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Although highly branched from the base all shrubs have short main axes linking canopies to root systems Main axes become increasingly segmented into independent canopy/stem/root segments as aridity increases across continents The resulting hydraulic modularity has been proposed as an adaption to low soil moisture that prevents runaway embolism and minimizes risk of hydraulic failure Here we test the hypotheses that (1) at a regional scale the importance of axis-splitting species in communities declines with increasing elevation as a proxy for precipitation and (2) that this decline is explained by lower occurrence of low-elevation dominant species We evaluated all species for axis splitting and determined importance values in plots along an elevational transect in the Mojave Desert As predicted as elevation increased the total importance of axis-splitting species declined from 100% at low-elevation sites to 75% at the highest elevation site However this decline was not due solely to the decline of the lower elevation dominant species At the high elevation site the influx of new species resulted in a sixfold increase in species richness and almost all of the new high elevation woody eudicotyledonous species exhibited axis splitting non-splitting species were represented by other growth forms (C) 2010 Elsevier Ltd All rights reserved