Effects of Small Rainfall Events on Haloxylon ammodendron Seedling Establishment in Northwest China

Small rainfall events (≤5 mm) account for a large proportion of rainfall amount, and may play an important role in triggering plant regeneration in arid ecosystems. However, their potential ecological importance in seedling establishment of desert shrub has been previously ignored. We conducted two parallel pot experiments to examine the effects of amount and interval of small rainfall events on seedling emergence, growth and survival of the dominant shrub species Haloxylon ammodendron in sand dunes of Northwest China. The results showed that: (1) decrease in rainfall amounts did not significantly lower seedling emergence, growth and survival in comparison to control, while the large increase (+20%) in rainfall amount resulted in significant increase in seedling emergence, growth and survival for both continuous and intermittent small rainfall events; (2) continuous small rainfall events were more effective than intermittent ones for triggering seedling emergence, growth and survival; (3) small rainfall events may impact the seedling establishment of H. ammodendron only in wet years. Our results provide insights into the effects of small rainfall events on seedling establishment processes, and highlight the inherent complexity in predicting how seedling establishment of shrub species in desert ecosystems will respond to future fluctuations in small rainfall events.