How to Rewild

Calcareous Grassland

Habitat Management Plan

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Calcareous Grassland
Habitat Guide

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Calcareous Grasslands are some of our most wildflower-rich habitats, but they are also fairly uncommon, on calcium-rich soils with a pH over 6.5. These grasslands are maintained in modern times by grazing – typically with sheep, and often influenced by the presence of rabbits. Neither of these animals are native, and in the past, it is likely that wild ponies and aurochs would have been the original ‘lawnmowers’.

The well-drained, nutrient-poor soils here overlie limestone, and calcium- or base-rich rocks like shales and dolerites. This creates poor conditions for plant growth, which leads to high competition, and so a high diversity of wildflowers. These in turn are host to a high abundance of invertebrates, with some threatened bird species also relying on the habitat. With patches of bare ground, this grassland is often ideal for reptiles, which use the exposed rock and earth as basking spots.

Sub Habitats

Grassland on soils with a pH above 6.5 on land under 300m in elevation and a characteristic mix of plant species. This is typically found on limestone hills and clifftops.

Grassland on soils with a pH above 6.5 on land over 300m in elevation and a characteristic mix of plant species. This is typically found on limestone hills and around exposed geological features.

Grassland on soils with a pH above 6.5 on land, which is typically lower in quality than the above habitats and not meet their strict species criteria (see the UKHab website).

Value

Compared with our other grassland types, this habitat can be extremely diverse, with 40 species of plant per square metre in some areas. This rich variety of plants creates an abundant and diverse community of invertebrates, including rare, specialist butterflies and bees. With such a varied collection of plants, there is a lot of diversity from one location to another, depending on soil type, climate, grazing pressure etc. This makes it more important than ever to get a survey of species, and identify any which might thrive under particular management regimes.

On highly-grazed sites, where livestock have exposed the rock or subsoil, these patches of bare ground are valuable basking sites for reptiles. However, high grazing pressure creates poor conditions for ground nesting birds, wildflowers and ants. Ant nests are often found across this habitat type, and their presence creates tussocks, increasing the structural diversity at ground level. Higher up, the presence of scrub can be extremely beneficial. In some areas, Juniper Scrub may be found – a specialist of nutrient poor soils, which tends to favour Calcareous Grassland.

Calcareous clifftop grassland
On thin clifftop soils over limestone and chalk rock, the soils may be 'base-enriched', allowing Calcareous Grassland to become established.

Protect

Calcareous Grassland is less common now than it was in our recent past due to shifts in farming practices. Habitats have been enriched with fertiliser, ploughed over, lost to scrub encroachment, quarrying and development. However, climate change is less of a threat here than in other grasslands, as the habitat is relatively drought-resilient and winter rain has only mild impacts on the fairly free-draining land.

The main threats to this habitat are encroachment of scrub or woodland, and enrichment from fertiliser and atmospheric nitrogen. Scrub encroachment typically happens when livestock are removed – though some amount of scrub can be beneficial, creating a more structurally-diverse habitat. When managing this habitat, avoiding overgrazing means being aware of the presence and impact of rabbits. While they individually leave little trace, dense populations may be as effective as larger livestock in maintaining a wildflower-rich grassland. Rabbit populations can fluctuate significantly though, due to factors such as disease (e.g. RVHD) and predation. 

Cattle are usually a better option than sheep, as they browse less selectively, creating a more diverse sward. Their hooves and activity also creates bare patches and tussocks which are ideal spots for wildflower seeds to germinate, and for reptile basking. The closer you can get to the ancestral wild aurochs, the better – these habitats have evolved alongside bovids (cattle), rather than ovids (sheep).

It is important not to remove grazers altogether, as they will maintain a variable sward height, which is essential for much of the community (plant, invertebrate, bird and reptile) dependent on this unique habitat. Fertilisers will increase the dominance and density of grass, and the sward height, turning this habitat into low value Modified Grassland. Grazing at low density is more suitable than mowing, and should take place from mid-July throughout the colder months until April, allowing a rest period without grazers for flowering and seeding.

Grazing creates a more variable grass height, but if mowing is the only option, it should take place once per year in September. Cut grasses should be raked off, and used offsite as hay, to avoid a build-up of nutrients and smothering wildflower growth. More regular mowing will lead to more vigorous grass growth.

Take care of grazing activity near streams and springs, to avoid nutrient pollution from dung. Buffer strips can be a useful strategy, especially on slopes where water easily runs across the ground. Our most diverse watercourses – chalk streams – often arise in calcareous grasslands, and improving their water quality will have huge benefits for biodiversity downstream.

Fern on scree slope
As alkaline scree slopes and other exposed rock succeeds to grassland, scattered ferns develop into a more vegetated grassland habitat.

Restore

Calcareous Grassland may have reverted to Modified Grassland if fertiliser has been added over time. This will have created a lush, tall sward that is likely to become overgrown with agricultural weeds like thistles, ragwort and dock when mowing or grazing ceases.  Restoring Modified Grassland back to Calcareous Grassland is possible, but difficult, and the method depends on the extent of modification. If the soil pH has become neutralised, then liming may be a quick fix that could mitigate the issue.

All of these methods involve knocking back vigorous grass growth, as grass outcompetes wildflowers. Grass typically grows faster on ground with high levels of fertiliser. Fertiliser contains multiple nutrients – nitrogen (N), phosphorus (P) and potassium (K); to get back to a diverse grassland habitat, we’ll either reduce their concentration or make it harder for plants to access them.

1 – Removing Inputs

Artificially high levels of nutrients in the soil will naturally decline over time, as they wash out and are taken up and ‘locked away’ in plants. That’s why farmers must re-apply fertiliser every year. So, one of the first things to tackle is removing any artificial inputs. This includes supplementary feeding of livestock (e.g. grain troughs) and runoff from neighbouring farms. By avoiding fertilisers/muck-spreading, stopping supplementary feeding, and preventing incoming runoff, you should see a slow decline in soil nutrients. However, it is possible that there may still be another input which hasn’t yet been identified, like high atmospheric deposition, enriched floodwater, or even dog excrement!

2 – Sowing Hemiparasitic Plants

These plants attach to the roots of grass and suck nutrients out directly, reducing the vigour of the grasses. But these short plants do poorly in habitats with a tall sward, as they only thrive when they can get enough light. So, managing the habitat with grazers and/or mowing strategically, to avoid chopping them before they set seed, is necessary for successful establishment. They also need bare soil to germinate, so scarifying the grass before scattering seed gives them a good head start. Eyebrights are an example of hemiparasitic plants which thrive in calcareous soil.

3 – Grazing

In general, grazing your land with livestock should reduce nutrient levels over time, for a few different reasons. The animals will excrete nutrients into the soil, where they are washed away, and nutrients are released as volatile compounds into the air; they’re removed in animal products like wool and milk; and also in their meat. The overall impact varies a lot depending on the livestock, site, soils, climate etc. This method is slow but steady, and creates biodiversity along the way, as the grassland will be more varied in height than if you use a mower. Grazing also has the added benefit that it ‘masks’ the effects of nutrient-enrichment – livestock prefer eating taller, dominant plants like grasses, allowing shorter wildflowers to get established, provided that the area isn’t overgrazed.

4 – Mowing

Over a decade or two, you’ll find that consistent cutting and removal of hay should reduce the available nutrients in the soil and create a more diverse grassland community. However, in the short term, frequent mowing can create more vigorous grass growth, especially if the ground is rich in nutrients. Mowing can also remove plant seed heads before they have a chance to scatter onto the soil. It’s a balancing act, finding the right timing and frequency – twice a year is typically recommended for nutrient-enriched sites. The hay must be removed each time, to prevent a steady build-up of nutrients and choking-out fresh growth.

5 – Rooting

Fertilised grasslands, and those which have been intensively grazed or mown for a long time are very resistant to change. The sward will have become dense and matted, and it will take many decades to ‘reset’ this habitat. We can help this process along by introducing pigs, which turn over the turf in patches, just like our native Wild Boar. This knocks back the grass and allows seeds below the soil to germinate – it is likely to lead to a flush of agricultural ‘weeds’ at first. These will add structure and biodiversity, and are eventually succeeded (with regular grazing/mowing) by a more diverse collection of wildflowers and grasses. Without pigs, we can have a similar, though slightly less effective impact, using a rotavator. Note that this process – with or without pigs – leaves the grassland tussocky and uneven – it’s great for biodiversity, but not for recreation.

6 – Soil Stripping

Nutrients are concentrated in plants and the topsoil, so we can strip off this top layer of turf to solve the problem. But even if this is achieved, there will be a significant medium term carbon footprint, and it will likely lead to runoff, soil compaction and loss of plant diversity. Removing strips of soil in rotation, will allow plant seeds and the soil community to transfer slowly from healthy grassland to recovering bare ground. While this method is very destructive, it is the only proven system for significantly reducing nutrients in one shot.

Aftercare

If you’re restoring Calcareous Grassland from Modified Grassland, you’ll also want to restore the unique plant community. This may return naturally from the seedbank in the soil if the habitat has only recently become degraded, but if this doesn’t happen, then green haying is also an option. This involves taking a cut of a healthy Calcareous Grassland meadow nearby and spreading the arisings on your land to transfer the seed. Bear in mind that the community of wildflowers tends to vary a lot from one location to another. And this will only spread plants which have seed heads at the time of the cut. Habitat Aid and Emorsgate Seeds also offer locally-sourced mixes of meadow seeds which are appropriate for your soils, that are typically sown on scarified grassland.

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