Open-top chambers for temperature manipulation in taller-stature plant communities

Open-top chambers simulate global warming by passively increasing air temperatures in field experiments. They are commonly used in low-stature alpine and arctic ecosystems, but rarely in taller-stature plant communities because of their limited height.
We present a modified International Tundra Experiment (ITEX) chamber design for year-round outdoor use in warming taller-stature plant communities up to 1.5m tall. We report a full year of results for the chambers’ effects on air and soil temperature, relative humidity, and soil moisture in a northern hardwood forest clearing and a southern early successional grassland site located in Michigan, USA. Detailed construction plans are also provided.
The chambers elevated daytime air temperatures at 1m height by 1.8ºC above ambient levels, on average over an entire year, at both the northern and southern site. The chambers did not affect relative humidity at either site. The chambers did not alter average soil temperature or moisture at the northern site and reduced soil temperatures and soil moisture at the southern site. The chambers increased variability in soil freeze/thaw cycles at both sites.
The chambers achieved predicted levels of warming for mid-century (2046-2065) scenarios consistent with the majority of Representative Concentration Pathways (RCPs) in the International Panel on Climate Change 5th Assessment Report, with minimal experimental artifact. This design is a valuable tool for examining the effects of in situ warming on understudied taller-stature plant communities and creates the opportunity to expand future comparisons across a diversity of systems.