Stemming the tide

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Cattle in a sea of thistle

 

Thistle is the bane of my life. It used to be cows but the focus of my rage and annoyance has shifted. After our epic fencing work in early spring, we have had one bovine Houdini who managed to limbo through an old section of fence but otherwise, fingers crossed, we have had no escapees. 

When you look out across the main marsh, it is fairly evident that there is a good deal of thistle. Forming thick stands it will start developing a purple haze over the marsh in the next couple of weeks as it comes into flower. This is great for many of our invertebrate friends, providing plenty of nectaring opportunities and for the Goldfinches that flock in their hundreds in winter to feed on the seed heads. The problem is that it is getting out of control and muscling out the other plants. The cows, quite rightly, won’t touch the stuff and therefore neither will the geese, wigeon or other species that depend on a short, grassy turf to sustain them through the winter. 

It is vital, therefore, that we try and stem the tide of thistle on the main marsh. Unfortunately for me this means sitting in a non air-conditioned tractor, slowly topping the worst areas. This is not only painful because of, without being overly dramatic, the oven like conditions that I have to sit in but because it has to be done with the utmost care so as not to mow over any nesting birds.

The key to effective topping of thistle is timing. Get them before they go to seed so they don’t spread but late enough so most of the birds have fledged and are running around. This is tricky when species like skylark have several broods in a season. Lapwing however only have one but can be late. This means that I have spent a lot of time monitoring them throughout spring and early summer. I have a handy map where all the territories are and they can therefore be avoided. Skylarks and meadow pipits are a bit tricky but they tend to fly off their nests when disturbed. So before I go to top an area, I spend 5 minutes or so thrashing around and watching for anything to fly up. If they do, I make a note and avoid that area, hopefully missing any nests.

Unfortunately I may hit one. I am not aware that I have yet and would be devastated to find out if I did. But, you have to weigh it up. If I don’t top, the marsh will steadily become more and more unsuitable until eventually wintering birds will suffer and nesting birds will have a much harder time. If I batter back the thistle over the next few years, the amount of topping needed will steadily reduce.

As I mention in most of my posts, it’s all about balance.

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Swamped by Mediterranean gulls and black-headed gulls whilst topping

 

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A little bit on grassland management

DSC_0846If 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.

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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.

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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.

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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.

A Helping Hand

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The lapwing have been nesting across the marsh, as have a number of other ground nesting species such as redshank, skylark and meadow pipits. They are very vulnerable at this time of year and so we do a few things to help give them a helping hand.

I’ve had a few questions recently about some of the things that we have done so I thought a blog post may help answer some of these questions. The main one that has come across is to do with the spikes that we have put on many of the fence posts around the main marsh. These are to deter avian predators such as crows, buzzards and magpies from perching all day and scanning the site for vulnerable eggs or chicks.

There has been some very nice studies produced that show the effect of vantage points on nesting success in ground nesting birds such as lapwing. One study saw that lapwing would not nest within, on average,  50 metres of a potential perching point. Therefore to maximise the number of territories within a site you have to deter birds from perching on all the very convenient posts that we have placed for them with our fencing.

We have had to look at natural vantage positions as well. Hedgerows with standards and high points act in the same way, allowing predators to comfortably sit and observe. This in mind, we dropped the height on many of the hedgerows in strategic places around the main marsh. This will be a staged approach where we will do some each year so that there is still plenty of nesting opportunities for species like sedge warbler and whitethroats but within a few years we will have all the hedges at a manageable height. Most of the work that we have done, the hedges are still bulky enough to have birds nesting in any way.

The next step is with the cattle. I have put in 36 cows into the main marsh. This is a fine balance between having too many and increasing the chance of squashing a nest and having too few and the grass be too long for the chicks to feed. Lapwing chicks need areas of short vegetation to feed on, gleaning invertebrates off the surface.

It’s an important balance that needs to be struck. Do you dissuade all predators across the site? Do you leave a natural level? What is a natural level? What you have to bear in mind is that when natural levels of predators existed there was a much more natural coastline where sites shifted and changed each year with coastal erosion and drift. This means that there were many more places for these bird species to nest. Now there are very few and Farlington Marshes nature reserve represents an important site in the area. A bad year here has significant effects on numbers in the area.