Environmental Signals Registered In Annual Rings Of Typical Tree Species Over The Southeast China

Southeast China(SEC)is located in the east margin of the Eurasia and under the impact of the Asian monsoon systems.The climate herein belongs to the typical humid subtropical one and is very sensitive to global change.The eco-environment of forests in SEC has been one of the focuses of national and regional policies due to the vital role in ecological security for the entire South China.Climate change acts as one of the main abiotic factors to influence the forest systems,which can dramatically shift the composition,the structure and the eco-function of forests via modulation of the metabolism of individual trees.As an important regulator of global hydrological and carbon cycles,the forests also feedback climate change.Because of the limited observations over time and space,only with tree rings can we benchmark climate and forest change in a long-term context and obtain a complete picture of dynamics.In this study,eight typical tree species in SEC(Pinus massoniana,Keteleeria fortune,Pinus taiwanensis,Cryptomeria fortune,Pinus fenzeliana,Fokienia hodginsii,Cunninghamia Lanceolata and Cinnamomum camphora)were used to explore the reginal forest and climate change through different indices of tree rings(ring width,stable isotope and anatomical characteristics).The main conclusions are shown as follows:1)Based on the traditional methods of Dendrochronology,five width chronologies were developed from P.massoniana,P.taiwanensis,C.fortune,P,fenzeliana and F.hodginsii trees over SEC and their associations with climatic factors.Tree growth of P.massoniana and K.fortune in Fuzhou is dominated by moisture conditions during the vegetation period.P.taiwanensis trees in Daiyun Mountains are located in the southernmost distribution and are directly modulated by temperature in summer rather than drought.Radial growth of C.fortune fengshui woods in Meihua Mountains tends to be insensitive to climate change,which may be related to various disturbances.Growth of F.hodginsii in Kuilong Mountains is closely associated with precipitation variations in the pre-growing season and at the mid-stage of growing season,as well as temperature in autumn.As for P.fenzeliana forests,drought during the previous year appears to be the most dominant factor for radial growth.Tree-ring samples of P.massoniana,K.fortune,P.taiwanensis,C.fortune and P.fenzeliana trees are classified into three different-age groups.It is found that young and old P.taiwanensis and P.fenzeliana trees that grow in hash environment show very similar growth response to climate.Young P.massoniana trees are sensitive to precipitation which old ones are mainly influenced by drought.As for K.fortune and C.fortune trees in moist and warm conditions,climate-growth relationships between young and old trees are very different.Young K.fortune trees are mainly dominated by summer drought,while old ones are strongly positively related to temperature.2)The process-based Vaganov-Shashkin(V-S)model is employed in this study to simulate the non-stationary and nonlinear response of tree growth of P.taiwanensis to climate variability linking daily length,temperature and precipitation.The result exhibits that the hypothetical growth curve is highly consistent with the actual tree-ring chronology during the period from 1954 to 2004,and output both agrees well with the statistical relationships between trees and climate as well as observational physiological behavior,i.e.temperature in summer acts as the most contributing role in tree-ring formation.However,the modelled and actual values have become distinct since 2004.This may be linked with the rapid warming over the past decade,which gives rise to the decline of P.taiwanensis forests.The recent warming is in good agreement with the strengthened western Pacific subtropical high,the position of which leans toward west.In addition,sea surface temperatures(SSTs)of eastern equatorial Pacific have been experiencing a dramatic cooling over the past decade,which also leads to warming conditions in SEC.3)The robust chronology from C.fortune fengshui woods are developed merely based on old trees,considering the great disparity of climate-growth relationships between old and young trees.Common growth anomalies of the Fengshui woods can well capture long-term moisture changes in spring(March-April-May)over the past 220 years in STC.Present chronology shows significant correlations with El Nino-Southern Oscillation(ENSO),indicating ENSO made great impacts on local springtime moisture.However,this teleconnection weakened during the 1920-1960 period when ENSO variance was relatively low.It is also observed that interdecadal variations of moisture in STC were closely modulated by temperature and North Atlantic Oscillation(NAO),based on stable covariability between the chronology and the reconstructed temperature in STC and NAO.Our results also reveal that "southern flooding and northern drought" pattern in China was conspicuous during epochs of 1860s-1870s,1920s-1930s and 1980s-1990s.Pluvial episodes in spring over STC cohered with an enhanced lower-tropospheric anticyclone over western North Pacific and anomalous upper-tropospheric westerly jets over East Asia,while North China in dry summers fall under the influence of an anomalous steady high pressure pattern at low and high levels.4)A new tree-ring cellulose ?13C chronology is developed for the C.fortune fengshui woods in Meihua Mountains,which is then normalized to remove the temporal variations of ?13C in atmospheric CO2 to obtain a carbon isotopic discrimination(?13C)time series.A distinct correlation is observed between ?13C and local spring(March-May)minimum temperature(SMT)(n = 58,r = 0.75,p<0.001)and we use this relationship to reconstruct SMT variations from 1800 to 2014.Spatial correlation analysis reveals that our reconstruction can well represent the large-scale SMT over the SEC.The low-frequency variations of the reconstruction agree well with that of the temperature reconstructions of Northern Hemisphere and the simulated CCSM-4 temperature variations in SEC.It is observed that the strongest and the most persistent cold events occurred in 1810s-180s and 1830?1870s,respectively.The former may be related to the eruption of the Tambora,and the latter caused the frequent conflicts between the native and the Hakka.Circulation analysis reveals that the cold SMT events are consistent with lower SSTs over the South Sea and the East Sea,as well as a distinct anticyclone over the Siberia and a distinct cycolone over the East China.5)Tree roots affected by soil erosion can register the evidence of disturbances in their annual rings,and thus provide a valuable precise tool for reconstructions of past erosion processes.In this study,we analyze and quantify anatomical reactions to exposure in coniferous(P.massoniana,C.amia lanceolata and F.hodginsii)and evergreen broadleaved(Cinnamomum camphora)tree roots in Chngting.A total of 204 cross sections were harvested from living roots that have outcropped.From each of these samples,micro-sections are prepared for determination of the exposure-related anatomical changes across species.In P.massoniana and C.lanceolata,exposure induces a distinct diminution in the lumen area of earlywood tracheids by almost 56.33%and 55.62%,respectively.As for F.hodginsii,no significant anatomical changes are observed in exposed roots.While in C.camphora a transformation from semi-ring-porous to diffuse-porous occurs in the anatomical structure,exposure also lead to a remarkable drop in the lumen area of vessels by 63.86%,and leave less drastic but still recognizable reduction(37.45%)in fibres.Reactions in P.massoniana,C.lanceolata and C.camphora start to emerge at a time when the edaphic cover is reduced to ? 70mm,40mm and 30mm,respectively.As a consequence,estimates of eroded soil thickness need to be adjusted to take account of this species-dependent bias for erosion reconstructions.We use these roots to reconstruct the local soil erosion,and observe that soil erosion among different sites is different.In addition,the regional erosion rates have been maintained a steady downward tendency over the past decades.