Responses of ground beetles (Coleoptera, Carabidae) to tree retention groups of various sizes support leaving them in clear-cut areas

The value of leaving tree retention groups (TRGs) in clear-cuts has been verified in the last 30 years on the basis of the responses of various organisms, including carabid beetles. Most such research in Europe has been conducted in the Fennoscandian taiga. However, there is a lack of such studies of TRGs in the lowland temperate pine forests of Central Europe. Therefore I conducted a follow-up of carabid beetles in TRGs over the first three years after clear-cutting. The treatments were TRGs of different sizes, i.e. large (0.07 ha), medium (0.05 ha) and small (0.02 ha), together with the surrounding space in the clear-cuts and the neighboring control, i.e. mature unharvested pine stands. There were 3 sites, each with 6 TRGs (2 TRGs in each of the 3 size). (1) The rarefied species number, abundance and percentage of small zoophages in the assemblages inhabiting the control stands and TRGs were similar. (2) The proportion of forest fauna was higher in the assemblages inhabiting the control stands than in the TRGs, which was associated with colonization of TRGs by non-forest fauna and by the dominance it achieved. (3) Between the first and second year, the rarefied species number increased in the control stands and in the largest TRGs. (4) As the distance from the TRGs increased, the abundance and percentages of individuals representing small zoophages and forest species decreased, while the percentage of hemizoophages, generalists and open-habitat species increased. (5) In successive years there was a decrease in the proportion of forest fauna in the clearing and an increase in the rarefied species number, abundance, and proportion of individuals representing large zoophages and open-habitat species. (6) In the first two years of the study the carabid assemblages living in the control stands and those in the large TRGs were the most similar. (7) At the species level, Carabus violaceus was characteristic of large TRGs, and Amara consularis of small TRGs. Harpalus latus was a species characteristic of the area of the clearing furthest from the TRGs. In contrast with other research, I conclude that even such small TRGs as the ones I studied provide support for forest carabids in the first few years after clear-cutting. However, among the three sizes of TRGs, the largest ones (0.07 ha) offer the best protection for forest fauna. It is important to leave several such TRGs in the clear-cut area to form an archipelago of habitat islands facilitating the movement and survival of forest species.

Automated summary

The study found that the number of carabid species, abundance, and proportion of small zoophages in the control stands and TRGs were similar. The proportion of forest fauna was higher in control stands than in TRGs. Over time, there was a decrease in forest fauna in the clearing area and an increase in the number, abundance, and proportion of large zoophages and open-habitat species. The largest TRGs provided the best protection for forest fauna.