Department of Botany, Program in Ecology, University of Wyoming, 1000 E. University Avenue, Laramie, WY 82072, USA.
Tree Physiol. 2012 May;32(5):599-611. doi: 10.1093/treephys/tps021. Epub 2012 Apr 25.
Boreal forests are crucial to climate change predictions because of their large land area and ability to sequester and store carbon, which is controlled by water availability. Heterogeneity of these forests is predicted to increase with climate change through more frequent wildfires, warmer, longer growing seasons and potential drainage of forested wetlands. This study aims at quantifying controls over tree transpiration with drainage condition, stand age and species in a central Canadian black spruce boreal forest. Heat dissipation sensors were installed in 2007 and data were collected through 2008 on 118 trees (69 Picea mariana (Mill.) Britton, Sterns & Poggenb. (black spruce), 25 Populus tremuloides Michx. (trembling aspen), 19 Pinus banksiana Lamb. (jack pine), 3 Larix laricina (Du Roi) K. Koch (tamarack) and 2 Salix spp. (willow)) at four stand ages (18, 43, 77 and 157 years old) each containing a well- and poorly-drained stand. Transpiration estimates from sap flux were expressed per unit xylem area, J(S), per unit ground area, E(C) and per unit leaf area, E(L), using sapwood (A(S)) and leaf (A(L)) area calculated from stand- and species-specific allometry. Soil drainage differences in transpiration were variable; only the 43- and 157-year-old poorly-drained stands had ∼ 50% higher total stand E(C) than well-drained locations. Total stand E(C) tended to decrease with stand age after an initial increase between the 18- and 43-year-old stands. Soil drainage differences in transpiration were controlled primarily by short-term physiological drivers such as vapor pressure deficit and soil moisture whereas stand age differences were controlled by successional species shifts and changes in tree size (i.e., A(S)). Future predictions of boreal climate change must include stand age, species and soil drainage heterogeneity to avoid biased estimates of forest water loss and latent energy exchanges.
北方森林对气候变化预测至关重要，因为它们的土地面积大，能够固碳和储存碳，而这又受到水分供应的控制。预计随着气候变化，这些森林的异质性会增加，表现为野火更频繁、生长季节变暖且更长、以及森林湿地可能会干涸。本研究旨在量化加拿大中部黑云杉北方森林中，排水条件、林分年龄和树种对树木蒸腾作用的控制。2007 年安装了热耗散传感器，并在 2008 年收集了 118 棵树（69 株黑云杉（Mill.）Britton、Sterns 和 Poggenb.（黑云杉）、25 株颤杨（Populus tremuloides Michx.）（颤杨）、19 株加拿大铁杉（Pinaceae banksiana Lamb.）（加拿大铁杉）、3 株北美落叶松（Larix laricina (Du Roi) K. Koch）（北美落叶松）和 2 株柳属植物（柳树））的数据，这 118 棵树位于四个林分年龄（18、43、77 和 157 年）的林分内，每个林分内都有一个排水良好和排水不良的林分。使用从林分和树种特定的异速生长关系计算出的边材（A(S)) 和叶片（A(L)) 面积，将 sapflux 得出的蒸腾估计值表示为单位木质部面积（J(S))、单位地面面积（E(C)) 和单位叶面积（E(L))。土壤排水对蒸腾的影响是可变的；只有 43 年和 157 年的排水不良林分的总林分 E(C)比排水良好的位置高约 50%。总林分 E(C)在 18 年至 43 年生林分之间最初增加后，随着林分年龄的增加而趋于下降。蒸腾作用的土壤排水差异主要受短期生理驱动因素（如蒸气压亏缺和土壤水分）的控制，而林分年龄差异则受演替物种更替和树木大小变化（即 A(S))的控制。未来对北方气候变化的预测必须包括林分年龄、物种和土壤排水的异质性，以避免对森林水分损失和潜在能量交换的有偏差估计。
