The project was initiated several years ago in response to the growing concern over an insufficient timber supply, and the need to protect agricultural land from erosion. Many of the forests have been harvested for timber, leaving large areas of soil exposed. The project mainly uses Paulownia and Poplar to achieve a "desired standard of greening," and has already met with measurable success. The goal of the project, or the "desired standard of greening" entails the following objectives:
Six experimental stations were established in 1979 to breed and select varieties of Paulownia appropriate for different climatic zones.
Forest cover on the plains has already increased from 2% to 10.7%, over some 3.15 million ha of farmland, or nearly half of the total area designated for the project.
A system called "four-sided" planting has been used in China since the 1950s. In this system trees are planted along the contours of roads, villages, ditches, and rivers. These serve as a general source of timber, fodder and fuelwood.
In China Paulownia is used most extensively in windbreaks. The beneficial microclimatic effects protect food crops from the drying winds that can destroy a crop. These windbreaks or "forestry nets" reduce wind speed at crop height by 30% and increase humidity by 7-12%.
P. elongata is commonly intercropped with wheat, rape, garlic, cotton, corn, bean, peanut, sweet potato, watermelon and vegetables. Most intercropping spacings are 5 x 20-50 m. Spacing of intercropped trees is important. When intercropped with Paulownia, wheat yields were the same as in an open field when the trees were planted 5 m apart with 10 m between rows. When the distance was increased to 20-40 m between rows, wheat yields increased 7-10%.
The project has improved the microclimate for crops and pasture, and provided an immediate economic benefit for local farmers in food production.
Within just 15 years the Chinese have made enormous progress in the implementation of this social forestry project. Benefits have been significant and quickly realized. There has been a remarkable increase in food production, timber supply, and livestock production, while land degradation has been halted over large areas.
A full-grown Paulownia can reach a height of 30 to 60 feet, and grow up to 8 feet in one year under ideal conditions. This tree is well-suited for agroforestry systems because of its deep tap root. It does not compete with shallow rooted crops. The roots condition the soil and retain moisture. The large leaves can be used as fodder. A 10-year-old tree can produce 30 kg of dry leaves annually, and 400 kg of young branches. The leaves also serve as a valuable soil amendment; they break down slowly, providing a slower release of minerals to the soil than small leaves.
Paulownia can adjust to many soil conditions, but is susceptible to water logging and prefers deep, well-drained soils. It proliferates readily on disturbed hillside soils. Sandy or heavy loam is favored, clay or stony soils are not. It can adapt to brown forest soils in temperate zones, yellow soils in subtropical zones, and a pH as low as 3-5. Annual precipitation range from 500-2,600 mm. A humid climate is preferred. A daily mean temperature of 24-30íC favors optimal growth.
This tree needs a lot of light. Careful spacing and management are necessary to optimize shade and other potential benefits. It is very similar to poplars in management. Paulownia is susceptible to insect attack, disease and an airborne fungus called witches broom. P. elongata is the fastest growing species.
Saik Yoon, C. and Toomey, G. Paulownia, China's wonder tree. IDRC Reports, April 1986.
Benge, M. 1987. Paulownia tormentosa, an Excellent Tree for Agroforestry and Windbreaks in the more Temperate Regions of the Developing Countries. S&T/FENR Agro-forestation Technical Series #23.
Dr. P. Beckjord
4304 Kenny St.
Beltsville, Md. 20705 U.S.A.