Distribution of knowledge among informants
This study documented a total of 3031 use reports from 163 informants. Among the informants, 46 were female and 117 were male. The selection of our information reporter was random, but resulted in more men and fewer women participants. The reason may be that the right to speak is mainly in the hands of men, who are mainly responsible for external affairs and livelihoods in most families, and women are mainly responsible for household affairs[46]. The informants were aged from 7 to 81 years old, the average age of all was 52, the average age of men was 53 and the average age of women was 49. Middle-aged people (40~59) have provided more use reports of plants. Young people under thirty years old and elderly people over 70 years old provide less UR than middle-aged people. (Fig. 2)
In the past, living conditions were relatively poor, and young people often followed their elders to gather food, medicine, fuelwood, etc. in the wild. However, today's rapid economic development has significantly supplemented material resources, and the collection of wild plants has become less necessary. More children now go to boarding schools in the county, and more young people go to more developed areas to make a living. Elderly individuals may be slowly losing their memory on wild plant uses because of the socioeconomic changes over the years. These reasons have caused obstacles to the inheritance of traditional knowledge, and these memories passed down from generation to generation have become blurred[23, 24].
Taxonomic diversity of wild plants used by locals
A total of 121 plant species belonging to 52 families and 91 genera were documented in the study area. The most cited family was Compositae (16 species), followed by Rosaceae (9), Polygonaceae (7), Ericaceae (6), Apiaceae (5) and Lamiaceae (5) (Table 1). Among the plants, 89 were herbaceous, 20 were shrubs, 10 were trees and 2 species were vines (Table 1).
In our survey, the most frequently used parts of these plants were whole plant (37), followed by fruits (27), roots (27), leaves (23), stems (16), aerial parts (13), flowers (12), bulbs (1), seeds (1), and burls (1). The prominently used parts were the whole plant, fruits, roots and leaves (Table 1).
The diversity of use categories
The interviewed informants referred to 3028 use reports (UR), 1177 (38.8%) food uses, 805 (26.6%) for medicinal uses, 560 (18.5%) for economic plants and 486 (16.1%) for other categories. There were 53 species of edible plants, 53 economic plants, 46 medicinal plants and 50 plants used for other categories, including animal food (18), social uses (12), environmental uses (6), materials (5), fuel (4) and other uses (10) (Table 2). Many plants have multiple utilization categories. There are 30 kinds of plants with three or more uses, 12 medicinal and edible homologous plants, 32 plants that can be used both as a source of income and as medicinal plants, and 15 plants that can be used as both a source of income and food (Table 1).
Tibetans have unique eating habits in special geographical environments and climatic conditions. Highland barley powder and ghee are the main foods of farmers and herdsmen, supplemented by dairy products such as yogurt and milk residue, and meat of mostly beef and lamb[47]. Fruits and vegetables are rare, but in Yadong, there are many wild vegetables and fruits used, and these two parts account for 80% of wild edible plants. With the increasing demand for medicinal plants in Tibetan traditional medicine or Chinese medicine, the commercial value of medicinal plants has increased. Yadong County is rich in medicinal plant resources, so economic utilization has become an important category of plant utilization there. In addition, animal husbandry is the main source of livelihood for local people and fermented yogurt plants, animal food, and seasoning plants related to animal husbandry are also frequently used in the local Yadong.
Food
Wild edible plants (WEPs) play an important role in food supplementation under normal circumstances[48] and are an important source, in addition to cultivated plants, for people to obtain nutrients, vitamins, minerals and other biologically active compounds[40, 49]. Food categories in Yadong include fruits (28 species), vegetables (16), seasoning (7), starches (3) and beverages (1). The most widely used part is the fruit. There are very few gardens and woodlands available for planting fruit trees in the local area, and the yield of local fruit tree varieties is extremely low. This may be one of the main reasons why the locals collect wild fruits from the wild as a nutritional supplement.
Fruits with high CI values are Rheum nobile (CIfruit = 0.4663) and Rosa omeiensis (0.3988). The tender stem of R. nobile are peeled and eaten raw as snacks by locals. The plant is mainly distributed on the local high mountains above 4000 m above sea level [40]. The use of plants of the same genus is very abundant in other Tibetan areas. Tibetans from Lithang collect and eat these plants on the spot, and after removing the skin, the stem of the two species of Rheum, chukyur (R. alexandrae) and chum (R. palmatum)[29]. Tibetans eat the tender stems of R. officinale and R. palmatum in Zagana, Gansu, China[30]. The Tibetans of Shangri-La, Yunnan, China eat the tender leaves of raw R. likiangense [26]. The ripe fruit of R. omeiensis, R. macrophylla var. glandulifera and R.sericea are wild fruits that locals, especially children, like to eat very much. R. omeiensis is also eaten as a fruit by Tibetans in Lithang, Sichuang, Zhagana, Gansu, China and Shangri-La, Yunnan, China[26, 29, 30]. In addition, the Luoba people in Douyu village,in southeastern Tibet, use it as a medicinal plant to treat anaemia and maintain youth [50]. F. nubicola can be eaten raw or made into jams and eaten with shaved ice. Tibetans of Mustan District in Nepal also eat this plant as fresh fruit[29].
The Urtica hyperborea (CIvegetable = 0.5644) and Pteridium aquilinum (0.4294) are vegetables with high CI values. The tender leaves of U. hyperborea were locally eaten as a wild vegetable. It was consumed in spring and stored as a reserve vegetable during the winter. Boiling with riceor tsampa is the main processing method by which the locals detoxify the plant. The tender stems of this plant are used to stew soup by Tibetans in Sapi, Ladakh, Jammu and Kashmir, India[29]. A study showed that its extract has the effect to lower uric acid[51]. Hyperuricaemia and gout affecting human globally[52]. There are abundant resources of U. hyperbore in China[53]. Therefore, U. hyperborea is expected to develop into a healthy food in plateau areas. The young leaves of P.aquilinum are collected by the local population, where they are blanched and soaked overnight. After soaking, it can be stir fried as seasonal vegetables. Locals say that soaking overnight is to remove the bitterness and to improve the taste of the young leaves. However, this plant contains a toxic compound ptaquiloside (PT), a compound that is carcinogenic[54]. Fortunately, this soaking process removes the toxic substance carcinogenic contained in this plant[55]. P. aquilinum is also eaten as wild vegetable by Tibetans in Zhagana in Gansu, China and Shangri-La in Yunnan, China[26, 30]. In addition, it has a high commercial value in Gongba, Gansu, China[28].
The top two popular seasoning species are Carum carvi (CIseasoning = 0.2270) and Nepeta discolor (0.2147). C. carvi, called “kuo nie” is the most frequently mentioned spice in Yadong. Local Tibetans collect its young leaves in May or June and fruit in August or September to consume. The fruits of C. carvi have a pungent, coriander-like flavor and aroma that comes from essential oils, mostly carvone, limonene and anethole[56, 57].C. carvi are the sources of cumin and caraway seeds respectively, which have been used since antiquity for the treatment of various indications in traditional healing systems in wide geographical areas[58]. Europe has used C.carvi as a seasoning spice and aromatic repellent since ancient times. It can not only improve eyesight but also, make the breath more fragrant. The seeds of this plant are also used as seasoning by Tibetans in Lithang, Sichuan, China and Mustang, Nepal[29]. In addition, the seed of C.carcvi is also used a cures for poisoning and fever, promotes appetite and improve digestive health in Lithang, Sichuan, China[59]. The local people collect the above-ground parts of N. discolor, and eat them as condiments after they are dried in the shade.
The locals mentioned three important starch supplement plants, Potentilla anserina (CIstarch = 0.2638), Polygonum macrophyllum (0.1902). Chuoma (P. anserina) was frequently used as staple in premodern Tibet. Roots of P. anserina are boiled and eaten with butter and sugar. This is a traditional dish served on important Tibetan holidays[28, 30]. Compared with traditional root foods such as Solanum tuberosum, Ipomoea batatas, Colocasia esculenta, the ratio of nutrients in this plant is more healthy and reasonable[60]. This plant is also eaten as a substitute for tsampa by the Tibetans of Litang in Sichuan, Zhagana in Gansu and Shangri-La in Yunnan, China[26, 29, 30]. In addition, the local people mixed the seeds of P. macrophyllum and Hordeum vulgare var. coeleste and grind them into flour. The Tibetans in Zhagana, Gansu, China have similar usages[30]. The wild starch plants have become an important source of supplementary starch.
Medicinal plant use
Different sociolinguistic groups in China have their own indigenous and traditional medical systems and unique knowledge of medicinal plants[61]. A total of 43 traditional medicinal plants belongs to 24 families and 39 genera were documented for treating 14 different disease types of human diseases, such as dermatologic disorders, gastrointestinal problems, respiratory diseases, diarrhea, arthritis. The most cited families of the medicinal plants were Compositae (7 species), followed by Polygonaceae (4), Gentianaceae (4), Lamiaceae (3). Plant parts most commonly used for remedies preparation are the root with which accounts for 45.5% of the total medicinal plants. In addition, there are 10 veterinary medicines used to treat 4 kinds of animal diseases(Table 1).
The FIC of 14 diseases ranged from 0.67 to 1, and the values of the FIC were the highest for toothache (1.00) and hypoimmunity (1.00), followed by inflammations (0.98), Skeleto-muscular system disorders (0.98) and respiratory complaints (0.97). The values of the FIC were the lowest for Infections (0.67). The most cited disease was respiratory complaints (321 use reports), followed by inflammations (142), gastrointestinal (118) and dermatopathya (116) (Table 3).
Based on the information provided by the informants, we conducted a quantitative analysis. The five most cited species are Gentiana veitchiorum (CImedicine = 0.5767), Neopicrorhiza scrophulariiflora (0.5215), Fritillaria cirrhosa (0.4969), Taraxacum tibetanum (0.3436), Fraxinus paxiana (0.3006) (Table 1).
It is worth noting that the top three cited medicine plants are all used to treat respiratory diseases and are usually stocked in the homes of locals to meet daily needs, much like a medical kit in a city family (Fig. 5). These plant species all were traditional Tibetan medicines [40, 41] and used to treat common ailments such as inflammation colds, coughs, diarrhea. The whole plant body of G. veitchiorum is used locally to treat colds and bronchitis and relevant studies have shown that plant species has antibacterial, antiviral and pharmacological activities for treating bronchitis[62-64]. The roots of N. scrophulariiflora were widely used by the locals as a medicine to treat cold. According to the Chinese Pharmacopoeia, this plant can treat many diseases [44]. However, there is no documented treatment for the common cold and veterinary medicine use. The bulbs of F. cirrhosa were used by the locals as a medicine to treat tracheitis, and this species is also rich in pharmacologically active compounds that have antitussive activity[65, 66].
T. tibetanum whole plant is used to boil water for drinking, to treat various inflammations, such as upper respiratory tract infections, pharyngitis, etc. The young leaves can be collected and used as wild vegetables, and they have a bitter taste. Locals say that this vegetable can “clear the heat and remove the fire” and act a supplement nutrition. Plants of the same genus are also used by the Sherpas in Chentang, China as medicines for cancer and gynaecological diseases, and the Tibetans in Shangri-La, China and Nepal are also used as wild vegetables[29, 67]. The dandelion plant has a variety of anti-inflammatory active ingredients, and contains various nutrients such as protein, sugar, vitamins, etc. required by the human body. It is a kind of medicinal and food homologous plant with great development value[68].
The bark of F. paxiana can be soaked in water to treat fractures, and it can be used by both humans and livestock. In addition, during the collection process, the local people do not girdling, which is also an important manifestation of sustainable collection (Fig. 4). The same usage is also available in Bhutan[69]. People in Nepal use plants of the same genus to treat body aches[70]. F. paxiana is mainly distributed in the subtropical rainforest below 2000 m above sea level in the Yadong River Valley, where the population is very small. The main source of F. paxiana is Bhutan, where the private sector exchanges and purchases them through trade channels. Local merchants also buy the bark of the plant from Bhutan and supply it to drugstores for trading. Although the plant is locally widely used, there is no similar documentation of it in traditional Tibetan medicine, and there is no documentation of its efficacy in treating fractures in Chinese medicine[71]. We theorize that the traditional knowledge of this plant was obtained by the locals in Bhutan's trade and cultural exchanges.
Economic plants
Yadong County is rich in medicinal materials and non timber forest products[72]. In the study area, we found 53 plants having commercial value. These plants mainly were sold to Tibetan doctors or Hui merchants. Among them, 32 species are used as medicinal plants by the locals (Table 1). The most frequently mentioned economic plant was Fritillaria cirrhosa (CIeconomic = 0.3374), followed by Saussurea tridactyla (0.3313), Rhodiola himalensis (0.3252), Angelica paeoniifolia (0.2454), Panax pseudoginseng (0.1779) (Table 1). In addition, the local people also collect Cordyceps sinensis or Exidia sp. as important source of income. In the local region, except for a small amount of wild economic plants that are directly used by collectors, most of the plants enter the local or foreign market in some way (Fig. 5).
In recent years, because Tibetan and Hui medicinal material merchants have collected a large number of medicinal plants in Yadong, a large number of medicinal species have been collected. The informants informed us that the collection of economic plants has become more intensive compared to approximately 10-20 years ago. However, with the development of commerce, the excessive collection of plants has caused a certain degree of damage to the local ecological environment[73]. The degree of collection and dependence on wild plants has a lot to do with the economic status of the local people. It is generally believed that when a certain plant has a high economic value, it may lead to the depletion of the plant resources due to excessive collection[74, 75]. For example, F. paxiana , which have high commercial value, have been excessively and indiscriminately excavated. Its resources are declining sharply and are on the verge of extinction[76].
The local government is also aware of the impact of this uncontrolled gathering on the natural vegetation. For example, locals realized that the excavation of Rhodiola himalensis will lead to soil erosion, and now the excavation of Rhodiola himalensis has been banned. Rhododendron anthopogon, A. paeoniifolia and F. nubicola, were introduced to cultivated as a commercial crop in Kangbu Township and Shangyadong Township. The hope is that this will increase local revenues while reducing the damage to natural resources.
Animal food
Livestock are a critical source of nutrition and a major means of sustenance for the Tibetan population in Yadong. Locals have a wealth of plant knowledge associated with yak breeding. A total of 18 species of wild plants are used as animal food. Among these 18 species, 16 are herbs, and 2 are woody plants. These include Heracleum nyalamense (CIanimal food = 0.1840), Thermopsis barbata (0.0798), Polygonum macrophyllum (0.0613), P. tortuosum (0.0552), and Cirsium eriophoroides (0.0429). H. Nyalamense is the most popular animal food plant for locals. Local people say cattle can grow stronger after feeding this grass.
The locals gathered large amounts of animal food plants during the summer and fed them to cattle in the winter. H. nyalamense is an important animal food plant for locals. Compared to animal grass food, tree fodder is very important in providing livestock with food during the dry season when other feed sources are in limited supply [54]. R. glaciale, R. takare var. desmocarpum are important woody animal food plants. Their thin branches and leaves are used by locals as a substitute for grass. This can slow down the degradation of grassland to a certain extent [23].
Social uses
Social uses are divided into two categories, one is ritual plants (11 species), and the other is tobacco substitutes (1). Tibetan people convey their wishes to the gods through various sacrificial activities, and offer many items to the gods, thus praying for happiness and well-being. A total of 11 species of plants are used in social uses activities. Among them, 9 species are used for incense, such as Rhododendron anthopogon (CISocial uses = 0.4417), Nardostachys jatamansi(0.2147), Juniperus indica(0.1840). Two species are used in funerals. The local people use purple pigment on root of Onosma hookeri(0.0675) to decorate the offerings. After a person has passed away, the sticks of Myricaria rosea(0.0123) were burned to pay homage to the deceased.
Tibetan incense is an important social use activity related to plants. Most social used plants are commonly used as incense matreials, such as R. anthopogon and J. indica (Fig. 6), and dry sticks of these species are burned in a censer, which is placed on the flat roof of a house or at the entrance to the village. These plants usually burned in the early morning to pray for the gods' blessing and good luck for the day. “Sang” is a kind of sacrificial social use method that prevails in Tibetan areas and has a long history[77]. In ancient society, when the men of the tribe returned after expeditions, hunting, or funerals, people thought that they were contaminated with all kinds of filth. Therefore, their family members used cypress branches and fireworks burned with various herbs to dispel filth for them to prevent its spread that could in turn bring disaster to the family[77].
The preference of local Tibetans to choose plants is influenced by the following factors: First, most of the plants burned in simmering mulberries have a fragrance. After these plants are burned, they give off a strong fragrance. The scent drift in all directions with the wind, so more gods can be reached, thereby winning the entertainment of these gods and providing better protection to the family. Second, most of the plants used for this ceremony are common things in people's lives and surroundings.