高频光密度测量法在崆峒山树轮年表建立中的应用

树木年轮是最常用的古气候代用指标之一,能提供高分辨率的气候变化信息。其中树轮宽度和密度是每年生长量必不可少的代用量测指标。但树木年轮宽度信息仅是表征树木的平均生长状况,其与气候关系复杂,所以树木的径向宽度生长数据并不能充分的用于气候变化重建;而树轮密度是树木细胞直径及木质部细胞壁厚度等结构的间接反映,其对于气候的响应则能提供更多的信息。已形成多种测量树轮密度变化值的方法,目前应用最广泛是X-ray密度测定法,但这种方法存在种种应用上的缺点。近年又形成一种新的树轮光密度值测定法-高频光密度测量法。尝试利用高频光密度测量法建立了甘肃崆峒山地区四种树轮密度年表,与史料、旱涝等级数据对比分析,有着良好的对应关系,与气象资料进行了相关函数和响应函数分析,分析结果满足统计学的要求,并能从树木生理学上对分析结果给予解释,表明这是一种有效的树木年轮气候研究方法。

Application of high-frequency densitometry in establishment of tree-ring density chronology from Mt.Kongtong,Gansu Province

The annual rings of trees provide one of the most useful high resolution paleoclimatic archives.Because it is widespread,easy to sample,well to replicate and has the characteristics of accurate dating,high resolution,ac-curate measuring,as well as the proxy data for past environmental changes,the tree ring data was used widely as an important archive in the Past Global Changes(PAGES)research.Tree ring widths and density are essentially proxy of annual tree's growth.In some cases,radial growth data may not be sufficient to reconstruct climatic trends due to complex connection with climate change,however,wood density was found to be a more sensitive indicator of climate,which may provide further information with respect to climate.So,wood density is of interest to dendro-climatology.Different methods have been developed to measure wood density variation,such as,X-ray images.X-ray densitometry,which proposed by Hubert Polge in 1 963,is still most commonly used in tree-ring density meas-urements.But it has many disadvantages,i.e.time-consuming and expensive.In this paper,a new instrument and a new type of densitometry,LignoStation and HF-densitometry were introduced.Martin Schinker et al proposed a new densitometry in 2003,the HF-densitometry,and compared with the density profile obtained by X-ray densi-tometry,validated this new method.LignoStation~(R) is developed on the basis of the new method by Rinntech~(R) Com-pany.It allows non-destruction,fast and accurate measurement of wood density variations.Based on the new meth-od and instrument,the paper tries to build four kinds of tree-ring density chronologies firstly from Mt.Kongtong,Gansu Province,China.The chronologies are coupling well with the historic document records and annual drought -flood rank material in Pingliang area,and correlation analyses and response analyses are applied to provide a basic estimate of the causal relationships between tree-ring density and climate factors.It indicates that the most statistically significant climatic variable correlated to minimum ring-density indices is summer precipitation(JJA).The correlation coefficient is-0.4.which is significant at the 0.001 level,and summer precipitation(JJA)is one of main controlling factors of the tree-ring density change.There is remarkable consistency between earlywood den-sity curve and summer precipitation(JJA)too,the correlation coefficient is-0.36,which is significant at the 0.005 level.It is also found that the summer air temperature(JJA),maximum ring-density,and latewood density ehronologies have a good corresponding relationship.And the correlation coefficients are -0.26 and -0.28 re-spectively,which are significant at the 0.05 level.According to these results,this method is proved valid and fea-sible.