest. Category A triggering species (stand alone) found on sections of the watercourse are likely to be a rich nationally and internationally important flora of uncommon hygrophilous oceanic bryophyte species.  The Planning Tool will outline the locations and likely locations where these species are found.
9. The report’s authors’ opinion regarding the appropriateness of installation is not supported by NatureScot and SEPA until all mitigation options have been pursued and exhausted. Use of the planning tool and early engagement is recommended.

Appendix 2. CR 449b Table 3 Categories used to classify West Highland watercourses by their bryological significance, for use in relation to proposed hydroelectric schemes

Category number	Category description
A	The site has been surveyed and has a score of 6 or more points indicating a rich, nationally/internationally important flora of uncommon hygrophilous bryophyte species. The whole site is associated with a particular watercourse (for example the site is a ravine), so the records contributing to the site score are all  relevant for consideration in relation to a proposed hydroelectric scheme. Therefore no further survey should be necessary in order to evaluate site importance in relation to a proposed  hydroelectric scheme; the score of 6 or more points indicates that the site is of such bryological importance that hydroelectric development could have a significant national/international impact on humidity-demanding oceanic bryophyte assemblages.
B	The site has been surveyed and has a score of 6 or more points (i.e. a rich flora of uncommon hygrophilous species), but the watercourse and its environs form only a part of the site. The site species list may include records made well away from the watercourse, and this watercourse may be one of two or more watercourses within the site. Some of the records contributing to the site score may not therefore be from this particular watercourse and may not be relevant for consideration in relation to a proposed hydroelectric scheme. Survey of this particular watercourse is therefore required, to assess its richness.
C	The site has a score of between 0 and 5 points, and the survey of the watercourse area was sufficiently thorough that it seems unlikely that further survey will produce enough additional records of uncommon hygrophilous species to raise the site score to 6 or more points. No further survey should be necessary in relation to a proposed hydroelectric scheme. With a score of <6 points the site is of low to medium bryological importance and hydroelectric development is unlikely to have a significant national/international impact on humidity-demanding oceanic bryophyte assemblages. However, the following points should be noted for a hydroelectric scheme at a site in this category: (1) the bryophyte flora may be of local importance, for example including a species that is rare locally or is at the edge of its geographical range; (2) the watercourse may be important for other groups such as invertebrates; (3) the ecological acceptability of a proposed scheme might be reduced if many other watercourses in the local area already have hydroelectric schemes (i.e. few unmodified watercourses left in the area concerned).
D	The site has a score of between 0 and 5 points and is either unsurveyed or only partially surveyed, but maps and aerial photographs show topography and/or woodland that suggest potential for a site score exceeding 6 points. Further survey of the watercourse area is required in relation to any hydroelectric proposal.
E	The site has a score of between 0 and 5 points and is unsurveyed (score = 0 points) or in a few cases partially surveyed, and maps and aerial photographs show a gentle watercourse gradient and/or little or no ravine topography or woodland, so it seems unlikely that the bryophyte flora present will score as much as 6 points. Photographs of the site should be taken (looking upstream at regular intervals along the watercourse), and from these the appearance and bryological potential of the habitats should be assessed by a bryologist (or other ecologist using guidance supplied by bryologists) and a decision made on whether the habitat has sufficient potential to require a bryophyte survey.