“Non-native” species are usually considered to be, at best, a bit of a pain. In many respects we are pretty lucky here on the Dee, that we only really have one unwelcome non-native plant species, Crassula helmsii (Or New Zealand Pygmyweed). Our colleague Ash, at Woolston Eyes, has much more to deal with; balsam, knotweed, Giant hogweed... (he may blog this about soon).
We may only have the one to contend with, but its one heck of a problem! Crassula is a plant that grows on wet grassland/mud/shallow flooded areas – so Burton Mere Wetlands is a perfect area for it! We try to manage the reserve to have as much mud as possible to feed the large number of breeding waders, but in recent years, this area has been taken over by Crassula. It simply chokes the mud and water bodies, severely reducing the feeding opportunities for birds. It is spread so easily – you only need a tiny bit on your boots, and it can grow on – it will even propagate from geese poo. We take great care not to spread it around, but we can’t stop the birds from doing that!
This area should be mud. The light green area is all Crassula (A. Grubb)
We try to limit its spread on the reserve, by spraying it with pesticide. This works quite well, when it is fairly thin, but when it gets to a thick matt, we simply just kill the top layer and it keeps growing from beneath. As the job is so large we try to target areas where it is most important, such as the scrape, the wet grassland ditches. Then we try to limit its spread on the larger areas such as Marsh Covert flood and Centenary Pool. As we spray it over the next few weeks, you should see it turning brown and dying off.
Content Cows (A.Grubb)
In the past couple of weeks though, we have had some very welcome “non-native” visitors... The Cattle! There are currently 50 cattle grazing away on the wet grassland, partaking in some essential habitat management. They are essentially living lawn mowers, grazing away at the vegetation all summer long. The aim is to get the grass length (sward) down to a suitable level for breeding lapwing and redshank. We could just mow the whole area, but the beauty of getting the cattle to do it is that they provide a much more diverse “sward structure” – by grazing some areas harder than others, they give nice short areas for Lapwing, and leave thicker areas, which favour redshank. ANd they break into areas that would be too wet to get a tractor... trust me. I've tried...
Stuck tractor (A. Grubb)
Cattle grazing also strips away most of the nutrients in the grassland, which increases the “floristic diversity”: If we just mowed it, the grasses would have plenty of nutrients, and simply out compete the flowers. Having grazed the area for many years now, the flowers out there are simply stunning! Vast swathes of red clover, red bartsia, common fleabane, camomile... And they’re all alive with insects feeding away.
A. Grubb
This photo shows how fantastic the display of poppies was out there this year – better than ever before. For the first time this year, we found Yellow Rattle out there too. This is particularly exciting as it parisitises on grass, giving the herb species even more chance.
The cows are slightly restricted at the moment while we spray the Crassula, but once this has been done, they will have full reign over the wet grassland, hopefully attracting in Cattle egrets as they did last year.
We also plan to have a small number of cattle grazing the old part of the reserve (IMF1) too this year. This will be good, as they should penetrate further in to the rushy areas and help to control the spread of this.
As always, if you have any questions about reserve management, please email me at alasdair.grubb@rspb.org.uk