Horacio Paz

Antecedentes: El bosque tropical caducifolio alberga una elevada diversidad de especies con características anatómicas en su madera sujetas a la marcada diferencia de precipitación a lo largo del año. Pregunta: ¿Los caracteres anatómicos de la madera puede revelar estrategias de las especies, asociadas a mecanismos de evasión o tolerancia a la sequía en un bosque tropical caducifolio? Especies de estudio: Ochenta y tres especies de Eudicotiledóneas leñosas (árboles y arbustos) del bosque tropical caducifolio en Tonatico, Estado de México; durante 2019-2023. Métodos: Las muestras se procesaron con las técnicas histológicas convencionales; se evaluaron nueve caracteres anatómicos y la densidad de la madera y realizaron análisis de correlación y de componentes principales. Resultados: El análisis de componentes principales explicó 65 % de la variación en los tres primeros componentes. Se reconocen dos posiciones extremas; en una de ellas se ubican principalmente especies que son arbustos con vasos numerosos (hasta 209 vasos/mm2), agrupados y angostos (< 48 µm); en contraste con las que se arreglan en el sentido opuesto; entre ambos se distribuyen especies con características intermedias en los rasgos mencionados. Conclusiones: Los resultados sugieren que existen diferentes arreglos en los atributos anatómicos que muestran un continuo, en donde se definen en los extremos opuestos aquellas especies orientadas hacia la tolerancia vs la evasión. La densidad de la madera también se asocia con los grupos de especies, siendo las más pesadas las tolerantes, que corresponden principalmente a los arbustos de la parte alta de la barranca.

In many terrestrial habitats, plants experience temporal heterogeneity in water availability both at the intra and inter annual scales, creating dry-wet pulse scenarios. This variability imposes two concomitant challenges for plants: surviving droughts and efficiently utilizing water when it becomes available, whose responses are closely interconnected. To date, most studies have focused on the response to drought following static designs that do not consider consequences of repeated transitions from one state to the other. In principle, different dry-wet pulse scenarios among years may differentially affect species performance, plant strategies, and promote coexistence through temporal niche separation. We predicted that short frequent droughts would disfavor drought-avoidant species, as rapid leaf loss and production could disrupt their carbon balance, whereas tolerant species, which maintain carbon gain during droughts, should thrive in such conditions. Prolonged droughts might harm tolerant species by causing severe cavitation. We assessed the survival and growth responses of seedlings from 19 tropical dry forest tree species to simulated natural dry-wet pulse scenarios, examining their relationships with the continuum of species’ functional strategies under field conditions, and used greenhouse experiments to accompany the field experiment. As expected, different dry-wet pulse scenarios favored different plant functional strategies. Contrary to predictions, the most tolerant outperformed the most avoiders under all drought scenarios, while rapid water-exploiters thrived under non-drought conditions. The superiority of tolerant over avoider species was reverted in the greenhouse, suggesting that in addition to physiology, the fate of species may depend on extrinsic factors as natural enemies. The interplay between the marked variability of dry-wet pulse scenarios across the years and the diversity of water use strategies may contribute to species coexistence in the tropical dry forests. This research is relevant in predicting changes in dominant tree species under future climate scenarios characterized by increased temporal variation in water availability.

Fine roots are specialized in nutrient and water acquisition and are critical for species performance and ecosystem functioning. Recent evidence has shown a broad root economic space determined by the orthogonal collaboration and conservation gradients related to resource acquisition and resource conservation, respectively. However, whether these gradients exist among tree species growing in degraded ecosystems where root growth is limited by soil conditions is much an open question. We measured six fine root traits (root diameter, specific root length, root dry matter content, root tissue density, branching intensity, and percentage of arbuscular mycorrhizal colonization) in 11 young tree species growing in sympatry for 9 years in degraded pastures in a tropical dry forest (TDF) in Colombia to determine (1) the covariation between fine root traits and (2) the patterns of belowground niche differentiation among 11 species coexisting under the same soil conditions. The covariation between fine root traits resembled the acquisitive-conservative, but not the collaboration gradient for this degraded habitat. The percentage of mycorrhizal colonization, a critical trait associated with the collaboration gradient, was unrelated to any fine root trait. Furthermore, we found a strong belowground differentiation among species, mainly across root diameter and branching intensity. Our results suggest that compacted degraded soils in TDF landscapes may affect the collaborative association with mycorrhizae, mostly allowing species differentiation along the do-it-yourself gradient. This finding suggests a hypothesis that needs to be tested with more species and sites. We discuss the importance of using root traits to aid species selection for restoration purposes.

We characterize the taxonomic and functional diversity of waterbird communities in mangrove forests of 23 coastal lagoons in the southern Mexican Pacific coast, to evaluate the hypothesis of decline of taxonomic and functional richness of waterbird communities in the face of loss of natural habitat cover and increased fragmentation. We quantified patterns of land use cover, considering the heterogeneity of natural and anthropized vegetation cover as a proxy for human-caused fragmentation, and used generalized linear models to explore the relationship between these two covers with the taxonomic richness and functional richness of bird communities. Results show that both aspects of biodiversity positively relate to larger natural habitat areas, while higher fragmentation values have a negative effect on them. Our results suggest that habitat loss and fragmentation of vegetation cover negatively affect the diversity of waterbird communities and can compromise their link to ecosystem functioning processes in coastal lagoons, by decreasing their functional diversity.

Las islas mexicanas representan un reservorio de biodiversidad importante que se encuentra amenazado por el cambio global. En épocas recientes, la isla Socorro, archipiélago Revillagigedo ha experimentado importantes pertubaciones tales como brotes poblacionales de la langosta centroamericana (Schistocerca piceifrons). En este estudio se evaluó la abundancia poblacional de la langosta en la isla Socorro y su efecto sobre la vegetación nativa, además, se exploró la relación de la abundancia anual histórica con variables climáticas. Se realizaron muestreos de S. piceifrons en 25 parajes con diferentes tipos de vegetación, en la temporada de lluvias y secas de 2018. También se evaluó el daño por herbívoros sobre las especies de plantas comunes. No se observaron mangas de S. piceifrons y las langostas fueron más abundantes en lluvias. Los niveles de herbivoría fueron bajos (< 7%). Se detectó que la abundancia de langostas se asocia con años en los cuáles se presentan temperaturas moderadas y alta humedad atmosférica. Debido a que en años anteriores se ha reportado una población numerosa de S. piceifrons, se recomienda monitorear periódicamente su abundancia; sin embargo, dada la situación actual, no se considera que deban llevarse a cabo acciones de control sobre las langostas.

Given the outstanding global progress of research on the hydraulic pathway in plants, and its important role as an indicator of plant mortality risk, we reviewed: (1) the adaptive basis of hydraulic traits and their importance for overall plant function; (2) the number of primary scientific articles on plant hydraulics that have been produced in Mexico in the last 40 years, (3) research related to specific environments in Mexico, and (4) the possible applications of plant hydraulics to natural resource management. Our systematic review included 83 articles. The number of publications per year steadily increased over time, reaching its maximum in 2021. Veracruz and Yucatán are the states where the majority of scientific articles on plant hydraulics have been produced, but for most states less than two publications on this subject appeared in ca. 40 years, and none was found for Oaxaca and Chiapas, the most biodiverse states. In plant hydraulics, the most studied biome in Mexico was the tropical dry forest, followed by crops; trees were the most studied growth-form, followed by herbaceous crops and epiphytes. We point to the need of enhancing research in the interface between plant hydraulic function and remote sensing, as well as developing applications in adaptive forest management and ecological restoration. We hope that this review may ignite a national collaborative effort to quantify critical traits that could inform the hydraulic functioning of Mexican ecosystems, particularly in the underrepresented and highly diverse states of Mexico.

Tropical dry forests are environmentally complex ecosystems with highly heterogeneous water availability, such that distinctive plant communities are found in contrasting habitats in close proximity to each other. This leads to the question of how resource heterogeneity has led to functional heterogeneity among communities. One hypothesis is that the main trade‐offs and the size of the functional space should diverge between communities that differ in their most limiting resource. To test this, we compared aboveground and belowground traits of saplings of 33 dominant species from the dry forest plant communities of two locations that differ in water and also in light availability. In the drier community, the major functional dimension described a trade‐off between drought tolerance and drought avoidance strategies. This dimension was also evident in the wetter community; however, traits related to the efficiency of resource capture were decoupled from the drought tolerance‐drought avoidance trade‐off. Trees from the wetter community tended to develop more efficient fine roots for resource capture. The functional space of the drier and more heterogenous forest was larger than the wetter forest, and plant strategies to deal with drought accounted for a much larger portion of trait variation. Overall, functional differentiation may occur between systems that are close in proximity but differ in the availability of resources such as water and light. These environmental differences cause plant communities to differ in functional properties both aboveground and belowground, likely promoting heterogeneous responses to anthropogenic and natural disturbances at the landscape scale.Abstract in Spanish is available with online material.

The study of above- and below-ground organ plant coordination is crucial for understanding the biophysical constraints and trade-offs involved in species’ performance under different environmental conditions. Environmental stress is expected to increase constraints on species trait combinations, resulting in stronger coordination among the organs involved in the acquisition and processing of the most limiting resource. To test this hypothesis, we compared the coordination of trait combinations in 94 tree seedling species from two tropical forest systems in Mexico: dry and moist. In general, we expected that the water limitation experienced by dry forest species would result in stronger leaf-stem-root coordination than light limitation experienced by moist forest species. Using multiple correlations analyses and tools derived from network theory, we found similar functional trait coordination between forests. However, the most important traits differed between the forest types. While in the dry forest the most central traits were all related to water storage (leaf and stem water content and root thickness), in the moist forest they were related to the capacity to store water in leaves (leaf water content), root efficiency to capture resources (specific root length), and stem toughness (wood density). Our findings indicate that there is a shift in the relative importance of mechanisms to face the most limiting resource in contrasting tropical forests.