Introduction
The Mosaic Approach (The Mosaic Approach: Managing Habitats for Species (B2020-009) is a Natural England document about integrating the requirements of species into habitat management. Most species require a range of elements within a site or a wider landscape in order to complete their life cycle. Many of these elements, such as small patches of bare ground, tall flower-rich vegetation, or scattered trees and scrub, are often absent from the English landscape. This has contributed to declines in many species, and providing a mosaic of these elements in the landscape would support the recovery of these species.
In biodiversity net gain (BNG) mosaics and ecotones are therefore important components of both existing habitats and proposed habitats, but they are poorly captured at present. One possible approach is to adapt the condition assessments for habitats to better account for these features.
The mosaic approach includes these factors for grassland:
- shelter
- bare ground
- tall flower-rich patches
- scrub & trees
- sward structure
- ecotones
Grassland condition assessment
How can these be incorporated into the condition assessment? Below is a proposed approach for grassland condition assessment which incorporates elements from The Mosaic Approach into condition assessment.
The Condition Assessment Criteria for Grassland – Medium, High & Very High Distinctiveness are as follows:
The appearance and composition of the vegetation closely matches characteristics of the specific grassland habitat type (see UKHab definition). Wildflowers, sedges and indicator species for the specific grassland habitat type are very clearly and easily visible throughout the sward. NB - This criterion is essential for achieving moderate condition for non- acid grassland types only.
Sward height is varied (at least 20% of the sward is less than 7 cm and at least 20% is more than 7 cm) creating microclimates which provide opportunities for insects, birds and small mammals to live and breed.
Cover of bare ground is between 1% and 5%, including localised areas, for example, rabbit warrens.
Cover of bracken is less than 20% and cover of scrub (including bramble) is less than 5%.
There is an absence of invasive non-native species (as listed on Schedule 9 of WCA, 1981). Combined cover of species indicative of sub-optimal condition, and physical damage (such as excessive poaching, damage from machinery use or storage, damaging levels of access, or any other damaging management activities) accounts for less than 5% of total area.
Additional Group (Non-acid types only)
- There are greater than 9 species per metre squared. NB - This criterion is essential for achieving good condition (non-acid grassland types only).
Review of existing condition assessment
Below I provide comments on the above criteria, as well as discussing how the features identified by the mosaic approach can be incorporated into the condition assessment.
Criterion 1 – This criterion is double counting the habitat identification. If the grassland types has already been identified using UKHab definitions, this criterion is redundant.
Criterion 2 – sward structure.
The Mosaic Approach includes tall flower-rich patches and sward structure. Criterion 2 describes sward structure, requiring 20% short grass and 20% tall grass. However, this does not capture tussocks or more open sward structures. Perhaps new criteria are required as follows:
- Presence of tall tussocks.
- Areas of open sward structure, with spaces between plants.
Criterion 3 - Bare ground
This includes exposed soil, pebbles, rock and lichen/moss carpets. This can include small scale poaching, track edge erosion and excavations.
The existing criterion limits bare ground to between 1% and 5%. This may not capture the type and extent of bare ground. For example large areas of poaching are considered indicators of poor condition, but small scale poaching is considered an indicator of good condition.
An edited version of criterion 3 could be as follows:
Cover of bare ground should be between 1 and 10%. Bare ground such as localised small scale poaching, exposed track edges or small excavations are indicators of good condition, but individual patches of bare ground should not exceed 1% of the total grassland area.
Criterion 4 – bracken and scrub cover.
The mosaic approach includes occasional trees and scrub of different sizes with gaps. The existing scrub criterion is lumped in with bracken. I think these should be separated and there should be a scrub criterion as follows:
Scrub and occasional trees present, including shrubs of different sizes with gaps between them, but overall cover less than 10%.
A new criterion for bracken should be created.
Criterion 5 – non-native species, damage and indicators of poor quality.
In the low distinctiveness grassland condition assessment some of these are separated and I don’t see why they couldn’t be for medium - very high distinctiveness grasslands.
New criteria
Shelter – a new criterion
Shelter describes grasslands, or patches, in direct sunlight, but protected from wind by either topography or vegetation. Examples include bays in scrub or woodland, sites against woodland edges or cliffs and sloping ground. An additional criterion could be:
Presence of sheltered areas, or entire grassland is sheltered. This could include bays in scrub or woodland, sites against woodland edges, or cliffs and sloping ground.
Ecotones
Ecotones describe the transition from habitat to another. Examples include:
- grassland – scrub – woodland
- grassland – wetland – woodland
- grassland – sand dune
- grassland – shingle
A new criterion could capture the presence of these features, as follows:
Presence of ecotone between the grassland and an adjacent habitat. This should describe a gradation between habitats and not a sharp change in habitat.
A revised condition assessment for grassland
A new condition assessment that includes mosaics and ecotones in describing the habitat could look like this:
Sward height is varied (at least 20% of the sward is less than 7 cm and at least 20% is more than 7 cm)
Presence of tall tussocks.
Areas of open sward structure, with spaces between plants.
Cover of bare ground should be between 1 and 10%. Bare ground such as localised small scale poaching, exposed track edges or small excavations are indicators of good condition, but individual patches of bare ground should not exceed 1% of the total grassland area.
Cover of bracken is less than 20%
Scrub and occasional trees present, including shrubs of different sizes with gaps between them, but overall cover less than 10%.
Presence of sheltered areas, or entire grassland is sheltered. This could include bays in scrub or woodland, sites against woodland edges or cliffs and sloping ground.
Presence of ecotone between the grassland and an adjacent habitat. This should describe a gradation between habitats and not a sharp change in habitat.
There is an absence of invasive non-native species (as listed on Schedule 9 of WCA, 1981).
Cover of species indicative of sub-optimal condition accounts for less than 5% of total area.
Cover of physical damage (such as excessive poaching, damage from machinery use or storage, damaging levels of access, or any other damaging management activities) accounts for less than 5% of total area.
Additional Group (Non-acid types only)
- There are greater than 9 species per metre squared. NB - This criterion is essential for achieving good condition (non-acid grassland types only).
Summary
Adapting the current condition assessment for grassland is one way to incorporate mosaics and ecotones into biodiversity net gain. This is a suggested approach for doing that. However, I am really keen to hear the views of the ecological community on this approach. Does this work? What other approaches are there? How can this be improved?
Please do get in touch with your views.