Dendroclimatology from Regional to Continental Scales: Understanding Regional Processes to Reconstruct Large-Scale Climatic Variations Across theWestern Americas - Dendroclimatology - page 202

Box 7.6 A network of tree-ring chronologies for northern
and central Mexico
The mixed conifer forests and riparian areas of northern and central Mexico
contain some of the most climate-sensitive species in the North American
region (Box Fig. 7.11 ) . Douglas-fir ( Pseudotsuga menziesii ) is one of these
species that has been widely recognized due to its sensitivity to climate (Fritts
1976 ) . Douglas-fir has a native latitudinal range covering at least 38 ◦ in the
Northern Hemisphere and extending well into southern Mexico at latitudes
below 17 ◦ N. In Mexico, Douglas-fir occurs in scattered insolated popula-
tions of mixed conifer forests located at high elevations, thriving in cool
microenvironments and scarped terrains of the Sierras Madre Occidental
and Oriental (Martínez 1963 ) . The annual ring of this species is anatom-
ically divided into two distinct layers: the earlywood (EW) is composed
of low-density, light-colored cells, whereas the latewood (LW) has smaller,
darker cells with thicker walls. The development of separate EW and LW
chronologies provides more information on the influence of intra-annual cli-
mate variability than using total ring width data (Cleaveland 1986 ; Stahle et al.
1998 ) .
Box Fig. 7.11 Tree-ring chronologies in Mexico