Abstract:

Based on the data collected for 17-years successive observation at Huitong National Key Field Scientific Experiment and Research Station, runoff changes in Chinese Fir plantations at different age classes were investigated. Results showed: Due to tending treatment (e.g. site preparation and weeding), the surface runoff in the stand at the age from 1 to 5 year (age class I) was the smallest among all age classes and the annual average surface runoff coefficient accounted for 0.007 1. However, the surface runoff increased with age class increase after tending treatments and reached the maximum value at the stand age from 10 to 15 year (age class III ), with annual average surface runoff coefficient of 0.18 4. A decline in surface runoff was found at the stand age from 15 to 20 year (age class IV). The annual average surface runoff coefficient was 0.009 8 and approximated to 50% of the stand at the age class III. The underground runoff gradually decreased with stand age class increase. The highest underground runoff coefficient of 0.301 2 occurred at the age class I, which was about 2 times of that in the mature stand before clear cutting (0.157 7). The underground runoff coefficient at stand age class IV declined to 0.208 2, about 65.8% of that at the age class I . The decrease of annual average underground runoff coefficient as stand growth was attributed to increase in interception and transpiration because of canopy development, and improvements in soil structure. The surface runoff only accounted for 2.3% to 7.% of the total runoff and underground runoff is the dominated pathway of watershed. The monthly runoff of all the age classes was proportional to the mean monthly rainfall. The rainfall during the period from April to August was 62.2% of the total annual rainfall and the runoff was amounted to 75.4% of the annual runoff. The average runoff coefficients from April to August were estimated to be 0.378 4, 0.322 4, 0.279 0 and 0.263 4 for the stand age class I, II, III and IV, respectively. The result of stepwise regression indicated that the monthly precipitation and stand age of the stand influenced the monthly runoff. The established multinomial regression equations could be used to forecast the monthly runoff.

Key words: Chinese Fir plantation, stand age, surface runoff, underground runoff, runoff coefficient, regression model