Effects Of Frozen Disturbance On Canopy Condition And Seedling Dynamics Of An Evergreen Broad-Leaved Forest In Damingshan

Forest canopy is the most direct and active layer interacting with the external environment in forest ecosystem. Species biodiversity in canopy, canopy and climate change has become one of hotspots in international ecology research. Canopy also gradually is developed as a discipline. In the present study, the changes of canopy of an evergreen broad-leaved forest after damaging by frozen rain and snow and its effects on the dynamic of tree seedlings were analyzed by continually surveying in 72 permanent sample plots (each plot was 400 m2) for 4 years in an evergreen broad-leaved forest in Damingshan Mountain. The objectives are to:(1) clarify the effects of ice storm disturbance on canopy and community regeneration; (2) provide data for deeper understanding the canopy characteristic of evergreen broad-leaved forest and enriching the Canopy theory in southern subtropics.The main results are as follows:(1) A total of 2538 trees with DBH≥5cm were identified in the 72 permanent sample plots, in which 1714 trees were suffered different degree of damage accounting for 67.53% of the total trees. Moreover, the proportion of not-damaged, slight damaged, and severe damaged trees were 32.47%, 47.75%, and 19.78%, respectively, suggesting slightly damaged was the major trends in this forest.(2) According to the investigation in the area between altitude of 943～943 m, the canopy damage condition in different slopes dominated by slight damage with the damage ratio from 66.24% to 68.89% and there were no significant differences between the canopy damage condition of different slope. The highest ratio of slight damage (52.38%) occurred in midslope, the lowest (40.94%) in upslope. Moreover, the highest ratio of severe damage (26.49%) occurred in upslope, the lowest (16.25%) in midslope.(3) Diameter at breast height is one of the main factors in determining the damage type. With the increase of diameter at breast height, canopy damaged ratio increased gradually, the highest value measured at 30～40 cm diameter class (upslope) and 40～81 cm diameter class (midslope and downhill); Proportion of broken branches (including less and more) increased with the increment of diameter at breast height, while broken tip and canopy loss decreases with increasing diameter at breast height. Deciduous trees tend to suffer broken branches and evergreen trees tend to suffer broken tip.(4) Compared with before freezing disasters in 2006, leaf area index of different slope decreased 18～41%. Leaf area index declining significantly increased the light intensity in understory. The light scattering coefficient and direct transmission coefficient increased 42-60% and 42-56%, respectively. Evergreen broad-leaved forest in Damingshan Mountain belongs to low leaf area index forest with relatively stable leaf area index averaged 1.98. This may be due to the long term ice storm disturbance in the middle-mountain drive the half-ball-shape canopy changing to confined cylindrical shape.(5) Ice storm disturbance was the major driving force for the regeneration of Lauraceae, Fagaceae, Styracaceae and Elaeocarpaceae plants. After disturbance, the genera and species numbers of these families increased. A total of 11 species in Lauraceae was detected in the regeneration plants accounting for 30% of regeneration seedlings. The individual numbers of these seedlings made up 34.12%～73.65% of all the regeneration individuals with an average of 56.28% in 3 years. The density of regeneration seedlings showed an initial increase and subsequent decrease, that is to say, the density increased from 2067～3717plants/hm2 in 2009 to 5267～7500 plants/hm2 in 2010, and decreased to 3267～4717 plants/hm2 in 2011.(6) With the extension of recovery, except for the upslope in 2010, the species richness, diversity index, Simpson index and evenness index decreased. However, there were no significant differences in these indexes in different years and slope position.(7) Slope position and years had different effects on the height class structure of regeneration seedlings with the seedling individuals in V class were the most and Ⅲ class the lest. In the first year after ice storm disturbance, there were few regeneration seedling individuals in Ⅰ, Ⅱ and Ⅲ class, even lost. However, the regeneration seedling individuals of different classes, especially the Ⅰand ⅡI class in the second year after disturbance increased. This suggested the gaps increased after ice storm disturbance improved the availability of resources, such as light, temperature and water, and promoted the regeneration and growth of seedlings.