Douglas-fir radial growth in interior British Columbia can be linked to long-term oscillations in Pacific and Atlantic sea surface temperatures

A major problem in modern dendrochronology is that the methods traditionally used for linking tree ring growth data to climate records are not well suited to reconstructing low-frequency climatic variations. In this study, we explored the alternative Ensemble Empirical Mode Decomposition to detrend tree-ring records and to extract climate signals without removing low-frequency information. Tree cores of Pseudotsuga menziesii var. glauca (Mayr.) Franco were examined in a semi-arid forest in southern interior British Columbia, western Canada. Ring width data were decomposed into five oscillatory components (intrinsic mode functions, IMFs) of increasingly longer periodicities. IMF 1 was considered white noise, IMF 2 was used to create the first diameter growth index (DGI-1), IMF 3 and IMF 4 were combined to create the second diameter growth index (DGI-2), whereas IMF 5 and the residual term together were considered as the trend term. The highest significant cross-correlations between DGI-1 and the NAOAugust, NIÑO12May, and PDOJanuary indices were found at 1-year lags. DGI-2 had positive and persistent correlations with NAOJune and PDOMay at 0 to 3 years lags, and with NAOMay at 2 and 3 years lags. Our results indicate that periods of slow growth in the tree ring record matched periods of drought in the North American Pacific Northwest. Such water limiting conditions are likely caused by oscillatory patterns in the Pacific Ocean sea surface temperatures that influence precipitation in the Pacific Northwest. These drought events are likely exacerbated by changes in winter precipitation (snowpack) related to oscillations of the Atlantic Ocean sea surface temperatures, highlighting the ecological effects of both oceans on terrestrial ecosystems. Such relationships could not be easily found by traditional tree-ring analysis that remove some of the low-frequency signal, and therefore we suggest Ensemble Empirical Mode Decomposition as an additional tool to establishing tree growth-climate relationships.Juan A. Blanco was supported by grants from the Spanish Ministry of Economy and Competitiveness (AGL2012-33465), a Marie Curie Action fellowship from the European Commission (CIG-2012-326718-ECOPYREN3), and a Campus Iberus grant for mobility of research staff

Possible Impacts of Climate Change on Potential Tree Plant Forms of a Mountain Region in Central Taiwan

this study we used Box’s model, which is based on the equilibrium relationships between macroclimate and plant forms, to assess the possible impacts of climate change on the potential tree plant forms of a mountain region in central Taiwan. To account for the effects of uncertainty associated with the projected climatic conditions on the model’s predictions, a Monte Carlo study was also carried out. For the temperature variables in the model, they varied between 0 and 5°C above the long-term average; for the precipitation related variables, the projected precipitation varied between ±30% of the long-term average. The responses of tree plant forms to temperature increases could be divided into three categories: (1) those that would not be influenced, (2) those that could disappear gradually, including summergreen tree species, which are more sensitive to temperature and require a lower temperature to exist, and (3) those that could appear gradually, including tropical tree species. Under the projected precipitation conditions, most of the tree plant forms currently present would not be influenced, except for rainforest and raingreen tree plant forms. The necessary data for Box’s model could be obtained easily from usual climatic databases, and the results have a higher resolution than Holdridge Life Zone model. When detailed information necessary to run high-resolution models is not available, the approach used in this study could be used as an alternative

Ensemble Empirical Mode Decomposition as an Alternative for Tree-Ring Chronology Development

Since its establishment, tree-ring analysis has benefitted several scientific fields. Because of its many advantages, dendrochronology is a first choice to reconstruct past environmental variability. Two major concerns about the current tree-ring reconstruction paradigm are the subjective choices of detrending functions and the lack of fidelity to data of chronology generation methods. It is difficult to recover the original tree-ring data once they have been detrended and standardized. In this study, ensemble empirical mode decomposition (EEMD) is introduced as an objective high-fidelity stand-alone approach for developing tree-ring chronologies. Basic concepts of EEMD, recommended steps in developing chronologies, and available public domain programs are discussed. To demonstrate the potentials of EEMD for chronology development, two examples are provided, one for climate and the other for streamflow reconstructions. In both examples, EEMD chronologies show higher correlations with the instrumental data and have more power in their spectra than the ones developed based on the current tree-ring reconstruction approach. General usage concerns and cautions are also addressed.This item is part of the Tree-Ring Research (formerly Tree-Ring Bulletin) archive. For more information about this peer-reviewed scholarly journal, please email the Editor of Tree-Ring Research at [email protected]