| This study is a part of national key program "Songyuan spot for Studying China network of forestry ecology(area)", began in 2000.3 plots with 2000m belts for protecting farmland, were located in 3 villages respectively in Changling county of Songyuan city of Jilin province, in which tree trial and model trial were made.In the trial, we studied the tree growth rule, belt regeneration, tree species and management, and conveyed the biomass of tree, maize and bean in the shelterbelt network, analyzed all the organs of tree and crop to determine the C, N, P, K, ash, organic matter and caloric, constructed GIS for protecting forest for farmland with forest resource data of Songyuan city in 2004, appraised shelterbelt distribution, planned new belts, estimated antiwind benefit and so on. We simulated the growth of belts and confirmed quantity mature age, technic mature age, protective mature age, reasonable regulation period and rotation. Computer simulating is new way to make management program of protective belts.By estimating the permeability, calculating the maximum protecting area ratio to the area protected necessarily, to present protecting area, we found that the anti-wind benefit is incomplete. The reasons are that permeability of some belts is more or less, the amount of belt is deficient, some of the belts have not reached ripe age.Based on survey data, tree height and DHB growth was modeled with 3 functions to make site index curve and growth table, and quantity maturity age was confirmed by 21st to 24th year, the protective maturity age 25th year, technics maturity age 24th to 28th year for shelterbelts on farmland in western of Jilin Province. Taking wood yield, protective benefit, and technic utilization into account, the generation age is not under 28th year. We modeled the cutting, regenerating and growing of belts with Visual Foxpro and estimated the status of every belts from 2006 to future 35 years with growth table in different regulation period and rotation exactly. Through comparing the time sequences and cutting yields of belts conserved in different regulation period and rotation, the regulation period is not under 15th year, the rotation is not under 35th year to ensure mature belts used sufficiently and sustainable.If the straw of bean and maize are used to generate electricity, the nutrient element N, P, organism and ash will be lose from environment 18.30, 0.3934, 534.05, 24.69 g·m-2 and 13.45, 0.5186, 1116.28, 42.55 g·m-2 Respectively. If only trunk is moved, nutrient element will lose 0.66, 0.01759, 426.08, 8.54 g·m-2 from environment per year.Maize straw above ground per hectare can release 113 318 800kJ equal to 3 184.18kg high quality coal and 796.05 RMB. Bean straw above ground per hectare can release 61 294 400kJ equal to 1 722.33kg high quality coal and 430.58 RMB. After utilizing straw, beside the grain benefit, the benefit would increase 16％per hectare maize and 11％per hectare bean. If all straw(except for seeds) is used to generate electricity, N losed from maize and bean land is equal to N of 500kg and 300kg compound fertilizer, to 1324 and 789 RMB. The expense to remedy nutrient losed from soil is high to the benefit obtained from generating electricity. The benefit from straw caloric is equal or less to the expense to recover soil fertility with man-made fertilizer, and unbalance nutrient in soil ecological system and deteriorate soil property.Therefore it is loss to generate electricity using straw. Part of straw is paid back to soil to solve the problem above, but the quantity repaid need to be examined furthermore.The belts affect the environmental conditions and crop growth in negative-effect area. The radiation decreases by 13.43％～35.72％on east and west of belt, and by 24.66～36.84％on south and north, and the radiation on west of belt is higher than east, on south than on north. The radiation changes with the distance from belts, the relationship of average radiation on each points in negative-effect area to distance can described with power and conic. The temperature decrease by 1.09％～3.66％on south and north of belt, by 0.45％-2.53％on east, and change unconspiciously on west. The temperature on south is higher than north significantly, but the temperature is less different. The temperature of surface of soil increases by 0.22％～10.11％on west of belt, by 3.24％～7.46％on east, by 3.24％～7.46％on south, but decreases by 5.02％～11.06％on north, it is higher on south than on north significantly. The water content decreased by 1.83％～16.11％on east and west of belt, and is less different on both sides. The root in OH on south and north of belt accounts for 1/2 whole root, 3/4 in 1/4H, 4/5 in 1/2H. The root distributes in 30～60cm soil mostly. The height of maize is higher significantly on south than on north, the height and biomass of single maize relate to distance from belt signicantly linar and the relationship can be described with unitary linear model.Through we appraised protective forest in Songyuan city with GIS, the result indicated that shelterbelt network is bad of shape, distribution, direction. On the base of present protective forest, we designed new shelterbelts, shelterbelts for improving soil, sand defence belts, shelterbelts on bank, shelterbelts on road, shelterbelts on grass, shelterbelts on farmland, their length are 2 462 913m, 131 931m, 2 278 476m, 7 346 266m, 8 924 636m, 15 950 555m. All of the belts designed can be stored, output on screen or on printer in digital type.Doing the studies, we made the GIS for protective forest on farmland. The system can realize managing map file, managing map and other ordinary function. It can evaluate shelterbelt, design shelterbelt, calculate the parameter about landscape automatically. It can add some lines(belts) on screen, split a line into two lines, delete some lines, and save all of the results. It can open or save file in different types.
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