| Nowadays, farmland forest netwoks is a kind of windbreaks with Chinese characteristics, and its structure and ecological function of farmland forest netwoks are key issues all the time in our country. How to manange its structure and ecological functions scientificaly, is a key factors to give full play to the integral protection effect. In this paper, the farmland forest netwoks in lowland of the Yellow River was taken as object study based on the theory and method of Ecological Field, in which the Field Effects of major ecological factors such as wind speed, air temperature and humidity etc., together with the spatial heterogeneities of each environmental factor were investigated by field suvey, and Ecological Factor Field models were set up to clarify its shelter mechanism and effectiveness. Their Effective Protection Areas were determined by caculating their effective protection spaces. Finally, their optimal composition of tree species, ages and densities of plantation were summarized for the shelterbelts in forest networks. The aims are to provide with theoretical and technical guidances for the construction of high standard farmland forest network system in the future management practices. The main results are as follows:(1) Integrated climatic effect fields of farmland forest networksThe wind speed field in the forest networks appeared a regular W-shape. For the forest networks with same area but different forest ages, i.e. 8yr, 6yr and 4yr, the average wind speeds were reduced by 31.0%, 40.7% and 46.7% , and their effective protection area ratio were 42.5%, 61.0% and 72.8%, respectively. Their overall protective effectiveness were networks 3(8a) > networks 2(6a) >networks 1(4a). While for the forest networks with different area, i.e. 150m×200m, 250m×200m and 300m×300m, the wind speed were reduced by 49.6%, 49.0% and 39.3%, and their mean effective protection area ratio were 56.2%, 52.0% and 37.2%, respectively. Their overall protective effectiveness were shelternets 4(150m×200m) > shelternets5(250m×200m) > shelternets6(300m×300m).Cooling effectiveness areas appeared in forest networks, which were lower temperature in border of forest belts and higher in the center networks. The temperature were respectively reduced by 10.5%, 15.2% and 21.8% by three forest belts of different age, and their effective protection area ratio were respectively 15.2%, 32.6% and 46.1%. Their total protection effect of them ranged as: shelternets3(8a) > shelternets 2(6a) > shelternets1(4a). The temperature were respectively reduced by 25.5%, 23.2% and 18.9% by three forest belts of different area, and their mean effective protection area ratio were respectively 61.9%, 55.6% and 39.8%. Their total protection effect of them ranged as: shelternets4(150m×200m) > shelternets5(250m×200m) > shelternets6(300m×300m).Measure of the air humidity field in forest belts showed that, most area of the forest belts belonged to high humidity effect zone, but in the center of the forest belts the air humidity was low. The air humidity were respectively reduced by 11.1%, 15.0% and 20.6% by three forest belts of different age, and their effective protection area ratio were respectively 11.6%, 46.2% and 87.3%. Their total protection effect of them ranged as: shelternets3(8a) >shelternets2(6a)> shelternets1(4a). The air humidity were respectively reduced by 41.8%, 39.4% and 37.2% by three forest belts of different area, and their mean effective protection area ratio were respectively 84.8%, 71.0% and 68.4%. Their total protection effect of them ranged as: shelternets4(150m×200m) > shelternets5(250m×200m) > shelternets 6(300m×300m).(2) Integrated climatic effect fields of forest beltsThe protective effects of 6 forest belts with different ages ranged as: main forest belt6 > main forest belt 5 > main forest belt 4 > main forest belt 3 > main forest belt 2 > main forest belt 1. Their were no significant differences for the forest belts larger than 8-year-old . That of different tree species were L-35>I-107>Zhonglin 46 >mixed forest belt 1 >mixed forest belt 2 >Zhonglin 23. In which, the protective effects of L-35, I-107 and Zhonglin 46 were relatively better while that of 2 mixed forest belts and Zhonglin 23 were relatively worse, and that of different planting densities were 3m×3m forest belt > 3m×5m forest belt > 4m×4m forest belt > 4m×6m forest belt. Forest belts of low density had better protective effects.(3) Optimal management models in the lowland of the Yellow riverBased on the results mentioned above, the optimal technical suits are forest age over 8 years, 2-3 line numbers L-35 poplar or I-107 poplar belts, 3m×3m or 3m×5m density,a quadrate shelternets that main forest belt(250m-300m) be perpendicular to assistant forest belt(150m×200m) ,which could achieve the optimal protective effectiveness. |
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