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Características físico-bióticas de la cuenca del río Grijalva

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Abstract

Se presenta una caracterización de los rasgos ambientales más importantes en los procesos que ocu­rren en la cuenca del río Grijalva. Reunimos para ello un conjunto de información bibliográfica relativamente dispersa, complementada con la interpretación de la cartografía regional, principalmente con escala 1:250 000 sobre los temas disponibles, y de es­cala 1:1 000 000 para el resto. La parte mexicana de la cuen­ca se delimitó usando información del INEGI (1:50 000) y la parte guatemalteca, con un modelo altitudinal digital (ASTER GDEM). Se describe la configuración del relieve, su hidrografía, y se explica su relación con la distribución espacial de los tipos climáticos. Se seña­lan algunos de los aspectos geológicos históricos y actuales que influyen fuertemente en la estructura de la cuenca y en los peligros naturales asociados. Se muestra la distribución de los suelos predominantes y se describen sus características sobresalientes. Se hace una descripción sucinta de la vegetación, asocia­da con la variación ambiental, y se discuten los prin­cipales cambios de uso del suelo que la han afectado; se in­cluye un apéndice con comentarios sobre el mapa de la provincia de Tabasco elaborado por Melchor de Al­faro Santa Cruz de 1579, y una reimpresión de la in­terpretación paleográfica sobre su toponimia y otras características de región. Palabras clave: clima, suelos, vegetación, Chiapas, Tabasco.

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... The basin lies between 14°55' and 18°35' north and 91°20' and 94°15' west [26]. The Usumacinta basin covers ≈77,000 km 2 of the Guatemalan and Mexican territories [27], while the Grijalva basin covers ≈57,000 km 2 [28]. The maximum altitude in the basin is 3800 m [20]. ...
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... Average annual precipitation ranges from 1,500 to 2,000 mm near the coast to 4,500 mm in the Northern Mountains of Chiapas (Plascencia-Vargas, González-Espinosa, Ramírez-Marcial, Álvarez-Solís, & Musálem-Castillejos, 2015). Average annual temperature varies from 12°C in the highlands of Chiapas to 26°C in the lowlands of Tabasco. ...
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... About 35% of Mexico's total freshwater ows through the Grijalva and Usumacinta rivers (CONAGUA 2011). Despite this, the rural communities settled along these rivers live in conditions of extreme poverty, with severe deterioration of natural resources and limited access to good quality water ( González-Espinosa et al. 2014, Plascencia et al. 2014). The combination of several biophysical, social and environmental factors generates a high degree of vulnerability to disasters caused by events such as landslides and oods, and there is great interest in the region in mining, an activity that can cause irreversible damage to the environment ( Laino-Guanes et al. 2015). ...
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... En los ríos Grijalva y Usumacinta escurre alrededor del 35% del total del agua dulce de México (CONAGUA 2011). Pero las comunidades rurales asentadas sobre estos ríos viven en condiciones de pobreza extrema, con grave deterioro de los recursos naturales y acceso limitado a agua de buena calidad , Plascencia et al. 2014). La combinación de varios factores biofísicos, sociales y ambientales genera un alto grado de vulnerabilidad a los desastres ocasionados por eventos como deslizamientos e inundaciones, además en la región hay gran interés por los recursos mineros, actividad que puede causar daños irreversibles al medio ambiente (Laino-Guanes et al. 2015). ...
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Tropical montane forests have been recognised as having global conservation importance. However, they are being rapidly destroyed in many regions of the world. Our study focuses on the rate of loss and patterns of fragmentation in tropical montane forests in the Highlands of Chiapas, Mexico, during a 25-year period. Data from Landsat satellite imagery from 1975 (MSS), 1990 (TM) and 2000 (ETM+) were used to ascertain annual deforestation rates of 1.3 and 4.8% for the 1975–1990 and 1990–2000 periods, respectively. Spatial patterns of forest fragmentation were identified using selected landscape indices. Increases in the number of forest fragments (3520–10,542), patch density (1.0–3.2 patches/100 ha), and total edge length (24,781–38,400 km) were associated with decreases in the mean patch size (65.0–8.7 ha), largest patch index (60.7–4.0%), total core area (99,422–9,611 ha), and mean proximity index (101,369–1405). The observed trends indicate increasing deforestation and fragmentation, particularly during the 1990–2000 period. Circa 50% of the forest cover in the Highlands has been lost in 25 years, and a proportion of the remaining forests have been degraded as a result of human use. Increasing human population and a more demanding use of soils for agriculture and timber arise as the major causes of deforestation in the study area. We suggest that conservation efforts should be focused on the management of the natural system and the management of the external influences on it, particularly the detection of hotspots, passive and active restoration and sustainable forest exploitation by the local indigenous communities.
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We studied the influence of anthropogenic disturbance on forest structure and composition in the highly populated Montane Rain Forests of northern Chiapas, Mexico. We evaluated species richness, basal area and stem density on 81 circular plots (0.1 ha each) along a categorical disturbance gradient due to forest extraction, livestock grazing, and fires. A total of 116 tree species (>5 cm DBH) were recorded in three major forest types recognized by TWINSPAN. The three forest types were: Quercus–Podocarpus Forest (QPF), Pinus–Quercus–Liquidambar Forest (PQLF), and Pinus Forest (PF). The number of canopy and understory trees species, absolute density, and basal area decreased with disturbance intensity. Mean basal area of Pinus spp. was high at intermediate and severe disturbed sites (27 and 19 m2 ha−1, respectively), and low (0.2 m2 ha−1) in well preserved old-growth stands. Distribution of life forms was heterogeneous among forest types, with a high number of understory trees species in QPF, and an impoverished composition in PF. A first axis obtained by factor analysis, represented a combination of anthropogenic disturbance along with environmental and structural variables. Scores of the first factor explained almost 50% of variation, and was positively correlated with livestock grazing, firewood extraction, basal area of Pinus spp. and soil pH, and negatively associated with elevation, plant cover and basal area of Quercus spp. A second factor explained an additional 12% of variation and was associated with forest fires and timber extraction. Distribution of size classes in the QPF was significantly different (p<0.05) than in the other two forest types, including the largest individuals in all inventories. Our results suggest that small scale, but frequent anthropogenic disturbance, increases the dominance of Pinus and drastically decreases floristic richness, mostly understory trees. This points to the need of developing restoration practices aimed to attain highly diverse mixed forests from induced depauperate pinelands. On the other hand, the remnant MRF stands are currently under risk of deforestation in a highly populated Mayan territory, and their conservation under criteria of sustainable use may require finding alternative high value uses not included in conventional commercial forestry.
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Livelihoods of people living in many protected areas (PAs) around the world are in conflict with biodiversity conservation. In Mexico, the decrees of creation of biosphere reserves state that rural communities with the right to use buffer zones must avoid deforestation and their land uses must become sustainable, a task which is not easily accomplished. The objectives of this paper are: (a) to analyze the conflict between people's livelihoods and ecosystem protection in the PAs of the Sierra Madre de Chiapas (SMC), paying special attention to the rates and causes of deforestation and (b) to review policy options to ensure forest and ecosystem conservation in these PAs, including the existing payments for environmental services system and improvements thereof as well as options for sustainable land management. We found that the three largest PAs in the SMC are still largely forested, and deforestation rates have decreased since 2000. Cases of forest conversion are located in specific zones and are related to agrarian and political conflicts as well as growing economic inequality and population numbers. These problems could cause an increase in forest loss in the near future. Payments for environmental services and access to carbon markets are identified as options to ensure forest permanence but still face problems. Challenges for the future are to integrate these incentive mechanisms with sustainable land management and a stronger involvement of land holders in conservation.
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Tropical montane cloud forests (TMCF) are among the most threatened ecosystems globally in spite of their high strategic value for sustainable development due to the key role played by these forests in hydrological cycle maintenance and as reservoirs of endemic biodiversity. Resources for effective conservation and management programs are rarely sufficient, and criteria must be applied to prioritize TMCF for conservation action. This paper reports a priority analysis of the 13 main regions of TMCF distribution in Mexico, based on four criteria: (1) forest quality, (2) threats to forest permanence, (3) threats to forest integrity, and (4) opportunities for conservation. Due to the diverse socio-environmental conditions of the local communities living in Mexican TMCF regions, their associated social characteristics were also evaluated to provide a background for the planning of conservation actions. A set of indicators was defined for the measurement of each criterion. To assign priority values for subregions within each main region, an international team of 40 participants evaluated all the indicators using multicriteria decision-making analysis. This procedure enabled the identification of 15 subregions of critical priority, 17 of high priority, and 10 of medium priority; three more were not analysed due to lack of information. The evaluation revealed a number of subjects that had hitherto been undetected and that may prove useful for prioritization efforts in other regions where TMCF is similarly documented and faces equally severe threats. Based on this analysis, key recommendations are outlined to advance conservation objectives in those TMCF areas that are subjected to high pressure on forest resources.