A seed–seedling conflict for <i>Atriplex polycarpa</i> shrubs competing with exotic grasses and their residual dry matter

Native saltbush, Atriplex polycarpa, shrub populations are widely diminished and fragmented in the southern San Joaquin Desert of California due to habitat conversion invasion by exotic annual grasses mostly Mediterranean origin. The role these play saltbush population demography is not well understood. We hypothesized that seedling recruitment growth limited competitive interactions with grasses, preventing stands from maintaining their expanding. predicted would be reduced (1) light moisture competition grasses; (2) physical barrier grass residual dry matter (RDM) formed during senescence. To test our predictions, we investigated under field conditions across six populations. examined how variations edaphic structure water availability site may have affected longer-term dynamics. In experimental plots where seeds were sowed, RDM emergence compared sown absence RDM; post-emergence was significant. Saltbush seedlings transplanted into had lower mortality less herbivory invaded grassy habitats planted bare zones between established, mature shrubs. Edaphic variation likely key factors affecting success both recruitment. Our results suggest there a seed–seedling conflict: Sites favorable for (minimal cover among shrubs) unfavorable survival high herbivory. Conversely, sites (high coverage away emergence. produced represents an important stabilizing feedback favoring continued dominance.