Spatial Variability and Optimal Number of Rain Gauges for Sampling Throughfall under Single Oak Trees during the Leafless Period

• Main Authors: Omid Fathizadeh, Seyed Mohammad Moein Sadeghi, Iman Pazhouhan, Sajad Ghanbari, Pedram Attarod, Lei Su
• Format: Article
• Language: English
• Published: MDPI AG 2021-05-01
• Series: Forests
• Subjects: geostatistic; leafless period; <i>Quercus brantii</i> var. <i>Persica</i>; sampling design; throughfall; variogram
• Online Access: https://www.mdpi.com/1999-4907/12/5/585

This study examined the spatial variability of throughfall (<i>T_f</i>) and its implications for sampling throughfall during the leafless period of oak trees. To do this, we measured <i>T_f</i> under five single Brant’s oak trees (<i>Quercus brantii</i> var. <i>Persica</i>), in the Zagros region of Iran, spanning a six-month-long study period. Overall, the <i>T_f</i> amounted to 85.7% of gross rainfall. The spatial coefficient of variation (<i>CV</i>) for rainstorm total <i>T_f</i> volumes was 25%, on average, and it decreased as the magnitude of rainfall increased. During the leafless period, <i>T_f</i> was spatially autocorrelated over distances of 1 to 3.5 m, indicating the benefits of sampling with relatively elongated troughs. Our findings highlight the great variability of <i>T_f</i> under the canopies of Brant’s oaks during their leafless period. We may also conclude that the 29 <i>T_f</i> collectors used in the present study were sufficient to robustly estimate tree-scale <i>T_f</i> values within a 10% error of the mean at the 95% confidence level. Given that a ±10% uncertainty in <i>T_f</i> is associated with a ±100% uncertainty in interception loss, this underscores the challenges in its measurement at the individual tree level in the leafless season. These results are valuable for determining the number and placement of <i>T_f</i> collectors, and their expected level of confidence, when measuring tree-level <i>T_f</i> of scattered oak trees and those in forest stands.