Land use, above-ground arthropod diversity and arthropod-affected processes
Arthropods, especially insects, are the most diverse group of animals on Earth and influence many ecosystem processes. Within the project Arthropods:
1) a long-term monitoring of insect and spider diversity is conducted in grasslands and forests
2) ecosystem processes, such as predation, dung depletion and seed removal are quantified
3) the role of deadwood insects in the decomposition of dead wood is analyzed as part of the BELongDead-experiment.
Arthropods are sampled in forests and grasslands during the whole vegetation period (March-October) as part of the long-term monitoring. Through this monitoring, we can not only quantify short-term but also long-term effects of land use on arthropod diversity in grasslands and forests. Additionally, important basic information is supplied for other projects. In addition to the long-term monitoring, the use of indicator species is tested and ecological information (traits) of the sampled species are collected to test for the effect of land use on community composition and to understand the processes underlying land-use effects. In collaboration with other projects, we conduct time series analyses and investigate the influence of the surrounding landscape, of historical land use and of structural variables on arthropod diversity.
- Increasing land-use intensity decreases the diversity and overall abundance of arthropods in forests and grasslands.
- Arthropod community composition changes with intensive land use, as species with certain characteristics become more abundant or rare.
Actively flying arthropods are sampled monthly in forests (including the new FOX experiment) with flight-interception traps.
In grasslands, ground-living arthropods and species which are found in the vegetation layer are caught by monthly sweep-net sampling.
We evaluate the impact of land use on the ecosystem processes predation, dung depletion and seed removal. We test experimentally, if an increase in diversity within extensively used systems accelerates process rates. Through the joined analysis of data from the long-term monitoring and the ecosystem process assessment, we are able to detect relationships between land use, arthropod communities and connected processes.
- Changes in arthropod community composition affect ecosystem processes (e.g. dung depletion) and the diversity of other taxa.
- Process rates are higher in natural forests as well as under extensive land use in grasslands.
We use dummy caterpillars made from modelling clay for assessing predation. Dummies are exposed in the field for 48 h and attack marks are used for determining predation rates.
For measuring dung depletion, we use cow dung as standardized bait. A defined quantity of dung is exposed for 48 h. Post-exposure weight of dung bait is used to quantify mass loss due to dung beetle activity.
Seed removal is measured with sunflower seeds placed on plastic trays. After 48 h, we count how many seeds have been consumed by animals.
Within the BELongDead experiment dead wood logs (length 4 m, diameter ca. 30 cm) of 13 tree species were exposed on a total of 30 plots. Since 2010, the emerging insects from those logs are caught with closed emergence traps. This allows us to analyze the role of forest management and tree species on the colonization by deadwood insects. Additionally, we evaluate the role of deadwood insects in the decomposition of the logs in collaboration with other projects.
- The community of deadwood insects differs in its diversity and composition among logs of different tree species.
- The diversity of the deadwood insect community is higher on native tree species compared to ‘exotic’ tree species.
- The diversity of the deadwood insect community is higher in natural forests compared to managed forests.
- The composition of the deadwood insect community changes during the course of the deadwood decomposition process.
- Abundance and diversity of deadwood insects have a positive influence on the decomposition rate.
One emergence trap (half round metal arch with dark cloth attached to its sides, see picture B) was installed on one log per tree species in 2010. The emergence traps are equipped with transparent sampling jars, in which the freshly emerged deadwood insects are caught. At the end of each year, the emergence traps are moved by 30 cm on the log to enable new colonization at the old position of the emergence trap.