What does 'environmental' mean?

[Janet Turnbull]

When BC says that butterflies are important indicators of the health of the environment, does that mean in the habitat sense of the word? Near Manchester United's practice ground there is a barrier manned by a a guy in a small cabin, heated by something requiring a diesel generator. All last winter and into the spring it pumped out masses of fumes yet the Orange-tips flourished nearby! So do I assume 'environment' for butterflies does not include air quality?

[David M]

Hard to judge fundamental air quality if heavy pollution has only been occurring for a short while. If diesel generators were in situ for several years then I would expect that to have a detrimental effect on most if not all wildlife, although there ARE good butterfly sites in places which are seemingly adversely affected by pollution, such as Aston Rowant, which is right alongside the busy M40 motorway.