Ecology of major Invasive Alien plant species (IAPs) across various habitats in Pakke Tiger Reserve, Arunachal Pradesh

Abstract

Proliferation of invasive alien plant species poses a significant threat to the structure and function of ecosystems, making this a critical area of focus within the scientific communities. These species cause extensive damage to the biodiversity, as they are capable of altering the ecosystems and outcompete the native biodiversity. Globally, their abundance has increased dramatically in forested and other natural areas due to rapid economic growths and anthropogenic activities. To counter this alarming situation, understanding the distribution pattern, climatic influences on phenophases and ecological impact on soil by invasive alien plant species is a priority. In northeast India, studies on invasive alien plant species diversity and their impacts are very limited, especially in Arunachal Pradesh. Therefore, the present study aims to determine the patterns of distribution, phenophases and physiochemical impacts by the dominant invasive alien plant species in five forest types (Assam Alluvial Plain Semi Evergreen Forest-AAPSEF, East Himalayan Mixed Coniferous Forest-EHMCF, East Himalayan Subtropical Wet Hill Forest-EHSTWH, Non-Forest-NF and Riverine Forest-RF) of Pakke Tiger Reserve, Arunachal Pradesh. The altitudinal range of Pakke Tiger Reserve is 150- 2050 m above the sea level (490 to 6725 feet), with an average annual rainfall of 2500 mm. The current study reveals a total of 43 invasive alien plant species in the study area. However, their species richness in five forest types was in declined trend with the increase of elevation. Across the forest types, AAPSEF (30%) display the maximum level of invasion and least incursion in EHSTWHF (16%) in the current study. Among the nine species selected for the study, Chromolaena odorata (L.) R.M.King & H.Rob. was found dominant and distributed extensively in all forest types, with highest relative density (51%) in EHSTWHF and relative abundance (10%) in NF. The entire selected species shows contagious distribution pattern (<0.5) in all forest types except for Urena lobata in NF displaying random distribution (0.025 - 0.5) in study area. Ageratum conyzoides L., Chromolaena odorata (L.) R.M.King & H.Rob. and Urena lobata L. are the species with extensive distribution in all forest types in comparison to other selected species showing their dominance over the native vegetation. Moreover, maximum area cover percentage was exhibit by Chromolaena odorata (L.) R.M.King & H.Rob. followed by Ageratum conyzoides L., Mikania micrantha Kunth and Urena lobata L. across the forest types in Pakke Tiger Reserve. Forest types such as AAPSEF, NF and RF display high level of disturbances while the EHMCF and EHSTWHF have fewer incursions by invasive alien plant species in the study area. Phenological pattern on the selected species shows that Bidens pilosa L. has the longest flowering phenophases while Chromolaena odorata (L.) R.M.King & H.Rob. has the maximum fruiting duration in EHSTWHF. For leaf fall and initiation, Urena lobata L. display the longest duration in RF. Moreover, coefficient of variation shows that most of the species display asynchronous phenophases across the forest types of Pakke Tiger Reserve. Repeated measures of ANOVA also display that Ageratum conyzoides L. display difference in flowering in NF and EHSTWHF while Chromolaena odorata (L.) R.M.King & H.Rob. leaf initiation show difference in EHMCF. Correlation and linear regression display influences of climatic parameters i.e., precipitation, relative humidity, minimum and maximum temperature to the selected species in the study area. CCA also indicates that precipitation, minimum and maximum temperatures directly influence the phenophases of the selected species. However, relative humidity influences the phenophases of the selected species when in cohesion with other climatic parameters. Ecological impact on native species by invasive alien plant species was determined by collecting the soil sample of the most dominant species i.e., Chromolaena odorata (L.) R.M.King & H.Rob. across the forest types in Pakke Tiger Reserve. The result shows that clay and copper contents were high in all invaded sites while soil pH, sand, boron and water holding capacity were significantly lower in invaded plots. Out of 16 soil variables, T-test reveals that AAPSEF and NF have variation in 13 variables while EHMCF, EHSTWHF and RF have difference in 12 variables. ANOVA between the invaded and uninvaded sites also indicates significant differences in Boron, iron, copper, nitrogen, water holding capacity, clay, silt and sand. Moreover, correlation shows eight of the variables display relation between them. Furthermore, PCA indicates that INNF soil properties were different from the remaining sites. The results indicate that Chromolaena odorata (L.) R.M.King & H.Rob. alter the soil properties of invaded areas by improving the fertility, making it ideal for the proliferation process in future scenarios.