Factors Affecting the Distribution of Shrub Live Oak (Quercus Turbinella Greene)

The disjunct distribution, reproduction, and rooting habits of Quercus turbinella in the Arizona chaparral were studied on quartz diorite, sedimentary, and volcanic substrata. The oak was less dense on the sediments and volcanics that on quartz diorite. Lower densities on the bedded sediments resulted from restricted root penetration which prevented access to deep soil moisture; on the volcanic substratum heavy clay soils gave an overall poorer moisture regime than soils developed from the quartz diorite. Shrubs growing on the less favorable sedimentary and volcanic substrata probably were more susceptible to damage by drought and fire, and low mobility and low seedling production tended on eliminate the species from these areas. It is suggested that the Q. turbinella i slands within large areas of grassland are relicts rather than evidence of invasion.