Sunday, 8 March 2020

Great bryophytes at Great Tew

Despite Storm Ciara pummelling parts of Britain, no less than five bryologists turned out for our trip to part of the Great Tew estate (the valley at the bottom of SP3730). In the event, despite getting rather wet, the valley sheltered us from the worst of the wind, and the only slightly hairy moment was the explosive crack of a branch coming down further along the valley.

Although bryologists have visited the Great Tew area previously (e.g. Eustace Jones recorded Grimmia orbicularis on the estate, and mentions a record of Orthotrichum tenellum in a "wet wood in valley north of Great Tew"  in his 1953 paper on the mosses of Berkshire and Oxfordshire), very few localised records actually exist in the database of the British Bryological Society (older records tend only to have been entered as hectad summaries). This, then, was a great chance to explore a private woodland (we had permission!) and make some localised records for an area that is not well-represented in records databases.

After picking up various common pleurocarps after dropping into the valley, we also found Isothecium alopecurum on the roots of ash and fertile Cirriphyllum crassinervium nearby on soil. Soon after we found one of the things that we had been hoping for, a tufa-forming stream emerging out of the valley-side, as is often found in cuttings and valleys on the Oolite in the north of Oxfordshire. This particular one was not particularly blessed with bryological interest, although a large stand of Palustriella commutata featured in the centre of the stream, accompanied by Cratoneuron filicinum and Pellia endiviifolia.

Palustriella commutata clump in tufaceous spring
Soon after, an uncommon sight in Oxfordshire was seen, that of Plagiomnium undulatum fruiting. Jones (1953) listed this species as "sterile" in Oxon., and still considered the fact of its fruiting "rare or very rare" after forty more years bryologising in the county (Jones, 1991).

Plagiomnium undulatum in fruit at Great Tew.
By this point of the day we were rather sodden, and thoughts were turning towards home. Perhaps the nicest thing of the afternoon was a good population of the liverwort Plagiochila asplenioides growing along a track through the wood further up the valley side. Whilst this livewort is fairly frequent in ancient woods on heavy basic soils, it is not common in Oxfordshire overall, and is always nice to see.

Plagiochila asplenioides at Great Tew.
And finally, a nice photo of the epiphytic liverwort Metzgeria violacea that seemed extremely happy in the humid environment of this hidden valley.

Metzgeria violacea

Oh, and for the non-bryologists, we also saw Dryopteris dilata growing epiphytically in the crown of a fallen oak, which is not a habitat most Floras list!

Dryopteris dilata growing as an epiphyte on oak (foreground; background fern is Polypodium interjectum)
The full list of bryophytes seen in the valley at Great Tew is given below:

Amblystegium serpens var. serpens Hypnum cupressiforme var. resupinatum Zygodon conoideus var. conoideus
Brachythecium rivulare Isothecium alopecuroides Conocephalum conicum s.str.
Brachythecium rutabulum Isothecium myosuroides Frullania dilatata
Bryum capillare Kindbergia praelonga Lophocolea bidentata
Calliergonella cuspidata Orthotrichum affine Metzgeria consanguinea
Cirriphyllum crassinervium Oxyrrhynchium hians Metzgeria furcata
Cratoneuron filicinum Oxyrrhynchium schleicheri Metzgeria violacea
Cryphaea heteromalla Palustriella commutata s.str. Pellia endiviifolia
Didymodon sinuosus Plagiomnium undulatum Radula complanata
Fissidens gracilifolius Plagiothecium nemorale Atrichum undulatum
Fissidens incurvus Rhynchostegium confertum Cirriphyllum piliferum
Fissidens taxifolius var. taxifolius Syntrichia virescens Didymodon insulanus
Homalothecium sericeum Thamnobryum alopecurum Leskea polycarpa
Hygrohypnum luridum Thuidium tamariscinum Orthotrichum pulchellum
Hypnum cupressiforme var. cupressiforme Ulota phyllantha Orthotrichum stramineum
Plagiochila asplenioides

Bryophytes of Dorchester (Oxfordshire)

Three bryologists met at Dorchester Abbey (SU5794) on a grey, drizzling morning for the fifth excursion of the season. The Abbey graveyard and buildings proved to have a lot to offer, with a grand total of 41 species, pipping our previous season's best churchyard at Bletchingdon (36 species). Probably the top find was Gyroweisia tenuis on the east facing walls of the Abbey. Gyroweisia can be easily confused with other species, particularly Leptobarbula berica, and the Sussex Bryological Group have an excellent blog on this topic.

Gyroweisia tenuis habitat (with Porella platyphylla in foreground)
The other nice find in the churchyard was Syntrichia papillosa. This is a species that appears to be spreading in lowland Britain, possibly helped by eutrophication of a range of substrates from various sources of nitrogen (e.g. NOx from car exhausts). On the other hand, it may be that the species is just recovering from losses during an earlier period of substrate acidification from SO2 pollution (and the loss of hedgerow elms). For example, Eustace Jones notes that Herbert Napier (recording in Oxon. 1909-1914) reported it as "not uncommon" and suggested that the species had increased since the time of Boswell (recording in Oxon. 1858-1897). Jones himself reported S. papillosa as "certainly rare" (this would have applied to the 1935-1953 period) and describes the species as typically only found in single locations within sites (and gives hedgerow trees, "usually elm", as the habitat). Perhaps at this point the species was still widespread but locally rare, meaning that it was often overlooked during surveys. Certainly it appears to have subsequently declined, as it was only recorded twice in Oxon. in the period 1953-1991 (Jones, 1991).

At Dorchester we found nice stands of the plant on a tombstone, but also on the slats of a park bench, suggesting a novel mode of gemmae movement! See the two pictures of the photogenic S. papillosa below:

The full list from Dorchester Abbey appears below:
Amblystegium serpens Grimmia pulvinata Rhynchostegium confertum
Barbula convoluta var. convoluta Gyroweisia tenuis Rhynchostegium murale
Barbula unguiculata Homalothecium sericeum Rhytidiadelphus squarrosus
Brachythecium rutabulum Hypnum cupressiforme Schistidium crassipilum
Bryum argenteum Hypnum cupressiforme var. lacunosum Syntrichia latifolia
Bryum capillare Kindbergia praelonga Syntrichia montana
Bryum rubens Orthotrichum anomalum Syntrichia papillosa
Calliergonella cuspidata Orthotrichum cupulatum Zygodon viridissimus var. viridissimus
Didymodon fallax Orthotrichum diaphanum Lophocolea bidentata
Didymodon insulanus Oxyrrhynchium hians Lunularia cruciata
Didymodon luridus Phascum cuspidatum Porella platyphylla
Didymodon nicholsonii Plagiomnium rostratum
Didymodon sinuosus Pseudocrossidium hornschuchianum
Didymodon vinealis Pseudoscleropodium purum
Fissidens taxifolius var. taxifolius Rhynchostegiella tenella

After lunch we walked a circuit through the Dyke Hills (SU5793) west of Dorchester, and then followed the Thames anti-clockwise back to the town.

The (flooded) Dyke Hills in winter.
The Dyke Hills are an Iron Age earthwork, and covered in a slightly improved form of calcareous grassland, the hills themselves presumably being formed from river gravels excavated locally. The bryophyte flora reflects this. After some time searching, we came up with the following, fairly meagre, list:
Weissia species Homalothecium lutescens
Barbula unguiculata Oxyrrhynchium hians
Brachythecium rutabulum Phascum cuspidatum
Bryum rubens Plagiomnium affine
Fissidens dubius Pseudoscleropodium purum

The riverside circuit turned up several expected riverside bryophytes, including Syntrichia latifolia, Cinclidotus fontinaloides, and Dialytrichia mucronata, whilst the close inspection of a multi-stemmed willow in the floodplain of the River Thame at SU580937 yielded an impressive 15 epiphytes on one tree, including more S. latifolia and S. papillosa.

Sunday, 16 February 2020

Chinnor Bryophytes

Our 4th bryophyte excursion of the 2019/20 season was to the old Chinnor Quarry at SP7500. Four bryologists were in attendance on what was a pretty grey and damp Sunday (12/01/2020). Despite this, things got off to a good start in the small, recently planted woodland adjacent to the car park at SP757004. Earlier in the year on a vascular plant survey this woodland had offered up some gems, including the White Helleborine (Cephalanthera damasonium), and it didn't disappoint now either. David quickly found Microbryum davallianum on crumbling soil along the central path through the woodland, alongside some infertile Aloina (most probably aloides judging by the amount of this species that we later saw in the old quarry).

Microbryum davallianum
Crossing over into the old quarry, now surrounded on one side by a housing estate, Aloina aloides (confirmed microscopically) was quickly picked up in the somewhat surreal damp chalky moonscape that dominates this area.

Aloina aloides
The Chinnor moonscape (ok, there was some grass as well...)
After inspecting what seemed like acres of Didymodon fallax, we picked up a few more unusual species, Campyliadelphus chrysophyllus for one. This is a species that is well-known to haunt the floors of damp chalk quarries, but it was the first time that any of us had seen it in Oxfordshire.

Campyliadelphus chrysophyllus at Chinnor
One species that we did hope to refind was Leiocolea badensis, a species recorded from the Chinnor quarries once in the 1960s, but never since. We found Leiocolea turbinata, its commoner congener, quite quickly, but, unfortunately, despite collecting several candidates for checking, we failed to locate the rarer species. Other interesting species in the quarry area included Campylium protensum, Cratoneuron filicinum, and Aneura pinguis, all in the vicinity of the large pond pictured below, and all species of damp calcareous habitats.

The pond area at SP759002
After lunch, we inspected an interesting area of sandy ground forming the football pitch of the housing estate previously mentioned. This was made of soil that had presumably been brought in for the purpose, and had abundant Phascum cuspidatum and occasional Pohlia annotina, the latter a species that has only four other records for Oxfordshire, and was last recorded for the vice-county in 1991. The rest of the excursion was filled by recording the wooded slope rising up to the Ridgeway footpath, and then circling back to the original car park. More Microbryum was encountered in patchy roadside grassland alongside the roundabout at SP758004, as was some Brachythecium mildeanum, our first record of this species for the season. The full list follows (duplicates are those recorded in the car park wood as well as the main square):

Mosses Liverworts
Aloina aloides s.str. Ctenidium molluscum Orthotrichum affine Aneura pinguis
Amblystegium serpens Dicranella varia Orthotrichum affine Cololejeunea minutissima
Barbula convoluta var. convoluta Dicranoweisia cirrata Orthotrichum diaphanum Leiocolea turbinata
Barbula unguiculata Didymodon fallax Orthotrichum diaphanum Metzgeria furcata
Brachythecium mildeanum Didymodon fallax Oxyrrhynchium hians Radula complanata
Brachythecium rutabulum Didymodon insulanus Oxyrrhynchium hians
Brachythecium rutabulum Fissidens incurvus Phascum cuspidatum
Bryoerythrophyllum recurvirostrum Fissidens taxifolius Plagiomnium undulatum
Bryum argenteum Fissidens taxifolius Plagiomnium undulatum
Bryum capillare Funaria hygrometrica Pohlia annotina
Bryum capillare Funaria hygrometrica Pseudocrossidium hornschuchianum
Bryum dichotomum Grimmia pulvinata Pseudoscleropodium purum
Bryum dichotomum Grimmia pulvinata Rhynchostegium confertum
Bryum pseudotriquetrum Homalothecium lutescens Rhytidiadelphus squarrosus
Bryum rubens Homalothecium lutescens Schistidium crassipilum
Calliergonella cuspidata Homalothecium sericeum Syntrichia laevipila
Calliergonella cuspidata Hypnum cupressiforme var. cupressiforme Syntrichia montana
Campyliadelphus chrysophyllus Hypnum cupressiforme var. resupinatum Syntrichia ruralis var. ruralis
Campylium protensum Kindbergia praelonga Thamnobryum alopecurum
Ceratodon purpureus Kindbergia praelonga Tortula muralis
Cirriphyllum piliferum Leptodictyum riparium Tortula muralis
Cratoneuron filicinum Microbryum davallianum Tortula subulata
Cryphaea heteromalla Microbryum davallianum Zygodon viridissimus var. viridissimus

Thursday, 23 January 2020

Atlas 2020, c'est tout finis

As you may have noticed, we are no longer in 2019, meaning that my favourite blog post topic, the BSBI's Atlas 2020 project, is finished. I have been meaning to write something to mark the occasion and celebrate everyone's hard work, but appallingly have been preoccupied with bryology and numerous other things this winter. However, I currently find myself becalmed in an Essex hotel, so here are some concluding thoughts on Atlas 2020 in VC23.

First, it has a been a great pleasure to receive everyone's records over the last three and a bit years. Seeing what local botanists have been up to has been very interesting and enjoyable, particularly being able to share in the excitement of unusual discoveries. I have had records from a relatively small number of regular contributors, either individuals or group recorders, some of whom have produced a considerable volume of records, as well as less frequent recorders. Many of the records that have come through me have been by email, but over the summer of last year the BSBI Distribution Database made friends with the iRecord database which gave me access to the 12,000 or so records from that source. Many of the iRecord records have been collected by a greater diversity of people than belong to the quite small circle of botanists associated with our local flora groups and the BSBI.

It is invidious of me to mention names, but special thanks must go to Tim Harrison, Jonathan Shanklin and Pete Stroh, none of whom live in the county (Jonathan and Pete live as far away as Cambridge and Peterborough, respectively) but who nevertheless spent a lot of time thoroughly surveying under-recorded areas of VC23. From the locals, we have also had regular and significant contributions from Sally Abbey, Fay Banks, Nick Barber, Brenda Betteridge, Susan Erskine, Renée Grayer, Sue Helm, Roger Heath-Brown, Frank Hunt, Clare Malonelee, Oli Pescott, Sally Rankin, Ruth Ripley, Barbara Spence and Frances Watkins. Judy Webb has been very helpful in sending me lists from her prodigious site monitoring work. Of course, as described in a previous blog, a huge contribution to the county's vascular plant data holding comes to me via my data sharing agreement with TVERC. I am very grateful to their data officer Ellen Lee for organising this, as well as to the many recorders who submit their records to TVERC, whom I am sure would be pleased to know that their records contribute to national recording projects like Atlas 2020.

Atlas records per year, excluding duplicates. Red lines are yearly number of records, on the left vertical axis, and blue lines the cumulative total, on the right. Solid and dashed lines are numbers of records with and without TVERC records.
Overall, the records gathered between 1st January 2000 and 31st December 2019 number a little over 320,800 (excluding duplicates). You can see how the records were accumulated in the graph to the left. This total is similar to most other English vice counties, being a little more than the median (~305,200) and less than the mean (~336,100). I have verified all of the Atlas records for VC23, confirming about 330,000 records (including duplicates). Questions marks remain over around 1,200, but thank you if you helped me resolve any queries.

I have shown the split between records from TVERC and other sources to highlight the importance of our data sharing agreement, which makes up more than half of the total records for Atlas 2020. This agreement with TVERC has provided a steady stream of records each year, particularly from important privately owned Local Wildlife Sites, contrasting with the more stop-start contributions direct to the BSBI. What is evident from the graph is the late start to systematic recording of the county for the Atlas project, which began I believe when Sue Helm took on the county recorder job and Atlas recording meetings were first organised. Many thanks to Sue for her hard work during her three year tenure as recorder. The spikes and troughs in the later Atlas period reflect the comings and goings of the non-VC23 based botanists thanked above.

In terms of spatial coverage and success, the county can be pleased with its Atlas dataset. This is summarised in the series of maps shown, which are stills from my interactive Atlas webmap. The project was never supposed to be a complete survey of every tetrad (2km square) in the county, but a repeat of previous hectad (10km square) national atlas surveys, based on a sample of tetrads. The re-recording rate (the coloured proportion of grid squares in the maps) is the crucial statistic for measuring progress — while there have definitely been changes to our flora, most species will still be present in most squares, so the higher the re-recording rate the more thorough and representative the sample is. The BSBI advised that a hectad re-recording rate of 70-80% should be aimed for, and this has been met for many hectads, and just about all compared to the recording period for the New Atlas (1987-1999). On the other hand, since we have no way of measuring abundance, records from too thorough a search might belie real declines, with for instance a formerly common plant reduced to a single plant both registering as present in the Atlas.

The above picture is somewhat complicated by recording effort over different periods and across taxa. The most intensive and extensive period of recording in the county was for the 1997 flora of John Killick et al, recording for which was largely complete by the late 1980s. In contrast, the New Atlas period saw less intensive recording than for the flora and the current atlas project. The difference between native and alien plants also obscures the picture, as many aliens are casual or sporadically recorded. This is well illustrated by the hectad with the city of Oxford (SP50), which has historic records of very many alien taxa from the city's old tips and waste ground. I will let the boffins at BSBI and CEH ponder how to deal with all these complications!

Drilling down to a scale more relevant to local recording, the tetrad coverage was good, indicated by the distribution, colour and size of the tetrad squares in the map shown. There were some solidly recorded areas, especially in the centre of the county, with effort thinning out to the south-east and north-west. Tim Harrison was a great help in improving several hectads in the south-east. The good results for the centre of the county doubtless reflect the very rich and varied sites around Oxford, but some recorder bias is clear, these sites also being much more accessible than in more remote areas (many are nature reserves) and this is where most of the botanists live. This includes myself, and Islip where I live (SP51H) stands out as among the most species-rich tetrads in SP51 together with the unimproved part of Otmoor (SP51R). In fact, Islip is fairly unexceptional compared with most of the nearby parishes (although there are two rivers) and many of the species I have recorded are garden escapes.

Summary of Atlas 2020 results in VC23, by hectads (top) and tetrads (bottom). The colour of grid squares is the number of species recorded (as shown in the legends), and the proportion of the coloured area is the proportion of species re-recorded from the comparison period (i.e. 1987-1999 or pre-2000). The tetrad map compares atlas records to all pre-2000 records.

After having worked so hard on Atlas, I am sure like me you are ready and rearing to start the next project. The BSBI has not yet announced the projects the society will work on over the coming years. However, it is likely that it will be something more ecology or conservation focused than Atlas 2020, for instance habitat surveys or developing site lists and registers. Myself, I'd like to direct some focus on data deficient taxa, but will be continuing the tetrad recording. The meetings I will be running this year will combine elements of these and less intense training sessions. I've already put dates in the calendar for this season — if you'd like to join me and are not already on my mailing list then do get in touch.