Cliff-dwelling plant species are highly specialized and adapted to a vulnerable, fragmented, and are mostly endemic, narrowly-distributed and threatened. As a contribution to the conservation efforts of endemic cliff-dwelling species, this study provides an overview of the effects of habitat loss on the abundance and distribution of Pachyphytum caesium (Crassulaceae) due to human disturbances. To achieve this objective, we first conducted a retrospective analysis from 2003–2013 to assess the effects of land use change on the abundance of P. caesium. Secondly, we estimate the abundance and distribution of P. caesium throughout the study area, as well as analyze the effect of rock-climbing activities on the density and population structure of P. caesium. The results suggest differences in population abundance among sites is due to the adverse effects of habitat loss. P. caesium presents a very restricted distribution with small and fragmented populations. In addition, guava agriculture has a significant impact on the chemical soil properties of the hillsides, causing a significant effect on the occurrence of P. caesium, while sport activities remove both the soil and the plants from the cliffs. According to the results, P. caesium is classified as a plant species with extremely small populations (PSESP), and it is highly vulnerable to habitat disturbance. Its conservation is thus a priority to ensure its permanence.
Las prácticas forestales implican una serie de actividades que pueden generar impactos negativos en la dinámica natural de este ecosistema. El objetivo de este estudio fue evaluar el efecto del manejo forestal en la estructura, composición y diversidad arbórea y arbustiva en Ixtlán de Juárez, Oaxaca. Para ello se establecieron 15 unidades de muestreo distribuidas en tres condiciones de manejo: franjas no aprovechadas (FNA), bordes (B) y franjas aprovechadas (FA) establecidos en bosques con tratamiento de matarrasa. Se describen los cambios en estructura, composicón florística y diversidad de los estratos de árboles y arbustos. Durante el periodo de estudio se identificaron 27 especies vegetales distribuidas en nueve familias. Las especies más frecuentes fueron: Quercus crassifolia Humb & Bonpl., Pinus pseudostrobus Lindl. y Quercus laurina Humb. & Bonpl. Las curvas de acumulación de especies mostraron que las FNA tuvieron un mayor número de especies que las otras dos áreas. La estructura, estimada a partir de los índices de valor de importancia (IVI) y de valor forestal (IVF), estuvo asociada a la presencia de las tres especies previamente mencionadas en las tres condiciones. La categoría fustal fue la dominante en FNA y B; mientras que en FA las categorías dominantes fueron las de latizal y brinzal. Los valores de riqueza fueron bajos en FNA, B, FA, pero con valores altos de equidad. El valor de dominancia fue solamente alto en FA; B y FA fueron los más semejantes entre sí. Se concluye que las prácticas silviculturales promueven la conformación de un bosque coetáneo con dominancia de pinos. Este patrón es menos severo dada la presencia de las FNA, las cuales podrían limitar la pérdida de la diversidad arbórea y arbustiva.
In the genus Quercus, regeneration by seed is reduced or absent in many species. The naturally protected area of the Sierra Fria, in Aguascalientes, Mexico contains forests that are fragmented and have been degraded due to human activities. The oak populations in this region demonstrate a very restricted sexual regeneration, with five of the most abundant species of this genus: Quercuseduardii, Q. grisea, Q. potosina, Q. resinosa and Q. sideroxyla presenting low seedling recruitment. In this study we evaluated seed viability and the effect of seed size on the germination, growth and survival of the trees, with the aim of recommending restoration and conservation program management actions for these oak species. In 2005 and 2006, 5000 acorns of each species were collected and viability, germination and growth experiments were performed in the laboratory and greenhouse. We found high seed viability and significant size effect (P < 0.05) on levels of germination, growth and survival of these five species of oaks. Our results suggest that environmental and ecological factors have implications for the quality of the seeds produced. This work provides a basis for low cost seed and appropriate management strategies for restoration programs.
Salvia ozolotepecensis, S. patriciae and S. sirenis (Lamiaceae) from Oaxaca, Mexico, are described and illustrated as three new species. The first one is characterized by its glandular-capitate pubescence in stems, leaves and inflorescences, mostly persistent floral bracts, entire and 5-veined upper calyx lip, red corolla, epapillate inside, included stamens, and connective ornate with opposed retrorse and antrorse teeth bordering an incision. It is most similar to S. perlonga and S. praestans to which it is compared. The second can be distinguished in having ovate to ovate-deltoid leaf blades, entire, acute and 7-veined upper calyx lips, red corollas, internally ornate near the base with two slender linguiform papillae, upper corolla lip shorter than the lower one, exserted stamens and glabrous style. This new taxon is morphologically similar to the species belonging to Salvia sections Cardinales, Charantia, Incarnatae, Flexuosa, Fulgentes, Iodophyllae and Pedicellata; although, it cannot be unambiguously assigned to one of these. In contrast, S. sirenis clearly belongs to S. sect. Scorodonia; amongst the species therein, the new species can be differentiated by the concolorous leaves, rounded to slightly oblique at base, 6–8-flowered floral nodes, longer floral bracts, pedicels, calyces and corollas, and 5 or 7-veined upper calyx lip. Also, it represents an addition to Mexican Salvia with white corollas. The molecular markers ITS, trnL-trnF and trnH-psbA were sequenced for two of the three new species, and their phylogenetic position is discussed.
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