Observed compression of in situ tree stems during freezing
Observed compression of in situ tree stems during freezing
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DOI：
10.1016/j.agrformet.2017.05.004
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发表时间：
2017-09
影响因子：
6.2
通讯作者：
E. Gutmann;J. Stan;J. Friesen;D. Aubrey;J. Lundquist
中科院分区：
文献类型：
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作者：
E. Gutmann;J. Stan;J. Friesen;D. Aubrey;J. Lundquist
冰冻温度会影响树木的材料特性。了解森林生物气象相互作用如何响应冰冻温度对于森林科学和管理非常重要，因为其影响可以通过耦合的水文和生态过程级联，包括对树木生长的限制、树冠拦截的变化以及对大气湍流的影响。这篇简短的通讯详细介绍了尼沃特岭山研究站（美国科罗拉多州）冬季（2013-2014 年）期间，低于冰点的温度对三个原位松树（大松）茎的机械位移的影响。尽管之前对采伐树木的研究表明，当温度降至冰点以下时，茎会发生纵向膨胀，但我们观察到低于 -3°C 的活茎的纵向压缩，与低至 -22°C 的零下气温呈线性相关。与冷冻相关的茎压缩通常会达到与施加 55 kN 压缩力 (800 μm) 相当的位移量。提出假设来解释由于冻结而观察到的显着机械位移：（1）当冻结前沿通过茎传播时，内部气体释放； (2)通过汁液渗出或优先冰晶生长来短期迁移水。由于观察到的茎压缩对冻结的反应是巨大的，因此未来对潜在过程和后果的研究是值得的。这里使用的测量技术可能对其他对茎冷冻动力学感兴趣的人有用。
Freezing temperatures can influence the material properties of trees. Understanding how forest biometeorological interactions respond to freezing temperatures is important for forest science and management, as its effects can cascade through coupled hydrological and ecological processes including limitations on tree growth, changes to canopy interception, and influences on atmospheric turbulence. This short communication details the effect of sub-freezing temperatures on the mechanical displacement of three in situPinus contortaDouglas (lodgepole pine) stems during a winter season (2013–2014) at Niwot Ridge Mountain Research Station (CO, USA). Although previous research on harvested trees suggests longitudinal stem expansion should occur as temperatures decrease below freezing, we observed longitudinal compression in live stems below −3 °C that linearl y correlated with sub-zero air temperatures ranging down to −22 °C. Freeze-related compression of stems frequently achieved displacement magnitudes comparable to applying 55 kN of compressive force (800 μm). Hypotheses are proposed to explain the significant mechanical displacement observed due to freezing: (1) internal gas release as freezing fronts propagate through stems; (2) short-term relocation of water via sap exudation or preferential ice crystal growth. As the observed stem compression response to freezing is substantial, future work on underlying processes and consequences is merited. The measurement technique used here may prove useful to others interested in the dynamics of stem freezing.