Changes in ground beetle assemblages above and below the treeline of the Dolomites after almost 30 years (1980/2009)

Very little is known about the changes of ground beetle assemblages in the lastfew decades in the Alps, and different responses to climate change of animalpopulations living above and below the treeline have not been estimated yet.This study focuses on an altitudinal habitat sequence from subalpine spruceforest to alpine grassland in a low disturbance area of the southeastern Dolom-ites in Italy, the Paneveggio Regional Park. We compared the ground beetle(Carabidae) populations sampled in 1980 in six stands below and above the tre-eline (1650–2250 m a.s.l.) with those sampled in the same sites almost 30 yearslater (2008/9). Quantitative data (species richness and abundance) have beencompared by means of several diversity indexes and with a new index, theIndex of Rank-abundance Change (IRC). Our work shows that species richnessand abundance have changed after almost 30 years as a consequence of localextinctions, uphill increment of abundance and uphill shift of distributionrange. The overall species number dropped from 36 to 27, while in the sitesabove the treeline, species richness and abundance changed more than in theforest sites. Two microtherm characteristic species of the pioneer cushion grassmats, Nebria germari and Trechus dolomitanus, became extinct or showed strongabundance reduction. In Nardetum pastures, several hygrophilic species disap-peared, and xerophilic zoophytophagous elements raised their population den-sity. In forest ecosystems, the precipitation reduction caused deep soil textureand watering changes, driving a transformation from Sphagnum-rich (peaty) tohumus-rich soil, and as a consequence, soil invertebrate biomass stronglyincreased and thermophilic carabids enriched the species structure. In threedecades, Carabid assemblages changed consistently with the hypothesis that cli-mate change is one of the main factors triggering natural environment modifi-cations. Furthermore, the level of human disturbance could enhance thesensitivity of mountain ecosystems to climate change.