Assessing the impact of threats, identifying favorable growing conditions, and predicting future population scenarios are vital for the conservation and management of threatened species. This study investigated the availability, microhabitat characteristics, threat status, and community associations of Swertia chirayta, a highly threatened Himalayan medicinal herb, in 22 populations in Sikkim, India, using the vertical belt transect method. Of the 14 microhabitats identified, open grassy slope emerged as the most favorable and wet grassy slope as the least favorable for S. chirayta. The species was dominant in 8 of the 10 major plant communities identified. Among 9 major types of disturbance identified, human movement and collection of non-timber forest products appeared as the biggest threats to S. chirayta. Disturbances significantly affected the availability of the species. S. chirayta, though under high anthropogenic threat, maintains high microhabitat pliability, which is vital for its conservation and management, provided immediate conservation measures are taken.
In recent years, extraction of natural resources, economic pressure, inappropriate forest management policies, inadequate knowledge, and insufficient legislative initiatives on sustainable use of bioresources (Wickens 1991; Uniyal et al 2011) have resulted in depletion of biodiversity (Badola and Aitken 2010). In addition, land-use changes and human-driven habitat fragmentation and destruction have become one of the biggest threats to existing ecosystems and a leading cause of species extinction (Duffy et al 2011; Yokogawa et al 2013). Estimating extinction risk and future population size based on current population structure (Guedje et al 2003), assessing the effect of habitat deterioration on population dynamics (Colling and Matthies 2006), and understanding the effects of natural and human-made changes to habitats (Hegland et al 2001) and their responses to disturbances (Ticktin 2004) are the most suitable practical approaches to determining the impact of exploitation.
Studies have found that species performance varies among microhabitats (Shrestha and Jha 2010; Pradhan and Badola 2012). Species with habitat specialization and a narrow range of microhabitats have greater risk of extinction than species with a broad habitat range (Brys et al 2005; Samant et al 1996). Therefore, knowledge of threatened plants’ microhabitat requirements would help in planning their conservation and management (Hegland et al 2001; Colling and Matthies 2006; Kalliovirta et al 2006; Pradhan and Badola 2012). This necessitates undertaking microlevel habitat assessment, which can help determine the performance of a species under different conditions and provide information on its ecological requirements (Hegland et al 2001; Pradhan and Badola 2012).
To address these critical issues, our study focused on the highly threatened Swertia chirayta (Roxb.) Karst. (Gentianaceae) (hereafter chirayta), a perennial herb indigenous to the temperate Himalaya that grows in Afghanistan, Bhutan, India, Nepal, and Pakistan from 1200–3000 masl. Chirayta has high pharmacological importance (Joshi and Dhawan 2005; Pradhan 2011). The entire plant is used in traditional medicine and in many herbal drugs such as Diabecon, D-400, Himoliv, and Melicon V (Pradhan 2011). Because of high commercial demand (Badola and Pal 2002; Pradhan 2011), chirayta has been vigorously harvested in different parts of the Himalaya (Anonymous 2008; Phoboo and Jha 2010), leading to tremendous pressure on its natural populations. Indiscriminate extraction has made the species vulnerable in Nepal (Phoboo et al 2010), and it has been prioritized for immediate conservation in India (Badola and Pal 2002). Despite its high conservation value, little quantitative information exists on its availability, microhabitat diversity, the impact of exploitation, and the degree to which it is threatened. Better data on chirayta populations (Guedje et al 2003) in the Himalayan region are needed to assess the conservation status of this important species.
This study aimed to (1) evaluate the current status of and threats to chirayta populations, (2) identify its microhabitat characteristics and community structures, (3) assess the likely future impacts of disturbances and of the presence of associate species, and (4) develop recommendations for its conservation and management.
Study area and research methods
Our study took place from May 2005 to November 2006 in the Sikkim Himalaya, India (Figure 1), which lies between 27°00′46″ and 28°07′48″ north latitude and 88°00′58″ and 88°55′25″ east longitude and from 220 to 8598 masl, covering an area of 7096 km2 (0.2% of the land area of India).
Before doing the field studies, we conducted an extensive literature review and consulted with state forest department field staff, villagers, and experienced harvesters and herders to identify possible distribution areas of chirayta in Sikkim. Subsequently, we conducted intensive field surveys and explored 22 populations with elevations from 1500–3000 masl in different parts of Sikkim (Figure 1). Populations were distinguished based on their separation by a physical barrier such as a river, mountain, or aspect or by a distance of at least 500 m (Osunkoya 1999).
For each population, we used the vertical belt transect method (Michael 1990) for sampling, in which a 20 × 150-m plot was marked and divided into 3 subplots (20 × 50 m). In each subplot, the density of chirayta was determined using 10 random quadrats (1 × 1 m), which created 30 quadrats for each population. Within each quadrat, we noted the microhabitat occupied