Climate change in trees with small populations: The case of Magnolia zotictla

The current geographic distribution of tree species on the planet is related to events that occurred gradually in the past, such as continental drift. In more recent time periods, climatic changes during the Quaternary glaciation allowed the migration and adaptation of plant populations to new environmental conditions and even the emergence of new species.

In contrast, current climate change and other disturbances caused by human activities, such as land use change and habitat fragmentation, among others, are occurring on extremely short time scales, so there is uncertainty about the responsiveness of plants to these rapid environmental changes.

Magnolia zotictla tree

The case of magnolias

The mountainous regions of the world harbor a high biological diversity and represent one of the last refuges of wildlife; although knowledge of the flora in these regions is becoming increasingly complete, new plant species are recorded and described every year.

In most cases, the newly described species share the common characteristic that their populations are made up of few individuals, which makes them more vulnerable to climate change and other natural and anthropogenic disturbances.

An illustrative example of this is the magnolias; in recent years a large number of species have been described in America and Asia, whose common denominator is that they have a restricted distribution, isolated populations with few individuals, and habitats at risk of disappearing due to human activities. In Mexico, in the last decade more than 10 species of magnolias have been described, all with limited distribution.

In 2015, Magnolia rzedowskiana was described as a new species endemic to the mesophyll mountain forest of the Sierra Madre Oriental, in the states of Hidalgo, Querétaro, San Luis Potosí and Veracruz. In the localities where wild populations of this tree species grow, people use its leaves and flowers in traditional medicine to treat heart problems; and the flowers are recognized and commercialized for their beauty, color, large size and pleasant smell. The common names for this species are heart flower (Yoloxochitl) or May flower, in reference to its flowering season, which occurs at the end of April and primarily in May.

Magnolia zotictla sapling

A particular case: Magnolia zotictla

In recent research with Magnolia rzedowskiana, in which the characteristics of its populations were analyzed in greater detail, one was found to differ clearly from the others in several attributes: leaf and flower morphology, flowering period (beginning at the end of February and continuing into March), wood anatomy and geographic distribution.

These differences, together, made it possible to propose this population as a new species, which was named Magnolia zotictla in honor of the locality where it was found, in the municipality of Acaxochitlán Hidalgo. Subsequently, more populations were found in some neighboring localities, in the municipality of Pahuatlán (Puebla), which is relevant because it increases the probability of conservation of this species.

The description of a species is a complex process that requires experience and the integration of different areas of knowledge. For the proposal to be reliable, it is mainly required to analyze its populations at genetic, morphological and anatomical levels, preferably throughout its distribution area, to describe its phenology (flowering and fruiting) and to analyze different ecological and biogeographical aspects.

In the particular case of Magnolia zotictla, there is morphological, anatomical and ecological evidence to support its description as a new species; and genetic analysis is in process to corroborate its taxonomic identity.

Flowering branches of Magnolia zotictla

Leaves and flowers Magnolia zotictla

Challenges and opportunities

Regardless of the results of the genetic analysis, the populations of Magnolia rzedowskiana and Magnolia zotictla are at severe risk of extinction: the indiscriminate extraction of their flowers, the fall of the trees due to natural causes (hurricanes) or illegal logging, the loss of their habitat, climate change, the lack of management and conservation plans, among other factors, suggest a dead end for both tree species.

However, in a positive sense, interest in this group of plants has recently grown. Civil associations and researchers from different educational and research institutions in the country, mainly from the Universidad Autónoma del Estado de Hidalgo, Universidad de Guadalajara, Instituto de Ecología A.C., are carrying out field and laboratory studies to learn more about the biological characteristics of magnolias. This is generating basic information that will make it possible to propose strategies for their use, management, and conservation in the short term.

The ancestors of today's magnolias are considered to be one of the first groups of flowering plants that appeared on the planet tens of millions of years ago, which is why they have managed to adapt and persist in space and time. However, the conditions in which they develop today are not adequate to guarantee their permanence, so it is essential to create management programs that reduce the pressure on the species.

Ripe fruit with seeds of Magnolia zotictla

The conservation and sustainable management of plant species and living beings in general is essential for the development of society due to the provision of environmental services, direct uses (food, medicine, ornamentation) and the intrinsic value they represent.

The description of Magnolia zotictla was accidental; it arose as part of a research project aimed at understanding the effect of climate change on relict populations of tree species. Based on this finding, a study has been initiated to define the current status of the populations of this species and to develop a protocol for its reproduction and propagation, in which the inhabitants of Zotictla and nearby towns are expected to actively participate in order to promote the adoption of conservation strategies and sustainable management of plant species for the benefit of the community.