冰雪灾害对森林的影响

冰雪灾害是一种常见的自然灾害,往往对森林造成很大破坏。随着冰在树冠上不断积累,产生的压力逐渐增大,最后超过该部位最大弯曲力矩时林木会受到伤害。受害程度与林分的多种特征,如树种组成和林分密度及林木的多种特征,如胸径、树高、树干尖削度、叶片表面积、树冠对称性、根系、林龄等有密切关系。影响冰雪灾害的外部因素有地形因子和土壤因子,包括海拔、坡度、坡向、坡位和土壤类型、土壤厚度、土壤水分含量。冰雪灾害对林下光照、土壤、凋落物、真菌和森林动物产生影响。冰雪灾害后的林下光照对树种更新、森林动态和恢复具有重要意义。研究冰雪灾害对天然林的影响,长期监测冰雪灾害后的森林动态、林下植物的光环境、森林的养分循环、土壤以及森林动物,特别是土壤微生物的变化,加强森林的防灾管理是今后该领域的研究方向。

Effects of ice-snow damage on forests

Ice-snow damage is a common natural disaster, and it often caused huge damage to forests. The frequency of ice storms may increase in response to climate change. Typically, warm, moist air overruns a shallow body of cold air, rain from warm air may become supercooled when it falls from the warmer clouds, causing it to freeze immediately upon contact. Ice-snow damage occurs when the ice loaded on crown exceeds the maximum bending moment for a tree of given size and species. Ice-snow damage of forests dependents on ice accumulation. Accumulation ice can cause tree damage ranged from the loss of tissues to structural failure. Ice-snow damage to trees can range from mere breakage of a few twigs, to bending stems to the ground, to moderate crown loss, to outright breakage of the trunk. There is a close relationship between ice-snow damage and forest characteristics, such as stand density and species composition as well as tree characteristics, such as diameter at breast height, tree height, stem taper, leaf area, crowns symmetry, root system and stand age, etc. The stands with the highest density are the most vulnerable to ice-snow damage, especially for a few years after thinning. Softwoods suffer less damage from the same degree of ice loading than do hardwoods. Trees with branches that droop or have pliable stems and limbs are better withstand ice-snow damage. Dominant canopy trees incur more ice-snow damage than sub-canopy trees. Moreover, ice-snow damage is affected by some external factors, such as topography and soil conditions, including elevation, slope grade, slope aspect, slope position, soil type, soil thickness and soil water content. Higher elevations are more prone to freezing rain. Elevation and aspects increasing exposure to stronger winds result in higher damage. Ice-snow damage also exerts an impact on forest understory light, soil, litter, disease fungi and wildlife. The understory light condition that followed ice-snow damages has great significance to species regeneration, forest dynamic and recovery. A transient increase in understory light following an ice-snow damage may accelerate the conversion of early successional stands to more shade-tolerant species. The rapid decrease in understory light following an ice-snow damage is likely a result of the recovery of both the overstory and understory vegetation. An ice-snow damage indirectly impacts natural plant regeneration by its impact on fruit and seed production. Wildlife first must endure the perils of the ice-snow storm-low temperatures, ice buildup, falling debris, and reduced mobility. Birds are especially vulnerable. Wounds caused by ice-snow damages permit infection by a wide array of disease fungi and become breeding grounds for bark beetles or other pests, especially when the injuries are large and do not heal rapidly. Ice damages also increase potential fire risk by elevating fuel loads. Future research in the field of ice-snow damage to forests should focus on effects of ice-snow damage on natural forests and the long-term research of nutrient cycling and soil, especially microorganism, wildlife, forest dynamics and forest understory light, and reducing the risk of ice-snow damage through forest management.