This study (led by Yale) determined that plant diversity and performance is especially influenced by soil organic content.
The abundance of flora and fauna in an area is dependent on a number of variables, but especially soil composition and health.
Thinking in terms of trophic levels, this makes sense.
Some environmental indicators, such as global mean temperature and atmospheric CO concentrations, are becoming widely accepted as measures of anthropogenic effects on global climate.
Ecological indicators are founded on much the same principles and therefore carry with them similar pros and cons ( Biodiversity is essentially everywhere, ubiquitous on Earth’s surface and in every drop of its bodies of water.