Plant resources of the Tehuacán-Cuicatlán valley, Mexico

Information on richness of plant resources, and their forms of use and management in the biosphere reserve Tehuacan-Cuicatlan, Mexico is analyzed. This 10 000 km² region hosts nearly 2700 vascular plant species, and it is acknowledged as one of the arid areas with the highest floristic diversity in North America. The seven indigenous ethnic groups that live in this region have cultural roots that date back almost 10 000 years. Based upon ethnobotanical and floristic studies, as well as bibliographical sources, a total of 808 useful plant species were identified, most of them (90%) being native, and 44 species being endemic to the region. A total of 681 species are wild plants, 109 are weeds and ruderal plants, and 86 are domesticated crops. However, it was noted that considerable overlap exists between the species of these 3 categories. For example, while wild and ruderal plants (706 species) are foraged by both humans and domestic animals, 59 species of this group are also managed in situ. On the other hand, 168 wild, ruderal and domesticated species are cultivated. The Tehuacán-Cuicatlan Valley is one of the richest regions of Mexico in plant resources. Local knowledge on use and management of plants is a valuable source of information for designing conservation and social development strategies for the biosphere reserve.     

Biological diversity in the Tehuacán-Cuicatlán Valley, Mexico

A general overview of the biological knowledge of the floristic province of the Tehuacán-Cuicatlán Valley in central-southern Mexico is presented. Floristic and faunistic richness and endemism, as well as uses of the flora are analyzed and discussed for this area, recently declared a biosphere reserve. The analysis shows that, in approximately 10 000 km² the Tehuacán-Cuicatlán Valley contains between 10 and 11.4% of the Mexican flora. In addition, the valley possesses 365 endemic species that represent 13.9% of its flora. With respect to the fauna diversity, the available information is less comprehensive than for plants. Nevertheless, the study shows that the 11 species of amphibians, 48 species of reptiles, and 91 species of birds recorded for the valley surpasses the diversity found in other dry-lands of the world. In relationship to the mammals of the region, the available data are poor for most of the groups except for bats, for which 24 species have been reported. Regarding the use of the flora, the analysis revealed that 815 species are utilized by the people in the valley. A discussion related to future research activities is also included.     

Plant Management in the Tehuacán-Cuicatlán Valley, Mexico1

Plant Management in the Tehuacán-Cuicatlán Valley, Mexico. Plant management types currently practiced in the Tehuacán-Cuicatlán Valley, México, were documented and analyzed based on ethnobotanical studies conducted in 13 villages with six indigenous groups and Mestizo people. The information was organized in a data base, and then detailed and guided to a consensus through six workshops carried out by ethnobotanists working in the area. From a total of 1,608 useful plant species, we identified 610 with at least one management type other than simple gathering. Managed species are mainly used as food, fodder, medicinal, and ornamental, and they belong to 101 plant families. The higher species numbers were recorded in Cactaceae, Asteraceae, Fabaceae, Crassulaceae, and Agavaceae. Nearly 60% of the managed species are native to the region and the rest are introduced from other regions of Mexico and the world. In total, 400 species are ex situ managed out of their natural environments through seed sowing and/or planting their vegetative propagules or entire young plants; 373 species are in situ managed in their natural habitats as follows: all these species are deliberately left standing during vegetation clearance, 76 species are also enhanced intentionally favoring their abundance through modifications of their habitat, or directly by planting their propagules, and 51 receive protection through regulations, particular strategies of extraction, and actions against herbivores, competitors, freezing, radiation, and drought. Most management forms involve artificial selection at different intensity levels. The information allows visualizing co-occurrence of incipient and advanced forms of management at different intensity levels within and among species, which helps to postulate testable hypotheses on factors influencing plant management and domestication in an important area for studying the origins of agriculture.     

Proposal for the Establishment of the Core Zones in the Biosphere Reserve of Tehuacán-Cuicatlán, Mexico

This work proposes the establishment of core zones in the Biosphere Reserve of Tehuacán-Cuicatlán (BRTC), based on plant species richness and endemism. A total of 561 species of the four most important plant families in the region (Asteraceae, Cactaceae, Leguminosae and Poaceae) as well as 174 endemic species of these and other families were used in the analyses. Distribution of these taxa was analyzed using two different iterative complementarity methods. Significant correlations were found between patterns of species richness and endemic plants distribution in the study area. These results were combined with other analysis where two different indices (species richness index and human population index) were used. The results suggest the delimitation of four core zones within the Biosphere Reserve, covering a total area of 105,300 ha. The core zones represent 21.8% of the area, and would protect 72.54% of the species from the selected plant families and 67.8% of endemic species.     

Endemic Mimosa species can serve as mycorrhizal "resource islands" within semiarid communities of the Tehuacán-Cuicatlán Valley,Mexico

This paper explores if Mimosa species (Fabaceae-Mimosoideae) can serve as arbuscular mycorrhizal (AM) and nutrient "resource islands" in six plant communities in the semiarid valley of Tehuacán-Cuicatlán, Mexico. Spatial heterogeneity related to the occurrence of Mimosa species results in temporal differences in AM-fungal spore numbers and soil nutrients. A higher number of AM-fungal spores were found in the soil below the canopies of six endemic Mimosa species than in the soil from non-vegetated areas. For four species, Mimosa adenantheroides, Mimosa calcicola, Mimosa luisana and Mimosa polyantha, the soil below their canopies had more AM-fungal spores than the soil in non-vegetated areas during the wet season than during the dry season. Two species, Mimosa lacerata and Mimosa texana var. filipes, however, had more spores under their canopies during the dry season than during the wet season. Although physical differences are present within and between sites, in general the soil below the canopies of Mimosa species had significantly higher nutrient levels than the soil from non-vegetated areas. Mimosa species thus form "resource islands" that are not only rich in nutrients but also in mycorrhizal propagules. Mimosa species can serve as mycorrhizal "resource islands" by directly affecting AM-fungal spore dynamics and/or by serving as spore-traps. A range of plants associated with Mimosa species may benefit from the higher number of AM propagules. We believe that the use of Mimosa resource islands as an option for biodiversity conservation and for land restoration ought to be considered in the Valley.     

Impact of climate change on the distribution of populations of an endemic Mexican columnar cactus in the Tehuacán-Cuicatlán Valley,Mexico

In this paper, we present a bioclimatic approach to (1) differentiate populations of the endemic Mexican columnar cactus Neobuxbaumia tetetzo within the Tehuacán-Cuicatlán Valley and (2) evaluate, under two possible future scenarios (years 2050 and 2080), the effects of climate change on the total species distribution in this area, as well as on groups of populations defined by their bioclimatic models. Four population groups were identified, and principal component analysis showed that the variables that explained more than 40% of the climatic variation were precipitation of the wettest quarter and temperature seasonality. Bioclimatic models under the different scenarios indicated that when the overall species distribution was analyzed, this area will probably have contracted by 19.5% by the year 2050 and 47.05% by the year 2080, whereas the separate analysis of population groups projected area contractions of 18.4% by the year 2050 and 51.95% by the year 2080. These results demonstrate the importance of exploring new approaches for evaluating and predicting current and future distribution of plant species.     

Plant management and biodiversity conservation in Náhuatl homegardens of the Tehuacán Valley,Mexico

Background

The Tehuacán Valley is one of the areas of Mesoamerica with the oldest history of plant management. Homegardens are among the most ancient management systems that currently provide economic benefits to people and are reservoirs of native biodiversity. Previous studies estimated that 30% of the plant richness of homegardens of the region are native plant species from wild populations. We studied in Náhuatl communities the proportion of native plant species maintained in homegardens, hypothesizing to find a proportion similar to that estimated at regional level, mainly plant resources maintained for edible, medicinal and ornamental purposes.

Methods

We analysed the composition of plant species of homegardens and their similarity with surrounding Cloud Forest (CF), Tropical Rainforest (TRF), Tropical Dry forest (TDF), and Thorn-Scrub Forest (TSF). We determined density, frequency and biomass of plant species composing homegardens and forests through vegetation sampling of a total of 30 homegardens and nine plots of forests, and documented ethnobotanical information on use, management, and economic benefits from plants maintained in homegardens.

Results

A total of 281 plant species was recorded with 12 use categories, 115 ornamental, 92 edible, and 50 medicinal plant species. We recorded 49.8 ± 23.2 (average ± S.D.) woody plant species (shrubs and trees) per homegarden. In total, 34% species are native to the Tehuacán Valley and nearly 16% are components of the surrounding forests. A total of 176 species were cultivated through seeds, vegetative propagules or transplanted entire individual plants, 71 tolerated, and 23 enhanced. The highest species richness and diversity were recorded in homegardens from the CF zone (199 species), followed by those from the TRF (157) and those from the TDF (141) zones.

Conclusion

Homegardens provide a high diversity of resources for subsistence of local households and significantly contribute to conservation of native biodiversity. The highest diversity was recorded in homegardens where the neighbouring forests had the least diversity, suggesting that management of homegardens aims at compensating scarcity of naturally available plant resources. Cultivated species were markedly more abundant than plants under other management forms. Diversity harboured and management techniques make homegardens keystones in strategies for regional biodiversity conservation.

     

Traditional Knowledge and Useful Plant Richness in the Tehuacán–Cuicatlán Valley,Mexico

Traditional Knowledge and Useful Plant Richness in the Tehuacán–Cuicatlán Valley, Mexico. This study systematizes ethnobotanical information about the interactions between people and plants, ethnofloristic richness, the relative importance of useful species richness in relation to general species richness, and plant management in the Tehuacán–Cuicatlán Valley of central Mexico. The study recorded a total of 1,605 useful vascular plant species (61.2% of the total species richness of the regional vascular flora), this being the region with the highest absolute richness of useful plant species in Mexico. The null hypothesis that plant families with a higher number of useful species would be those having a higher general species richness was analyzed through residuals method. The plant families richest in useful species were Poaceae, Asteraceae, Cactaceae, Cyperaceae, Mimosaceae, and Solanaceae, most of which also have the highest general floristic richness. However, analyses of use categories did not generally corroborate our hypothesis. About 1,335 of the useful species are wild, more than 500 species are submitted to some type of management (62 species are tolerated, 34 protected, 50 enhanced, and 358 cultivated), but only a few have been studied to document their process of domestication. This information can be useful for developing regional strategies of sustainable management of plant resources.     

Mycorrhizal perennials of the "matorral xerófilo" and the "selva baja caducifolia" communities in the semiarid Tehuacán-Cuicatlán Valley,Mexico

We investigated the mycorrhizal status of perennial xeric plant species occurring in the "matorral xerófilo" (arid tropical scrub) and the ecotone of the "selva baja caducifolia" (tropical deciduous forest) communities in the semiarid valley of Tehuacán-Cuicatlán, south-central Mexico. The perennial species examined are dominant/codominant elements within the "matorral xerófilo" and the "selva baja caducifolia", both endangered communities in the Biosphere Reserve Tehuacán-Cuicatlán Valley. Of the 50 sampled species, 45 were mycorrhizal. To our knowledge, we report arbuscular mycorrhizae (AM) for the first time in 37 species, of which 21 are endemic to Mexico and nine are endemic to the Valley. We also report AM for the first time in three genera, Buddleja, Hechtia and Zornia, and in one plant family, Buddlejaceae. Beaucarnea gracilis, a threatened species, and Mimosa purpusii, a potentially rare species, are both mycorrhizal. This is the first study of the mycorrhizal status of plant species within the Valley.     

Effect of mycorrhizae on seedlings of six endemic Mimosa L. species (Leguminosae–Mimosoideae) from the semi-arid Tehuacán–Cuicatlán Valley, Mexico

Mimosa is an important genus of legumes in arid and semi-arid ecosystems of the world, but scarce information is available about its interaction with microbial symbionts. In Mexico, there are no reports on the responsive of endemic Mimosa species to arbuscular mycorrhizal (AM) fungal colonization. In this study, the AM association with seedlings of six endemic Mimosa species, M. adenantheroides, M. calcicola, M. lacerata, M. luisana, M. polyantha and M. texana var. filipes, is reported. Field conditions were simulated in the greenhouse. Seeds were collected from plants and soil from the localities where the species occur within the semi-arid Tehuacán–Cuicatlán Valley, Mexico. Four treatments were applied: (1) control, (2) benomyl, (3) phosphorus, and (4) benomyl plus phosphorus. Mycorrhizal seedlings of five species, M. adenantheroides, M. lacerata, M. luisana, M. polyantha and M. texana var. filipes, showed a higher shoot and total dry weight than non-mycorrhizal seedlings. The only species that did not show any difference between mycorrhizal and non-mycorrhizal seedling performance was M. calcicola. M. luisana, M. polyantha and M. texana var. filipes had a higher root/shoot ratio; in general, benomyl treatments promoted seedling biomass allocation to the root, while control, phosphorus and benomyl plus phosphorus treatments decrease root/shoot ratio. Shoot P content was significantly higher in mycorrhizal than in non-mycorrhizal plants, although no significant differences were found for M. adenantheroides in all treatments. Benomyl and benomyl plus phosphorus treatments reduced AM colonization in all the species under study. Benomyl significantly reduced the number of N₂-fixing root nodules, while the phosphorus treatment generally stimulated nodulation. The species M. lacerata, M. luisana, M. polyantha and M. texana var. filipes had a high mycorrhizal dependency index indicating that plant growth was strongly increased by arbuscular mycorrhiza activity. Our results indicate that the response of all Mimosa species to mycorrhization was highly variable. To our knowledge, this is the first report about the effect of AM fungi and phosphorus on Mimosa species, which may be useful in biodiversity and soil conservation programs.     

Real-time PCR and microscopy: are the two methods measuring the same unit of arbuscular mycorrhizal fungal abundance?

To enable quantification of mycelial abundance in mixed-species environments, eight new TaqMan((R)) real-time PCR assays were developed for five arbuscular mycorrhizal fungal (AMF, Glomeromycota) taxa. The assays targeted genes encoding 18S rRNA or actin, and were tested on DNA from cloned gene fragments, from spores, mycelia, and from root-free soil, and on reverse-transcribed rRNA templates from entire mycelia and from colonized roots. The assays showed high specificity, sensitivity, and reproducibility, enabling reliable quantitation over broad ranges of template molecules. From cultured mycelia, DNA and RNA measures both correlated with spore number rather than extraradical hyphal length, and epifluorescence microscopy identified pronounced heterogeneity in vitality and nuclear distribution in hyphae. Root colonization was also spatially heterogeneous, as shown by a mixing experiment with root fragments of different length. Therefore, although real-time PCR can reproducibly and accurately quantify AMF nucleic acids, these are poorly correlated with visual measures because of spatial heterogeneity.     

Intra-cultural Differences in the Importance of Plant Resources and Their Impact on Management Intensification in the Tehuacán Valley,Mexico

Management of plant resources is a complex process that involves the interaction of numerous cultural, environmental, economic, and ecological factors Therefore, understanding factors influencing management decisions requires multidisciplinary approaches, including both quantitative and qualitative perspectives. This study explores quantitative approaches as methodological tools with which to identify patterns underlying more intensive management of plant resources. The research was conducted in the village of Santa María Tecomavaca, Oaxaca, in south-central México, within the semiarid Tehuacán-Cuicatlán Biosphere Reserve. Three models explaining the management intensity tendencies were identified, consistent with the pattern of multiple variables influencing plant management.     

Traditional knowledge and genetic diversity ofopuntia pilifera (cactaceae) in the tehuacán-cuicatlán valley, Mexico

Traditional Knowledge and Genetic Diversity of Opuntia pilifera (Cactaceae) in the Tehuacán-Cuicatlán Valley, Mexico. Economic Botany 59(4)366-376, 2005. Most studies of the genusOpuntia have focused on economically important species, and therefore more knowledge concerning the genetic diversity among wild and locally managedOpuntia species is needed for an expanded use of cacti in the future. The present study is part of ongoing ethnobotanical work in the Tehuacán-Cuicatlán Valley of Mexico and focuses on six traditionally classified forms ofOpuntia pilifera used as food by the indigenous Popoloca people in San Juan Atzingo. Traditional knowledge of how to distinguish these forms based on fruit flavor, color, size, and number of spines on the fruits and cladodes is preserved in the local community. Genetic fingerprinting with 129 AFLPs did not correlate with this traditional morphological classification of 67 cacti. Yet, these AFLPs distinguished the analyzed 67Opuntia pilifera cacti easily from the out-group comprising 17 wildOpuntia velutina.     

Genetic variation and evolution of Polaskia chichipe (Cactaceae) under domestication in the Tehuacán Valley, central Mexico

Polaskia chichipe is a columnar cactus under artificial selection in central Mexico because of its edible fruits. Our study explored the effect of human manipulation on levels and distribution of genetic variation in wild, silviculturally managed and cultivated sympatric populations. Total genetic variation, estimated in nine populations with five microsatellite loci, was H(T) = 0.658 +/- 0.026 SE, which was mainly distributed within populations (H(S) = 0.646) with low differentiation among them (F(ST) = 0.015). Fixation index (F(IS)) in all populations was positive, indicating a deficit of heterozygous individuals with respect to Hardy-Weinberg expectations. When populations were pooled by management type, the highest expected heterozygosity (H(E) = 0.631 +/- 0.031 SE) and the lowest fixation index (F(IS) = 0.07) were observed in wild populations, followed by cultivated populations (H(E) = 0.56 +/- 0.03 SE, F(IS) = 0.14), whereas the lowest variation was found in silviculturally managed populations (H(E) = 0.51 +/- 0.05 SE, F(IS) = 0.17). Low differentiation among populations under different management types (F(ST) 0.005, P < 0.04) was observed. A pattern of migration among neighbouring populations, suggested from isolation by distance (r2 = 0.314, P < 0.01), may have contributed to homogenizing populations and counteracting the effects of artificial selection. P. chichipe, used and managed for at least 700 generations, shows morphological differentiation, changes in breeding system and seed germination patterns associated with human management, with only slight genetic differences detected by neutral markers.     

Renegotiating gender and class in the berry fields of Michoacán,Mexico

This article examines the renegotiation of gender and class in a rural Mexican community where economic crisis in the sugar industry led foreign agribusinesses to promote blackberry and raspberry production for export and hire primarily women as berry pickers. Analysis focuses on the transition from a sugar economy where mostly men worked in the cane fields to non-traditional agricultural exports when women entered agricultural waged labor in unprecedented numbers. This restructuring of the regional economy raises important questions regarding the marginalization of differentiated subaltern groups and the nature of new sets of power relations between transnational agribusinesses, berry growers, and waged workers. I analyze the contradictions of this changing social field that connects Northern consumers, transnational company executives, berry growers, and waged laborers in a web of differential power relations as they reverberate along the commodity chain from campesino households to the global market.     

Effect of land use on the structure and diversity of riparian vegetation in the Duero river watershed in Michoacán,Mexico

Riparian vegetation performs important ecosystem functions, since it maintains regional biodiversity and provides a range of environmental services. However, anthropogenic activity, land use type, and edge effects are factors that modify the riparian species assemblage and properties. The present study analyzes the influence of adjacent land use on the structure and diversity of riparian vegetation in four hydrographic regions that form the watershed of the river Duero, in the state of Michoacán, Mexico. Using a survey of woody plants of dbh ≥ 2.5 cm in ten different 0.1 ha sites, we found that the average number of stems and individuals was lower under agricultural (AGR) and urban (URB) land use, compared to forested areas (FOR). The proportion of multistemmed plants differs among land uses: this value was greater in AGR than in the FOR and URB categories. This proportion also differed among the four hydrographic regions. The land use type FOR presented the highest alpha and beta diversity, with a high number of native species occurring only in areas defined by this land use. The results indicate that the category FOR plays an important role in the conservation of regional flora and is a possible source of germplasm for restoration programs in sites degraded by human disturbance. This study shows how anthropogenic activities affect riparian vegetation and highlights the importance of further study of this ecosystem to apply sustainable management strategies that are compatible with its conservation.     

Local adaptation to soil hypoxia determines the structure of an arbuscular mycorrhizal fungal community in roots from natural CO₂ springs

The processes responsible for producing and maintaining the diversity of natural arbuscular mycorrhizal (AM) fungal communities remain largely unknown. We used natural CO(2) springs (mofettes), which create hypoxic soil environments, to determine whether a long-term, directional, abiotic selection pressure could change AM fungal community structure and drive the selection of particular AM fungal phylotypes. We explored whether those phylotypes that appear exclusively in hypoxic soils are local specialists or widespread generalists able to tolerate a range of soil conditions. AM fungal community composition was characterized by cloning, restriction fragment length polymorphism typing, and the sequencing of small subunit rRNA genes from roots of four plant species growing at high (hypoxic) and low (control) geological CO(2) exposure. We found significant levels of AM fungal community turnover (β diversity) between soil types and the numerical dominance of two AM fungal phylotypes in hypoxic soils. Our results strongly suggest that direct environmental selection acting on AM fungi is a major factor regulating AM fungal communities and their phylogeographic patterns. Consequently, some AM fungi are more strongly associated with local variations in the soil environment than with their host plant's distribution.