Climate-warming Simulation in Tundra: Enhanced Precision and Repeatability with an Improved Infrared-heating Device

Abstract

Climate-warming experiments in tundra require an accurate and repeatable technique for temperature increase, as temperatures are low and vegetation often heterogeneous. However, remote locations have constrained most studies to using uncontrolled, passive enclosures. Here we present an improved prototype of our Free Air Temperature Increase (FATI) system, an apparatus to elevate vegetation temperature in the open field by electronically modulated infrared irradiation. Three modifications are introduced to enhance precision and repeatability: (1) noncontact sensing of canopy temperature (T_canopy) with semiconductors, (2) an optimizing device to attune individual FATI-units, and (3) high-speed data logging. Performance tests in the High Arctic tundra of northeast Greenland during autumn 1998 demonstrated more reproducible warming compared with the original system: average increments of canopy temperature (ΔT_canopy) obtained in different patches of vegetation varied no more than 0.16°C. Most fluctuation in ΔT_canopy was also eliminated, with instantaneous values within ±0.5°C of the target increment of +2.5°C for at least 87% of the time. Average warming in the upper soil layers was close to average ΔT_canopy, and decreased gradually with depth from +2.7°C at 2.5 cm to +2.0°C at 20 cm below the surface (means for three FATI-units). The improved technique is not only of interest to investigations in the Arctic, but also to other applications which depend highly on accurate temperature control, for example, studies of climate-warming effect on ecosystem carbon balance or plant growth.