Abstract
Rapidmajor shifts in vegetation types are most often attributed to abrupt climate changes. However, recent studies have revealed non-linear vegetation responses to current global warming on theTibetan Plateau [1]. This also seems to be the case for the Holocene vegetation on the Tibetan Plateau. This high-elevation region is under the control of the Asian monsoon, causing relatively moist summers and dry winters. Monsoon influence rapidly decreases from the southeastern to the northwestern parts of the plateau, leading to steep climate gradients. As a consequence, the vegetation covers range from forest (with precipitation of >ca. 400mm), steppe/meadow (precipitation ranging from ca. 200 to 500mm) and desert (with precipitation of <ca. 200mm) across the gradients (Fig. 1A). From the last deglacial time to the Holocene, monsoon precipitation gradually increased in response to the summer insolation changes and to the global boundary conditions [2], reaching maximum intensity around ca. 9–6 kyr BP. Vegetation changes on the Tibetan Plateau inferred from dozens of pollen records are marked by the establishment of interglacial type (‘establishment shift’), the optimum state around the mid-Holocene, and followed by the deterioration (‘collapse shift’) during the late part of the Holocene. Such overall trends are obviously consistent with the orbital-induced gradual monsoon changes. Vegetation zone
Highlights
From the last deglacial time to the Holocene, monsoon precipitation gradually increased in response to the summer insolation changes and to the global boundary conditions [2], reaching maximum intensity around ca. 9–6 kyr BP
Another feature is that the timing of the onset of the vegetation shift is asynchronous for individual sites across the Tibetan Plateau
Far north to Naleng Lake, three pollen records from the Zoige Basin indicate an abrupt change from meadow to forest meadow at ca. 10.5 kyr BP and a return to meadow at 4.3 kyr BP [4]
Summary
From the last deglacial time to the Holocene, monsoon precipitation gradually increased in response to the summer insolation changes and to the global boundary conditions [2], reaching maximum intensity around ca. 9–6 kyr BP. The Holocene vegetation changes on the plateau displayed several prominent features that are not readily explainable by such orbital-scale gradual climate trends. The pollen record from Naleng Lake in the south part of the Tibetan Plateau shows an abrupt vegetation change from alpine meadow to montane forest at 10.7 kyr BP and back to meadow at 4.4 kyr BP [3].
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