Old-growth tropical forests harbor an immense diversity of tree species but are rapidly being cleared, while secondary forests that regrow on abandoned agricultural lands increase in extent. We assess how tree species richness and composition recover during secondary succession across gradients in environmental conditions and anthropogenic disturbance in an unprecedented multisite analysis for the Neotropics. Secondary forests recover remarkably fast in species richness but slowly in species composition. Secondary forests take a median time of five decades to recover the species richness of old-growth forest (80% recovery after 20 years) based on rarefaction analysis. Full recovery of species composition takes centuries (only 34% recovery after 20 years). A dual strategy that maintains both old-growth forests and species-rich secondary forests is therefore crucial for biodiversity conservation in human-modified tropical landscapes.

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.

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 Ángel 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.

Background: La Chinantla, a topographically and geomorphologically complex region, and probably the most humid in the country, hosts a diverse but largely unknown biota, particularly at higher elevations. Questions: How many plant species are present in La Chinantla? How are these species distributed along the elevational gradient encompassed in the region? Studied species: Lycopodiophyta, Pteridophyta, Gimnospermopsida, Magnoliidae, Eudicots, Monocots. Study sites and years of study : We studied the flora of the La Chinantla hyper-humid region, Northern Oaxaca Range, southern Mexico, from 1993 to 2017. Methods: We collected 2,654 specimens in 73 main localities distributed across an elevational range from 250 to 3,020 m (but concentrated above 800 m). Numerous experts in plant taxonomy examined the specimens and provided or confirmed identifications. Results: The checklist of the vascular plants includes 1,021 species, 471 genera and 162 families of vascular plants. The specimens/species ratio (2.6) reflected a satisfactory collecting effort. The most diverse families were Asteraceae, Rubiaceae, and Orchidaceae, whereas the most speciose genera were Peperomia, Miconia and Piper. Most listed species are herbs (47.3 % of the total) and trees (35.2 %), whereas the terrestrial (85.4 %) and epiphytic (15.9 %) growth habits were the most frequent ones (some species presented more than one growth form or growth habit category). Conclusions: Based on the magnitude of the current checklist, we estimate that the actual number of species in this region must be around 1,650. The recorded richness of vascular plant species of La Chinantla confirms the large diversity and uniqueness of its flora and calls for efficient conservations efforts to ensure its maintenance in the future. Key words: cloud forest, floristics, lower montane forest, plant growth form, tropical rain forest, upper montane forest. Lista de la flora vascular de una porción de la región hiperhúmeda de La Chinantla, Sierra Norte de Oaxaca, México ResumenAntecedentes: La Chinantla, una región compleja en su topografía y geomorfología, y probablemente la más húmeda en el país, alberga una biota diversa pero desconocida en gran medida, particularmente en las partes altas del gradiente altitudinal. Preguntas: ¿Cuántas especies de plantas están presentes en La Chinantla? ¿Cómo se distribuyen estas especies a lo largo del gradiente altitudinal? Especies estudiadas: Lycopodiophyta, Pteridophyta, Gimnospermopsida, Magnoliidae, Eudicotiledóneas, Monocotiledóneas. Sitio de estudio y fechas: Estudiamos la flora de la región hiperhúmeda de La Chinantla, Sierra Norte de Oaxaca, sur de México, de 1993 a 2017. Métodos: Recolectamos 2,654 especímenes en 73 localidades principales distribuidas a través de un intervalo altitudinal de 250 a 3,020 m (con énfasis arriba de la cota de 800 m). Numerosos taxónomos expertos examinaron los especí-menes y proporcionaron o confirmaron las determinaciones. Resultados: La lista de plantas vasculares incluye 1,021 especies, 471 g...

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