How to Rewild

Acid Grassland

Habitat Management Plan

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Acid Grassland
Habitat Guide

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Acid Grassland has relatively low biodiversity, but it is an important breeding habit for ground-nesting birds, reptiles and some invertebrates. The low grasses on acid soils are maintained by grazing, and without livestock, this habitat quickly succeeds to Bracken and Heathland. 

In today’s landscape, large expanses of Acid Grassland are managed by hill farmers, but in the past, wild ponies and aurochs would likely have created a patchwork of grazed lawns, heathland, scrub and woodland in these same areas.

With well-drained, nutrient-poor soils which may overlie gravel, sandstone or igneous rocks, the vegetation cover here can often be patchy, with areas of bare ground, lichen, fungi and mosses. The habitat may at first appear degraded, but it can support a high level of invertebrate diversity in summer months.

Sub Habitats

Grassland on soils with a pH below 5.5 on land under 300m in elevation. This is typically found on heathland or cliffs. 

Grassland on soils with a pH below 5.5 on land over 300m in elevation. This is typically found on heathland, mountainous landscapes and on the edges of bog habitats.

Grassland habitats dominated by the perennial fern, Bracken, which shades out other vegetation and deposits nutrient-rich leaf litter.

Value

When any kind of Acid Grassland becomes dominant in a landscape, it tends to create areas with relatively low diversity. This is due to the low structural diversity of the system, and the grass-dominated community with relatively few wildflowers compared to Calcareous Grassland. But the main benefit of Acid Grasslands are that they are often found in a mosaic structure, alongside Heathland, Bracken, Wet Woodland, Upland Oakwoods and similar habitats. Here, they create valuable open areas, which are used for reptile basking and hunting, bird and invertebrate foraging, and bird nesting.

Acid Grasslands may also be a fungi hotspot, with Waxcap Grasslands a threatened habitat in the UK due to the decline of traditional grazing practices and the enrichment of upland soils.

Bracken tends to have a negative impact on local biodiversity, as the leaf litter smothers wildflowers and enriches the soil. This habitat can be dangerous for land managers and walkers due to the abundance of ticks, which in many areas now carry Lyme disease. However, in a mosaic landscape, it can provide cover for reptiles, mammals and birds, while playing an important role in the succession of nutrient-poor grassland to biodiverse woodland.

Acid Grassland
Acid grassland is typically managed by grazing, and these exposed habitats are most suited to hardy breeds of livestock.

Protect

The main threats to this habitat are encroachment of scrub or bracken, and enrichment from fertiliser and atmospheric nitrogen. Climate change also threatens marginal areas where summer droughts can alter plant communities and high winter rainfall can lead to waterlogging and erosion. Scrub and bracken encroachment typically happens when cattle are removed – though some amount of scrub can be beneficial, creating a more structurally-diverse habitat. When sheep are grazed at moderate stocking densities, Bracken may start to encroach as they find the fern unpalatable. If cattle, ponies or sheep are grazed at high intensity, patches of Heathland and Bracken may revert to Acid Grassland.

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

As Bracken is a nitrogen-fixing species, its presence enriches the soil and shifts the habitat away from the nutrient-poor community of plants typically found in Acid Grassland. Bracken is part of the succession process that shifts this habitat towards scrub and woodland. The plant’s toxicity to livestock makes it more likely to dominate in heavily-grazed upland areas. It may be worth keeping this plant under control with cattle and/or ‘rolling’ to maintain diversity.

Upland acid grassland
Without effective management replicating natural processes, Acid Grassland will often revert to Bracken over time.

Restore

Acid 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 Acid Grassland is possible, but difficult, and the method depends on the extent of modification.

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 acidic 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 Acid 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 Acid Grassland meadow nearby and spreading the arisings on your land to transfer the seed. 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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