NE Indian forests are vulnerable to bioinvasion of non-native tree species ?

Soraisam Hira / Z Philamazan Peace Shimray *

Trekking to Shirui Peak, Ukhrul as part of Shirui Lily Festival in May 2022 :: Pix - Lamdamba Oinam

The North East region is one of the ten major biogeographic zones in India. It also covers two of the four biodiversity hotspots of India, i.e., the Himalayan and Indo-Burma biodiversity hotspot regions. Of the total forest area of 68 million hectares in India, the Northeastern states account for over 17 million hectares, roughly one-fourth of the country's forest cover.

The forests of these regions have enormous variation in their typology and floral characteristics, harboring 50% of the flowering plants of the Indian subcontinent, also displaying a mix of both tropical and temperate climates. This region originated important gene pools of Citrus, Mangifera spp, Oryza spp, and Musa spp. The region has a vast range of genetic diversity and a significant level of endemism that makes it crucial in forest genetic research.

Monitoring of bioinvasion in such an important region is necessary to safeguard the existing biodiversity. Non-native species can potentially outcompete the native species, which can also have significant economic consequences. Native trees play a crucial role in various recreational and industrial activities, including specific utilization by the ethnic communities, and a decline in their populations can result in financial setbacks, too.

Non-native species can have severe and transformative ecological impacts, affecting short-term and long-term eco- systems. The endemic/ indigenous/ diversified flora and fauna are dependent on native ecology as a whole, and any alterations can result in disturbance of the equilibrium. Checking and documenting the dominance and origin of species is crucial to identify potential threats to the ecological balance of forests.

It is vital to trace the nativity of the dominant species to understand the ecosystem dynamics, connectivity, and resilience and to put forth better conservation efforts. Furthermore, to understand the magnitude of invasion effects and implement effective conservation strategies prioritizing immediate and biodiversity protection protocols.

It will also aid in monitoring and managing alien species invasions, the second most significant threat to forest degradation after habitat fragmentation, by keeping track of their distribution in the database and developing suitable strategies.

This article reviewed the dominant species of the region to confirm whether the bio-invasion of non-native forest species threatens the forests.

The most dominant/abundant tree species of the northeastern states are cumulated from the State Forest Reports (SFR, 2019) provided by the FSI (Forest Survey of India) for both the RFA (Recorded Forest Area) and TOF (Trees Outside Forests). The nativity was traced using the KEW website and GBIF (Global Biodiversity Information Facility).

Are the non-native tree species dominating the North East Forest?

All states of northeastern India have been differently affected by the invasion of non-native tree species. The dominant tree species in the recorded forest of Arunachal Pradesh are U-Thangjing (Castanopsis spp), Tolhao (Terminalia myriocarpa), Sal (Shore-aassamica), Figs (Ficusspp) and Tal (Duabanga grandiflora). These dominant species are native to the region as they grow within their native ranges, which also cover the State of Arunachal Pradesh.

Usoi (Schima wallichi), Chingsoo (Tectona grandis), Khok (Albizia spp), Tera (Bombax ceiba), and Fragrant padritree (Stereo-spermum-chelo-noides), are the dominant tree species in Assam forests. Among them, only Stereospermum-chelonoides are non-native to the region, while the rest are all growing within their native range in Assam.

Usoi (Schima wallichii) is also the most dominant species in the forests of Manipur. The other dominant species, Tal (Duabanga grandiflora) and Uchan (Pinuskesiya), are native to the region. Many of Castanopsis spp and Oak (Quercus spp) are native to the region.

The State of Meghalaya also has non-native trees dominating its forests. Theibong (Artocarpus heterophyllus), which is non-native, grows dominantly in their forests. The most dominant species, Schima wallichii and other dominant species i.e. Pinus kesiya, Sal (Shorea robusta), Ficus spp. are native dominant trees growing in Meghalaya's forests. The dominance of non-native trees may be due to the degradation and conversion of forests.

Their sacred forests have experienced increasing human interference. Shifting cultivation has also interfered with the structure of their forests.

Kharpa (Macaranga spp), Schima wallichii, Albizia spp, Tectona grandis, and Sahata (Dysoxylum-binecta-riferum) are the dominant tree species in the forests of Mizoram. There are both native and non-native species of Macaranga growing in these forests. Overall, the species mentioned above dominant in Mizoram are native, and their native range covers the State of Mizoram.

The forests of Nagaland are dominated by Schima wallichii, Macaranga spp, Quercus spp, Ficus spp, and Alder (Alnus spp). Some of these dominant genera are also native species growing within their native range, while some are non-native.

In the forests of Sikkim, the dominant species are Schima wallichii, Castanopsis spp, Shorea robusta, Pumsi (Machilus spp), and Alnus spp. These dominant trees are also native and growing well within their native range. Unsurprisingly, these species thrive in Sikkim's climate and environment.

Most of the dominant trees of the forests in Tripura are native species. Shorea robusta, Tectona grandis. Albizia species are native, while Rubber Tree (Hevea brasiliensis) and Kanak champa (Pterosper-mumacerifolium) are non-native to the State and still grow as dominant trees in their forests.

The rubber tree was introduced to Tripura in 1963, and it is one of the most important cash crops in the State. Perhaps this explains the abundant growth of the non-native species in its forest.

It was found that the forests of the region are adorned and occupied mainly by species native to the region. However, some introduced species grow and thrive in the forests of Tripura and Assam as dominant species.

Among all North Eastern States, the forests of Tripura are the most threatened by bio-invasion of non-native tree species, followed by Assam, Meghalaya, Mizoram, Nagaland, Arunachal Pradesh, Manipur and Sikkim, respectively.

Therefore, it is recommended that the species endemic to the North East only be prioritized in afforestation, reforestation, and ecological restoration activities by various Government organizations and stakeholders. It is also suggested that policymakers should have a long-term vision emphasizing native species in all such citizens' programs.

Views in the article are personal.