Trade-Offs Between Machete and Fire as Site Preparation Tools for Native Tree Planting in Eastern Madagascar

Abstract

Background and Research Aims: Forest restoration is urgently needed in eastern Madagascar, but natural regeneration in very degraded habitats is slow and tree planting projects lack resources and technical knowledge. Moreover, many regenerating forests are threatened by frequent wildfires. Local farmers understand the benefits of fire for preparing sites for temporary annual crops and deliberately stage fires to replenish soil. The risks of such fires are apparent for soil and biodiversity conservation, but the use of fire as a site preparation technique for forest restoration is unexplored. Methods: We conducted an experiment by planting native tree seedlings on two adjacent hilltop plots at the same time in 2017, with plots differing only in site preparation: hand-cleared with machete or post-wildfire. We tracked seedling survival, growth and natural regeneration over six years. Results: After three years, native trees planted on the burned hilltop experienced 9.5 ± 2.8% (P = 0.014) greater survival than trees planted on machete-cut land. However, surviving trees planted on cut land grew 33.8 ± 2.8% larger than on burned land (P < 0.001). We also found 4× more naturally regenerating woody species (mostly Ravenala madagascariensis and non-native vegetation) in burned areas. Discussion: Overall, higher growth in the cut plot makes it a more effective long-term option for restoration. Initially the burned plot remained weed-free, but after several years had considerably greater recruitment of non-native trees. Fire facilitated colonization for non-native species by clearing out native competition, which may have also contributed to slower planted tree growth. Implications for Conservation: Our observations indicate that land burned in Madagascar’s frequent wildfires may be opportunistically planted with native trees, that such sites may require lower weed maintenance in the first few years post-planting than sites cleared with machete, and that non-native tree recruitment may also be greater on burned sites.