Variable temperature effects of Open Top Chambers at polar and alpine sites explained by irradiance and snow depth

Abstract

Environmental manipulation studies are integral to determining biological consequences of climate warming. Open Top Chambers (OTCs) have been widely used to assess summer warming effects on terrestrial biota, with their effects during other seasons normally being given less attention even though chambers are often deployed year-round. In addition, their effects on temperature extremes and freeze-thaw events are poorly documented. To provide robust documentation of the microclimatic influences of OTCs throughout the year, we analysed temperature data from 20 studies distributed across polar and alpine regions. The effects of OTCs on mean temperature showed a large range (-0.9 to 2.1 °C) throughout the year, but did not differ significantly between studies. Increases in mean monthly and diurnal temperature were strongly related (R(2) = 0.70) with irradiance, indicating that PAR can be used to predict the mean warming effect of OTCs. Deeper snow trapped in OTCs also induced higher temperatures at soil/vegetation level. OTC-induced changes in the frequency of freeze-thaw events included an increase in autumn and decreases in spring and summer. Frequency of high-temperature events in OTCs increased in spring, summer and autumn compared with non-manipulated control plots. Frequency of low-temperature events was reduced by deeper snow accumulation and higher mean temperatures. The strong interactions identified between aspects of ambient environmental conditions and effects of OTCs suggest that a detailed knowledge of snow depth, temperature and irradiance levels enables us to predict how OTCs will modify the microclimate at a particular site and season. Such predictive power allows a better mechanistic understanding of observed biotic response to experimental warming studies and for more informed design of future experiments. However, a need remains to quantify OTC effects on water availability and wind speed (affecting, for example, drying rates and water stress) in combination with microclimate measurements at organism level.

The Impact of Experimental Temperature and Water Level Manipulation on Carbon Dioxide Release in a Poor Fen in Northern Poland

“…This result may be explained by the fact that OTCs did not affect the temperature as measured with the sensors placed 5 cm below the surface (Chivers et al 2009). However, the impact of OTC may be noticeable during the freeze-thaw and extremely high temperature events (Bokhorst et al 2013). Indeed, we have found significant effects of OTC on plots' microclimate using maximum daily Ta.…”

Forage plants of an Arctic‐nesting herbivore show larger warming response in breeding than wintering grounds, potentially disrupting migration phenology

“…We experimentally warmed vegetation plots at small scale using hexagonal open‐top chambers (OTCs) with a basal diameter of 100 cm, a height of 50 cm, and a side angle of 60°, made from LEXAN polycarbonate (non‐UV resistant; Figure 1). Our open‐top chambers were constructed according to the protocol for the International Tundra Experiment (ITEX) program, which are used in many studies of climate warming (Bokhorst et al., 2013; Elmendorf et al., 2012; Marion et al., 1997; Molau & Edlund, 1996). Open‐top chambers typically warm the soil temperature with 1–3°C (Marion et al., 1997; Molau & Edlund, 1996), which is line with expected climate warming in this century (Stocker et al., 2013).…”

Examination of Surface Temperature Modification by Open-Top Chambers along Moisture and Latitudinal Gradients in Arctic Alaska Using Thermal Infrared Photography

“…A key variable in the interpretation of the treatment responses is the effectiveness of the OTC experimental warming within the different climate regimes, vegetation types, and soil microclimates of the tundra biome. The increase in mean air temperatures within OTCs ranges from 1 to 3˝C and is dependent on size and design, site climate, ecosystem type, and soil properties [3,4,[16][17][18][19][20][21][22]. Soil temperatures at depth have been regularly tested in OTCs, but generally do not show a significant increase [23,24], although surface temperatures do [22].…”

“…The increase in mean air temperatures within OTCs ranges from 1 to 3˝C and is dependent on size and design, site climate, ecosystem type, and soil properties [3,4,[16][17][18][19][20][21][22]. Soil temperatures at depth have been regularly tested in OTCs, but generally do not show a significant increase [23,24], although surface temperatures do [22]. Most of the research has focused on air temperatures measured by shielded resistive sensors or thermocouples rather than tissue or surface temperatures, but the measurements have been limited to just a few locations per plot.…”