Decline in length of the summer season on the Kola Peninsula, Russia

By analysing records made in the northern taiga forests of the Lapland Reserve (Kola Peninsula, Russia) during 1930-1998, we unexpectedly discovered a decline in the length of the snow-free and ice-free periods by 15-20 days due to both delayed spring and advanced autumn/winter. Respective seasonal temperatures best explained the dates of all phenological phases: 1degreesC shift in temperature was approximately equal to 2-5 day shift in phenology. However the phenological shifts during the observation period are much larger than could be expected from the slight (0.56degreesC) drop in temperatures during August-September, suggesting that the biotic effects of a very slight cooling have been enhanced by one or more unknown factors. Although emissions of sulphur dioxide from the nickel-copper smelter at Monchegorsk may have contributed to the observed trend (via changes in regional radiative budget), we found no evidence of direct pollution impact on dates of birch autumnal coloration or birch leaf fall, which exhibited the largest (22 days) shift between 1930 and 1998. The detected phenological trends agree with an increase in winter (snow) precipitation in the study area by 44%; however, effects of precipitation on any of the investigated phenological phases were far from significant. Our results highlight the importance of phenological records for the assessment of past regional environmental changes, and demonstrates that the prediction of even the simplest biotic responses to the Global Changes requires a profound understanding of the interactive impact of abiotic factors on the ecosystem.