The Species Group Trend Index (STI) is the average national index of 13 cold-loving species (birds, day butterflies and amphibians). All these species are supposed to be sensitive to warmer temperatures. There is also an STI for 35 warmth-loving species (birds, reptiles, amphibians, day butterflies and dragonflies): these species are likely to benefit from the current climate change.
The combined index has been developed to gauge the impact of climate change on biodiversity in the context of the Convention on Biological Diversity (CBD).

Data on trends are based on national grids breeding species (SOVON), reptiles, amphibians (RAVON), dragonflies and day butterflies (Vlinderstichting) belonging to the Network Ecological Monitoring. The selection of warmth and cold-loving species is based on the shift of areas and the so-called climate envelope models. The models are used to predict the distribution of species on the basis of the current relation between climate and the incidence of species.