Search

Historical information on wildfires and dendrochronological studies offer meaningful clues about fire and climate regimes, factors that affect forest structure and dynamics. This study aimed to determine the effect of fire history on vegetation dynamics and successional pathways of areas under different fire management policies in the Lagunas de Montebello National Park (LMNP), Chiapas, Mexico. The selected study sites were El Parque area under fire exclusion policies since 1961; Tziscao-inhabited area under fire prohibition since 1984; and Antela area with a traditional agricultural fire management history. A Pinus oocarpa ring-width chronology was used as a proxy for climate variability to which wildfire occurrence was mapped and to determine the establishment patterns of this dominant species. Current vegetation composition and structure and fuel loads were determined to characterise the study sites. Large wildfires, like those occurring in 1984 and 1998, were associated with periods of high humidity followed by intense droughts; they were linked to strong El Nino events and severely impacted the LMNP. Vegetation dynamics indicated simplification of mesophyll forest (climax) to pine-oak-sweetgum forests, with Pinus dominating the overstorey in all sampling sites. Pine, oak and sweetgum species were the dominant juvenile trees in Antela, El Parque and Tziscao, respectively. Late-successional seedlings (i.e., Prunus) were present in Antela and El Parque, while were absent from Tziscao where several wildfires had occurred. Fuel accumulation in sites within protected areas subject to fire exclusion policies was very high (40-68 t ha-1); in contrast, it was the lowest in rural Antela (24 t ha-1). Considering vegetation vulnerability to wildfires associated with extreme humid-dry climate events, increased fire hazard due to fuel accumulation, and the socio-ecological impacts of these events, we recommend revising the fire exclusion policies currently implemented in the LMNP and applying an integrated fire management approach that incorporates local socio-ecological conditions.

La ordenación de comunidades vegetales puede usar métodos multivariados para hallar patrones de respuesta y generar hipótesis sobre las posibles relaciones existentes en la composición de especies con respecto a gradientes ambientales. El objetivo fue registrar patrones de distribución y usos de la vegetación en el municipio de Catorce, San Luis Potosí. En 2019, se muestrearon seis transectos, desde pie de monte bajo al oeste de la Sierra de Catorce, valle o planicie de drenaje endorreico y sierra baja plegada con lomerío. En cada sitio se analizó la composición florística, la estructura vertical y horizontal y las características del suelo. Se hallaron matorrales desérticos rosetófilo, micrófilo y bosque espinoso. Los factores ambientales indirectos que mejor explican la distribución son la porosidad del suelo, pH, K, Ca, Fe y altitud, factores que influyen en la disponibilidad de agua. El principal uso de las plantas es medicinal tradicional.

The present study employs petrology, rock magnetics, and paleointensity on four lava flows (seven sites) of the El Jorullo volcano; a historical (1759–1766 AD) cinder cone in the Michoacan-Guanajuato Volcanic Field. El Jorullo lava flows cover an extensive area of ∼10.8 Km2, and a volume ∼0.35 Km3. Rock-magnetic experiments and microscopic observations reveal pseudo-single domain size Ti-poor titanomagnetite as the main carrier of magnetization in all sampled flows. Notably the calculated mean direction from all the sites show a slight westwards bias when compared against the secular variation global models. The mean paleo-direction for the El Jorullo historical eruption is: Dec = 2.5°, Inc = 37.5°, kappa = 214, α95 = 1.8, N = 31; the Virtual Geomagnetic Pole has Plat = 87° N, Plong = 307° E, Kappa = 260, A95 = 1.6; paleointensity data: 45.4 ± 3.6 μT; and Virtual Dipole Moment: 10.3 ± 1 × 1022 Am2. The paleodirections and the paleointensity values from these lava flows are well-constrained and reliable. These results allow to improve the accuracy and reliability of the global and regional secular variation models available for the last centuries.

The lithic in the Cerro Colorado tephra deposits is dominated by clasts from shallow country rocks for a diatreme not well mixed, or, by a combination of material that reflects the relative proportions of country rock in a well-mixed diatreme. The clasts in a tephra ring bed might be ideal to use the paleomagnetic study to determine the emplacement temperature. We report emplacement temperature ranges of pyroclastic lithic fragments from the Cerro Colorado Tuff Ring in the El Pinacate Volcanic Field, Sonora, northwestern Mexico. Paleomagnetic analyses, particularly the thermoremanent magnetization procedure was carried out in 38 small cores, drilled from the 10 to 30 cm in size lithic fragments. It estimates the emplacement temperature ranges of the juvenile basaltic cauliflower bombs and not-juvenile diverse blocks produced in the phreatomagmatic eruption. Titanomagnetite and titanohematite are the main magnetic carriers, along with titanomaghemite. The 22 emplacement temperatures determined in this study are grouped in three temperature ranges, low (310–370 °C), medium (400–460 °C) and high (>500 °C). The low and medium temperature samples show two or more components, while the high temperature samples have, in general, only one component. This wide range of emplacement temperature could be related to the composite thermal history of the pyroclastic material incorporated in the water saturated pyroclastic flow deposit. The comparison of the mean direction of the secondary magnetization component with the secular variation curve of the global model SHA.DIF.14, suggests an age of 3915 ± 59 yr. BP.

The oyamel forests, as Abies dominated forests are commonly known as, register their largest distribution (95% of their population) along the Trans-Mexican Volcanic Belt (TMVB). Although efforts have been made to study these forests with various approaches, dendrochronology-based studies have been limited, particularly in pure Abies forests in this region. The objective of this study was to reconstruct fire regimes in an Abies religiosa forest in the Sierra Norte in the state of Puebla, Mexico. Within an area of 50-ha, we collected 40 fire-scar samples, which were processed and analyzed using dendrochronological techniques to identify 153 fire scars. The fire history was reconstructed for a period of 118 years (1896–2013), with low severity surface fires occurring mainly during in the spring (92.8%) and summer (7.2%). Over the past century, fires were frequent, with an mean fire interval (MFI) and Weibull median probability of (WMPI) of five years when considering all fire scars and less than 10 years for fires covering larger areas (fires recorded by ≥25% of samples). Extensive fires were synchronized with drought conditions based on Ring Width Indexes, Palmer Drought Severity Index (PDSI) and El Niño Southern Oscillation (ENSO). After 1983, we observed a change in fire frequencies attributed to regulated management. Longer fire intervals within the last several decades are likely leading to increased fuel accumulations and could potentially result in more severe fires in the future, threatening the sustainability of these forests. Based on our finding, we recommend management actions (silvicultural or prescribed fire) to reduce fuels and the risk of severe fires, particularly in the face of climatic changes.

Introducción: El objetivo de esta investigación es comprender los cambios en las prácticas de uso del fuego en dos comunidades indígenas del Parque Nacional Lagunas de Montebello, Chiapas, México, donde a raíz de la implementación de políticas públicas sobre la supresión del uso del fuego, se han presentado repercusiones sociales y ecológicas. El incendio de 1998 ha sido considerado como el punto de quiebre para los cambios y tensiones que están ocurriendo actualmente en la región.Método: Se realizaron 66 entrevistas semiestructuradas y a profundidad a pobladores de dos comunidades indígenas ubicadas dentro (Tziscao) y fuera (Antelá) del Parque. Los temas tratados fueron: las experiencias durante el incendio de 1998; las políticas públicas en torno al uso del fuego; y la voz de la comunidad para comprender quiénes son, dónde y cómo se ha producido el nacimiento de los “Sin fuego”.Resultados y discusión: En las narrativas de las personas entrevistadas se mencionan diversas interpretaciones en cuanto a las prácticas del uso del fuego, principalmente en las actividades agrícolas, donde el uso del fuego ha sido severamente criminalizado. Estas políticas de supresión, implementadas después del gran incendio ocurrido en 1998, han influido negativamente en el territorio, marcando un antes y un después del catastrófico evento. En general, estas políticas públicas se contraponen a la lógica tradicional, y generan un “epistemicidio” o liquidación de formas de conocimiento y de prácticas de uso del fuego en territorios donde ancestralmente culturas lo han utilizado con diversos objetivos. Algunas prácticas que incluían el uso del fuego, como la roza-tumba-quema, han desaparecido por completo en Tziscao, una comunidad donde el fuego era un elemento central de la cultura, de las formas de vida y una manera de construcción del territorio. Actualmente, los habitantes están temerosos de utilizar el fuego en sus prácticas, por las repercusiones en multas al provocar incendios y el riesgo de la disminución del turismo. En Antelá, ubicada fuera del Parque y que no depende en gran parte del turismo sino de la milpa, la relación con el fuego no está ausente, se mantiene activa y la práctica de roza-tumba-quema se conserva. Conclusión: De mantenerse esta tendencia de supresión del fuego, no solamente se intensificará un proceso de transformación cultural, sino también de degradación ambiental con relación a la construcción del territorio. De manera más significativa, se puede generar una modificación drástica del paisaje, que puede desencadenar nuevos incendios catastróficos. El desafío a largo plazo no es invisibilizar ni excluir al fuego, sino incluirlo en el mantenimiento del paisaje, partiendo de la experiencia y conocimientos que tienen las comunidades campesinas; la investigación de ecología del fuego disponible; y sensibilizar e integrar a las autoridades gubernamentales para la elaboración de planes de manejo del fuego que integren las prácticas locales.

Tree mortality is an estimator of fire severity. In this work, the probability of mortality by fire of Pinus oocarpa was analyzed in four areas at the ejido Corazon del Valle, Chiapas, Mexico. The study included three burned areas (prescribed burning, conducted fire and forest fire) and one area that had not been burned for more than 30 years. Logistic models were used to analyze the influence of dasometric and fire-damage variables in order to identify the ones that explain mortality. The results show that total height and diameter to the breast height are significant variables that allow to estimate the probability of mortality by fire in the area affected by forest fire. Tree survival was: 100% in the prescribed burning area as well as in the area not burned during the past 30 years, 98.9% in the conducted forest fire, and 37.6% in the forest fire. These models may be useful to formulate burning prescriptions and to estimate the tree survival in case of forest fire.

Understanding the spatiotemporal links between drought and forest fire occurrence is crucial for improving decision-making in fire management under current and future climatic conditions. We quantified forest fire activity in Mexico using georeferenced fire records for the period of 2005–2015 and examined its spatial and temporal relationships with a multiscalar drought index, the Standardized Precipitation-Evapotranspiration Index (SPEI). A total of 47 975 fire counts were recorded in the 11-year long study period, with the peak in fire frequency occurring in 2011. We identified four fire clusters, i.e., regions where there is a high density of fire records in Mexico using the Getis-Ord G spatial statistic. Then, we examined fire frequency data in the clustered regions and assessed how fire activity related to the SPEI for the entire study period and also for the year 2011. Associations between the SPEI and fire frequency varied across Mexico and fire-SPEI relationships also varied across the months of major fire occurrence and related SPEI temporal scales. In particular, in the two fire clusters located in northern Mexico (Chihuahua, northern Baja California), drier conditions over the previous 5 months triggered fire occurrence. In contrast, we did not observe a significant relationship between drought severity and fire frequency in the central Mexico cluster, which exhibited the highest fire frequency. We also found moderate fire-drought associations in the cluster situated in the tropical southern Chiapas where agriculture activities are the main causes of forest fire occurrence. These results are useful for improving our understanding of the spatiotemporal patterns of fire occurrence as related to drought severity in megadiverse countries hosting many forest types as Mexico.

Introducción: La influencia del relieve es importante en la distribución espacial y heterogeneidad de la vegetación arbórea en las selvas. Objetivo: La estructura y diversidad arbórea se analizaron en tres relieves de la costa de Oaxaca: planicie, premontaña y montaña baja. Materiales y métodos: En cada relieve, con tres unidades de muestreo de 1,000 m2, se registraron altura total, cobertura de copa y diámetro normal de tres clases de tamaños: fustales, latizales y brinzales. La estructura se caracterizó mediante estratificación vertical, distribución diamétrica, índice de valor de importancia (IVI) y forestal (IVF); la diversidad con el índice de Shannon-Wienner (H´); y la semejanza florística con el coeficiente de Sorensen. Resultados y discusión: Las especies con mayores IVI e IVF fueron Bravaisia integerrima (fustales) y Pithecellobium dulce (latizales y brinzales) en planicie; Faramea occidentalis (fustales, latizales y brinzales) en premontaña; Cecropia obtusifolia (fustales), Cupania dentata (latizales) y Nectandra globosa (brinzales) en montaña baja. La diversidad H’ fue significativamente mayor (P < 0.05) en montaña baja (3.24) que en premontaña (1.76) y planicie (2.07). La semejanza florística de fustales y latizales fue menor entre planicie y premontaña, y para brinzales fue menor entre planicie y montaña baja. Conclusión: La riqueza y diversidad de especies fueron diferentes en cada clase de tamaño en al menos un relieve.

[Background] Fire responses of species in arid environments have only been scarcely studied. We studied four species (Dasyliron lucidum Zucc., Juniperus deppeana Steud., Echinocactus platyacanthus Link & Otto, and Agave potatorum Zucc.) in the Tehuacán-Cuicatlán Biosphere Reserve, Mexico. The objectives were to describe and quantify survival and resprouting, as well as the factors determining them, for the selected species. Six months after a 330 ha wildfire in 2014, 32 plots were established on three transects. Forest dasometric and fire severity variables were recorded. Logistic regression was utilized to obtain mortality and resprouting probability models, as well as linear regression to detect relationships among post- and pre-fire variables., [Results] All species had high survival rates (74.5 to 97.7%). All surviving D. lucidum individuals resprouted apically. For J. deppeana, the probability of mortality was directly related to fire scar height on the trunk and inversely related to its diameter, whereas the probability of crown recovery was inversely related to the proportion of the tree height scorch. For E. platyacanthus, necrosed height was directly related to plant height. There was a positive relationship between basal area and the emission of new leaves for the A. potatorum., [Conclusions] In the different species, several traits that allowed high fire survival rates were observed (e.g., thick cortex or bark, fleshy non-flammable leaves, flammable leaves that reduce fire intensity, high volume to surface ratio). Many of these were primarily linked to drought resistance. All species gain fire resistance or tolerance as they increase in size. We concluded that the studied arid ecosystem of Mexico can withstand an altered or a base fire regime., Funding for this study was provided in part by Fondo Mexicano para la Conservación de la Naturaleza, USDA Forest Service, US Agency for International Development, Universidad Autónoma Chapingo (Ajusco Project on Fire Ecology, Fire Management and Restoration of Burnt Areas), and FOCSEC Project (PROMETEO/2016/21), on the role of fire and aridity in plant communities.

The Popocatepetl volcano resumed its eruptive activity in 1994 and is still active. The largest eruption recorded during this new stage of activity occurred in December 2000. We traced the volcanic activity signal in tree-rings from Pinus hartwegii trees located in the north slope of the volcano, located at ∼3 km from the volcanic cone. Annually resolved tree-ring widths, elemental and stable δ13C and δ18O isotope composition were measured during the period 1989–2014 to study the effects of the volcanic activity on trees. Our results indicate a high increase in the concentration of metal elements (Co, Cr, Cu, Fe, Li, Mo, Ni, Pb, Rb, Sr, Ti, Zn) in tree rings following the major 2000 volcanic eruption, compared to the pre-eruption period from 1989 to 1993. Other chemical elements such as Al, K and S peaked 2 years later, in the 2003 tree ring, that matched with the formation of a very narrow ring that year. This sharp reduction of growth was probably driven by a combination of harsh climatic conditions (drought) with the lagged negative effects of the 2000 eruption. Carbon isotope discrimination (Δ13C) and δ18O increased from 1995 to 2006, suggesting reduced stomatal conductance, photosynthetic activity and water use efficiency due to the large dust veil covering the study zone. The variation of relevant elements (Ca, Mn) showing significant correlations with tree growth, Δ13C and δ18O can be attributed to the selective availability of elements following the soil acidification caused by the volcanic activity. Our findings suggest that the recent activity of the Popocatepetl might have increased tree vulnerability, as reflected in the sharp reduction of growth following the drought recorded 2 years after the large eruption of December 2000. Our results warn about the cumulative negative effects of volcanic activity and harsh climatic conditions on tree growth and functioning.

The Pinacate Volcanic Field is a Neogene volcanic sequence at the northwestern part of Mexico. This paleomagnetic study (directional and paleointensity) will continue to improve the global paleomagnetic databases. It is the first full vector paleomagnetic analysis within the more than 400 volcanic structures of the Pinacate Volcanic Field, e.g. scoria, cinder cones, large ‘pahoehoe’ and ‘aa’ lava flows. A total of 140 oriented standard paleomagnetic cores from 16 sites of lava flows were collected. Rock magnetic experiments such as thermomagnetic analyses show that Ti-poor titanomagnetite is the main magnetic carrier of the remanence. Microscopy of oxide minerals supports this observation. Parameters from hysteresis and FORC diagrams suggest pseudo-single domain grain sizes or a mixture of single and multidomain particles. The directional analysis of 11/12 volcanic structures provides a mean paleomagnetic direction and corresponding mean paleomagnetic pole (calculated from the site VGPs): Dec = 0.1°, Inc = 54.5°, n = 11, α95 = 6.7°, k = 48, Plat = 86.5°, Plong = 247.8°, A95 = 7.5°, respectively. The mean paleointensity, obtained by using the Thellier-Coe protocol, and estimated from seven volcanic structures is 42.2 ± 3.6 μT, and VDM is 8.1 × 1022Am2. The obtained directions are compatible with the Late Pleistocene paleodirection as expected from the geocentric axial dipole (GAD) field. The virtual geomagnetic pole scatter (Sb) was calculated at 13.5° which is consistent with the paleosecular variation value expected from El Pinacate latitude.

Forest fires are a cause of global concern, which requires generating knowledge on their spatial behavior. By hypothesizing that the spatial pattern of forest fires across Mexico is randomly distributed, this study aimed at making an analysis of the distribution of forest fires (2005-2015) using remote sensing information and field data collected by CONAFOR (National Forest Commission) and MODIS (Moderate-Resolution Imaging Spectroradiometer). The study compared both sources of information through the G-statistic test that identified clustering patterns. The “hot spots” analysis identified clustered areas with significant values in both data sources. These zones were extended through Sierra Madre Occidental, Penínsulade Yucatán, northern Sierra Madre Oriental and Península de Baja California. The highly coincidental clusters were found in the central-western region along the Eje Neovolcánico, as well as in a small part of Sierra Madre del Sur. The analysis of spatial correlation determined that both sources of information complement each other, enhancing their scope. It is concluded that forest fires in Mexico follow a spatial clustering trend., Los incendios forestales son una causa de preocupación mundial, lo que requiere generar conocimiento sobre su comportamiento espacial. Hipotetizando que el patrón espacial de los incendios forestales en México se distribuye de manera aleatoria, este estudio tuvo como objetivo analizar la distribución de los incendios forestales (2005-2015), utilizando información de sensores remotos y datos de campo recopilados por CONAFOR (Comisión Nacional Forestal) y MODIS (Espectrorradiómetro de Imágenes de Resolución Moderada). El estudio comparó ambas fuentes de información a través de la prueba del estadístico G que identificó patrones de agrupamiento. El análisis de "puntos calientes" identificó áreas de agrupación con valores significativos en ambas fuentes de datos. Estas zonas se extendieron a través de la Sierra Madre Occidental, la Península de Yucatán, el norte de la Sierra Madre Oriental y la Península de Baja California. Las agrupaciones altamente coincidentes se encontraron en la región centro-oeste a lo largo del Eje Neovolcánico, así como en una pequeña parte de la Sierra Madre del Sur. El análisis de correlación espacial determinó que ambas fuentes de información se complementaron entre sí, mejorando su alcance. Se concluyó que los incendios forestales en México siguen una tendencia espacial de agrupamiento.

Hace casi 470 millones de años, durante el periodo Silúrico, comenzaron los incendios forestales en el planeta. La actividad de los incendios ha experimentado altas y bajas en la historia de la Tierra, principalmente relacionadas con cambios en la concentración de oxígeno atmosférico y los niveles de humedad que han caracterizado la evolución del clima. La presencia de los incendios ha tenido picos en el Carbonífero, Jurásico y el Cretácico, así como en el Cuaternario, en particular luego de la aparición del hombre. Las primeras adaptaciones al fuego se remontan casi al mismo tiempo en que las plantas colonizaron la superficie terrestre. Con la separación de la Pangea, en el Triásico, el clima inicia su marcha hacia los patrones actuales y ello comienza a perfilar las temporadas de incendios anuales y la configuración de regímenes de fuego parecidos a los de la actualidad.

La agroforestería es una antigua práctica de uso del suelo que ha cambiado en la comunidad de El Fortín, municipio de Atzalan, Ver., debido a que la gran diversidad de componentes que existía se simplificó en monocultivos de café, cítricos y plátano. Esto trajo como consecuencia la sobreexplotación de los recursos naturales, el incremento de la pobreza y la migración. Ante esta problemática se planteó la presente investigación para estudiar los Sistemas Agroforestales (SAF) existentes en la zona de estudio, bajo la Metodología de Diagnóstico y Diseño (D D), proponer modificaciones y hacer nuevas propuestas de diseños agroforestales. Como resultado se propusieron tres sistemas agroforestales donde se sugiere un mejor manejo. Las especies consideradas son: melina (Gmelina arborea), pimienta bola (Pimienta dioica), guanábana (Annona muricata), cocolmeca (Smilax aristolochiaefolia) e iquimite (Erythrina poeppigiana), además de pasto insurgente (Brachiaria decumbens). Dichos cambios se respaldaron con las evaluaciones financieras ex post y ex ante realizadas a todos los sistemas estudiados para un periodo de 20 años, a fin de mostrar que estos sistemas pueden proporcionar más ingresos económicos para aminorar la pobreza y la migración y conservar más los recursos naturales en la zona de estudio. Los sistemas agroforestales (agrosilvícolas y silvopastoriles) ex ante superaron por más del 80 % a los ingresos netos que se obtuvieron por los ex post.

Traditionally, forest fires in Mexico, the Caribe, and Central America have been perceived, by both urban and some rural societies and government agencies, only as destructive phenomena. Certainly 40% of forest fires originate from agricultural and pastoral practices. However, there are many native rural communities that make a refined use of fire, harmonizing food production and care for the environment. In the past couple of decades, however, a slight and gradual change in perspective has occurred, such that for fire managers, preserves managers, researchers, and non-government organizations, the fire ecology as well as the management of fire by rural communities have been incorporated into what is now referred to as “integral fire management.” This term may be defined as the fusion of firefighting and prevention with the ecological use of fire and community fire management in order to preserve nature and to make the land productive. In initiating the implementation of integrated fire management, key roles have been played by national and regional governmental agencies, international and regional non-governmental agencies, as well as research universities and institutes.

Pine-oak forests cover 14.2 million hectares in Mexico, a country that has the richest pine and oak diversity in the world. These diverse forests are a source of goods and services for rural and urban society, but they are being degraded and deforested. A cause of degradation is the alteration of the fire regime caused by fire exclusion or excessive burning. Little information is available on how to restore ecologically appropriate fire regimes in Mexican pine-oak ecosystems. Less is known about the fire ecology of the oak species. To determine which of these pine-oak and oak forests are fire-maintained and which are sensitive to fires, and to provide insight into the restoration of appropriate fire regimes, this paper categorizes oak species according to the following characteristics: climate and type of vegetation, environment and succession, fire regime, growth form, vegetative regeneration, regeneration niche, acorn size, foliage type, bark thickness, subgenus, and understory. Frequent low-intensity surface fires are recommended for the restoration and maintenance of many of these forests and to reduce the ecological, economic, and firefighting impacts that result from large-magnitude wildfires, although it is recognized that for some species of pine and oak, periodic high-intensity fires are required. Because the source of more than 40% of the wildfires in Mexico is agricultural and grazing activities, it is essential to consider the needs of rural communities who use fire for their livelihood, and how burning might help restore and maintain these ecosystems. Resumen: Los bosques de pino-encino cubren 14.2 millones de hectareas en Mexico, pais que cuenta con la mayor diversidad de pinos y encinos en el planeta. Estos bosques son fuente de bienes y servicios para la sociedad rural y urbana, pero estan siendo degradados y deforestados. Una fuente de degradacion es la alteracion de los regimenes de fuego ocasionada por la exclusion del fuego o por incendios excesivos. Existe poca informacion relativa a la restauracion de regimenes de fuego ecologicamente adecuados en los ecosistemas de pino-encino mexicanos. Hay todavia menos informacion sobre la ecologia del fuego en encinares. Para determinar cuales de esos bosques son mantenidos por los incendios, cuales son sensibles y proveer informacion para la restauracion de regimenes de fuego adecuados, este trabajo categoriza las especies de encinos acorde con las siguientes caracteristicas: clima y tipo de vegetacion, ambiente y sucesion, regimen de fuego, forma de crecimiento, regeneracion vegetativa, nicho de regeneracion, tamano de la bellota, tipo de follaje, grosor de corteza, subgenero y sotobosque. El fuego frecuente, de baja intensidad, es recomendado para la restauracion y mantenimiento de muchos de estos bosques y para reducir los impactos ecologicos, economicos y de combate que resultan de incendios de gran magnitud, aunque se reconoce que para algunas especies de pino y encino se necesita fuego periodico de alta intensidad. Debido a que la fuente de mas de 40 por ciento de los incendios en Mexico son las actividades agropecuarias, es esencial considerar la necesidad de la gente en las comunidades rurales, quienes utilizan el fuego en sus sistemas de produccion, y como el uso del fuego puede ayudar a restaurar y a mantener estos ecosistemas.

Con frecuencia se realizan inventarios de combustibles forestales, pero los trabajos sobre su dinámica son muy escasos. Por ello se estudió la carga de este material y la dinámica de sus combustibles finos en un bosque de encino-pino de Chignahuapan, Puebla. Se consideraron dos condiciones: un bosque quemado un año antes de la toma de datos y otro adyacente no quemado recientemente. Se realizó un muestreo aleatorio por conglomerados para estimar la carga de todos los tipos de combustibles forestales superficiales. Para los materiales leñosos se utilizó la técnica de intersecciones planares, el resto de los combustibles se cosechó y deshidrató para estimar su carga. Se emplearon métodos estadísticos multivariados, univariados, prueba de t y prueba de normalidad, con la ayuda de los programas SAS y R. Los resultados indican que la carga total media en el área quemada fue de 7.099±1.78 t ha-1, mientras que la no quemada resultó de 31.726±1.93 t ha-1. En la primera, los combustibles leñosos con tiempo de retardo (TR) de 100 h fueron los más abundantes, y en la segunda la mayor proporción de la carga fue para los combustibles leñosos podridos con TR de 1 000 h. La tasa de descomposición de los combustibles finos fue de k=0.383 para el área no quemada y de k=0.532 en la quemada. El periodo de retorno estimado fue de 2.68 años y 1.98 años, respectivamente, lo que refleja un efecto de los tratamientos (P=0.0016).

I propose several broad fire regimes and provide an analysis of fire ecology for the principal vegetation types in Mexico. Forty percent of Mexican ecosystems are fire-dependent (pine forests, several oak forests, grasslands, several shrublands, savannas, palm lands, wet prairies, “popal” and “tular” swamps), 50% are fire-sensitive (tropical rain forests and tropical seasonal forests, tropical cloud forests, mangrove, fir forests, several oak forests, and several shrublands), and the remaining 10% fall into fire-influenced (such as several gallery forests) and fire-independent categories (shrublands in most xeric environments, very high-altitude prairies). I also present an analysis of current fire-management trends, highlighting the trend toward integral fire management, which merges prevention and control, community-based fire management, and ecological fire management.

The genus Pinus extends into tropical environments in the neotropics of Mesoamerica, the Caribbean islands, and the southern tip of the Florida peninsula. In Old World tropics, pines occur from southeast China to the Philippines and Southeast Asia. Only one species, Pinus merkusii De Vries in Sumatra, occurs south of the equator. Pines in the tropics, as elsewhere, are associated with stressed and/or disturbed environments. In seasonal environments, they are frequently linked to fire, with some species, and the ecosystems they characterize, dependent on recurring fire. This chapter focuses on the role of fire in tropical pine ecosystems. We rely on a limited literature base; a wealth of information from analogous ecosystems in warm temperate environments, particularly those found on the southeastern coastal plain of North America; observations made by the authors in the neotropics; and a growing body of information coming from recent and ongoing studies in the highlands of Mexico.

Resprouting is a common recovery strategy of many tree and shrub species in fire-prone environments and is an important determinant of post-fire dominance and vegetation dynamics in many ecosystems. Top-kill, mortality and resprouting of the trees Quercus crassifolia, Arbutus xalapensis and Pinus teocote were studied on contiguous burned and unburned sites in the pine–oak forests of Chignahuapan, Puebla, Mexico. The study sample consisted of 375 individual trees, 199 on the burned site and 176 on the unburned site. T-tests and logistic regression were used in the statistical analysis. The number of resprouts per tree increased significantly (P 0.05) regardless of fire or lack of fire. With Q. crassifolia, top-kill and tree death were greatest in the smaller-diameter individuals. Also, the probability of top-kill was much greater than the probability of mortality; however, this difference diminished at diameters greater than 16 cm. Similarly, with A. xalapensis, there was an inverse relationship between diameter and probability of tree death.

In forests of young Pinus hartwegii Lindl. on the Ajusco volcano in southern Mexico City, central Mexico, a study was made of tree mortality resulting from low and high intensity prescribed burns. Low intensity burns (backing fire in early morning with high relative humidity) and high intensity burns (head fire at midday with low relative humidity) were conducted in two different seasons: 21 March and 29 May 2002. Five contiguous sites were selected, each consisting of open stands (300–700 trees ha–1) and closed stands (900–2500 trees ha–1). Two sites were used for morning burns, two for afternoon burns, and the fifth remained an unburned control plot. Logistic regression was used to estimate probability of mortality 1 year after the burns as a function of fire season, fire intensity, stand density, and tree diameter at breast height (dbh). Logistic regression was also used to estimate probability of infestation by bark beetles as a function of crown kill. A multiple linear regression model was used to show the effect of crown kill and tree height on live crown area. The probability of mortality was greatest in May high intensity burns, on closed stands and for low dbh trees. May burns had the driest conditions, and closed stands had needle layers that produced fire smouldering. The root system heating is a key mechanism influencing mortality of Pinus hartwegii in closed stands. The treatments creating greatest mortality also resulted in lower live crown areas. According to the multiple regression model, the lower the tree height and the higher the crown kill, the lower the live crown area. The probability of infestation by bark beetles also increased with crown kill. Resume. Se estudió la mortalidad de Pinus hartwegii Lindl. juveniles ante quemas prescritas de baja y alta intensidad, en el volcán Ajusco, México central. Las primeras fueron en contra de viento y pendiente, por la mañana, con alta humedad relativa; las segundas a favor de viento y pendiente, a mediodía, con baja humedad. Se condujeron en dos épocas: marzo 21 y mayo 29 de 2002. Fueron establecidas cinco parcelas contiguas, cada una con masas abiertas (300–700 árboles ha–1) y masas densas (900–2500 árboles ha–1). Dos parcelas fueron usadas para quemas por la mañana, dos para quemas por la tarde, y una como testigo. Se empleó regresión logística para estimar la probabilidad de mortalidad a un año de las quemas como función de época de quema, intensidad, densidad arbórea, y diámetro normal. También se usó regresión logística para estimar la probabilidad de infestación por insectos descortezadores como función del chamuscado de copa. Mediante regresión lineal múltiple se relacionó el chamuscado de copa y la altura del árbol con el área de copa viva. La mayor probabilidad de mortalidad correspondió a la combinación: quemas en mayo, alta intensidad, masas densas y árboles de diámetro pequeño. Las quemas en mayo mostraron las condiciones más secas, y las masas densas tuvieron hojarasca como combustible principal, que produce combustión sin llamas. El sistema de calentamiento de la raíz es un mecanismo clave que influencia la mortalidad de Pinus hartwegii en masas densas. Los tratamientos con mayor mortalidad exhibieron menores áreas de copa viva. Se tuvo menor área de copa viva a menor altura del árbol y a mayor chamuscado de copa. La probabilidad de infestación por descortezadores aumentó con el chamuscado de copa.

Many Mexican pine ecosystems are characterized by great biological diversity and are strongly influenced by fire. We summarize fire ecology information for 35 taxa (including infraspecific taxa) in terms of nine types of fire traits: serotiny, seed germination after fire, grass stage, fast initial growth, thick bark, protected buds, self-pruning capacity, resprouting, and canopy recovery from scorch. The majority of Mexican pine species appear to be adapted to a predictable, stand-thinning fire regime. Current fire regimes are often altered from long-term historical patterns due to a combination of natural fires plus anthropogenic fires. Human-caused fires are the most common and burning practices have deep historic and socioeconomic roots. As a consequence, there are three main categories of fire conditions: (1) pine forests endangered by excessive anthropogenic fire (eventually leading to deforestation); (2) pine forests maintained by an appropriate fire regime; and (3) pine forests with insufficient fire or fire exclusion due to fire protection. For managers, conservationists, and landowners concerned with maintaining the important benefits associated with fire, such as fuel hazard reduction and nutrient cycling, different approaches are needed. While recognizing the difficult social and economic factors that foster forest degradation, we recommend basing fire management in pine forests upon a site-specific and species-specific understanding of the historical and ecological role of fire, trying to reduce excessive anthropogenic burning, maintain appropriate burning, and restore fire into fire-excluded forests. The interaction of fire with other resource uses, such as timber harvesting and livestock grazing, should also be balanced in a holistic ecosystem management approach. These changes must be made in the context of seeking alternative economic options for rural residents and by thoughtful planning to obtain as many ecological and economic benefits from fire as possible while minimizing negative impacts.

Desde el punto de vista ecológico, los incendios tienen efectos positivos sobre la vida silvestre y su hábitat en ecosistemas mantenidos por el fuego y bajo regímenes poco alterados. En México prácticamente no se ha estudiado su impacto en la avifauna. En el presente trabajo se evaluó su influencia en la riqueza y diversidad de aves en un bosque de encino-pino de Chignahuapan, Puebla, bajo tres condiciones: 1a. No quemado recientemente (más de cinco años, C1); 2a. Quemado un año antes a baja severidad (C2) y 3a. Quemado un año antes con alta severidad (C3). Para llevar a cabo el muestreo, se aplicaron los métodos de parcelas circulares y de red de niebla, además, se siguieron las claves correspondientes para identificación de avifauna. Los resultados condujeron al registro de 30 especies de aves, pertenecientes a seis órdenes y 20 familias; 22 de dichas especies se agrupan en C1, 12 en C2 y 10 en C3. Se estimó la diversidad de la avifauna con el índice de Shannon-Wiener para cada condición. Con base en la prueba t Hutchenson, se verificaron diferencias en diversidad entre C2 (2.079) y C3 (1.040) a partir de la red de niebla; y, con las parcelas circulares, C1 (2.198) difirió de C3 (1.850). Con base en los resultados encontrados, se concluye que el fuego es un factor ecológico que provoca cambios importantes en la diversidad y riqueza de aves a corto plazo.

International audience; Casas Grandes is a prehistoric culture area located between Chihuahua, northern Mexico, and New Mexico, southwest of United States of America. It had an intense occupation with large buildings during the ceramic period, from 0 to 1450 CE, developing very particular painted potteries. In this study, magnetic properties and archaeointensity experiments were investigated on two special ceramic types called Mimbres and polychrome Ramos. They come from four archaeological sites from Casas Grandes region in northern Chihuahua: Paquimé, Villa Ahumada, Galeana, and Samalayuca. Archaeological timing and typology assign Mimbres and Ramos to an age period between 900 and 1450 CE, but no absolute ages are available. Magnetic properties show that Mimbres and Ramos have different magnetomineralogical properties, suggesting that pottery making materials were different. Mean archaeointensity results were obtained from nine different pottery sherds, five from Mimbres and four from Ramos polychrome, for a total of 35 specimens. Intensity value range from 49 to 59 µT for Mimbres type and from 41 to 49 µT for Ramos type. Archaeomagnetic dating was performed using the SHAWQ2k global model and the Maghoub regional paleosecular variation curve. Archaeomagnetic dating give an absolute age range of 960–1100 CE for Mimbres type, and of 1300–1600 CE for Ramos samples, confirming that both ceramic types were manufactured at different times. These results highlight the potential of archaeomagnetism to precise the chronological framework of Casas Grandes culture.