西藏色林错湖相沉积物的花粉分析

HOLOCENE PALYNOLOGICAL RECORDS IN LAKE SELINCUO,NORTHERN XIZANG

通过对藏北色林错湖相沉积物的花粉分析，得到１１０００年以来该地区植被与环境发展的历史。约１１０００－９６００年前期间，低花粉浓度指示植被稀疏，气候寒冷干燥，与今日的高山稀疏植被相当。约９６００－６０００年前期间草原代替高山稀疏植被，在大的范围内森林植被扩展，林线下降，气候明显变暖，距今６００年以来，植被虽然仍以草原为主，但高花粉浓度及乔木花粉数量的增加都说明植被更加繁茂，气候较现在温暖。

Selincuo (31°34'-31°57'N, 88°31'-89°21'E)is one of the great lakes in northern Xizang surrounded by alpine grassland,composed mainly of Stipa purpurea ,S. subsses-sifolia var. bassipulomosa. A 3. 08 m long core has been taken from a water depth of 27 m, 3 km to the north from the lake. Palynological records of the core combined with surface sample results have revealed from the regional as well as local vegetational and environmental history since the last 12 000 a BP,a very low pollen concentration(19-209 grains/g) ,mainly of airborne pollen,which indicated a treeless alpine sparse vegetation. A great vegetation change took place at Ca. 9 600 a BP when alpine sparse vegetation was replaced by alpine grassland lasting until Ca. 6 000 a BP. Quite a number of tree pollen grains found in this time interval might be explained as a result of expansion of forests somewhere around the Xizang Plateau. These changes must have caused by climatic warming during the Early Holocene. During the last 6 000 years the vegetation had remained as the alpine grassland, although probably more luxurouste than before, but their was an obvious increase of arboreal pollen,such as the increase of Abies during Ca. 6 000-4 000 a BP,Picea 4 000-2 200 a BP,Pinus 2 200-1 000 a BP which indicated continuous expansion of forests growing around the plateaus. During the last 1 000 years both the concentration and proportion of the arboreal pollen decreased and those of Cypraceae pollen increased sharply. This might mean a reduction of the forests around the plateau and an expansion of swamps around the lake.