Elevation is decisive for the diversity of soil fauna

Beetles, millipedes or ants are hugely important for the functioning of soils. This is especially true in mountain forests, which are being particularly affected by climate change. The Swiss Federal Institute for Forest, Snow and Landscape Research WSL and the University of Basel have now jointly investigated how soil fauna diversity has evolved and been distributed across the altitudinal zones.

Quite a lot of research has been done on plant occurrences in mountains, but little on soil-dwelling animals. "The fauna groups we studied are relevant to ecosystem functioning, and some of them have important roles in nutrient cycling, such as millipedes, or in relation to soil structure, such as soil-dwelling ants," says co-author Stephan Zimmermann of WSL's Soil Functions and Protection research group. He further points that these groups are representative of numerous other arthropod groups: spiders are predators, while millipedes break down litter to provide nutrients.

The Alps are particularly affected by climate change, and these small animals cannot migrate easily. A research team from WSL and the University of Basel has now studied organisms such as spiders, centipedes, millipedes and various beetles to better understand their occurrence at different altitudes. 

The Swiss National Park has been largely untouched by humans since as early as 1914. Therefore, it was ideally suited for this study. At elevations ranging from 1800 to 2750 meters, the research team captured over 14,000 individuals by eye search or by artificial shelters and ground traps. They belonged to altogether 248 species from six animal groups: spiders, ground beetles, centipedes, millipedes, rove beetles and ants.

Next, the researchers used statistical methods to look for patterns in the altitude distribution and found three distinct ones: a steady decrease with increasing altitude (centipedes), a constant number and then a rapid decrease at high altitudes (ants and rove beetles), and a peak in the number of species at medium altitudes combined with a decrease at high altitudes (spiders and millipedes). The number of species and where they occurred depended almost exclusively on altitude for all animal groups. Most other soil and vegetation characteristics had little influence because they themselves depended on elevation, the researchers report in the journal PLOS ONE. They mention as noteworthy that the patterns are very disparate. "Looking at just one group can yield misleading results for species diversity as a whole," Zimmermann says. The authors recommend that future studies of elevation should always consider multiple species groups.