Plant succession following nuées ardentes of Mt. Merapi volcano, Java Indonesia

[Truncated] Tropical volcanic ecosystems, particularly in Asia, have been relatively understudied. Mt. Merapi volcano, in Java Indonesia provides an opportunity to study succession following nuées ardentes events which essentially reset the successional clock of the montane forest. Information regarding the development of the vegetation on Mt. Merapi during early succession is scarce. Using a chronosequence approach, my study documented the patterns of vegetation succession following nuées ardentes and wildfires in tropical montane forests on Mt. Merapi. I examined primary succession in areas directly affected by nuées ardentes and secondary succession in areas affected by fire associated with nuées ardentes. There was a rapid colonization by vascular plants in both primary and secondary succession as the sites aged. Imperata cylindrica, Eupatorium riparium, Anaphalis javanica, Athyrium macrocarpum, Brachiaria paspaloides, Dichantium caricosum, Selaginella doederleinii, Eleusine indica, Cyperus flavidus, Calliandra callothyrsus and Acacia decurrens were the species mainly responsible in explaining the differences between sites. In primary succession, the species richness and diversity reach their peak 14 years after disturbance. In secondary succession, the species richness was similar to the reference site in only a little after two years - however, the peak of species diversity was 14 years after the nuées ardentes disturbance. Native and exotic invasive species varied in abundance among sites. The native invasive I. cylindrica dominated the early succession but then disappeared under the shade of the emerging tree species. In contrast, invasive exotic species such as Eupatorium spp and Brachiaria spp remained in the system long after the nuées ardentes had occurred and forest structure had developed. In the secondary succession the forest structure developed throughout the succession with the older sites, regaining nearly complete stratified forest vegetation after 14 years. In terms of species interspecific associations, positive associations were greater than negative associations as time progressed in the primary succession. The nitrogenfixing species Calliandra callothyrsus had the highest number of positive interspecific associations compared to the other species, which may suggest that this legume species has a prominent role in facilitation. An examination of soil nutrient status showed improvement in soil condition as time progressed. There was a clear pattern of increase in N, C, and exchangeable cation concentration with age of site, whereas the P concentration decreased with time. There was also a significant relationship between species composition and the measured soil nutrients (P, N, Ca++, Na+ Mg++ and K+). Results from this study have shown that the ecosystem is resilient to volcanic disturbance as shown by the significant increase in species richness and diversity, increase in positive species association, and improvement in soil nutrients within 14 years of disturbance. However, this study had also raised some concern regarding invasive alien species in the succession...