Abstract:

The functions of canopy interception on energy conversion processes in a Chinese Fir plantation ecosystem were studied with the long-term observation data in Huitong. The results showed that the solar radiation absorbed, transmitted, and reflected were 2.554 30 billion (with a absorption ratio of 0.827), 0.253 06 billion (with a transmissivity of 0.082) and 0.274 32 billion J·m ^-2 a^-1 (with a reflection ratio of 0.091) on the canopy, respectively. The conversion of net solar radiation to latent heat with the processes of evaporation from canopy interception amounts to 0.636 95 billion J·m^-2 a^-1 (accounting for 22.9% of the total ecosystem net radiation, and 30.4% of the ecosystem evapotranspiration.), which was an important part of the system energy budget. Canopy interception consumed the raindrop kinetic energy in overcoming the branches and leaves resistance, which gathered raindrops together by branches and leaves and then followed with potential energy in raindrops converted to kinetic energy with falling raindrops. In general, diameter of raindrops from the canopy is bigger than that of the raindrops above the canopy as result of gathering effect of canopy. The kinetic energy of raindrops from the canopy, therefore, was higher than that of raindrops in the atmosphere. And the drop_size distribution from the canopy was influenced by the structure of the canopy layer rather than amount of precipitation and precipitation intensity. The canopy had no significantly efficient effects on decreasing raindrop kinetic energy in the case study with branch height of 7 m and precipitation amount of over 3 mm. However, the canopy would play a key role in decreasing raindrop kinetic energy in both cases of a little amount of precipitation and heavy precipitation intensity, which the canopy could intercept most amount of precipitation in the former condition and the canopy could scatter bigger raindrops to smaller raindrops with striking to leaves in the latter.

Key words: canopy, crown-interception, radiation energy, latent heat energy, raindrop kinetic energy