RING POROSITY AND EARLYWOOD VESSELS: A REVIEW ON EXTRACTING ENVIRONMENTAL INFORMATION THROUGH TIME
Many anatomical features in trees result from their reaction to fluctuating environmental conditions, and some can be measured and dated. Recently, quantitative wood anatomy has been used to build time series, and consequently to study the responses of trees through time. This involves the application of dendrochronological techniques, although some methodological adaptations are necessary when using anatomical variables. Until now, the study of continuous anatomical series has proven to be very promising when applied to the earlywood vessels of ring porous trees, due to their great physiological relevance.In this paper, we review the main aspects that must be considered when building continuous series of earlywood vessel features of ring porous trees as compared to 'classical' dendrochronology. We first discuss the procedures for building individual series and chronologies, starting with the selection of variables, examining their statistical properties, and assessing how crossdating and detrending should be adapted. We also show that time series of earlywood vessels usually exhibit a low common signal, but in contrast are strongly related to climate, and often reveal responses not recorded by the classical dendrochronological variables.In addition, we deal with the optimization of environmental signals, by first evaluating multiple potential variables to be used, and indicate how to reduce their number according to the relations among them. As earlywood variables are basically determined by vessel number or vessel size, we discuss the search for the most appropriate variable to characterize vessel number, as well as the advantage of progressively selecting earlywood vessels attending to their size and position.Finally, we extend the application of these methodologies to diffuse porous species as compared to ring porous trees, and show that the climatic signal contained in their anatomical features is also relevant, provided that vessels are carefully selected upon their location within the ring.