Contributions of Tree Improvement Program to Increase Forest Productivity and Achievement of Indonesian Nationally Determined Contributions (NDCs)

The forest area of Indonesia is the second-largest tropical forest in the world, with a total forest area of more than 120 million ha. Indonesia's tropical forest is one of the most biodiverse terrestrial ecosystems in terms of species richness and endemism, supporting 18.7% of the world's plant biodiversity. Thus, the existence of tropical forests is vital to reducing emissions and maintaining climate and resources. They provide timber, food materials, medicinal plants, and natural fibers, as well as recreation, aesthetic value, ecological benefits and more. However, Indonesia's tropical forests have been declining due to, among other things, forest fires, illegal logging, over-exploitation, and conversion of forests to other land uses. The highest rate of forest loss in Indonesia was in the period 1996-2000 (3.51 million ha), while the deforestation rate in the period 2019-2020 decreased by 75 percent to 115 thousand ha, the lowest rate since 1990. Preventing forest degradation could reduce around 15% of total greenhouse gas emissions, which would help combat climate change. Thus, Indonesia joined in signing the Paris Agreement for a better life and environment in the future. Based on the latest Nationally Determined Contribution (NDC) documents, Indonesia should reduce emissions by 31.89% (with self-effort) and up to 43.20% (with international support) by 2030. Of the total emission reduction targets from different sectors, almost 60 percent of the emission reduction targets will rely on the forestry sector. Thus, the government of Indonesia has an array of climate actions to achieve its Forest and Other Land Use Net Sink (FOLU Net Sink) 2030 targets. Some activities to achieve the FOLU Net Sink 2030 goals are the establishment of plantation forests, the sustainable management of natural forests, and the rehabilitation of forests on degraded lands. Forest rehabilitation uses improved seeds to increase forest productivity through intensive silviculture (SILIN), which consists of tree improvement, environment manipulation, and pest and disease management programs. For example, implementing tree improvement in clonal teak plantations could increase forest productivity by >300% compared to using unimproved teak seed. In 20 years after planting, the trunk diameter, timber volume, and carbon sequestration in the clonal teak plantation were 42 cm, 300 m3/ha, and 200 tons C/ha, respectively. Meanwhile, the rehabilitation of natural forests dominated by dipterocarp species could be established by enrichment planting with native species such as Shorea leprosula, S. parvifolia, S. johorensis, S. macrophylla, and S. platyclados. Enrichment planting with native species could increase forest productivity from 25-30 m3/ha to 200-300 m3/ha in 25 years after planting. Furthermore, enrichment planting with native species increased carbon storage in the secondary natural forest, reaching 139.52 tons C/ha. This study suggested that tree improvement programs using the SILIN technique should be implemented to improve land forest cover and forest productivity and achieve Indonesia's NDCs.