4.1 The important plants in home gardens
Based on the quantitative analysis, we found that some plants were important. These plants were cultivated commonly in the home gardens or cited frequently by the informants (Fig 5).
Fig 5 the Top 5 important plants in home gardens
Notes: 1: Dendrobium nobile, 2: Zingiber officinale, 3: Capsicum annuum, 4: Citrus medica, 5: Prunus persica, 6: Prunus mira
Su-lan-tsao (Dendrobium nobile) was the most frequently cited and cultivated plants in the home gardens. The plant was cultivated as featured product in the tropical and subtropical regions of Motuo County. D. nobile was the original plant of the Traditional Chinese Medicine “Shi-hu (石斛)” and the Traditional Tibetan Medicine “Bu-shes-tse” [41-42], and it could be sold for a high price in traditional medicine markets. Thus, D. nobile was popular to cultivated by local people for selling. Besides, another purpose of Tsang-la people to cultivate the plant was for decorating home gardens, Because of its beautiful flowers.
Sa-ga (Zingiber officinale) was multipurpose in local communities. The tender rhizomes of Z. officinale were seasonal vegetable in springs, and the mature rhizomes which were rich in aromatic oil were used as spice in cooking. Local Tsang-la people also used the rhizome as medicine to treat cold. Z. officinale was the original plant of Traditional Tibetan Medicine “Ga-kya” which was used to treat digestion problems and the complications of “rlung (wind)” and “bad-gan (fluid)” diseases [42].
Capsicum annuum was the most important spice flavor in typical Tsang-la daily cuisines, and it was used in almost every local dish. Two ethno-species of Capsicum annuum were cultivated by Tsang-la people in the study area. The two ethno-species were identified based on the pungency level and origin places. One was named as “Soe-lu” which had temperate pungency, and the other one was named as “Bon-ga-soe-lu” which had strong pungency. “Soe-lu” was native while “Bon-ga-soe-lu” was introduced from India. We found that the morphological feature of “Bon-ga-soe-lu” was similar with “Bhut Jolokia (India's ghost pepper)” of India [42].
Nying-pa (Citrus medica) was common in local home gardens. Tsang-la people cultivated it for collecting fruits as medicine, traditionally. Tsang-la people collected the fruits of C. medica, then sliced up and dried the fruits in shade. The dried fruits were used as herbal tea to treat cold in local Tsang-la medicine. Local people named C. medica as “Motuo Da Ningmeng (墨脱大柠檬, Big Lemon of Motuo County)” in Chinese language, because the smell of its fruits were very similar with lemon. Besides, C. medica was the origin plant of Traditional Chinese Medicine “Xiang-yuan (香橼)” [40], so local people also collected its fruits and sold to traditional druggists.
Kham-pu (Prunus persica) was another highly frequent ethno-species in local home gardens. P. persica was cultivated as fruiter. Besides, Kham-pu was an important ritual plant in traditional culture which symbolized auspiciousness in Xizang district [44]. Anather Prunus species, P. mira was also called as Kham-pu by local people, but local people thought it was not the same ethno-species with P. persica. Because the species was used for other purpose and not harvesting fruits. P. mira was common wild plant in Yarlung Tsangpo Canyon, and local people introduced it into home gardens as rootstocks for grafting P. persica.
4.2 Local knowledge of the identification of ethno-species
The diversity of ethno-species could indicate the local knowledge of understanding plants. In the study area, Tsang-la people identified the ethno-species from the use purpose and origin of plants. The ethno-species could mostly match to the botanical species, but sometimes under-differentiated or over-differentiated to botanical species [28, 30]. For example, Brassica rapa (total UR=31) was the most frequent botanical species in the present study. Brassica rapa was identified as four ethno-species by local people, according to the differences of their cooking methods and morphological characteristics among them. For another example, Tsang-la people divided the plants of genus Musa into two ethno-species as “Tsun-ma-lai-su”, of which the tender shoots and flowers were edible as vegetable, and “A-ni-lai-su”, of which the fruits were edible as banana, although we found that at least four botanical species of the genus were used by local people. Further, Tsang-la people divided the local cultivated populations of “A-ni-lai-su” into “Krung-go-a-ni-lai-su”, which was native or introduced from other regions of China, and “Ni-ra-a-ni-lai-su”, which was introduced from India, based on their origin places.
4.3 The important functions of the local home gardens
4.3.1 The self-service “food supermarkets” and “herb shops” of local people
Home gardens not only had high plant diversity, but also many functional plants including edible and medicinal plants [1-2].
From the previous studies, food plants were the most frequently cited in most of the home gardens through the world [1-3]. The results of our study was no exception. The plants used as vegetable (218 use-reports) were cited most frequently in the home gardens in the present study. The edible plants could provide carbohydrates, proteins, vegetable oil, vitamins and minerals [3, 45, 46, 9]. Our previous study in Yunnan province of China showed that the edible plants in home gardens and wild could help people to fight against famine [47]. Nepali experts also found that home gardens were important to food supply in remote mountain area of Nepal [10].
Asteraceae was the most frequently cited families containing 12 botanical species in the present study, and seven of them were used vegetables. The plants of genus Dioscorea and Solanum were cited frequently, these species were used as food and medicine.
Thirty-three ethno-species were cultivated for medicinal uses. These medicinal plants were used to treat common ailments by local people, and some of them were sold to the druggists. The previous studies in Yunnan Province of China and Chiang Mai of Thailand also showed similar results [5, 8].
Home gardens were also used as “crops seedling bases” by local people. Rice was the staple crop in the low altitude regions of Beibeng Township (the Tsang-la language “Hbras-spung” meant “rice field”). Local people raised the rice seedlings in the home gardens then planted the seedlings into the field in every spring. Beside rice seedlings, the seedlings of vegetables, fruit trees and some medicinal plants were also raised in home gardens. Local people usually built small greenhouses for crop seedling in their home gardens.
Besides, the home gardens were also the bases of local people for introducing alien plants from other places, and most of these plants were edible or medicinal plants. These plants enriched the food tables and herb chests of local people.
The surplus products from home garden could be sold in local small markets. Moreover, some plants, such as Dendrobium nobile and Camellia sinensis, were cultivated for selling, specially. Thus, local home garden could be seen as local “supermarkets” or “shops” for increasing incomes of local people. According to some previous studies, the farming in home gardens could be as one of the ancillary incomes for local people especially women [1-3, 48-50]. In the present study, we found that most of the local home gardens were as if managed by women, and also, the number of female informants were actually more than male informants. But we could not conclude that women were more important than men in the farming and management of local home gardens, because the detailed related information were not enough in the present study. We need to collect more information in future field researches.
4.3.2 The base of local native endangered plants conservation and sustainable use
Home gardens may contribute to the conservation of native species [51].Four species in the home gardens were designed as endangered plants by IUCN, and three of them including Coptis teeta (EN), Cephalotaxus hainanensis (EN) and Juniperus pingii (NT) were native species [39]. All of the plants of Orchidaceae were recorded as endangered plants in the Information System of Chinese Rare and Endangered Plants (ISCREP) [40]. These plants were important for local medicine, ornament and religion (table 5). Local people introduced them from forests and cultivated and bred them carefully in their home gardens. Some previous studies indicated that this phenomenon could help conserve the local endangered useful plants, and it was an efficient way to rare plant resources sustainable uses [1-4, 51-54]. Besides, the previous studies showed that local home gardens were important in conserving the regional biocultural heritage of local economic plant resources [55-57]. It was worth mentioning that local people told us that the reason why they cultivated these endangered plants was for increasing the available resources of these plants. “These plants are extremely rare”, a home garden owner told us, “if we always collect these plants in the forest rather than attempt to cultivate them, they will disappear”.
Table 5 the endangered plant species in the home gardens
Dendrobium nobile was the most frequent plant in local home gardens of Tsang-la people, and it was important sample commodity in health product markets. However, it was identified as endangered species in ISCREP [40], and the wild population commercial collection and cross-border trade of the species was illegal in China [58]. The artificial cultivation of medicinal plants was considered as an efficient way to reduce the collection from wild population. The function for biodiversity conservation of the local home gardens could coincide the concept of the “Biodiversity conservation through use" [59]. Home gardens could emerge as an effective means for both economic well-being and biodiversity conservation [60].
4.3.3 The important part of beautiful homes
Home gardens provided many beautiful plants for decorating daily lives, and many of these plants were with great potentials to be developed as ornamentals in modern Horticulture [61]. In the present study, we recorded 49 ethno-species which were cultivated as ornamental plants, and 32 of them were called as “Mong-nang” by local people. “Mong-nang” meant “beautiful flower” in Tsang-la language. In Tsang-la communities, “Mong-nangs” were important decorations in home gardens and balconies. Local people collected ornament plants from native forests and other places, then introduced to their home gardens. The informants told us that a big part of the “Mong-nangs” (we had recorded 29 ethno-species) were introduced from Lhasa, the center city of Xizang Autonomous Region, and they got the seedlings in Lhasa, and secured them carefully on the long way home. The informants claimed that beautiful flowers were essential in their lives. Interestingly, local people did not seem to know the Tsang-la name of each “Mong-nang”, but called them collectively as “Mong-nang”. It might because that most of these plants were introduced form other places, they had no Tsang-la names. According to the study on traditional culture of the ethnic groups in Tibetan plateau, the ideal homes should be surrounded by beautiful gardens with many blooms [62].
Interestingly, the ornamental plants of Orchidaceae especially Genus Cymbidium were cited frequently and cultivated carefully in the home gardens by local people. Local people named them as “Lan-tshao”. We inferred that the name was from Mandarin “Lan-cao (兰草)”. The ornamental Orchidaceae plants were important in traditional Chinese culture, and they could fetch a good price in flower markets [63].
4.4 The impact factors of the plant diversity and arrangement in home gardens
From the results of multidimensional scaling (ALSCAL) (Fig 4), we could divided the communities into four groups, with their positions in the four quadrants of Fig 4. We found that all of the communities in quadrant 1 and 2 located on the west side of Yarlung Tsangpo River while most of the communities except Spa-gdeng in quadrant 3 and 4 located on the east side of the river. And, the altitudes of all of the communities in quadrant 1 and 4 were over 1000m while the altitudes of most of the communities except Spa-gdeng in quadrant 2 and 3 were below 1000m.
Spa-gdeng shared many home garden plants with the low altitude communities on the east side of Yarlung Tsangpo River especially Hbras-spung (J=0.19, the second-highest of the values of Jaccard Index), although it was a high altitude community located on the west side of the river. Why Spa-gdeng was so different with other communities? We inferred that it might because Spa-gdeng was near the main road, which provided many chances for the people of Spa-gdeng to exchange plants and information with people from other places.
Therefore, we inferred that the altitude might be the most important impact factor of the plant diversity and composition of home gardens, and the traffic conditions also impact the plant diversity and composition. Similarly, a previous study in Africa indicated that the major factors of the plant diversity in home gardens were geographical distance between sites and differences in altitude of farms [64]. Furthermore, the previous studies in central Himalaya and Nicaragua showed that the factors of the plant composition in home gardens included climate, local social-economic condition, personal preference and cultural background of the owners [65-67]. In the present study area, because of the huge altitude variations in the relatively small region, the altitude might be the principal factor of local climate conditions of different communities.
Other factors, such as local terrain, was also impact the plant diversity of home gardens. Hbras-spung and Gder-kong had not only the most number of home gardens but also the highest diversity of plants in the home gardens. We inferred that the possible reason was that the two communities located at mesas or broad valleys, and they had more available flat fields for cultivating than other communities which usually located at rough terrain places. One home garden usually belonged to one household, in general. But in the local communities, we found that some home gardens were not private but shared by several households. Because of the limited available flat fields, the households usually shared home gardens, especially in the communities located at rough terrain places, such as Spo-gdong, Spa-gdeng and Jang-shing. Thus, we categorized the local home gardens into “private” and “public” home gardens (Fig 2). A typical example was that, in Spa-gdeng, most of the households shared two big public home gardens, while just few households could have their own private small home gardens. We found that the diversity of public home gardens was much richer than private home gardens, because the public home gardens were larger. A previous study in Kumaun Himalaya region suggested that large home gardens are more efficient than the small home gardens and are ecologically, socially and economically diversified [68].
4.5 Issues of the impaction of the old houses reconstruction to the local home garden
Dig-gdong was a large community included 130 households, and the community had enough flat fields. But the big project of old houses reconstruction were in progress in the community, and most of the old facilities including houses and home gardens were dismantled. Thus, just only four survive home gardens were recorded. Interestingly, we recorded the largest number of home gardens and richest diversity of plants in Hbras-spung, of which the old houses reconstruction projects had been finished several years ago. Because the information of the plants in the home gardens in Hbras-spung before the old houses reconstruction projects was not available, we could not do further analysis. Therefore, it was difficult to know how the projects impact the diversity and composition of plants in the home gardens of local communities.
With the rapid economic development, the old houses reconstruction had implemented in more and more rural communities of developing regions [26]. The related researches in Southeast Asia showed that recent socio-economic changes of local home gardens were converting subsistence-oriented home gardens into commercial ones [69]. However, few studies focused on that how the old houses reconstruction change the landscape patterns including the plant composition of home gardens of rural communities. Future researches should pay more attention to the issues.