Department of Biology at the University of Rochester
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The cottonwood gallery forest has enirely grown up along the San Bernandino River in Arizona since cattle were removed in 1979. The last tree sits at the international border, but the river continues south (to the right). Cattle which were on Rancho San Bernandino, Mexico until 2000 eliminated cottonwoods, although many young individuals not visible in the picture are now established.


The area we have studied most intensively is in the San Bernardino Valley of southeastern Arizona, USA and northeastern Sonora, Mexico. Formerly a single large cattle ranch, this area is now set aside for conservation. In the United States (
), cattle were removed in 1979. In Mexico (, cattle were removed in 2000, the year our studies of bees and plants were initiated.

Along with studies of bees, we have been monitoring vegetation changes in the riparian, grassland, desert, and arroyo habitats. As the photo on this page illustrates, some habitats in Arizona and Mexico now differ strikingly.