Unique long-term agro-meteorological measurements of Mongolian grasslands enabled us to investigate the relationship between the phenology of Stipa spp., one of the dominant perennial species (such as emergence, heading, flowering, maturity, and senescence), and moisture conditions for three stations representative of the major vegetation zones, during 1993 to 2002.
The results showed that the emergence date relates neither to a specific temperature nor to an effective accumulative temperature, but to the presence of precipitation that occurs within five days prior to the emergence in most cases. For a northern-most wettest forest steppe region (Bulgan), the precipitation amount, and period of days from emergence to heading are significantly correlated (r = 0.93), while a southward typical steppe region (Arvaikheer) also exhibited a positive correlation (but not exceeding the 5% significance level). The positive correlation occurred at Bulgan most likely, because for drought years, Stipa spp. tended to switch a phenological stage from the vegetative growth (that is, a biomass increase), to reproductive phase (that is, seed production) earlier than for a normal year. One possible trigger for the switching is a decreased soil moisture, associated with a break of the rainy season.