Effect of land-use changes on the soil macrofauna community

Michael Steinwandter

 

1 Introduction

The soil communities in alpine soils as well as the alpine ecosystems themselves are currently in a state of change. On the one hand it is suspected that global warming will lead to a shift in plant species composition (BENISTON 2003) and to an increased litter decomposition rate. Higher temperatures will positively affect litter quality and soil fauna communities, large decomposers such as earthworms may migrate to high-altitude sites (AERTS 2006). It is also predicted that vegetation productivity, especially woody plant biomasses will increase due to global warming, which will cause a higher amount of annual litter fall in the alpine area and will therefore counteract direct warming enhancement of litter decomposition (CORNELISSEN ET AL. 2007).

On the other hand the structural composition of the soil macrofauna community is strongly influenced by land-use, especially abandonment, as alpine meadows and pastures are increasingly taken out of management due to socio-economic changes (MACDONALD ET AL. 2000). Studies on the Kaserstattalm (Stubai Valley, Central Alps, Austria, SEEBER ET AL. 2005) have shown that traditionally managed meadows and pastures favour the occurrence of ecosystem engineers (sensu LAVELLE ET AL. 1997) such as Lumbricus rubellus, a epigeic/hemiedaphic earthworm species, which is capable of bioturbation. Due to its high numbers and biomass on alpine meadows and pastures at the research site it can be defined as a keystone species of decomposition, acting at the beginning of the decomposition process by ingesting the litter material and incorporating it into the mineral soil. Generally, the macrofauna community on managed areas is mainly composed of large-bodied earthworms (besides L. rubellus the endogeic species Octolasion lacteum and Aporrectodea rosea) as well as Diptera and Coleoptera larvae. After abandonment the soil invertebrate community becomes more diverse, centipedes, millipedes, and insect larvae significantly increase in numbers, while L. rubellus declines both in abundance and biomass. Other earthworms such as the epigeic Dendrobaena octaedra become more abundant, but due to its small size and lack of bioturbation ability this species cannot compensate the decomposition efforts of L. rubellus. Millipedes, which are also important decomposer species, can mainly be found on abandoned areas, the dominant species are Cylindroiulus meinerti and C. fulviceps as well as the small Enantiulus nanus (all Julidae).

Both climatic change and abandonment of management cause habitat and diet conditions to change profoundly for soil invertebrates. The first step to better understand and evaluate the so caused changes in the community composition is to monitor the soil community for a longer period of time. Most ecological studies are carried out over relatively short periods due to mostly financial reasons (CALLAHAN 1994), but real effects might only be measurable in the long run and might also change with time. We therefore propose to resample the sites investigated ten years earlier to get an insight into how land-use changes affect the soil macrofauna community.

2 Aims and impact of the project

Soil invertebrates play a crucial role in maintaining ecosystem functioning by mediating important ecosystem processes such as litter decomposition, nutrient (especially carbon) cycles, water infiltration and storage in soil (HÅGVAR 1998). Changes in their structural composition will therefore have considerable impacts on the function and stability of alpine ecosystems. Studies from 2002 have shown that the soil community becomes more diverse after abandonment, however, due to the retreat of large-bodied earthworms, its process effort decreases (SEEBER ET AL. 2005, 2006). Abandoned sites sampled in 2002 had been taken out of management for 10-15 years, the soil community now has had ten more years to adapt to the changed conditions. By comparing data from managed, 10-15 year-old and 20-25 year-old abandoned sites we will be able to draw statistically better verified conclusions on how abandonment affects the soil community composition. This will be an important basis for further studies on the effect of land-use changes on the function and stability of alpine ecosystems.