Time series of stem diameter variations (SDVs) recorded by dendrometers are composed of two components: (i) irreversible radial stem growth and (ii) reversible stem shrinking and swelling caused by dynamics in water storage in elastic tissues outside the cambium. However, SDVs measured over dead outer bark (periderm) could also be affected by absorption and evaporation of water from remaining dead bark layers after smoothing the stem surface to properly mount dendrometers. Therefore, the focus of this study was to determine the influence of hygroscopicity of a thin dead outer bark layer on the reversible component of dendrometer records of Scots pine (Pinus sylvestris) under field conditions. To accomplish this, SDVs deduced from dendrometers mounted over dead outer bark were compared among living and dead saplings and mature trees. Results revealed that dead trees showed high synchronicity in reversible daily SDVs compared to living trees throughout several growing seasons (mean Pearson correlation coefficient (r) = 0.844 among saplings and r = 0.902 among mature trees, respectively; P<0.001). Furthermore, diurnal and long-term SDVs closely followed changes in relative air humidity (RH) in living and dead trees. A multiple linear regression analysis of environmental influence on SDVs in dead and living trees revealed that the most important predictor of daily SDVs was RH (relative importance 64 %). Hence, results indicate that dendrometers mounted over dead outer bark with a thickness of <4 mm record hygroscopic shrinking and swelling of the bark tissue, which can amplify fluctuations in whole-tree water status. To conclude, hygroscopic processes must be taken into account when extracting intra-annual radial growth, determining environmental drivers of SDVs, and evaluating changes in tree water status from SDVs recorded by dendrometers, which were mounted over even thin dead outer bark layers.

中文翻译：

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苏格兰松（Pinus sylvestris L.）在短期和长期尺度上，薄死外树皮层的吸湿特性强烈影响茎直径变化

由测树仪记录的茎直径变化 (SDV) 的时间序列由两个部分组成：(i) 不可逆的径向茎生长和 (ii) 由形成层外弹性组织中储水动态引起的可逆茎收缩和膨胀。然而，在使茎表面平滑以正确安装测树仪后，在死皮外皮（周皮）上测量的 SDV 也可能受到剩余死皮层吸收和蒸发水分的影响。因此，本研究的重点是确定在野外条件下，薄的死皮外皮层的吸湿性对苏格兰松（Pinus sylvestris）树状计记录的可逆成分的影响。为了实现这一点，从安装在死树皮上的测树仪推导出的 SDV 在活树和死树苗和成熟树之间进行了比较。结果表明，在几个生长季节，死树与活树相比，在可逆的每日 SDV 中表现出高度同步性（树苗中的平均皮尔逊相关系数 (r) = 0.844，成熟树中的 r = 0.902，P<0.001）。此外，昼夜和长期 SDV 密切关注活树和死树的相对空气湿度 (RH) 的变化。环境对死树和活树中 SDV 的影响的多元线性回归分析表明，每日 SDV 的最重要预测因子是 RH（相对重要性 64%）。因此，结果表明，安装在厚度小于 4 毫米的枯死外树皮上的测树仪记录了树皮组织的吸湿收缩和膨胀，这会放大整棵树水状态的波动。总结一下，