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The oak species Q. crassifolia produces reliable annual rings with better climatic sensitivity than many conifer species commonly used for hydroclimatic reconstructions in Mexico. Most dendrochronological research in Mexico has been done with conifers, but broadleaf species have been underutilized. Mexican oaks are found among those species receiving limited attention for dendrochronological purposes, despite Mexico being a primary center of oak diversity with over 160 species. The objectives of this study were: (1) date the annual radial increments of oaks (Quercus crassifolia Bonpl.), and (2) analyze the dendrochronological potential and climatic response of the species to reconstruct historical climatic variability and the influence of ocean–atmospheric modes. The study was located at the Barajas site, municipality of Tepehuanes, Durango, Mexico. Wood samples consisted of 60 cross sections, 30 of them obtained at the base of the stem, and 30 more ca. 20–30 cm above the first cross section, which were analyzed by dendrochronological techniques. A tree-ring width chronology 177 years long (1840–2016) was developed indicating suitable values of series intercorrelation (0.52), mean sensitivity (0.26), signal-to-noise ratio (8.98), first-order autocorrelation (0.21), rbar (0.28), and expressed population signal (0.86) for the period 1890–2016. Dendrochronological parameters were similar or superior to those obtained from conifer species in the region. The chronology shows the strongest relationship with October–May precipitation, explaining ca. 60% of its variability (1951–1984, r = 0.78, p

The extreme hydroclimatic events in the Conchos River Basin, are strongly associated with ocean–atmospheric phenomena such as the El Nino Southern Oscillation, Pacific Decadal Oscillation, and Atlantic Multidecadal Oscillation, the streamflow reconstruction showed the occurrence of up to 10-year droughts. Dendrochronology is a modern science used to study hydroclimatic events through the measurement and standardization of tree-rings. Long-term dendrochronological series contribute to the improvement of our knowledge of past climatic events and provide information for wise management of water resources. The objective of this study was to generate an actualized streamflow volume reconstruction with a regional chronology and identify extreme hydroclimatic events in the Conchos River Basin. We analyzed the hydroclimatic behavior of the streamflow volume through a dendrochronological network in the Basin. The regional earlywood chronology was analyzed by single correlation and principal component analysis, which allowed obtaining the transfer model to determine extreme hydroclimatic events and defined the influence of large-scale ocean–atmospheric phenomena. Nine earlywood series showed a common variance and responded significantly (r = 0.68, n = 67, p

Dendrochronological series are reliable sources of information to analyze past hydrological and climatological variation that provides useful information for the management of water resources within basins. We analyzed dendrochronological series obtained from the upper Mayo River Basin using principal components analysis to determine a common climatic signal. Although the complete series extended for over 350 years, the representative period common to all series was from 1750 to 2014 (265 years) with an expressed population signal of over 0.85. Climate data (precipitation and temperature) were collected from the North American Land Data Assimilation System 2 model of the Land Data Assimilation System and hydrometrics records were obtained from the National Commission of Water in Mexico. The results of the response function showed an association of mean monthly temperature with the ring width series for the months of December of the previous year, May and October of the year of growth, and seasonally from January to July (r = -0.75, n = 36, p < 0.05). A significant response to rainfall of earlywood growth was observed for June, November, and December of the previous year, January and February of the growth year, and seasonally, from October of previous year to May of the current growth year (r = 0.70, n = 35, p < 0.05). Significant association also was found between earlywood and the accumulated runoff from October of the previous year to May of the growth year, which was used for reconstruction of the runoff flow between 1750 and 2014, which showed evidence of decadal drought. Significant correlation was found between the reconstructed runoff series, and the Southern Oscillation index (r = -0.42, n = 228, p < 0.05), but not significant with the Pacific Decadal Oscillation index (r = 0.16, n = 115, p < 0.05). We also observed significant (p < 0.05) associations with the drought indices Palmer Drought Severity Index and Standardized Precipitation Evapotranspiration Index (r = 0.56, r = 0.41, respectively). Our study demonstrated the potential of assimilated data for dendroclimatic reconstructions and the feasibility of generating hydroclimatic information of extreme events that have not been recorded in the available climatic and hydrological instrumental records.

Cool- and warm-season precipitation totals have been reconstructed on a gridded basis for North America using 439 tree-ring chronologies correlated with December–April totals and 547 different chronologies correlated with May–July totals. These discrete seasonal chronologies are not significantly correlated with the alternate season; the December–April reconstructions are skillful over most of the southern and western United States and north-central Mexico, and the May–July estimates have skill over most of the United States, southwestern Canada, and northeastern Mexico. Both the strong continent-wide El Niño–Southern Oscillation (ENSO) signal embedded in the cool-season reconstructions and the Arctic Oscillation signal registered by the warm-season estimates faithfully reproduce the sign, intensity, and spatial patterns of these ocean–atmospheric influences on North American precipitation as recorded with instrumental data. The reconstructions are included in the North American Seasonal Precipitation Atlas (NASPA) and provide insight into decadal droughts and pluvials. They indicate that the sixteenth-century megadrought, the most severe and sustained North American drought of the past 500 years, was the combined result of three distinct seasonal droughts, each bearing unique spatial patterns potentially associated with seasonal forcing from ENSO, the Arctic Oscillation, and the Atlantic multidecadal oscillation. Significant 200–500-yr-long trends toward increased precipitation have been detected in the cool- and warm-season reconstructions for eastern North America. These seasonal precipitation changes appear to be part of the positive moisture trend measured in other paleoclimate proxies for the eastern area that began as a result of natural forcing before the industrial revolution and may have recently been enhanced by anthropogenic climate change.

Baldcypress, a long-lived species of riparian habitats, is sensitive to interannual climate variability. The annual radial growth is associated with the Standardized Precipitation Evaporation Index (SPEI) and Palmer Drought Severity Index (PDSI), both depending on a water balance. The baldcypress (Taxodium mucronatum Ten.) is a long-lived species and Mexico’s national tree. The objective of this study was to analyze the dendroclimatic response of baldcypress at sites located on the transitional zone between the semiarid and subtropical regions of Mexico, known as the Middle Zone of the state of San Luis Potosi, Mexico. The first site, Los Peroles (LPO), is a wetland where the oldest known baldcypress specimens in Mexico are found. The second site, Rio Verde (RVDE), is a riparian site located along a tributary of the Moctezuma River that drains into the Gulf of Mexico. Two ring-width chronologies were analyzed. The first one from LPO with a length of 633 years and the second one from RVDE with a length of 423 years. The species responded positively to the seasonal January–July precipitation (r = 0.52, p = 0.001) and negatively to the maximum monthly temperature of January, May, and June (r = − 0.42, −0.46, and −0.34; respectively). The average chronology was significantly associated with the mean January–August Standardized Precipitation Evaporation Index (SPEI) (r = 0.62, p = 0.000). An SPEI reconstruction was developed for the period 1575–1996 where the most prolonged and severe droughts were found at 70-year peaks in the El Nino Southern Oscillation frequency band. The annual radial growth of the species is a suitable indicator of the January–August water availability, and is important information that can be used to establish water management strategies for this semiarid environment and to preserve millennial baldcypress specimens.

Volcanic activity can have a significant effect on the growth and survival of trees. The objective of our research was to analyze the effects of the 1855–1856 eruption of the Tacaná volcano and the ashfall from the 1902 eruption of the Santa María volcano, Guatemala, on the radial growth of trees at Tacaná. Dendrochronological sampling was carried out on sites covered by Pinus hartwegii Lindl., and a ring-width chronology was built using 102 increment cores from 75 trees. The ring-width chronology shows two statistically significant suppression events. One of these events occurred from 1857 to 1868 and was potentially caused by the historic eruption of Tacaná (1855–1856). The second suppression event occurred from 1903 to 1908, during which tree growth was affected 1 year after the ashfall caused by the 1902 eruption of Santa María. The growth suppression did not have the same magnitude in all sampled trees and may be related to the thickness of the ash layer deposited around each tree. For the first time, we show that tree growth at Tacaná is reduced by ashfall from volcanic eruptions. Our results may contribute to the evaluation of risks associated with the volcanic activity of the Tacaná volcano.

Introduction: In the United States of America, forest pests are associated with climate variability. Such studies are scarce in Mexico. Objectives: To create a data base of historical outbreaks of bark beetles and analyze their relationship with drought. Materials and methods: Historical records of outbreaks of bark beetles were obtained from official documents in Mexico, Guatemala, and Honduras. Dendroclimatic indices were used as a climate proxy. The relationship between pest outbreaks and climate was analyzed with the Superpose Epoch Analysis (SEA). Results and discussion: A database of 120 years (1895-2015) of bark beetle outbreaks was created. The most frequent species were Dendroctonus mexicanus Hopkins, Dendroctonus frontalis Zimmermann and Dendroctonus adjunctus Blandford. A total of 106 records of outbreaks in 15 states of Mexico were recorded during the period 1903-2015; 16 outbreaks in Guatemala during the period 1895-2013, and 15 outbreaks in Honduras during the period 1962-2015. Historically, outbreaks were recorded in years with below-average precipitation (550 mm) and have increased since 1970. The SEA determined that bark beetle outbreaks in Mexico, Guatemala and Honduras were recorded during dry years (P 0.05) of NINO 3 and PDSI (Palmer Drought Severity Index) and significant negative indices (P Conclusion: A significant relationship was determined between bark beetle outbreaks and drought conditions for the last 120 years.

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.

Antecedentes y Objetivos: El bosque de Abies religiosa o bosque de oyamel se distribuye en parches aislados y sus áreas continuas más extensas se localizan en la Faja Volcánica Transmexicana. Diversos estudios aportan información sobre aspectos ecológicos y florísticos del bosque de oyamel en México. Sin embargo, aún es necesario responder cuestiones ecológicas básicas, que pueden ser útiles para proponer y establecer estrategias de manejo y conservación de este tipo de vegetación. Por esta razón, los objetivos de la presente investigación fueron: (1) estimar la variación en la estructura poblacional de Abies religiosa y (2) determinar la estructura y composición arbórea y arbustiva del bosque de oyamel bajo diferentes condiciones de manejo. Métodos: El área de estudio incluyó cinco localidades con bosque de oyamel del estado de Hidalgo, México, con diferentes condiciones de manejo y altitud. En total se colocaron 25 parcelas de muestreo (0.01 ha cada una) para obtener datos estándar a nivel poblacional (altura, densidad, diámetro) y comunitario (densidad, área basal y frecuencia de las especies). Resultados clave: Dentro de las cinco localidades, tres poblaciones de A. religiosa se clasificaron como dinámicas, por presentar predominio de individuos pequeños; las dos restantes fueron normales, con alto porcentaje de plantas de tamaño intermedio. A nivel de comunidad, se registraron 15 especies de árboles y 15 de arbustos. La estructura del bosque difirió entre localidades, en especial las más lejanas geográficamente, corroborando el papel del manejo del bosque y de las condiciones ambientales locales. Conclusiones: Abies religiosa dominó el dosel en todas las localidades. Las características estructurales a nivel de población y comunidad difirieron entre sitios de muestreo probablemente a causa del manejo forestal y de las diferentes condiciones ambientales locales.

How tree growth responds to climate is determined by temperature and water availability, but climate change is causing shifts in forest growth that could be evaluated through tree-ring growth studies given that it is annual radial increase is influenced by interannual and multiannual climatic variations. We evaluated the influence of oceanic-atmospheric indices and the climate response on the annual radial increase of Pinus hartwegii Lindl. A total of 140 increment cores were obtained from 82 selected P. hartwegii specimens growing at the treeline of the Tancitaro stratovolcano, Michoacan, Mexico to develop a 348-year long ring-width chronology. Correlation and response function analyses were carried out between the tree-ring series and monthly climate records and by subperiods of 50 yrs. Climate records were obtained from six weather stations near the study site and oceanic-atmospheric indices were downloaded from international climatic sources. The chronology was related to drought indices involving precipitation, temperature, evaporation, and soil water content. The results indicated that accumulated precipitation from February to April, and the mean and minimum temperature from March to May and from September to November of the current growth year, had a positive correlation with the P. hartwegii ring-width chronology. The maximum temperature of March and May of the current growth year produced a negative correlation and in November positive correlation. The analysis of the response function indicated that P. hartwegii had a negative growth response to the average and maximum temperature of March. The analysis of the response function in 50-year subperiods indicated a stable response in precipitation from February to April of the period 1925 to 2000. However, when the temperature increased, the stability of the growth response became negative, mainly due to an increase in temperature in combination with low precipitation volumes, which usually occurs from March to May. The association between the ring-width series, and indices of ENSO (MEI, El Nino 4) showed a significant positive correlation, but negative with SOI. Similarly, the relationship with the PDO was positive, but negative with AMO. The association with drought indices (PDSI + JJA, PDSI*, SPEI) was positive and significant. We conclude that the populations of P. hartwegii of the Tancitaro stratovolcano constitute an ecological indicator of long-term precipitation and temperature variability and is a high-resolution proxy for regional rainfall reconstruction at least for the last three centuries.

Annual tree-ring patterns are a source of ecological and environmental information including the history of fires in forested areas. Tree-ring based fire histories include three fundamental phases: field collection, laboratory methods (preparation and dating), and data analysis. Here we provide step-by-step instructions and issues to consider, including the process for selecting the study area, sampling sites, plus how and which fire-scarred trees to sample. In addition, we describe fire-scar sample preparation and dating which are done in the laboratory. Finally, we describe basic analysis and relevant results, including examples from studies that have reconstructed fire history patterns. These studies allow us to understand the historical fire frequency, changes in those frequencies related to anthropogenic factors, and analyzes of how climate influences fire occurrence over time. The description of these methods and techniques should provide a greater understanding of fire history studies that will benefit researchers, educators, technicians, and students interested in this field. These detailed methods will allow new researchers to this field, a resource to start their own work and achieve greater success. This resource will provide a greater integration of tree-ring aspects within other studies and lead to a better understanding of natural processes with forested ecosystems.

La reconstrucción de variables hidroclimáticas es importante para comprender el funcionamiento de las cuencas forestales y tomar decisiones sobre su manejo. En este trabajo se reconstruyó la precipitación y el caudal medio a partir de información de anillos de crecimiento de Pseudostuga menziesii en la cuenca del río Piaxtla. Con la información de siete series dendrocronologías, se construyó una sola cronología regional. Se probó la correlación de la cronología regional con eventos de fenómenos océano-atmósfera como El Niño Oscilación del Sur, Oscilación Decadal del Pacífico, Oscilación Multidecadal del Atlántico e Índices de la Severidad de Sequía de Palmer. Los resultados mostraron que fue posible la reconstrucción de la precipitación de noviembre-abril y el caudal medio noviembre-agosto a partir de la serie de madera temprana con ecuaciones verificadas y validadas: Precipitación = -271.538 + 447.764*(índice de madera temprana), (r = 0.85, n = 49, p < 0.0001) y caudal medio = 5.123 + 0.623*log10(índice de madera temprana), (r = 0.68, n = 46, p < 0.001). Excepto por la Oscilación Multidecadal del Atlántico, todos los fenómenos globales mostraron correlación significativa con la información de los anillos de crecimiento. Este estudio confirma que los bosques de P. menziesii de la Sierra Madre Occidental son altamente sensibles al clima, lo que se refleja en la anchura de anillos de crecimiento y a su vez en la variabilidad del caudal medio de la cuenca. Por lo anterior se debe aprovechar el potencial de este tipo de trabajos para prever los cambios en la disponibilidad de recursos hídricos, así como ampliar su uso en la valoración de servicios ambientales hidrológicos.

Introducción: El cambio de la cobertura original de suelo y la erosión consecuente, son problemas comunes en la cuenca del río Conchos, con un impacto directo para más de 1.3 millones de habitantes. El problema se acentúa con la tala desmedida, los incendios, la sobreexplotación y la contaminación del agua superficial y subterránea. Así mismo, acorde a los pronósticos de cambio climático, se prevé una pérdida de biodiversidad y modificación del régimen hidrológico en esta importante cuenca productora de agua.Método Se evaluó la cobertura reflejada por diferentes usos de suelo mediante el software ERDAS Imagine V 2014; a su vez, la pérdida potencial de suelos se analizó espacialmente, mediante la Ecuación Universal de Pérdida de Suelo (EUPS) y la cuantificación de escurrimiento, de acuerdo con la norma oficial mexicana NOM-011-CNA-2000.Resultados y discusión: Se determinó reducción en la cubierta forestal y la zona de pastizal, detectándose un notorio incremento de superficie en zonas agrícolas y matorrales. La erosión hídrica mostró una tendencia fluctuante, donde la clase más severa de pérdida fue de 0.02 y 0.008 tm ha-1 para los años de 1980 y 2000, y aumento de 0.01 para 2018. Los volúmenes de escurrimiento máximo para 1980, fueron de 348.38 M m3 con reducción de 137.36 M m3 para el 2000, y con aumento significativo para 2018 de 743.08 M m3.Conclusiones: El uso de información climática procedente de datos asimilados, permitió detectar espacialmente los procesos de pérdida de suelo y volúmenes de escurrimiento superficial, siendo el año 2018 el más susceptible a erosión de suelo, con 1689.15 hectáreas (ha) afectadas, y con un volumen de escurrimiento medio de 379.17 M m3. De acuerdo con el hidrograma en ciertos años, las altas precipitaciones no precisan grandes volúmenes, debido a que son lecturas in situ; sin embargo, a través del presente estudio se detectaron espacialmente las zonas afectadas, donde el cambio de uso de suelo y las precipitaciones sí modifican las condiciones, lo que permitirá un mejor control y conservación de los recursos naturales.

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.

We present a new record of atmospheric Δ14C from 1926–2002 AD constructed from annual measurements of dendrochronologically dated tree rings from Nuevo Leon in Northeast (NE) Mexico. The results are very similar to the Northern Hemisphere Zone 2 compilation, indicating that this location provides a suitable record of background atmospheric Δ14C. Closer examination of the atmospheric bomb peak years (1962–1965 AD), however reveals subtle differences from the Zone 2 compilation that may reflect transport of 14C-depleted air from the south during the summer season influenced not only by the northward migration of the Intertropical Convergence Zone but also by the North American Monsoon system and tropical storms and hurricanes over the Gulf of Mexico. These differences decrease after 1965 indicating that Northern Hemisphere atmospheric mixing had largely occurred by this point. Examination of the pre-bomb peak period reveals a steady decrease in F14C associated with fossil fuel derived CO2 emissions from 1922–1950 AD. The NE Mexico record is enriched in 14C relative to a record from the Pacific Northwest during this period, potentially reflecting a greater impact of fossil fuel emissions and/or release of aged CO2 from Pacific upwelling in this region. This record from NE Mexico represents the longest such record from North America and will contribute to improved characterization of the spatial and temporal variability of atmospheric Δ14C in the Northern Hemisphere.

Pinus cembroides exhibits an excellent potential for dendrochronological studies on the basis of statistical parameters and its response to climatic variables, in particular seasonal winter–spring precipitation. Studies of forest growth under induced climatic variations allow estimating the intensity of impacts on forest ecosystems and understanding them. In the present study, the climatic response of Pinus cembroides radial increase was evaluated based on precipitation and average temperature (maximum, minimum and mean temperature). The study was carried out in Sierra del Cubo, Guanajuato, in the upper course of the Laja River. A correlation response function analysis was used to evaluate P. cembroides growth in response to climatic factors. Correlation analysis indicates that P. cembroides growth is positively associated with precipitation of October and December of the previous year, as well as with January–February, May–August and October of the current-year precipitation. Regarding temperatures, the average minimum temperature of the previous December and of January and May of the current year favored P. cembroides growth. Mean and maximum average temperature had a negative influence on annual radial growth. Response function analysis indicates that P. cembroides response to precipitation was quite unstable for the 1925–2011 period and possibly affected by climatic anomalies recorded over the last decades. The main climatic factors exerting a dominant effect on P. cembroides radial growth are, first, the winter–spring seasonal rainfall and, second, the average winter temperature. P. cembroides forests in Sierra del Cubo are highly affected by environmental variables, and its habitat could decline if winters tend to be drier and temperatures are higher as it is predicted to occur by Intergovernmental Panel of Climate Change models.

Earlywood (EW) and latewood (LW) chronologies can be used to analyze seasonal climatic variation. We constructed and analyzed total ring (RW), EW, and LW ring growth in Abies religiosa and Pinus pseudostrobus trees from the Monarch Butterfly Biosphere Reserve and evaluated their climatic signal (monthly precipitation and mean average, minimum and maximum temperatures) in the growth of tree rings by correlation and response function analyses. Precipitation during October and December of the previous year and during January, February, April, and May of the year of growth had a positive influence in the growth of both P. pseudostrobus and A. religiosa. Mean maximum temperatures had a negative effect on tree growth in both species. Additionally, growth of A. religiosa was more sensitive to variations of mean, minimum, and maximum temperatures in comparison with P. pseudostrobus, and monthly mean minimum temperature was positively correlated with EW and LW series in A. religiosa. We conclude that EW a...

Growth-ring analysis is a valuable source of information for reconstructing environmental history. In this study, ring-width series of a sample of Fagus grandifolia subsp. mexicana were used to identify the main events that have affected populations of this species. Core samples were extracted in three representative beech forests in Mexico. These are forests where F. grandifolia subsp. mexicana dominates the canopy. A total of 3355 years of growth rings were measured and three ring-width chronologies were generated. Average annual ring widths were similar between the three sites and ranged from 0.98 to 1.08 mm. A pattern of multiple suppressions and releases was observed, mainly associated with local events, but with a slight climatic influence. Correlations between the ring-width index and climate variables were not statistically significant, with the exception of a seasonal January–June precipitation pattern (1982–2001). There has not been a large-scale disturbance of natural or human origin in the beech forests of the state of Hidalgo in the past 150 years, except in El Gosco, where anthropogenic disturbances have increased in the past decade.

En México existen especies arbóreas, específicamente, el grupo de las coníferas, las cuales permiten analizar y reconstruir las variaciones climáticas del pasado de una o varias regiones geográficas. El objetivo de este estudio fue determinar el potencial de respuesta dendrocronológica de Abies guatemalensis Rehder a la variabilidad climática en Ixtlán de Juárez, Oaxaca. Se desarrollaron cronologías de madera temprana, de madera tardía y de anillo total de 206 años (1810-2015). El análisis de correlación estacional señaló una relación directa entre la cronología RWI residual con la precipitación de invierno-primavera (r = 0.67, p < 0.01) y una relación indirecta con la temperatura máxima de primavera (r = -0.42, p < 0.01) del año actual de crecimiento. Mediante un modelo de regresión lineal se reconstruyó la precipitación acumulada de febrero a abril, de los últimos 136 años (1880-2015), el modelo explicó 44% de la variabilidad de los registros meteorológicos locales del período de calibración (1952-2010). Los períodos más secos ocurrieron en las décadas 1880, 1900, 1940, 1970, 1980, 1990 y 2000. El análisis espectral de la reconstrucción mostró una periodicidad cuasi-cíclica de 2.2 años y 3.8 años, indicando una asociación con el fenómeno ENSO. La sensibilidad de la especie a variaciones climáticas reflejadas en el grosor de los anillos de crecimiento, sugiere que A. guatemalensis tiene potencial para reconstrucciones hidroclimáticas, lo que permitirá extender en el tiempo los registros instrumentales para análisis más amplios de fluctuaciones en el clima y sus tendencias en esta región del país.

La reconstrucción histórica de los regímenes del fuego, fundamentada en métodos dendrocronológicos, aporta información para el entendimiento de este fenómeno. Con el objetivo de reconstruir la historia de incendios en un bosque de pino-encino en Mezquital, Durango, se colectaron 78 muestras de Pinus durangensis , P. ar i z o n i c a, P. ayacahuite, P. teocote y Pseudotsuga menziesii con cicatrices de incendios; 73 y 27 % de las muestras se tomaron de árboles vivos y muertos, respectivamente. Se fecharon 75 muestras (96 %) y 535 cicatrices. Los regímenes se reconstruyeron de 1746 a 2013; el año 1779 representó el primer registro de incendio. Se reconstruy ó un intervalo medio de frecuencia de incendios (MFI) de 2.0 años y un intervalo medio de probabilidad de Weibull (WMPI) de 1.8 años, cuando todas las cicatrices fueron incluidas; al considerar 25 % o más (incendios extensos) se determinaron MFI y WMPI de 7.0 y 5.9 años, respectivamente. En primavera se categorizó 92.2 % de los incendios y solo 7.8 % en el verano. No hubo inf luencia significativa ( P < 0.05) de la lluvia y de El Niño Oscilación del Sur (ENSO) en la frecuencia; sin embargo, los incendios extensos se asociaron positivamente a la disminución de lluvia y eventos ENSO (fase La Niña).

The highest densities and largest areas of Fagus grandifolia subsp. mexicana in Mexico grow in the cloud forest of the state of Hidalgo. Although this taxon is endangered, there is little information about its population structure. This study provides data on the structure of heights, diameters and ages of Fagus in three populations in Hidalgo. Additionally, information was obtained on the structure of the beech forests, whose canopy is dominated by Fagus . At each locality, three to five 400 m2 sample plots, depending on the size of the respective forest, were randomly selected. Within each plot, density and basal area of each species of tree and shrub with diameter greater than 2.5 cm (1.30 m) were estimated. At the species level, populations are dynamic, with a high percentage of young individuals; however, at one of the localities, changes have occurred in the last decade due to anthropogenic activity, and the structure of sizes and diameters in the youngest age categories has changed. Diameter was a good indicator of the age of the trees. At the community level, the dominance of Fagus and other species differed between localities, which is probably related to the degree of disturbance. Population and community structure are related and could be considered as indicators of changes in environmental conditions in the recent past and today.

An increase in winter-spring precipitation appears to have a positive effect on radial growth of P. hartwegii a treeline species in Mexican volcanoes. To address the degree to which high-elevation trees reflect climatic variability, a ring-width chronology of 308 years (1705–2012) was developed from a pure stand of Pinus hartwegii forest at the upper treeline of Monte Tlaloc in the Trans-Mexican Volcanic System. A series of variables were used to verify the climatic correlation of the chronology, including climate data, historical archives dealing with agricultural crises and climate anomalies in central Mexico, regional dendroclimatic reconstructions of precipitation, values of the Southern Oscillation Index (SOI), and Tropical Rainfall Index, which are estimators of El Nino/Southern Oscillation phenomena (ENSO). Correlations with local and regional climate data suggested that wet conditions in the winter–spring season had a positive effect on radial growth. Reduced growth was associated with extreme droughts in central Mexico, with some exceptions, such as in 1997, when, due to the massive warming of sea surface temperatures and low precipitation, growth did not begin until May or June and peaked during the cool season. The ring-width chronology indicated an increase in radial growth when SOI values were negative and precipitation was above-mean during the growing season. The lowest recorded growth measurements are associated with extreme droughts and strong warm ENSO events. Given the significant relationship between climate and radial growth of P. hartwegii, this study highlights the potential vulnerability of this high-elevation species to climate change.

Las especies forestales como Pseudotsuga menziesii (Mirb.) Franco son sensibles al clima y muestran anillos de crecimiento claramente definidos. La selección cuidadosa de árboles dominantes con fuste circular permite el análisis de tendencias de crecimiento arbóreo. En este estudio se utilizaron mediciones directas del incremento del área basal (IAB) para explicar las periodicidades biológicas y elaborar predicciones del crecimiento en el abeto Douglas-fir que crece en el oeste de México. Para eliminar el efecto de la edad en el crecimiento de los árboles se hizo un análisis en términos de la edad del cámbium. Los resultados mostraron correlación significativa (P < 0.05) entre IAB y la precipitación de enero a julio. Además, se encontraron periodicidades de 7, 21, 27 y 60 años en el crecimiento de los árboles; el periodo de 60 años fue determinante para la construcción de un modelo ARIMA (0,1,1) para realizar predicciones del IAB en las próximas décadas. Las proyecciones del crecimiento proponen una reducción del IAB en árboles maduros dominantes en las próximas décadas. Dicha reducción es un resultado inesperado, debido a que el IAB en árboles dominantes permanece constante hasta una edad biológica de senescencia. Los resultados concuerdan con una tendencia general de reducción en el crecimiento en otros bosques del mundo debido a estrés hídrico, lo cual sugiere que la variabilidad climática futura puede empeorar la condición de salud del abeto Douglas-fir de los bosques del norte de México.

Se determinó la sensibilidad climática de Pinus pinceana Gordon y su potencial para reconstrucciones climáticas en diez de sus poblaciones localizadas en la región noreste (Zacatecas y Coahuila), norte-centro (San Luis Potosí) y centro (Hidalgo y Querétaro) de México. Se fecharon al año de formación de sus crecimientos anuales las poblaciones del noreste, centronorte y centro de la república; excepto la población de El Arenalito en la cual no se encontró un patrón similar de crecimiento. En las poblaciones del centro (MAG, TEP y CRI) se encontraron los árboles más jóvenes y como resultado se generaron cronologías de corta extensión; en contraste, en los sitios PAL y NOR se encontraron los árboles de mayor edad. Los valores de correlación (0,61 a 0,77), sensibilidad media (0,49 a 0,69) y relación señal-ruido (11 ,72 a 33,64), fueron altos para las series dendrocronológicas generadas. Los parámetros estadísticos indican que Pinus pinceana es climáticamente sensible, además muestra un comportamiento similar a otras coníferas del norte de México empleadas en análisis dendrocronológicos previos. Con base en el análisis de función de respuesta (programa ARSTAN), se determinó que las poblaciones del noreste y centro-norte responden de manera significativa al periodo común de precipitación estacional enero-julio (estaciones invierno-primavera). Las poblaciones del centro no mostraron una respuesta significativa a la precipitación. La identificación de anillos con crecimiento reducido fue clave para encontrar patrones de crecimiento y realizar el fechado cruzado, básico para la generación de índices dendrocronológicos.

Understanding the effects of climate on the growth of trees is important to project the response of forests to climate change. Dendrochronological analysis offers a “proxy” source for the effects of climatic variation on tree growth at different spatial and temporal scales. To examine influences of temperature and precipitation on radial growth of Pinus pseudostrobus and Abies religiosa, this study combines measurements of radial growth patterns of forest trees in the Monarch Butterfly Biosphere Reserve (MBBR) in central Mexico with temperature and precipitation variables from instrumental records. Dendrochronological samples were collected as cross sections and increment cores by using a chainsaw and increment borers, respectively. Total ring-width chronologies were developed for each site. Principal component analyses (PCA) were used to identify common temperature, precipitation and tree growth variation patterns. Correlation and response function analyses between chronologies and records of temperature and precipitation were used to evaluate the relation of climate variables on tree growth. The months during which tree growth was most strongly affected by precipitation were January, February and October from the previous year; only the temperature of September from the previous year affected the tree growth. In some chronologies, May’s average monthly maximum temperature was negatively correlated with tree growth. PCA and a comparison of PCA factor scores of climatic variables and chronologies showed no significant differences between northern, central or southern portions of the MBBR. Apparently, tree growth in the MBBR is reduced in years of low January–May precipitation combined with high summer (September of the previous year) temperatures, a scenario which is likely to occur as a consequence of global climate change.

During the Medieval Climate Anomaly (MCA), Western North America experienced episodes of intense aridity that persisted for multiple decades or longer. These megadroughts are well documented in many proxy records, but the causal mechanisms are poorly understood. General circulation models (GCMs) simulate megadroughts, but do not reproduce the temporal clustering of events during the MCA, suggesting they are not caused by the time history of volcanic or solar forcing. Instead, GCMs generate megadroughts through (1) internal atmospheric variability, (2) sea-surface temperatures, and (3) land surface and dust aerosol feedbacks. While no hypothesis has been definitively rejected, and no GCM has accurately reproduced all features (e.g., timing, duration, and extent) of any specific megadrought, their persistence suggests a role for processes that impart memory to the climate system (land surface and ocean dynamics). Over the 21st century, GCMs project an increase in the risk of megadrought occurrence through greenhouse gas forced reductions in precipitation and increases in evaporative demand. This drying is robust across models and multiple drought indicators, but major uncertainties still need to be resolved. These include the potential moderation of vegetation evaporative losses at higher atmospheric [CO2], variations in land surface model complexity, and decadal to multidecadal modes of natural climate variability that could delay or advance onset of aridification over the the next several decades. Because future droughts will arise from both natural variability and greenhouse gas forced trends in hydroclimate, improving our understanding of the natural drivers of persistent multidecadal megadroughts should be a major research priority.

Cofre de Perote National Park (CPNP) in Veracruz, Mexico is part of the Transmexican Volcanic Belt, and its Pinus hartwegii forests reflect a balance between the various natural factors that represent the region's climatology and hydrology. Like many other areas in this region, the historical fire regimes of these forests and their relationship with climate are unknown, but are needed for sustainable management plans. The main objectives of this study were to reconstruct the historical fire regime in a Pinus hartwegii forest and decipher the influenced of climate. Our investigation focused in two study areas, Valle la Teta (VT) and Barranca Honda (BH). The VT study area was divided into three sites based on humidity and elevation: 1) Humid (VTH), 2) Dry Low (VTDL) and 3) Dry High (VTDH). The approximated area for each site was ​​30, 30, 35 and 50 ha, for VTH, VTDL, VTDH and BH, respectively. We collected 162 fire scarred samples to reconstruct the fire history for the last 550 years (1461−2013). The fire scarred samples contained 1240 fire scars, with most fires occurring in spring (95 %) or summer (5%). Prior to 1973, these sites were characterized by a frequent surface fire regime. In all four sites, the mean fire intervals ranged from 5 to 6 years (for fires that scarred ≥ 10 % of the samples) and 13–23 years (for fires that scarred ≥ 25 % of the samples). Extensive fires (≥ 10 %) coincided with significantly dry conditions based on the Standardized Precipitation Index (SPI), influenced by El Nino Southern Oscillation (ENSO) and the Pacific Decadal Oscillation Index (PDO). We also found a significant relationship between fire occurrence and ENSO, both in its warm phase, El Nino (21 fires ≥ 10 %) and in its cold phase, La Nina (32 fires ≥ 10 %). Synchronization of the cold phase of ENSO (La Nina) with the cold phase of the PDO (negative), facilitated severe drought conditions, resulting in fires with the greatest spatial extent. Since 1973, extensive fires have been absent from the study area most likely due to anthropogenic activities including active fire suppression. These results show a strong climate-fire relationship in these high elevation forests. The lack of fire in the last four decades is concerning and could potentially lead to unnatural stand-replacing fires, unless the historical fire regime is restored to maintain natural processes and increase forest resilience.

Este estudio analizo la respuesta climatica, potencial endrocronologico e influencia de fenomenos oceanoatmosfericos en anillos de crecimiento de Pinus hartwegii Lindl. en 3 sitios de la Faja Volcanica Transmexicana. Se recolectaron de 36 a 40 nucleos de crecimiento por sitio. Las muestras se analizaron y fecharon mediante tecnicas dendrocronologicas. La anchura de anillo total se midio en un micrometro. La verificacion del fechado se efectuo mediante analisis de correlacion. Se descargaron los registros de estaciones meteorologicas cercanas a los sitios de estudio de la base de datos CLICOM, se identificaron periodos de respuesta clima-crecimiento radial y se realizaron correlaciones entre las cronologias de arstan y los indices de ENOS, ODP y OMA, con el fin evaluar la influencia de dichos fenomenos en el crecimiento radial. El analisis de los parametros dendrocronologicos indico un potencial dendrocronologico de P. hartwegii de intermedio a alto. La sensibilidad climatica mayor de la especie se registro en el Nevado de Colima. La precipitacion invierno-primavera fue la variable que influyo mas sobre el crecimiento, mientras que la temperatura maxima promedio afecto negativamente el crecimiento. ENOS y OMA no influyeron el crecimiento. Sin embargo, en el Nevado de Colima, ODP influyo positiva y significativamente en el crecimiento.

Lava flow, pyroclastic flows and ash deposition can impair the vitality and growth of tree growing on or next to volcanoes, and sometimes even remove entire forest stands. In the case that trees are only injured, but not killed, past volcanic process activity can be analyzed through the growth disturbances left in the tree-ring records. We investigated disturbances in growth ring series of Pinus hartwegii trees associated with a pyroclastic flow that covered portions of the northern flank of Popocatepetl volcano on 22 January 2001. In addition, we also documented the post-eruptive colonization of trees on the resulting deposit. The pyroclastic flow burned and killed at least 190 trees and locally shifted the timberline downslope by ~40 m in elevation. A large number of trees were injured to show noticeable fire scars. We analyzed and characterize the damage in flow-surviving trees. Sixteen years after the event, whorl counts on 244 P. hartwegii shoots growing on the surface of the pyroclastic flow deposit showed average ages of 8 yr (this is the age at ~1.4 m height). The ecesis interval or Germination Lag Time (GLT) of trees on the pyroclastic flow deposit was 7 yrs (±2 yr), and the Colonization Time Gap (CTG) was 15 yrs on average (CTG is the sum of GLT and the interval between seedling germination and growth at ~1.4 m height), with local differences related to altitude and/or location on the bare surface. Results obtained at this site can be used to date and to identify the extent of pyroclastic flow deposits on active volcanoes, thereby providing valuable information on the volcanic history (in terms of frequency and runout distances) and therefore also for hazard prevention plans. In addition, it can be useful to calibrate the minimum ages of volcanic landforms.

Under climate warming the presence of key microsite facilitators modify soil moisture levels associated with successful tree recruitment at the treeline ecotone ofPinus hartwegii. Alpine treelines in Mexico are represented by high-elevation forests dominated by P. hartwegii Ldl. To address the degree to which the presence of suitable microsite facilitators are factors for successful recruitment within the treeline ecotone of P. hartwegii and modulate their responses to climate warming, year of natural tree establishment, number of trees recruited, and the presence of shelter elements at different exposures of Monte Tlaloc (in the Trans-Mexican Volcanic System) were recorded. For tree recruitment and microsite facilitation we recorded each tree and the type of potentially protective elements that may improve microsite conditions within a total of 32 circular plots (r = 18 m) in the alpine treeline ecotone (above 4000 m). Temperatures for Monte Tlaloc at 4000 m were estimated using the thermal gradient for the study area, and standard dendrochronological methods and a regression model were used to date tree recruitment. Vector generalized linear models show that maximum growing season temperatures have significantly influenced the temporal pattern of tree recruitment in this system over the past 50 years, but this influence was mediated by the presence (or absence) of specific shelter elements (shrubs, soil depressions, rocks or bare soil) within a specific treeline ecotone exposure, also shaping the spatial pattern of tree recruitment. The response of the treeline ecotone to climate warming at local scales is qualitatively modified by the presence of microscale features, requiring sufficient soil moisture to be available on the site of recruitment.

Se desarrolló una red de siete cronologías de Pinus lumholtzii en la Sierra Madre Occidental para el desarrollo de reconstrucciones históricas de precipitación estacional. Los valores de los parámetros dendrocronológicos en general fueron similares a los de series de crecimiento desarrolladas con otras coníferas en esta región: sensibilidad media (0.25 - 0.38), inter-correlación entre series (0.52 - 0.66), relación señal/ruido (1.16 - 18.51) y autocorrelación de primer orden (0.01 - 0.30). El primer componente (PC1) que incluyó las cronologías involucradas se utilizó para realizar una reconstrucción de precipitación acumulada noviembre-junio en el período común de las series (1890-2001), donde el crecimiento anual explicó más de 80% de la precipitación ocurrida en dicho período; asimismo, se utilizó la cronología residual del sitio Sauz para reconstruir la precipitación acumulada de los últimos 346 años (1668-2013), la cual detectó períodos extremadamente secos (1665-1688, 1695-1718, 1767-1778, 1890-1896, 1948-1963). La respuesta de las cronologías de esta especie a fenómenos atmosféricos de circulación general, como El Niño Oscilación del Sur (ENSO, por sus siglas en ingles), también fue similar a la obtenida con cronologías de especies con probado potencial dendroclimático. La ventaja de extender la red dendrocronológica de P. lumholtzii se fundamenta en que su potencial dendroclimático es equiparable con el de especies tradicionalmente usadas con este fin; su amplia distribución y el poco disturbio antropogénico que han sufrido sus poblaciones favorece la posibilidad de encontrar individuos longevos. Por su excelente sensibilidad climática, la red dendroclimática de P. lumholtzii es fundamental para estudios dendroclimáticos, particularmente en regiones donde se carece de registros climáticos instrumentales.

The Bosque la Primavera (BLP) is a natural preserve that provides environmental services for the metropolitan area of Guadalajara. Human activities, however, have altered its ecological stability. The objective was to analyze the interannual climate variability of dominant conifer Pinus oocarpa a climate-sensitive species. Earlywood (EWI), latewood (LWI), and ring-width (RWI) chronologies 165 years in length (1850-2014) were developed for the BLP. The residual EWI chronology had a significant association (r = 0.775, p < 0.000) with seasonal October-May rainfall from neighbor weather stations, and a negative but significant response with January-June mean maximum temperature (r = -0.622, p < 0.000). The association between EWI and precipitation was used to build a linear model to reconstruct seasonal rainfall. The most severe and prolonged drought in the reconstruction took place from 1909 to 1925, but additional dry periods were present, i.e., 1850´s, 1890´s, 1950´s, 1990´s, and 2,000´s. Most of these droughts have been observed in previous reconstructions for the region suggesting the influence of atmospheric circulatory patterns such as ENSO. The rise in maximum temperature for the last three decades in the Guadalajara metropolitan area has induced a radial growth decrease of P. oocarpa, probably triggered by an increase in greenhouse gases. Increased maximum temperatures and reduced growth of the species is threatening its ecological stability and may put in risk the provision of vital environmental services for this metropolitan area.

The occurrence of wildfire is influenced by a suite of factors ranging from “top-down” influences (e.g., climate) to “bottom-up” localized influences (e.g., ignitions, fuels, and land use). We carried out the first broad-scale assessment of wildland fire patterns in northern Mexico to assess the relative influence of top-down and bottom-up drivers of fire in a region where frequent fire regimes continued well into the 20th century. Using a network of 67 sites, we assessed (1) fire synchrony and the scales at which synchrony is evident, (2) climate drivers of fire, and (3) asynchrony in fire regime changes. We found high fire synchrony across northern Mexico between 1750 and 2008, with synchrony highest at distances oscillations, especially El Niño-Southern Oscillation, were important drivers of fire synchrony. However, bottom-up factors modified fire occurrence at smaller spatial scales, with variable local influence on the timing of abrupt, unusually long fire-free periods starting between 1887 and 1979 CE. Thirty sites lacked these fire-free periods. In contrast to the neighboring southwestern United States, many ecosystems in northern Mexico maintain frequent fire regimes and intact fire–climate relationships that are useful in understanding climate influences on disturbance across scales of space and time.

Dendrochronological studies are limited in tropical regions because not many tree species form annual growth rings. This work reports an evaluation of the dendrochronological potential of tropical ash (Fraxinus uhdei) and its use as a bioindicator of fossil CO2 concentration in urban areas by means of radiocarbon analysis on growth rings. We analyzed a cross-section of a tree that grew during the period 1932–2007 in San Luis Potosí, one of the most industrialized cities in Mexico. The Δ14C values obtained follow the same variation pattern as the calibration curve of the Northern Hemisphere (NH) zone 2 (Hua and Barbetti 2004), with the peak centered in 1964, but they are lower by up to 124′. The high correlation coefficient (r = 0.990, p < 0.001) between the variation patterns indicates that this species does form annual growth rings, and the lower values can be attributed to the 14C dilution caused by fossil CO2 emissions. The magnitude of the Suess effect varied between −6.9% and −0.5%, equivalent to fossil CO2 concentrations ranging between 21.9 and 1.5 ppmv. The Suess effect and fossil CO2 values have significant variations with no apparent monotone increasing trend, suggesting that the CO2 emissions during the studied period have diverse sources. It is concluded that F. uhdei has potential for dendrochronological studies in tropical areas because its growth rings are formed annually and, furthermore, it can be used as a bioindicator of atmospheric 14C variations and fossil CO2 concentration in urban areas.

La cuenca alta de la región hidrológica Presido San Pedro genera el agua de uno de los afluentes de Marismas Nacionales en el área limítrofe entre los estados de Sinaloa y Nayarit. En esta cuenca Pinus durangensis es una conífera dominante, pero debido a su explotación intensiva quedan pocos rodales remanentes sin disturbio. Para analizar el potencial dendrocronológico de la especie, se colectaron núcleos de crecimiento de 63 árboles, que se procesaron con técnicas dendrocronológicas convencionales. La inter-correlación ente series (0.463), sensibilidad media (0.309), autocorrelación de primer orden (0.41) y relación señal-ruido (5.24), entre otros parámetros estadísticos indicaron excelente potencial de la especie para estudios dendrocronológicos. Se generaron series de tiempo de madera temprana, tardía y de anillo total que se extendió de 1780 a 2012 (232 años). Los índices de madera temprana, respondieron a la precipitación acumulada promedio del período enero-agosto, procedente de cuatro estaciones climáticas circunvecinas al sitio, por lo que se generó un modelo lineal, para una reconstrucción de lluvia invierno a inicios de verano. La variabilidad hidroclimática detectada fue similar a otras desarrolladas previamente para la región hidrológica Presidio San Pedro, donde El Niño Oscilación del Sur (ENSO) es el fenómeno circulatorio que determina la variación interanual y multianual en la precipitación invernal. No se encontró una relación significativa entre la precipitación de verano y los índices de madera tardía, lo que supone poca variación interanual del Monzón de Norteamérica, no obstante ser causante de 70% de la precipitación anual en esta región hidrológica.

El bosque de Pinus hartwegii en el ejido Rinconada, municipio de Chignahuapan, representa la region de mayor incidencia de incendios forestales en el estado de Puebla. Con el objetivo de reconstruir la historia del fuego y determinar su asociacion historica con el clima, se tomaron 43 muestras con cicatrices de incendios y se analizaron con base en tecnicas dendrocronologicas; de 40 muestras, se lograron datar 235 cicatrices de incendios. Se reconstruyo la historia del fuego para el periodo 1876-2011 (136 anos). El 91,7 % de los incendios se registro en la estacion de primavera y el 8,3 % en verano. El intervalo medio de incendios (MFI, por sus siglas en ingles) y el intervalo de la mediana de probabilidad de Weibull (WMPI, por sus siglas en ingles) al considerar todas las cicatrices fue de 5,6 y 5,0 anos, respectivamente; mientras que para los incendios mas grandes o extensos cuyas cicatrices se registraron en el 25 % de las muestras o mas, los valores de MFI y WMPI fueron de 9,2 y 8,5 anos, respectivamente. La presencia de incendios fue continua hasta la primera decada del siglo XXI; sin embargo, posterior a 1988 se observo una disminucion en su frecuencia. Se determino una relacion positiva entre la disminucion de la precipitacion (sequia) y la ocurrencia de incendios. De igual manera, valores negativos de NINO 3 y PDSI, asociados a condiciones de sequia, han influido positivamente en la modulacion de la frecuencia historica de incendios en esta region del centro de Mexico.

Se desarrolló una cronología de anillo anual de 264 años (1750 a 2013) con 33 series derivadas de 50 especímenes de Juniperus monticola Martínez (enebro, cedro blanco) del Monte Tláloc, en un intervalo altitudinal de 3980 a 4060 m. A pesar de la irregularidad de las secciones transversales y de la variabilidad en el ancho del anillo anual, los parámetros dendrocronológicos de COFECHA y ARSTAN como sensibilidad media (0.41), inter-correlación entre series (0.55) y relación señal-ruido (1.24) indicaron que la especie es viable para estudios dendrocronológicos. La correlación de la serie cronológica con la temperatura media anual fue estadísticamente significativa (r = 0.45, n = 54, P < 0.01), y también se encontró una correlación significativa (P < 0.01) con series fechadas de Pinus hartwegii de los volcanes Iztaccíhuatl y Pico de Orizaba, lo que confirma su potencial dendrocronológico. Asimismo, se obtuvieron correlaciones significativas con índices SOI (r = -0.27, P < 0.01, n = 113) y con el PDSI reconstruido para junio en el centro de México (r = 0.25, P < 0.01, n = 109), lo que es una prueba de la factibilidad para interpretar fenómenos climáticos a partir de anillos de enebro en altitudes elevadas (> 3500 msnm) del centro de México. Para la especie estudiada la temperatura media fue la variable más correlacionada con su crecimiento radial. Los años intensos de El Niño, que producen sequías severas en el centro de México, se asociaron con mayores incrementos radiales. El enebro es idóneo para realizar estudios de la influencia de este fenómeno y para comprender la variabilidad climática histórica de alta y baja frecuencia.

El análisis espacial del paisaje, con técnicas de Percepción Remota (PR) y herramientas de Sistemas de Información Geográfica (SIG), es un procedimiento poco usado en la identificación de sitios potencialmente idóneos para el muestreo dendrocronológico. En el presente trabajo se diseñó un protocolo para identificar áreas con árboles climáticamente sensibles, empleando un análisis espacial de variables biofísicas. El diseño consistió en el análisis de la pendiente del terreno, la orientación de laderas y la distribución de Cobertura Vegetal y Uso de Suelo (CVUS), mediante el uso de técnicas de PR y herramientas de SIG. El protocolo se validó mediante un muestreo dendrocronológico en dos sitios adyacentes. Los análisis estadísticos del ancho de anillos de crecimiento se realizaron mediante los programas COFECHA y dplR. Los resultados indicaron que 18% de la Reserva de la Biosfera Mariposa Monarca presenta características aptas para colectar muestras dendrocronológicas sensibles a variación climática. Los análisis estadísticos indican que existen diferencias entre los dos sitios en edad de árboles, diámetro y ancho de los anillos. La propuesta del diseño de muestreo permitió ubicar sitios con árboles longevos y sensibles, lo que se traduce en alta variación interanual en el ancho de anillos. El análisis espacial de variables biofísicas previas al muestreo dendrocronológico, contribuye a la identificación de sitios con árboles sensibles y a eliminar menos muestras. El protocolo propuesto es eficiente y puede ser replicable en otras áreas.

La Sierra de Zapalinamé (SZA) es la fuente de agua más importante para Saltillo, Coahuila y poblaciones aledañas. La presión sobre los recursos hídricos debido al incremento poblacional, demanda un conocimiento detallado de su variabilidad hidroclimática histórica con fines de planeación. En este trabajo, se integraron tres series dendrocronológicas regionales a lo largo del gradiente altitudinal de SZA, con una extensión de 412 años (1595-2006), 306 años (1700-2005) y 603 años (1400-2002), para la parte baja, media y alta, respectivamente. La cronología de la parte baja, desarrollada con Pinus cembroides fue más sensible a periodos secos. Sequías de gran magnitud e intensidad se presentaron en todo el gradiente altitudinal en las décadas de 1440 y 1450; 1530, 1590, 1640 , 1660, 1690, 1710, 1740, 1750, 1760, 1790, 1860, 1890, 1920, 1950 y 2000, con impacto en la disponibilidad de alimentos y presencia de epidemias y hambrunas generalizadas a nivel local y regional. Eventos secos de alta intensidad se presentaron en periodos aproximados de 100 años, con sequías intermedias cada 50 años. El impacto histórico de patrones atmosféricos circulatorios como ENSO, no indicó una influencia significativa en la variabilidad hidroclimática de SZA y el efecto de otros fenómenos atmosféricos (frentes fríos, huracanes, tormentas tropicales), pudieran explicar con mayor detalle el comportamiento climático de esta montaña.

Earlywood, latewood, and total ring width series from Pseudotsuga menziesii were developed in a mixed conifer forest at Cerro El Mohinora”, Chihuahua. The tree-ring series extended for the period 1657-2005 (349 years) and were used to analyze hydroclimatic variability for southwestern Chihuahua. A seasonal winter-spring precipitation reconstruction was developed with the objective to determine high and low frequency precipitation variability and to analyze the impact of dominant atmospheric circulatory patterns. The reconstruction indicated high interannual, decadal and multiannual variability. Severe droughts were reconstructed for the periods 1695-1715, 1753-1760, 1785-1792, 1798-1806, 1819-1830, 1841-1870, 1890-1897, 1906-1912, 1924-1941, 1971-1977, and 1994-2005. The most extended droughts took place in the periods 1695-1715, 1841-1870, and 1924-1941. The last three decades of the 20th century and the current years of the 21st century have been particularly dry for northwestern Chihuahua but the ecological and socieoconomical impacts have not been determined.

The radiocarbon variation for northwestern Mexico during the period 1950–2004 was studied by accelerator mass spectrometry (AMS) and liquid scintillation counting (LSC) analyses of tree rings. Two tree-ring sequences of Pseudotsuga menziesii, sampled in a site isolated from urban centers and active volcanoes (26.18°N, 106.3°W, 3000 m asl), were dendrochronologically dated and separated in annual rings prior to 14C analysis. Results obtained show a similar profile to the values reported for the Northern Hemisphere (NH), having significant correlation coefficients with the compilation curves for NH zone 2 (r = 0.987, p < 0.001) and NH zone 3 (r = 0.993, p < 0.001). The maximum peak is centered at 1964.5 with a δ14C value of 713.15 ± 9.3‰. The values obtained for the period 1958–1965 are lower than zone 2 values and higher than zone 3 values. For the period 1975–2004, the values obtained are higher than the NH compilation curve and other NH records. We attribute the first divergence to the North American monsoon that may have carried 14C-depleted air from the south during the summer months; the second divergence may be attributable to 14C-enriched biospheric CO2.