The giant tree rhododendron Rhododendron protistum var. giganteum is the largest species of rhododendron, reaching up to 30 m in height and 1 m in basal diameter. It appears to be restricted to the southern part of Gaoligong Mountain in Yunnan, China, and is categorized as Critically Endangered on the 2004 China Species Red List (but has not yet been assessed for the global Red List). Lack of knowledge of the species, however, has hindered a full evaluation of the species' conservation status. A joint project was therefore launched via Fauna & Flora International, involving scientists and staff of Gaoligongshan National Nature Reserve, through the Global Trees Campaign, to improve our understanding of this species. We combined data from field surveys and information obtained from interviews with local people, especially nature reserve rangers, to elucidate the main threats to this species.
Field surveys were carried out at Hecaodi (at 2,320–2,730 m altitude) and Cizhuhe (2,410–2,550 m), in the Gaoligong Mountain range, Tengchong County, Yunnan Province, where the giant tree rhododendron has previously been recorded by staff of Gaoligongshan National Nature Reserve. Ten people surveyed for a total of c. 20 days on three occasions from February 2010 to March 2012. In total, we recorded 1,439 individuals: 1,325 at Hecaodi, of which 1,115 were adult and 210 juvenile trees, and 114 at Cizhuhe, of which 44 were adult and 70 juvenile trees. The area of occupancy of the species on Gaoligong Mountain is 2,458 km2.
Hecaodi and Cizhuhe are located at the edge of the core area of Gailigongshan Nature Reserve. Our surveys and information from interviews with local people and nature reserve rangers indicated there are some potential threats to this tree: (1) it is rare to find seedlings, potentially indicating high seedling mortality (those found were all growing on rotten wood), (2) thunder and lightning destroy large branches, probably because of its height, and large branches sometimes break under the weight of heavy snowfall, (3) it always grows on slopes, where soil is easily lost following rainfall, and (4) lack of conservation awareness amongst tourists, increasing numbers of tourists and road construction within the species' range pose threats to this rhododendron and its habitat.
Some conservation activities for the giant tree rhododendron have started and a monitoring plan has been launched, and publicity materials to raise the conservation awareness of tourists and local people are in preparation. Information on seed germination, seedling establishment and the reproductive biology of the species is required, and it could be beneficial to install lightning rods on the largest individuals. Propagation for conservation has already started, both within the species area of distribution and in Kunming Botanical Garden. To elucidate the species' conservation status fully, further surveys are required in other areas of its potential range (i.e. the northern part of Gaoligong Mountain and Motuo in Tibet), as indicated by specimens from the herbarium of the Kunming Institute of Botany, Chinese Academy of Sciences (KUN) and by information from rhododendron experts.