After the Rhodies have 'gone'

Following the clearance of blanketing thickets of Rhododendron in parts of Cwmdulais a few years back, I have made a few casual records of what has been recolonising. The only lower plants (which currently provide the bulk of the ground cover) noted in a small sampling area during a casual Christmas Eve stroll, were (in decreasing levels of abundance) Campylopus introflexus, Cladonia chlorophaea agg., Dicranella heteromalla, Hypnum cupressiforme var. cupressiforme, Polytrichum juniperinum, Cladonia coniocraea and Dicranum scoparium. Clearly there is more diversity than this in the valley (see my previous post HERE on this subject), but to date recolonisation of cleared Rhododendron in the valley has been by a rather limited suite of species. Needless to say the Rhododendron is showing good signs of recovery!

A small, mildly basic flush at SN61730358 did provide a point of interest amongst this predominantly acid tolerant vegetation, with species noted (again in decreasing levels of abundance) including Dicranella varia, Riccardia chamedryfolia, Aneura pinguis, Cratoneuron filicinum, Didymodon fallax, Philonotis Fontana, Didymodon tophaceus, Didymodon insulanus, Pellia endiviifolia, Pohlia wahlenbergii var. wahlenbergii, Bryum pseudotriquetrum & Pseudocrossidium hornschuchianum. I'm not sure if this vegetation comprises recent colonists or was hiding beneath the Rhodendrons prior to clearance?

Coal spoil at Penygroes

A total of 60 bryos were recorded growing directly on coal spoil at this development site in Penygroes, vc44. Most interest was focused on the mildly basic 'Cratoneuron filicinum-Bryum pseudotriquetrum' seepages found around the margins of the site, with noteworthy species including Bryoerythrophyllum ferruginascens and Palustriella falcata. Both were rare on site and it's the first time that I have encountered the latter on spoil, the location of the only patch I saw shown below. 

The central plateau was much less interesting, being dominated by Campylopus introflexus and Lotus corniculatus, which together with locally frequent Cladonia spp. formed a distinctive coal spoil community.

An odd Campylopus introflexus site

Another example of the remarkable colonising ability of C. introflexus. I noticed a small patch of it near the office in Swansea yesterday, apparently growing directly out of the mortar on the shaded site of a stone wall. On closer inspection, it was growing on some well rotted organic material - probably an old rhizome of polypody or another fern.

Campylopus introflexus (Heath Star-moss)

Campylopus introflexus (Heath star-moss)

You may have ambivalent feelings for this alien bryophyte, but it is rather beautiful and it has a remarkable natural history in Britain. Its native range is in the southern hemisphere where it is represented in Australia, South Africa and South America. It was first recorded in Britain in Sussex  in 1941, perhaps arriving with horticultural imports. It remained unfamiliar to British bryologists in the 1950s -   it wasn't included in the first edition of Vernon Watson's 'British Mosses and Liverworts', but now it is one of the most common bryophytes in Britain, In fact in an article I wrote for British Wildlife a few years ago I suggested that it was the most successful alien plant in the British Flora. I still stick by that, because its range expansion in just 70 years is truly remarkable. How has it been able to do this?  Two of its attributes have given it an enormous advantage as a recent colonist. Firstly it has very wide ecological tolerance in terms of climate, soil reaction and substrate. It can colonise peat, gravel, coal spoil, mine spoil and, under suitable conditions, sand, slate and rock. It seems fairly indifferent to soil pH. In Denmark it is one of the most successful colonists on calcareous grey dunes. and, closer to home, it is one of the first colonists of the bare peaty ground that is exposed after Sitka Spruce is clear-felled or when heathland is burned. Secondly it has a formidable dispersal strategy. It often produces abundant fruit (even though it is dioecious) and the small spores (10-14 microns) are capable of dispersal over huge distances. As an example of this, plants had colonised the Faroe Islands before they were recorded in mainland Scandanavia. It has conquered western Europe and it is galloping across central Europe as we speak! And it has already made significant inroads into North America. Local dispersal is also very effective via broken leaf tips, a strategy not very different to that used by other Campylopus species.
Campylopus introflexus is a primary colonist capable of smothering large areas of bare ground, so I guess it must have an impact as an alien. But I'm not aware of any meaningful studies that have been undertaken to measure its affects on native bryophyte biodiversity. I love the way the capsules are buried in the leaves (again like other Campylopus species) and the fascinating movement of its hairpoints - when plants dry out you can watch it happening. I presume the deflexed hair points help to decrease the short-wave radiation load in hot weather. Who knows. Just because we can now land a fridge on a comet 350 million miles away, we shouldn't stop asking these little mossy questions.