Cross-community comparison of ecosystem effects of dust-caused early snowmelt

Background/Question/Methods

In alpine and subalpine ecosystems snow depth and the timing of snowmelt drive plant development and water, nitrogen, and carbon cycles. It has been shown that early snowmelt may delay plant development and alter population dynamics, decease runoff on the scale of large watersheds, and increase fire frequency and intensity by causing drier conditions in mid-elevation forests. The changes in the C and N cycles in alpine and subalpine ecosystems that may result from earlier snowmelt can also act as important feedbacks in the global climate system and may have a number of local consequences in biotic communities. We are carrying out a study to measure the effects of early snowmelt on the timing of plant phenophases, soil respiration, mineral N and N mineralization. The study includes 12 blocks across 4 subalpine herbaceous plant communities. Each block contains a dust addition treatment used to advance snowmelt timing, a dust addition following snowmelt to control for fertelization from dust, and a control plot. All plots are 5 X 5 meters. Our treatments are applied near the end of March and we monitor the effects through September. Our study site is on the Wasatch Plateau in central Utah at elevations between 2500 and 2900 meters.      

Results/Conclusions

During 2011, our dust treatments advanced snowmelt by 6-11 days, which is less than the differences reported in similar experiments. We attribute this disparity to continuing snow accumulation late into the spring and a preponderance of cloudy conditions. The treatments advanced plant phenophases throughout the growing season and resulted in significantly less NH₄⁺-N early in the growing season, but not later, with no significant difference in NO₃^—-N at any time during the growing season. These results indicate a difference in the timing of NH₄⁺-N immobilization, and possibly uptake as well. We expect that the results of this season’s treatments will be different because of less snow accumulation this year. By comparing our data to those reported in previous studies, we conclude that the effects of climate change on ecosystem processes tied to snowmelt will be incremental and discontinuous. While alpine and subalpine communities may experience directional shifts in composition and ecosystem processes, these shifts will likely result from ratcheting that occurs in events dispersed between variable years rather than constant and continuous change. Furthermore, the discontinuous nature of snowmelt timing may contribute to stability in community composition and ecological interactions over longer time scales.