23 February 2023

Chalk stream project identifies 4 near-threatened species

A habitat and invertebrate survey was recently commissioned to assess the health of the Upper River Crane Corridor, a chalk winterborne stream which runs through the Cranborne estate.

Chalk streams are extremely rare, thought to be only 200 in number globally, existing mostly in southern Britain and northern France. Chalk winterborne streams, which only run during the wetter months of the year are even rarer, and have their own very specific set of flora and fauna.

Due to their rarity and abundance of wildlife, chalk streams are often likened to tropical rainforests are home to some to some of our most loved wild species, such as the water vole.

Chalk streams are among the most biodiverse of the UK’s rivers, representing one of our most important contributions to global biodiversity, but are under severe pressure from pollution and other negative factors, posing a severe threat to the natural habitat that thrive there.

The survey reports were  supported by the Farming in Protected Lanscapes (FiPL) environment fund, which is administered by The Cranborne Chase Area of Outstanding Natural Beauty (AONB).

The objective of the survey was to assess the health of the river by analysing:

Stream habitat


Fresh water invertebrates – an excellent indicator of water quality



Dead-wood invertebrates

During the survey, 198 different plant species were identified, including 4 which are classified as ‘Near Threatened’ meaning that it is a species that is close to, or likely to be classed as ‘Threatened’ in the near future. These are –

Ragged Robin

Common Valerian

Marsh Valerian

Marsh Ragwort

The findings have resulted in vital recommendations which outline improvements to enhance the biodiversity of the river. The new plan focuses on restoring natural process by removing man-made structures, averting pollution, cutting a proportion of trees and laying woody debris in the river channel. Wetland scrapes will be created to provide an attractive environment for a variety of invertebrates, and provide important feeding areas for breeding wading birds and their chicks.

Cranborne takes a scientific approach to managing the rural estate and are passionate about measuring the positive impact that each and every initiative brings to the environment and local communities. Part of the enhancement plan includes producing some educational information boards and organising events for local schools and farmer groups highlighting the importance of chalk streams and the actions local people can take in helping maintain these rich environments.

Images courtesy of Wessex Rivers Trust

Chalk stream project identifies 4 near-threatened species - Cranborne Estate