Population Structure of Cupressus tortulosa Griffith along the Altitudinal Gradients of Tsendenanag Ridge in Punakha, Bhutan Kaka 1 , Dhan B. Gurung 2 , Yeshey Khandu 2 , Om Katel 2 , Purna B. Chhetri 3 , Pema Wangda 1 1 Watershed Management Division, Thimphu 2 College of Natural Resources, Lobesa 3 Research and Development Centre, Yusipang Corresponding author: dbgurung.cnr@rub.edu.bt Copyright©BJNRD, 2014 Received Aug. 2014. Accepted Sept. 2014. www.bjnrd.org BJNRD (2014), 1(1): 24-31 Bhutan Journal of Natural Resources & Development Article Open Access doi: http://dx.doi.org/10.17102/cnr.2014.04 J BJNRD Abstract The Cupressus tortulosa Griffith, which had been popularly known as Cupressus corneyana Carriere and Cupressus himalaica Silba, is locally known as Tsenden. There are knowledge gaps in the ecology and population dynamics of Tsenden. Using the Vegetation Survey method, this study focused on the population structure of the Tsenden along various altitudinal gradients, including its ecology and habitat within natural stands. The study was conducted at Tsendenanag of Taewang Geog, Punakha Dzongkhag. Nine designated plots (20 x 20 m) were set up, covering altitudes ranging from 1700 to 2700 m above sea level. Tsenden was the dominant species associated with Quercus lanata, Q. glauca, Pinus wallichiana, Myrsine semiserrata, with undergrowth consisting of Eurya acuminata, Rhododendron species, and bamboo – Yushania species. Tsenden was abundant on steep rocky precipices with a slope percent ranging from 49% to 80%, occupying the aspects of northeast, southeast, east, and southwest. In undisturbed areas, Cupressus regeneration was absent; whereas, profuse regeneration was observed in disturbed (fire and landslide) sites, indicating that a certain level of disturbance is required to initiate regeneration. At higher altitudes, species dominance changes from Cupressus to Q. glauca, P. wallichiana and Rhododendron species. Key words: Cupressus tortulosa, Tsenden, dominance, regeneration, species richness Introduction Several species of Cypressus, belonging to the family Cupressaceae , are found in Southeast Asia; especially in Bhutan, Nepal, Tibet – the autonomous Province of China, and the Indian States of Assam, Arunachal Pradesh, and Uttarakhand. Cupressus tortulosa Griffith, which is known in Bhutan as the Tsenden, is found growing naturally on steep and rocky precipices at altitudes ranging from 1800 to 2700 m above sea level in Punakha, Wangdue Phodrang, Lhuntse, and Trashigang Dzongkhags (districts) of Bhutan (Wangdi et al., 2012). The Tsenden was known as Cupressus corneyana Carriere and Cupressus himalaica Silba (Grierson and Long, 1983; Maerki, 2013), and is the National tree of Bhutan. Tsenden grows on rugged mountain terrain with well- drained soil, and in cool, moist, and temperate environmental conditions where there are fewer competitors. It is a light-demanding pioneer species, initiating primary forest succession and secondary succession following the destruction of broadleaf understory forests resulting from anthropogenic disturbances or episodic fires (Miehe et al., 1999). Tsenden forms the top canopy in cool broadleaf and evergreen oak forests in deep soils (Miehe and Miehe, 1998). Natural Tsenden forests are predominantly associated with species of Quercus, Castanopsis, Rhododendron, Betula, Alnus, Acer, Benthamedia, Sorbus, Rhus, Ilex, Symplocus, and Tsuga with Laurophyllous tree species as the understory, and Pinus wallichiana and Quercus semecarpifolia as overstory. It is usually common in moderately dry areas of central Bhutan (Wangdi et al., 2012). While a comprehensive study on nationwide distribution of Tsenden was carried out by Wangdi et al. ( 2012), almost no research has been conducted BJNRD (2014), 1(1): 24-31 24 ISSN 2409–2797 (Print) ISSN 2409–5273 (Online)