|RICH, R - University Of Minnesota|
|STEFANSKI, A - University Of Minnesota|
|MONTGOMERY, R - University Of Minnesota|
|HOBBIE, S - University Of Minnesota|
|KIMBALL, B - US Department Of Agriculture (USDA)|
|REICH, P - University Of Minnesota|
Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2014
Publication Date: N/A
Interpretive Summary: In order to study the likely effects of global warming on future ecosystems, including agricultural fields, a method for applying a heating treatment to open-field plant canopies [i.e., a temperature free-air controlled enhancement (T-FACE) system] is needed which will warm vegetation as expected by the future climate. One method which shows promise is arrays of infrared heaters. Therefore, University of Minnesota scientists and an ARS collaborator established a T-FACE experiment on two sites, one at Cloquet, MN, where hardwood trees grow, and a second slightly north near Ely, MN, where conifers grow. Eleven species of tree saplings were planted in both open and closed canopy habitats. Two levels of warming were imposed and overall mean growing season differences of +1.84°C and +3.66°C at 10-cm soil depth and of +1.82°C and +3.45°C of plant canopies for increases in temperature of the heated plots above those of ambient control plots were achieved. As expected, plots with warmer plants and soils had lower soil moisture than ambient plots. Aboveground treatment stability and control were better during nighttime than daytime and in closed versus open canopy sites due to calmer conditions. Heating efficacy in open canopy areas was reduced with increasing canopy complexity and size. This research will benefit all consumers of food and fiber.
Technical Abstract: Conducting manipulative climate change experiments in forests is challenging, given their spatial heterogeneity and canopy complexity. One specific challenge involves warming both plants and soils to depth in ecosystems without much bare ground. We describe the design, implementation, and performance of an open-air warming experiment called Boreal Forest Warming at an Ecotone in Danger (B4WarmED) that addresses the potential for projected climate warming to alter tree function, species composition, and ecosystem processes at the boreal-temperate ecotone. The experiment includes two forested sites in northern Minnesota, USA with plots in both open and closed canopy habitats; seedlings of 11 tree species were planted into native ground vegetation. Treatments include three target levels of plant canopy and soil warming (ambient, + 1.7 'C, + 3.4 'C), as anticipated for 2080-2100. Warming was achieved by independent feedback control of voltage input to infrared heaters aboveground and buried resistance heating cables belowground. The treatments emulated patterns of observed diurnal, seasonal, and annual temperatures but with superimposed warming. For the 2009 to 2011 field seasons, we achieved temperature elevations near our targets with growing season overall mean differences ('Tbelow ) of +1.84°C and +3.66°C at 10-cm soil depth and ('Tabove ) of +1.82°C and +3.45°C for the plant canopies. As expected, plots with warmer plants and soils had lower soil moisture than ambient plots. Aboveground treatment stability and control were better during nighttime than daytime and in closed versus open canopy sites due to calmer conditions. Heating efficacy in open canopy areas was reduced with increasing canopy complexity and size. This experiment resulted in an imperfect performance relative to strict treatment targets, but our results better matched seasonal patterns of long-term climate change in northeastern Minnesota, where summer daytime temperature elevations from climate change have also been lower than in other times of the year.