Department of Forest Resources, University of Minnesota, St. Paul, MN, 55108, USA.
Glob Chang Biol. 2015 Jun;21(6):2334-48. doi: 10.1111/gcb.12855. Epub 2015 Mar 6.
Conducting manipulative climate change experiments in complex vegetation is challenging, given considerable temporal and spatial heterogeneity. One specific challenge involves warming of both plants and soils to depth. We describe the design 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 (recently clear-cut) and closed canopy habitats, where 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). Warming was achieved by independent feedback control of voltage input to aboveground infrared heaters and belowground buried resistance heating cables in each of 72-7.0 m(2) plots. 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 (∆T(above) ) of +1.82°C and +3.45°C for the plant canopies. We also achieved measured soil warming to at least 1 m depth. Aboveground treatment stability and control were better during nighttime than daytime and in closed vs. open canopy sites in part due to calmer conditions. Heating efficacy in open canopy areas was reduced with increasing canopy complexity and size. Results of this study suggest the warming approach is scalable: it should work well in small-statured vegetation such as grasslands, desert, agricultural crops, and tree saplings (<5 m tall).
在复杂植被中进行人为操控气候变化实验具有挑战性，因为这涉及到相当大的时间和空间异质性。其中一个具体的挑战是对植物和土壤进行深度加热。我们描述了一个名为“处于危险中的北方森林生态交错带变暖实验”（Boreal Forest Warming at an Ecotone in Danger，B4WarmED）的露天加热实验的设计和性能，该实验旨在解决预计的气候变暖可能改变北方森林-温带生态交错带树木功能、物种组成和生态系统过程的问题。该实验包括美国明尼苏达州北部的两个森林地点，其中包括开阔地（最近采伐过的空地）和郁闭地两种生境中的样地，样地中种植了 11 种树木的幼苗和本地的地被植被。处理措施包括三个目标水平的树冠和土壤加热（环境温度、+1.7°C、+3.4°C）。通过对每个 72-7.0 m(2)样地的地上红外线加热器和地下埋置电阻加热电缆的独立反馈控制来实现加热。处理措施模拟了观测到的昼夜、季节和年际温度模式，但叠加了变暖效应。在 2009 年至 2011 年的野外季节，我们实现了接近目标的温度升高，在 10 厘米土壤深度处，生长季整体平均差异（∆Tbelow）为+1.84°C 和+3.66°C，植物冠层的（∆T(above)）为+1.82°C 和+3.45°C。我们还实现了至少 1 米深度的土壤加热测量。与白天相比，夜间和郁闭地的样地的地上处理稳定性和控制效果更好，部分原因是环境条件更为平静。在开阔地的树冠区域，随着树冠复杂性和大小的增加，加热效果会降低。本研究的结果表明，这种加热方法具有可扩展性：它应该适用于小体型植被，如草原、沙漠、农业作物和幼树（<5 米高）。
