Marco Antonio Romero-Romero

Predicting Tropical Dry Forest Successional Attributes from Space: Is the Key Hidden in Image Texture?

Biodiversity conservation and ecosystem-service provision will increasingly depend on the existence of secondary vegetation. Our success in achieving these goals will be determined by our ability to accurately estimate the structure and diversity of such communities at broad geographic scales. We examined whether the texture (the spatial variation of the image elements) of very high-resolution satellite imagery can be used for this purpose. In 14 fallows of different ages and one mature forest stand in a seasonally dry tropical forest landscape, we estimated basal area, canopy cover, stem density, species richness, Shannon index, Simpson index, and canopy height. The first six attributes were also estimated for a subset comprising the tallest plants. We calculated 40 texture variables based on the red and the near infrared bands, and EVI and NDVI, and selected the best-fit linear models describing each vegetation attribute based on them. Basal area (R 2 = 0.93), vegetation height and cover (0.89), species richness (0.87), and stand age (0.85) were the best-described attributes by two-variable models. Cross validation showed that these models had a high predictive power, and most estimated vegetation attributes were highly accurate. The success of this simple method (a single image was used and the models were linear and included very few variables) rests on the principle that image texture reflects the internal heterogeneity of successional vegetation at the proper scale. The vegetation attributes best predicted by texture are relevant in the face of two of the gravest threats to biosphere integrity: climate change and biodiversity loss. By providing reliable basal area and fallow-age estimates, image-texture analysis allows for the assessment of carbon sequestration and diversity loss rates. New and exciting research avenues open by simplifying the analysis of the extent and complexity of successional vegetation through the spatial variation of its spectral information.

Oak Forests of the Hyper-Humid Region of La Chinantla, Northern Oaxaca Range, Mexico

The southern part of Mexico lies within the tropical region of North America. This geographical consideration, however, contrasts with the fact that much of its existing or potential vegetation has a temperate character (Rzedowski 1978). This is due to the presence of large mountain ranges or sierras, which largely characterize the Mexican landscape (de Czerna 1989). The geo-climatic history of these mountains appears to be responsible for the extreme diversification of Quercus and Pinus, two typical holarctic genera (Perry 1991; Nixon 1993; Valencia-A and Nixon 2004; Chap. 1). Only in Central Mexico, there are 45 oak species, suggesting that this is one of the major diversification centres of this genus (Valencia-A 2004) and of other plant groups. Despite this large biodiversity and the fascination it causes among ecologists and evolutionary biologists, highland forests of Mexico are disappearing very rapidly. For one, areas originally covered by oak forests have been preferred for agricultural development owing to their benign climate and good soils (Challenger 1998, and see Chap. 8). In contrast to this trend, La Chinantla, located in the northern part of Oaxaca State, is one of the few regions in Mexico where large, undisturbed tracts of oak forests still remain. In this chapter, we synthesize the existing literature for the oak forests of La Chinantla.We combine floristic information with quantitative descriptions derived from vegetation sampling at some localities. Descriptions are given not only for oak-dominated forests, but also for some other communities, mostly various kinds of cloud forests, where oaks form part of the forest structure.

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.