Bcs. Hansen et Dt. Rodbell, A LATE-GLACIAL HOLOCENE POLLEN RECORD FROM THE EASTERN ANDES OF NORTHERN PERU, Quaternary research, 44(2), 1995, pp. 216-227
A pollen and sediment record of a core 4.2-m-long from Laguna Baja (7
degrees 42' S, 77 degrees 32' W, 3575 m) in the Cordillera Oriental of
northern Peru suggests several episodes of major vegetational and cli
matic change over the past 13,000 yr. The oldest pollen assemblage con
sists of a mixture of paramo elements (tropical alpine vegetation), in
cluding high percentages of Poaceae (40%) that decline upward, moist m
ontane forest (Compositae and Polylepis), and wet montane forest (e.g.
, Hedyosmum and Podocarpaceae). Organic carbon content range from <2%
to 8%. About 11,600 yr B,P. this mixed pollen assemblage was replaced
by Poaceae (>60%), with high percentages of Jamesonia, a fern characte
ristic of paramo, and decreasing values of Plantago tubulosa and the w
et montane forest elements Hedyosmum and Podocarpaceae. Charcoal perce
ntages are at a maximum during this: period, magnetic susceptibility a
nd sand percentages are high, and percentages of organic matter are lo
w. Several explanations for these changes are possible, including a re
duction in temperature and moisture, more frequent periods of aridity
with increased fires, or natural succession. The Holocene record begin
s with pronounced increases in organic carbon and pollen of wet montan
e forest, primarily Hedyosmum, Podocarpaceae, and Urticales. High valu
es of Podocarpaceae pollen (>35%) and a decline in charcoal suggest te
mperature and moisture levels above modern-day values. Wet montane for
est pollen remain high and charcoal values are low from about 10,000 t
o 6000 yr B.P., suggesting that warm and moist conditions prevailed fo
r about 4000 yr. Subsequently Podocarpaceae and Urticales decline, and
for a brief time Alnus is prominent in the pollen record. Following t
he Alnus maximum at about 5000 yr B.P., Poaceae, Ambrosia and Chenopod
iaceae/Amaranthaceae become frequent, Increased paramo and disturbance
indicator pollen suggest increased anthropogenic activities in this r
egion from the middle Holocene to the present. (C) 1995 University of
Washington.