USFS CitSci: Vernal Windows

In this project, we are providing five classrooms in New Hampshire and Maine with low-cost instruments to track changes in the vernal window using Global Learning and Observations to Benefit the Environment (GLOBE) protocols (snow depth, soil frost, and canopy green-up), and an additional low-cost protocol using soda lime base traps to estimate winter soil respiration.

The vernal window is a key period for the functioning of seasonally snow-covered, forested ecosystems. This window encompasses a time when neither a snowpack nor a closed forest canopy is present, allowing for direct inputs of solar radiation to soils and water bodies (Grime, 1994; Tockner et al., 2010). It opens with snowmelt and closes with emergence of the forest canopy (Creed et al., 2015; Contosta et al., 2017), and historically has been considered a period of ecological opportunity when herbaceous plants on the forest floor and phytoplankton in aquatic ecosystems might experience a surge in productivity (Grime, 1994; Tockner et al., 2010).


Photo mosaic that includes the vernal window—from snowmelt to canopy closure. Photo by Eirik Solheim.

The vernal window contains a series of dramatic transitions that rapidly cross thermodynamic and biogeochemical thresholds. For example, albedo (surface reflectivity) changes three-fold, soils warm upwards of 5ºC, and streamflow increases from its winter baseline to maximum spring freshet within hours to days. While shifts toward earlier transitions during the vernal window are well documented individually, the ecological implications of these changes, including introduction of asynchronous transitions, are less well understood and could result in critical mismatches between organisms, ecosystem surface energy, hydrology, and carbon/nutrient cycling.


An eddy covariance tower in Durham, NH measures carbon dioxide fluxes and albedo over a partially snow covered field. Photo by Elizabeth Burakowski.

Coordinated ground-based observations of several key vernal window transitions would meet a critical data need across broad spatial scales. The vernal window coincides with a typical United States spring school semester and provides an ideal opportunity for teachers to create outdoor classrooms for studying how local weather patterns influence vernal transitions. Furthermore, the GLOBE program has established field sampling protocols that measure can be used to study three important vernal window transitions. The protocols include (1) snow depth, (2) soil frost depth, and (3) forest canopy green-up ( Here, we include an additional tried-and-true protocol to measure soil biological activity using soda lime base traps. Together, the four protocols can be used to track the vernal window.


The protocols used to track the vernal window in seasonally snow-covered lands include (1) GLOBE snow depth, (2) GLOBE soil frost depth, (3) GLOBE canopy green-up, and (4) soda lime base traps to estimate winter soil respiration.

In addition to providing classrooms with in-the-field training and instruments, we will be working with the teachers to co-create learning activities and lesson plans that incorporate the vernal window measurements in their classrooms.