Abstract
Abstract. This paper describes the operational methods to achieve and measure both deep-soil heating (0–3 m) and whole-ecosystem warming (WEW) appropriate to the scale of tall-stature, high-carbon, boreal forest peatlands. The methods were developed to allow scientists to provide a plausible set of ecosystem-warming scenarios within which immediate and longer-term (1 decade) responses of organisms (microbes to trees) and ecosystem functions (carbon, water and nutrient cycles) could be measured. Elevated CO2 was also incorporated to test how temperature responses may be modified by atmospheric CO2 effects on carbon cycle processes. The WEW approach was successful in sustaining a wide range of aboveground and belowground temperature treatments (+0, +2.25, +4.5, +6.75 and +9 °C) in large 115 m2 open-topped enclosures with elevated CO2 treatments (+0 to +500 ppm). Air warming across the entire 10 enclosure study required ∼ 90 % of the total energy for WEW ranging from 64 283 mega Joules (MJ) d−1 during the warm season to 80 102 MJ d−1 during cold months. Soil warming across the study required only 1.3 to 1.9 % of the energy used ranging from 954 to 1782 MJ d−1 of energy in the warm and cold seasons, respectively. The residual energy was consumed by measurement and communication systems. Sustained temperature and elevated CO2 treatments were only constrained by occasional high external winds. This paper contrasts the in situ WEW method with closely related field-warming approaches using both aboveground (air or infrared heating) and belowground-warming methods. It also includes a full discussion of confounding factors that need to be considered carefully in the interpretation of experimental results. The WEW method combining aboveground and deep-soil heating approaches enables observations of future temperature conditions not available in the current observational record, and therefore provides a plausible glimpse of future environmental conditions.
Highlights
Measurements through time and across space have shown that the responses of terrestrial ecosystems to both chronic and acute perturbations of climatic and atmospheric drivers can lead to changes in ecosystem structure and ecosystem function
This paper describes the operational methods applied to achieve both deep-soil heating, or in this case, deep peat heating (DPH), and whole-ecosystem warming (WEW) appropriate to the scale of the 6 m tall boreal forest and underlying peat
WEW in the S1-Bog was achieved by warming air throughout the vertical profile of tall vegetation within an opentopped enclosure combined with belowground warming using low-wattage electrical resistance heaters optimized to the 12 m diameter space
Summary
Measurements through time and across space have shown that the responses of terrestrial ecosystems to both chronic and acute perturbations of climatic and atmospheric drivers can lead to changes in ecosystem structure (e.g., species composition, leaf area and root distribution; IPCC, 2014; Walther et al, 2002; Cramer et al, 2001) and ecosystem function (e.g., plant physiology, soil microbial activity and biogeochemical cycling; Bronson, 2008, 2009). The projected magnitudes and rates of future climatic and atmospheric changes, exceed conditions exhibited during past and current interannual variations or extreme events (Collins et al, 2013), and represent conditions whose ecosystem-scale responses may only be studied through manipulations at the field scale. A mean warming of as much as 2.6 to 4.8 ◦C during the summer and winter respectively is expected by the end of this century, based on global carbon model calculations for the IPCC RCP8.5 scenario. That level of warming exceeds the typically observed variation in mean annual temperatures (±2 ◦C) and represents a range of conditions that necessitate experimental manipulation. Future extreme summer heat events may expose ecosystems to acute heat stress that exceed historical and contemporary long-term conditions for which extant vegetation is adapted
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