Key message

A lack of snow cover and increased soil freezing may not only have short-term impacts on trees but longer-lasting lagged effects on radial growth.

Abstract

Soil temperature and soil frost intensity are affected by the depth of insulating snow cover and the timing of snowmelt which are predicted to change by climate warming. This may increase tree growth if there is less soil freezing or decrease growth if there is no insulating snow cover, but frost temperatures still exist. Previously, we showed that the changes in soil frost by snow manipulations in a ~ 50-year-old stand of Norway spruce [Picea abies (L.) Karst.] in eastern Finland in two winters (2005/2006 and 2006/2007) led to short-term changes in physiology, morphology, and the growth of the shoots and roots. The treatments were: (1) control with natural insulating snow accumulation and melting; (2) snow removal during winter; and (3) snow removal in winter and insulation at the top of the forest floor in late winter to delay soil thawing. In this study, we examined the lagged effects of those treatments by radial trunk increment cores during the nine-year recovery period after the termination of the treatments. Annual ring width index (AWI) was calculated for each year by normalization of the ring width in the respective year in proportion to the ring width in the last year (2005) before the treatments. No differences in AWI were found between the treatments before or during the snow manipulation period. However, differences started to appear 1 year after the treatments were finished, became significant 4 years later in 2011 and lasted for 3 years. The radial increment was lower in the treatment with snow removed than in the control and in the treatment with insulation to delay soil thawing, but there were no differences between the latter two treatments. The results indicate that a lack of snow cover may not only have short-term impacts but longer-lasting consequences on the radial growth of trees. The positive effects of prolonged growing season by the increasing summer temperatures on forest growth predicted for the boreal region may therefore not be fully realised due to the negative effects of decreased snow cover and increasing soil freezing.

中文翻译：

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土壤霜冻延迟影响挪威云杉茎直径的增长

关键信息

积雪不足和土壤冻结增加不仅可能对树木产生短期影响，而且对径向生长的影响会持续更长时间。

抽象

土壤温度和霜冻强度受保温雪覆盖深度和融雪时间的影响，预计随气候变暖而改变。如果土壤冻结较少，这可能会增加树木的生长，如果没有隔热的积雪，这可能会降低树木的生长，但是霜冻温度仍然存在。以前，我们显示了在约50年的挪威云杉林中，通过除雪对土壤霜冻的变化[ Picea abies[L.] Karst。]在芬兰东部的两个冬季（2005/2006和2006/2007）导致生理，形态以及芽和根生长的短期变化。处理方法是：（1）进行自然保温积雪和融雪的控制；（2）冬季除雪；（3）冬季除雪，并在冬季后期在森林地面顶部进行隔热，以延缓土壤融化。在这项研究中，我们研究了在终止治疗后的9年恢复期中，放射状躯干增量芯对这些治疗的滞后作用。每年的年环宽度指数（AWI）是通过将各年的环宽度与治疗前最后一年（2005）的环宽度成比例地归一化而得出的。在除雪期间或之前，在处理之间没有发现AWI差异。但是，治疗结束后1年开始出现差异，在4年后的2011年变得很明显，并持续了3年。除雪处理的径向增量比对照和绝缘处理的延缓土壤融化的径向增量要低，但是后两种处理之间没有差异。结果表明，积雪不足可能不仅对树木的径向生长产生短期影响，而且会产生更持久的后果。