Robert Nold via pbs
Mon, 02 May 2022 11:59:26 PDT

That leads to another topic, the influence of rocky habitat in providing moisture to plants in arid climates, where fog or dew condenses on the rocks and trickles down. 
Whatever the books tell you, that is not "baking."

It probably is just exactly that (baking), for the plant. 
"Owing to the strong solar radiation at higher altitudes the soil in the mountains becomes more heated than in the lowlands." (Landolt and Urbanska, Our Alpine Flora)
Plants found above timberline are low-growing because that allows them to take advantage of the heat right at soil level. Some alpine plants have been found to be able to continue photosynthesis even at 50C. 

I suppose the myth, common among rock gardeners, that alpine plants "prefer cool conditions" originated because of the air temperature at the height of the human looking down on the plants. 

"Trickles down" is an exact description of the process utilized by plants growing in highly-porous soils. Nothing to do with "drainage", and everything to do with rapid infiltration, as well as providing a high percentage of soil oxygen. Most xerophytes grow in such soils in order to get almost every bit of rain and it's easier for roots to pull water from porous soils than from denser soils.

Bob Nold
Denver Colorado

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