The naturalized vascular flora of Malesia

Abstract

Major regional gaps exist in the reporting and accessibility of naturalized plant species distribution data, especially within Southeast Asia. Here, we present the Malesian Naturalized Alien Flora database (MalNAF), the first standardized island-group level checklist of naturalized vascular plant species for the Malesian phytogeographical region. We used MalNAF to investigate the composition, origins, and habitat preferences of the naturalized flora. The naturalized vascular flora of Malesia consists of at least 1177 species. Richness is highest in the Philippines (539 spp.) and lowest in the Maluku Islands (87 spp.). But, the Lesser Sunda Islands had the highest naturalized species richness relative to native richness and Singapore has a higher naturalized plant species richness than would be expected given its size. When comparing the data for Malesia with a global dataset, we found that naturalized richness increased with area for islands but not for continental regions. Across the archipelago, 31 species are widespread, occurring in every island group, but the majority have a limited distribution of 2.4 ± 2.3 (mean ± SD) island groups per naturalized species. The naturalized plant species are representatives of 150 families, twenty of which are newly introduced to the region. Families richest in naturalized plant species in Malesia were Fabaceae (= Leguminosae) (160 spp.), Poaceae (= Gramineae) (138 spp.), and Asteraceae (= Compositae) (96 spp.). Most of these have a native range that includes tropical Asia, closely followed by those from Southern America (inclusive of the Caribbean, Central and South America), although at the island-group level, most have a higher proportion with a Southern American native range. Most naturalized species occur in anthropogenic habitats, but many are present in “natural” habitats with fewer species, such as Leucaena leucocephala, reported from specialized habitats like drylands. MalNAF provides a baseline for future studies of naturalized plant species distributions in the region.

Naturalizations have led to homogenization of the Malesian flora in the Anthropocene

“…Reductions in turnover and nestedness both contributed to homogenization to varying degrees heterogeneously across Malesia (Figure 4b,c). Declines in turnover are partly caused by the 15% of naturalized plant species that are now widespread throughout the archipelago (Holmes et al., 2023), increasing the total shared taxa among all island groups and some island pairs. Many of these taxa are the same ‘superinvaders’ (Daehler, 2003; Stohlgren et al., 2011) that have had a substantial influence on homogenization globally (Daru et al., 2021) and are therefore likely to also increase the similarity of the Malesian flora with geographically disparate floras, especially those with similar climates (Yang et al., 2021).…”

“…The analysis utilized two checklists for terrestrial and freshwater vascular plants. The first is the Malesian Naturalized Alien Flora database (MalNAF) (Holmes et al., 2023), and the second is a native species checklist for Malesia based on published data. The MalNAF database includes distribution information (presence/absence) for 1177 naturalized plant species at the level of islands or island groups for Malesia, covering 10 biogeographic units (Holmes et al., 2023).…”

“…The first is the Malesian Naturalized Alien Flora database (MalNAF) (Holmes et al., 2023), and the second is a native species checklist for Malesia based on published data. The MalNAF database includes distribution information (presence/absence) for 1177 naturalized plant species at the level of islands or island groups for Malesia, covering 10 biogeographic units (Holmes et al., 2023). We excluded distribution information for native and naturalized plant species for Thailand south of the Kangar Pattani line because data were not available at suitable spatial resolution.…”

“…The analysis utilized two checklists for terrestrial and freshwater vascular plants. The first is the Malesian Naturalized Alien Flora database (MalNAF) (Holmes et al, 2023), and the second F I G U R E 1 (a) Study area with selected phytogeographic boundaries for the region: Sunda in the west bounded by the Huxley Line, Wallacea is a transitional zone bounded in the west by the Huxley Line and the east most commonly by Lydekker Line (although various boundaries exist), and Sahul traditionally lies to the east of the Lydekker Line; (b) Species area relationship for native and naturalized plant species as represented by the Arrhenius (power law) model (Arrhenius, 1921). Key for island group names: BOR, Borneo; JAV, Java; LSI, Lesser Sunda Islands; MAL, Maluku; NWG, New Guinea; PHI, Philippines; PNM, Peninsular Malaysia; SUM, Sumatra; SUL, Sulawesi.…”

“…Post‐1950, expansion of monocultural plantations, urbanization and globalization (Zhao et al., 2006) further opened up new areas for naturalized taxa to establish within Malesia and improved access to novel source pools for new aliens to be introduced (Seebens et al., 2018). Malesia now hosts over a thousand alien naturalized plant species (Holmes et al., 2023).…”