Effects of canopy interception on energy conversion processes in a Chinese fir plantation ecosystem

Abstract

The functions of canopy interception on energy conversion processes in a Chinese fir plantation ecosystem were studied with the aid of long-term observation data in Huitong. The results showed that the absorbed, penetrated and reflected amounts of solar radiation were, respectively, 2.5543 × 10⁹ J/(m²year) (absorption rate of 0.827), 2.5306 × 10⁸ J/(m²year) (penetration rate of 0.082), and 2.7432 × 10⁸ J/(m²year) (reflection rate of 0.091) by the canopy. The conversion of net solar radiation to latent heat in the process of evaporation from canopy interception amounted to 6.3695 × 10⁸ J/(m²year) (accounting for 22.9% of total ecosystem net radiation and 30.4% of ecosystem evaporation), which was an important part of the budget of the energy system. Canopy interception consumed kinetic energy of raindrops in overcoming resistance of branches and leaves, which collected raindrops, followed with the conversion of potential energy in raindrops to kinetic energy with falling raindrops. In general, the diameter of raindrops from the canopy is larger than that of the raindrops above the canopy as a result of the collection effort by the canopy. The kinetic energy of raindrops from the canopy, therefore, was higher than that of raindrops in the atmosphere. The drop-size distribution from the canopy was affected by the structure of the canopy layer rather than the amount of precipitation and precipitation intensity. The canopy had no important nor efficient effects on decreasing the kinetic energy of raindrops in our case study with a first branch height of 7 m and precipitation amounts over 3 mm. However, the canopy would play a key role in decreasing kinetic energy of raindrops in two cases, that of a small amount of precipitation and one of heavy precipitation intensity, in which the canopy could intercept the largest amount of precipitation in the former condition and the canopy could scatter bigger raindrops to smaller raindrops with striking leaves in the case of heavy precipitation.

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