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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. [ABSTRACT FROM AUTHOR]

Open-top chamber (OTC) climate change simulation was used to predict the potential effects of climate change on biogeochemistry, including: 1) soil decomposition of three litter types (trembling aspen ( Populus tremuloides Michx.), black spruce ( Picea mariana (Miller) BSP), and Sphagnum); 2) soil nutrient supply rates, and; 3) soil acidity. We assessed the effects of OTCs on these biogeochemical factors in the presence or absence of Sphagnum moss substrate at post-fire and logging sites, in the transitional mixedwood-boreal zone of northwestern Quebec. Higher air temperatures and cooler, drier soils created by the OTC treatment resulted in lower decomposition rates and a higher C:N ratio of aspen litter, and lower Ca concentrations of the Sphagnum litter after 14 months of incubation, as well as lower K concentrations of spruce litter after 24 month incubation. There were no effects of the OTC treatment on decomposition rates for Sphagnum and spruce litter. The nutrient supply rates of Ca and Mg were consistently lower in the OTCs. The supply rates of N were significantly higher in the control plots at the logging site than at any other combination of the OTC treatment and disturbance site. Soil pH was lower in the OTCs by the end of the growing seasons in 2006 and 2007. The results suggest that the impact of climatic changes, as simulated by the OTC treatment, on the soil system of mixedwood-boreal post-disturbance sites is likely to affect biogeochemical processes such as nutrient supply rates and the soil pH, but the effects on decomposition may be minimal. [ABSTRACT FROM AUTHOR]