Why are Native Herbs in the Chilean Matorral More Abundant Beneath Bushes: Microclimate or Grazing?

(1) Native perennial herbs in central Chile tend to be most abundant beneath bushes. This may be because the humid microclimate under bushes prevents desiccation (the absence of herbs from open spaces would then be explained by water stress), or it may be because herbivores which eat the herbs forage more in the areas between rather than under the bushes. (2) The problem was studied experimentally by removing half the canopy of eight individual bushes of the same species, and then preventing grazing of the herbs in one half of the removed section with an exclosure. This design allowed comparison of areas protected against desiccation and herbivores (the uncut half of the shrub), with areas protected against herbivores but not desiccation (inside the exclosure), and with unprotected areas exposed to both desiccation and grazing. (3) Results after 1 year showed that grazing (most likely by introduced rabbits) was the main cause of the scarcity of native herbs between bushes, and hence of their relative abundance beneath bushes.