Companion Plants of Tea: From Ancient to Terrace to Forest

China is one of the origins of ancient tea gardens, with a long history of tea culture and tea cultivation. Guizhou Province is an important tea production place in southwest China with rich forest tea resources. The purpose of this study is to obtain historical information on companion plants in historical tea gardens and provide a theoretical basis for the sustainable development of forest tea gardens in Guizhou Province. We conducted a statistical analysis and comparison of plant species among ancient tea gardens, terrace tea gardens, and forest tea gardens from a diachronic perspective, based on 21 ancient tea literature studies, 116 terrace tea garden documents, and 18 sampled plots of forest tea gardens in Guizhou. A total of 24 companion plants species belonging to 16 families and 22 genera were found in ancient tea gardens, 81 species were found in terrace tea gardens belonging to 37 families and 74 genera, and 232 species were found in sample plots of forest tea gardens belonging to 90 families and 178 genera. Companion plants can be divided into three categories. Most of the plant families recorded in the literature also appeared in the forest tea garden we surveyed. In ancient tea gardens, terrace tea gardens, and forest tea gardens, Poaceae, Fabaceae, and Rosaceae were the most dominant families, respectively. The intercropping of tea gardens has been practiced since ancient times. Companion plants in natural forest tea gardens not only provide important insights into intercropping of terrace gardens but also hold significant implications for the conservation of existing forest tea gardens and the sustainable development of tea gardens.


Introduction
Tea has a long history in China.Tea plants originate from forests.They are one of the characteristic and important tree species of subtropical evergreen broad-leaved forests.In a stable plant community structure, they are found as tall trees or shrubs in the understory of the forest.According to legends, Shennong, an ancient Chinese ruler, tasted various herbs and encountered seventy-two toxic substances in a single day but was healed by tea (神农尝百草，一日遇七十二毒，得荼而解之), which was believed to be the main function of tea in ancient China.In the Ming Dynasty, Shen Yang's "Dan Qian Record" (the year 1547) states that "tu 荼 is the ancient word for tea 茶.Additionally, Yu Lu's "The Classic of Tea" (the year 780) from the Tang Dynasty mentioned that tea originated from the Shennong family 茶之为饮，发乎神农氏.According to Gu Ban's "White Tiger Tongyi" (the year 79) in the Eastern Han Dynasty, the Shennong period was the primary agricultural stage of China's Urgesellschaft.At present, archaeological discoveries have revealed that the Shennong period began over 10,000 years ago, and it can be inferred that the history of tea might also extend over 10,000 years [1].
Chinese tea culture has a rich and extensive history, dating back to the Pre Qin period, appearing also in the literature of the Jin Dynasty and Han Dynasty, and thriving in the Tang Dynasty and Song Dynasty."The Classic of Tea" (the year 780) written by Yu Lu marks the formal establishment of Chinese tea culture and also allows the study of Chinese tea culture to enter the academic field of vision [2].The emergence of the "The Classic of Tea" (the year 780) led to the rise of the tea literary works, such as Tingyun Wen's "Tea Picking Record" (the year 860), Ran Jiao's "Cha Jue" 茶决 (the year 784), Wen Fei's "Cha Shu" 茶述 (the years 811-813), etc.During the Song and Yuan Dynasties, the trend of drinking tea flourished day by day, and tea was an indispensable drink in the daily lives of the people from the emperor to the countryside.Moreover, there were stunning verses such as " Tea is for civilian use, equivalent to rice and salt, and cannot be consumed without it for a day" in Anshi Wang's "Yi Cha Fa" 议茶法 (the year 1059) of the Song Dynasty, and "those what are indispensable every day are firewood, rice, oil, salt, sauce, vinegar and tea", recorded in Zimu Wu's "Dream of Liang Lu" (the year 1274) of the Song Dynasty.In addition, tea-drinking customs such as tea parties, tea competitions, and tea banquets are also quite popular, and this further illustrates the important position of tea at that time [3,4].
The cultivation of tea plants in China also has a long history.Chaosheng Wang [5] inferred that the tea planting by ancient people in China has a history of at least 2000 years through his understanding of the two ancient tea literatures "Huayang Guo Zhi" (the years 348-354) and "Sichuan General Records" (the year 1816).The earliest records of tea tree cultivation techniques in China can be traced back to "Guang Zhi" (the year 270), which was written in the Western Jin Dynasty.There are also numerous pieces of literature from later dynasties that record the cultivation of tea plants.Lin Luo's "Cha Jie" 茶解 (the year 1609) of the Ming Dynasty recorded the method of preserving tea seeds to facilitate planting in the coming year."Dongxi Shi Cha Lu" (the years 1049-1054) and "Da Guan Cha Lun" (the years 1107-1110) of the Song Dynasty recorded "Tea is suitable for the shade of high mountains, but prefers the early morning of the sun"."Beiyuan Bie Lu" (the year 1196) and "Cha Jie" (the year 1609) of the Song and Ming Dynasty recorded "where was better place for tea plantation, and what were good companion trees to tea".
During the Ming and early Qing dynasties in China, the Tea culture was a stage of stable and sustainable development, but in the end of Qing Dynasty, it was a stage of abnormal development followed by rapid decline [6].In the Ming Dynasty, not only did the cultivation of tea plants expand but later Ming treasure voyages spread Tea culture further.Moreover, there was a big improvement in tea cultivation techniques with the emergence of tea seedling transplanting methods and tea garden intercropping practices.In the early Qing Dynasty, the area of tea plantations continued to expand, and asexual propagation methods of tea branch cutting and layering were invented [7,8].There have also been further improvements in tea garden management, such as tea tree pruning, weeding, and fertilization.From the late Qing Dynasty to the establishment of the People's Republic of China, Chinese tea farming entered a period of decline [9][10][11][12].
After the establishment of the People's Republic of China, the tea economy developed gradually.During this period, great efforts were devoted to developing terrace tea gardens, from learning methods to improve terrace tea garden management to increasing investment in labor, funds, fertilizers, and pesticides in terrace tea gardens.As a result, the area of terrace tea gardens was expanded, and the yield of terrace tea gardens was significantly increased nationwide.For example, from 1954 to 1965, the terrace tea garden in Yuhang Tea Experimental Field increased its area by 153.3 hectares, with an average yield of 1200 kg per hectare [13].According to the data from the China Tea Marketing Association, the total area of China's terrace tea gardens reached 3.165 million hectares in 2020.Although the development of terrace tea gardens in this way can play a great role in the economy, there are serious problems such as ecosystem instability caused by single planting, ecological environment destruction, pesticide residues, and chemical fertilizer residues [14][15][16][17].
In December 2022, Professor Shengji Pei defined a Forest Tea Garden as "it is a tea community of the genus Camellia (sect.Thea, including C. sinensis var.sinensis, C. sinensis var.assamica, C. sinensis var.dehungensis, C. taliensis, C. crassicolumna) of family Theaceae, managed in a traditional way, meeting the green and organic planting standards, with the goal of producing ecological tea and an area of more than 0.5 hm 2 , accompanied by at least one other wild or cultivated woody plant that forms a canopy over 10% and reaches a height of over five meters" [18].Guizhou Province is an important tea production area in Chinese history, and it was also one of the eight major tea regions in China during the Tang and Song dynasties, Plants 2023, 12, 3061 3 of 13 known as the "Qianzhong Tea Region" [19].Records of forest tea in Guizhou could be traced back to Yu Lu's "The Classic of Tea".It was written that the taste of "Du Ru Gao Shu Tea" (also known as Wu Chuan Da Shu Tea) was highly enjoyable.Tingjian Huang of the Song Dynasty also praised the Du Ru Gao Shu Tea of Qianyang, which had a bitter taste and helped to relieve the dizziness in his "Jian Cha Fu" (the years 1057-1061).Guizhou Province is rich in wild tea forest resources.According to the survey, Fanjingshan Nature Reserve in Tongren City alone has an area of 13,700 hm 2 of wild tea forest [20].
The purpose of this study is to conduct a diachronic comparison of the similarities and differences in companion plants among ancient tea gardens, terrace tea gardens, and forest tea gardens by analyzing ancient tea literature and terrace tea garden literature, as well as a sample plot survey.Also, it aims to provide a theoretical basis for the sustainable development of forest tea gardens in Guizhou Province.

Review of Ancient Literature in China before the Late Qing Dynasty
In this study, 21 pieces of ancient tea literature including articles, books, and poetry written before the end of the Qing Dynasty of China were selected using the keywords "ancient", "tea garden", "companion plants", and "intercropping" (Figure 1).The author's name, literature name, the year of completion, the Chinese name of companion plants, and reference fragments regarding companion plants of ancient tea literature were summarized (Table 1).
one other wild or cultivated woody plant that forms a canopy over 10% and reaches a height of over five meters" [18].Guizhou Province is an important tea production area in Chinese history, and it was also one of the eight major tea regions in China during the Tang and Song dynasties, known as the "Qianzhong Tea Region" [19].Records of forest tea in Guizhou could be traced back to Yu Lu's "The Classic of Tea ".It was written that the taste of "Du Ru Gao Shu Tea" (also known as Wu Chuan Da Shu Tea) was highly enjoyable.Tingjian Huang of the Song Dynasty also praised the Du Ru Gao Shu Tea of Qianyang, which had a bitter taste and helped to relieve the dizziness in his "Jian Cha Fu" (the years 1057-1061).Guizhou Province is rich in wild tea forest resources.According to the survey, Fanjingshan Nature Reserve in Tongren City alone has an area of 13,700 hm 2 of wild tea forest [20].
The purpose of this study is to conduct a diachronic comparison of the similarities and differences in companion plants among ancient tea gardens, terrace tea gardens, and forest tea gardens by analyzing ancient tea literature and terrace tea garden literature, as well as a sample plot survey.Also, it aims to provide a theoretical basis for the sustainable development of forest tea gardens in Guizhou Province.

Review of Ancient Literature in China before the Late Qing Dynasty
In this study, 21 pieces of ancient tea literature including articles, books, and poetry written before the end of the Qing Dynasty of China were selected using the keywords "ancient", "tea garden", "companion plants", and "intercropping" (Figure 1).The author's name, literature name, the year of completion, the Chinese name of companion plants, and reference fragments regarding companion plants of ancient tea literature were summarized (Table 1).

A Survey of Companion Plants in Terrace Tea Gardens after the Establishment of the People's Republic of China
One hundred and sixteen Chinese documents regarding companion plants in terrace tea gardens were found in the CNKI database (www.cnki.net,accessed on 16 August 2023) using the keywords "tea garden", "intercropping", "companion plants", "ecological benefit", "terrace tea garden", and "tea growth".The types of publications were articles and reviews, and the period of publication was 1957 to 2022.

Sample-Plot Survey
Eighteen sample plots were chosen in the forest tea gardens located in Sandu County and Puding County, Guizhou Province (Table 2, Figure 3a).The specific details of another 10 plots in Sandu County could be seen in our previous study [21].Each sample plot covered an area of 20 m by 20 m and trees with a diameter at breast height exceeding 5 cm were recorded.Additionally, four middle squares (5 m by 5 m) were established along the diagonal of each sample plot to examine the shrubs.Furthermore, four smaller plots (1 m by 1 m) were arranged in the center of each shrub layer sample to study the herbaceous plants [22].

Sample-Plot Survey
Eighteen sample plots were chosen in the forest tea gardens located in Sandu County and Puding County, Guizhou Province (Table 2, Figure 3a).The specific details of another 10 plots in Sandu County could be seen in our previous study [21].Each sample plot covered an area of 20 m by 20 m and trees with a diameter at breast height exceeding 5 cm were recorded.Additionally, four middle squares (5 m by 5 m) were established along the diagonal of each sample plot to examine the shrubs.Furthermore, four smaller plots (1 m by 1 m) were arranged in the center of each shrub layer sample to study the herbaceous plants [22].

Diversity of Companion Plant Species in Three Different Types of Tea Gardens
In this study, a total of 24 companion plant species belonging to 16 families and 23 genera were found in ancient tea literature, including 12 species of tree plants, 7 species of shrub plants (with 5 species of them being both trees and shrubs), and 10 species of herbaceous plants (Table 3).
The companion plants found in terrace tea gardens include 81 species belonging to 37 families and 74 genera, including 40 species of tree plants, 10 species of shrub plants (with 9 species of them exhibiting dual life forms), and 40 species of herbaceous plants (Table 3).According to the selected articles, intercropping economic trees (apples, mulberry trees, etc.) in tea terrace gardens demonstrated favorable strategic selection, while young terrace tea gardens (1-4 years old) were generally intercropped with leguminous plants (peanuts, peas, etc.).
The companion plants found in forest tea garden sample plots include 232 species belonging to 90 families and 178 genera, including 64 tree species, 98 shrub species, and 111 herbaceous species (Table 3, Table A1).In the sample plots of forest tea gardens we surveyed, the total vegetation coverage exceeded 92.44%.The JQ02 plot (Altitude 877 m) situated in Sandu County exhibited the highest species richness with 43 recorded species, while the CJ01 plot (Altitude 1301 m) located in Puding County presented the lowest species count of 25.

Diversity of Companion Plant Species in Three Different Types of Tea Gardens
In this study, a total of 24 companion plant species belonging to 16 families and 23 genera were found in ancient tea literature, including 12 species of tree plants, 7 species of shrub plants (with 5 species of them being both trees and shrubs), and 10 species of herbaceous plants (Table 3).The companion plants found in terrace tea gardens include 81 species belonging to 37 families and 74 genera, including 40 species of tree plants, 10 species of shrub plants (with 9 species of them exhibiting dual life forms), and 40 species of herbaceous plants (Table 3).According to the selected articles, intercropping economic trees (apples, mulberry trees, etc.) in tea terrace gardens demonstrated favorable strategic selection, while young terrace tea gardens (1-4 years old) were generally intercropped with leguminous plants (peanuts, peas, etc.).
The companion plants found in forest tea garden sample plots include 232 species belonging to 90 families and 178 genera, including 64 tree species, 98 shrub species, and 111 herbaceous species (Table 3, Table A1).In the sample plots of forest tea gardens we surveyed, the total vegetation coverage exceeded 92.44%.The JQ02 plot (Altitude 877 m) situated in Sandu County exhibited the highest species richness with 43 recorded species, while the CJ01 plot (Altitude 1301 m) located in Puding County presented the lowest species count of 25.

The Categories of Companion Plants
The companion plants could be divided into three categories.The first type was companion plants that have ecological value.For instance, tall trees such as Firmiana simplex (L.) W. Wight and Morus alba L. can provide shade for the tea plant, as tea plants prefer shade.Also, some companion plants could be multi-purpose (nitrogen fixing, fly attracting, water storage for tea, and so on).There was a multi-purpose tree written in several pieces of ancient literature named Albizia chinensis (Osh.)Merr, which not only can provide shade for tea but also attracts flies to avoid the gathering of flies around tea and contaminating the tea leaves.At the same time, it can also help regulate the soil moisture in the tea garden.The second type referred to aromatic plants, such as Osmanthus fragrans Lour.and Yulania liliiflora (Desr.)D. L. Fu.The third type included companion plants that have economic value (fruits and economic crops).In the terrace tea gardens, fruits trees like Prunus salicina L., Mangifera indica L., and Punica granatum L. were often used to provide shade for tea while economic crops like Vicia faba L., Zea mays L., and Sorghum bicolor (L.) Moench were often planted to change the microclimate of tea gardens and obtain economic benefits.

Dominant Family of Companion Plants in Three Different Types of Tea Gardens
According to ancient tea literature, a greater diversity of companion plant species was documented within the families of Poaceae, Urticaceae, and Fabaceae in ancient tea gardens.In terrace tea gardens, higher species diversity was observed in the families Fabaceae, Rosaceae, and Poaceae.Meanwhile, the predominant families were Rosaceae, Asteraceae, and Dryopteridaceae in sample plots of forest gardens in Guizhou (Figure 4).The findings demonstrated the prevalence of the Rosaceae family within both terrace and forest tea gardens, while the Poaceae and Fabaceae families exhibited dominance in ancient tea gardens and terrace tea gardens.was documented within the families of Poaceae, Urticaceae, and Fabaceae in ancient tea gardens.In terrace tea gardens, higher species diversity was observed in the families Fabaceae, Rosaceae, and Poaceae.Meanwhile, the predominant families were Rosaceae, Asteraceae, and Dryopteridaceae in sample plots of forest gardens in Guizhou (Figure 4).The findings demonstrated the prevalence of the Rosaceae family within both terrace and forest tea gardens, while the Poaceae and Fabaceae families exhibited dominance in ancient tea gardens and terrace tea gardens.

The Common Family of Companion Plants in Three Different Types of Tea Gardens
The highest affinity in terms of companion plant species at the family taxonomic level was observed between ancient tea gardens and terrace tea gardens (Jaccard Index, JI = 0.23), and a high resemblance also occurred between terrace tea gardens and forest tea gardens (JI = 0.22), whereas the lowest similarity was detected across all three garden types (JI = 0.07).The level of similarity between ancient tea gardens and forest tea gardens fell within an intermediate range (JI = 0.12).

Discussion
Tea plants thrive beneath the canopy of arboreal vegetation in the forest and have evolved over an extended period of systematic cultivation to acquire distinctive genetic traits associated with shade endurance, temperature and humidity preferences, and the ability to efficiently harness diffused light [23].Our research shows that the companion plants found in forest tea garden sample plots include 232 species belonging to 90 families and 178 genera, and there is a rich diversity of plant species in the Guizhou forest garden.It is found that as early as the Tang Dynasty in China, ancient people discovered that companion plants in tea gardens are beneficial to tea plants [24].Appropriate plant diversity can improve the microclimate of tea gardens, improve the physical and chemical properties of soil, and increase beneficial insects in tea gardens [25][26][27][28], which further proves the importance of companion plants in tea gardens.
Currently, there are still serious issues that need to be addressed in the terrace tea garden.Primarily, commencing from the latter half of the 20th century, certain terrace tea gardens have employed substantial quantities of agrochemicals (pesticides, fertilizers) with the intention of achieving heightened tea yields.Regrettably, this practice has engendered soil microbiota, the dissipation of vital nutrients, and disruption to the ecological equilibrium of terrace tea gardens, thereby exerting a significant influence on the biodiversity of indigenous plant species [29,30].In congruence with existing research findings, it has also come to our attention that a few forest tea gardens have suffered artificial degradation [31][32][33].These gardens are susceptible to pests and diseases, resulting in suboptimal rates of tea plant resource utilization.
The intercropping of tea gardens has been practiced since ancient times and most of the intercropping plants in terrace tea gardens were fruits trees (pomegranate, loquat, and pear), economic trees (chestnut and rubber tree), legumes (broad bean, mung bean, and cowpea), and grain (corn and sorghum).In our research, we also found that only a small number of companion shrub plants were intercropped in terrace tea gardens.The reason for this may be that the tea planted in terrace tea gardens was mostly shrub tea plants, and there was a competitive relationship between shrubs.The intercropping of shrub species might lead to competition between them and tea plants for nutrient elements, which is unfavorable for tea growth and development [34].Introducing intercropping practices encompassing clover, straw, and other herbaceous species offers a pragmatic method for diminishing soil erosion in terrace tea gardens, concurrently upholding soil element stability [35,36], and intercropping trees such as magnolia and chestnut in the middle of terrace tea gardens can contribute to the moderation of microclimatic conditions, fostering a cooler and more humid environment that benefits tea vegetation [37,38].
The Rosaceae family exhibits a relatively higher diversity of companion plant species within both terrace tea gardens and forest tea gardens.This phenomenon could be attributed to their considerable economic significance, expansive geographical distribution, and high endurance to climate change [39].
Comparing the three garden types, the family-level similarity is lowest among the companion herbaceous plants (which possess relatively greater species richness in forest tea gardens), while companion trees exhibit the highest level of similarity.This disparity could be attributed to the fact that certain companion herbs in forest tea gardens may be got rid of as weeds in terrace tea gardens, whereas certain companion trees play a favorable role in tea plant growth and garden development.The majority of the families observed in ancient tea gardens and terrace tea gardens can also be found in the forest tea gardens we investigated.These findings suggest that the inspiration for planting companion plant trees in ancient tea gardens and terrace tea gardens might have originated from natural forest tea gardens, which demonstrates the feasibility of promoting the vigorous development of forest tea gardens.

Conclusions
Our study indicates that the utilization of companion plants in tea gardens has been prevalent since antiquity, showcasing a diverse array of companion plant species.Notably, Poaceae, Fabaceae, and Rosaceae emerge as the most prevalent botanical families.These diverse companions can confer distinct advantages to tea cultivation.During the establishment of tea gardens, it is recommended to deliberate on approaches that ensure the preservation of the ecological balance and the optimal utilization of companion plant resources.This will facilitate the attainment of sustainable progress across a spectrum of tea garden contexts.

Figure 1 .
Figure 1.Historical records of major ancient tea literature.

Figure 2 .
Figure 2. Location of the forest tea gardens in Guizhou Province, China.

Figure 2 .
Figure 2. Location of the forest tea gardens in Guizhou Province, China.

Figure 3 .
Figure 3.The comparison of forest tea gardens and terrace tea gardens in Guizhou, China.(a) Forest tea garden.(b) Terrace garden.

Figure 3 .
Figure 3.The comparison of forest tea gardens and terrace tea gardens in Guizhou, China.(a) Forest tea garden.(b) Terrace garden.

Figure 4 .
Figure 4. Families with many companion plant species appear in tea gardens.Figure 4. Families with many companion plant species appear in tea gardens.

Figure 4 .
Figure 4. Families with many companion plant species appear in tea gardens.Figure 4. Families with many companion plant species appear in tea gardens.

Table 1 .
A summary of companion plants in ancient tea literature.

Num- ber Ancient Tea Literatures Names Author The Year of Completion Chinese Name of Companion Plants Reference Fragment
Figure 1.Historical records of major ancient tea literature.Table 1.A summary of companion plants in ancient tea literature.

Number Ancient Tea Literatures Names Author The Year of Completion Chinese Name of Companion Plants Reference Fragment
1 Huayang Guo Zhi 华阳国志 Qu Chang Eastern Jin Dynasty (348-354) Mo Yu There are fragrant konjac and fragrant tea in the garden.园有芳蒻、香茗 2 Si Shi Zuan Yao 四时纂要 E Han Late Tang and five Dynasties (Around 900) Sang, Zhu, Su, Ji, Ma Under the mulberry trees and bamboo shades, any place is suitable for planting… There is no restriction on planting ramie, millet, and barley.

Table 1 .
Cont. branches emerge from plum tree in the bamboo gate, and a few stacks of green trees lie horizontally on the pine outside the mountain.The people gradually pick tea on the hills of Longfu, while many households brew rice wine for sale at market.

Table 2 .
Specific information of the sample plots in Puding County.

Table 2 .
Specific information of the sample plots in Puding County.

Table 3 .
Companion plants in ancient gardens and terrace tea gardens.

Table 3 .
Companion plants in ancient gardens and terrace tea gardens.