Frost drought refers to the chronic or acute desiccation of trees exposed to high evaporative pressures while being rooted in cold or frozen soils. This phenomenon has been known for more than a century but is still poorly characterized. Summer desiccation manifests itself as long-term stem contractions. Similar contractions have been reported in winter. In this study, we investigated the causes of total winter stem contraction (WSC) using 14 years of dendrometer data from evergreen (P.abies) and deciduous (L.decidua) mature trees growing along an elevational transect (from 800 to 2200 m asl) in the Swiss Alps. Results indicated that WSC varied between $30\mathrm{\mu }\mathrm{m}$$30\mathrm{\mu }\mathrm{m}$ and $1478\mathrm{\mu }\mathrm{m}$$1478\mathrm{\mu }\mathrm{m}$ and were strongly dependent on species, elevation, and tree height. Moreover, the magnitude of contractions was strongly associated with stem contractions subsequent to freeze–thaw events ($\Delta$$\Delta$F). We suggest that both $\Delta$$\Delta$F and WSC are the consequences of water losses due to ice blockage associated frost drought, occurring when the distal parts of the tree are thawed and transpiring, while the larger basal parts remain frozen, thus inhibiting water uptake and creating a hydraulic imbalance.

中文翻译：

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茎粗变化的霜冻干旱迹象


霜冻干旱是指树木在扎根于寒冷或冻土时暴露在高蒸发压力下的慢性或急性干燥。这种现象已经为人所知一个多世纪了，但仍然没有得到很好的描述。夏季干燥表现为长期的茎收缩。据报道，冬季也有类似的宫缩。在这项研究中，我们使用了瑞士阿尔卑斯山沿海拔样带（从 800 到 2200 m asl）生长的常绿 （P.abies） 和落叶 （L.decidua） 成熟乔木的 14 年树木测量仪数据调查了总冬茎收缩 （WSC） 的原因。结果表明，WSC 在 $30\mathrm{\mu }\mathrm{m}$ 和 $1478\mathrm{\mu }\mathrm{m}$，强烈依赖于物种、海拔和树高。此外，收缩的幅度与冻融事件后的茎收缩密切相关 （Δ> F）。 我们建议 Δ”>F 和 WSC 是由于冰堵塞相关的霜冻干旱而造成的水分流失的后果，发生在树木的远端部分解冻和蒸腾时，而较大的基部保持冻结状态，从而抑制水分吸收并造成水力不平衡。