Most cash crops of the Commonwealth of the Northern Mariana Islands (CNMI) are susceptible to damage from wind or salt spray. Pacific trade winds blow east to west from late September to early April, peaking in December and January. But damaging winds can occur at any time of year.
Windbreaks can protect fragile plants from damage and help reduce soil moisture loss; however productive farmland is limited. The average CNMI farm size is 1 hectare (2.5 acres). A functional windbreak of suitably sized and spaced trees can dominate up to 20% of the available space within a farm plot. A solution is to establish a windbreak that produces a marketable crop, thereby enhancing the environment without sacrificing economic return. The project team set out to test marketable trees as windbreaks to create an income-generating conservation practice.
Establish a dense, multi-row windbreak/shelterbelt that will protect fragile crops from prevailing and seasonal wind damage and, at the same time, provide a marketable crop.
The project is located on a banana plantation on the island of Rota on a cliff field overlooking the ocean and exposed to prevailing northeast winds. Soils are Dandan-Chinen complex with 5 to 15% slopes. Seedlings, acquired from the local Division of Forestry nursery or started from seeds collected from the forest, were laid out along the north and east boundaries.
Three rows were established. Da’ok (Calophyllum inophyllum) made up the primary, or windward, row. Citrus (lemon, tangerine and calamansi) comprised the second and third, or leeward, rows, extending further into the fields between banana plants, which would be phased out as the citrus matured into a healthy windbreak. Trees were spaced 12 feet apart within and between rows and staggered to create a closed wall of leaves at maturity. It is typhoon resistant and, although it grows slowly, it can reach 30 feet, providing excellent shade and wind protection. Various citrus trees were planted in the inside rows, staggered to create a closed wall of leaves at maturity.
As expected, seedling mortality was high – 40 to 50% – but acceptable for the site conditions, and ample seedlings were available to replace dead trees. Because planting began during the rainy season, mortality was attributed to soil and site conditions rather than a lack of moisture. Water was supplied to trees near a water line, but was not available to all seedlings evenly.
On July 7, 2002, Typhoon Chata’an, with sustained winds of 85 mph and gusts of 125, caused significant damage, some from large banana plants falling onto seedlings but most from salt spray. Seedlings that survived began showing salt damage the second week after the storm. Dead and dying seedlings were replaced, but many seedlings in the temporary nursery were also damaged. The da’ok seedlings fared better than the citrus because there were smaller and less susceptible to wind damage. On Dec. 8, 2002, Super Typhoon Pongsona, unseasonably timed and with wind speeds topping 185 mph, struck just as the surviving seedlings were making a strong comeback from Chata’an five months earlier. The project site received the full brunt of the storm. The bananas were a near total loss and most of the windbreak trees were killed. The nursery stock was also devastated, so recovery has been slow.
As of this final report, one year after Pongsona, reconstruction efforts continue and the island’s limited resources are stretched thinly. New trees have been planted, but stocks are insufficient for replanting the entire planned windbreak. On a bright note, a handful of the original seedlings survived both typhoons and are growing well today.
As an alternative action, the project team planted a primary row of Casuarina equisetifolia, or ironwood, which provides a faster-growing windbreak. This violates the principle of planting only trees that produce a marketable product, but ironwood is fast growing, readily available and more salt-tolerant than citrus. Meanwhile, the decision has been made to shift species composition in the windbreak more heavily toward da’ok. The seedlings are more readily available, those planted before the typhoons weathered the storms better than citrus and the potential market for da’ok oil appears to be more lucrative, thanks to efforts by Northern Marianas College to focus on creating markets for the oil. To that end, a nursery has been established on a banana field and the seedlings are spaced more closely for easier watering and tending until they are stronger for transplanting into the windbreak.
BENEFITS OR IMPACTS ON AGRICULTURE
Windbreaks can virtually eliminate damage from prevailing winds to fragile crops like bananas, papayas, taro and okra. No windbreak is typhoon proof, but a well planned windbreak of sturdy trees can reduce storm effects. Windbreaks can also reduce windborne disease and moisture loss from evaporation, and the trees improve the property’s aesthetics. Because trees like da’ok are native to the island, their growth could benefit wildlife as well.
The ideal windbreak would comprise tall da’ok as the primary row, then one or two rows of citrus and finally shorter shrubby trees like sour sop, sweet sop, star fruit and guava. In addition to preventing or reducing wind damage, the layers of trees would provide value-added products. An Internet search for da’ok oil found prices average $300 a liter, and an adult tree can produce 15 liters per year. Given the cultural aspects of the islands, it is doubtful that row cropping will cease, but windbreaks could provide both environmental and economic benefits.
The typhoons set back not only this project but efforts and resources of other island farmers. It is hoped that once the trees are of production size, local adoption will begin. The USDA Natural Resources Conservation Service has been promoting the use of windbreaks, and several producers have installed, or plan to install, windbreaks of da’ok and citrus. But none is of commercial size.
RECOMMENDATIONS OR NEW HYPOTHESES
Despite the setbacks, it’s too early to assess the project’s success. The potential benefits of producing the windbreaks remain to be seen, and the idea remains worth pursuing. Indeed, on many island soils, fruit and nut trees are the only suitable crop, slope, soil depth and rock outcrops precluding any other form of production.
Despite the typhoon curtailing demonstrations of planting, pruning and seedling care, several tours of the project have been conducted to show property placement of da’ok trees. The project team does plan to disseminate lessons learned from the project once the windbreak trees reach maturity.