Characteristics analysis of surface runoff for three types of forests in Hainan Island, southern China

ObjectiveThe aim of this study was to provide a scientific basis for the accurate evaluation of water conservation benefits in three forest types and sustainable management of plantations. We discussed the monthly dynamics of surface runoff from eucalyptus plantations, rubber plantation and secondary forest and the surface runoff laws of different rainfall levels.

MethodRunoff fields were established in different forests in Limu Mountain, Hainan Province, southern China, including four fields in eucalyptus plantations (F1, F2, F3, F4), one field in rubber plantation (F5), and one field in secondary forest (F6). Surface runoff observation was carried out from April 2010 to March 2011 and the surface runoff characteristics of three forest types were compared and analyzed. The monthly ground runoff coefficient was predicted by the basic idea of G(2,1) model and sigmoid model.

Result(1) The annual surface runoffs of F1−F6 fields were 230, 49, 170.1, 84.2, 340, 396.4 mm, of which the rainy season accounted for 90.28%, 91.61%, 87.89%, 92.74%, 91.86%, 90.88%. (2) The monthly surface runoff was all ordered as F6 > F5 > F1 > F3 > F4 > F2. (3) The total runoff of the secondary forest in the rainy season was 1.75−8.11 times of the eucalyptus plantations, and the rubber plantation was 1.49−6.89 times of the eucalyptus plantations. Surface runoff occurred when the rainfall exceeded 10 mm, and the surface runoff increased with the rainfall level. The rainfall greater than 60 mm accounted for 57.95% of the total annual rainfall, while the surface runoff from F1 to F6 fields accounted for 84.92%, 89.08%, 82.14%, 87.75%, 79.56%, 83.49% of the annual surface runoff. (4) The sigmoid model predicted that the surface runoff coefficient of the rainy season was higher than the dry season, but the surface runoff prediction of each field in August 2010 was more biased.

ConclusionOur results indicate that the surface runoff of 5-year-old eucalyptus and 6-year-old rubber plantations in the region are not always larger than that of secondary forests. It is necessary to consider the forest age and geographical location when evaluating the water conservation capacity of plantations.