In the grasslands, desert, etc. They are provided extra nutrition from this mycorrhizal assoc. If we have one of those funny midwinter droughts they are helped with deeper water from the 'mother plants' on site. In our short growing season, limited as it is to moisture, the 100 times more surface area and 10,000 times more surface length of mycorrhizal roots in relation to non-mycorrhizal roots is a significant advantage. Also the rainfall that does fall is captured, in the below ground biosphere and there is little or no runoff or leaching.
Effective rainfall is increased.
It is very possible that the lush prairie described by Muir did exist and can again, but we have to establish back as much of the whole community as possible. The annual wildflower's significance to the community has been ignored. It now appears that wildflowers are essential to the functioning of the community and are poorly replaced by non-native annuals. As our native wildflowers decline and die during their short season, their nutrition, moisture and some of their biomass is transferred to the other mycorrhizal hosts on the fungal 'grid'. Cyclically the annual energy cycle is transferred from the wildflowers to the perennials, shrubs and trees and back to the spring wildflowers.