Ecosystem responses to experimental manipulations of temperature provide key evidence for predicting effects of climate change.  Direct simulations of increased radiative forcing have been concisely achieved using electric infrared heaters.  However, cost and feasibility have limited the deployment of such active heaters to a relatively small set of studies and sites.  Passive devices for warming plants and soil have therefore been widely adopted, particularly open-top chambers in temperature-limited environments.  We propose an alternative approach for passive warming of plants and soil, in which sky radiative forcing is directly simulated with minimal interruption of precipitation and convection.  The design is comprised of a horizontal panel containing nearly vertical slats of clear glazing spaced at several cm intervals, referred to as the “louvered frame”.  In a replicated experiment, we examined the microclimate effects of a louver frame that was 1 x 1 m and elevated 50 cm above ground, and constructed of clear acrylic and wood slats.  Comparisons were made with a design having only a horizontal, solid sheet of glazing arranged similar to the louver panel, and a traditional open-top chamber design (ITEX chamber), and all were compared to unmanipulated control conditions. 

Results/Conclusions

The louver frame generated as much or more warming of minimum daily temperatures of soil and model plant surfaces (mean increase of 1.5C, maximum increase near 4C) compared to the other designs, mainly by increasing longwave radiation from the upper hemisphere to plants and soils.  In contrast, the ITEX chamber created up to 18C of warming during days by reducing convective cooling.  The louver frame had substantially less interception of snow and rainfall than the other design types.  Compared to previous passive warming devices, the louver frame offers a more effective means for simulating increases in minimum temperatures, with much less disruption of convection and precipitation.