Introduction

The flora of Mexico is one of the most varied and complex of the planet. Various estimates have been made of floristic richness ranging from 22 000 (^{Rzedowski, 1991}) to 31 000 species (^{Toledo, 1993}). As a result of this complexity the plants have adapted to different environmental conditions, which has led them to develop strategies in their way of life, one of them is epiphytic.

Epiphytes are plants that grow on other plants, roots serve to anchor its host tree or phorophyte (^{Granados et al., 2003}) therefore they do not penetrate the phorophyte’s vascular tissues to extract water and nutrients; they feed on particles floating in the air and from the material deposited in the trunks and branches on which they live (^{Benzing, 2008}). They are located mainly in tropical and humid temperate forests, which places them as a community indicating the ecological quality and the conservation state of the forests. They are very sensitive to weather conditions and often show slow growth, which makes them even more vulnerable than other plants (^{Hietz, 1999}; ^{Barthlott et al., 2001}; ^{Zhu et al., 2004}).

Epiphytes are of paramount importance for the functioning of certain ecosystems, because, when stratifying vertically from trees trunks up to the tops of the canopy they offer a variety of niches and resources such as water and food. The characteristics mentioned contribute to interactions with insects, bats, frogs and snakes (^{Stuntz et al., 2002}). Also they occupy an important place in the cycle of nutrients (^{Toledo, 2014}). These plants are adapted to an environment with adverse conditions such as lack of water, high light intensities and phorophyte or host instability (^{Granados et al., 2003}; ^{Mondragon et al., 2011}).

This group of epiphytic plants includes non-vascular, inferior vascular and angiosperm (^{Toledo, 2014}). ^{Mondragon et al. (2011)} indicate that the families that constitute the main vascular epiphyte component are: Orchidaceae, Piperaceae, Araceae and Bromeliaceae.

Bromeliads are epiphytes herbs, terrestrial or saxicolous, acaulescent or caulescent, with simple leaves, rosetted or acicular, distich is rare, they have a short or absent escaped with terminal or lateral inflorescences, erect or pendulous (^{Diego et al., 2013}). In Mexico the number of species of bromeliads exceed 363 in 18 genera, of which 70% are endemic (^{Mondragon et al., 2011}). The State of Oaxaca has 189, of which 123 species belong to the Tillandsia genus and 11 to Catopsis; therefore, it represents a significant portion of the floristic richness of Mexico (^{Flores and Granados, 2011}).

Bromeliads are considered a non-timber forest resources (RFNM) of economic importance to rural communities (^{Miranda et al ., 2007}). In the community of “El Punto” Santa Catarina Ixtepeji, Oaxaca, located in the Sierra Norte of Oaxaca, which is considered an area of great floristic diversity and a high degree of endemism (^{Mondragon et al., 2006}) villagers gather the bromeliads of the trees in december since immemorial time and since 2008 by means of two Management Units for the Conservation of the Wildlife (UMA) “Catopsis” EX-00011-OAX and “Bromelias” INT-105-OAX) the first allows collecting Tillandsia carlos-hankii and Catopsis berteroniana species, and the second authorizes sale of plants; so they function as one, collecting only bromeliads fallen from trees throughout the year in specific areas of the forest.

Forests have variations in temperature and humidity, which at low levels are the main environmental factors limiting the diversity and abundance of epiphytes such as bromeliads (^{Acebey and Kromer, 2001}; ^{Zotz, 2005}; Rzedowsk, 2006; ^{San Martin et al., 2008}). Another important aspect related to diversity is the identity of phorophyte. This has variations according to physical properties (shape, height, texture, foliage architecture and evergreen or deciduous condition) and its nutrient richness (^{Granados et al., 2003}; ^{Hietz 2005}; ^{Benzing, 2008}; ^{García and Damon, 2013}). Previous studies have established that the greatest diversity of epiphytes is located in altitudinal gradients of 1 500 to 2 000 m (^{Benzing, 2000}; ^{Zotz, 2005}).

In terms of diversity of epiphytic plants, alpha diversity has been used to measure the species richness of a particular community through the Shannon and Wiener index (^{García and Tarín, 2008}; ^{García and Toledo, 2015}). This index is one of the most used to measure or quantify the specific biodiversity (Godínez and López, 2002; Martella, 2012).

The objective of this research was to determine the diversity and abundance of bromeliads in each UMA collection area in El Punto, through the analysis of alpha diversity, to generate an indicator for proper forest management.

Materials and methods

Study area. El Punto is a Municipal Agency that belongs to the Municipality of Santa Catarina Ixtepeji, and to the District of Ixtlán de Juárez (Figure 1). Its geographical coordinates are 96° 35’ 2” north latitude and 17° 13’ 18” west longitude at a height of 2 304 m. Its population is 501 inhabitants, of which 44% are men and 56% are women. 6% of the population speaks an indigenous language, has an average of 7 years of schooling and 2% of them did not go to the school. The economically active population is 52% (INEGI, 2010).

Figure 1 Localization and vicinity of the community of “El Punto”, Santa Catarina Ixtepeji, Oaxaca. (INEGI,2005). 

According to the classification system of Köppen modified by ^{García (2004)} the climatic group to which it belongs is: C (w) temperate subhumid most of the time. The orography is mountainous, with an irregular relief, typical of the mountainous areas of the Sierra Madre of Oaxaca. This feature favors the existence of a large number of vegetal associations, habitats and species. The main economic activities of the community are timber forest production, the use of RFNM, floriculture and ecotourism (^{SmartWood, 2002}).

The field work was carried out in 2015 by: field trips for the identification of zones or harvesting sites. As well as, digital photographs of each zone and altitude data, geographic coordinates, relative humidity, vegetation and forófito types, were taken.

Journeys together with the members of the UMA with the purpose of making the collection and botanical determination of the bromeliads in the agroecological zones. A part of the collected material was classified as recommended by ^{Lot and Chiang (1986)} and copies were placed in the Herbario-Hortorio of the Colegio de Postgraduados: T. oaxacana, T. prodigiosa and T. macdougallii (CHAPA, 2016). Furthermore they donated three bromeliads individuals: T. oaxacana, T. plumosa and T. magnusiana, with key BROM-103, BROM-104, BROM-105 respectively to the Center for Sustainability Incalli Ixcahuicopa (Centli), Tlalmanalco, Estado de Mexico.

Considering the total collection área of 77 096 m2 a directed random sampling was carried out in La Cruz de Yovaneli, La petenera, La Curva de San Miguel and Reynoso which have an area of approximately 17 067.371 m2, 6 456.607 m2, 2 998.715 m2 and 50 573.947 m2 respectively, and a sampling area of 3 308.527 m2, 1 030.125 m2, 641.676 m2 and 6 502.605 m2 with a total sampling area of 11 482 m2. In all cases the sampling area was higher than 10%, as recommended (^{Quiñonez and Mendoza, 2009}; ^{Bautista, 2011}). In each zone three transects of 50*2 m in length were drawn (^{Artigas and Díaz, 2013}) for epiphyte plants. In each one, 10 trees were selected (30 in each agroecological zone). In each tree, bromeliad species were identified and quantified. In order to estimate the number of individuals of the Tillandsia usneoides species, due to its morphology and growth it was estimated by spheres of 15 cm diameter approximately, where each sphere is equivalent to one individual.

The Shannon-Wiener index was made considering the total number of individuals per species contributing to the analysis of alpha diversity, according to the following formula. Shannon-Wiener diversity index: H’= -Σpi ln pi. Where: pi= ni/N; N= Σni; ln= natural logarithm; ni= represents the importance value of class i; and can be assessed through abundance (^{Mostacedo and Fredericksen, 2000}).

Results and discussion

Types of vegetation. Three types of vegetation were identified according to observations in the field and the ^{Rzedowski (2006)} classification in four areas of forest use (Table 1).

Diversity and abundance of bromeliads. In total 9 763 individuals of bromeliads were counted. Table 1 shows the results of the species found in each area of use, highlighting the presence of two genera of epiphytic bromeliads, Catopsis with one species (berteroniana) and Tillansia with 11 species, the latter genre showed the greatest diversity and abundance.

At La Curva de San Miguel were counted from 7 to 123 individuals per tree with a total of 2 163 individuals

corresponding to seven bromeliads species of the Tillandsia and Catopsis genera. In Reynoso were found 17-344 individuals per tree with a total of 6 362 individuals of bromeliads, coinciding with the number of species and genera of Curva de San Miguel.

Curva de San Miguel y Reynoso, both very close geographically areas were those that showed greater diversity latter being the most abundant especially on two species: T. plumosa y T. magnusiana. Figure 2 shows that these two zones share five species, of the genus Tillandsia and one of Catopsis, the berteronian species, which is locally known as “jarrita” which is under special protection (NOM-059-SEMARNAT-2010). It was also observed that they differed only by two species of the same genus, the first zone with T. juncea and the second zone with T. calothyrsus.

Figure 2 Abundance of bromeliads in La Curva de San Miguel and Reynoso. 

Figure 3 shows the abundance of La Petenera, which was of 457 individuals Tillandsia genera, with two species, T. macdougallii and T. prodigiosa, finding from 2 to 44 individuals per tree. In Cruz de Yovaneli, 7 to 60 individuals were counted per tree, finding a total of 781 individuals of bromeliad of the Tillandsia genus with two species T. oaxacana and T. carlos-hankii; it should be noted that this last one called “mechudita” is a threatened species (NOM.059 SEMARNAT-2010). These two areas have the same type of vegetation, but do not share the same species, as they are very distant geographically from one another.

Figure 3 Abundance in La Cruz de Yovaneli and La Petenera. Forofito type 

Three types of phorophytes or host of bromeliads were observed, which were: oak (Quercus sp.), pine (Pinus sp.) and one tree of Bursera sp. The oak was the most frequent forophyte, close to 72%; followed by pine with about 26% (Table 2).

Conclusions

The diversity and abundance found in the agroecological zones evaluated show specificity of species determined by the type of forophyte, by the height above sea level and by the climatic conditions. The T. macdougalli and T. prodigiosa species and are found only in La Petenera agroecological area, T. oaxacana and T. carlos- hankii are only found in Cruz de Yovaneli area; T. juncea is specific for the Curva de San Miguel while T. calothyrsus and Catopsis verteroniana are only found in Reynoso, although the latter two zones share five species of Tillandsia genera (T. bourgaei, T. plumosa, T. fasciculata, T. magnusiana and T. usneoides) although in the area of Reynoso the abundance found (6 362 individuals) is much greater.

The vertical abundance with higher values were Reynoso and Curva de San Miguel with 17-344 and 7-123 individuals per tree for Reynoso and Curva de San Miguel, respectively, while in Curva de Yovanelli and Petenera values of 7-60 and 2-44 individuals per tree were found.

The Shannon indices indicate that the diversity in the agroecological zones of Reynoso and La Curva de San Miguel was average and for the areas of La Cruz de Yovaneli and Petenera is low.

Abundance and diversity data can be used as indicators for differentiated use of bromelias by areas and species, without endangering natural populations and allowing the regeneration of their populations.