Yuriana Martínez-Orea

Evaluación del estado de conservación de la vegetación de los bosques de una cuenca heterogénea del Valle de México

Studies that evaluate conservation status of ecosystems in Mexico often lack the integration of some theoretical bases as well as some methodological tools t...

Seed rain as a source of propagules for natural regeneration in a temperate forest in Mexico City1

Abstract The regeneration of temperate forests is important, especially for those located in urban areas. Sources of propagules, such as seed rain, shape the structure and composition of systems where the availability of diaspores from forest species contribute to both local biodiversity and ecosystem services; these elements are crucial in Mexico City. Over the course of one year, we estimated natural regeneration potential through an analysis of the seed rain deposited in traps that were placed at soil level in plots in three vegetation types: oak, fir and pine forests. We addressed the following questions: Do abundance, density, species composition and diversity of seed rain differ among vegetation types and seasons? How similar is the seed rain to the standing vegetation? Is seed rain a potential source for the natural regeneration of temperate forests? The results showed that the abundance and density of seeds were significantly higher for oak and fir forests due to a higher number of herb, shrub, and tree species in the standing vegetation. The most abundant species in the total seed rain was Ageratina enixa (B.L. Rob.) R.M. King & H. Rob. (12%), but inside individual forest plots, the most abundant were Quercus rugosa Née (16%), Abies religiosa (Kunth) Schltdl. & Cham. (17.5%) and Pinus hartwegii Lindl. (41%). Diversity index values differed among vegetation types but not seasons. Most diaspores in the seed rain corresponded to native species (97%). The similarity between seed rain and the standing vegetation was 40%. In total, 62% of the species are anemochorous, as a result of the high number of Asteraceae species present, and endozoochory is the second most important (17%) dispersal syndrome. A slight asynchrony was observed between the peaks of anemochorous and zoochorous species.

Reproductive phenology of understory species in an Abies religiosa (Pinaceae) forest in the Magdalena River Basin, Mexico City1

Abstract Study of reproductive patterns of understory species is of great importance because they influence the regeneration dynamics of a forest, and the biogeographic origin of these species will also define their responses to environmental conditions. In this study, we answer the following questions: Are there temporal patterns in the reproductive phenology of understory species? If so, what are the variables that influence them? How do the reproductive patterns of the species differ according to their biogeographic origin? To answer these questions, in the Abies religiosa forest in the Magdalena River Basin, Mexico City, we determined the flowering and fruiting patterns of 55 species using multivariate analyses. Spearmans correlations were calculated between the patterns found and the environmental variables, and Augspurgers synchrony indexes were also calculated. Our results showed three flowering and three fruiting patterns. The correlations showed a significant and positive relationship between flowering and precipitation during the rainy season. A significant and negative relationship was found between dry season fruiting pattern and soil moisture. The highest values of flowering and fruiting for both introduced species and native weeds occurred in different months than for characteristic understory species. Our results suggest strong relationships between reproductive patterns and biotic factors, mainly those related to species growth form and biogeographic origin. This is the first phenology study of this area, and it forms a basis for generation of hypotheses related to forest management and conservation.

Dynamics and conservation of the flora of the desert scrub of the Ecological Reserve of the Pedregal de San Angel (D. F., Mexico)

The xerophytic scrub located on the lava field produced by the Xitle volcano has been almost completely destroyed by the urban sprawl of Mexico City. The Pedregal de San Angel Ecological reserve (1.77 km2) offers protection to one of the most important remnant portions. Despite such protection status, this plant community is presently still affected by invasion of exotic species, pollution, illegal extraction of selected species, and recurrent fires. The aim of this study was to update the floristic knowledge of the reserve and to analyze possible changes in the floristic richness and composition that have taken place in the last 50 years. Out of the total 337 species that are included in the present checklist (193 genera, 74 families), 152 species had already been reported by Rzedowski (1954) in a pioneer study that covered the entire lava field (80 km2). Contrastingly, 166 species recorded by him for this xerophytic scrub were not encountered in this study, although 21 of them do occur in another ecological reserve (Lomas del Seminario) located on the same lava field but at a higher elevation. The analysis of the distribution of species of the present checklist by vegetation type showed that only 34 of them occur exclusively in xerophytic scrub, whereas the remaining also occur in other plant communities. The information provided in this study is expected to serve as the basis for future monitoring studies aimed at assessing the dynamics of this flora through time.