Materials and methods

Study area. The Sierra de Chiconquiaco is a montane massif that traverses the coastal plain of the Gulf of Mexico from west to east, at latitude 19º N. The name Chiconquiaco comes from the Náhuatl Chikon-kiaho-ko meaning “in the seven rains”, the name given by the indigenous Totonac people in honor of the god of the storms. It is also the name of a municipality and settlement, located in the central part of the montane massif. From a biogeographic perspective, its vegetation belongs to the Holarctic realm, to the Mesoamerican Montane region and to the Sierras Meridionales floristic province. The coastal area corresponds to the Neotropical realm, to the Caribbean floristic region and to the province of the Gulf of Mexico coast (^{Rzedowski 1978}), which extends in a continuous strip along the coast of the states of Veracruz and Tabasco, as well as some adjacent low portions of Tamaulipas, San Luis Potosí, Hidalgo, Puebla, Oaxaca, Chiapas and Campeche (^{Morrone 2005}).

Delineation and zonation. Delineation of the Sierra de Chiconquiaco is based on morpho-structural features derived from the state physiographic regionalization (^{INEGI 1988}) and from the geomorphological regionalization of Veracruz (^{Geissert 1999}). In general, it was established delimited to the north by the fluvial plain of the Nautla river, to the northeast, east and southeast by the coastal plain of the Gulf of Mexico, to the south by the tectonic depression of Actopan and to the west by the canyon of the Bobos river. The precise boundary was traced manually on a shaded relief model produced from the DEM “Continuo de Elevaciones Mexicano 3.0” of ^{INEGI (2015)}. Hydrological characterization was conducted with the information of the Conjunto de Datos Vectorial Hidrológico of ^{INEGI (1999)}, climatic characterization with the Conjunto de Datos Vectorial Climático of ^{INEGI (2000)} and soil characterization with the Conjunto de Datos Vectorial Edafológico of ^{INEGI (2007)}.

Geomorpho-geological zonation of the Sierra of Chiconquiaco was also conducted from the Continuo de Elevaciones Mexicano 3.0, using ArcGis Desktop 10.2. This continuum of elevations is constantly updated and, unlike other elevation models (SRTM-NASA, ASTER GDEM-METI), its spatial resolution of 15 meters per pixel provides greater detail. The landforms were obtained following ^{Priego et al. (2003)}, based on the vertical dissection of the relief. The values were re-categorized into three landform types: steep mountainous (> 400 m/km²), gentle mountainous (100-400 m/km²) and hills and minor elevations (40-100 m/km²). The map of slopes was derived from the same continuum of elevations and featured four slope classes: low (< 5º), moderate (5-20º), steep to very steep (20-45º) and abrupt (> 45º). The geological information came from the Conjunto de Datos Vectorial Geológico by ^{INEGI (1986)}. To create the partial maps that led to the final results, the following ArcGis tools were used: Create Fishnet, Dissolve, Interpolate to raster, Clip, Intersect, Eliminate, Smooth polygon and Slope. For the definitive geomorpho-geological zonation, the minimum mapping unit criterion was applied, which consists of only representing polygons greater than 500 ha. The cartography and inputs were processed in Projection UTM Zone 14 Q.

Floristic and vegetation studies. The type localities, presence of 19^th century collectors, floristic and vegetation studies, endemics and species registered in the NOM-059 ^{SEMARNAT (2010)} were identified with bibliographic support. Databases of the herbarium XAL and MEXU were chosen to generate a floristic list of species within an altitudinal range of 50 to 3,000 m a.s.l., since they contain information from many collections in the study zone. A raster map of density of points or sites was obtained from the geographic coordinates of the collections, as well as areas that presented the least historical collection effort.

Results and discussion

Geographic characteristics. The polygon of the Sierra of Chiconquiaco presents in its central part a variable length of 70-75 km (east-west) and a width of 50-55 km (north-south) covering an area of 3,632 km². The maximum altitude is close to 3,000 m a.s.l. in the central portion, while the minimum is between 35 and 50 m a.s.l. adjacent to the peripheral coastal plain. The municipalities of Acatlán, Chiconquiaco, Coacoatzintla, Colipa, Juchique de Ferrer, Landero y Coss, Miahuatlán, Misantla, Naolinco, Tatatila, Tenochtitlan, Tepetlán, Tlacolulan, Tonayán and Yecuatla, as well as part of the municipalities of Actopan, Alto Lucero, Altotonga, Atzalan, Nautla, Martínez de la Torre and Vega de Alatorre (Figure 1).

Topography of the central-western sector (11 % of the area) comprises steep slopes of 20 to ≥ 45º with relative heights of over 600 m (Figure 2). This is the result of destruction by Pliocene-Quaternary fluvial erosion of upper Tertiary age andesitic and basaltic lava flows and pyroclastic flows (breccia). As a result, deep ravines were excavated in the northern mountainside, while the Quaternary lava flows on the southern side protected the topography from fluvial dissection (^{Geissert-Kientz 1999}).

Landforms of moderate (5-20°) and steep slopes (20-45°) occupy most of the Sierra of Chiconquiaco (76 % of the area), overwhelming sedimentary rocks (limestone and sandstone) on the northern mountainside and igneous extrusive rocks on the southern side. The rest of the area is covered by hills and minor elevations, with slopes of less than 20º, over different geological substrates, mainly on the northern side (Figure 3).

The first stage of structural deformation began with the tectonic uplift of the Paleozoic geological basement along a dominant east-west direction (^{López-Infanzón 1991}). This basement was subsequently covered by marine formations that produced the Jurassic and Cretaceous limestone and limestone-lutite, forming the geological structure of the Sierra Madre Oriental. Finally, the products of Cenozoic igneous activity covered the previous formations and, in its central part, a basaltic plateau formed between the Miocene and lower Pliocene (^{Ferrari et al. 2005}). Quaternary lava flows, associated with volcanic monogenetic cones, occurred in the vicinity of Naolinco to the southwest, Chiconquiaco in the center and between Plan de las Hayas and Candelaria to the east, in the direction of Palma Sola.

The summits of the central part of this area constitute the divide of the “Nautla river and others” watershed that belongs to Hydrologic Region 27 (Tuxpan-Nautla) towards the north, and the “Río Jamapa and others” watershed of the Hydrologic Region 28 (Papaloapan) towards the south. Within the Sierra de Chiconquiaco, all of the main rivers (Bobos, Misantla, Colipa, Sedeño, Naolinco) and their tributaries are montane in character and flow quickly through ravines of variable depths.

According to Köppen’s system modified by ^{García (1988)}, the following climatic groups are distinguished from north to south: warm humid with abundant summer rains (type Am(f)) in the northern and northeastern sectors, at elevations below 250 m a.s.l.; warm humid with rains throughout the year (type Af(m)) in a northern strip between 250 and 400 m a.s.l.; semi-warm with rains throughout the year (type (A)C(fm)) up to around 1000 m a.s.l. in the southwest sector and up to 1,800 m a.s.l. in the central and central-eastern sectors. Above these altitudes, the climate changes to temperate humid with rains throughout the year (type C(fm)) or temperate humid with summer rains (C(m)). Descending the southeast sector, the climate becomes semi-warm with abundant summer rains (type (A)C(m)) and, finally, warm subhumid with summer rains (type Aw₁(w)) at altitudes below approximately 400 m a.s.l. towards Actopan and Mozomboa.

The representative soil types are: a) on the northern mountainside, Luvisols on landforms below approximately 1,000 m a.s.l., over both sedimentary and igneous materials; Andosols on slopes above 1,000 m a.s.l. (central and western sectors, between Chiconquiaco and Altotonga), exclusively over volcanic ash deposits; Phaeozems on the upper valley fluvial plains and Vertisols on the lower fluvial and coastal plains (from Martínez de la Torre to Vega de Alatorre); b) on the southern mountainside, Andosols extend in the central-western (Altotonga-Las Vigas) and central-southern (Naolinco-Alto Lucero) sectors; Phaeozems in the eastern sector (Plan de las Hayas/Alto Lucero towards the coast) and Vertisols at the bottom of the valleys and on the narrow coastal plains to the south of Emilio Carranza.

Collectors, floristic and vegetation studies. Collections began in 1829 with the German botanists Christian Julius Wilhelm Schiede and Ferdinand Deppe. Franz Leonhard von Schlechtendal and Adelbert von Chamisso subsequently described various species. Schiede and Deppe visited this region in order to search for roots of the Xalapa Jalapa (Ipomoea purga Wender., and wild vanilla (Vanilla spp.). They travelled from Xalapa to El Espinal, Almolonga and Paso del Toro (Malpaís de Naolinco), Naolinco, via Cuesta Grande de Chiconquiaco to Acatlán and to Misantla by Cumbre del Obispo and Papantla. They returned to Xalapa via Hueytamalco, Puebla and Cuesta Grande de Jalacingo and Valle de Perote.

From 1841 to 1843, the Danish botanist Michael Frederick Liebmann conducted intensive collections in Mexico, most of which took place in Veracruz, Puebla and Oaxaca, and produced 8,000 records (^{Rzedowski et al. 2009}). The main interest of this author was ferns and he published a book in 1849 about this group of plants in Mexico. Liebmann left Veracruz in 1841 accompanied by the Russian botanist Wilhelm Friedrich von Karwinski (1780-1855) and both travelled to Papantla, Colipa, Yecuatla, Misantla, Tlapacoyan and Teziutlán. Karwinski separated from Liebmann at El Pital (close to San Rafael) and travelled to Papantla.

In 1905, the German botanist Karl Albert Purpus (1851-1941) established himself in the Hacienda de El Mirador, in the municipality of Totutla (Veracruz state), and travelled from there to different regions of the country to collect plant specimens. On various occasions, he crossed the entire Sierra de Chiconquiaco from Naolinco (^{Sousa 1969}).

^{Gómez-Pompa (1966)} mentioned Ludwig Hahn, George Lewis Fisher and Carl August Ehrenberg, who collected specimens in this Sierra, without recording the exact dates. Between 1950 and 1970, Isabel Kelly and Ladislao Paray also collected specimens. In 1962, the Instituto Nacional de Investigaciones Forestales (INIF), through the Comisión de Estudios Sobre la Ecología de las Dioscóreas, sampled the vegetation of certain areas of the Sierra. Manuel Martínez collected a notable 700 specimens, from 1960 to 1965, and Gómez-Pompa obtained more than 2,000 records, almost always accompanied by Ramón Riba (^{Gómez-Pompa 1966}). From 1970 up to the early 1990s, Francisco Ventura Aburto collected around 1900 specimens for the herbarium of the Escuela Nacional de Ciencias Biológicas. The work of Celso Gutiérrez between 1980 and 1988 is both for the number of specimens collected and the broad range of sites visited, and comprises more than 1,200 records. Roberto Acosta Pérez collected more than 700 specimens in the Sierra Manuel Díaz, located to the southeast of the Sierra de Chiconquiaco, close to the lagoon of La Mancha (^{Acosta 1986}). Miguel Cházaro and his students Luis Robles, Pedro Padilla, Juan Márquez, Apolonia Hernández and Patricia Hernández, collected specimens intermittently from 1981 to the present in locations such as the volcano of Acatlán, Planta del Pié, Barranca de Rincón Grande, Monte de Oro, Cerro de La Magdalena and Las Magdalenitas, Malpaís de Almolonga-Tepetlán, Monte Real, Moxillon, among others, collecting around 500 records. Collectors with more than 100 records in different sites of this Sierra include: Antonio Lot Helgueras, Armando Rincón Gallardo, Carlos Vázquez Yanes, Fructuoso Vázquez Blanco, Mario Vázquez Torres, Gonzalo Castillo Campos, Juan Alba Landa, Javier Chabelas Polito, Jesús Dorantes López, Juan Ismael Calzada, Lorin I. Nevling, Mirna Ambrosio Montoya, Michael Nee, Ma. Teresa Mejía-Saulés and Roberto Ortega Ortiz.

A further result of the different explorations conducted in the Sierra of Chiconquiaco is that 72 species have been recorded with the type locality, 35 of which were early described by D.F. von Schlechtendal and/or F. von Chamisso (Table 1). In recent decades, the studies undertaken became more diverse and featured different approaches. ^{Acosta (1986)} produced an inventory of the flora of the Sierra Manuel Díaz; ^{Ortega-Ortiz (1981)} observed the edge effect on tree densities in fragments of tropical montane cloud forest in Coacoatzintla; ^{Pavón-Hernández (1992)} studied the spatial distribution of Tilia mexicana Schltdl. in Naolinco; ^{Bravo-Navarro (1993)} conducted an ethnobotanical study in the municipality of Naolinco; ^{Álvarez-Aquino (1997)}) carried out a population study of Fagus grandifolia subsp. mexicana (Martínez) A.E. Murray in Acatlán; ^{Zamora-Crescencio & Avendaño-Reyes (1998)} studied the vegetation of the municipality of Yecuatla; ^{Ambrosio-Montoya & Avendaño-Reyes (1999)} recorded the useful plants of the municipality of Misantla; ^{Williams-Linera et al. (1996)} studied the tropical montane cloud forest across an altitudinal gradient in central Veracruz; ^{Godínez-Ibarra & López-Mata (2002)} recorded the northern limit of distribution of the tropical medium sub-evergreen forest in Santa Gertrudis, in the municipality of Vega de Alatorre; ^{Torres-Cantú (2009)} produced an inventory of bromeliads, and ^{Cortés-Flores (2009)} of orchids, in the watersheds of the Nautla, Misantla and Colipa rivers; ^{Casildo (2004)} produced a floristic inventory in the region Cerro de los Muertos, in the municipality of Altotonga; ^{Gómez-Ortega (2010)} contributed to the knowledge of the vegetation and flora of the municipality of Acatlán. Ethnobotanic and management systems of Oecopetalum mexicanum Greenm. & C.H. Thomps., were studied by ^{Lascurain-Rangel et al. (2013)} and ^{López-Acosta et al. (2014)}. Finally, Carbajal-Hernández et al. (2014) recorded 81 species of ferns in the region.

Vegetation types of the Sierra de Chiconquiaco. Based on the studies of ^{Gómez-Pompa (1966)}) and ^{Gutiérrez-Báez (1993)}, and with the aim of standardizing the terminology, the vegetation classification by ^{Miranda & Hernández X. (1963)} was applied. Seven vegetation types were thereby identified (Table 2):

Bosque de pino-encino (Oak-Pine forest).- This type of forest is found on the northern mountainside from 2,100 to 3,000 m a.s.l., comprising communities of Pinus pseudostrobus Lindl., Cupressus lusitanica Mill., Fagus grandifolia subsp. mexicana and Hamamelis virginiana L. (^{Gutiérrez-Báez 1993}). According to observations made by the present authors on the mountains of La Magdalena and Las Magdalenitas (municipalities of Tlacolulan and Tonayan) on the southern mountainside between 2,400 and 2,900 m a.s.l., the Oak-Pine forest is dominated by Pinus patula Schiede & Deppe ex Schltdl., associated with Quercus glabrescens Benth., Q. crassifolia Bonpl. and Q. rugosa Née. This vegetation type is located on steep and moderate slopes over extrusive igneous rock.

Bosque caducifolio (Deciduous forest).- This vegetation type covers the majority of the area (Table 2) and is located between 1,100 and 2,100 m a.s.l., from the middle to the summits of both the northern and southern sides (^{Gutiérrez-Báez 1993}). The dominant arboreal species are: Alchornea latifolia Sw., Alnus acuminata subsp. arguta (Schltdl.) Furlow, Bejaria aestuans Loefl, Capparidastrum quiriguense (Standl.) Cornejo & Iltis, Clethra mexicana DC., Cupressus lusitanica Mill., Diospyros riojae Gómez-Pompa, Drypetes lateriflora (Sw.) Krug & Urb., Fagus grandifolia subsp. mexicana, Guarea glabra Vahl, Hamamelis virginiana, Juglans pyriformis Muhl., Liquidambar styraciflua L., Matudaea trinervia Lundell, Osmanthus americanus (L.) Benth. Hook. f. ex A. Gray, Podocarpus matudae Lundell, Quercus affinis M. Martens & Galeotti, Q. castanea Née, Q. ghiesbreghtii M. Martens & Galeotti, Q. lancifolia Schltdl. & Cham., Q. laurina Bonpl., Q. germana Schltdl. & Cham., Q. polymorpha Schltdl. & Cham., Q. rugosa Née, Q. salicifolia Née, Q. sartorii Liebm., Q. xalapensis Bonpl., Symplocos coccinea Humb. & Bonpl., S. limoncillo Bonpl. and Taxus globosa Schltdl. (^{Gómez-Pompa 1966}, ^{Gutiérrez-Báez 1993}, ^{Zamora-Crescencio & Avendaño-Reyes 1998}). In one of the highest sites (2,250 m a.s.l.), known locally as Planta del Pié (municipality of Chiconquiaco), ^{Williams-Linera et al. (1996)} identified the most notable arboreal species as: Ageratina ligustrina (DC.) R.M. King & H. Rob., Alnus acuminata subsp. arguta, Clethra mexicana, Cleyera theaeoides (Sw.) Chosy, Drimys winteri J.R. Forst. & G. Forst., Ilex discolor var. tolucana (Hemsl.) Edwin ex T.R.Dudley, Osmanthus americanus, Ocotea helicterifolia (Meisn.) Hemsl., Quercus salicifolia, Saurauia leucocarpa Schltdl., Ternstroemia sylvatica Cham. & Schltdl., Viburnum rhombifolium Hemsl., and Weinmannia pinnata L. Other species described as new are also found: Ardisia liebmannii Oerst., Bactris mexicana Mart., Begonia multinervia Liebm., Goeppertia misantlensis (Lascur.) Borchs. & S. Suárez, Centradenia grandifolia (Schltdl.) Endl., Chamaedorea pinnatifrons Oerst., Cuphea calaminthifolia Schltdl., Deppea purpusii Standl., Diospyros riojae, Epidendrum tuxtlense Hágsater, García-Cruz & L. Sánchez, Gunnera mexicana Brandegee, Hydrangea nebulicola Nevling & Gómez Pompa, Magnolia schiedeana Schlecht., Oecopetalum mexicanum, Persea schiedeana Nees, Prunus tetradenia Koehne, Rumex obtusifolius L., Saurauia leucocarpa, Tibouchina purpusii Brandegee, Tilia mexicana, Vaccinium leucanthum Schltdl. and Vernonanthura patens (Kunth) H. Rob. The deciduous forest is randomly distributed on steep and moderate slopes over extrusive igneous rocks, steep slopes with limestone, moderate slopes upon sandstone and limestone.

Selva alta subperennfolia (Tropical high sub-evergreen forest).- This vegetation type is found the lowlands, between 400 and 850 m a.s.l., on low hills with low slopes. It was called “tropical Lauraceae forest” by ^{Gómez-Pompa (1966)} due to the predominance of species of this family. It is possible to find fragments of this vegetation type in the riparian zones of the streams, with trees of between 20 and 30 m in height. The physiognomically important species include: Alchornea latifolia, Beilschmiedia anay (S.F. Blake) Kosterm., B. mexicana (Mez) Kosterm., Brosimum alicastrum, Calatola costaricensis Standl., C. mollis Standl., Cymbopetalum penduliflorum Baill., Dendropanax arboreus (L.) Decne & Planch., Drypetes lateriflora, Ficus microcarpa L.f., Guarea grandifolia DC., Ocotea sp., Oecopetalum mexicanum, Persea schiedeana, Protium copal (Schltdl. & Cham.) Engl., Quercus oleoides Schltdl. & Cham., and Tapirira mexicana Marchand, among others. The tropical high sub-evergreen forest is located on moderate slopes with different geological (extrusive igneous, sandstone and limestone), hills and minor elevations over extrusive igneous rock and on alluvial plains and minor elevation hills over sandstone.

The ecotone of deciduous forest and tropical high sub-evergreen forest, indicated by ^{Gutiérrez-Báez (1993)}, corresponds to a transition between both vegetation types on wet soils between 850 and 1,100 m a.s.l. The typical species of this association are: Calatola mollis, Coccoloba hirtella Lundell, Drypetes laterifolia, Ficus aurea Nutt, Meliosma alba Walp., Nectandra sp., Oecopetalum mexicanum, Platanus mexicana Moric., Protium copal, Pseudolmedia glabrata, Talauma mexicana G. Don, Tapirira mexicana and Ulmus mexicana Planch.

Selva mediana subperennifolia (Tropical sub-evergreen forest).- ^{Godínez-Ibarra & López-Mata (2002)} reported this vegetation type in Santa Gertrudis (municipality of Vega de Alatorre) at an altitude of between 400 and 651 m a.s.l. The canopy is greater than 20 m in height and the following floristic components are representative: Psychotria L. spp., Brosimum alicastrum, Ficus L. spp. Cojoba arborea (L.) Britton & Rose, Leucaena leucocephala (Lam.) de Wit, Bursera simaruba (L.) Sarg., Trophis racemosa (L.) Urb., Manilkara zapota (L.) P. Royen, Aphananthe monoica (Hemsl.) J.-F. Leroy, Dendropanax arboreus, Cedrela odorata L., Pleuranthodendron lindenii (Turcz.) Sleumer and Nectandra ambigens (S.F. Blake) C.K. Allen. As with the tropical high sub-evergreen forest, the medium sub-evergreen forest is located on moderate slopes with extrusive igneous rocks, sandstone and limestone, on hills and minor elevations over extrusive igneous rock and sandstone, and on alluvial plains.

Selva baja caducifolia (Tropical low deciduous forest, secundary vegetation).- ^{Acosta (1986)} described this vegetation type in the Sierra Manuel Díaz (municipality of Actopan) with the following notable floristic components: Tabebuia chrysantha (Jacq.) G. Nicholson, Cochlospermum vitifolium Spreng., Ipomoea wolcottiana Rose, Plumeria rubra L., Bursera simaruba, Ceiba aesculifolia (Kunth) Breitten & Baker f. and Lysiloma divaricatum (Jacq.) Benth.. This vegetation type covers the slopes of the mountain close to the Gulf of Mexico coast, up to 900 m a.s.l. ^{Dorantes & Acosta (1975)} also described the tropical low deciduous forest near Farallón (municipality of Actopan) as presenting the following principal woody components: Annona globiflora Schltdl., Bursera simaruba, Caesalpinia cacalaco Bonpl., Cochlospermum vitifolium, Cordia dentata Poir., Diospyros verae-crucis Standl., Ehretia tinifolia L., Enterolobium cyclocarpum (Jacq.) Griseb., Euphorbia schlechtendalii Boiss., Luehea candida Mart., Lysiloma acapulcense (Kunth) Benth., Tabebuia chrysantha and T. rosea DC. This vegetation type is distributed on steep slopes with extrusive igneous rocks, moderate slopes with extrusive igneous rocks and sandstone and on hills and minor elevations with extrusive igneous rock and sandstone.

Encinares (Oak).- This vegetation type is found between 300 and 400 m a.s.l. and, according to ^{Zamora-Crescencio & Avendaño-Reyes (1998)}, on flat areas on the northern mountainside over clay soils. The arboreal stratum does not exceed 10 m in height and is dominated by Quercus oleoides, accompanied by Piscidia piscipula (L.) Sarg., Dendropanax arboreus, Guazuma ulmifolia Lam., Bursera simaruba, Mimosa albida Humb. & Bonpl. ex Willd., among other species. According to Gómez-Pompa (1977), the oak forests can be divided into the temperate and warm climatic groups. The temperate oak forests, or those of medium height, are found between 1,000 and 1,300 m a.s.l., in duripan soils (locally called “tepetate”) in Mesa de Guadalupe, Alto de Tío Diego, Alto Lucero and Alto del Tizar (^{Cházaro-Basáñez 1992}). This is an arboreal community of 8-15 m in height, of which the notable floristic components are: Quercus peduncularis Née, Q. polymorpha Schltdl. & Cham., Q. sapotifolia Liebm. and Zinowiew integerrima (Turcz.) Turcz. ^{Ortega-Ortiz (1981)} also described an oak forest close to El Espinal (municipality of Naolinco), composed of Quercus polymorpha and Quercus castanea Née. The oak forests of warm regions, or tropical oak forest, are found at an altitude of 10 to 400 m a.s.l., between Colipa and Vega de Alatorre (^{Gómez-Pompa 1966}), as well as in the vicinity of Laguna Verde-Palma Sola (^{Gómez-Pompa 1972}) and on the heights of Los Atlixcos and Topilitos (municipality of Vega de Alatorre) (^{Cházaro-Bazañez 1992}). The landforms on which it is found correspond to moderate slopes with extrusive igneous rocks, hills and minor elevations over sandstone and on alluvial plains.

Riparia (Riparian).- This vegetation type azonal distribution and is found along permanent or temporary streams, brooks and rivers. Its characteristic species are: Platanus mexicana, Salix humboldtiana Willd., Salix exigua Nutt., Ficus insipida Willd. and Syzigium jambos (L.) Alston, and its accompanying species are: Baccharis salicifolia (Ruiz & Pav.) Pers. and Pithecellobium lanceolatum Benth. (^{Zamora-Crescencio & Avendaño-Reyes 1998}). Regarding landforms and geology, riparian vegetation has a ubiquitous distribution and can be found on moderate slopes with extrusive igneous rocks and sandstone, on hills and minor elevations with extrusive igneous rocks, sandstone and conglomerate and on the alluvial plains.

Number of species recorded on the Sierra de Chiconquiaco and rarely explored sites. According to the database of the herbarium XAL and MEXU, there were 3,016 species recorded up to correspond to 35 % of the flora of Veracruz (^{Villaseñor 2016}). The taxa exclusively endemic to the Sierra are: Ceratozamia morettii Vázq. Torres & Vovides, Chusquea enigmatica Ruiz-Sánchez, Mejía-Saulés & L. G. Clark, recently described on the volcano of Acatlán (^{Ruiz-Sánchez et al. 2014}), Eugenia mozomboensis P.E. Sánchez, Monstera florescanoana Croat, T. Krömer & Acebey, Nama linearis D.L. Nash, Piper colipanum C. DC., Salvia chazaroana B.L.Turner, Zamia inermis Vovides, J.D. Rees & Vázq. Torres. Castilleja eggeri and Echeveria cuquita. The latter two species are currently being described.

The floristic information remains incomplete, since the 4,320 (XAL) specimens collected only cover 30 % (1,061 km²) of the total area. The remaining 70 % (2,570 km²) has undergone little or no collection. The zones with limited history of collection are described below, labelled as zones I to VI and shown in Figure 4.

Zone I, Centro del municipio de Alto Lucero (126 km²).- The zone corresponds to tropical low deciduous forest in Mesa de Tigres and El Tabacal, oak forests located in Las Mesitas, Rancho Nuevo, La Cañada and close to Topiltepec (Arroyo de la Peña and Arroyo de los Cedros), Barranca Hernández and Río de la Barranca to the south of Topilito de Zaragoza. The zone is located on moderate slopes with extrusive igneous rock.

Zone II, Municipio de Actopan (140 km²).- The zone is characterized by tropical low deciduous forest located east of San José Pastorías and San José de la Punta, north of Agua Fría and northeast of Llano de Zárate, Cerro de Tres Picos (Sierra Manuel Díaz) and surroundings. In the vicinity of the mountain La Paila (near Monte de Oro) to the extreme southeast of the municipality of Alto Lucero, towards the coast and between the lagoons of Farallón and Laguna Verde, oak forest communities predominate, while in the northern part of the municipality an area of tropical low deciduous forest extends in the localities of Rancho Italia and Cerro de los Metates in the ravines of the Limón river. The zone is of moderate to steep slopes on extrusive igneous rocks, moderate slopes on sandstone, hills and minor elevations upon extrusive igneous rocks associated with alluvial plains, as well as hills and minor elevations built on sandstone.

Zone III, Sierra La Bandera (63 km²).- The zone corresponds to a tropical medium sub-evergreen forest located in the Sierra La Bandera and to the south of Santa Gertrudis, with the possible presence of secondary vegetation of tropical high evergreen forest. It also includes riparian vegetation along the Juchique river. This zone features moderate slopes with extrusive igneous rocks and sandstone, and hills and minor elevations.

Zone IV, Barrancas de Chiconquiaco-Tepetlán (32 km²).- The zone comprises deciduous and oak forests at Loma Alta, Vista Hermosa, the gullies of El Huérfano, La Sombra, Cerro Totola and Xucuyul (municipality of Chiconquiaco), and in the north of the municipality of Tepetlán in Colonia Cuauhtémoc and the locality of Ocote. The sites of the Rincón Grande canyon, Tepetlán and “malpaís” de San Lorenzo Tepetlán have had little collection. In general, this is a zone of steep and moderate slopes with extrusive igneous rocks.

Zone V, Laderas bajas del norte de la Sierra de Chiconquiaco (94 km²).- The zone extends to the north of the municipality of Misantla, south of Nautla, west of Vega de Alatorre and center of Colipa. The secondary vegetation of tropical high and medium sub-evergreen forest is present in Misantla: El Diamante, the mountains Quebrado and Vista Hermosa; in the municipality of Nautla: the mountains Dos Hermanos and Peña Colorada, El Salto and Pilancones; in Vega de Alatorre: Agua Santa and El Tepe; in Colipa, the mountain El Tigre and El Ocotillo. The zone is characterized by moderate slopes on extrusive igneous rocks and sandstone, hills and minor elevations with extrusive igneous rocks, and sandstone, associated with alluvial plains.

Zone VI, Laderas escarpadas (260 km²).- It corresponds to the most extensive zone (nine municipalities), where no collection has occurred in the remnants of deciduous forest vegetation. The zone forms a strip that traverses the Sierra of Chiconquiaco from east to west and also includes fragments of secondary tropical high and medium subevergreen forest in the south of the municipality of Atzalan, near the mountains Huizozoco, Naranjal, Plan de la Luz and Martinica, as well as in the northeast of the municipality of Altotonga, on the peaks of Relicario, Cerro de los Muertos and Loma del Arco. Likewise, pine-oak and pine vegetation is found on the La Cebollana-Tlacolulan altitudinal gradient in the municipality of Tlacolulan. Steep and moderate slopes, extrusive igneous rocks and limestone characterize the zone.

Zones of interest for conservation and research. The Serie V (^{INEGI 2013}) regarding land use and vegetation indicates that the overall surface covered by vegetation does not exceed 25 % of the total area. Remnants of vegetation presenting different degrees of disturbance only remain on the abrupt slopes. Among these nine zones with potential for conservation and future research were recognized and labelled as ZCR 1 to 9 (Figure 5). Five of them are the zones with less botanical ZCR 1 (corresponds to Zone I), ZCR 2 (Zone II), ZCR 3 (Zone III), ZCR 4 (Zone IV), and ZCR 5 (Zone VI). The rest of the zones with interest for conservation a future research are associated with cultivated crops and pastures and correspond to:

ZCR 6. Barrancas de Yecuatla (70 km²), located between the Zones IV and VI with little history of collection, as a strip of deciduous forest to the southwest of Yecuatla, and the localities of Los Brincos towards the south, Chiconquillo to the east and the mountain Pesmón to the west.

ZCR 7. Barranca Diamante (50 km²), located to the southeast of Zone V, with little collection and formed by isolated fragments of tropical high and medium sub-evergreen forest, in the localities of La Planilla to the north, El Naranjal to the south, El Mango towards the east and El Tigre to the west. This zone also includes gallery vegetation along the limits of the municipalities of Vega de Alatorre and Misantla.

ZCR 8. Barranca Chapopote (27 km²), delimited by Rincón Grande to the north, Alto Tío Diego to the south, Las Palomas to the east and Los Cedros to the west, contains sites with deciduous and oak forests that cross the municipality of Tepetlán in a northeast-southeast direction.

ZCR 9. Laderas al este del cerro Acatlán (17 km²), which mostly comprise deciduous forest and diverse fragments of oak forest to the southeast. In other areas of the Sierra of Chiconquiaco, there are numerous disperse fragments of oak forests in the El Tecuán canyon, oak and tropical medium sub-evergreen forests in Los Atlixcos and gallery vegetation to the east of Misantla, along the river of the same name.

According to ^{CONABIO (2004)}, three of the Veracruz state priority zones for conservation cover the Sierra de Chiconquiaco and correspond to approximately 13 % of its total area (Figure 5): “Pico de Orizaba-Cofre de Perote”, comprising a small area (0.03 km²), “Coastal dunes of central Veracruz” with 27 km² and “Tropical oak forests of the Veracruz coastal plain” which presents the largest area (447 km²).

According to the NOM-059-^{SEMARNAT (2010)}, 57 species at risk are recorded in the flora of this Sierra (Appendix 1). They are mainly related to the genus Chamaedorea Willd. and Tillandsia L., with four species each. In that same inventory there are 198 species referenced in ^{CITES (2015)}, there are registered 36 endemic species from Veracruz (^{Castillo-Campos et al. 2005}), that can be found there. Among them, it is worth mentioning the genus Eugenia L. and Calyptranthes Sw. with three species each one (Table 3).

Oncidium stramineum Lindl., Mammillaria eriacantha Link & Otto ex Pfeiff. y M. sartorii J.A. Purpus are endemic to Veracruz (^{Castillo-Campos et al. 2005}) and are registered in ^{CITES (2015)} appendix II. Tillandsia tricolor Schltdl. & Cham. and Hydrangea nebulicola Nevling & Gómez Pompa, are endemic to Veracruz and are also registered in the NOM-059-^{SEMARNAT (2010)}; Zamia inermis Vovides, J.D. Rees & Vázq. Torres, is in appendix II, endemic to Veracruz and in the NOM-059-^{SEMARNAT (2010)}.

Conclusion

Through analysis of geomorphological attributes in a geographic information system, the boundaries of the Sierra of Chiconquiaco were established. Based on a bibliographic review, records of the herbaria, studies and field exploration, seven vegetation types were described, as well as a floristic list of species. Six zones scarcely documented in the herbaria and nine potential areas for conservation and research were detected.

Regarding land use and vegetation of its total area, pastures occupy 50 %, agriculture 23 %, secondary vegetation 19 %, conserved vegetation 7 % and of water and urban zones occupy the remaining 0.7 %. This is an indication that there is still 25 % of land covered by vegetation with different degrees of disturbance in the region. The nine zones of interest for conservation (786 km2) together account for only 22 % of the area. Due to the hitherto scarce exploration, these zones could have the potential for the discovery of new species and endemisms. In this Sierra, different types of arboreal vegetation still exist in an altitudinal range between 800 and 2,500 m a.s.l., where deciduous forest occupies the largest area and extends in a strip towards the municipalities of Hueytamalco, Teziutlán, Zongozotla, Zapotitlán de Méndez, Tlaola and Pahuatlán, among others in the state of Puebla.

Floristic importance of the area. The eight exclusively endemic species have rarely been collected and some are of recent description. It is therefore possible to find them in other sites. Evaluation of endemism and its distribution and abundance will be crucial in order to formulate and undertake measures for its protection through conservation strategies. This contribution is considered a baseline from which future studies can be conducted in the Sierra of Chiconquiaco related to floristic inventories, quality and estimation of the vegetation cover, land use change, strategies of natural resource management and detection of priority areas for conservation and restoration based on native species and those of traditional use. Floristic and vegetation studies at regional level will continue to be of great importance to the knowledge, use and conservation of biodiversity and to measures for the mitigation of the environmental deterioration of this particular site in Veracruz.

Dedication

The authors dedicate this contribution to Dr. Arturo Gómez-Pompa for his important studies in the Sierra de Chiconquiaco visionary of the conservation and use of biodiversity of Mexico, and professional guidance.