A radiation and energy balance study of mature forest and clear-cut sites
A radiation and energy balance study of mature forest and clear-cut sites
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成熟森林和砍伐场地的辐射和能量平衡研究
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发表时间：
1985
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通讯作者：
J. Mccaughey
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作者：
J. Mccaughey
1981年夏天，在安大略省Chalk河的Petawwa国家林业研究所，对一片空旷的区域和一片成熟的混交林测量了辐射和能量平衡的组成部分。这项工作集中在砍伐地点，那里支撑着主要由蕨类植物和伐木残留物组成的冠层。在砍伐地点收集了40天的辐射数据。经过前四周的测量(绿色季节)，大多数蕨类植物很快死亡，它们的叶子从绿色变成棕色(棕色季节)。在绿色季节，太阳辐射的日平均反射系数为0.20，而在棕色季节，日平均反射系数降至0.13。根据有限的数据量，森林的对应值为0.13。由于较高的反射系数和较大的白天长波辐射发射，砍伐地在24小时和白天分别比森林减少11%和21%的净辐射。为了通过差示湿度测量来确定鲍文比(β)，在每个地点都使用了包含10个结热电堆的反转温差测量系统。这两个系统都表现良好，特别是森林上空的RTDMS，它能够解决非常小的温差，通常在3米高度上小于0.2℃。平均每小时鲍文比，从0800到1600小时的值计算，在森林的变化范围为0.2到1.0，在绿色季节的砍伐地为0.4到0.8。在砍伐地发现了能量平衡的一个重要的冠层储热成分QS。清晨，部分可用能量被用来加热树冠层内的生物质材料和空气。林冠内储存的热量在当天晚些时候被释放，增加了可用能量总量。在空旷地的‘绿色’季节，Priestley-Taylor系数α(Priestley and Taylor，1972)的日平均值为1.14，个体数值在潮湿的地表条件下有增加的趋势，在地表干燥时下降。林冠干燥时的白天平均α为1.05，湿润时的昼间平均值较高。湿润森林的α增强是截留雨水蒸发的结果(不受气孔阻力的限制)，并伴随着感热向森林的转移。
Components of the radiation and energy balances were measured over a clear-cut area and a mature, mixed forest during the summer of 1981 at the Petawawa National Forestry Institute, Chalk River, Ontario. The work concentrated on the clear-cut site which supported a canopy layer composed primarily of bracken fern and logging remnants.Forty days of radiation data were collected at the clear-cut site. After the first four weeks of measurements (the ‘green’ season), most of the ferns quickly died, and their foliage changed appearance from a green to brownish colour (the ‘brown’ season). The daily mean reflection coefficient of solar radiation determined over the ‘green’ season was 0.20 and decreased to 0.13 for the ‘brown’ season. The corresponding value for the forest was 0.13, based on a limited amount of data. The clear-cut site received 11% and 21% less net radiation than the forest on a 24-hr and daylight-hours basis, respectively, as a consequence of the higher reflection coefficient and larger daytime longwave radiation emission.A reversing temperature difference measurement system (RTDMS), incorporating ten-junction thermopiles was employed at each site in order to determine Bowen ratios (β) via differential psychrometry. Both systems performed well, especially the RTDMS over the forest which was capable of resolving very small differences of temperature, typically less than 0.2 °C over a height of 3 m. The mean hourly Bowen ratio, calculated from values from 0800 to 1600 hr, varied from 0.2 to 1.0 for the forest and from 0.4 to 0.8 for the clear-cut site in the ‘green’ season.A significant canopy heat storage component of the energy balance, QS, was found at the clear-cut site. In the early morning, a portion of the available energy was used to heat the biomass materials and air within the canopy layer. The stored heat within the canopy was released later in the day, increasing the available energy total.The daily mean value of the Priestley-Taylor coefficient α (Priestley and Taylor, 1972) for the ‘green’ season at the clear-cut site was 1.14, and individual values tended to increase during wet surface conditions and decrease when the surface dried. The daylight mean α value during dry canopy conditions at the forest was 1.05, and much higher values occurred when the canopy was wet. The enhancement of α for the wet forest was a result of the evaporation of intercepted rain (which is not limited by stomatal resistance) and the concomitant transfer of sensible heat to the forest.