If you have been to either Farlington Marshes or Southmoor nature reserves you will have noticed that last month our furry lawnmowers appeared. Cattle are now used extensively in conservation to graze sites to achieve the specific goals that are needed. In most cases this is to maintain grassland/heathland in a perpetual state of suspended animation.
This is essentially what most conservation management is. You halt succession at a designated point that achieves certain goals for that site. This may be a flower rich grassland, grazing to stop woodland from establishing. It may be even earlier in the successional history, maintaining lichen rich heaths, early pioneering stages of habitats. It could also be for specific species, mixed height heathland for nightjars and woodlark for instance.
The ins and outs and rights and wrongs of this type of management and the persuasion towards a more ‘natural’ management scenario is a topic for another post. This one really is for looking at how we graze our sites and why we do it.
From Spring until late Autumn, Farlington Marshes and Southmoor are grazed. The numbers are built up steadily until a peak in June/July when there can be as many as 200 on the main marsh. The overall aim is to get the grass nice and short for winter when the brent geese arrive and need somewhere to graze. Their short bills are perfect for tearing at grass up to 5cm. That’s why you see them on sports pitches so much.
You can’t however just shove 200 cattle on at the end for a few months, there are other aspects to look at, mainly our breeding birds. Lapwing, redshank, meadow pipit and skylark all use the main marsh areas to breed in. They need to have a mixture of short and long grass to feed and nest in. Too long and the young chicks won’t be able to find food easily. Too short and the nests will be easily found by predators. This means that a low number of cattle through their breeding season should provide a mosaic of sward heights, (or if you want to be fancy, structural heterogeneity).
If you overstock it, you run the risk of the nests being trampled. A rather good study looking at skylarks found that a density one cow every 3 ha has minimal effects on breeding success. This needs to be balanced out with the weather conditions. If you get a really hot spring with frequent rain, the grass will shoot up and you will need some more cattle to obtain the correct height and vice versa for a cold, dry one.
In a way Farlington is more like farming than many of my other sites. The overall picture is more about grassland structure rather than floral diversity, though the grazing method produces some excellent diversity on top of it being quite an interesting grassland anyway (coastal grazing marsh and transitional salt marsh). Other sites such as Swanwick Lakes and Hookheath nature reserves are grazed very differently. Cattle come on in July for a few months, leaving around October. This has a much better effect on plants as they have mostly gone to seed by this point and then you are removing the main bulk of the vegetation slowly. This benefits invertebrates by not being as sudden as cutting by machine. It also means that there are more flowering plants throughout the summer for invertebrates to take advantage of, hence why both of these sites are so good for butterflies.
Grazing isn’t the be all and end all though. Last year for instance I supplementary cut two meadows at Swanwick as I felt that the cattle had not eaten enough and over the years a thatch had developed. This is a layer of tougher grasses that stop other plants from growing up. I therefore had it cut and the cuttings removed. This will hopefully allow more flowering plants, especially annuals, to grow this year. Hopefully the effect of the cutting will not have detrimentally affected the invertebrate population. You do however need to balance out the effect of cutting with the benefit of having more flowering plants, as the more of these you have the more inverts you will ultimately support.
So you’ve looked at your site, thought about what you want from it, decided on the stocking density (the number of cows you need to do the job) and the length of time and time of year. Great, shove them on and let them do their stuff. It doesn’t however stop here. You get plants in all swards that become dominant and these tend to be the ones that are unpalatable or super tough. Creeping Thistle is a big problem at Farlington and has a hold on a big section of the main marsh. This has to managed separately to the grazing by cutting it with machinery before it sets seed, preferably a couple of times. Hookheath has a lot of hemlock water dropwort which is a bit of a brute on wet pasture. This is managed in the same way, cut back after the cattle have done their bit.
So, grassland management is a complicated beast as no grassland is the same, all have different facets to the sites that cause things to grow differently and a slight stray from the optimum management can have long lasting negative effects. If you churn up the ground in winter, for instance, you can ruin the soil structure which affects the sward for years to come. Managing the cows themselves can be an absolute nightmare – they escape, get ill, get stuck, give birth when you least expect it. That all said Hampshire has some amazing, hugely rich and diverse grassland sites, with colleagues at the Wildlife Trust doing excellent work on many of these (Winchester area and South Downs have some incredible grassland). So as we go into summer, get out there and take a look.
A big thank you has to go out to all our volunteer wardens and lookers, across the whole Trust who keep an eye on our cattle whilst we have them. We couldn’t do it without them.