Onllwyn Coal Tips

 A few days ago, in dismal conditions, H and I spent an hour strolling around an area of reclaimed coal tip in Onllwyn (Dulais Valley). Coal tips often support ecological mosaics of calcifuge and calcicole plants and their physical and mineral characteristics are interesting. The Onllwyn bryophyte community was remarkable for its large proportion of base-loving species; e.g. Calliergonella lindbergii, Campyliadelphus chrysophyllus, Ctenidium molluscum, Didymodon ferrugineus, Ditrichum gracile, Encalypta streptocarpa, Fissidens adianthoides, Tortella tortuosa, Trichostomum crispulum. We also noted a nice patch of Climacium dendroides.

Calliergonella lindbergii

Campyliadelphus chrysophyllus

Climacium dendroides

We usually pick up Campyliadelphus chrysophyllus as scattered individuals along tracks (often associated with Didymodon ferrugineus), but here it was present in fairly dense patches. In fact, at first I wasn't sure whether it was Campyliadelphus or small Campylium protensum. The costa in Campyliadelphus leaves is really difficult (for me) to see in the field, but later microscopic observation confirmed it.
The steep, wooded side to the coal tip had a more eclectic, luxuriant pleurocarp mixture with Eurhynchium striatum, Hylocomium splendens, Loeskyobryum brevirostre, Pseudoscleropodium purum, Rhytiydiadelphus loreus and R. triquetrus, a fairly typical community for wood and scrub on reclaimed coal tips in NPT.
Coal tips are nitrogen deficient habitat. Their ecological remediation and reclamation often involves planting nitrogen-fixing  trees, shrubs and herbaceous species in order to enrich the soil with combined nitrogen, e.g. legumes such as clovers and Sainfoin and non-legumes like Alders and Sea Buckthorn. In the last few years research into the nitrogen input dynamics of northern boreal forests (also fairly nitrogen deficient ecosystems) has revealed fascinating associations between moss species such as Pleurozium schreberi and Hylocomium splendens and free-living cyanobacteria (e.g. Nostoc) in loose 'symbiotic' nitrogen-fixing relationships. In these relationships the N-fixing cyanobacteria do not appear to integrate themselves into the tissues of these mosses in the same way as they do in the cavities found in certain liverworts (e.g. Blasia pusilla) and hornworts (e.g. Anthoceros agrestis). The reason I mention this is because some of our moss collections from Onllwyn had significant amounts of free-living colonial cyanobacteria (probably Nostoc spp.) associated with them (see photo below of colony found intermingled with Ceratodon purpureus).

Filamentous cyanobacterial colony associated with Ceratodon purpureus

The colony in the photo contains lots of heterocysts, (the larger, colourless cells in the filaments), which is where N-fixation takes place in the colony. I'm sure that most of you have observed cyanobacterial colonies like this among your collections from time to time, so I thought that it might be of interest if we occasionally note species and habitats where such associations occur in South Wales. Other nitrogen deficient habitats where you might observe this are heathland (e.g among Pleurozium and Hylocomium), bogs (among Sphagnum spp.), tarmac, and perhaps epiphytic habitats.

To put this into perpesctive, the mineral nitrogen input from the moss-cyanobacteria associations into northern boreal ecosystems is at least equal to that which comes from the atmosphere -  it is a very significant contribution.