Holocene vegetation history from fossil rodent middens near Arequipa, Peru

Rodent (Abrocoma, Lagidium, Phyllotis) middens collected from 2350 to 2750 m elevation near Arequipa, Peru (16 degreesS), provide an similar to 9600-y r vegetation history of the northern Atacama Desert, based on identificatio n of > 50 species of plant macrofossils. These midden floras show considera ble stability throughout the Holocene, with slightly more mesophytic plant assemblages in the middle Holocene. Unlike the southwestern United States, rodent middens of mid-Holocene age are common. In the Arequipa area, the mi dden record does not reflect any effects of a mid-Holocene mega drought pro posed from the extreme lowstand (100 in below modern levels, > 6000 to 3500 yr B.P.) of Lake Titicaca, only 200 km east of Arequipa. This is perhaps n ot surprising, given other evidence for wetter summers on the Pacific slope of the Andes during the middle Holocene as well as the poor correlation of summer rainfall among modern weather stations in the central Andes-Atacama Desert. The apparent difference in paleoclimatic reconstructions suggests that it is premature to relate changes observed during the Holocene to chan ges in El Nino Southern Oscillation modes. (C) 2001 University of Washingto n.