Grassland Vegetative Analysis
What do the associated plant species tell us about the soil chemistry of Sidmouth's grassland sites?
The presence of certain plant species serves as an indicator of the underlying soil chemistry. While the National Vegetative Classification system categorises plants based on soil preferences (acid, neutral, calcareous), these naturally occurring communities aren't found in Sidmouth. However, the survey data still provides insights. For instance, Lincombe, situated where sandstones meet chalk cliffs, shows a dominance of calcareous plants, with around 65% of all recorded calcareous species found there. Peak Hill, on the acidic Upper Greensand, is home to four out of six recorded acid grassland plants. The widespread presence of neutral soil plants across sites, with an average of 20.7 per site compared to 11.9 for calcareous and just 1.5 for acidic, suggests that past agricultural practices, like the use of fertilisers and animal faeces, have largely neutralised the natural soil influences. Many calcareous and neutral plants can tolerate neutral conditions, but acid conditions are generally less favourable for both.
Both scrub species and weeds of cultivation are significant components of Sidmouth's grassland flora, reflecting historical land use and proximity to human activity. Scrub habitat, commonly found surrounding former grazing areas, indicates a lack of recent management. On average, 26.9 scrub species were found per site, accounting for 24.5% of all recorded species. Sites like Combe Wood Farm, Lincombe, and The Knapp, with higher scrub presence, may have been grazed less recently, although their larger size could also contribute. Weeds of cultivation are remnants of past agricultural practices like ploughing and also include garden species that have spread from nearby housing. On average, there are 25.6 such 'weeds' per site. Sites like Peasland Knapp, being steep and likely never cultivated, have fewer weeds, while The Knowle, with a history of cultivation and recent reseeding, has significantly more. The presence of these weeds isn't necessarily detrimental to biodiversity, as seen at Alma Field where a high percentage of 'agricultural weeds' coexists with a rich invertebrate population.
Beyond soil indicators and the influence of scrub and weeds, several other conclusions emerge from the floral analysis. The survey recorded a considerable diversity of plants, with 'weeds of cultivation' being the largest group (114 species) followed by scrub species (92). The presence of species associated with improved grassland, such as crested dog’s tail and timothy grasses, white clover, and common daisy, across almost all sites indicates that nearly all Sidmouth grasslands have been 'improved' for agriculture at some point. The total number of species recorded on each site appears to correlate with the size of the site, suggesting that larger areas tend to support greater floral diversity. The Knowle site stands out with the highest number of introduced and cultivated species and the lowest diversity of grass species, likely due to its history as a garden and recent reseeding efforts. Conversely, Combe Wood Farm, recently used for cattle rearing and now undergoing rewilding, is a site to watch for changes in its floral profile.
No, the National Vegetative Classification (NVC) system does not accurately reflect naturally occurring plant communities in the Sidmouth area. The NVC is designed to aid in the identification of plant communities that have developed naturally over time based on environmental factors. While the survey recorded plants associated with acid, neutral, and calcareous grasslands according to the NVC, there are no such naturally occurring plant communities in Sidmouth. The presence of these plants primarily indicates the underlying soil chemistry rather than the existence of distinct NVC plant communities.
Lincombe is particularly notable due to its location at the geological transition point where the dominant Sidmouth sandstones give way to chalk cliffs. This geological setting results in calcareous soil conditions. Consequently, Lincombe has a significant presence of plants that prefer calcareous soils. The survey found that approximately 65% of all calcareous-preferring species recorded across the entire survey area were found at Lincombe, making it the only site where calcareous plants were dominant.
The prevalence of neutral soil plants across most Sidmouth grassland sites, despite the underlying geology potentially suggesting otherwise, points towards a history of agricultural 'improvement'. The average number of neutral soil plants per site is significantly higher than calcareous or acidic plants. This neutrality is likely a result of past agricultural practices such as the application of nitrogen fertilisers and the presence of faeces from grazing animals, which have altered the natural soil chemistry by neutralising its inherent acidity or alkalinity. This suggests that Sidmouth's grasslands are largely "semi-improved."
The presence of scrub and weeds of cultivation is strongly linked to the historical land use and location of the grassland sites. Scrub is common because grasslands were historically used for grazing, often surrounded by hedgerow scrub to contain livestock. Unmanaged grasslands will also naturally transition to scrub. The abundance of scrub on sites like Combe Wood Farm, Lincombe, and The Knapp might reflect a longer period since active grazing occurred. Weeds of cultivation are present due to past agricultural activities like ploughing, where crops may have been grown. Their presence is also influenced by the sites' proximity to human habitation, with garden species 'escaping'. Sites further from human settlements, like Delderfield and Peak Hill, tend to have fewer 'weeds', while sites with a history of gardening or recent reseeding, like The Knowle, have significantly more.
Four species are identified as being associated with 'improved' grassland: crested dog’s tail grass, timothy grass, white clover, and common daisy flowers. The survey found that almost all Sidmouth grassland sites had at least three of these species present, with an average of 3.3 per site. White clover, crested dog's tail, and common daisy were almost universally found, while timothy grass was less common. The widespread presence of these species strongly indicates that virtually all of these grassland sites have been subject to 'improvement' for agricultural purposes at some point in their recent past.