Ecosystem Gross Primary Productivity After Autumn Snowfall and Melt Events in a Mountain Meadow

Abstract

Vegetation productivity is increasing in the U.S. Northern Great Plains but decreasing in some nearby Northern Rocky Mountain grasslands due to increases in aridity. It is unclear if decreases to montane grassland productivity from drying autumns can be partly offset by late‐season green‐ups after precipitation events. These include the multiple snowfall and snowmelt periods that often characterize the summer‐to‐winter transition, but are difficult to observe due to logistical constraints. Here, we quantify changes to vegetation indices and ecosystem carbon uptake that occurs after snowfall and melt in climatological autumn in a montane grassland in Montana, USA using eddy covariance, phenological camera, and remote sensing analyses. Carbon dioxide flux follows a diurnal pattern after autumn snowmelt events despite overall ecosystem C loss, suggesting that post‐snowmelt photosynthesis helps dampen C loss during autumn and provides fresh photosynthate to support ecosystem functioning. Light‐saturated photosynthesis after three snow events was not statistically different than before snowfall (∼6 μmol CO2 m−2 s−1 in 2016 and ∼2.5 μmol CO2 m−2 s−1 in 2017). Observations are consistent with the notion that canopy photosynthesis is resistant, rather than resilient, to autumn snow. MODIS indicates that post‐snow greenups can occur, but not every year. Such events likely play a small role in the annual ecosystem carbon balance but may be disproportionately important for organisms faced with dwindling late‐season forage. Future efforts should seek to understand the community and ecosystem consequences of vegetation functioning during autumn as part of an expanded effort to understand phenological changes during this under‐studied and changing time of year.

Drivers of contemporary and future changes in Arctic seasonal transition dates for a tundra site in coastal Greenland

“…The monthly (Jun–September) wind speed ranged from 1.5 to 2.6 m/s (Figure S7), thus we hypothesized such a small range of wind speed could not determine the EOF variations in this study. Sporadic snowfall events before SOD of the following snow cover season could change land surface characteristics and soil thermal environment, but the vegetation photosynthesis is resistant to cool soil temperatures resulting from autumn snow melt (Barrere et al., 2018; Stoy et al., 2022). Moreover, senescence is more synchronous than the onset of the growing season across large areas because it is cued by not only air temperature and precipitation but also photoperiod and radiation (Borner et al., 2008; Ernakovich et al., 2014).…”

A 21st century shift in the mechanisms of the early-winter United States snowfall variability

“…Snowfall invariably influences both human society and natural ecosystems with positive or negative impacts (Schmidlin and Kosarik 1999, Smith and Matthews 2015, Stoy et al 2022, Zhu et al 2022, Do et al 2023. In December 2022, a sequence of winter storms hit the majority of the United States (US), which killed at least 87 people and caused billions of dollars in damage (National Centers for Environmental Information 2023).…”

“…We will focus primarily on the early-winter season (i.e. October-December or OND) when the US snowfall typically starts to accumulate and could cause severe societal impacts although the total amount of snowfall may be less than that for winter (Schmidlin and Kosarik 1999, Stoy et al 2022, Yao et al 2023. As we will show later, this is also the season when a prominent teleconnection pattern shift relevant to US snowfall variability is identified.…”