It is sometimes useful to look back when moving forward.
The future requires that the challenges of creating sustainable systems that provide food security and nutritional diversity, be met. Intensive, monoculture based agricultural systems, commonly in use today, directly contribute to environmental issues such as desertification, eutrophication of rivers, and soil degradation. The ability to create sustainable systems that provide food security and nutritional diversity is severely compromised under such conditions.
Systems that meet these challenges have been used before. Historically, intercropping systems—planting different but complimentary crops in close proximity to each other--have been used to sustainably provide food security and nutritional diversity. More recently, intercropping systems have been used at the core of holistic systems that, while providing agricultural sustainability, also serve as economic development platforms through the sale of surplus production. Concomitantly, microfinancing programs have been used to accelerate the creation, development and maturation of these platforms through capital injections. These intercropping systems offer more sustainable agriculture production with reduced input, stabilized yield and improved nutrient uptake without the associated environmental degradation caused by intensive monoculture systems. Intercropping with high value tree species adds a sustainable economic development aspect to the system which is highly attractive.
Intercropping can be understood as a multiple cropping system in which two or more crops are grown simultaneously, in alternate rows, while minimizing competition (Federer, 1993). Field crops, vegetables, fruits and trees can be successfully intercropped provided species are selected carefully for complimentarity. Light, water and nutrients are more efficiently converted to crop biomass because of differences in competitive ability for growth factors between intercrops (Ghaffarzadeh, 1999). The more efﬁcient utilization of growth resources, therefore, tends to create yield and nutritional advantages and increased crop stability, compared to monoculture based systems. Consequently, intercropping is a viable option for sustainable low-input, high yield cropping systems with the associated food security, nutritional diversity and economic beneﬁts for communities.
Adding high value tree species, such as paulownia tomentosa to this model, creates sustainable economic development opportunities and more food diversity through the addition of animals. The focus here is on paulownia but virtually any tree species can be incorporated in this system. In China, intercropping with the paulownia tree has been successfully used on nearly two million hectares of farmland. This kind of agroforestry system has helped alleviate timber and fuelwood shortages; provide animal fodder; and increase the number and diversity of animals incorporated into agricultural production. Concomitantly, the trees improve soil conservation through their extensive root systems and enhance environmental remediation of areas previously contaminated through overuse of fertilizers, pesticides and herbicides. How is this possible?
Scientists at the Paulownia Research Institute of Forestry, Chinese Academy of Forestry, in Beijing have determined that intercropping with Paulownia creates a microclimate under the trees. This area is cooler, more humid, and sheltered from the wind, and consequently promotes increased yields of crops such as wheat, millet, maize, and a variety of vegetable crops. This microclimate can be created quickly as paulownia grows approximately 4 metres in its first 6 months and reaches heights of approximately 20 metres in 5 years.
Livestock can be incorporated into this system. The trees produces branches, leaves, and flowers that are rich in protein, carbohydrates, and minerals, making them ideal animal feed and green fertilizer (IDRC, 1991). The livestock also provide fertilizer and animal proteins which can be incorporated into human diets as desired. Overall agricultural production increases in intercropping systems. The surplus production can be sold as part of economic development initiatives. The marketability of wood products from the trees provides a larger economic opportunity however.
As a forestry product, paulownia creates economic opportunity through the cutting, sawmilling and selling of wood products useful for a number of non-structural applications including millwork, furniture, plywood and musical instruments. Microfinance can accelerate this process through the purchase of seedlings and the acquisition of tools and equipment required in forestry and sawmilling operations. Paulownia seeds and seedlings are readily available from a variety of sources particularly in China and the Philippines. Once sexually mature, the trees reproduce naturally. It should be noted that if a tree is harvested for timber or fuelwood, the stump will naturally regenerate, producing several shoots which can be selectively trimmed and grown to produce the next generation of timber or fuelwood.
Due to its long use in agroforestry projects, best practices for planting and managing paulownia plantations have been thoroughly studied and training materials are also widely available. For timber production, it is recommended the planting grid for a crop growing plantation is 4 x 4 (4 meters between rows and 4 meters between trees in each row) or 5 x 5, which is 500 or 600 trees per hectare. For field crop and vegetable production, tighter spacing can be used to create suitable microclimates. 5 x 4 is suitable for most plant species.
Alternatively, for plantations in which livestock are raised, and the requirements for fodder and shade change compared to a foodcrop growing plantation, tighter spacing within the row can be used. In these situations, 5 x 4 or even 5 x 3 have been used. For remediation sites or plantations focusing on biomass development, even tighter spacing can be used, creating plantations with 3500 and 10 000 trees per hectare (Bio-Tree, n.d.). This system is therefore, highly adaptable as plantations do not need to be a certain size; total area is not as important as spacing on the planting grid.
Paulownia trees are adaptable to a variety of situations but optimal conditions are:
· Elevations from sea level up to 1000m;
· Temperature range of 22 - 40 degrees Celsius;
· Deep (1.5 - 2 meters), well drained soils with pH from 5.0 to 8.9. Soils that are over 25% clay with a porosity under 50% are not recommended. Salinity over 1% is also not recommended.
· Watering is necessary in the first year if the annual rainfall is under 100mm per month. Watering is needed in the following years if the monthly rainfall is under 50mm.
Paulownia can be intercropped with wheat, corn, soybean, peas, beans, barley, cotton, and a virtually any vegetable crops. Livestock can successfully be incorporated into the system. These systems provide food security and create nutritional diversity in their first year of operation. Economic development opportunities are created when the trees are harvested as required for timber or fuelwood. Communities using this system can have food security and create effective economic development opportunities. The system is also eminently sustainable.
 As a tropical hardwood, paulownia is not suitable in all climates. Nor is it viable on some terrain. Indeed many argue against importing foreign, potentially invasive species to new ecosystems. In such cases, other native species can be substituted.