Range collapse of a tropical cervid (Cervus eldi) and the extent of remaining habitat in central Myanmar

The thamin (Cervus eldi) is an endangered species of deer whose present range is greatly reduced from its original distribution covering the deciduous forests throughout south-east Asia. We mapped the present distribution of thamin using ground surveys and tied this information to habitat types derived from satellite images in order to detect patterns that might indicate the landscape features which precipitated the decline. We conducted a survey of 24 out of 28 Myanmar townships that were reported to contain thamin in 1992, and evidence of thamin were found in 23 of these townships, predominately in mixed deciduous forests where dipterocarp trees were present. There was no significant correlation between the number of thamin detected and forest remaining in the township, or the size of the human or livestock population. A landcover classification of Landsat Thematic Mapper images indicated 58% of the study area contained deciduous forest, of which 12% was dipterocarp forest. Forest tracts containing thamin were digitized and landscape analyses were conducted on a resampled habitat map that emphasized dry and dipterocarp deciduous forest. Of six landscape variables measured only core area size was a significant predictor for the presence of thamin. None of the unsurveyed indaing forest tracts possessed a core area large enough to support thamin. The pattern of thamin decline matches predictions that peripheral, rather than central, populations are more likely to persist in declining species. All correspondence to: William J. McShea. Tel: 540-635-6563; Fax: 540-635-6506; E-mail: [email protected]. one known population of approximately 150 individuals within a fenced reserve in Hainan (Song, 1996) and possibly a population in northern Cambodia (Humphrey & Bain, 1990). Populations of the third subspecies, C. eldi thamin, occur in scattered areas of central Myanmar (Tun Yin, 1967; Salter & Sayer, 1986). Within Myanmar, thamin were considered common throughout the 1940s, and their distribution was described as patchy, but abundant, in 1967 and 1986 (Tun Yin, 1967; Salter & Sayer, 1986). Thamin are grazers and opportunistic browsers, who supplement their diet with wild fruit and cultivated crops, particularly rice (Lekagul & McNeely, 1977). Probably few pristine thamin habitats remain, and populations have been reported to occupy areas ranging from dry scrub and thorn forest to open deciduous forest (Salter & Sayer 1986; Wemmer, 1987). The least disturbed of these habitat types is deciduous forest. Deciduous dipterocarp (indaing) forest is the most abundant forest type within south-east Asia (Rundel & Boonpragob, 1995). In 1990, Myanmar was approximately 50–58% forested, with 14% covered with some form of deciduous forest (UNEP, 1995; Achard & Estreguil, 1995). Rainfall, soil type and terrain account 174 W. J. MCSHEA ET AL. Fig. 1. Historical and present range of Cervus eldi in south-east Asia. Historical range, indicated by diagonal stripes, is derived from maps by Whitehead (1972) and shows the range of the three subspecies C. eldi eldi (A), C. eldi thamin (B) and C. eldi siamensis (C). The present range, indicated by stippling, is adapted from Tun Yin (1967) and Salter & Sayer (1986) and includes two semi-captive populations in India and Hainan Island, and a postulated (Humphrey & Bain, 1990) population in northern Cambodia (?). for most of the variation in forest types across southeast Asia (Richards, 1979; Rundel & Boonpragob, 1995). Although rainfall amounts are variable across the historical thamin range, the remaining thamin range in central Myanmar receives 100 cm of rain during the monsoon season (Salter & Sayer, 1986). Thamin are considered to occur only in deciduous forests (Tun Yin, 1967; Salter & Sayer, 1986; Humphrey & Bain, 1990), of which three types are found in this region; dipterocarp (indaing), dry (thandahat) and mixed deciduous (teak) (Stamp, 1925). All three types are confined to the region that annually receives 100–200 cm of rainfall (Stamp, 1925). Determining the abundance and distribution of these forest types is a focus of our research. Myanmar has one of the highest proportions of forest cover in the Asian–Pacific region (UNEP, 1995). This forest inventory was based on NOAA AVHRR satellite data and it estimated cover of closed forest at 43.3% (29.33 million ha) of the country. Although forest cover, in general, is extensive in Myanmar, there may be significant losses of deciduous forest types. In Thailand, the only south-east Asian country for which reliable data are available, indaing forest has declined 45–60% over the last 20 years (Rundel & Boonpragob, 1995). Overall deforestation rates in Myanmar were estimated at onethird those of Thailand for 1980–1991 (Achard & Estreguil, 1995). The thamin population in Myanmar was estimated to be 4000 animals in the 1970s (Whitehead, 1972), but the first countrywide questionnaire distributed by the Wildlife Department in 1992 estimated that 2200 deer remained within Myanmar, with the largest population (>1200 deer) in Chatthin Wildlife Sanctuary (Myint Aung, 1994). This survey reported thamin in 28 townships, six townships fewer than reported in 1967 by Tun Yin (1967) (Fig. 2). Chatthin Wildlife Sanctuary (268 km2) is composed of secondary indaing and mixed deciduous forest, and was originally established as a fuel reserve forest in 1941. Sight surveys for thamin along 65 km of line transects were conducted at Chatthin beginning in 1982 by the Food and Agriculture Organization (FAO: Salter & Sayer, 1986), and were repeated annually from 1992–1996 by forest rangers of the Wildlife Department (Table 1). These surveys estimated a 40% decline in thamin abundance since 1983. Despite declines in the abundance of Eld’s deer, both across its entire range and within Myanmar, no systematic field studies have been conducted. With respect to Myanmar, this is largely because it is one of the least externally-funded and internally-protected tropical countries in Asia (Balmford & Long, 1995). Our goals were to conduct a ground survey for thamin across the central plains of Myanmar, and to relate information on thamin abundance and distribution to maps of forest abundance and distribution. The result may serve both as a management guide for proposed protected areas, and to help determine landscape patterns that might explain the decline in the species.