Post-reforestation vegetation development on abandoned highland fields in Java, Indonesia

• Previous reforestations failed to restore the upland ecosystem.
• Tree regeneration was low in all habitats.
• Woodland and shrubland did not differ significantly in structure and composition.
• Pioneer and ruderal species dominated the undergrowth layer.
• Reforestation with exotic species did not foster regeneration of native species.

In the Dieng Mountains, encroachment of the protection forest by locals has resulted in conversion of the land into agricultural fields, followed by abandonment. Subsequent reforestation projects by the local authority have been uneven and ineffective in bringing back the protective function of the forest. With current farming practices, the trend of regrowth forest formation will persist into the future. We evaluated the reforestation approach in the Dieng Mountains by investigating the development of regrowth forests, and based on the result, suggest improvements to present restoration efforts. Vegetation data were collected using stratified systematic sampling on three types of disturbed habitats found in the area: woodland, shrubland, and grassland. The importance value index of each species was calculated; species richness and diversity were estimated using the Species Prediction and Diversity Estimation (SPADE) program. The development of the secondary vegetation in the Dieng Mountains was highly influenced by its land use history and the local government’s reforestation programs. The low tree regenerations in all the habitats may be attributed to harsh environmental conditions caused by the high altitudinal location and the impact of forest clearings, as well as competition with herbs and the effect of human activities. Tree species planted during the reforestation programs, Acacia decurrens, Cupressus sempervirens, and Schima wallichii, dominated all habitats. Pioneer shrub species Melastoma affine and grasses Imperata cylindrica and Isachne globosa, as well as ruderal species Eupatorium odoratum, Eupatorium riparium, Buddleja asiatica, and Rubus rosaefolius dominated the undergrowth vegetation. Gleichenia dichotoma’s domination seemed to suppress the growth of coexisting grass species, leading to the domination of Conyza javanica over pioneer grass species in grassland. Compared with similar studies in other secondary forests, the richness of plant species found in the Dieng Mountains was considerably lower, especially that of woody plants. As human populations in the Dieng Mountains continue to expand, the fate of the secondary vegetation in this area may be determined by future interference by humans.