Semi-improved Grassland

What is the key difference between unimproved and semi-improved grassland?


The fundamental difference lies in their past and present management intensity. Unimproved grassland has experienced minimal impact from modern intensive agricultural practices, while semi-improved grassland has been modified by such methods, including artificial fertilisers, slurry, intensive grazing, herbicides, or drainage. Semi-improved is considered a transitional category.

How does species diversity compare between unimproved and semi-improved grassland?


Unimproved grassland is characterised by significantly higher species diversity, or a richer flora, compared to semi-improved areas. Ancient chalk grassland, a type of unimproved calcareous grassland, can support a remarkable number of species per square metre, indicating its age and lack of recent fertiliser application. Semi-improved grassland has a more restricted range of species and generally lower diversity than unimproved grassland in the same locality.

What types of plant species are typically found in unimproved grassland?

Unimproved grassland supports species characteristic of the specific area and soil type (acid, neutral, or calcareous) with a very low percentage of agricultural species. It often includes specific indicator species depending on the soil. Examples given include snake's-head fritillary or green-winged orchid for unimproved neutral grasslands, and cowslip, kidney vetch, or various orchids for unimproved calcareous grasslands. Mosses can also be abundant.

What are the characteristics of species composition in semi-improved grassland?


Semi-improved grassland has a more restricted list of species compared to unimproved grassland. While it may originate from acid, neutral, or calcareous types, the improvement practices tend to reduce the distinct character of these soil types. It is not always easy to distinguish semi-improved grassland in the field, and surveyors need to be aware of local species compositions that are indicative of this condition.

How can surveyors help distinguish semi-improved grassland in the field?

Surveyors can identify semi-improved grassland by looking for a lack of the signs of substantial improvement. This includes not having over 50% cover of aggressive agricultural species like Lolium perenne and Trifolium repens, not presenting a bright green and lush sward, and having low forb diversity. If these signs of significant dominance by agricultural species are absent, the grassland is likely semi-improved.

Can semi-improved grassland originate from different types of unimproved grassland?
Yes, semi-improved grassland can originate from the partial improvement of formerly acid, neutral, or calcareous grassland.

Does the improvement of grassland reduce the distinct characteristics of the original soil type?
Yes, the improvement practices applied to formerly acid, neutral, or calcareous grasslands tend to reduce their distinct characteristics. This can make it more challenging to distinguish the original soil type in semi-improved grassland.

Is the presence of a high percentage of agricultural species an indicator of semi-improved grassland?


No, a high percentage of agricultural species, such as over 50% Lolium perenne and Trifolium repens, along with a bright green/lush sward and low forb diversity, are indicators of substantially improved grassland, not semi-improved grassland. Semi-improved grassland is characterised by a lack of these signs of significant dominance by aggressive agricultural species.