Search Results (3)

Extreme drought events reduce the productivity of forest ecosystems. One approach for estimating the effects of drought on forests is by assessing their resilience. The objective of this study was to estimate resilience rates at different heights along the tree stem of Pinus durangensis Martínez. The radial growth of 200 cross sections extracted at four heights of tree stems (0.07–0.15, 1.3, 6.3, and 11.0–12.0 m) was analyzed and subsequently transformed into ring-width indices (RWI). These indices were correlated with the Standardized Precipitation-Evapotranspiration Index on a six-month time scale (accumulated drought of six months in the period February–May; SPEI06_FM). Seven extreme drought events were identified (1890, 1902, 1956, 1974, 1999, 2006, 2011), and radial growth before, during, and after each event was determined. Based on ring-width index values, resistance, recovery, and resilience indices were calculated. The results indicated a significant correlation (p ≤ 0.05) between annual radial increment and climate indices along the stem (0.56 to 0.80). Climatic sensitivity was higher in the lower part of the stem, with mean sensitivity (MS) and expressed population signal (EPS) values of 0.38 and 0.97, respectively. Resistance index values ranged from 0.44 to 0.76 and were better expressed in higher sections of the stem. Resilience indices changed over time. Regardless of the height of the tree stem, the latest extreme drought events (1999, 2006, and 2011) have led to a lower resilience of trees, indicating that their recovery capacity has decreased. Therefore, forestry practices in the study area may consider managing tree density as a strategy to regulate the stress in competition and to increase the tolerance of trees to drought. Full article

In recent decades, droughts associated with climate change have increased in frequency and intensity. Given this trend, the understanding of climate variability over time has raised great interest. The main objective of this study was to reconstruct the standardized precipitation-evapotranspiration index (SPEI) from tree rings of Pinus durangensis Martinez at a representative site in the western region of the Durango State, Mexico. To this end, we used radii of 286 cross-sections, which were processed through conventional dendrochronological techniques. In addition, chronologies of total ring and early and latewood were generated, covering 296 years. In parallel, we analyzed the association between the chronologies obtained and the cumulative SPEI for 3, 6, 9, and 12 months. The earlywood residual chronology (EWres) showed the closest association with the six-month cumulative SPEI for February–May (SPEI6_FM). Thus, the SPEI6_FM for the past 296 years was reconstructed through a simple linear regression model. In this reconstruction, 18% of the years were wet, 16% dry, and 66% average. In addition, an increase in the frequency of droughts was observed from 1880 onwards, which might have been related to the rise in temperature due to climate warming. Therefore, the annual rings of P. durangensis are suitable for use as a proxy for the reconstruction of historical climatic events in this region of northern Mexico. Full article

The existence of endangered tree species in Mexico necessitates an understanding of their vulnerability to the predicted climate changes (warming and drying trends). In this study, the sensitivity to climate of earlywood (EW) and latewood (LW) widths of the threatened Picea chihuahuana was determined. The response of EW and LW to climate variables (maximum temperature, minimum temperature, precipitation, evaporation, and a drought index) was analyzed by means of correlation analysis using dendrochronology over the period of 1950–2015. EW and LW production were enhanced by cool and wet conditions during winter prior to the start of growing season. During the growing season, EW and LW production increased in response to cool spring and summer conditions, respectively; temperatures and year-round evaporation, excluding summer and the previous drought in the period prior to the growing season. EW was sensitive to seasonal drought, which is a concern considering the predicted aridification trends for the study area. These results provide further knowledge on the dendroecological potential of Picea chihuahuana. Full article