Materials and methods

Study area. The community of San Juan Luvina is in the district of Ixtlán de Juárez (Sierra Juárez), Oaxaca (17° 30′ 16.9′′ N, 96° 32′ 56.1′′ E; 2040 m asl; Figure 1). It has protected natural areas and for forest management and agriculture (^{Hernández-Rodríguez et al. 2019}). The climate is temperate humid, with an average annual temperature between 16 and 20 °C (^{Trejo 2004}). The community is part of an area of high biological, economic, and cultural importance (^{Mittermeier et al. 2004}). The vegetation types in the region include pine-oak, oak-pine, and cloud forest that represent large non-fragmented areas with a high conservation level in Mexico (^{Arriaga-Cabrera et al. 2000}, ^{García-Mendoza et al. 2004}). The main disturbances include forestry by local communities (^{Bray 1991}, ^{Chapela 2007}, ^{Álvarez & Rubio 2013}) and deforestation for crops and cattle pastures. San Juan Luvina has a population of approximately 560 inhabitants, whose native language is Zapotec. San Juan Luvina was chosen for our study because it retains many traditions, and according to ^{López-Santiago (2015)}, there is an extensive traditional knowledge of more than 200 vascular plants.

Figure 1 Location of San Juan Luvina in the district of Ixtlán de Juárez (Sierra Juárez), Oaxaca, Mexico. The dotted line indicates highway 175 Oaxaca-Tuxtepec. 

Dendropogonella rufescens. D. rufescens is an epiphytic moss whose stems can exceed 30 cm in length with irregular pinnate branches up to 3 cm long reddish-brown or green in color, with thin and soft texture (^{Manuel 1994}). It grows on different tree species as conifers and oaks at an altitude between 200 to 2,800 m (Figure 2). Its neotropical distribution includes Guatemala, El Salvador, Honduras, Costa Rica, Panama, Venezuela, and Brazil. In Mexico, in addition to Oaxaca, its distribution consists of the states of Veracruz, Puebla, and Chiapas (^{Gradstein et al. 2001}).

Figure 2 Dendropogonella rufescens (Schimp.) E. Britton in the Sierra Juárez, Oaxaca. A) Habitat and life form in an ecotone of cloud forest and oak-pine forest; B) D. rufescens usually grows on the branches of young pine trees where its stems can reach 50 cm in length. 

Data collection. We interviewed 90 people in three age categories to identify generational differences in the TK among community members: 15-41 (youth), 42-68 (adult), and 69-95 years (old). Each age category included 15 men and 15 women. We established these age categories based on the social roles of community members and their possible influence on the knowledge and use of their natural resources. People between 15 and 41 years of age perform roles related to agriculture and forestry. Those between 42 and 68 years of age carry out work of exploitation of timber and non-timber resources and hunting activities. Finally, people between 69 and 95 years old are guides for people in the second category in forest management because they have greater knowledge about the area and distribution of natural resources. We selected informants randomly through home visits. In the interviews, we avoid forming groups of individuals that could bias in the informant responses.

The interviews included questions about the beginning of the use of D. rufescens by the community, how people used it, collected it, and recycled or disposed of it after use. For the interviews, we brought moss parts, and we showed photos of the plant in its natural habitat to guarantee that people could reliably identify it. We also show interviewees photos of different bryophytes (mosses and liverworts) from the area to avoid confusion with other species used. We did the interviews in the Zapotec language during March 2020 (Appendix 1). Interviews in the native language are useful in reducing confusion among interviewees regarding the taxa investigated and enriching the data quality with a more precise description of the knowelge and traditional uses (^{Berlin & Berlin 2005}). For the interviews, we requested permission from the municipal authorities in charge of the environment and wildlife and the local social affairs office (Presidency of the locality).

Data analysis. To assess uses richness in each age category, we performed rarefaction/extrapolation (R/E) curves with the Hill number 0 for incidence data (^{Begossi 1996}, ^{Chao et al. 2014}). The curves were performed with an extrapolation twice the number of informants per age category (60), 999 bootstrap replications, and 95 % confidence intervals. We did the R/E curves in the R languaje (^{R Core Team 2021}) using the iNext package (^{Hsieh et al. 2016}). To evaluate the TK of D. rufescens, the uses mentioned in the interviews were classified according to the plant use categories proposed by ^{Bernal-Ramírez et al. (2019)} (Table 1). We counted the number of people in each age category who mentioned uses in each category. This number was divided by 30 (total number of people in each age category) and multiplied by one hundred to determine a percentage that indicates the representativeness of traditional uses between the age categories.

Results

All people interviewed visually recognized D. rufescens, despite having different names for it. It is known principally as Begachi yaa'xia (from Zapotec Begachi = moss and yaa'xia = yellow), or pastle amarillo (from pastle a variant word from Náhuatl pachtli = herb that grows and hangs from trees and Spanish amarillo = yellow). Other less commonly used Spanish names include cortinas amarillas (yellow curtains), barba de los árboles (tree beard), and musgo amarillo (yellow moss) (Figure 2).

Over the years, D. rufescens has been managed only locally by residents, meaning no selling or exchanging with other communities. It was not possible to precisely learn the year in which the community began using it. However, people in the oldest age category (69-95 years) indicated that their parents and grandparents were familiar with using this plant. Although there are no written records or photographs, community knowledge has been preserved through oral transmission over generations. Therefore, we estimated that the historical use of D. rufescens in the community of San Juan Luvina dates to at least 100 years.

Harvesting is done manually, and when located high up in trees, people use wooden hooks to reach the moss. Bags are used for storage and transport to the population center. According to the interviews, people previously conducted harvesting near the community, but presently they go further into the forest to obtain it.

For D. rufescens, we recorded around 40 traditional uses classified into seven categories (Figure 3) (Table 2). According to the R/E curves, there are no significant differences in the number of uses by age category. For category 1 (15-41 years) and 3 (69-95 years), the asymptotic tendencies in the curves suggest we recorded almost all the uses. However, more sampling is needed for category 2 (42-68 years) to record unfrequent uses of D. rufescens (Figure 4).

Figure 3 Proportion of traditional uses recognized by inhabitants of San Juan Luvina by age category. 

Figure 4 Number of traditional uses curves by age category with intrapolation/extrapolation. Each curve has confidence intervals of 95 %. Confidence intervals overlapping indicate no significant differences in the number of uses observed and estimated between age categories. 

The uses recorded for D. rufescens are:

1) Ceremonial: This is the category most recognized in San Juan Luvina, where D. rufescens is used mainly as decoration in religious events. These events include weddings, Christmas (December), Easter (between March and April), Virgin of Guadalupe (December 12^th), or Day of the Dead (November 2^th). The local church's interior is decorated for these occasions. In the San Juan Bautista celebration (June 24), which is the most important in the community, arches made of stems of Arundo donax L. (Poaceae) are entirely covered by the moss and decorated with floral arrangements of Dasylirion lucidum Rose (Asparagaceae). These structures measure approximately 3 m high by 2 m wide and are placed at the local church main entrance (Figure 5A,B).

Figure 5 Some traditional uses of D. rufescens in San Juan Luvina. A. Arches made with stems of A. donax, covered with D. rufescens, and decorated with floral arrangements of D. lucidum during the San Juan Bautista celebration. B. Floral arrangements of D. lucidum with D. rufescens in the background. C, D. Elaboration of poultry nest and toys by women using D. rufescens from San Juan Luvina community. 

2) Construction: This category includes uses no longer practiced as material in the construction of household roofs and tombs. For the roofs, a dense layer of branches was padded with D. rufescens. Later, this process evolved to sandwiching a layer of the moss between two layers of "tejamanil" (long thin sheets of wood of Pinus L.) so that rainwater did not seep into the house. For tombs, portions of D. rufescens were placed next to the deceased person, along with offerings consisting of food and flowers. Subsequently, everything was covered with smooth stones. The use of the moss and rocks was to prevent odors from being released by decomposition. This knowledge is maintained mainly by people in the third age category and was not recorded in youth.

3) Craft: The plant is used to elaborate beds for dogs, poultry nests, school models, toys (stuffing for dolls and balls), costume items (wigs and mustaches) in local carnivals, and flower arrangements with pine branches (Pinus sp.) (Figure 5C, D). In the past, the moss was an important material to make "petates," a traditional rug used for a quick rest in the forest. To make these items, people collected thin stems of A. donax from streams that were joined with "ixtle," a fiber obtained from Agave americana L. subsp. americana (Asparagaceae). Finally, they added a layer of D. rufescens to the rug as a coating. Another option was to spread a dense layer of D. rufescens directly on the ground like a carpet to provide comfort while resting and maintaining body heat. Also, because of its soft texture, it has been used as padding material for pillows. Hats made with this moss show that it was also incorporated into garments. The process consisted of molding the moss until it obtained a hat shape, which then served as head protection in the winter season.

4) Environmental: People use D. rufescens as an indicator of humid areas as it is a plant that captures, maintains, and provides water. Also, reducing the moss population has been useful to detect environmental impact in the forest caused by local silvicultural management and wildfires. The environmental use category received the fewest mentions and was only recognized by men of the second age category.

5) Fuel: The plant is employed for forest rangers to create bonfires. It is useful to get fire in local garbage burners.

6) Medicinal: According to people in the third category, before the arrival of modern medicine (the 1960s), the moss provided treatment for the discomfort of women after childbirth. The moss was boiled and cooled a little before a patch was placed on the woman's abdomen. The therapy was repeated until the patient felt better. Another treatment gave pain relief to the body and bones. In this case, the moss was used with other plant parts that included corn ear styles and the central maguey stalk (Agave americana L. (Asparagaceae)). Patients breathed the smoke created by burning these three ingredients. Nowadays, D. rufescens is served as a drink to whet the appetite, for kidney and lung health, as well as for treatment of diabetes-related ailments, blindness, or only for quenching thirst. The infusion is consumed either warm or cold at any time of the day.

7) Ornamental: The moss is found as ornamental on trees in family gardens, but also as an ornament for tables, home entrances, and in living spaces, hung on strings. Furthermore, it serves as a decoration material for festivities such as Mother's Day (May 10), national holidays (September 15 and 16), and the inauguration of government authorities (January 1) in the main square of the community. In the square, it is hung on thin ropes to resemble the natural growth habit in the forest.

For each traditional use category, except for the ceremonial, less than 50 % of the interviewees recognized the traditional use, but the proportions differed by age class (Figure 3). The third age (69-95 years) better recognized the craft, construction, fuel, and ornamental categories as compared to the rest of the age groups. Although individuals of the first and second age categories reported the medicinal uses more than older people, they do not know how to prepare it, nor for which ailment. The second and third ages mentioned the construction category, but there is an evident difference between them. Only the second age did indicate environmental use, but it is represented poorly. The three age categories had similar recognition only for the ornamental category.

After use, D. rufescens is most often cast away. However, it is possible to recycle it. An alternative is to use it as fertilizer on farmland or flowerpots or reuse it as an ornamental plant on trees in home gardens. Still, another option is to dry it, store it, and finally rehydrate when needed. The last possibility, that was referenced by fewer interviewees, is to return it to its natural habitat.

Discussion

With seven categories of traditional uses, D. rufescens is currently the bryophyte with the highest number of uses and TK in Mexico. Records in the country include one species (e.g., Braunia secunda for medicinal purposes) or a species set by use category (e.g., Bryum sp. and Thuidium delicatulum in ceremonial activities) (^{Cornejo-Tenorio & Ibarra-Manríquez 2019}, ^{Delgadillo 2000}). The different uses of D. rufescens may be due to its durability, size, and long flexible stems, which make it a versatile and malleable multi-purpose material (^{Pant & Tiwari 1990}). Its prolonged use (100 years) may be explained by its abundance in the region of Sierra Juárez.

People of the three age groups recognize the use of all traditional categories. The most representative one is ceremonial, and there is a consensus about how the moss is used in Christian rituals and festivities in the community. All other categories represent infrequent uses that younger generations no longer practice. Although the entire population recognizes the use in all categories, their knowledge of how and when to use the moss varied among age categories. For example, younger generations recognized craft uses as beds for dogs, poultry nests, or toys, while the older generation recognized only traditional rugs or hats. In the medicinal category, young generations participate in the D. rufescens harvesting for this use, but only members of the third age group know the type of disease and how it should be used. Because this traditional knowledge is the product of a long-term observation process, if it is not passed on to younger generations, it may be lost (^{Gomez-Baggethun et al. 2013}). The most evident differences are in the construction and environmental categories. In the first case, the younger generation ignores the use of moss for roof or tomb construction. In the environmental category, only seven percent in the second group, in charge of silvicultural management, perceived that forestry activities could reduce D. rufescens populations. At the same time, this support to that knowledge differs between community members is related to their roles (^{Boster 1986}, ^{Garro 1986}). This relation is more evident in the fuel category where there are differences due to the degree of participation of the population in tasks such as burning garbage or protecting the forests; creating fire to burn garbage or to get warm in the forest are activities frequently performed by people in the second and third categories and to a lesser extent by younger people.

Documenting traditional practices with plants provides information on their ecological aspects such as growth habits, size of colonies, or the distribution and abundance in a region (^{Camou-Guerrero et al. 2016}). Names assigned to D. rufescens in Zapotec and Spanish (e.g., yellow moss or yellow curtain) imply an awareness of its hanging growth form in the forest and appearance by color and size the colonies (Figure 2). Also, D. rufescens use in the production of hats and temporary beds or the construction of house roofs can provide information about bryophyte properties as insulating material and water absorption capacity. Additionally, the increasing searching distance for D. rufescens harvest indicates that its populations have declined over time. One explanation is likely due to the sensitivity of D. rufescens to the environmental disturbance driven by forest degradation and climate change (^{León 2008}, ^{Song & Liu 2013}). It is also possible that frequent harvest has damaged the natural recovery of these populations (^{Anastacio Martínez et al. 2017}) in San Juan Luvina since D. rufescens is still present in conserved areas in the Sierra Juárez region.

To explain the use changes of the moss overtime in San Juan Luvina, changes in the community customs should be considered. According to the interviews, making pillows and hats, roof construction, and medicinal therapies with D. rufescens ceased with introducing synthetic construction materials and modern medicine in the community. These findings agree that the modernization process is related to the reduction of knowledge of plants' use (^{Benz et al. 2000}). Thus, the results obtained here help reconstruct the past life of these communities and the natural history of D. rufescens populations in the region (cf. ^{Moller et al. 2004}).

This study shows that D. rufescens is a plant of great cultural importance for a community of the Sierra Juárez since it is part of its traditions and customs. One way to maintain these cultural traditions is their transmission to the younger generations. However, migration and socio-cultural changes as the language loss in the San Juan Luvina population can prevent the generational communication of this knowledge (^{Pardo de Santayana & Gómez Pellón 2002}, ^{Foreman 2006}, ^{Saynes-Vásquez et al. 2013}, ^{Riestenberg & Manzano 2019}). Future studies will be necessary to evaluate the traditional knowledge resilience and its permanence in the community.

Research is required to explore how current harvesting practices of D. rufescens for traditional uses affect its populations' viability and ecosystem services it provides. For example, due to its high biomass, this moss plays an essential role in the water cycle, which can be affected by its harvesting (^{Romero et al. 2005}, ^{Ah-Peng et al. 2017}). Also, it is convenient to evaluate if it is already at risk or threatened by its harvesting according to the IUCN guidelines for bryophytes (^{Bergamini et al. 2019}). To evaluate this, studies on the D. rufescens ecology, including knowing the humidity levels in which it develops, host tree species, and growing populations time, will be needed. With this study, we established a working link with the San Juan Luvina community. This represents an opportunity to develop more studies and promote conservation initiatives that include disseminating the traditional ecological knowledge of some of its members (^{Kimmerer 2002}). This knowledge include the effect of forest activity on D. rufescens populations, its hydrological importance, and alternatives for their reuse and management. Specifically, some community members have observed the reduction of the moss populations, which could affect their ability to retain and release water, a resource highly valued by the indigenous communities in the Sierra Norte of Oaxaca (^{Clark-Tapia et al. 2016}). Likewise, some local people store the moss for reuse, and others reincorporate it into the forest after using it, which represents alternatives to reduce its harvest through rational management (^{Berkes 2008}).

Regarding the last alternatives, residents point out that mosses can re-attach and develop on trees once they returned them to their natural habitat in the rainy season, essential knowledge for ecological restoration of the bryophyte's population (^{Kimmerer 2000}). Finally, an aesthetic appreciation of D. rufescens exists among the people in San Juan Luvina that can contribute to its conservation. This valorization could help develop bryophyte conservation strategies covering more species in the region (^{Rozzi et al. 2020}).

There is no evidence of the use of D. rufescens in other parts of Mexico despite its distribution in other states. This may be due to the lack of studies documenting the use of bryophytes or to a low abundance of the specie that does not allow its use as in the community of San Juan Luvina. In the case of the Sierra Juárez region, its good conservation status and its high levels of humidity (^{Ponce-Reyes et al. 2012}) are elements that can favor the high frequency and abundance of D. rufescens. Thus, preserving the region is crucial to the conservation of D. rufescens and other bryophytes species.

Mexico, in general, and Oaxaca state have high biological and cultural diversity (^{Anderson et al. 2011}, ^{Berger 2019}). Under this premise, future ethnobotanical studies, including bryophytes, may increase the records of species used and their traditional knowledge. Although mosses can be a part of traditional practices and knowledge in various communities across the state and country, they are generally ignored in ethnobotanical studies. Studies on the relationship between people and bryophytes can provide valuable information for biological sciences, anthropology, and history. We expect that this work will serve as a reference for future ethnobotanical research, thus increasing knowledge of plants of great biological importance. Finally, this study provides a list of use categories with specific information on the utilization of D. rufescens offers valuable material to conserve part of the historical and biological-cultural heritage of the San Juan Luvina community (^{Boege 2008}).