THE EFFECT OF TREE CANOPY ON RAINFALL, DEW, SOIL MOISTURE, AND PH

Tree canopy can reduce sunlight, rainfall, dew, and modify the rainfall pH beneath the tree compared to that beyond the tree canopy. Beneath an oak tree with full leaf canopy on October 17, 2006, a 4.4 cm precipitation event was reduced by 32% to 3.0 cm precipitation beneath the canopy. Later in the fall on November 5, 2006 a partial a partial leaf canopy reduced a 2.7 cm precipitation event by 26% to 2 cm of precipitation. The pH of rainwater beneath the canopy is less acid than that beyond the canopy, perhaps because of carbonate dust from a nearby gravel road on the leaves. Similarly, between rainfall events, dew measurements on October 21 and 23 were 54 and 80% less beneath the canopy than beyond the canopy. Thus the dew reduction beneath the full canopy was considerably greater than rainfall reduction beneath both full and partial canopies.

Soil moisture content and pH beneath and beyond the canopy reflect the differences in rainfall, dew, oak leaves, and carbonate dust in a complex way. As expected, the soil moisture was greater in all samples beyond the canopy than in those beneath the canopy, reflecting increased precipitation and dew reaching the ground beyond the canopy. However, the pH of the soil beneath the canopy was more acid than that beyond the canopy, perhaps due to leaching of acid from fallen oak leaves. The soil beneath the canopy contains 40% less calcium (3571 ppm) than that beyond the canopy (2118 ppm). It is hypothesized that the calcium is derived from road dust from the limestone surfaced county road nine meters south of the study area.