Photosynthetically Active Radiation in the Clearcut Site at Harvard Forest 2013

The purpose of these measurements was to capture the light attenuation of the canopy throughout the growing season, which can help in determining leaf area/canopy openness at the site. Measurements were done along a 50-m-long transect (one of the ones used for line-intercept vegetation surveys, on the side of the EC-tower). Eight measurement locations were established along the transect, equidistant, and marked with a bright orange flag. Measurements were taken with a LI-COR LI-191 Line quantum sensor as described below. Before and after measurements along the transect, PAR-readings were taken in an open area (away from canopy cover) either at a log along the access road to the site or up on the fire tower nearby. At each location along the transect, two measurements were taken – one at the ground surface and one at a height of 1.3m (diameter at breast height).

本次测量旨在获取整个生长季内林冠的光衰减特性，所得数据可辅助确定样地的叶面积与林冠开阔度。测量沿一条长50米的样带开展，该样带为涡度协方差塔（EC-tower）一侧用于截线法植被调查的样带之一。该样带上共设置8个等间距测量点位，并以亮橙色旗帜进行标记。本次测量采用LI-COR LI-191型线状量子传感器开展，具体操作说明如下。在沿样带完成测量的前后，需在远离林冠遮蔽的开阔区域采集光合有效辐射（PAR）读数，采集点位可设置在通往样地的进场道路旁的原木处，或附近的森林防火瞭望塔上。在样带的每个测量点位上，需完成两次测量：一次采集地表位置的数据，另一次采集1.3米高度处的数据，该高度为胸高直径测量的标准高度（diameter at breast height）。