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

Abstract

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.

Temporal and spatial variation in how vegetation alters the soil moisture response to climate manipulation

“…Longer running studies in wetter systems such as those in the arctic carried out in conjunction with the International Tundra Experiment (ITEX) and on the Tibetan Plateau report only minor effects of OTCs on soil moisture averaged across the growing season (Marion et al 1997;Klein et al 2004; but see Aerts 2006;Dabros et al 2010). We would use some caution in comparing our results, which are based on measurements taken off-center where there would be more interception of precipitation, to those from other studies in which moisture measurements were made in the center of OTCs.…”

“…We manipulated climate using passive warming open top chambers (OTC), similar to those used in other systems (Marion et al 1997;Klein et al 2004) and created areas of bare ground inside the OTCs to evaluate explicitly the effect of vegetation on soil moisture and its dynamics. Because passive warming chambers alter precipitation and air advection and convection in addition to temperature (Marion et al 1997), we recognize them as climate manipulators, not solely warming devices (see Dabros et al 2010). As response variables, we examine standing soil moisture and the rate of soil drying, an approach that compensates for the interception of some precipitation by the climate manipulators.…”

Open-Top Chambers with Solar-Heated Air Introduction Tunnels for the High-Temperature Treatment of Paddy Fields

“…Dabros et al (2010) revealed that the absolute humidity at the time of maximum temperature in an OTC that was set in a transitional mixed wood forest was higher than that in the control during summer. We did not measure the humidity and wind speed inside the chamber.…”

Snow cover manipulations and passive warming affect post-winter seed germination: a case study of three cold-temperate tree species

“…The results of Marion et al (1997) for a variety of passive warming experiments show that desired increases in air temperature can be limited for certain locations, times of day or seasons. Moreover, the results of Dabros et al (2010) show that OTCs can sometimes lead to cooling, possibly caused by cold air that is trapped in a chamber and cannot mix with surrounding warmer air. Marion et al (1997) discussed multiple factors that may affect the temperature response in passive warming devices, including convective heat loss by wind, vegetation shading and efficiency of the chamber heat trap.…”

“…However, they are not often used in forests or during winter (exceptions: Dabros et al 2010, De Frenne et al 2011). This may be because the passive warming ef fect of OTCs depends on the trapping of radiant heat that is emitted when sunlight is intercepted and converted into infrared radiation.…”