Studies On Tree Species Selection And Arrangement In The Conversion Of Farmland To Forest(CFF) Project On The Loess Plateau

In this paper, it was commented on the current situation, main problems and the technology of drought resistant for afforestation in the conversion of farmland to forest (CFF) project on the Loess Plateau. The water consumption of six main plantation tree species on the Loess Plateau under water supply normally was studied in greenhouse. The water consumption patterns of seedlings in normal water supply were observed. Moreover, it was also studied by analyzing of grow situation, soil water content, volume weight of soil, soil porosity, soil nutrient elements and chemical properties of different arrangement in typical field. Target of the researches is to meet the need in choice of tree species with lower water consumption, higher survival rates, and the reasonable spatial structure and stand density in CFF project on the Loess Plateau.The results of studies on water consumption of Pinus tabulaeformis, Platycladus orientalis ,Populus tomentosa, Fraxinus velutina, Sophora japonica and Salix matsudana Koidz in normal water supply showed that the daily variations in WCA and WCR of seedlings were clearly. The daily highest amount and rate of water consumption of seedlings was at 10:00-14:00. Moreover, the WCAs were half of that in whole day, the water was consumed mainly in daytime, and the daytime WCA of seedlings was occupied about 85% to 95% of the amount of whole day. The daytime WCR of seedlings in August was 8.5 to 9.5 times as much as that of night. The average hourly WCA in daytime of seedlings is highest in sunny weather, lower in cloudy day and lowest in rainy day. The results of research on water consumption properties of seedlings showed that the coniferous species such as Pinus tabulaeformis and Platycladus orientalis obviously lower than broadleaf tree species in average hourly WCA in daytime, WCAs and WCR .The results of research on different density showed that average hourly WCR indaytime of five seedlings aside from Salix matsudana Koidz were higher in single than that of in two or in three in the same species. That is to say , the average hourly WCR in daytime of seedlings in two or three were decreased in different extent than that of in single. Though seedlings in different density, the permutation of WCR of different seedlings is constant: Salix matsudana Koid>Fraxinus velutina>Populus tomentosa> Sophora japonica> Platycladus orientalis>Pinus tabulaeformis. It is very important to select tree species, which has lower water consumption and drought tolerance such as Pinus tabulaeformis and Platycladus orientalis, and set reasonable stand density in recovery and reconstruction of forest vegetation in CFF project on the Loess Plateau.The results of studies on the effect of different tree species arrangement on the typical field in CFF project showed that soil water content, soil organic substance, total of nitrogen, phosphorus and potassium in different arrangement were higher than that of sloping-farmland. And the soil nutrient elements has been improved in different extent than that of sloping-farmland. So recovery and reconstruction of forest vegetation would be advantageous of water and soil conservation, decrease in loss of soil nutrient elements, improved on soil fertileizer and adjusting micro-climate and micro-ecology condition. By application of drought-resistant afforestation technology in CFF project on the Loess Plateau, it wasn't only decrease soil water content, but also increase soil water content only if selected suitable tree species and set reasonable stand density.