Altitude is one of the factors that affect the damage degree of trees. However, the difference of stand damage in different areas is very significant under the influence of altitude. The damage degree of trees in high altitude areas is much larger than that in low altitude areas. Because the higher the altitude is, the lower the temperature is. What's more, the high altitude areas where the humidity is greater are more prone to freeze, resulting in a greater accumulation of snow and ice on the canopy, as well as longer freezing time and snow and ice resistance to trees more severer. Some scholars had statistics on the frost damage of navel oranges at different elevations in a certain area in 2008 and found that as the elevation increases(shown as table1 ), the composite index of frost damage increases. In the altitude range of 200 to 300 meters, the proportions of navel oranges without freezing injury in three orchards were 55.0%, 65.0% and 65.0% respectively. With the elevation increasing,the degree of frost damage deepened. In the orchards whose altitude range are 401 to 500 meter，the proportion of frost damage above Grade three obviously increased, accounting for 15.0%, 15.0%, 20.0% respectively.In the three orchards whose altitude are 501 to 600 meter , the frost damage rates of grade three or above were 65.0%, 55.0% and 75.0% respectively. The percentage of frost damage in grade three or above in orchards whose altitude are above 600 meter were 90.0%, 85.0% and 80.0% respectively.
Table1 The freezing injury of navel orange at different altitudes
| Citrus types | Altitude/m | Freezing injury proportion/% | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Xilingxia Xintan Village | Jiuwantang Zhouping Village | Xiongjialing, Guojiaba Village | |||||||||||
| Grade0 | Grade1 | Grade2 | >Grade3 | Grade0 | Grade1 | Grade2 | >Grade3 | Grade0 | Grade1 | Grade2 | >Grade3 | ||
| Navel Orange | 200-300 | 55 | 35 | 10 | 0 | 65 | 30 | 5 | 0 | 65 | 35 | 0 | 0 |
| 301-400 | 30 | 40 | 25 | 5 | 45 | 45 | 10 | 0 | 30 | 50 | 20 | 0 | |
| 401-500 | 10 | 35 | 40 | 15 | 20 | 20 | 45 | 15 | 20 | 30 | 30 | 20 | |
| 501-600 | 0 | 0 | 35 | 65 | 0 | 5 | 40 | 55 | 0 | 5 | 20 | 75 | |
| 601-700 | 0 | 0 | 10 | 90 | 0 | 0 | 15 | 85 | 0 | 0 | 20 | 80 | |
In addition to the altitude, slope and aspect also have a significant impact on the destruction of ice-snow damage to forest vegetation. It can be basically affirmed that the steepness of slope has a significant positive correlation with the degree of forest damage. Due to the phototropism of trees, the asymmetry in the growth of tree canopies at steep slopes results in an unbalanced quality of snow and ice backed up by the crown, causing severe breakage and overturning.
Table2 ANOVA of comprehensive index of the slop in different direction and location to the freezing injury about Pon-kan citrus
| Citrus types | Direction | Position | Comprehensive index of freezing injury | Means±SD | Difference between positions | ||
|---|---|---|---|---|---|---|---|
| Garden in Fenghuang Mountain | Wuligang Garden in Banyue Town | Garden in Zigaisi Forest Centre | |||||
| Pon-kan | Lunar | Bottom | 68.8 | 61.3 | 67.5 | 65.8±4.0 | a |
| Middle | 45.0 | 48.3 | 45.0 | 46.1±1.9 | d | ||
| Top | 51.3 | 56.7 | 52.5 | 53.5±2.8 | c | ||
| Solar | Bottom | 58.3 | 58.3 | 61.7 | 59.4±2.0 | b | |
| Middle | 40.0 | 41.7 | 41.7 | 41.1±1.0 | e | ||
| Top | 48.3 | 50.0 | 48.3 | 48.9±1.0 | d | ||
Some scholars also have calculated the frost damage of navel orange in different slopes in 2008 in a certain area (Table 2), the average proportion of frost damage in the three orchards on the solar slopes (bottom frost damage ratio+ middle frost damage ratio + top frost damage ratio) were 18.3%, 16.7% and 21.7%, respectively, and those without frost damage were 18.3%, 16.7% and 15.0% respectively. The average rates of frost damage on shady slopes of three orchards were 41.7% 33.3% and 41.7% respectively. The proportions of non-frost damage were 15.0%, 15.0% and 15.0% respectively. The comprehensive index of frost damage on lunar slopes is greater than the solar slope, showing that the orchard on the lunar slopes is more susceptible to frost damage. Because the windward slope of the canopy growth more asymmetric, and the outlet prone to freezing, coupled with the wind itself has some impact on the forest, making the windward slope suffered heavy losses. Without enjoying the sunlight, the forest vegetation damage is more serious which is due to lower temperature and less melting of ice-snow on the lunar slopes. In addition, forests in the ravine are more susceptible to damage than those on hilltops or in the middle. For different directions of the hillside (such as the southern slope, the northern slope), the extent of its damage to the forest varies depends on the circumstances.
The information is provided by Disaster Risk Reduction Knowledge Service.
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