Bramblefields Ceramic mound

Background:

Bramblefields nature reserve is situated in the north east of the city in an urban area. The site sits alongside residential properties, a school, an allotment and now the Cambridge North railway station and hotel complex. Previously the reserve had enjoyed being adjacent to the East Chesterton railway sidings, an important brownfield site that had been adopted as a City Wildlife Site. This connection benefited the site by providing a vital wildlife corridor to the wider countryside plus providing a sizable habitat to species, which could utilize the many opportunities a brownfield site could provide. It was the loss of the railway sidings that prompted the idea for the project. Although the wildlife corridor had been lost perhaps the brownfield habitat conditions could be recreated on the reserve, to act as compensation for the species displaced by the development of the railway station.

 

The project:

As mitigation for increased disturbance for the reserve and it’s species some funds were secured by the City Council from the developers of the North Cambridge railway station. Initially the idea of a second pond was thought of, as the original pond had always been a very successful breeding site for smooth newts. The new pond was dug but to eliminate the cost of removing the spoil it was piled up next to the new pond.

 

Ideas around including elements of Eco mimicry for urban nature sites have been growing among conservationists as a way to increase available habitats on these types of sites. This concept involves recreating habitats along with their specific substrates, plant diversity and structures to capitalize on the conservation value of a site.

 

With this in mind the mound of spoil was seen as setting where a recreation of a different habitat or Eco mimicry could take place. The environment to be imitated was the lost brownfield site of East Chesterton sidings. The elements desired would include lots of dry, undulating, nutrient poor ground. The easiest and quickest way to replicate this was installing a substrate that had these characteristics. After some research a green roof substrate was sourced which was made up of crushed ceramics previously used as baths and toilets. This substrate was nutrient poor, held heat, could be laid at varying depths to create micro-climates and altering conditions, all mimicking the kind of habitats to be found on a brownfield site. It also had the added benefit of being a recycled product.

A thick membrane was put down first on top of the mound to stop the inevitable growth of nettle and bramble and other prolific growers.

Then the ceramic substrate was laid on top. At this point it has to be pointed out that the City Council’s conservation volunteers carried out this task, which was actually a huge ask.

 

weed resistant membrane

28 tons of substrate moved by wheelbarrow across the reserve for many days until the desired depth was achieved and the substantial pile had disappeared from the reserve entrance to the mound. A legendary show of volunteer power!

man with wheelbarrow

The fun could really begin with the re-profiling of the substrate to include the undulations, log piles, varying topography, even small areas which would collect water, all elements that mimicked the lost adjacent brownfield site. The mound was surrounded by larger blocks of broken concrete, this provided basking sites for reptiles and insects, but also plenty of nooks and crannies to give shelter, hiding places or hibernation possibilities. It also acted as a barrier to slow the onslaught of bramble and nettles growth on to the mound.

The last step was to sow a seed mix of native flowering chalk grassland species. This type of plant thrives on hot, nutrient poor ground when other species cannot. The added bonus of these plants is that they are nationally scarce as pristine chalk grassland is a habitat which in massively on the decline in this country.

Although other plant species suited to this substrate would inevitably grow too it was felt that establishing a good colony of native wild flowers first was preferable for pollinators and more appealing to the public.

 

Impact of the project:

Flora – the mound is already supporting a good suite of native flowering plants, most of which were in the seed mix put down. Plants such as; Kidney Vetch, Viper’s Bugloss, Oxeye Daisy, Wild Clary, Common Knapweed, Scarlet Pimpernel but others which have arrived on their own such as Narrow-leaved ragwort, Poppies, Candy Tuft and Verbascum. All of which are welcome. Selective weeding has to be done to reduce the presence of plants which have a dominating growth habit that could out compete some of the finer plants.

thin leaved ragwort flower

Fauna: the mound has so far proved to be a fantastic habitat for bees and butterflies. 7 species of bumblebees have been recorded there and 10 species of butterfly, including the Marbled White butterfly which is a species associated with chalk or limestone grassland.

 

Aside from establishing another habitat within Bramblefields, the mound has also been seen as an experiment in how to create a floristically rich habitat relatively quickly and sustainably with low maintenance once established. An idea, which if rolled out to the wider urban area, for example on roundabouts or motorway embankments even verges, could offer a viable solution to our declining pollinator populations while also looking attractive and providing interest for the public.

If you would like more information on this project please email: parks@cambridge.gov.uk