First application of the QBS-ar index in the tropical montane Andes reveals soil biological quality across agroforestry systems and forest succession.

Assessing soil quality is essential for effective monitoring, conservation, and management. However, most current assessment approaches tend to overlook the biological component of soils, limiting their value for sustainable resource management. The Soil Biological Quality index based on microarthropods (QBS-ar index) is one of the few tools that incorporates this biological dimension. Yet, its applicability has not been tested in tropical South American ecosystems, particularly under different land-use contexts, successional stages, or across climatic seasons. In this study, we evaluated the sensitivity of the QBS-ar index to changes in soil biological quality in response to different land-use systems, seasonal variation, and forest succession in tropical montane ecosystems of the Andes. We collected 186 soil samples across 20 plots (each 20 × 20 m) representing agroforestry systems and forests with secondary and mature successional stages in the Colombian Andes. Our results revealed significant differences in index values across land-use systems, demonstrating the index's effectiveness in detecting soil biological quality based on the disturbance levels. The QBS-ar index was also sensitive to seasonal changes, showing lower values during dry periods, likely due to declines in the abundance and richness of eudaphic taxa. Additionally, the QBS-ar index was positively associated with forest biomass, as well as with the richness and abundance of soil microarthropods, supporting its potential as a reliable indicator of ecological succession. Overall, our findings support the QBS-ar index as a useful and cost-effective tool for monitoring soil biological quality and ecological succession in tropical Andean ecosystems.