False advertising! On a more practical note, simply counting the number of species in an area by carefully identifying the fruiting bodies can give you a strong indication not only of fungal but overall biodiversity. Things that can negatively affect terrestrial fungal diversity include: concreting, poison, lawn treatments, and sewage overflow, lack of moisture, general lack of biomass. The presence of certain insects, such as the small fly-like fungus gnats, can indicate the presence of fungi, as can particular smells for certain odorous types, even if you can't see them. The best time to count fruiting bodies is often a day or two after a prolonged warm and moist period that had a sudden temperature drop. Late summer/early autumn. Coming up soon in the northern hemisphere.