WOOD DENSITY OF Pinus hartwegii Lind. AT TWO ALTITUDE AND EXPOSITION LEVELS.

Abstract

The wood density of the forest species that form annual growth rings represents a natural archive related with climate variability. The objective of this study was to evaluate if the X-ray computed tomography (XRCT) method is able to detect radial changes in wood density and if it varies according to altitude and exposition of the site; therefore, that method with a medical equipment (XRCT) was used to obtain radial density profiles for Pinus hartwegii Lind. The wood samples came from four contrasting sites at the Tláloc volcano, two altitudinal levels (3500 and 3900 masl), and two exposition levels (NW and SW). A general linear model —including the total ring width as a co-variable— was used to evaluate the simple and interaction effects of altitude and exposition on wood density. There were statistically significant differences among sites (p?0.001). The altitude*exposition interaction was significant (p?0.001), which indicated that changes in wood density are influenced by altitude; however, the degree of change depends on the exposition. In the NW exposition, altitude had a positive effect on wood density, while, in the SW exposition, there was no effect. There was a greater wood density in the site with NW exposition and an altitude of 3500 masl. The ring width —as a transformed variable— helps to explain a significant part of the variance of the radial density of wood between sites. X-ray computed tomography allowed to study the variation of wood density and, reliably and accurately, to deduce which changes can be attributed to the recent climate variation