Materials and methods

Study area. Situated within the coordinates 14°36’57’’ and 15°28’12” latitude N and 92°03’28’’ and 92°40’58’’ longitude W, the TBR covers an area of 3,462.63 km² distributed between the municipalities of Cacahoatán, Huehuetán, Huixtla, Mazapa de Madero, Mazatán, Motozintla, Porvenir, Tapachula, Tuzantán, and Unión Juárez (Figure 1). The area considered includes the Priority Terrestrial Regions (PTR) of Selva Espinosa Alto Grijalva-Motozintla, El Motozal, and Tacaná-Boquerón, or PTR 134, 135, and 136, respectively (^{Arriaga et al. 2000}). According to García (2001) the climate at lower elevations is warm-humid, with an average annual temperature of 22-26 °C, annual rainfall of 2,500-4,880 mm and the percentage of rain in the dry season less than 5 %, or between 5 and 10.2 %. At higher elevations the climate is semi-warm, temperate-humid, with an average temperature of 18-22 °C, average annual rainfall of 3,730-4,090 mm and the percentage of rain in the dry season less than 5 %. In the driest areas the climate is warm sub-humid with an average annual temperature of 22.2 °C, precipitation of 829 mm, with the percentage of rain in the dry season less than 5 %. The greater part of the rainfall occurs in summer and autumn and increases during periods of cyclone activity; furthermore, cloud cover is frequent throughout the year at higher elevations. According to the National Forest Inventory (INIFAP 2010), vegetation types in the study area are: oak forest, pine-oak forest, tropical mountain cloud forest, oyamel forest, pine forest, alpine grassland, high evergreen tropical forest, and extensive areas of secondary vegetation derived from the ecosystems above mentioned, as well as areas dedicated to agriculture.

Figure 1 A map of Chiapas showing the study area, and municipal divisions (numbers 1-10), and superimposing a Landsat satellite image downloaded from http://eros.usgs.gov/about-us/data-citation. 

Sources of information. We searched the literature for relevant floristic studies, and the data bases of various herbarium collections (AMO, ARIZ, CHAPA, ECOSUR, ENCB, FCME, HEM, MEXU, OAX, TEX, and UAMIZ) to localize orchid specimens collected in the study area.

Fieldwork. Visits to various sites within the study area were carried out between November 2007 and June 2008 and samples of orchid plants with reproductive structures were collected, processed in the Herbarium of ECOSUR, Tapachula and divided up to be deposited in the Herbaria OAX and ECOSUR. Species for which no reproductive individuals were found were cultivated in the orchidarium of the Regional Botanical Garden “El Soconusco” to be identified when flowering occurred, whereupon samples of flowers were preserved in liquid (^{Bedford & James 1995}) or herbarium specimens were prepared. Between 2009 and 2015 further explorations were carried out in the area to obtain additional registers.

Orchid inventory. The inventory is presented in phylogenetic order, with observations. Each taxon includes the correct name, authors of the name, habitat, risk category (when applicable, following ^{SEMARNAT 2010}), and supporting evidence of their presence in the study area. The assignation of specific and intraspecific names follows ^{Soto-Arenas et al. (2007b)}, ^{Salazar (2011)} and ^{Solano-Gómez et al. (2011b)}, and for generic and suprageneric categories ^{Chase et al. (2015)}. Vulnerable species within the orchid flora of the TBR were identified by the fulfilling one or both of two criteria: i) included in a risk category according to the Mexican legislation (^{SEMARNAT 2010}) and ii) with a distribution in Mexico restricted to the study area. Orchid species richness in the study area was compared with other regions in Mexico (Table 1) by means of richness index (I), which is calculated in the following manner: I = R/A × 1000, where R is the orchid species richness and A is the total area of the region in km² (^{Romero 1996}).

Table 1 Values for comparison of the orchid richness among several orchid floras from South-Southeast of Mexico; R = orchid species richness, A = surface in km², I = richness index. 

Geographic Information System. Using the software ArcGIS 10.2 (^{ESRI 2012}) and a map of Chiapas, georeferenced records were mapped to explain the distribution of the orchid species according to the parameters of land use and vegetation type (INIFAP 2010), climate (García 2001), altitudinal intervals, edaphology (^{INIFAP 2001}), contour lines (^{CONABIO 2001}) and Priority Terrestrial Regions for conservation (^{Arriaga et al. 2000}). To analyze the patterns in the distribution of orchid species richness, the percentage of species found within per category for each parameter was calculated.

Results

Orchid Diversity. From a total of 1,235 registers for the TBR and surrounding areas we report 105 genera and 325 species, including two identified at intraspecific level, and two natural hybrids, belonging to three subfamilies, nine tribes and 22 subtribes; the commented list is presented in the Appendix 1. The subtribes with the greatest richness of genera were Oncidiinae (18), Laeliinae (17), Pleurothallidinae (11) and Spiranthinae (13), whereas the subtribes with the greatest species richness were Laeliinae (82), Pleurothallidinae (60), Oncidiinae (51), Maxillariinae (20) and Spiranthinae (20). The genera with the most species were Epidendrum L. (39), Maxillaria Ruiz & Pav. (17), Stelis Sw. (17), Oncidium Sw. (14), Prosthechea Knowles & Westc. (12) and Lepanthes Sw. (11). Analyzing life forms, 256 (79.5 %) of the orchid species registered were epiphytes, 63 (18.63 %) were terrestrial and six (1.87 %) were rupicolous.

Nine of the species reported in this study were new additions to the Mexican flora, with three of those, Stelis annedamoniae Solano, S. hagsateri Solano and S. soconuscana Solano, described as species new to science (^{Solano-Gómez 2011}). Three taxa corresponded to species possibly undescribed in Catasetum Rich. ex Kunth, Cyclopogon C.Presl. and Habenaria Willd. The other species, Acianthera herrerae (Luer) Solano & Soto Arenas, Maxillaria brunnea Linden & Rchb.f., Oncidium poikilostalix (Kraenzl.) M.W.Chase & N.H.Williams (previously known as Sigmatostalix poikilostalix Kraenzl.) and Telipogon helleri (L.O.Williams) N.H.Williams & Dressler, were previously known in other Central American countries, but are registered here for the first time in Mexico (^{Solano-Gómez et al. 2011a}). Furthermore, Plectrophora alata (Rolfe) Garay was rediscovered in the study area having been considered extinct due to no reports of this species after 1935 (^{Soto-Arenas et al. 2007a}, ^{Solano-Gómez et al. 2011a}). Two orchids reported here correspond to natural hybrids: Trichocentrum xquintanarooensis (Cetzal & Balam) J.M.Hsaw and another not described whose putative parents belong to the Epidendrum arbuscula complex.

Comparing the orchid flora of the TBR with that of other regions in southeast Mexico (Table 1), for both R (325) and I (93.86) values, the TBR had the second highest value, behind the region of El Momón-Las Margaritas-Montebello (R = 333, I = 222), which, however, also covers a smaller area. Other regions, covering wider areas and with high orchid species richness, such Chimalapas-Uxpanapa (in the states of Oaxaca and Veracruz) and the Lacandon Forest (in the state of Chiapas and extending into Guatemala), had lower values for I. On the other hand, regions covering a similar area but with lower orchid species richness, such as Sierra Mixe, Juquila-Coatlán and Cañada-Cuicatlán (in the state of Oaxaca) also present lower I values.

Patterns of distribution of orchid diversity. Land use and vegetation.- The orchids in the TBR were registered in almost all the land use and vegetation types present in the region (Figure 2). Four of the land use categories that involved disturbance due to anthropogenic productive activities had the highest percentages of orchid species richness (Figure 7a): permanent seasonal agriculture (45.31 %), annual seasonal or shifting agriculture (28.12 %), secondary vegetation derived from mountain cloud forest (25.93 %) and induced pasture (13.43 %). Considering primary vegetation, mountain cloud forest had the highest percentage orchid species richness (13.12 %), followed by pine-oak forest (7.81 %), alpine meadow (4.68 %), low deciduous forest (0.93 %), and pine forest (0.62 %).

Figure 2 Distribution of the orchid records in the study area on a map of land use and vegetation types (INIFAP 2010). Green dots are epiphytic orchids, red dots are lithophytic orchids, and yellow dots are terrestrial orchids. Codes for use land and vegetation types are as follows: permanent seasonal agriculture (ATP), annual seasonal agriculture (ATA), secondary arboreal vegetation derived from mountain cloud forest (VSA-BMM), induced pasture (PI), mountain cloud forest (BMM), human settlements (AHu), pine-oak forest (BPE), secondary arboreal vegetation derived from pine-oak forest (VSA-BPE), secondary shrub vegetation derived from pine-oak forest (VSAr-BPE), semi-permanent irrigation agriculture (ARSp), alpine meadows (PAM), secondary shrub vegetation derived from pine forest (VSAr-BP), secondary arboreal vegetation derived from pine forest (VSA-BP), cultivated pasture (PC), secondary shrub vegetation derived from mountain cloud forest (VSAr-BMM), urban zone (ZU), secondary arboreal vegetation derived from low deciduous forest (VSA-SBC), semi-permanent seasonal agriculture (ATSp), low deciduous forest (SBC), secondary arboreal derived from tropical rain forest (VSA-SAP), pine forest (BP), secondary arboreal vegetation derived from oak-pine forest (VSA-BEP), semi-permanent and permanent irrigation agriculture (ARSpP). 

Climate.- The orchids in the TBR were registered in all the climate types present in the region (Figure 3). Areas with a semi-warm humid (A)C(m) climate had the highest percentage orchid species richness (60 %), followed by the temperate humid C(m) (40 %), warm humid Am (36 %) and semi-warm subhumid (A)C(w2) (25 %) climates. The least preferred climates were the semi-warm subhumid (A)C(w1), and both categories of warm subhumid Aw1 and Aw2 climates (Figure 7b).

Figure 3 Distribution of the orchid records in the study area on a map of climate types (García 2001). Green dots are epiphytic orchids; red dots are lithophytic orchids, and yellow dots are terrestrial orchids. 

Elevation.- Orchids were registered at most of the elevations present in the TBR, from just above sea level to high up on the Tacaná volcano (Figure 4). However, almost half (48.13 %) of the orchid species were registered at elevations between 1,500 and 1,999 m, followed by 43.28 % registered at elevations of 1,000 to 1,499 m, 39.55 % for 2,000 to 2,499 m, and 27.24 % for 500 to 999 m. Below 500 m and above 2,500 m similar, lower values for percentage orchid species richness were recorded (13.43 % and 13.06 %, respectively), and very few species were found above 3,000 m (5.22 %) (Figure 7c).

Figure 4 Distribution of the orchid records in the study area on a map with 250 m elevation intervals (^{CONABIO, 2001}). Green dots are epiphytic orchids, red dots are lithophytic orchids, and yellow dots are terrestrial orchids. 

Soils.- Considering the soil types found in the TBR, nine propitiated environments that are favorable for orchids (Figure 5). More than half of the orchid species richness (55.31 %) was found in humic acrisol type soil; followed by humic andosols (41.25 %), eutric regosols (27.5 %) and ocric andosols (19.37 %). To the contrary, areas of the TBR with ortic acrisols, eutric fluvisols, eutric cambisols, haplic feozems and chromic cambisols all had less than 6 % orchid species richness (Figure 7d).

Figure 5 Distribution of the orchid records in the study area on a map of edaphology (^{INIFAP, 2001}). Blue dots are epiphytic orchids, red dots are lithophytic orchids, and yellow dots are terrestrial orchids. 

Priority Terrestrial Regions.- Almost two thirds (64.37 %) of the total orchid species richness registered within the study area were found within the polygon that corresponds to the Tacaná-Boquerón Region (TBR). The region Selva Espinosa Alto Grijalva-Motozintla had 20.31 %, whereas El Motozal had only 3.43 %. Areas outside of these three priority regions had 17.81 % of the total species richness (Figure 6).

Figure 6 Distribution of the orchid records in the study area on a map of Priority Terrestrial Regions for Conservation in México (CONABIO, 2004). Green dots are epiphytic orchids, red dots are lithophytic orchids, and yellow dots are terrestrial orchids. 

Figure 7 A) Percentage of orchid species richness in the study area by land use and vegetation types. B) Percentage of orchid species richness in the study area by climate types. C) Percentage of orchid species richness in the study area by elevation intervals. D) Percentage of orchid species richness in the study area by soil types. 

Orchid vulnerability, threats and conservation. The TBR is host to 55 species of orchids considered here as vulnerable, of which 39 are included in a risk category in the Mexican legislation and 21 species have a distribution in the country restricted to the study area (see Appendix 1). Epidendrum alticola Ames & Correll, Oncidium wentworthianum Bateman ex Lindl., and Rhynchostele uroskinneri (Lindl.) Soto Arenas & Salazar are at risk species which are also restricted to the study area. Amongst these at risk orchids, four are considered to be in danger of extinction: Lycaste skinneri (Bateman ex Lindl.) Lindl., Rhynchostele majalis (Rchb.f.) Soto Arenas & Salazar, R. uroskinneri and Rossioglossum grande (Lindl.) Garay & G.C.Kenn. A further 15 species are considered as threatened and 20 are subject to special protection.

The orchid species that are restricted to the study area are Acianthera herrerae, Catasetum sp., Epidendrum alticola, Domingoa gemma (Rchb.f.) van den Berg & Soto Arenas, Funkiella stolonifera (Ames & Correll) Garay, Lepanthes lenticularis Luer & Béhar, L. motozintlensis Salazar & Soto Arenas, L. tecpanica Luer & Béhar, L. tenuiloba R.E.Schult. & G.W.Dillon, Maxillaria brunnea, M. soconuscana Breedlove & D.Mally, Oncidium poikilostalix, O. wentworthianum, Plectrophora alata, Rhynchostele uroskinneri, Stelis annedamoniae, S. hagsateri, S. soconuscana, S. tacanensis Solano & Soto Arenas, S. vespertina Solano & Soto Arenas and Telipogon helleri.

The factors which pose threats to the conservation of orchids in the TBR can be divided into three categories: 1) of anthropogenic origin, such as the transformation of the habitat for shifting and seasonal agriculture, the introduction of cattle, the increase of human settlements, the illegal extraction and commercialization of timber and orchids (and other species of flora and fauna); 2) phenomena related to climate change, such as extended dry periods, periods of extreme frosts or greater frequency of heavy rains (although these factors could be an indirect consequence of human activities, here we prefer to consider them as climatic phenomena); 3) intrinsic factors related to the life cycle of some species, such as preference for a specific phorophyte, pollinator or mycorrhizal fungus, highly specialized reproductive systems, low pollination rates and/or very low recruitment rates.

The only natural protected area in the TBR is the Tacaná Volcano Biosphere Reserve, covering an area of 63.78 km², most of which has an elevation above 1,500 m. Due to the fact that orchid species richness is greatest between 500 and 2,499 m, this reserve does not guarantee the protection of orchids found below 1,500 m, and which is also where the highest deforestation rates are encountered.

Discussion

Orchid species richness. The orchid flora of the TBR and adjacent areas represents 67.7 % and 24 % of the generic and specific diversity, respectively, of the orchids known in Mexico, and almost 66 % and 44 % of the genera and species, respectively, estimated for the state of Chiapas (^{Soto-Arenas et al. 2007b}, ^{CONABIO 2012}). As is commonly found in other biological groups, there is a bias in the taxonomic distribution of this species richness in relatively few genera, and in the case of orchids, in only six of 105 genera (Epidendrum, Maxillaria, Stelis, Oncidium, Prosthechea, and Lepanthes) in which 34 % of the total species are concentrated, meanwhile five of 22 subtribes contain almost two thirds of the genera and almost three quarters of the species. According to Govaerts (2014) these five subtribes are amongst the most species rich within the Orchidaceae: Laeliinae (2,094), Maxillariinae (819), Oncidiinae (1,604), Pleurothallidinae (4,571) and Spiranthinae (518); the first four are lineages exclusive to the Neotropics.

At national level, the values of R and I for the orchid flora of the TBR are the second highest in Mexico, only exceeded by the region El Momón-Las Margaritas-Montebello, also in Chiapas, where ^{Soto-Arenas (2001)} registered a similar number of orchid species (333) in a smaller area (1,500 km²). The orchid flora of the TBR is greater than that of other regions in the southeast of Mexico, which, although covering larger areas, have lower orchid species richness and lower I values, such as the Lacandon Forest with 20,000 km² and 271 species (^{Martínez-Salas et al. 1994}), Chimalapa-Uxpanapa with 5,910 km² and 298 species (^{Hágsater et al. 1998}), the Triqui-Mixteca hills with 3,935 km² and 207 species (^{Pichardo-Ramírez 2011}), and Los Tuxtlas-Catemaco with 3,486.54 km² and 200 species (^{Carmona 1996}, ^{Ibarra-Manríquez & Sinaca-Colín 1997}).

According to the recent classification of the Orchidaceae (^{Chase et al. 2015}), at national level, the Orchidaceae is divided up into four subfamilies, eleven tribes, 22 subtribes, and 155 genera. It is notable that the diversity of orchids in the TBR is represented by three subfamilies (75 %), nine tribes (81.8 %), 22 subtribes (100 %), and 105 genera (67.7 %). In this way, the study zone is not only important for hosting almost 25 % of all Mexican orchids, but also for the high diversity of phylogenetic lineages represented.

Patterns of distribution of the diversity of orchids. Without doubt, the elevation gradient present in the TBR has been fundamental for the development of the variety of vegetation types, climates and soils in the region, and the second most diverse orchid flora in Mexico. Orchids are to be found in practically all the vegetation, climate, soil, and land use types registered in the region. However, species richness is concentrated in the humid areas at elevations of 500 to 2,499 m, where 93 % of the orchid species have been registered; within this altitudinal interval the climate ranges from humid warm to humid temperate, with humic acrisols, humic andosols or eutric regosols soils, which are environmental factors that are also associated with the highest orchid species richness in the region.

It is interesting to note that the greatest species richness of orchids in the TBR occurs in areas disturbed by permanent or shifting agriculture and cattle ranching. To the contrary, areas that still maintain intact primary forest have much lower species richness. This reflects the extensive deforestation that the region has suffered, where the original forests have been reduced to isolated fragments, with reduced functional integrity, immersed in a landscape that, although diverse, is dominated by anthropogenic productive activities, which has resulted in the assignation of a low priority status for conservation in this area (^{Arriaga et al. 2000}, ^{Challenger et al. 2010}).

The ecosystem that registered the greatest orchid species richness in the TBR corresponded to areas now designated for permanent agriculture, wherein coffee and cocoa are the most important crops. Originally arabic coffee (Coffea arabica L.) was planted, and in the so called traditional plantations using trees from the original forests as shade, in which the greater part of the original diversity of flora and fauna continued to coexist with the coffee crop and at the same time the human element satisfied its economic needs. For that reason, historically, traditional coffee plantations have been labeled as conservationist agroecosystems compatible with biological conservation in the tropics (^{García-Franco & Toledo-Aceves 2008}, ^{Espejo-Serna et al. 2005}). However, in the last few years, the scene has changed dramatically and in the coffee growing zone of Soconusco it is now very unusual to find orchids in the plantations. There are now very few traditional coffee plantations, and large areas have been replanted to robusta coffee (Coffea canephora Pierre ex A. Froehner) which is not a good host, or phorophyte, for epiphytes. There are few coffee plantations with a diversity of shade tree species and most now have monospecific shade trees, which are usually heavily pruned, introduced species of Inga Mill. (Fabaceae). As well as causing severe erosion in the zone, the implementation of technological packages, combining the use of herbicides, insecticides, fungicides, the elimination of moss, lichens and epiphytes from the trunks and branches of the coffee bushes, and the heavy pruning of the coffee bushes and shade trees, has reduced to virtually nil the biodiversity that could have continued to coexist with the economically viable activity of coffee growing.

Nonetheless, it should be recognized that, being one of the most important coffee growing regions in Mexico for more than a century, coffee has been an important factor in the history of the region’s orchids, and various species had adapted to grow almost exclusively upon the coffee bushes themselves, particularly miniature species. According to the literature, the first collections in the region carried out by Eizi Matuda and Otto Nagel, in the decade of 1930, were carried out in the large coffee “fincas” that had spread through the region. Many of the orchids collected by those botanists have been observed or collected recently in traditional coffee plantations, confirming that, during more than a century, coffee plantations set up in these areas of maximum orchid species richness have served as a refuge for these plants, despite the extensive disturbance. Many of the orchids reported in this study as novelties for the national or regional flora, were discovered in the few remaining traditional coffee or cocoa plantations, such as Oncidium poikilostalix, Plectrophora alata and Telipogon helleri. Furthermore, in these same environments populations of orchid species considered as threatened have also been registered, including Erycina crista-galli (Rchb.f.) N.H.Williams & M.W.Chase, Guarianthe skinneri (Bateman) Dressler & W.E.Higgins, Oncidium guatemalenoides M.W.Chase & N.H.Williams (formerly named as Sigmatostalix guatemalensis Schltr.), O. wentworthianum, Pleurothallis nelsonii Ames, P. saccatilabia (C.Schweinf.), Restrepia trichoglossa F.Lehm. ex Sander, and Specklinia lateritia (Rchb.f.) Pridgeon & M.W.Chase (^{Avendaño-Vásquez 2010}).

Vulnerable orchids, threats and conservation. Considering the Orchidaceae as an example, this study shows high species richness and heterogeneity of environments in the TBR, characteristics that indicate high conservation value. The region, however suffers from a high degree of fragmentation and low functional integrity of the ecosystems, which, to the contrary suggests a low value for conservation (^{Arriaga et al. 2000}, ^{Challenger et al 2010}). Although mention has been made in the literature that the TBR has few or no endemic or threatened species ^{(Challenger et al. 2010)}, the results presented here suggest the contrary: the region is host to 55 orchids considered as vulnerable, of which 39 are threatened species and represent 21.5 % of the Orchidaceae included in the NOM-059-SEMARNAT-2010 (^{SEMARNAT, 2010}). Taking into account the criteria indicated by ^{Margules & Sarkar (2007)} and ^{Sarkar et al. (2006)}, the TBR certainly represents a priority for conservation for the number of orchid taxa considered vulnerable, and three species in particular stand out (Epidendrum alticola, Oncidium wentworthianum and Rhynchostele uroskinneri) due to being threatened and also because the only populations in Mexico are found in the TBR. Rhynchostele uroskinneri and three other species (Lycaste skinneri, Rhynchostele majalis and Rossioglossum grande) are species considered as in danger of extinction in Mexico, and comprise four of the total of 15 species in that highest risk category in Mexico.

The risk factors that orchids face in the TBR are fundamentally of anthropogenic origin, related to the loss and transformation of habitat for shifting and permanent agriculture, cattle ranching, timber extraction, transformation of the traditional coffee plantations and an increase in human settlements (^{Soto-Arenas et al. 2007a}, ^{Challenger et al. 2010}, ^{Avendaño-Vásquez 2010}). Other factors affect species of high ornamental value, whose populations are subject to illegal extraction and sold in local or national markets. Additionally, in the last few years the possible effects of climate change have been observed in the study area, such as extended dry periods, and increased frequency of heavy rainfall, which can interact with anthropogenic factors (such as subsistence agriculture and poor land management) and combine to cause major effects upon the resident biodiversity in vulnerable environments, which may have high orchid species richness ^{(Soto-Arenas et al. 2007a)}.

The Tacaná Volcano Biosphere Reserve is the only protected area within the TBR, where the greater part of area (63.78 km²) is situated above 1,500 m, wherein the forests are in a better state of conservation, the human population is much smaller and with fewer invasive and destructive activities. However, a significant part of the TBR consists of lower elevations where fragmentation of the ecosystems is greater, there is far greater intensity of agriculture and cattle ranching, human populations are far larger and there is no provision for the conservation of these lower altitude ecosystems. This study demonstrates that 93 % of the orchid species richness in the study area is to be found at elevations of 500 to 2,499 m with 71 % registered at elevations above 1,500 m, and not only on the Tacaná Volcano. It is clear that the designation of the Tacaná Volcano Biosphere Reserve is insufficient to guarantee the protection of the majority of the region’s orchids and the forests and other ecosystems where they grow; the designated area is also insufficient to buffer the severe effects of certain natural phenomena such as hurricanes and fires in the region.

There is a proposal to extend the Tacaná Volcano Biosphere Reserve to connect with the Boquerón peak (^{CONANP 2011}), increasing the area protected to 482.19 km², which is slightly less than the area determined as the PTR Biological Corridor Tacaná-Boquerón (574 km²). If the proposal is accepted, not only will the protected area be increased but also the variety and extension of the environments and species that inhabit them, and the biological connectivity of the ecosystems will be increased, with better prospects for the maintenance of ecological and evolutionary processes and the environmental services that natural ecosystems provide.

The extension of the Tacaná Volcano Biosphere Reserve to connect with the Boquerón peak implies sufficient area to contribute to the conservation of almost two thirds of the orchids of the TBR, and corresponds to the Tacaná-Boquerón Biological Corridor, recognized as a Priority Terrestrial Region in Mexico. For the remaining third of the orchid species, especially those that grow at elevations below 1,000 m, that are not included in the proposed extended protected area and where the forests have been extensively modified by agricultural activity, conservation efforts should include the renovation of traditional and organic coffee plantations, a strategy that if well planned and coordinated could contribute towards the creation of agroecosystems that are compatible with long term conservation and human needs in the lower elevations in the region.

Conclusions

The orchid flora of the Tacaná Boquerón Region is the second richest in Mexico, representing 24 % and 44 % of the species richness for the Orchidaceae, for Mexico and the state of Chiapas, respectively. This orchid flora is phylogenetically rich, including three quarters of the subfamilies, nine of the eleven tribes, all of 22 subtribes, and 105 of the 155 genera of Mexican orchids.

Orchids are present in all of the types of vegetation, climates, soils and anthropogenic environments registered in the TBR, but the major part of this total species richness is to be found at elevations of between 500 and 2,499 m, in environments given over to permanent or shifting agriculture, and it is interesting to note that primary forests have a relatively lower orchid species richness. Considering areas of permanent agriculture, traditional coffee plantations have in the past registered the greatest number of orchids, however, in the last few years these plantations have been totally transformed and are now almost devoid of orchids and other epiphytes.

The TBR is host to 55 vulnerable species of orchids, of which 39 are protected by the Mexican legislation (four are considered to be in danger of extinction), and 20 are species whose distribution en the country is restricted to this region.

The Tacaná Volcano Biosphere Reserve is the only protected area within the TBR, but clearly offers insufficient protection for the region’s orchid flora, as it does not include the areas at lower elevations that are host to the greatest orchid species richness. The proposal to extend the reserve to include the Boquerón peak would increase the protected area, include more low elevation areas and protect almost two thirds of the orchids found in the TBR. In the remaining unprotected areas at lower elevations, the renovation of organic and traditional coffee plantations with Coffea arabica, and a diversity of native tree species which would remain without pruning, could be an extremely important alternative for the conservation of the greater part of the orchid species richness of the TBR.