The Amazon rain forest is a good example of mineral availability. The soils under the forest are deficient in minerals. All of the minerals are either locked up in the growing vegetation or being released back to the growing vegetation as the dead vegtation decomposes. Toni, this is an even better example of system instability than global warming since the outcome actually occurs far faster.
Trees do attract or cause rainfall to occur.
It isn't a matter of a gradual ramping up or down between the vegetation type but more of a sharp line of event. Within 30 metres of the edge of the vegetation the effect is measurable and statistically significant. Something less than perfect understanding is not dangerous to the ecosystem. This is what gets my goat.