The response and recovery mechanisms of forests to damage from freezing rain and snow events are a key topic in forest research and management. However, the relationship between the degree of damage and tree age, i.e., whether seedlings, young trees, or adult trees are most vulnerable, remains unclear and is rarely reported. We investigated the effect of tree age on the degrees of vegetation damage and subsequent recovery in three subtropical forest types-coniferous, mixed, and broad-leaved-in the Tianjing Mountains, South China, after a series of rare icy rain and freezing snow events in 2008. The results showed that damage and recovery rates were both dependent on tree age, with the proportion of damaged vegetation increasing with age (estimated by diameter at breast height, DBH) in all three forest types and gradually plateauing. Significant variation occurred among forest types. Young trees in the coniferous forest were more vulnerable than those in the broad-leaved forest. The type of damage also varied with tree age in different ways in the three forest types. The proportion of young seedlings that were uprooted (the most severe type of damage) was highest in the coniferous forest. In the mixed forest, young trees were significantly more likely to be uprooted than seedlings and adult trees, while in the broad-leaved forest, the proportion of uprooted adult trees was significantly higher than that of seedlings and young trees. There were also differences among forest types in how tree age affected damage recovery. In the coniferous forest, the recovery rate of trees with broken trunks or crowns (DBH > 2.5 cm) increased with tree age. However, in the mixed and broad-leaved forests, no obvious correlation between the recovery rate of trees with broken trunks or crowns and tree age was observed. Trees with severe root damage did not recover; they were uprooted and died. In these forests, vegetation damage and recovery showed tree age dependencies, which varied with tree shape, forest type, and damage type. Understanding this dependency will guide restoration after freezing rain and snow disturbances.

Most studies of temporal and spatial distribution characteristics for droughts and oods analysis were conducted only from the perspective of a single factor (precipitation), while ignoring the impact of the characteristics of the underlying surface on the formation of droughts and oods. Using the daily precipitation data of 88 meteorological stations in Hainan province from 1970 to 2019, the 30m resolution DEM data and land use dataset, etc, the precipitation Z index is used to evaluate the drought and ood levels in Hainan. The analysis results were revised by underlying surface data to evaluate the spatiotemporal characteristics of the drought and ood area in Hainan. The drought-prone areas and ood prone areas in Hainan Island were divided, and on this basis, the set pair analysis method was used to identify the regions with alternating drought and ood areas in Hainan. The results show that the overall arid area shows an obvious downward trend, while the ood area presents an increasing trend.The drought-prone areas throughout the year are more concentrated in the northeast of Hainan Island, while ood prone areas are mainly distributed in the eastern coastal areas. The regions where drought and ood occur alternately are small but concentrated. The drought and ood prone areas and alternate drought and ood areas before and after the revision by the underlying surface were compared. It can be seen that the overall trend is relatively similar and obvious before and after the revision. The result of drought areas before revision is 7.97 times larger than that after revision. The ood prone areas before revision are 2.91 times larger than that after revision. Finally, combining climate and underlying surface factors, suggestions for drought and ood prevention are put forward.

The traditional drought and flood analysis method had not fully considered the proportion analysis of different drought and flood grades in the historical years of each rainfall station. This made results unconvincing and made it difficult to deeply understand the characteristics and applicability of various methods. Based on the daily rainfall data of 88 stations in Hainan Island from 1970 to 2019, the China-Z index and the Standardized Precipitation Index (SPI) were used to compare and analyze the spatial and temporal distribution characteristics of droughts and floods from three different time scales (flood season, non-flood season and the whole year). The results showed that both SPI and China-Z index can well reflect the actual drought and flood situations in Hainan Island. The analysis of the proportions of different drought and flood grades in the historical years of each rainfall station and regional historical drought and flood statistics suggested that the China-Z index had a better indication effect than SPI on the extreme drought and flood grades. The alternation of drought and flood between different eras were obvious. Hainan Island generally presented an east-west reverse drought-flood variation trend, as well as a north-south reverse drought-flood variation trend. The drought and flood in the central mountainous area of Hainan Island had been relatively stable. The distribution pattern of drought and flood had a good spatial consistency in the three periods. On the whole, Hainan Island had shown a trend of flood in the east and drought in the west in the past 50 years.

Most studies of temporal and spatial distribution characteristics of droughts and floods analysis were conducted only from the perspective of a single factor (precipitation), while ignoring the impact of the characteristics of the underlying surface on the formation of droughts and floods. Using the daily precipitation data of 88 meteorological stations in Hainan province from 1970 to 2019, the 30m resolution DEM data, land use dataset, etc, the precipitation Z index is used to evaluate the drought and flood levels in Hainan province. The analysis results were revised by underlying surface data to evaluate the spatiotemporal characteristics of the drought and flood area in Hainan province. The drought-prone areas and flood prone areas in Hainan province were divided, and on this basis, the set pair analysis method was used to identify the regions with alternating drought and flood areas in Hainan. The results show that the overall arid area shows an obvious downward trend, while the flood area presents an increasing trend. The drought-prone areas throughout the year are more concentrated in the northeast of Hainan Province, while flood prone areas are mainly distributed in the eastern coastal areas. The regions where drought and flood occur alternately are small but concentrated. The drought and flood prone areas and alternate drought and flood areas before and after the revision by the underlying surface were compared. It can be seen that the overall trend is relatively similar and obvious before and after the revision. The result of drought areas before revision is 20.43 times larger than that after revision. The flood prone areas before revision are 8.50 times larger than that after revision. The alternating drought and flood areas before underlying surface revision in spring and summer are 17.50 times larger than that after revision. Similarly, it is 48.64 times in summer and autumn, and 17.62 times in autumn and winter. Finally, combining climate and underlying surface factors, suggestions are put forward for drought and flood prevention.