My textbook says that in all cases of ecological succession (xerarch, hydrarch, etc.), the ultimate climax community, assuming constancy of environment, is a mesic community. Xeric or hydric pioneers are ultimately succeeded by mesic climax communities. Why is this so? In an environment under consideration, if for example water stress prevails (characteristic of xeric environments) shouldn't the final community be xeric and hence better adapted to the environment? Is my book wrong, or is there something I am missing in the understanding of the development of climax communities?
Moreover, I did find it written somewhere that mesic communities do depend on the climate of the place. But then doesn't the fact it is mesic contradict a few climatic conditions wherein ecological succession might occur?