Discrete versus continuous analysis of anatomical and δ13C variability in tree rings with intra-annual density fluctuations

Abstract

Intra-annual density fluctuations (IADFs) are anomalies of tree rings where wood density is abruptly altered after sudden changes in environmental conditions. Their characterisation can provide information about the relationship between environmental factors and eco-physiological processes during tree growth. This paper reports about the variability of anatomical traits and stable carbon isotopic composition along tree rings as resulting from the application of two different methodological approaches: (a) the separation of each ring into different regions (earlywood, latewood and IADF) and the comparison of anatomical and isotopic parameters measured in those specific sectors and (b) the analysis of such features in continuum along ring width. Moreover, different parameters of vessels (i.e. ecd-equivalent circle diameter, elongation, sphericity and convexity of vessel lumen) were considered to identify those more appropriate for the representation of intra-annual anatomical variations. The analysis was conducted on Arbutus unedo L. growing on the Elba Island (Italy); tree rings of this species form IADFs with features clearly responsive to the environmental conditions experienced during plant growth. Results showed that the first approach, although more suitable to obtain data for subsequent statistical comparisons and for the calculation of correlations with environmental parameters, suffers from elements of subjectivity due to the size and position of the selected tree-ring regions. The in continuum method allows a clearer identification of the variation of tree-ring properties along ring width. Regarding anatomical parameters, shape indexes were not suitable indicators of intra-annual variability. The overall analysis suggested that using both methodologies in synergy helps to gain complete information and avoid misleading interpretations of IADFs in tree rings.

Cambial activity of Pinus elliottii var. densa reveals influence of seasonal insolation on growth dynamics in the Florida Keys

“…In all four trees, which had similar growth dynamics, IADFs occurred between July and August. The relationship between IADFs and climate has been studied in various temperate species (e.g., Wimmer et al 2000;Rigling et al 2001Rigling et al , 2002Masiokas and Villalba 2004;) and Mediterranean species (e.g., Cherubini et al 2003;De Micco and Aronne 2009;Copenheaver et al 2010;Campelo et al 2006Campelo et al , 2007de Luis et al 2011;Battipaglia et al 2010), and the ecophysiological processes responsible for their formation can be difficult to interpret (De Micco et al 2011). The majority of the aforementioned studies, which defined IADFs as being thin bands of radially flattened tracheids, found drought stress to cause IADFs during the growing season.…”

“…As De Micco et al (2011) highlighted, specific and robust methodologies are necessary to avoid misleading interpretations of IADFs in tree rings. Hence, our data are not appropriate for making strong suggestions on the relationships between IADFs and climatic factors in slash pine given our study design.…”

Changes in climate-growth relationships and IADF formation over time of pine species (Pinus halepensis, P. pinaster and P. sylvestris) in Mediterranean environments

“…IADFs may appear at different positions within a tree-ring depending on the time of the year when the triggering factor occurred (Campelo et al, 2007;Edmondson, 2010;de Micco et al, 2012). IADF type E is triggered by dry periods during spring and early summer.…”

Drought impact on water use efficiency and intra‐annual density fluctuations in Erica arborea on Elba (Italy)

“…The same authors proposed to apply a novel approach for the identification of IADFs and other wood features, based on the collection of vessel size data in continuum , within the ring, in standardized transects on digital images (De Micco et al . ). This method, tested on A. unedo , seems to allow better characterization of tree‐ring formation, using the IADFs as intra‐seasonal proxies to infer climate constraints on growth.…”