The mushrooms can be classified into different groups. For example mushrooms and parasol mushrooms are saprtrophic, which feed on organic material, eg. fallen leaves. Chanterelles and porcini mushrooms are on the other hand mycorrhizal fungi. These species live symbiotically with the roots of trees or shrubs. They increase the surface area of the roots, making them more able to absorb water and nutrients. The trees and plants provide the fungi in turn with products of photosynthesis.
The fact that mushrooms grow better and longer, is because the season has become longer due to global warming. Krisai-Greilhuber and Damon demonstrated from the analysis this when they were part of a European team developing mushrooms from 1970-2007 in Austria, Switzerland, Scandinavia and England. The picture is the same everywhere, even with the saprotrophic fungi: there are more mushrooms and they are around for longer, especially in England.