New Year Meeting, 28th December 2012: The Ashes of Ocknell Sling

The New Year meeting looked at the richest Ash Fraxinus excelsior site in the New Forest, the riverine woodland along the Highland Water below Lucas Castle. The aim was to record the lichen flora of the Ash trees along with the other tree species, before any potential negative effects from Ash dieback. We met at 10.30am at the pull-in by Highland Water Inclosure at the Canadian Memorial SU240093. This wood is a strip of old pasture woodland along the Highland Water with the highest concentration of old Ash trees on the open Forest. This narrow wood is nameless on maps, with lichenologists calling it either "South Ocknell Wood" or Lucus Castle but Richard Reeves, has found its old name; Ocknell Sling.

The meeting was attended by Neil Sanderson, Mark Jackson, Pat and Nicola Prince, Phil Budd, Jenny Seawright, Ginnie Copsey, Kat Evans and Andy Cross, with Neil leading and Andy keeping the list. The weather was not brilliant; grey and overcast and it had rained heavily, with the tree bark very wet, but at least the rain kept off.

We walked down the side of Highland Water Inclosure, ignoring most of the heathland lichens, but noting Cladonia rangiformis on the path edges on passing (SU239 097). Reaching the woods we were distracted by some fungi, with a tooth fungus growing out of a split at the base of an Oak causing some speculation but no conclusion. Once at the wood we started recording in square SU2409. At the beginning we looked at a fallen Beech (Waymark 1435, SU24721 09904) where Neil had spotted Buellia erubescens Nb (IR) high on the trunk new to the wood the previous January, but the bark was so wet we could not make much out. Across the path was a massive ancient Oak with Rinodina roboris Nb (IR), Schismatomma niveum, Nb (IR), Pertusaria amara f. pulvinata Nb (NR) Lecanographa lyncea Nb (IR) and a known colony of Enterographa sorediata NT (NS/IR/S41).

Down by the river we look at the first Ash pollard (Waymark 1436, SU24767 09905) by the bridge. This supported Wadeana dendrographa NT (NS/IR/S41), one of the most Ash-dependant rare species, along with Mycobilimbia epixanthoides (new to wood) and Thelotrema lepadinum along with the moss Homalothecium sericeum. Working up the river we were in an area of scattered old Oaks and some mature Ash set in younger Ash regeneration. A mature riverside Ash at Waymark 1437 (SU24761 09943) with acid bark had Thelotrema lepadinum F, Pertusaria hymenea R, Anisomeridium ranunculosporum A, Enterographa crassa LF and Cladonia coniocraea R. A Sallow nearby supported the base rich bark species Pachyphiale carneola and Normandina pulchella, an unusual find for the New Forest, where Sallow bark is usually quite acid. About here Phil Budd found a strong patch of the oceanic liverwort Saccogyna viticulosa on a bank; a rare species as far east as Hampshire and this is a completely new site.

The oceanic liverwort Saccogyna viticulosa

Further on a large Oak by riverside supported abundant Cresponea premnea Nb (IR) with Thelotrema lepadinum and a Beech at Waymark 1438 (SU24730 09975) had the lovely little ancient woodland lichen Cladonia caespiticia. Oaks also added Phaeographis dendritica, Lecanactis abietina and Schismatomma niveum Nb (IR) and Lecanora jamesii was recorded on Beech.

We then moved into 1km grid square SU2410 and started a new species list. A young Ash at Waymark 1441 (SU24683 10062) added Pertusaria multipuncta and an Oak branch on the ground allowed the recording of the canopy species: Hypotrachyna afrorevoluta, Fuscidea lightfootii, Punctelia subrudecta, Parmelia saxatilis, Hypotrachyna revoluta s. str. and Graphis elegans. A young Ash grove at Waymark 1442 (SU24665 10110) had Anisomeridium ranunculosporum, Phlyctis argena, Lecanactis abietina, Cladonia coniocraea, Parmotrema perlatum, Parmelia sulcata, Enterographa crassa, Pertusaria hymenea, Graphis elegans and Lecanora chlarotera.

Beyond this was one of the special features of Ocknell Sling; the last known surviving Lobaria amplissima Nb (IR) colony on the New Forest. This consists of a single thallus on the root buttress at the base of an old Oak (Waymark 1443, SU24647 10167). This is a very sensitive species to acidifying pollution, which suffered from even the lowish levels of sulphur dioxide pollution that effected the New Forest in the latter part of the 20th century. As is typical of stressed Lobaria amplissima at the edge of its survival envelope, the thallus is sterile and lacks the coralloid shrubby cephalodia with cyanobacteria, so has no means of reproducing. The thallus, however, was still healthy and seemed to have grown a little since it was last looked at by Neil Sanderson in 2005. Also on this tree was Pachyphiale carneola and Lecanographa lyncea Nb (IR), the latter parasitised by Milospium graphideorum [NS].

Lobaria amplissima colony

On up the river, Hypotrachyna afrorevoluta and Usnea cornuta were added for Ash and there was fertile Cladonia caespiticia on a fallen Oak at Waymark 1445 (SU24612 10211). From here on we started to get much older Ash. On one large Ash at edge of riverbank at (Waymark 1446, SU24627 10228) Neil spotted two thalli with sterile grey isidia, which had a strong resemblance to Caloplaca herbidella VU (NR/S41), a speciality of the wood, which had not been seen since 1990. Neil was reasonably confident at the time but left final decision until he could study it more, under a contract for Plantlife to research this declining lichen. On the second visit in May, with more experience of Caloplaca herbidella, the identity was still not clear. The colour and form of the isidia were acceptable, but no tiny red pycnidia could be seen and the location on the east side of the tree was unusual for this species. On the balance of probability it was decided then that, this was a bleached Bacidia biatorina and not Caloplaca herbidella. Still not satisfied with this I went back during the write up of the Caloplaca herbidella report and by careful transferring a few of isidia to tissue paper and adding K produced a K + purple reaction; finally Caloplaca herbidella s. str. was confirmed. Also on this tree were Schismatomma niveum Nb (IR), Candelaria concolor (new to wood), Enterographa crassa, unbleached Bacidia biatorina and Melanelixia glabratula.

The Ash with possible Caloplaca herbidella in May

On younger Ash here were Lecanora jamesii, Normandina pulchella, Flavoparmelia caperata, Physcia aipolia (on a branch, new to wood and rare in the open Forest), Xanthoria parietina (1 thallus on twig), Physcia tenella parasitised by Illosporiopsis christiansenii (new to the open Forest woods), Arthonia radiata, Ochrolechia turnerii agg., Ochrolechia androgyna, Candelariella reflexa, Melanelixia glabratula, Normandina pulchella and Lecanora albella (twig). On a fallen Beech branch was a fertile Flavoparmelia caperata thallus parasitised by Abrothallus microspermus [NS] (new to wood).

We stopped for lunch in the open area here. After we continued up stream, at Waymark 1447 (SU24619 10261) Pertusaria amara f. amara was added from an Ash, which had the striking fungi Cordiceps militaris near its base. On the west bank we located an ancient Ash pollard (Waymark 1448 SU24620 10321), with more Wadeana dendrographa NT (NS/IR/S41) along with Rinodina roboris Nb (IR), Acrocordia gemmata, Pyrenula chlorospila, Opegrapha vulgata, Schismatomma cretaceum Nb (IR), Pertusaria hymenea, Schismatomma decolorans and Pyrenula macrospora. This pollard had Ramonia nigra CR (NR/IR/S41) on lignum inside the hollow trunk in 1990 and 2004, so Neil climbed up and had a look inside but failed to find it.

Pollard with Wadeana dendrographa

Across the river was another old Ash Pollard at Waymark 1449 (24630 10325) with a well-known Lobaria pulmonaria colony. The Lobaria pulmonaria Nb (IR), was still present, abundant and healthy along with frequent Wadeana dendrographa NT (NS/IR/S41). Other species seen were Thelopsis rubella, Leptogium teretiusculum, Acrocordia gemmata, Gyalecta truncigena, Cladonia pyxidata and Normandina pulchella along with the mosses Homalothecium sericeum and Zygodon rupestris. In 2004, this tree still had Collema subflaccidum and Pannaria conoplea Nb (IR) as well, but in the wet soggy bark in 2012 they could not be refound, but the good news is that they were refound in small quality in dry conditions in May 2013 by Neil Sanderson.

Old Ash Pollard with Lobaria pulmonaria

Carrying on upstream an old Ash at Waymark 1450 (SU24614 10340) supported Agonimia octospora NT (NS/IR), Bacidia biatorina and Schismatomma cretaceum Nb (IR). The moss Ctenidium molluscum var. sylvaticum was nearby on ground. A young leaning Ash tree had Lecanora chlarotera, Pertusaria multipuncta and Caloplaca obscurella (new to wood) and at Waymark 1451 (SU24603 10363) and Ash with Pertusaria albescens var. corallina was searched as suitable Caloplaca herbidella habitat, without a result. An Oak had Cliostomum flavidulum Nb (NS) (new to wood) and Pertusaria hemispherica and another (Waymark 1454, SU24599 10398) had Biatoropsis usnearum (new to wood) parasitising Usnea cornuta on Oak. Further oak additions were Chrysothrix flavovirens, Hypogymnia tubulosa, Evernia prunastri, Punctelia subrudecta and Graphis elegans on young Ash. At Waymark (1455) (SU24598 10567) a large old Ash stool supported more Wadeana dendrographa NT (NS/IR/S41) and small amount of Lobaria virens Nb (IR) resulting from a translocation from an adjacent fallen Ash in the late 1990s.

From here the narrow riverine woodland widens up slope and only a small area of this Oak – Beech – Holly wood was looked at. An Oak (waymark 1456, SU24627 10663) with acid bark supported a large colony of Schismatomma quercicola Nb (IR) along with Loxospora elatina and Micariea prasina s. lat. Apart from the main group, Neil found a group of rich base-rich Oaks (waymark NAS1, SU24663 10820) with a rich assemblage including Agonimia octospora NT (NS/IR) and Porina hibernica NT (NS/IR/S41), the latter surprisingly new to the wood. A huge old pollard Oak with girth measure of c.5.24m at Waymark 1457 (SU24644 10831) added Micarea doliiformis Nb (NS/IR) (new to wood) with Schismatomma decolorans and a dead Oak (waymark 1458, SU630 10837) with soft, fibrous wood exposed added the pinhead fungi Microcalicium ahlneri Nb (NS), new to the wood. Finally a large old Oak at waymark 1459 (SU24619 10854) had abundant Rinodina isidioides NT (NS/IR/S41) some of it fertile.

This group of three oaks were the last area that we looked at in the woodland. The walk out took us west and then along the high ground near the A31. Neil pointed out that we walked through the last remains of a plateau woodland, a woodland habitat that is scarce on the Forest.

Finally in an old WWII gravel pit in the heathland we looked at a lichen rich heath in the gathering dark and recorded Cladonia subcervicornis, Baeomyces rufus and Dibaeis baeomyces at waymark 1460 (SU23808 09789).

We recorded 74 taxa from the woodland and noted an additional four lichens on the heath. Of the woodland taxa, 10 were new to the wood and one lichen fungal parasite was new to the open Forest woods. The list scores 24 on the NIEC index (southern oceanic ancient woodland indicators), with 6 RDB species, one Vulnerable species and five Near Threatened species (five of these Section 41 species (AKA BAP species)) and 15 Notable species. See species list.

Ash was clearly important to the lichen diversity of this wood, although many species were also found on Oak. Species of particular importance only seen on Ash were Lobaria pulmonaria Nb (IR) (has been recorded from Oak in the wood but not refound recently), Lobaria virens Nb (IR), Caloplaca herbidella s. str. VU (NR/S41) and Wadeana dendrographa NT (NS/IR/S41). For the larger leafy species active translocation to Oak may be mitigation against Ash dieback impacts, but the crust-forming species are likely to be lost if the Ash are lost. Of all the species that we looked at, the future of Wadeana dendrographa is intimately tied to how Ash dieback plays out; if the predicted impacts of the disease come true, it’s not looking good for Wadeana. The Caloplaca herbidella s. str. colony is one of only two refound in England in a recent survey, but at least the other (in Savernake Forest) is on Oak.

The route taken can be viewed on Google Earth by downloading the KMZ file and can also be viewed as a picture by clicking on the link below.

Andy Cross & Neil Sanderson