Ecological wood anatomy of Alnus nepalensis (Betulaceae) throughout Nepal

Variation in the wood structure of Alnus nepalensis D. Don (Betulaceae) in relation to tree size and habitat altitude was studied in four areas of Nepal: Tamur, Rolwaling, Budi Gandaki, and Bajhang-Khaptad. Alnus nepalensis is a pioneer tree distributed in the Himalayas from northern India to southwestern China and grows throughout Nepal in a wide altitudinal range from 200 m in the tropical zone to 3030 m at the upper limit of the temperate zone. Ecological trends in the wood structure of Alnus nepalensis varied between the studied areas, distinct in the Tamur area, but indistinct in other areas, and tended to be detected in areas with specimens from altitudinal ranges of 2000 m. When all the specimens were separated at 1800 m in elevation and analyzed as two altitudinal groups, features of vessel size and distribution and the ratio of solitary vessels had a significant correlation with tree height in both groups, and tall trees tended to have larger, more solitary vessels. Vessel element and fiber lengths did not have any significant trends in the lower group but had a negative correlation with altitude in the upper group along with the reduction of tree height. Thus, vessel size seems to facilitate the height growth of this pioneer tree, and shorter tracheary elements and more vessel multiples seem to be related to the adaptation of smaller trees at higher elevations.

Anatomía de la madera de especies arbóteas de un bosque mesófilo de montaña: un enfoque ecológico-evolutivo

In order to investigate trends in ecological wood anatomy of a cloud forest, 29 tree species from Ocuilan, State of Mexico, were studied. The results suggest that the homogeneous climate of the area determines the absence of growth rings for most species; also, a narrow relationship was observed between rings and the phytogeographic origin of taxa. With respect to the remaining anatomical characters, there is a high percentage of wood with diffuse porosity; also, medium and long vessel elements are common, with small diameters and scalariform perforation plates, along with long fibers with thin walls, of libriform type, or fibrotracheids in which septs may be present or not; axial parenchym is scarce and rays are heterogeneous, of type I. These characters are discussed from an ecological and evolutionary point of view.

ECOLOGICAL WOOD ANATOMY OF OCOTEA CURUCUTUENSIS

We studied wood anatomy and specific gravity in a total of 18 trees of Ocotea curucutuensis, a recently described species, lacking wood anatomical information. Nine sample trees were obtained in each of two areas, Pico do Itapeva (PI) and Núcleo Curucutu (NC), both in the state of São Paulo, Brazil. These areas have marked differences in precipitation, altitude, and temperature. Anatomical differences between the two populations appeared related to tree size, and possibly indirectly to climate. Higher wood specific gravity related with the smaller diameter in NC trees is hypothesized to contribute to mechanical support of the epiphyte-laden trees and to resistance against the prevailing strong winds.

Ecological Wood Anatomy of Miconia Sellowiana (Melastomataceae) in three vegetation types of paraná state, Brazil

Miconia sellowiana (Melastomataceae), a widespread species occurring in Araucaria Forest, Montane Dense Forest and Upper Montane Forest (Paraná state, Brazil) has a highly variable foliar morphology. This study investigated whether the wood anatomy follows this pattern influenced by environmental conditions. Samples of six individuals per area were collected, fixed and prepared, according to standard techniques in wood anatomy. ANOVA indicated differences for length and diameter of vessel elements and fibres, fibre wall thickness, width of rays and ray frequency, especially regarding the population of the Upper Montane Forest. The secondary xylem from this vegetation is characterized by shorter vessel elements and fibres, thicker fibre walls and wider rays. These characteristics are associated to a certain degree of water stress imposed to the plants in the Upper Montane Forest, mainly due to the shallow neosol soils. The Araucaria Forest and the Montane Dense Forest have more similar environmental conditions, supported by the Cluster analysis. The Principal Components Analysis explained 98% of the total variance, where fibre and vessel element lengths showed a posi-tive correlation; however, this analysis did not allow the separation of three distinct groups. Although less pronounced, the wood anatomical differences corroborate the results obtained with foliar morphology, where leaves from the Upper Montane Forest presented the most xeric characteristics among the populations of Miconia sellowiana studied.

Commentary: Typology, Homology, and Homoplasy in Comparative Wood Anatomy

Comparative wood anatomy consists of two main efforts: wood identification and evolutionary studies. Evolutionary studies can be divided into two main areas: systematic wood anatomy and ecological wood anatomy. The goal of wood identification is the association of a name with a sample; that of systematic wood anatomy is the discovery of the nested hierarchy of synapomorphies that characterize the phylogeny of the woody plants; the main thrust of ecological wood anatomy has been to identify structure- function relationships that have evolved repeatedly across clades. Wood anatomical characters can be divided into three types: typological, homologous, and homoplasious. Wood identification can and should use all three types; systematic wood anatomy must focus on homologies; homologies may be of interest to ecological wood anatomy, but homoplasies have been its principal focus. The use of typological characters developed for wood identification can produce misleading results in studies of evolutionary wood anatomy and must be avoided. Robust phylogenies are important for discovering wood anatomical homologies and homoplasies; also important is the need to make explicit, testable hypotheses, and to identify the type of causation (ultimate or proximate) that is of interest for a given study.