Abstract: Based on the observation data obtained from 69 sampling sites of diffe rent age class forests, and by using biomass expansion factor function, the regr ession equations of stand biomass and volume of the main forest types in Pearl R iver Delta were built, and the regional forest biomass and its dynamics were est imated on the basis of forest inventory data. The results showed that most of th e forests in Pearl River Delta were of young-medium age, which occupied 80% or more of the total forest area, and their undergrowth biomass accounted for abou t 33% of the total forest biomass, indicating that the regional forest biomass c ould be estimated more exactly if undergrowth biomass was fully concerned. In th e periods of 1989〖KG-*2〗-〖KG-*7〗1993, 1994〖KG-*2〗-〖KG-*7〗1998 and 1999〖KG-*2〗-〖KG-*7〗2003, the forest biomass in Pearl Riv er Delta increased by 1467×106 t in total, among which, Pinus massoniana  forest, evergreen broadleaf forest, and conifer and deciduous mixed forest co ntributed about 80%. Young-medium age forest biomass accounted for 90% of the t otal, but the proportion was decreased gradually. The forest area in the Delta a lmost kept unvaried, and the forest biomass was increasing year after year, with an annual increment of about 12%. Better fostering and managing the existing forests is very important to have more forest biomass and better environmental e ffect that regional forests offered.

Key words: Tomato, Nitrogen fertilizer, Nutrient uptake, Calcium fertilizer