High proportion of cactus species threatened with extinction

This is the author accepted manuscript. The final version is available from Nature Publishing Group via the DOI in this record.Consejo Nacional de Ciencia y Tecnologí

Seed germination of Trichocereus terscheckii (Cactaceae): Light, temperature and gibberellic acid effects

In this paper, we evaluated the effect of light and temperature and addition of gibberellic acid (GA(3)) in the germination of seeds of Trichocerelis terscheckii in order to provide information about Germination requirements which could be use for conservation studies. The germination response within a temperature gradient was evaluated for seeds arising from two populations: La Pedrera and Cuesta del Obispo (Salta, Argentina). Seeds of T terscheckii germinated within a range from 15 to 35 degrees C. Maximum germination percentages were found under white light and no germination was recorded in darkness. GA(3) at any concentration promoted germination either in white light or darkness neither at a constant temperature nor at an alternating one. (c) 2006 Elsevier Ltd. All rights reserved

Mexican cactus diversity: environmental correlates and conservation priorities

This paper analyzes Mexican cactus diversity to determine those states with high species richness, endemism, and endangerment, which may be important for the conservation of these plants. Relationships between environmental factors and species richness and endemism were also examined. Species richness and number of endemic and endangered species were recorded for each state, along with its total area, temperature, and precipitation. Data were analyzed with simple and multiple linear regressions, and complementarity analysis. Results showed that San Luis Potosi, Coahuila, Nuevo Leon, Oaxaca, Zacatecas, Tamaulipas, and Sonora had more than 100 species. There were significant relationships between species richness and endemism, and species richness and number of endangered species. Nine states had higher species richness than expected according to their total area. The aridity of each state was the environmental factor most significantly correlated with species richness and endemism. Eight states are needed to preserve 80% of the total cactus diversity

Regeneration responses to climate and land-use change of four subtropical tree species of the southern Central Andes

Land-use and climate change are impacting species and ecosystems around the world. The reproductive phase of plants is especially vulnerable to environmental change. Global environmental changes normally act collectively with nonlinearities and synergistic interactions being reported. Here we combined two techniques (i.e. a space for-time substitution approach and a full factorial experiment) to assess the combined effects of climate and land use change on the regeneration (seed production, seed germination and seedling survival and growth) of four subtropical forest tree species of the southern Central Andes (Yungas forest) in Argentina. We focus on temperature and precipitation changes and on decreased shading at the forest floor, a likely impact of changing land use and management. We detected species-specific and phase-specific responses. Seed mass and quality was influenced by elevation (here used as a proxy for temperature change) while germination, seedling survival and growth were mainly affected by changes in the seedbed conditions (i.e. changes in shading and in moisture related to precipitation change). Despite the influence of environmental conditions on all the phases of plant regeneration studied here, we show that the major bottleneck of the regeneration phase of these species is germination. Interactive effects between the elevation of the seeds' provenance, precipitation and shading underpin the importance of studying the effects of different environmental changes collectively on plant regeneration to better forecast the effects of climate and land-use change on the Yungas forest

demographic trends in the cactaceae

Although our biological knowledge regarding cactus species is thorough in many areas, only in recent years have ecologists addressed their demographic behavior. Here we attempt a first review of the present knowledge on cactus demography, including an analysis of the published information on species with different growth forms and life-history traits. Our review shows that cactus distribution ranges are determined by environmental heterogeneity and by species-specific physiological requirements. Temperature extremes may pose latitudinal and altitudinal distribution limits. At a more local scale, soil properties dramatically affect cactus distribution. Most cacti show a clumped spatial distribution pattern, which may be the reflection of a patchy resource distribution within their heterogeneous environments. The association of cacti with nurse plants is another factor that may account for this aggregated distribution. Many cacti grow in association with these perennial nurse plants, particularly during early life-cycle phases. The shade provided by nurse plants results in reduced evapotranspiration and buffered temperatures, which enhance cactus germination and establishment. In some cases a certain degree of specificity has been detected between particular cactus species and certain nurse plants. Yet some globose cacti may establish in the absence of nurse plants. In these cases, rocks and other soil irregularities may facilitate germination and establishment. Cacti are slow-growing species. Several abiotic factors, such as water and nutrient availability, may affect their growth rate. Competition and positive associations (i.e., mycorrhizae and nurse-cacti association) may also affect growth rate. Age at first reproduction varies greatly in relation to plant longevity. In general, cactus reproductive capacity increases with plant size. Populations are often composed of an uneven number of individuals distributed in the different size categories. This type of population structure reflects massive but infrequent recruitment events, apparently associated with benign periods of abundant rainfall. A few cactus species have been analyzed through the use of population-projection matrices. A total of 17 matrices were compiled and compared. Most of them reflect populations that are close to the numerical equilibrium (lambda = close to unity). Elasticity analyses revealed that the persistence of individuals in their current size category ("stasis") is the demographic process that contributes the most to population growth rate. Also, adult categories (rather than juveniles or seedlings) show the largest contributions to lambda. No differences were apparent regarding this matter between cacti with different life-forms. This review shows that our knowledge of cactus population ecology is still incipient and rather unevenly distributed: some topics are well develope