Invasive alien plants and their impact in Mizoram, a part of Indo-Burma biodiversity hotspot in India

Introduction

The verdant landscapes of Mizoram, nestled in the northeastern parts of India, have long been revered for the rich biodiversity and pristine natural beauty. Mizoram, as a part of the Indo-Burma biodiversity hotspot, characterized by undulating hills and dense natural forests, is home to a unique assemblage of flora and fauna including many endemics (FSI, 2021). These important ecosystems play a pivotal role in providing habitat for numerous species, supporting watershed functions, and contributing to the livelihoods of local communities. However, in the recent decades, due to the increasing population pressure and expanding developmental activities as well as shifting cultivation, the unique natural forest ecosystem of Mizoram is subjected to rapid habitat fragmentation becoming susceptible to disturbances (Barik & Adhikari, 2012). Such disturbance regime by various anthropogenic activities have paved way for a silent intruder to the luxuriant ecosystem in recent years - the proliferation of invasive alien plants. This phenomenon of invasion by alien plants poses as immense threat to the ecological balance of Mizoram’s natural forests, with far-reaching consequences for both the environment and the communities dependent on these ecosystems.

Alien plants, either introduced or disseminated beyond their native environments, have impacted biodiversity in nearly every ecosystem globally posing as a threat to the biodiversity (UN, 2014). The introduction of invasive alien plants is a global phenomenon, facilitated by human activities such as trade, travel, and agriculture. Some of these alien plants possess advantageous traits to prevail over naturally occurring species of the native ecosystem and gradually become invasive. Invasive alien plants (hereafter, IAPs) exhibit aggressive growth patterns and subsequently outcompete native vegetation leading to the degradation of natural habitats (GISP, 2010; CBD, 2018). IAPs also directly or indirectly influence the natural resources changing structural and functional equillibrium of natural ecosystems (Downey & Richardson, 2016). The successful establishment of alien plants relies on key processes such as an efficient seed dispersal mechanism, rapid growth rates, and remarkable adaptability to a variety of environmental conditions (Simberloff, Parker, & Windle, 2005). Alien plant species tolerant to a wide range of environmental attributes exhibit a greater physiological niche appearing to be more invasive (Higgins & Richardson, 2014). Nearly 0.5–0.7% plant species of the world is invasive outside their native range of occurrence (Rejmánek & Richardson, 2013). In the context of global environmental change, invasive alien species play a crucial role, as they exhibit unregulated proliferation in all directions once established. This phenomenon is particularly evident in environments conducive to their growth, such as rugged and uneven mountain terrains (Rumlerová et al., 2016). The ongoing effects of global climate change have further accelerated the introduction and spread of alien species into regions they were previously absent or enhanced their advantageous traits prevail over the native species. This is evident in various instances, where invasive alien species like Ageratum conyzoides, Ageratina adenophora, Chromolaena odorata, Lantana camara, Mikania micrantha, and Parthenium hysterophorus have wreaked havoc in terrestrial ecosystems. Similarly, in aquatic ecosystems, species like Eichhornia crassipes and Pistia stratiotes have significantly altered native vegetation composition (Raizada et al., 2008). Invasion Scenario in Mizoram.

Susceptibility of anthropogenically altered landscapes of Mizoram to alien plant invasion is exacerbated by its geographical location, topography, and changing climatic conditions. The state shares international borders with Myanmar to the east and Bangladesh to the west, making it susceptible to the inflow of alien species through anthropogenic activities and natural dispersal mechanisms (FSI, 2021). The undulating terrain and diverse climatic zones provide a varied range of microhabitats, creating niches that invasive plants can exploit to establish themselves. Furthermore, the “Jhum” or “Shifting cultivation” practiced traditionally in Mizoram, lead to creation of open disturbed areas or fallow lands (Sati, 2019) where IAPs can colonize rapidly as primary regenerating species leading to invasion to nearby natural forests.

The introduction of alien plants in Asian countries including India, expanded during colonial period dated back to the 15th century indicating European colonisation in the Asian continent (Callaway, 2022). Initially, only the food crops were introduced, subsequently followed by aesthetic and economically valuable alien plants to the parts of the colonised countries (Lockwood et al., 2009; Lenzner et al., 2022). Even during the World War-II period, the Indian subcontinent was under colonial rule including entire North-East India (including Khasia & Jaintia hills (K&J hill), Lushai Hills, Manipur were under Assam province). Lushai hills province of colonial era is known as the state of “Mizoram”. Some reports of alien plant collection from the state of Mizoram (then “Lushai Hills”) were found from the herbarium records housed at CAL and as per the collections, Mikania micrantha dated back to 1956, Chromolaena odorata in 1938, Ageratina riparia in 1958 and Ageratina adenophora in 1931 from this region (Sengupta & Dash, 2020). Mikania micrantha was reported to be introduced during World War-II as ground cover plant for tea estates and camouflage for the airfields during World War-II in this region (Shankar, Yadav, Rai, & Tripathi, 2011). Therefore, it can be estimated that introduction of noxious alien plants in Mizoram might have followed the K&J hill- Silchar-Aizawl-Lushai hills route and gradually invaded throughout the disturbed habitats of the state.