97 research outputs found

    Análisis preliminar de la diversidad y estructura arbórea-arbustiva del bosque mesófilo en el Sistema Volcánico Transversal de Michoacán, México

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    ResumenEl objetivo del presente análisis es determinar la biodiversidad y estructura del bosque mesófilo de montaña (BMM) ubicado en el Sistema Volcánico Transversal de Michoacán (SVTM), actualmente amenazado por los intensos cambios de uso de suelo. A través de muestreos en transectos de 50×2m en un número variable de acuerdo con la superficie de los 11 fragmentos muestreados. Se encontraron 2 083 individuos que representaron a 57 especies arbóreas y arbustivas. Los resultados obtenidos con el índice de Shannon, los de similitud (Jaccard con 45% y Sorensen con 31% máximos), el diámetro normalizado, la estructura vertical y de copa demuestran una importante heterogeneidad en los fragmentos, pero con elementos florísticos de BMM. El 50% de las especies reportadas presentan un diámetro normalizado promedio entre 2.5–9.49cm y el 13% tienen <38cm. El área basal estimada va de 7.59 (fragmento 3) a 114.4m2 ha−1 (fragmento 6). Considerando el valor de importancia relativa sobresalen Styrax argenteus, Pinus pseudostrobus y Ternstroemia lineata como las especies dominantes en todo el BMM. En cada fragmento se observó que el BMM en el SVTM se encuentra confinado a barrancas y que la superficie de los fragmentos reportados por el Inegi están sobrestimados en su área. La comparación de las especies que se presentaron en los BMM analizados contra sitios cercanos y regionales del mismo ecosistema, resultó en una baja similitud, encontrándose que a mayor distancia mayor es la disimilitud de especies.AbstractThe objective of this study was to analyze the biodiversity and structure of Cloud Mountain Forest (CMF) located in the Trans Volcanic System in Michoacán (TVSM), Mexico, which is threatened by current land use changes. We sampled a variable number of 50×2m transects depending on the total area in each of 11 CMF fragments. We found a total of 2 083 individuals representing 57 tree and shrub species. Results obtained with species abundance, Shannon Index, Similitude (Jaccard with 45% and Sorensen with 31%, as maxim values for both), normalized diameter, vertical structure and cover showed an important heterogeneity in the fragments but with floristic elements from CMF. Fifty percent of reported species had normalized diameters between 2.5–9.49cm, and 13% had normalized diameters <38cm. Estimated Basal area ranged from 7.59 (fragment 3) to 114.4m2 ha−1 (fragment 6). Styrax argenteus, Pinus pseudostrobus and Ternstroemia lineata were dominant in terms of the relative importance value in all CMF fragments sampled. We observed that CMF in the TVSM is confined to ravines, and that area of fragments reported by Inegi was overestimated. Comparisons between the occurrence of species in the CMF analyzed and in nearby and regional sites with the same ecosystem, showed a low similitude, with a higher dissimilitude the distance to the CMF we studied was larger

    DISTRIBUCIÓN Y ABUNDANCIA DE LAS ESPECIES ARBÓREAS Y ARBUSTIVAS EN LA SIERRA FRÍA, AGUASCALIENTES, MÉXICO

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    Our objectives were to recognize the composition of forest species, characterize theirdistribution and abundance, and identifythe factors that determine their presence orabsence in the area of Sierra Fria, Aguascalientes, Mexico. A sampling plan was elaborated using three criteria: altitude, relief andforest cover. Sixty samplings were realizedin sites of 600 m2 and randomized in different solar expositions. The arboreal andbrush species, the frequency, and ecologicalconditions that determine their presence or100Núm. 34: 99-126 Agosto 2012absence in site were identified. A CanonicalCorrespondence Analysis and Montecarlo’stest (α≤0.05) was conducted. We identified50 species; three are new reports in the area.Quercus potosina was found and Juniperusdeppeana is more widely distributed; themost abundant are J. deppeana, Q. potosina,and Pinus leiophylla. The greater ß diversityis in convex sites (ßw= 5.80) and sites withaltitudes of 2400 and 2600 m (ßw = 7.22).The altitude, relief, the slope and solar exposition are variables more implicated in thedistribution and abundance of the species(Montecarlo’s test, p = 0.0020). For thisreason, the interventions of handling mustconsider the relation species-environmentEl presente trabajo tuvo tres objetivos:1) identificar la composición de especiesleñosas forestales, 2) caracterizar su distribución y abundancia y 3) relacionarlascon variables del medio ambiente en laSierra Fría, Aguascalientes. Para ello seelaboró un plan de muestreos usando trescriterios: altitud, relieve y exposición. Serealizaron 60 muestreos en parcelas de600 m2 donde se identificaron las especiesarbóreo-arbustivas, así como su frecuenciay se anotaron las condiciones ambientalesprevalecientes en cada sitio. Posteriormentese realizó un análisis de correspondenciascanónicas, corroboradas mediante la pruebade Montecarlo (α ≤ 0.05). Los resultadosnos muestran un total de 50 especies registradas en la zona de estudio, de las cualestres son nuevos reportes. Las especies másampliamente distribuidas son Quercuspotosina y Juniperus deppeana,; las másabundantes son J. deppeana, Q. potosinay Pinus leiophylla. La diversidad ß esmayor en los sitios convexos (ßw = 5.80)y en sitios con altitudes mayores a 2 400y 2 600 m (ßw = 7.22). La altitud, relieve,pendiente y exposición a la radiación solarson los descriptores que mejor explican ladistribución y abundancia de las especies(prueba de Montecarlo, p = 0.0020). Losresultados de este trabajo contribuyen amejorar las intervenciones de manejo en elANP Sierra Fría. En particular en lo referente a la conservación de la biodiversidad y ala restauración de zonas degradadas

    Ecology of Plant Communities in Central Mexico

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    In Central Mexico converge three biogeographic provinces: Altiplano sur, Sierra Madre Occidental and Costa del Pacífico. Each one of them is composed by different plant communities: Thorn Forest, Temperate Mountain Forest and Dry Tropical Forest respectively. Our objective is to show, through phytoecological analysis, the species richness, diversity and the structure of the plant communities from the Temperate Mountain Forest and from the Tropical Dry Forest. In the Temperate Mountain Forest, 50 forest species were recorded, with a Shannon Wiener diversity index H´ = 1.63 on altitudes from 2400 to 2600 m. The Whittaker β index is Bw = 7.22. In the tropical dry forest, we identified 79 plants species with a mean diversity index H´ = 3.49 on altitudes from 1951 to 2100 m. In this ecosystem the Bw index is 8.12. This study offers important information for the establishment of management practices, considering the protection status from the areas in which this vegetation type is distributed

    Lianas Suppress Seedling Growth and Survival of 14 Tree Species in a Panamanian Tropical Forest

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    Lianas are a common plant growth form in tropical forests, where they compete intensely with trees, decreasing tree recruitment, growth, and survival. If the detrimental effects of lianas vary significantly with tree species identity, as is often assumed, then lianas may influence tree species diversity and community composition. Furthermore, recent studies have shown that liana abundance and biomass are increasing relative to trees in neotropical forests, which will likely magnify the detrimental effects of lianas and may ultimately alter tree species diversity, relative abundances, and community composition. Few studies, however, have tested the responses of multiple tree species to the presence of lianas in robust, well‐replicated experiments. We tested the hypotheses that lianas reduce tree seedling growth and survival, and that the effect of lianas varies with tree species identity. We used a large‐scale liana removal experiment in Central Panama in which we planted 14 replicate seedlings of 14 different tree species that varied in shade tolerance in each of 16 80 × 80 m plots (eight liana‐removal and eight unmanipulated controls; 3136 total seedlings). Over a nearly two‐yr period, we found that tree seedlings survived 75% more, grew 300% taller, and had twice the aboveground biomass in liana‐removal plots than seedlings in control plots, consistent with strong competition between lianas and tree seedlings. There were no significant differences in the response of tree species to liana competition (i.e., there was no species by treatment interaction), indicating that lianas had a similar negative effect on all 14 tree species. Furthermore, the effect of lianas did not vary with tree species shade tolerance classification, suggesting that the liana effect was not solely based on light. Based on these findings, recently observed increases in liana abundance in neotropical forests will substantially reduce tree regeneration, but will not significantly alter tropical tree species diversity, relative abundance, or community composition

    A Standard Protocol for Liana Censuses 1

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    A recent increase in published studies of lianas has been paralleled by a proliferation of protocols for censusing lianas. This article seeks to increase uniformity in liana inventories by providing specific recommendations for the determination of which taxa to include, the location of diameter measurement points on individual stems, the setting of minimum stem diameter cutoffs, the treatment of multiple-stemmed and rooted clonal groups, and the measurement of noncylindrical stems. Use of more uniform liana censusing protocols may facilitate comparison of independently collected data sets and further our understanding of global patterns in liana abundance, diversity, biomass, and dynamics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75009/1/j.1744-7429.2006.00134.x.pd

    Increasing dominance of large lianas in Amazonian forests

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    Ecological orthodoxy suggests that old-growth forests should be close to dynamic equilibrium, but this view has been challenged by recent findings that neotropical forests are accumulating carbon and biomass, possibly in response to the increasing atmospheric concentrations of carbon dioxide. However, it is unclear whether the recent increase in tree biomass has been accompanied by a shift in community composition. Such changes could reduce or enhance the carbon storage potential of old-growth forests in the long term. Here we show that non-fragmented Amazon forests are experiencing a concerted increase in the density, basal area and mean size of woody climbing plants (lianas). Over the last two decades of the twentieth century the dominance of large lianas relative to trees has increased by 1.7–4.6% a year. Lianas enhance tree mortality and suppress tree growth, so their rapid increase implies that the tropical terrestrial carbon sink may shut down sooner than current models suggest. Predictions of future tropical carbon fluxes will need to account for the changing composition and dynamics of supposedly undisturbed forests

    Annual Rainfall and Seasonality Predict Pan-tropical Patterns of Liana Density and Basal Area

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    We test the hypotheses proposed by Gentry and Schnitzer that liana density and basal area in tropical forests vary negatively with mean annual precipitation (MAP) and positively with seasonality. Previous studies correlating liana abundance with these climatic variables have produced conflicting results, warranting a new analysis of drivers of liana abundance based on a different dataset. We compiled a pan-tropical dataset containing 28,953 lianas (≥2.5 cm diam.) from studies conducted at 13 Neotropical and 11 Paleotropical dry to wet lowland tropical forests. The ranges in MAP and dry season length (DSL) (number of months with mean rainfall <100 mm) represented by these datasets were 860–7250 mm/yr and 0–7 mo, respectively. Pan-tropically, liana density and basal area decreased significantly with increasing annual rainfall and increased with increasing DSL, supporting the hypotheses of Gentry and Schnitzer. Our results suggest that much of the variation in liana density and basal area in the tropics can be accounted for by the relatively simple metrics of MAP and DSL.Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btpPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/78581/1/j.1744-7429.2009.00589.x.pd

    Temporal patterns of active fire density and its relationship with a satellite fuel greenness index by vegetation type and region in Mexico during 2003-2014

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    Background: Understanding the temporal patterns of fire occurrence and their relationships with fuel dryness is key to sound fire management, especially under increasing global warming. At present, no system for prediction of fire occurrence risk based on fuel dryness conditions is available in Mexico. As part of an ongoing national-scale project, we developed an operational fire risk mapping tool based on satellite and weather information. Results: We demonstrated how differing monthly temporal trends in a fuel greenness index, dead ratio (DR), and fire density (FDI) can be clearly differentiated by vegetation type and region for the whole country, using MODIS satellite observations for the period 2003 to 2014. We tested linear and non-linear models, including temporal autocorrelation terms, for prediction of FDI from DR for a total of 28 combinations of vegetation types and regions. In addition, we developed seasonal autoregressive integrated moving average (ARIMA) models for forecasting DR values based on the last observed values. Most ARIMA models showed values of the adjusted coefficient of determination (R2 adj) above 0.7 to 0.8, suggesting potential to forecast fuel dryness and fire occurrence risk conditions. The best fitted models explained more than 70% of the observed FDI variation in the relation between monthly DR and fire density. Conclusion: These results suggest that there is potential for the DR index to be incorporated in future fire risk operational tools. However, some vegetation types and regions show lower correlations between DR and observed fire density, suggesting that other variables, such as distance and timing of agricultural burn, deserve attention in future studiesAntecedentes: Una adecuada planificación del manejo del fuego requiere de la comprensión de los patrones temporales de humedad del combustible y su influencia en el riesgo de incendio, particularmente bajo un escenario de calentamiento global. En la actualidad en México no existe ningún sistema operacional para la predicción del riesgo de incendio en base al grado de estrés hídrico de los combustibles. Un proyecto de investigación nacional actualmente en funcionamiento, tiene como objetivo el desarrollo de un sistema operacional de riesgo y peligro de incendio en base a información meteorológica y de satélite para México. Este estudio pertenece al citado proyecto Resultados: Se observaron en el país distintas tendencias temporales en un índice de estrés hídrico de los combustibles basado en imágenes MODIS, el índice “dead ratio” (DR), y en las tendencias temporales de un ìndice de densidad de incendios (FDI), en distintos tipos de vegetación y regiones del país. Se evaluaron varios modelos lineales y potenciales, incluyendo términos para la consideración de la autocorrelación temporal, para la predicción de la densidad de incendios a partir del índice DR para un total de 28 tipos de vegetación y regiones. Se desarrollaron además modelos estacionales autoregresivos de media móvil (ARIMA en inglés) para el pronóstico del índice DR a partir de los últimos valores observados. La mayoría de los modelos ARIMA desarrollados mostraron valores del coeficiente de determinación ajustado (R2 adj) por encima de 0.7 to 0.8, sugiriendo potencial para ser empleados para un pronóstico del estrés hídrico de los combustibles y las condiciones de riesgo de ocurrencia de incendio. Con respecto a los modelos que relacionan los valores mensuales de DR con FDI, la mayoría de ellos explicaron más del 70% de la variabilidad observada en FDI. Conclusiones: Los resultados sugirieron potencial del índice DR para ser incluido en futuras herramientas operacionales para determinar el riesgo de incendio. En algunos tipos de vegetación y regiones se obtuvieron correlaciones más reducidas entre el índice DR y los valores observados de densidad de incendios, sugiriendo que el papel de otras variables tales como la distancia y el patrón temporal de quemas agrícolas debería ser explorado en futuros estudiosFunding for this work was provided by CONAFOR-CONACYT Project 252620 “Development of a Fire Danger System for Mexico.” This work was also cofinanced by the Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria and European Social Fund (Dr. E. Jiménez grant)S

    Liana Impacts on Carbon Cycling, Storage and Sequestration in Tropical Forests

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    Mature tropical forests sequester large quantities of atmospheric CO2, which they store as plant biomass. These forests are changing however, including an increase in liana abundance and biomass over recent decades in Neotropical forests. We ask here how this increase in lianas might impact the tropical forest carbon cycle and their capacity for carbon storage and sequestration. Lianas reduce tree growth, survival, and leaf productivity; however, lianas also invest significantly in leaf production, and the increase in lianas could conceivably offset liana‐induced reductions in tree canopy productivity with no adverse effects to the forest‐level canopy productivity. By contrast, lianas decrease the total ecosystem uptake of carbon by reducing tree biomass productivity. Lianas themselves invest little in woody biomass, and store and sequester only a small proportion of the biomass in tropical forests. As lianas increase they may effectively displace trees, but the greater liana carbon stocks are unlikely to compensate for liana‐induced losses in net carbon sequestration and storage by trees. A potentially important additional consideration is the impact of lianas on the tree community. By competing more intensely with shade‐tolerant, more densely wooded trees than with fast‐growing, light‐wooded trees, lianas may shift tree composition toward faster‐growing species, which store relatively little carbon, and thereby further reduce the carbon storage capacity of tropical forests. Overall, current evidence indicates that the increase in lianas will negatively impact the carbon balance of tropical forests, with potentially far‐reaching consequences for global atmospheric CO2 levels and associated climate change
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