IMPACT OF DAMS ON Taxodium mucronatum Ten. IN THE SAN PEDRO-MEZQUITAL RIVER, DURANGO

Abstract

The study was carried out in a transect with dead cypress trees along the San Pedro-Mezquital river with the aim to determine the impact of dam building on the annual radial growth of cypress trees due to a decrease and to a diphase on the streamflow. Dead and alive cypress trees were selected along a transect of one kilometer length with over 300 dead trees and increment cores were obtained at breast height with an increment borer, a similar sampling procedure was implemented in a nearby transect but with alive trees. Increment cores were prepared and dated following standard dendrochronological techniques and two ring width series were developed for comparison purposes. Most of the death trees died in 1991(last complete ring was formed in 1990) and a few more between 1992 and 2003. Differences in growth between the tree-ring series were observed after the building of the Guadalupe Victoria dam in 1962. A combination of variables could have caused cypress mortality, such as a decrease in the streamflow due to its storage in the Guadalupe Victoria and Santiago Bayacora reservoirs, this last built in 1989, location of cypress tress far away from the main stream, a severe dry year occurred in 1989, and diversion of the streamflow for irrigation purposes. The results allow us to improve our knowledge on the effect of dams on annual radial growth of cypress trees a dominant species in riparian ecosystems of northern Mexico.