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The Tale of the Crassula Coffins

Posted: Wednesday 29th November 2017 by LowerAireValley

Crassula removal on The Lines WayCrassula removal on The Lines Way

Yesterday it was time to have a trip down to one of our more unusually shaped reserves, The Lines Way.

This site is very much a nature corridor as it intersects several other sites across it’s 4 miles of disused train line, which used to form part of the ‘Bowers Junction to Garforth’ section of the old Leeds, Castleford and Pontefract Junction Railway, closed since 1969!

Wandering travellers can take their pick of nipping into Letchmire Pastures, Hollinhurst Wood, Owl Wood and Pit Plantation or Townclose Hills along the way, but this rather narrow reserve still provides opportunities for a bit of nature spotting itself. The few ponds dotted about it’s length share some of the more interesting inhabitants, as well as being home to a rather, shall we say – boisterous - inhabitant.

This particular pond-dwelling inhabitant, Crassula helmsii hails all the way from the other side of the world, as indicated by it’s common names; New Zealand pigmyweed or Australian swamp stonecrop, and it is the cause of much raking and squelching through mud to deposit in what is known to us as the ‘Crassula coffin’. You know things have gotten serious when coffins enter the equation, but this is a dual use coffin, which also (fittingly) inflicts death upon the occupant, or so we hope!

The name Crassula might ring a bell to some, as the genus is home to benign species such as the jade plant and many other popular succulents (crassula is Latin for thick, referring to the succulent leaves). Fear not, none of these will require a DIY Crassula coffin, but Crassula helmsii is something of an outlier, (as many things from Australia are) and it is a serious threat to our native freshwater habitats, which the ponds along The Lines Way show. First noticed lurking in the wild within ponds of the New Forest in Hampshire in 1976, it threatens native wildlife by forming characteristically dense, impenetrable mats within ponds, lakes, reservoirs, ditches etcetera – it isn’t particularly fussy. This ends up excluding our native aquatic species by reducing areas of bare ground by which they might be able to colonise, and percentage species cover of Crassula can reach all the way up to 100%, so it’s serious business.

Add in the fact that it can reproduce from tiny fragments and you start to see the need for our Crassula coffins. These are essentially a long rectangular wooden frame which we heave the Crassula into, and then cover it with a dark fabric to deprive this invader of light so that fragments of all shapes and sizes perish. This ultimatum arrives after the difficult business of donning your wellies or waders and wobbling around in pond mud with a rake to claw back it’s advance into the pond, then wiggling a pitchfork into the pile of green spaghetti to carry it to a gloomy demise in the Crassula coffin.

Our efforts were given a nudge as the adjacent pond still bore the signs of the previous year’s Crassula raking efforts. This shows that this naughty little pigmyweed can be managed to an extent with simple methods, and hopefully future efforts will be similarly effective, and in this way we can limit the spread to other sites in Kippax and further afield.

This form of practical conservation must have looked odd to the many passing by The Lines Way yesterday, although it didn’t deter that bold little red-breasted robin from flitting about our coffin with an eye for creepy crawly morsels, as they are wont to do.

The moral of this story, as with many of the Invasive Non-Native Species (INNS), is not to release new species into the wild unless you have a particularly good reason; as in the case of Crassula, it was sold as an ‘oxygenating’ plant for aquariums, and consequently this is one way in which it has likely been spread, via improper disposal. Life goes on however and attempts are underway to uncover new and potent techniques for managing INNS such as New Zealand pigmyweed, and we still managed to scoop up and relocate a few frogs up that were lolling about the pond (they’ll be right as rain in the surrounding woodland).

So if as you wander along The Lines Way and happen to spot a curious cuboidal contraption close by the ponds, you can tell fellow onlookers the curious tale of the Crassula coffins…

Peter Gurney

Lower Aire Valley Trainee


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