Impacts of large-scale oscillations on pan-Arctic terrestrial net primary production

Analyses of regional climate oscillations and satellite remote sensing derived net primary production ( NPP) and growing season dynamics for the pan- Arctic region indicate that the oscillations influence NPP by regulating seasonal patterns of low temperature and moisture constraints to photosynthesis. Early- spring ( Feb - Apr) patterns of the Arctic Oscillation ( AO) are proportional to growing season onset ( r = - 0.653; P = 0.001), while growing season patterns of the Pacific Decadal Oscillation ( PDO) are proportional to plant- available moisture constraints to NPP ( I-m) ( r = - 0.471; P = 0.023). Relatively strong, negative PDO phases from 1988 - 1991 and 1998 - 2002 coincided with prolonged regional droughts indicated by a standardized moisture stress index. These severe droughts resulted in widespread reductions in NPP, especially for relatively drought prone boreal forest and grassland/ cropland ecosystems. The influence of AO and PDO patterns on northern vegetation productivity appears to be decreasing and increasing, respectively, as low temperature constraints to plant growth relax and NPP becomes increasingly limited by available water supply under a warming climate.