A summary of MSc dissertation by Gemma French (summer 2005)
An area of arable land was brought into the nature reserve in 2001, managed in a non-intensive way to benefit wildlife through the implementation of beetle banks, conservation headlands and wild bird cover areas, all elements of agri-environment schemes encouraged by government to increase biodiversity in the UK.

The study assessed the value of these features at Paxton Pits Nature Reserve on the Carabidae populations by collecting them in pitfall traps from each agri-feature and within the arable fields. Traps were also set at a gradient from the beetle banks into the centre of the fields to provide data on community structure. Traps were sampled once every seven days for eight weeks between 18 May and 6 July 2005.

Ground beetles are classed as the family Carabidae; there are over 25,000 species worldwide and over 250 species in Britain that occupy a variety of habitats from woodland and grassland to wetland and coast. They are primarily found on the ground and many species are flightless. During the day, Carabids are found in sheltered and moist areas such as in leaf litter and under rocks and logs. In winter they hibernate under bark, in hollow stems or in the base of grass tussocks. Some may even create an oval burrow in the substrate for overwintering. Ground beetles will emerge in spring and some will migrate. They vary in size from 3mm to 36mm and have a variety of colours.

A total of 2722 individuals were collected and 45 species identified. This provides baseline data of what species were found on the reserve and their relative abundance. Three individuals of two nationally scarce species were found - Harpalus ardosiacus and Chlaenius nigricornis; these are thought to be vagrants.

The six most common species were Pterostichus cupreus, Harpalus rufipes, Nebria brevicollis, Harpalus aenus, Amara ovata and Pterostichus madidus, making up 83% of the total. The most dominant of the species was P. cupreus making up 36%. The area with the highest abundance of carabids and highest number of species was the two-year old Wild Bird Cover, whereas the one-year old Wild Bird Cover (WBC1) had the lowest diversity and abundance, less even than the middle of the fields.

The beetle banks held the least number of species and the least number of individuals (with the exception of WBC1), whereas the adjacent fields maintained a wide variety of species and a high abundance, suggesting that although the beetle banks provide an overwintering refuge, they do not harbour many species all year round but provide the source of species to the surrounding environment. The results suggested that the beetle banks had the desired effect of increasing carabid beetle diversity and abundance in the arable land but they do not necessarily support high diversities and numbers of species themselves. Certain species showed significant association with particular habitat types.

Overall, the study suggests that the use of artificial grass strips in fields has a significantly positive affect on the abundance and diversity of Carabidae present at Paxton Pits Nature Reserve. It also enables species to overwinter that may not otherwise survive in the field itself. Cereal fields are prone to drastic soil disturbance, seasonal changes in soil surface microclimate and availability of prey as the crop grows and so providing a refuge such as the beetle banks allows the population of carabids to continue even when there is disturbance to their habitats.