Holocene insights for tackling Anthropocene environmental challenges in Malesia

Understanding long-term environmental change is essential for informed decision making in response to the threats posed by anthropogenically altered critical Earth Systems in the Anthropocene. This thesis focused on generating and synthesising novel datasets to contribute towards tackling two of these environmental challenges: introduction and establishment of alien plant species, and the degradation and loss of resilient ecosystems. Less research has been conducted on these phenomena in tropical regions, especially in Southeast Asia and Africa. Therefore, the geographic scope of this research is focussed on one of these areas and is best delimited by the phytogeographic region of Malesia which stretches from Peninsular Malaysia in the west, to New Guinea in the east. Analysis of distribution information at the level of island/island group for 31,580 native and naturalized (alien and established) plant species identified that 1,177 naturalized species have been introduced since prehistory, with many introduced due to European colonialism, and this has resulted in taxonomic homogenization (increase in similarity) of the flora. Most naturalized plant species in the region occur in anthropogenic, followed by open forest, habitat-types and the floras of Java and the Lesser Sunda Islands increased in similarity the most. For the second environmental challenge of focus for the thesis, multi-proxy palaeoecological data from three sediment cores in North Sulawesi, Indonesia, are presented as a case study for using palaeoenvironmental data to support mangrove management and conservation through the study of recovery and resilience. This revealed the rich biodiversity of mangrove ecosystems in North Sulawesi and their resilience over millennia to many forms of natural disturbance as well as phenomena to which they are more vulnerable. Assessing mangrove pollen abundance and composition indicated that the contemporary mangroves (at Mantehage and Likupang) are currently recovering and are on a trajectory towards their respective Holocene baselines. The results from both case studies enhance our understanding of key ecological processes (invasion and resilience), can be galvanised to support ecosystem management across scales (e.g., watchlist of naturalized taxa at risk of spread into a new island, guiding species selection for mangrove restoration), and directly support international commitments - especially the Kunming-Montreal Global Biodiversity Framework Targets 2, 3, and 6.