Study On 3PG Model For Eucalyptus Plantations In Leizhou Peninsula

It's used to be mainly management means for forest managers to scientifically, effectively plan and manage forest production by forest growth and yield models, but most among these are empirical models instead of mechanistic models or processed models. With the great improvement of forest production intensivism and increasing attention of environmental protection, processed-based forest growth models can be more and more attached importance to by forest researchers and its resource managers, as a great number of subjects such as physiological plant ecology, computers agrology, meteorology, etc, make an immense progress.3PG model is introduced on the papers, which can predict stand productivity with combinations of climate, site condition, management and species and is widely applied as a planning tool by forest managers in many countries and regions throughout the world. It uses a series of equations to simulate the carbon balance, water balance and diminishing solar radiation in order to simulate dynamically monthly change of forest and its environment. The model calculates total carbon fixed from canopy quantum efficiency and utilizable, absorbed photosynthetically active radiation, obtained by correcting photosynthetically active radiation by a forest canopy, simulated by Beer-Lambert law relating the absorption of light, for the effects of temperature, nutrition, atmospheric vapor press deficit, stand age and soil water availability. The carbon fixed by forest canopy is partitioned into leaves, stems and roots respectively as to some allocation proportions. At the end, the volume is got from amount of carbon in stems. At the same time, in view of the change of soil water storage, it simulates dynamitic change among atmospheric rainfall, groundwater, irrigation, forest transpiration, deep drainage and soil water.Measure of tree and stand growth, biomass relationships , soil available water content and its depth , groundwater depth and water use from plantations on the Leizhou Peninsula of western Guangdong province have used to estimate model parameters values for major commercial eucalyptus genotypes: E.urophylla, ABLw5, and CloneU6. Climate data for modeling may be satisfactorily estimated from routine daily meteorological observation including temperature, rainfall, and solar radiation etc.The comparison between modeled and observed values of stand volume, DBH, height, LAI, leaf weight, stem weight of above three Eucalyptus plantations and water use of E.Europhylla showed that 3PG model is a convenient and efficient means of predicting the productivity of Eucalyptus plantations with the satisfactory accuracy and reliability of modeled predictions and could provide a successful and versatile basis for decisions on stand establishment, tending and harvesting for forest managers in relation to planting location, climate, soil conditions and forest management; it's advisable to make 7-year rotation for Urophylla and 6 year for other species; the total yearly transpiration with not more than 600 mm that is far less than rainfall in the area ,which proves that the opinion of Eucalyptus plantaions depleting too much groundwater can't hold water. At the same time, growth of Eculyptus plantations in 10 years, their weibull diameter distributions can be predicted and volume distribution map in the whole Leizhou Peninsula can be demonstrated. As the development of the model, it will play more and more important role in the future if it can be integrated into other systems like GIS.