Background/Question/Methods   Climate dynamics are complex and can occur at multiple temporal scales. In the southwestern United States, short-term climate events such as ENSO (El Nino-Southern Oscillation) are widely recognized to play an important role in the dynamics of deserts. Less well understood are multi-decadal climate oscillations such as the Pacific Decadal Oscillation (PDO). The Pacific Decadal Oscillation is a recently discovered phenomenon related to multidecadal patterns in sea surface temperatures in the Pacific. The PDO has been shown to alter the relationships between warm and cold ENSO events and winter precipitation in the southwest (Gutzler et al 2002). However, how these long-term changes in winter precipitation patterns driven by shifts in the PDO affects biological communities is less understood. We use data from a long-term site near Portal, AZ, which started monitoring of a Chihuahuan Desert ecosystem at the start of the previous PDO cycle to examine the response of plant and animal communities to multidecadal climate shifts.

Results/Conclusions   Long-term shifts in winter precipitation resulted in at least a 3-fold increase in the number of shrubs at the site. We show that long-term changes in the rodent community started several years after the PDO cycle shifted from a cool phase to a warm phase in 1977. Rodent community composition continued to change directionally over most of the 30 years of the study (p < 0.05). Long-term increases in the abundance of species affiliated with shrublands (p <0.05) suggest that changes in the rodent community are linked with shift in habitat. A recent shift in the PDO from a warm cycle to a cool cycle yields an opportunity to understand how cyclical climate changes drive community dynamics.