Effects of open-top chambers on physical properties of air and soil at post-disturbance sites in northwestern Quebec

Ecosystem responses to current global climate change can be predicted through experimental climate simulations. One such simulation method is the open-top chamber (OTC). The effects of OTCs on environmental factors are potentially complex, and recognizing the numerous interactions among these factors is crucial for the proper use of chambers. We studied the effects of OTCs on microclimatic factors including ambient temperature, relative humidity, soil temperature, and soil moisture. Plant abundance responses were also assessed. Our study involved the construction of 20 OTCs (1 m in diameter and 0.75 m in height; made of clear acrylic plastic) and 20 control plots on substrates with and without Sphagnum moss, at post-fire and logging sites of the transitional mixedwood-boreal forest in the southern part of James Bay region, Quebec. Experimental trials were also conducted to test the effects of OTCs on snowmelt in the Montreal region. Our results suggest that OTC treatment is most evident in terms of increased daytime maximum temperatures (2°C to 3°C), and cooler (up to ～2.4°C), drier (up to 10% volumetric moisture content) soils. Advanced thawing of the insulating snow cover and exposure of soil in the OTCs to low spring temperatures appeared to prolong soil freeze and result in cooler soils. Earlier snowmelt probably also led to earlier onset and overall increased evaporation of meltwater in the OTCs, leading to drier soils. Plant abundance responses to OTC treatment differed depending on plant species. Overall, open-top chambers provide an effective and simple method of climate change simulation, but it is highly advisable that the complex interactive effects, both desired and undesired, are well understood and appreciated before using OTCs for experimental climate simulation.