Vegetation Succession And Surface Moisture In Hani And Mokhovoe Peatlands And Their Responses To Climate Change

Changbai Mountain area,located at the southern edge of the northern peatland,has the same latitude as the Altay Mountain area,and lives on both sides of the Asian continent,with weak impact of human activities.It is worth discussing whether the development of peatland and its response to climate change in the two regions are comparable.In this study,Hani and Mokhovoe peatland,which belong to two regions,were selected as the research objects.Through identification of plant residues in the profile,the vegetation succession process of peatland was revealed,and the relationship between plants and water level was used to reconstruct the change of surface humidity,and then the similarities and differences of vegetation succession in mountain peatland on both sides of the Asian continent in response to regional hydrological and climate changes were discussed.The main conclusions were as follows:（1）The vegetation succession in Hani peatland has experienced the following stages since the mid Holocene:From 8200 cal yr BP to 5400 cal yr BP,the vegetation succession was dominated by Carex community,accompanied with Vaccinium uliginosum,Equisetum hyemale and Drepanocladus aduncus,at this time,the carbon accumulation rate was consistently high,with a mean value of 27.9±5.3 g C m^-2 yr^-1.From 5400 cal yr BP to 3900 cal yr BP,Carex was still dominant,and S.sect.Sphagnum took place of Drepanocladus aduncus,at this time,the carbon accumulation rate decreased slightly,with a mean value of 23.6±6.5 g C m^-2 yr^-1.From 3900 cal yr BP to 2000 cal yr BP,both of Carex and mosses were dominant,with associated plants including Larix olgensis and Vaccinium uliginosum,at this time,the carbon accumulation rate fluctuated greatly,with the mean value of 24.4±9.4 g C m^-2 yr^-1.From 2000 to 800 cal yr BP,Carex and moss still dominated,but the proportion of moss decreased,at this time,the carbon accumulation rate decreased with a mean value of 18.9±6.5 g C m^-2 yr^-1.From 800 to 300 cal yr BP,Carex was dominant,and the associated plants were Larix olgensis-Vaccinium uliginosum-Drepanocladus aduncus,and woody plants increased,at this time,the carbon accumulation rate fluctuated,with a mean value of 23.3±8.9 g C m^-2 yr^-1.（2）Based on the plant macrofossil of Hani peat core,depth to water table（DWT）was reconstructed quantitatively using transfer function.The results showed that DWT fluctuated between 3.8 and 9.2 cm during 8200–5400cal yr BP,the mean value was 5.1 cm.During 5400–3900 cal yr BP,DWT fluctuated between 3.4 and 17.6 cm,and the mean value was 7.9 cm.During the period of 3900–2000 cal yr BP,DWT fluctuated between 3.5 and 6.9 cm,and the mean value was 4.5 cm.During 2000–300cal yr BP,DWT fluctuated between 3.5-8.9 cm,and and the mean value was 4.7 cm.（3）By comparing the change of vegetation succession,carbon accumulation with the climate change reconstructed by pollen and isotope,we found that in the mid Holocene,the climate is warm and wet,mire surface moisture is high,and the vegetation succession is dominated by Carex.At this time,the carbon accumulation rate is high.In the late Holocene,the climate became cold,the mosses in the surface layer of the peatland increased,and the carbon accumulation rate fluctuated.During the Medieval Warming Period,the climate became warmer,vegetation was dominated by Carex,with both of the primary productivity and carbon accumulation rate increased.S.sect.Acutifolia replaced Drepanocladus aduncus during the Little Ice Age,and the mire surface became dry,the primary productivity of vegetation decreased,with the carbon accumulation rate decreased.（4）The vegetation succession of Mokhovoe peatland has experienced the following stages since the mid Holocene:During 12800–8700 cal yr BP,the Cyperaceae was dominant,and the associated plants were Sphagnum;During8700–7800 cal yr BP,the vegetation was dominated by Drepanocladus aduncus,accompanied by Cyperaceae.During 7800–6100 cal yr BP,although Cyperaceae and moss were dominant,woody plants increased.During 6100–1400 cal yr BP,the Cyperaceae dominated,accompanied by woody plants and Sphagnum.Since 1400 cal yr BP,Sphagnum were dominated with woody plants and Cyperaceae.（5）The DCA analysis results of Mokhovoe peatland were compared with the regional climate reconstructed by using pollen and other indicators in this area.The results showed that the temperature of Altay Mountain and its surrounding areas rose at the end of the Younger Dryas event,peatland began to develop,and the surface humidity was high;In the early middle Holocene,the climate of Altay Mountain and its surrounding areas was warm and humid,and the Drepanocladus aduncus accounted for a large proportion,and the surface moisture reached the maximum.since then,affected by the autogenetic succession process of peatland and the climate,the peat moss dominated,and the surface moisture was low;From the middle Holocene to the late Holocene,the climate of the Altay Mountain and its surrounding areas turned cold to dry,and Cyperaceae replaced mosses to dominate,with moderate surface moisture;In the late Holocene,the climate of Altay Mountain and its surrounding areas was cold and dry,and affected by the autogenetic succession process of peatland and the climate,Sphagnum once again dominated,with the minimum surface moisture.（6）By comparing the vegetation succession and surface humidity of Hani and Mokhovoe peatland with the climate reconstructed by pollen and other indicators in the two regions,it is found that the two peatland have responded well to the regional climate since the middle Holocene.For example,in the mid Holocene,the climate was warm and wet,and wet-preferring species both appeared in the two peatlands,but not similar in the late Holocene.On the centennial scale,during the warm period of the Middle Ages,wet loving species grew in both places,while during the Little Ice Age,dry-preferring species increased.In addition,the formation and development of peatland were also affected by exogenous factors such as geology,geomorphology,hydrology and autogenetic factors such as vegetation succession.Therefore,it is necessary to take the above factors into full consideration when using plant macrofossils to reconstruct past climate and environment changes,and avoid replacing regional environmental changes with local scale.