Herbaceous Phytosociological Characters in Forested Stream of Nagaland, North-East India

Introduction

Vegetation composition and diversity reflect the ecological conditions of a site and its interaction with environmental gradients. Phytosociological analysis provides a quantitative framework to evaluate such species composition, dominance, and distribution, offering insights into their structure and function of plant communities under varying environmental conditions [1]. Such studies are particularly useful in fragile hill ecosystems where land-use intensity, moisture gradients, and anthropogenic disturbance significantly influence vegetation dynamics [2].

Herbaceous species form a vital component of riparian and forest-edge ecosystems, contributing significantly to primary productivity, soil stabilization, and nutrient cycling. Their diversity and abundance are closely governed by edaphic and microclimatic factors such as soil moisture, light availability, and disturbance intensity. Studies across the Indian Himalayan region have shown that shifts in these parameters often lead to distinct community assemblages and variation in diversity indices [3-5]. Phytosociological assessment of herbaceous vegetation, therefore, serves as an effective tool to monitor ecological stability and habitat quality.

Nagaland, forming part of the Indo-Myanmar Biodiversity Hotspot, supports diverse vegetation types along sharp elevational gradients. The Khichi Ghoki stream, located in Zunheboto district and flowing through Lumami village, represents an important ecological corridor sustaining both biodiversity and local livelihoods. The riparian vegetation plays a crucial role in maintaining stream bank stability, regulating hydrological flow, and supporting nutrient cycling. However, increasing anthropogenic pressure, agricultural encroachment, and localized disturbances have led to changes in the structure and composition of the herbaceous community.

Understanding spatial variations of the herbaceous vegetation along hydrological gradients is vital for local biodiversity conservation and for interpreting vegetation–environment relationships in hilly terrain. Hence, the present study was undertaken to compare the phytosociological characteristics of herbaceous vegetation between the upstream and downstream regions of the Khichi Ghoki stream in Zunheboto district, Nagaland, and to assess variation in species richness, diversity and dominance in relation to human disturbances.

Materials and Methods

Study Area

The study was conducted along the KhichiGhoki stream near Lumami village, Zunheboto district, Nagaland, India (26.2257°N, 94.4851°E). The site lies approximately 2 km from Lumami village and about 40 km from Zunheboto town. The stream, which eventually joins the Doyang River, is surrounded by subtropical forest vegetation and agricultural landscapes. The region experiences a monsoonal climate with distinct wet and dry seasons, and the riparian zone supports diverse herbaceous flora influenced by hydrological and anthropogenic factors.Two zones were delineated for the studyviz., 1. Upstream: representing relatively undisturbed, shaded, and moist conditions and 2. Downstream: characterized by open canopy, higher human activity, and moderate disturbance due to agricultural and domestic use.

Sampling Design and Vegetation Analysis

Phytosociological assessment was carried out using the line transect–quadrat method. In each zone (upstream and downstream), ten 1 × 1 m quadrats were laid randomly along the stream margins, giving a total of 20 quadrats. Within each quadrat, all herbaceous species were identified, counted, and photographed for reference. Species identification followed standard regional floras and taxonomic keys [6-10].Standard phytosociological parameters i.e.,frequency, density, abundance, and basal area were computed using the formulae of Curtis and McIntosh [11]. The Importance Value Index (IVI) of each species was derived as the sum of its relative frequency (RF), relative density (RD), and relative dominance (RDo).

The basal area was estimated using:

where r is the stem radius measured at ground level.

Diversity Indices

Pants community diversity was assessed using the following indices:

1. Shannon–Wiener diversity index (H′) [12]:

where pᵢ is the proportion of individuals belonging to the ith species.

2. Pielou’s evenness (E) [13]:

where S is species richness.

3. Simpson’s dominance index (D) [14]:

These indices were used to compare species composition, dominance and community stability between upstream and downstream areas respectively.

Results and Discussion

Species Composition and Family Distribution

A total of 30 herbaceous species belonging to 17 families were recorded from both sites (Tables 1–2). The Asteraceae family was the most represented (11 species), followed by Commelinaceae, Oxalidaceae, and Plantaginaceae (two species each). The remaining families, including Urticaceae, Zingiberaceae, and Lamiaceae, were represented by a single species. Dominance of Asteraceae aligns with reports from tropical and subtropical ecosystems where members of this family exhibit wide ecological amplitude and adaptability [15].Asteraceae is one of the largest and most ecologically versatile plant families globally, comprising roughly 25,000 species [16]. Its members display exceptional adaptability across environmental gradientsfrom tropical and subtropical to temperate regions—owing to diverse physiological and morphological traits. The family’s success is partly attributed to its specialized fruit morphology, such as pappus structures that enhance wind-mediated long-distance seed dispersal, and its capitulum-type inflorescence that attracts a broad range of generalist pollinators, promoting reproductive assurance under variable conditions. Members of the Asteraceae frequently dominate disturbed and anthropogenically influenced habitats due to their pioneer or early-successionalbehaviour. Their rapid growth rates, competitive ability, and capacity to modify soil nutrient cycling favor dominance in areas subjected to grazing, fire, or cultivation. Studies have demonstrated that invasive Asteraceae species can significantly alter soil physicochemical properties and arbuscularmycorrhizal fungal communities, thereby creating positive feedbacks that further sustain their dominance [17]. Such ecological traits explain the strong representation and high IVI values of Asteraceae species such as Ageratum conyzoides and Bidenspilosa in the present study, particularly in the disturbed downstream habitats of the Khichi Ghoki stream.

Phytosociological Attributes

Upstream and downstream zones showed distinct variation in species dominance. In the upstream zone, Phegopterisconnectilis exhibited the highest IVI (24.37), followed by Ageratum conyzoides (21.16) and Bidenspilosa (20.28). The lowest IVI was recorded for Curcuma longa (3.07). In contrast, the downstream zone was dominated by Ageratum conyzoides (IVI = 37.13), Phegopterisconnectilis (28.35), and Bidenspilosa (26.83), while Phyllanthusurinaria (6.95) recorded the lowest IVI.The dominance of Ageratum conyzoides and Bidenspilosa in the downstream site may be attributed to their disturbance-tolerant and invasive nature, thriving in open and nutrient-rich environments [18]. Conversely, the presence of Phegopterisconnectilis in shaded upstream areas reflects its preference for moist and less disturbed microhabitats. Similar distributional trends have been documented in riparian herb communities of the Eastern Himalaya [19].

Diversity Indices

The upstream zone exhibited higher species richness (S = 30) and diversity (H′ = 3.019) compared to downstream (S = 21, H′ = 2.617). Simpson’s dominance index was lower in the upstream site (D = 0.067) than in the downstream (D = 0.104), indicating greater evenness and reduced dominance. Correspondingly, Pielou’s evenness index was slightly higher in the upstream (E = 0.888) than downstream (E = 0.860).These results suggest that the upstream vegetation is more heterogeneous and ecologically stable, whereas the downstream community exhibits reduced diversity and higher dominance due to disturbance pressure. Comparable findings were reported by Kumar &Verma[20] and Bhat et al. [5], who noted that human intervention and open canopy conditions often favor a few aggressive species, reducing overall species evenness.

Ecological Interpretation

The contrast between upstream and downstream vegetation reflects the influence of hydrological and anthropogenic gradients on community organization. Upstream areas, being shaded and moist, promote species coexistence and niche differentiation. Downstream sites, exposed to periodic disturbance and resource enrichment, encourage dominance of opportunistic herbs such as Ageratum conyzoides, indicative of successional or disturbed-stage communities.Higher Shannon and lower Simpson indices in the upstream area indicate greater resilience and lower competition, while the reduced diversity downstream signals incipient habitat homogenization. Similar upstream–downstream contrasts in herbaceous diversity have been documented in riparian systems across the Indo-Myanmar region [15, 21].

Conclusion

The present study revealed distinct variation in herbaceous plant composition and diversity between the upstream and downstream regions of the KhichiGhoki stream in Zunheboto district, Nagaland. A total of 30 species belonging to 17 families were recorded, with Asteraceaeemerging as the most dominant family. The upstream zone exhibited higher species richness, diversity and evenness, indicating a more heterogeneous and ecologically stable habitat compared to the downstream area, which showed reduced diversity and greater dominance of disturbance-tolerant species such as Ageratum conyzoides.These findings highlight the influence of disturbance gradients on herbaceous community structure in riparian ecosystems. Conservation measures emphasizing the protection of less disturbed upstream habitats and the control of invasive species are essential to sustain the ecological integrity of riparian zones in Nagaland’s hilly terrain. Continuous monitoring of vegetation dynamics will further aid in understanding long-term changes under increasing anthropogenic pressures.

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