Understanding how trees respond to extreme events is important to predict how climate change will impact forests in the future. In this study, we report changes in radial growth and tree-ring carbon (δ 13 C) and oxygen (δ 18 O) stable isotope ratios of Pseudotsuga menziesii (Douglas-fir) in western Mexico. Tree growth was compared with δ 13 C and δ 18 O ratios recorded during dry and wet periods caused by El Niño-Southern Oscillation since 1850. The three driest and three wettest events during the studied period caused tree growth decline of up to 50% followed by 6-10 years of slow recovery until baseline growth was regained. Wet events resulted in up to 17% growth increase, a positive effect that persisted for no more than 3-5 years. Stable isotope ratios recorded physiological adjustments that in some cases correlated significantly with tree growth. Excursions in tree-ring Δ 13 C and δ 18 O isotope ratios suggest that trees cope with dry and wet periods with proportional but divergent adjustments in photosynthesis versus stomatal conductance. Notably, the intrinsic water-use efficiency-that is, the ratio between carbon assimilation and water loss through transpiration-was positively correlated with tree basal growth only during dry periods. We found no significant correlations between growth and intrinsic water-use efficiency during wet periods. Contrary to expectations, rising CO 2 levels over the past~160 years did not affect tree growth response to precipitation variability.

Basal area increment series of dominant trees oftrunk section allow the analysis of tree growth trajectories. In this study, we used direct measurements of basal area increment (BAI) to explain biological periodicity and forecast basal area growth of Douglas-fir growing in Western Mexico. To remove the age effect on tree growth we also ran the analysis in terms of cambial age. Results showed significant (P < 0.05) correlation between BAI and precipitation from January to July. We found periodicities in tree growth of 7, 21, 27 and 60 years.However, the 60-year period, was determinant to build an ARIMA model (0,1,1), to forecast BAI for the next decades. Tree growth projections suggest reduced BAI in mature dominant trees for the next decades. Decreased tree-growth is an unexpected result, as BAI in dominant trees remains constant up to the biological age. Our finding is concurrent with a general decrement in tree growth in other forests of the world due to water stress, which suggests that the future climatic variability may worsen health conditions of Douglas-fir forests in North Mexico. ResumenL as 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.Received: October 21, 2015 / Accepted: July 20, 2016. Palabras clave:Dendrocronología, anillos de crecimiento, productividad forestal, bosques templados, análisis de series de tiempo.

Introducción: En Estados Unidos de América, las plagas forestales se asocian a la variabilidad climática. Este tipo de estudios son escasos en México. Objetivos: Generar una base de datos de brotes históricos de descortezadores y analizar su relación con la sequía. Materiales y métodos: Se obtuvieron registros históricos de brotes de descortezadores de documentos oficiales en México, Guatemala, y Honduras. Como proxy del clima se emplearon índices dendroclimáticos. La relación entre los brotes de plagas y el clima se analizó con el programa Superpose Epoch Analysis (SEA). Resultados y discusión: Se generó una base de datos de brotes de descortezadores de 120 años (1895-2015), siendo las especies más frecuentes Dendroctonus mexicanus Hopkins, Dendroctonus frontalis Zimmermann y Dendroctonus adjunctus Blandford. Se documentaron 106 registros de brotes en 15 estados de la México en el periodo 1903-2015; 16 brotes en Guatemala durante el periodo 1895-2013, y 15 brotes en Honduras en el periodo 1962-2015. Históricamente, los brotes se registraron en años con precipitación por debajo de la media (550 mm) e incrementaron a partir de 1970. El SEA determinó que los brotes en México, Guatemala y Honduras se registraron durante años secos (P < 0.05) con valores positivos no significativos (P > 0.05) de NIÑO 3 y PDSI (Palmer Drought Severity Index) e índices negativos significativos (P < 0.01) de NIÑO 3 y PDSI en el año previo al brote, condiciones que implican intensa sequía. Conclusión: Para los últimos 120 años se determinó una relación significativa entre brotes de descortezadores y condiciones de sequía.

The resilience of forests to drought events has become a major natural resource sustainability concern, especially in response to climate change. Yet, little is known about the legacy effects of repeated droughts, and tree species ability to respond across environmental gradients. In this study, we used a tree‐ring database (121 sites) to evaluate the overall resilience of tree species to drought events in the last century. We investigated how climate and geography affected the response at the species level. We evaluated temporal trends of resilience using a predictive mixed linear modeling approach. We found that pointer years (e.g., tree growth reduction) occurred during 11.3% of the 20th century, with an average decrease in tree growth of 66% compared to the previous period. The occurrence of pointer years was associated with negative values of the Standardized Precipitation Index (SPI, 81.6%) and Palmer Drought Severity Index (PDSI, 77.3%). Tree species differed in their resilience capacity, however, species inhabiting xeric conditions were less resistant but with higher recovery rates (e.g., Abies concolor, Pinus lambertiana, and Pinus jeffreyi). On average, tree species needed 2.7 years to recover from drought events, with extreme cases requiring more than a decade to reach pre‐drought tree growth rates. The main abiotic factor related to resilience was precipitation, confirming that some tree species are better adapted to resist the effects of droughts. We found a temporal variation for all tree resilience indices (scaled to 100), with a decreasing resistance (−0.56 by decade) and resilience (−0.22 by decade), but with a higher recovery (+1.72 by decade) and relative resilience rate (+0.33 by decade). Our results emphasize the importance of time series of forest resilience, particularly by distinguishing the species‐level response in the context of legacy of droughts, which are likely to become more frequent and intense under a changing climate.

Under the current climate crisis, the ecological integrity of forest ecosystems is key to increasing resilience and the sustainability of water and soil resources. Most forests around the world have experienced deforestation and degradation in the past few decades; however, the rate at which these occur varies depending on many factors, including the type of trees, management, and climate. We conducted a review of the deforestation, degradation, and soil erosion of the pine-oak forest within the Rio Conchos basin in northern Mexico. Preference was given to recent studies (last 10 years) conducted within this basin. Out of 27 recent publications on oak forests in Mexico, 19 focused on this forest and half of them were in Spanish. The results show that pine trees are more affected than oak trees, also that the deforestation rate has increased with time and is greater at higher elevations, making this area vulnerable to loss of topsoil during extreme hydrological events. Studies report an annual change in cover rate between 1985 and 2016 of −1.2% for pine, oak and mix vegetation. More recently, between 2000 and 2018, the change in pine cover was calculated as −2.8% concurrent with a +3.4% increase in cover of oak and other secondary vegetation. Proposed conservation strategies vary from runoff control to increased collaboration between landowners, government agencies, and stakeholders.