Study area: observations were made in St. Marcel valley (Valle d’Aosta) along three transects (with a north-east exposition) along an altitudinal gradient (1700 m Druges, 1900 m Bren and 2100 m upper Bren), in mixed larch and spruce forest in the two lower transects and a larch forest in the highest transect.
Observation protocol: linear transects of 240 m, with traps placed every 10 m (glasses of 0.5 l buried to their brims in the ground, partly filled with vinegar and salt, protected by a stone). Sampling frequency and timing: traps baited from April to October and checked every 15 days. Determination of the specific level of adults and counting of individuals for each trap and date.
Results: Monitoring over three years resulted in a collection of 2904 individuals belonging to 12 different species: Pterostichus flavofemoratus (Dejean, 1828), Calathus melanocephalus (Linnaeus, 1758), Calathus micropterus (Duftschmid, 1812), Carabus depressus (Bonelli, 1810), Carabus heteromorphus (Daniel, 1896), Cymindis scapularis (Schaum, 1857), Notiophilus biguttatus (Fabricius, 1787), Synuchus vivalis (Illiger, 1798), Amara equestris (Duftschmid, 1812), Leistus nitidus (Duftschmid, 1812), Pteristichus oblongopunctatus (Fabricius, 1787) and Oreonebria castanea (Bonelli, 1810). Only P. flavofemoratus was considered for the purpose of investigating variations in abundance in the three years, as it is the only species present in all transects with a significant number of individuals.
At the three sampling sites two different trends were observed. While in the transect at low altitude (Laycher 1500 m asl), the abundance of the species investigated increased gradually from 2009 to 2010, in the other two transects located at higher altitudes (Druges, 1700 m and Bren, 1900 m) remained steady during the first two years and then decreased in 2011.
Analysis of the indicator species, conducted using IndVal index, shows that altitude is a significant explaining variable for eight species, including two for the site at the lowest altitude (Laycher, 1500 m) and six for that at the highest altitude (Bren, 1900 m). The transect located at an intermediate altitude (Druges, 1700 m) was not positively selected for by any species.
Advantages: carabids can be used as biomarkers for many types of environmental changes, since they are widely known in ecological and taxonomic terms. In addition, some species are highly selective against certain habitat due to their high sensitivity to environmental variations (temperature, humidity, vegetation structure, etc.). It should finally be pointed out that the sampling is conducted with extreme facility and low costs in terms of materials by means of a visual search or with the classic pitfall traps.
Disadvantages: in the study area, investigated in the period 2009-2011, the research identified a coenosis relatively poor in species compared to those known for other areas of the same region. Therefore the only species that was abundant was P. flavofemoratus.