Medicinal plants are an essential part of indigenous pharmaceutical systems. We studied the medicinal plants used by the Popoluca of the Sierra Santa Marta (Eastern Mexico). This study is part of a series on the ethnopharmacology of various Macro-Mayan groups. During 16 months of ethnobotanical fieldwork, 614 taxa used medicinally and 4488 individual use-reports were documented. The data are analysed using the concept of the "healers' consensus" in order to identify culturally important medicinal plants. The medicinal uses of the plants were grouped into 13 illness categories. The responses for each species were summarized for each of the categories and were ordered by frequency of mention. The most frequently recorded medicinal plants of the Popoluca are Hamelia patens, used to stop bleeding from wounds, and Byrsonima crassifolia, used against diarrhoea. The high-ranked medicinal species were assessed pharmacognostically using published phytochemical and pharmacological data. Popoluca medicinal uses were fairly consistent with published data on active ingredients for those plants for which such data exist. However, data is still lacking for many other species. Toxicological studies are particularly scarce. This study will be used as a basis for subsequent studies on the pharmacology and phytochemistry of medicinal plant species.

Species for restoration forestry on degraded lands in the tropics are often restricted to a few well-known exotic timber species. This selection frequently leads to failed projects, as local people expect trees to cover a number of uses, not only timber. We studied local knowledge of the usefulness, scarcity and importance for wildlife of native tree species in central Veracruz, Mexico, a region with mainly secondary vegetation and remnants of tropical dry forest. Data were obtained from several workshops, in depth interviews of 40 key informants, field walks with informants, and botanical collections. Analysis included indices for cultural importance, scarcity and wildlife relevance. We documented 76 species in one or more of the categories, from primary, secondary, agroforestry and riparian habitats. Fabaceae was the most important family. All of the species were useful for humans, mainly for rural construction, food, fence posts and fuel. Two-thirds of the species were considered scarce though they were not necessarily rare-some were highly useful, overexploited species with populations insufficient for demand; this category included five of the ten most important species culturally. Also, two-thirds of the tree taxa were considered important for wildlife, especially species of Moraceae. The study shows that the local population is highly aware of the varying functions of trees in the landscape. However, few of the important species are available from regional nurseries. We propose a number of species for restoration forestry, agroforestry systems and enrichment plantings that would be valued by landowners.

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Studies on the resistance of communities to plant invasions at different spatial scales have yielded contradictory results that have been attributed to scale‐dependent factors. Some of these studies argue either for or against Elton's notion of biotic resistance against invasions through diversity. We studied the correlation between alien weeds and native species, dividing the latter group into weedy and non‐weedy species, integrating various factors that influence diversity into an analysis on the scale of the federal states of Mexico. The resulting multiple‐regression models for native and alien weed species are robust (adjusted R2 = 0.87 and R2 = 0.69, respectively) and show a strong partial correlation of the number of weed species (native and alien) with the number of non‐weed native species. These results agree with studies showing a positive correlation between the number of native and alien species on larger scales. Both models also include human population density as an important predictor variable, but this is more important for alien weeds (β = 0.62) than for native weeds (β = 0.32). In the regression model for native weed species richness, the non‐cultivated (fallow) area (β = 0.24) correlated positively with native weed richness. In the model for alien weed species richness, the native weed species richness was an important variable (β = −0.51), showing a negative partial correlation (rpart = −0.4). This result is consistent with Elton's biotic resistance hypothesis, suggesting that biotic resistance is scale independent but that this may be masked by other factors that influence the diversity of both weeds and non‐weeds.