A 5200-year record of vegetation dynamics and variations in the Indian Summer Monsoon from the Garhwal Himalaya, India

Pollen analysis of a 3.80-m-long sediment core, comprising 55 pollen samples, from Deoria Tal, Garhwal Himalaya, India, provides a 5200 year record of vegetation history and variations in the Indian Summer Monsoon (ISM). The study demonstrates that a Pinus -dominated broad-leaved/conifer forest surrounded the site between ~5200 and 4000 cal yr BP, reflecting the influence of a cool, dry climate and a moderate ISM for much of this interval. Shifts in the relative abundance of the dominant arboreal taxa ( Pinus , Quercus , Aesculus ), and non-arboreal taxa, including terrestrial herbs and pteridophytic and marshy taxa, suggest that the interval between 4400 and 4000 cal yr BP was characterized by a highly variable ISM. A notable, abrupt increase in the Oak/Pine ratio evident at ~4250 cal yr BP corresponds with previously documented elemental and sedimentological evidence from the site of an abrupt, short-lived climate event at 4200 cal yr BP. Between ~4000 and 2650 cal yr BP the density of the Pinus -dominated broad-leaved/conifer forest increased, suggesting the site was influenced by a warmer, wetter climate, particularly between 4000 and 3200 cal yr BP. Between ~2600 and 1000 cal yr BP, mixed (temperate) broad-leaved /conifer forest expanded in response to a warm and moist climate, as evidenced by increases in Quercus and aquatic and marsh taxa, reflecting an extended interval of a strengthened ISM. The interval between ~1000 and 600 cal yr BP (~ 950–1350 CE) was characterized by fluctuations in the density of the mixed (temperate) broad-leaved/conifer forest, likely reflecting the influence of a moderately strong ISM, followed by a progressively weakening of the ISM, particularly after ~800 cal yr BP. The timing of the phase of increased ISM precipitation broadly coincides with the Medieval Climate Anomaly (MCA). Finally, between ~600 and 300 cal yr BP (~1350–1650 CE), a reversion to a Pinus -dominated mixed broad-leaved/conifer forest suggests that this interval, which correlates with the Little Ice Age (LIA; 1550–1850 CE), was characterized by a reduction in the strength of the ISM. • Pollen from Deoria Tal, Uttarakhand, was used to characterize long-term and abrupt hydroclimatic conditions in northern India. • Variations in arboreal and non-arboreal taxa were utilized to reconstruct regional hydroclimate variability during the mid- to late Holocene. • Inferred changes in vegetation community composition reflect the occurrence of major hydroclimate anomalies at 4200, 3100 and 2000 cal yr BP. • Evidence of a de-coupling of the climate-vegetation relationship at ~800 cal yr BP is coincident with the intensification of agriculture.