黄土高原中部麻栎宽度年表的气候响应特征初探

The climate signal recorded by Quercus acutissima tree-ring chronology from the central Loess Plateau

黄土高原是世界上水土流失最严重和生态环境最脆弱的地区之一,由于人类活动的日益频繁,森林面积急剧缩小,现有林地多为人为破坏后形成的天然次生林。目前很难在该区找到适合树轮气候学研究的老龄针叶树种,在此背景下,寻找适合开展树轮气候学研究的替代树种尤为重要。本研究以黄土高原中部桥山林区的老龄麻栎林为研究对象,为该区建立了近一百多年的标准年表(1891—2016)和差值年表(1884—2016),评估其树轮气候学研究潜力。相关计算表明,麻栎差值年表与当年3—7月降水量相关最高(r=0.58,p<0.001),几乎达到了可以重建的水平。该年表还与陕西中北部旱涝指数和黄土高原西部树轮降水重建序列显著相关,共同反映了区域降水变化历史。空间相关分析也进一步说明了桥山麻栎差值年表对区域降水量变化具有较强代表性。本文首次利用黄土高原中部阔叶树种开展树轮气候学研究,发现了麻栎树轮宽度年表具有记录过去降水变化的巨大潜力。

Background,aim,and scope The Loess Plateau is one of the areas of the world with the severe soil erosion and the extremely vulnerable ecological environment.Its forest area has decreased dramatically,and only natural secondary forest can be found on the Plateau since the intensive destruction by human beings.Currently,it is difficult to find old coniferous trees to carry out dendroclimatology studies.Given this situation,it is necessary to assess alternative deciduous trees that are suitable for climate reconstruction.Materials and methods Sixtyfour cores were collected from 34 Quercus acutissima trees by increment corers in the Qiaoshan region.The cores were fixed,dried,and polished following the standard method of dendrochronology.Tree-ring width was measured by LINTAB at a resolution of 0.01 mm.The COFECHA program was used to ensure the accuracy of cross-dating,and the ARSTAN program was used to build the final tree-ring chronologies.The arithmetic average of the climate data(e.g.,temperature,precipitation and relative humidity)from Yan’an,Xifeng and Yaoxian meteorological stations were used to analyse growth/climate relationships.Pearson correlation analyses were used to identify the relationship between chronology and climate factors.We also conducted spatial correlations to assess the spatial representativeness of the Qiaoshan RES chronology.Results The statistical results showed a high expressed population signal(EPS)and signal noise ratio(SNR),which demonstrated the high quality of the Q.acutissima chronology that contained relatively more climate signals.The Mann-Kendall method revealed that the climate in the study area has had a significant warming and drying trend since the 1960s.The Pearson correlation calculation showed that the STD and RES chronology was negatively correlated with the temperature and positively correlated with precipitation and relative humidity during the growth seasons.The RES chronology of Q.acutissima showed the highest correlation with precipitation in March—July of the current year(r=0.58,p<0.001)and could be regarded as the precipitation series for the past 136 years.Discussion Treering chronologies from semiarid regions are usually sensitive to precipitation.The low values of the Q.acutissima RES chronology from the Qiaoshan region corresponded well with the drought events recorded by historical documents and with the observed climate data.The Q.acutissima RES chronology was also significantly correlated with the dry and wet index(DWI),which was derived from historical documents,in central and northern Shaanxi and with the regional precipitation reconstruction for the western Loess Plateau by an ensemble of ten tree-ring width chronologies.The good association among these chronologies confirms the potential of the Q.acutissima chronology for future climate reconstruction.Spatial analysis indicated that the RES chronology had a strong spatial representativeness for the March—July precipitation variability.Conclusions Q.acutissima is a moisture-sensitive species on the central Loess Plateau and shows great potential for climate reconstruction in the future.Recommendations and perspectives This study established the first oak Q.acutissima tree-ring chronology,which demonstrated a strong precipitation signal,on the central Loess Plateau.This study will contribute to ecological studies and climate reconstructions in the future.