Invasive alien species (IAS) are non-native organisms that pose risks to both human health and the environment. They are regarded as the second most significant threat to biodiversity after habitat loss (Bellard et al., 2016). Whether introduced intentionally or unintentionally, the introduction, dispersal, and utilization of alien species have had profound impacts on ecosystems and economies. Because many invasive alien species are highly adaptable, capable of rapid growth and reproduction, the environmental damage they cause is often irreversible and can lead to the extinction of endemic species. Furthermore, biological invasions have severe socio-economic and public health impacts (Shackleton et al., 2018). According to (Castro-Díez et al., 2019), the perceived socio-economic benefits of certain potentially invasive plant species in urban and rural areas have contributed to the rapid spread of some IAS in forest ecosystems.

Numerous studies have been conducted worldwide to examine the effects of invasive alien species on human health, ecosystem services, biodiversity, and economic activities (Katsanevakis et al., 2014). However, research on the impacts of IAS in the Philippines remains scarce. Owing to its archipelagic nature, which promotes geographic isolation and endemism (P.T.F.C.F., 2015), the Philippines is recognized as one of the world’s 17 mega-diverse countries (Keong, 2015). Yet, island ecosystems are particularly vulnerable to invasive alien species, which can cause population declines and extinctions, especially among endemic taxa.

Samar Island Natural Park (SINP), located on the country’s third-largest island, is a designated forest reserve with exceptionally rich biodiversity. Recent ecological assessments have documented 212 tree species, 182 terrestrial vertebrates, 24 amphibian species (Diesmos et al., 2015); (Diesmos et al., 2020), and 31 snake species (Levitonet et al., 2018); (Weinell et al., 2020). Additional floral (Quimio, 2016) and faunal (Patindol, 2016) surveys have been conducted in five SINP watersheds. Floristic inventories of alien species are essential for developing conservation programs and policies aimed at addressing forest conservation challenges. Effective management is better achieved through comprehensive strategies that map relationships between invasive species and at-risk native species rather than focusing solely on individual taxa. Globally, invasive species are among the leading drivers of ecosystem-wide biodiversity loss and species extinctions.

The purpose of this study is to identify invasive alien plant species (IAPS) in the riparian areas of Allen, Biri, Catarman, Gamay, Mapanas, Laoang, Las Navas, Lapinig, Lavezares, and Pambujan in Northern Samar, Philippines, focusing on species composition, endemism, and conservation status. Conducting research on invasive plant species is crucial, as it helps shed light on the ecological consequences of non-native plant invasions. The findings will raise public awareness and promote recognition of the harmful effects of such species. Moreover, the study encourages the development of new approaches to mitigation and restoration, including management interventions and the evaluation of IAPS impacts. This research was conducted in the aforementioned riparian areas because no prior studies have examined invasive plant species in these habitats, even though riparian zones often harbor numerous invasive species that can outcompete or displace native vegetation.

Invasive plant species are plants that invade the natural ecosystem where they are not normally found, causing substantial damage to the new environment. One of the primary factors that led to the successful establishment of invasive alien species in the environment is the presence of rivers in these areas. Seeds may be dispersed by wind or water, allowing them to colonize new areas rapidly. The constant flow of water also provides an express highway for dispersing propagules downstream. Once these plant species became established in these areas, they could outcompete native plant species and become widespread. Invasive species, by competitive exclusion, niche relocation, or hybridization with related species, can cause the extinction of native species. As a result, in addition to their economic consequences, such invasions can cause significant changes in the structure, composition, and global distribution of biota, resulting in the homogenization of the world’s fauna and flora and biodiversity loss (Shuvar et al., 2021).

Invasive plant species can significantly damage the environment where they are introduced. Invasive species can harm agriculture and society (Pratt et al., n.d.). Recent studies show that invasive plant species can cause significant damage to several sectors when successfully establishing new habitats (Shackleton et al., 2019); (Shrestha et al., 2019). For example, in this study, Chromolaena odorata is considered one of the most aggressively spreading invasive weeds. It has been designated one of the world’s 100 worst invasive plant species. It’s spread substantially threatens various ecosystems from subtropical to tropical regions (Koutika & Rainey, 2018). It typically invades roadsides, fallow areas, and forest environments, establishing dense monocultures (Thapa et al., 2021); (Tiébré et al., 2018). In invaded ecosystems, the weed displaces native species, affects species composition, and severely affects livestock and agricultural fodder (Shackleton et al., 2017); (Thapa et al., 2021). Such negative effects of C. odoroata on native ecosystems have become a significant environmental challenge.

Across all global regions, the number of alien plant species is continuously increasing. In riparian habitats, these populations are frequently abnormally high, seriously affecting ecosystem services and native species communities (Pabst et al., 2022). Various factors influence disturbance’s function in enabling plant invasions in riparian zones. Since riparian vegetation structure is substantially impacted by land use and land cover changes, riparian sites with a more natural land use type tend to have fewer IAPs (Zelnik et al., 2020); (Fonseca et al., 2021). Higher human pressures and hydrological disturbances in low-lying riparian areas produce a profusion of young, disturbed ecosystems that are more vulnerable to invasion, such as river bars (Liendo et al., 2020). How land is used next to riparian zones affects how vulnerable the communities are to invasion (Zelnik et al., 2020). Controlling invasive plant species in restoration areas can be accomplished through various techniques. The most effective chemical control method relies on several elements, including the species being managed, the available funds, laws (Dechoum et al., 2018), and even individual beliefs. Effective management initiatives have typically increased biological diversity. However, it suggests that effective eradication may affect local species and unanticipated ecosystems. When an invasive plant species is removed, for instance, it may result in fewer resources being available for native fauna if other restoration measures are not implemented. Furthermore, once removed, some invasive plant species may continue to impact the system because of their residual effects on the root symbiont and soil microbial communities (Koziol et al., 2018).

Ten (10) species were recorded as Invasive plant species on the Global Invasive Species database, namely: Chromolaena odorata, Elephantopus mollis, Sphagneticola trilobata, Ipomoea aquatica, Leucaena leucocephala, Pueraria montana, Abelmoschus moschatus, Psidium guajava, Imperata cylindrica,and Lygodium microphyllum Table 4. On the other hand, twenty-two (22) species of Invasive plants were listed in the Global Register of Introduced and Invasive Species database - Philippines Database these are Amaranthus spinosus, Cyathula prostrata, Ageratum conyzoides, Chromolaena odorata, Elephantopus mollis, Mikania micrantha, Pseudelephantopus spicatus, Heliotropium indicum, Leucaena leucocephala, Mimosa pudica, Senna occidentalis, Hyptis brevipes, Sida acuta, Urena lobata, Psidium guajava, Piper aduncum, Eleusine indica, Imperata cylindrica, Scoparia dulcis, Lantana camara, Stachytarpheta jamaicensis and Hedychium coronarium Table 4. Furthermore, five species that are common in the two databases include the Chromolaena odorata, Elephantopus mollis, Leucaena leucocephala, Psidium guajava, and Imperata cylindrica Table 4.

Northern Samar’s riverbanks have many introduced invasive plants, mostly herbs and shrubs, coming from different families like Poaceae and Asteraceae. These plants grow differently in each area because of changes in soil, weather, and human activities like transportation and gathering. Rivers help spread their seeds, making it easier for them to take over. These invasive plants can outcompete native ones and harm the local environment. To protect nature and native plants, it’s important to manage and reduce the disturbances that help these invasive species spread.