A rapid ecosystem function assessment (REFA) to promote basic and applied ecology
The last decades have seen an increasing interest in ecosystem functions in the fields of (1) biodiversity - ecosystem functioning research, (2) ecological conservation and restoration, and (3) the valuation of ecosystem services. However, there is a lack of standardized and easy-to use methods to quantify ecosystem functions. Consequently, there is a gap between the data available and the data needed to answer topical questions both in basic and applied ecology. We identify a set of functions spanning productivity and soil nutrient conditions, the saprophagic break-down of organic material and consumer-plant interactions as a basic descriptor of overall ecosystem functioning. We aim at proposing REFA methods to measure proxies for these important functions. Proposed methods were specifically selected to be low-tech, easy to use, repeatable, and cost-efficient. Thus, they enable standardized and comparable measures of functions on a large scale within and across studies. The identified methods are introduced and examples using REFA along an experimental plant-diversity gradient and in an applied land-use context are presented and compared to results obtained with more detailed measurements.
Primary productivity (above and belowground) can be approximated by standing plant biomass (leaves/stems and roots, respectively). As an overall indication of belowground faunal activity, the number/biomass of fauna extracted from soil cores by heat can be used and decomposition is approximated by the weight loss of a standardized substrate like small wooden sticks. To quantify the size of the consumer compartment aboveground, suction samples from a defined area can be taken and the number/biomass of invertebrates be determined. Vertebrate herbivory is best estimated via exclusion with fences. Invertebrate herbivory can be measured scoring leaves for damage. In the same way plant infections can be quantified. Invertebrate predation can be quantified as the attack rate on exposed artificial caterpillars made from play doe, pollination as the number of insects attracted to pan traps, and seed dispersal as the removal of a standardized grain. We show that REFA methods were able to reproduce the relationships between functions, diversity and land-use that have been documented using more detailed and labor-intensive methods. Therefore, we conclude that there is not only a need for more comparable data on ecosystem functioning but also a great potential for employing REFA-methods that quantify proxies suitable to answer critical questions about drivers of functioning in different ecosystems under global change and the best management to sustain provision of ecosystem functions and services.