Assessment of rock wall terraces on steeplands in southern Honduras: Landslide hazard mitigation and long-term sustainability

Deforestation of tropical steeplands is a serious natural resource concern. The loss of forest cover and the associated decomposition of deep root systems which tie the soil onto the hillslopes contribute to soil erosion and increase susceptibility to devastating landslide events. In southern Honduras, extensive conversion of steepland forests to agronomic cropland, combined with intense rainfall events that are characteristic of the region, resulted in many landslides. Consequently, the Honduran government, working with the U.S. Agency for International Development, fostered installation of rock terraces on select steepland fields used for crop production in southern Honduras during the 1980s and 1990s. In 1998, Hurricane Mitch, one of the most powerful hurricanes of the 20th century struck southern Honduras, triggering extensive landslides and flooding throughout the region. An objective of this study was to determine if the installation of rock wall terraces reduced the risk of landslide hazard associated with Hurricane Mitch. This investigation was conducted through analysis of aerial imagery taken over several days following the storm. A second objective of the study was to determine the current status of the rock wall terraces and associated land use 15-20 years after installation. Results of the analysis show that a significantly lower amount of field area was affected by landslides on fields with rock wall terraces compared to non-terraced sites. Forested areas had fewer landslides than fallow cropland; fallow cropland had fewer landslides than cultivated fields. On sites receiving more than 700 mm annual average precipitation, rock wall terraces continued to be maintained by farmers even though the government programs espousing the value of rock wall terraces ended 13 years prior to the study. Conversely, almost all rock wall terraces that had been installed on sites receiving 700 mm/yr or less had not been maintained, suggesting that rainfall and the associated land use patterns are important factors determining whether farmers find it worthwhile to maintain terraces. Following the installation of rock walls, there was a significant shift in the pattern of land use on terraced fields. Many terraced fields shifted from grain cultivation to a mixed agroforestry production system. In contrast, adjacent, non-terraced fields continued to be used primarily for traditional grain cultivation. Conservation organizations can use the results of this study to assess the benefit of continuing to invest in similar soil conservation methods.