Abstract
This study examined the spatial variability of throughfall (Tf) and its implications for sampling throughfall during the leafless period of oak trees. To do this, we measured Tf under five single Brant’s oak trees (Quercus brantii var. Persica), in the Zagros region of Iran, spanning a six-month-long study period. Overall, the Tf amounted to 85.7% of gross rainfall. The spatial coefficient of variation (CV) for rainstorm total Tf volumes was 25%, on average, and it decreased as the magnitude of rainfall increased. During the leafless period, Tf 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 Tf under the canopies of Brant’s oaks during their leafless period. We may also conclude that the 29 Tf collectors used in the present study were sufficient to robustly estimate tree-scale Tf values within a 10% error of the mean at the 95% confidence level. Given that a ±10% uncertainty in Tf 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 Tf collectors, and their expected level of confidence, when measuring tree-level Tf of scattered oak trees and those in forest stands.
Highlights
Tree canopies significantly affect the terrestrial hydrological cycle by modifying the distribution of water received during rainfall events
Does the presence of trees affect the amount of water reaching the forest floor, but it determines the spatial distribution of Tf [6,7]
Similar variogram studies of small-scale spatial Tf autocorrelation are scarce; for example, 1–3 m for the isolated olive trees in Spain [41] and 3–4 m for an individual deciduous beech tree in Belgium [43], and likewise at the stand scale; for example, 6–7 m for a 120-year-old beech forest in Luxembourg [44]; 2–6 m for a 42-year-old mixed-hardwood forest [45]; 2.6, 5.3, and 3.9 m in a teak plantation, young secondary forest, and an old secondary forest, respectively [46]; and 4–6 m in a rubber plantation [47]
Summary
Tree canopies significantly affect the terrestrial hydrological cycle by modifying the distribution of water received during rainfall events. The Tf can be further divided into free throughfall, the water reaching the forest floor without coming into contact with vegetation, and release throughfall, which splashes or drips downward from the canopy [5]. Does the presence of trees affect the amount of water reaching the forest floor, but it determines the spatial distribution of Tf [6,7]. To optimize forest management in terms of the availability of water and nutrition in the soil, a better understanding of the spatial distribution of Tf within forests and its controls is imperative [10]
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