Talk by Dr. Yuriko Yano (Ecology Dept, MSU)

3/7/2019  Wilson Hall 1-144  3:10-4:00pm


In montane ecosystems of the western US, winter snowpack is predicted to decline with rising air temperatures. Winter snowpack not only provides water for trees but also help maintain warmer soil temperatures and higher soil microbial activities over winter. Thus, the decline in snowpack is expected to affect soil nutrient (i.e., nitrogen) availability through altered decomposition rates in soils, and subsequently, forest productivity. However, the direct links between snowpack and nitrogen availability across complex mountain terrain is not clear. Furthermore, it is uncertain whether trees' new growth in spring is supported by nitrogen stored in their old tissues or by that taken up directly from soils. In this presentation, I will present some of the findings from our study in the Lubrecht Experimental Forest in western Montana.

We found that spatial patterns of snowpack was strongly influenced by both elevation and topographic locations (slopes vs. hollows). The spatial heterogeneity in snowpack, in turn, influenced soil temperature, moisture, and nitrogen availability throughout the year. More importantly, soil moisture and nitrogen availability during the summer appeared to be more influenced by antecedent snowpack from the previous year than by current-year summer rain. A whole-tree nitrogen mass balance approach suggested that most of the nitrogen supporting new growth in our Douglas-fir trees was not drawn from nitrogen stored in old tissues. Instead, our results suggest that the trees were using newly acquired nitrogen from belowground to support new growth. Our findings suggest that changes in soil nitrogen availability in the future due to declining snowpack and more severe droughts could hinder trees' ability to acquire enough nitrogen to support new growth.