Fachbereich Prähistorische Archäologie, Institut für Archäologie, University of Zurich, Zurich, Switzerland.
Forest Ecology, Institute of Terrestrial Ecosystems, Department of Environmental System Science, ETH Zurich, Zurich, Switzerland.
PLoS One. 2020 Sep 24;15(9):e0239425. doi: 10.1371/journal.pone.0239425. eCollection 2020.
Regional differences in tree growth can be used to approximate the geographical provenance of ring-width series ('dendro-provenancing'). This method relies on cross-dated ring-width series (reference chronologies) that are thought to represent the radial growth signal of trees in a given region. Reference chronologies are often established from ring-width series of living tree populations. Frequently, they are too short to allow for investigating the provenance of historical wood. Thus, references are extended by ring-width series from buildings and art-historical objects that exhibit best matching growth patterns with the living tree references. Yet, series from other provenances may erroneously be included. Thereby the local or regional growth signal of the references is progressively contaminated, but this has received little attention to date. I investigate this contamination risk using a simulation approach that allows for generating pseudo site chronologies that preserve the relevant statistical properties of the real site chronologies. While the exact provenance of historical wood is unknown, for simulated ring-width series the provenance is unambiguous. Hence, pseudo reference chronologies may be established while monitoring the signal mixture. Specifically, 15 site chronologies of Norway spruce (Picea abies (L.) H. Karst.) from northeastern Switzerland were used to generate 15 pseudo site growth signals that span 1000 years. The simulation demonstrates that quasi uncontaminated references can be established in ideal circumstances for the study area. However, the thresholds for the similarity in between-series correlation must be very high. Even then, contaminated pseudo references occurred in rare cases during the simulation. Yet, elevation-specific pseudo references were established with lower thresholds. Simulation currently offers the only approach for assessing the contamination risk of reference chronologies, and it allows for elucidating the conditions under which acceptable levels of contamination can be guaranteed. Therefore, the present approach paves the way towards a practical simulation tool for dendro-provenancing.
树木生长的地域差异可用于大致估算树木年轮序列（“树木起源”）的地理起源。该方法依赖于交叉定年的树木年轮序列（参考序列），这些序列被认为代表了特定区域树木的径向生长信号。参考序列通常是从活树种群的年轮序列中建立的。通常，它们的长度不足以调查历史木材的起源。因此，通过与活树参考具有最佳匹配生长模式的建筑物和艺术史物体的年轮序列来扩展参考序列。然而，可能会错误地包含来自其他起源的序列。从而，参考序列的局部或区域生长信号逐渐受到污染，但迄今为止，这一点很少受到关注。我使用模拟方法来研究这种污染风险，该方法可以生成保留真实站点序列相关统计特性的伪站点序列。虽然历史木材的确切起源未知，但对于模拟的年轮序列，起源是明确的。因此，在监测信号混合的同时，可以建立伪参考序列。具体来说，使用来自瑞士东北部的挪威云杉（Picea abies (L.) H. Karst.）的 15 个站点序列生成了跨越 1000 年的 15 个伪站点生长信号。模拟表明，在研究区域的理想情况下可以建立几乎无污染的参考。但是，序列间相关性相似性的阈值必须非常高。即使这样，在模拟过程中也很少会出现污染的伪参考。然而，特定海拔的伪参考可以通过较低的阈值建立。目前，模拟是评估参考序列污染风险的唯一方法，它可以阐明在何种条件下可以保证可接受的污染水平。因此，目前的方法为树木起源的实际模拟工具铺平了道路。
