Crassula Invasion

Not only is this invasive weed at Parc Slip but it is also infesting two out of three remote ponds at our newest west Glamorgan reserve, the Dranges.

Paul and Crassula filled pond

Paul and Crassula filled pond

This job became a priority due to the need to attempt to get the weed under control before the growing season and also because of the pretty heavy vegetation clearance we needed to do to gain access to the ponds and we needed to get that done before bird nesting and also we wanted to get the areas covered before spawning of frogs and toads took place to reduce the impact on them. 

It has redirected our efforts away from woodland management and now as the sun shines bright we will only return to woodland management to tidy some log stacks.

Crassula is an invasive non-native which can quickly dominate a water body and is spread by fragments of the weed taking root, has been found in two of the three ponds in the Cheesefield. The bankside vegetation was desperately in need of management anyway so we have focused on clearing about 30-40% of this this week to benefit the pond habitat and big habitat piles have been created as potential grass snake egg laying sites.

Covering a crassula filled pond with a UV filter

Covering a crassula filled pond with a UV filter

The task of covering the crassula with UV proof membrane was completed on 7th March 2014, this is a recognised way in which to begin eradication. The next move is to get the appropriate permits to treat it with herbicide. For this the weed needs to be exposed so the pond will be drained down with pumps. Particular care needs t be taken when using herbicides in waterbodies, not only so as not to contaminate ground water or pollute downstream but because too much decomposing vegetation at any one time in a pond or river can cause serious oxygen depletion in the water .

Currently less than a quarter of the area of the ponds is infested so herbicide treatment will be fine and to not take action is not an option. A small isolated area of crassula in the second pond is going to be hand pulled, we will assess this methods effectiveness. A big thank you to the volunteers who helped with this job. Without their help it would not have been possible. 

UV filter in place covering the Crassula

UV filter in place covering the Crassula