Within a tree the lumen of the xylem conduits varies widely (by at least 1 order of magnitude). Transversally in the stem conduits are smaller close to the pith and larger in the outermost rings. Axially (i.e. from petioles to roots) conduits widen from the stem apex downwards in the same tree ring. This axial variation is proposed as being the most efficient anatomical adjustment for stabilizing hydraulic path-length resistance with the progressive growth in height. The hydrodynamic (i.e. physical) constraint shapes the whole xylem conduits column in a very similar way in different species and environments. Our aim is to provide experimental evidence that the axial conduit widening is an ineluctable feature of the vascular system in plants. If evolution has favoured efficient distribution networks (i.e. total resistance is tree-size independent) the axial conduit widening can be predicted downwards along the stem. Indeed, in order to compensate for the increase in path length with growth in height the conduit size should scale as a power function of tree height with an exponent higher than 0.2. Similarly, this approach could be applied in branches and roots but due to the different lengths of the path roots-leaves the patterns of axial variations of conduit size might slightly deviate from the general widening trend. Finally, we emphasize the importance of sampling standardization with respect to tree height for correctly comparing the anatomical characteristics of different individuals.
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Tommaso Anfodillo, Giai Petit and Alan Crivellaro
Fritz H. Schweingruber and Alan Crivellaro
Alan Crivellaro, Katherine McCulloh, F. Andrew Jones and Barbara Lachenbruch
Climbers and self-supporting woody plants have different constraints on their stems. Although plants of both growth forms need wood that functions mechanically and hydraulically, climbers have a lower need for mechanical self-support and an elevated need for hydraulic conductance to enable longer-distance water transport. We sampled all the woody climbers (10 species) and most of the woody subshrubs (25 species) of the island of Cyprus in the eastern part of the Mediterranean, to characterize their vessel and fiber anatomies relative to hydraulic and mechanical function. Consistent with their lower need for self-support, on average the climbers had lower wood density than did the subshrubs (0.44 g/cm3 ± 0.15 vs. 0.59 g/cm3 ± 0.20, means ± s.d.) and had a lower proportion of their cross section devoted to fibers (29% ± 11 vs. 49% ± 15). Consistent with climbers’ need for higher hydraulic conductance and total plant height, climbers had vessel sizes and frequencies closer to the theoretical packing limit than did subshrubs. Lastly, we grouped species within a growth form by site water availability (dry vs. wet site), site temperature (cold vs. hot site), site water equability (low vs. high), and xylem ring porosity (ring porous, semi-ring porous or diffuse porous). Climbers had different vessel lumen diameters or vessel frequencies for six of these eight groupings, whereas subshrubs showed no such differences, illustrating the wide variation in climber wood structure compared to the relatively conservative anatomy of the subshrubs.
Flavio Ruffinatto, Alan Crivellaro and Alex C. Wiedenhoeft
With the adoption of a number of anti-illegal logging laws, treaties, memoranda, and international agreements around the world, there is broad and renewed interest in wood identification, especially in the field at the macroscopic level. In response to this interest, and to begin to fill an obvious gap in the corpus of wood anatomical reference material, we review several prominent English-language publications on macroscopic wood identification in order to form a list of characters. We compile characters and organize them in the spirit of the IAWA lists for hardwood and softwood microscopic identification, present the state of the art as it exists, attempt to reconcile the different sets of definitions, characters, and character states, then present our proposed working-list. It is our intent with this publication to open an international discussion regarding the standardization of macroscopic wood identification features, and it is our hope that such a discussion can include critical works from the non-English literature. We also call for an illustrated glossary to accompany the proposed list. A standard lexicon to describe wood at the macroscopic level will simplify the preparation of identification documents and permit the ready translation of keys and other references for easy use and deployment around the world.
Flavio Ruffinatto, Gaetano Castro, Corrado Cremonini, Alan Crivellaro and Roberto Zanuttini
Wood identification has never been more important to serve the purpose of global forest protection, by controlling international illegal timber trade and enabling the enforcement of timber trade regulations. Macroscopic wood identification is the fastest method for the first identification of an unknown timber and, with proper training, it can be performed by operators in the timber industry, restorers and curators of cultural heritage, wood traders, designers, students and customs officers. Here we describe a wood atlas and accompanying software, SIR-Legno, developed for the identification of 48 Italian timber species based on a recently proposed list of macroscopic features for wood identification. For each species the atlas provides a complete macroscopic description plus information on natural durability, end-use class, physico-mechanical properties, conservation status, maximum diameter of the bole and most frequent uses. For each genus covered by the atlas, information about species number, CITES-listed species, main commercial timbers, similarly-named timbers from other genera, geographical distribution and notes on species or species group recognition at macroscopic and microscopic level are provided. SIR-Legno is an educational product, a handy identification key and a tool to search woods by their natural durability, end-use class and physico-mechanical properties. Both the atlas and the software can be freely downloaded from the web. Thanks to the adoption of a codified list of characters and a transferable design, SIR-Legno can be easily replicated or expanded to other databases in order to include new species. SIR-Legno is freeware and works on any version of Windows.
Martina Lazzarin, Alan Crivellaro, Cameron B. Williams, Todd E. Dawson, Giacomo Mozzi and Tommaso Anfodillo
Across land plants there is a general pattern of xylem conduit diameters widening towards the stem base thus reducing the accumulation of hydraulic resistance as plants grow taller.
In conifers, xylem conduits consist of cells with closed end-walls and water must flow through bordered pits imbedded in the side walls. As a consequence both cell size, which determines the numbers of walls that the conductive stream of water must cross, as well as the characteristics of the pits themselves, crucially affect total hydraulic resistance. Because both conduit size and pit features influence hydraulic resistance in tandem, we hypothesized that features of both should vary predictably with one another. To test this prediction we sampled a single tall (94.8 m) Sequoiadendron giganteum tree (giant sequoia), collecting wood samples from the most recent annual ring progressively downwards from the tree top to the base. We measured tracheid diameter and length, number of pits per tracheid, and the areas of pit apertures, tori, and margos. Tracheid diameter widened from treetop to base following a power law with an exponent (tracheid diameterstem length slope) of approximately 0.20. A similar scaling exponent was found between tracheid length and distance from tree top. Additionally, pit aperture, torus, and margo areas all increased (again with a power of ~0.20) with distance from tree top, paralleling the observed variation in tracheid diameter and length. Pit density scaled isometrically with tracheid length. Within individual tracheids, total permeable area of pits, measured as the sum of the margo areas, scaled isometrically with lumen area. Given that pores of the margo membrane are believed to increase in parallel with membrane area, from a strictly anatomical perspective, our results support the interpretation that pit resistance remains a relatively constant fraction of total resistance along the hydraulic pathway.