The Cadereyta Regional Botanic Garden is a nonprofit institution committed to the conservation of flora from its two regions of influence: the semiarid zone of Querétaro and Hidalgo (together comprising the southern end of the Chihuahuan Desert), and the entire state of Querétaro. Part of the state lies in the rain shadow of the eastern Sierra Madre, where it hosts a distinctive and threatened flora: the seasonally dry forest. The plants of this biome have been poorly understood—seen as dry scrub, believed to be too slow-growing to respond robustly to active propagation programs. In this article, we describe the seasonally dry forest in its geographic and ecological context, and discuss our efforts to develop protocols for propagating select species not only to conserve and reforest this region, but to share this distinctive group of plants with the public. With the success of this program in mind, we conclude by examining the state of private and public-sector forest conservation in Mexico today, and roles for public gardens and arboreta in preserving Mexico’s distinctive floristic communities.
A Densely Diverse Landscape
The wide variety of landscapes of the state of Querétaro in Central Mexico lies in the combination of its abiotic components. Being a small territory of 11,699 square kilometers—less than one percent of the national territory—it encompasses three physiographic regions: the Eastern Sierra Madre, the Trans-Mexican Volcanic Belt, and the Central Plateau, each with unique characteristics that influence the weather, soils, vegetation types, and, of course, human activities.
In the northeastern part of the state, the Eastern Sierra Madre contains karst mountains with steep slopes of sedimentary rock, narrow valleys, deep canyons, and considerable variation in altitude. The highest elevations produce an orographic or “rain shadow” effect, which defines the region’s southernmost part as the driest area of the state, contrasted with the temperate and tropical forests of the humid northeast area. Running through the southern region, the Trans-Mexican Volcanic Belt’s hills, mountains, and plains are filled with pumice and lacustrine deposits. This region contains the state capital, Santiago de Querétaro, which is located in a tectonic pit. The Central Plateau includes the Sierra del Zamorano Mountains, small plateaus, and volcanic structures—a variety of physiographic features reminiscent of the complexity of the Mexican landscape as a whole, resulting in an intricate mosaic of vegetation, including almost all of the country’s significant plant groups.
The influence of the encounter between Holarctic and tropical flora is evident in the landscape through the presence of Northern Hemisphere–flora, including Cupressaceae, Pinaceae, Taxaceae, and Taxodiaceae, which are well represented by a wide range of conifers such as Abies, Cupressus, Juniperus, Pinus, Pseudotsuga, Taxodium, and Taxus. The distribution of these genera is concentrated in the Eastern Sierra Madre in the north-northeast and in the Sierra del Doctor, a singular calcareous massif attached to the range, though with different origins and features. Some of these conifers can still be found in small patches of single-species forests, such as Abies, Cupressus, and Juniperus. Other species grow in forests of Pinus or Quercus, and still others appear in the cloud forests of the northeastern corner of Querétaro.
The presence of the Fagaceae is important, as it links with the temperate flora of the Northern Hemisphere. Of the 161 Mexican oak species, 37 are distributed throughout Querétaro, and 11 are endemic to the region. They can be found in Quercus-dominated forests or mixed in with other vegetation under various environmental conditions. Oaks are essential elements of the cloud forest, the Abies and Juniperus forests, Pinus or Quercus forests, the tropical deciduous forests of drier landscapes, and are even found in xerophytic or dry scrub communities. It is worth noting that in the central and southern portions of Querétaro, oak forests are typical of soils derived from igneous rocks. These patches are frequently adjacent to grasslands and xerophytic scrub, with several such oak species being shrub-like. However, some relevant species of trees of the Ericaceae (Arctostaphylos), Salicaceae (Salix), and Scrophulariaceae (Buddleja) can also be found here, in combination with Pinus and Quercus.
Superimposed and intertwined with these Northern Hemisphere-influenced flora is a significant variety of arboreal vegetation of tropical origin. The Eastern Sierra Madre hosts a meaningful number of tropical deciduous forests and small but critical patches of cloud forest. The former presents a community of short trees—branched from lower levels with broad crowns—that lose their leaves for half of the year. One may find remarkable species of Apocynaceae (Thevetia), Bombacaceae (Bombax), Burseraceae (Bursera), Fabaceae (Erythrina, Lysiloma, Vachellia), Moraceae (Ficus), Myrtaceae (Psidium), Oleaceae (Fraxinus) and Rutaceae (Casimiroa, Esenbeckia) sharing habitat with other cast members. A distinct type of tropical deciduous biome, the seasonally dry forest, is distributed throughout the southwest and is still present in relicts in the vicinity of the capital city of Querétaro. A detailed description of this forest forms the core of this article.
The central portion of Querétaro lies beyond the mountainous terrain of the Eastern Sierra Madre. Appearing bare and deserted at first glance, the region nevertheless hosts a relevant catalog of tropical plant communities with xerophytic affinity, organized as different types of scrublands. Considered the southern end of the Chihuahuan Desert, the area hosts a remarkable diversity of endemic Cactaceae, including noteworthy examples of columnar, tree-like cacti (Cephalocereus, Lophocereus, Myrtillocactus, Opuntia, Pilosocereus, Stenocereus). Throughout this shrubby community, certain trees determine the look and use of the landscape, including members of the Asparagaceae-Agavoideae (Yucca), Convolvulaceae (Ipomoea), Fabaceae (Bauhinia, Erythrina, Eysenhardtia, Prosopis, Senna, Vachellia), and Rubiaceae (Nernstia).
The primary source of knowledge of local flora is the book Flora del Bajío y Regiones Adyacentes, which has compiled information on 225 families since its initial publication in 1991. The recently updated list of Mexican vascular flora, compiled by Villaseñor in 2016, enumerated 4,411 characteristic species in Querétaro. Over the years, several authors have compiled lists of flora in Querétaro, including the booklet “Árboles nativos del Estado de Querétaro con potencial ornamental and Catálogo básico y formas de propagación,” published by the Cadereyta Regional Botanic Garden in 2017. The latter refers specifically to trees, and includes 388 species in 79 families, most of them with ornamental potential.
The Seasonally Dry Forest of the Bajío Mexicano
The seasonally dry forest may have originated in the Pliocene epoch, some 2.58 million years ago, as fluctuations in climate gave way to an increase of dry conditions of the Pleistocene. Massive geological and climactic events—such as the rising of the Eastern Sierra Madre and the Trans Mexican Volcanic Belt—protected central-western Mexico from cold and chilly northerly winds. A period of climatic instability in the tropics occurred in the late Pleistocene, which may have influenced the distribution of today’s seasonally dry forest, which had flourished along a strip of warm and dry environments. Geologic and climate events were decisive factors in the emergence of the Bajío Mexicano in the Trans-Mexican Volcanic Belt—a group of valleys, plateaus, and minor mountain ranges around 2,000 meters above sea level that are distributed in what today include the states of Querétaro, Guanajuato, Jalisco, Aguascalientes, Zacatecas, and San Luis Potosí. According to some estimates, seasonally dry forests in the Bajío Mexicano covered around 11,000 square kilometers until quite recently—8,000 years ago. Today, this forest type has all but disappeared.
A combination of abiotic features was decisive in establishing these tropical seasonally dry forests that thrive in higher altitudes with cooler temperatures—averaging around 20–22°C—and with a low seasonal rainfall of around 600 millimeters per year. The distribution of these forests at altitudes of 2,000 meters above sea level has led some authors to call them “high seasonally dry forests.” These forests change their appearance drastically depending on the season, looking misleadingly drab and sad during late autumn, winter, and into early spring. This all changes in late spring, when many species of plants bloom and summer’s rainy season covers the plants’ canopies with dense, bright green foliage.
The seasonally dry forest houses considerable biological richness and endemic species because its flora influences sub-humid and xeric affinity communities. Its catalog of trees and shrubs includes at least 124 species from 43 families. The most common families are Fabaceae, Cactaceae, and Asteraceae.
Rise of the City, Fall of the Forest
In the Bajío Mexicano, the seasonally dry forest remnants are small patches of a few square kilometers, isolated and surrounded by agricultural areas and transitional xerophytic scrubs with some trees, shrubs, and columnar-arborescent cacti. Estimates suggest that only five percent of the community belongs to the original vegetation, while the remaining ninety-five percent is under succession. In Querétaro, the development of its capital city, Santiago de Querétaro, was a decisive factor in the transformation of the landscape and the disappearance of the seasonally dry forest.
This urban area, located on the eastern edge of the Bajío Mexicano, originated in volcanic plains, plateaus, and gentle slopes. Its first inhabitants settled in small, scattered populations around 400 BCE. Spanish colonization brought about new and intensive land-use practices. Significant ecological disruption dates from the eighteenth century, linked to resource exploitation that occurred as the city was becoming one of the most prosperous and beautiful towns of New Spain. Intensive agriculture and livestock farming led to the disappearance of natural vegetation at an accelerated rate. With predators and competitors eliminated or reduced, introduced domestic animal species grazed freely. Mining required a large amount of wood and coal. The growth of all these activities eventually led to the establishment of the Camino Real de Tierra Adentro, a vital commercial route from Mexico City to Santa Fe, which had a strong influence on the territory and the landscape.
In the nineteenth century, the city’s growth rate slowed, until 1950, when real estate development transformed the outskirts of the city. By 1960, Santiago de Querétaro was known as an industrial and commercial center; from 1970 to 2000, its population increased fivefold. By 2020, it was still the second fastest-growing city in Mexico, an extension of urban sprawl that has irreversibly affected the few relicts of the seasonally dry forest. Despite its biological relevance, this type of vegetation is severely threatened; by the 1980s, it was labeled a “vestigial community.”
Mexican tree diversity is threatened by an increasing demand for resources, due to the tenfold population growth in the last century. The need for national action is acute. According to recent inventories, vascular plants from Mexico comprise more than 23,000 species, making it the fourth-ranked country globally in terms of plant diversity and the second by number of endemic species (approximately 50 percent). The recent Global Tree Assessment ranks Mexico tenth in the world in terms of tree species diversity, with 3,620 arborescent species, two-thirds of which are threatened (see Arnoldia Spring 2022 for reporting on the Global Tree Assessment). Nearly 60 percent of endemic and near-endemic tree species in Mexico are listed as “threatened” by the International Union for Conservation of Nature.
Steps Towards Conservation
The Cadereyta Regional Botanic Garden is committed to the conservation of flora from its two regions of influence: the semiarid zone of Querétaro and Hidalgo, and the entire state of Querétaro. In 2006, the Mixed Funds (Fondos Mixtos or FOMIX) of the National Council of Science and Technology (CONACYT), which support state and municipal scientific and technological development, published a call for proposals “to determine the forms of propagation of native plant species (by seed, cuttings, propagules, tissue culture) that best result for reforestation programs,” giving highest priority to “arboreal, shrubby, and endemic” species. The botanic garden prepared a proposal to fulfill the request through two chief products: a publication with propagation techniques for native plants, and a stock of plants reproduced with such practices. The objective was not only to foster ex-situ conservation, but also to prepare the way for reforestation.
In the first stage of work, following extensive review of existing records in herbaria and relevant publications, we conducted a field survey to catalog trees and shrubs of the seasonally dry forest. Next, an index for selecting key species was built to prioritize selection, field collection of germplasm, and subsequent trial and development of propagation techniques. The index integrated not only the morphological and ecological characteristics of the species, but also their anthropogenic uses. The resulting list of 45 key plant species, consisting almost entirely of trees along with woody shrubs, tree-like miniature succulents, and some relevant herbaceous species, provided a basis for determining which plants to propagate for the conservation of the seasonally dry forest.
The objective was not only to foster ex-situ conservation, but also to prepare the way for reforestation.
The core task of the second stage was the development of propagation techniques or protocols, along with the installation and equipment of two greenhouses and one shade house at the Wild Plants Propagation Unit (Unidad de Propagación de Plantas Silvestres, UPPS) of the garden. At this stage, a sequence for the propagation of the selected species was designed and proposed through a production line adjusted to an intermediate technology level. Propagation by seed was the preferred mechanism, although other possibilities of asexual reproduction were explored. The original proposal aimed to develop standardized protocols keyed to least 20 species; the final version included 35, including planting methods without pre-germination treatment (12), with pre-germination treatment (16), in vitro tissue culture (4), and by cuttings (3).
The published work offers a detailed guide to each species, including a synthesis of its known and potential uses, the procedure for its introduction to cultivation, its landscape value, and a watercolor illustration. It also offers general procedures for tree cultivation and management to be put into practice at the botanic garden, developed with the distinctive requirements of dry-forest flora in mind. The recommended period for germination runs from March to October or November. Regular watering, phytosanitary supervision, and growth monitoring should be constant throughout the process. Winter lets the plants have a natural dormancy period. When required, pruning is done in the cold season.
In the third stage, 3,000 native plants were potted and given to Querétaro Environmental Trust (Fideicomiso Queretano del Medio Ambiente, or FIQMA)—the organization that had put the original request for research proposals to CONACYT.
Fieldwork allowed us to collect enough information to evaluate the structural organization of the seasonally dry forest. Initially, we organized the plant community of this forest into four groups according to the species’ biological characteristics: first, woody shrubs with single stems, with leaves, with or without thorns; second, woody shrubs with multiple stems and leaves, with or without thorns; third, succulents with spines, with tree-like structures; and fourth, tree species with a well-defined trunk. However, the species in these groups may occur in different organized patterns according to the forest’s age and condition and may play different roles—either as early colonizers, pioneer trees and shrubs, or as water keepers. In light of this, we reorganized the 45 key species of the seasonally dry forest into one of the three groups based on their ecological role.
At the Cadereyta Regional Botanic Garden, the propagation of key species of the seasonally dry forest has been ongoing in subsequent years. Thousands of seedlings have grown into young trees. Thousands of people have learned about the importance, value, and unfortunate rarity of this type of forest while walking along the stretch of “Trees from the Querétaro Valley” (Árboles del Valle de Querétaro). In contrast to other sections of the botanic garden—which generally display specimens collected as mature plants from their natural habitats—this one features young trees grown from seed. This collection is a powerful tool to communicate the importance of cultivating native species. Home gardeners in Mexico often prefer popular quick-growing exotics like Jacaranda and Eucalyptus. But in contrast to common belief, it is possible to plant a patch of seasonally dry forest and watch it grow—and our public collection may induce gardeners to trial these fascinating endemic plants for themselves.
All visits to the garden include guided tours, available 365 days a year. Responses to special requests are offered on demand, and publications on the subject are available for consultation at the botanic garden’s library. With its public dimension, scale of successful propagation, and rigorous protocols, the seasonally dry forest program played a crucial role in the Cadereyta Regional Botanic Garden achieving ArbNet Accreditation (Level II) in 2019.
Mexican Forest Legislation: a Long and Winding Road
The threats to the conservation of Mexican forests are multiple. Historical context and a lack of legislation are determining factors for the loss of forests and the consequential damage to biodiversity. A brief review of Mexican forest history and policy from the previous century will emphasize the need to reinforce tree conservation.
By the early 1900s, no regulations existed for forest management or extraction. Implicit policies of open access to natural resources, paradoxically, led to dispossession and, consequently, to complaints of inequity from small-hold farmers and other rural producers. The most remarkable outcome of the Mexican Revolution was the Constitution of 1917, Article 27 of which grants “the Mexican Nation ownership of the land and water within the territory.”
For decades, the management of forests fell to the ministries of agriculture, where they were neglected. By the late 1930s, 18 percent of forests had been distributed to peasants, who were uninformed about legal limits on the extraction and processing of forest materials. In 1940, a new Forestry Law reaffirmed the value of forests. Lumber concessions were awarded by the federal government, but did not produce hoped-for results, as many small-scale efforts ended in closures and bankruptcies, and inefficient operations had negative impacts on the forest. Nevertheless, community participation may have led to an increased awareness of forest resources and the importance of conservation. Through subsequent logging bans, a conservationist approach began to emerge across the country.
In the 1970s, Mexican agricultural policy included aggressive removals of forest tracts. By the 1980s, 80 percent of Mexican rainforests had disappeared. By then, regional community alliances were emerging, claiming control of forests. In the 1980s, forestry development objectives called for dismantling quasi-governmental forestry companies and promoting community-based forest enterprises in their stead. Recent reforms to the Forestry Law have outlawed forest concessions and recognized the rights of communities (1986), promoted community access to products and markets for technical forest services (1992), and pushed large-scale forest plantations (1997). Moreover, since 1994, the Ministry of Environment and Natural Resources has been responsible for the administration of forests. By that time, Mexico had already signed the Convention on Biological Diversity and engaged internationally on topics including biodiversity, conservation, and sustainable use of forests. Since 2012, the Mexican Strategy for Plant Conservation 2012–2030 (Estrategia Mexicana para la Conservación Vegetal, EMCV), drafted in line with the UN Convention on Biological Diversity’s Global Strategy for Plant Conservation, has been implemented across all member sectors, including the National Forestry Commission.
An Intersectoral Coordination Committee comprised of public and private members monitors compliance with the EMCV, among whose chief objectives is the improvement of the conservation of plant diversity. One of the specific goals in this context is the strengthening of living collections in botanic gardens and arboreta.
Not Enough Arboreta, nor Data About Them
Today in Mexico, there are approximately 90 institutions identified as botanic gardens, most of which have trees in their living collections. However, only twelve specify having an Arboretum or a distinct section devoted to trees. Furthermore, the scope of their specific efforts around tree research, propagation, and ex-situ conservation is not well documented.
Five institutions explicitly identified as arboreta exist in Mexico, unevenly distributed across the nation and not organized as a group. It is very difficult to find information about their history, objectives, and progress. This lack of information and action must be addressed through an integrated scheme. The model described above, developed for the trees of the seasonally dry forest of the Bajío Mexicano, offers general principles for arboriculture in Mexico: identifying the most important species to be preserved and propagated in a living collection, and documenting the most appropriate methods for their propagation. These can be adapted to other threatened forest vegetation in different regions. We aim to help the ex-situ preservation and sustainable use of native tree species for several purposes: in-situ recovery of patches of a natural and very rare vegetational community, urban gardening and reforestation, ecological restoration, and finally, raising awareness of the importance of native trees. It is crucial to identify threatened species to bring into cultivation in botanic gardens and arboreta close to their distribution sites, and to institute training programs to reinforce propagation schemes, conservation, and propagation of under-represented species and families. Taken together, these measures can advance ex-situ living collections in Mexico.
In Mexico, the Preservation of Trees Still Takes Time and Effort
The legal framework and infrastructure for the conservation of plants in Mexico took a long time to develop. Nonetheless, legislation has emerged and strengthened over the years, and today, we have domestic laws and internationally binding regulatory and reference agreements. Despite this, the Mexican government has not formally recognized the living plant collections of botanic gardens and arboreta in official figures for plant conservation.
The support and recognition of the entire system of living collections—botanic gardens and arboreta—is essential for the general conservation of plants and diversity. By 2030, The Mexican Strategy for Plant Conservation aims to keep 100 percent of threatened species in ex-situ living collections and implement cultivation programs for 90 percent. In 2020, however, the numbers suggested that progress is not moving at a pace sufficient for the conservation of threatened species (with only 52 percent represented in ex-situ collections) or propagation (with only 23 percent under active propagations and cultivation programs), and that there is an uneven distribution of threatened families and species. It is not unusual to overrepresent specific taxa and groups in living collections. Now that we have identified relevant species of trees among those underrepresented and under-cultivated, we can take steps to address the deficit.
In addition to sturdy global arguments for environmental conservation and biodiversity to fight against climate change, there are historical reasons to strengthen Mexico’s living collections of plants. Their planning, construction, and maintenance require significant mobilization and displays of resources, labor, and long-term commitment. However, the reinforcement of our botanic garden and arboretum communities is essential to in-situ conservation efforts and goes beyond investing in the present and future. Querétaro’s seasonally dry forest is only one of Mexico’s many endemic floristic communities. As the Cadereyta Regional Botanic Garden has shown, regional efforts can play a crucial role in ex-situ conservation, horticultural knowledge production, and public consciousness. It’s imperative that such regional efforts scale nationwide, and beyond. Every effort to understand, preserve, and cultivate this precious biodiversity is essential.
The authors are affiliated with the Cadereyta Regional Botanic Garden in the State of Querétaro, México. Emiliano Sánchez Martínez is director; María Magdalena Hernández Martínez is curator of the living collection; Yazmin Hailen Ugalde de la Cruz assists with scientific research coordination and curatorial tasks, and Beatriz Maruri Aguilar is scientific research coordinator.
References
Armando Bayona Celis. “El Estado de Querétaro”, In Historia natural de Querétaro, eds. Robert Jones and Valentina Serrano (Universidad Autónoma de Querétaro, 2016), 15–22.
Miguel Carrillo Martínez, “Contribución al estudio geológico del macizo calcáreo El Doctor, Querétaro.” Revista del Instituto de Geología de la Universidad Nacional Autónoma de México 5, no. 1 (1981):25–29.
José Hernández Oria, “Desaparición del bosque seco en el Bajío Mexicano: implicaciones del ensamblaje de especies y grupos funcionales en la dinámica de una vegetación amenazada”. Zonas Áridas 11, no. 1 (2007):13–31.
Mahinda Martínez y Díaz de Salas and Luis Hernández Sandoval, Plantas nativas y naturalizadas en Querétaro (Universidad Autónoma de Querétaro, 2015).
Leticia Merino-Pérez and Gerardo Segura-Warnholtz, “Las políticas forestales y de conservación y sus impactos en las comunidades forestales en México”. In: Los bosques comunitarios de México, eds. David Bray, Leticia Merino and Deborah Barry (Secretaría de Medio Ambiente y Recursos Naturales, 2007), 77–98.
Jerzy Rzedowski and Brenda Bedolla García, “Catálogo de especies de plantas vasculares registradas del Estado de Querétaro”. Flora del Bajío y Regiones Adyacentes Fascículo complementario XXXVII (2021).
Marie-Stéphanie Samain, Salvador Guzmán Díaz, Karina Machuca Machuca, Alejandra Celeste Dolores Fuentes, Ana Gabriela Zacarías Correa, Dagoberto Valentín Martínez, Fabián Augusto Aldaba Núñez, Rosario Redonda Martínez, Sara F. Oldfield and Esteban Martínez Salas, “Meta-analysis of Red List conservation assessments of Mexican endemic and near-endemic tree species shows nearly two-thirds of these are threatened.” Plants People Planet (2022):1–19. https://doi.org/10.1002/ppp3.10308
Emiliano Sánchez Martínez, María Magdalena Hernández Martínez, Beatriz Maruri Aguilar, “Árboles nativos del Estado de Querétaro con potencial ornamental. Catálogo básico y formas de propagación”. Cuadernillos del Jardín Botánico Regional de Cadereyta 5 (2017).
Emiliano Sánchez Martínez, José Hernández Oria, María Magdalena Hernández Martínez, Beatriz Maruri Aguilar, Luis Enrique Torres Galeana, Ruth Chávez Martínez, Técnicas para a propagación de especies nativas clave para la forestación, la reforestación y la restauración en el municipio de Querétaro y su área de influencia. (Consejo de Ciencia y Tecnología del Estado de Querétaro, 2011).
Yazmin Hailen Ugalde de la Cruz, Beatriz Maruri Aguilar, María Magdalena Hernández Martínez, Emiliano Sánchez Martínez, E. 2017. “Diversidad y conservación de las especies del género Quercus (Fagaceae) en Querétaro”. Nthé no. 18, vol. 8 (2017):63–70.
José Luis Villaseñor, “Checklist of the native vascular plants of México”. Revista Mexicana de Biodiversidad no. 87, vol. 3 (2016):559–902
Sergio Zamudio Ruiz, Jerzy Rzedowski, Eleazar Carranza and Graciela Calderón de Rzedowski. La vegetación en el Estado .de Querétaro. (Consejo de Ciencia y Tecnología del Estado de Querétaro, 2012).
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