Effect Of Ice Storm On The Structure Of Evergreen Broad-Leaved Forest In Mt.Nanling

Nanling montains is the important climate dividing line between mid-subtropical zone andsouthern-subtropical zone of China, and one of the biodiversity hotspots of China wheretypical subtropical evergreen forests are distributed. Heavy snow and freeze disaster occurredin southern China during January to February in2008greatly damaged evergreen forests inNanling. In order to understand the effect of this damage to Nanling evergreen forests, we setup sampling plots in Shi'er Dushui Natural Reserve, Dadingshan Protection Station of NanlingNational Nature Reserve, Shixing Chebaling National Nature Reserve and TianjingshanNational Forest Park. All these reserves are in Guangdong Province. The main results obtainedfrom our investigation and analyses are as follows:(1) Damaged plant community in the mid-section of Nanling is situated in the importantpart of China-Japan forest vegetation zone dominated by China-endemic species, and whoseflora has the property that transited from subtropics to tropics. In both broad-leaved evergreensecondary forests (SF) and broad-leaved evergreen old-growth forest (OF), their dominant treespecies belong to Fagaceae, and the difference is found in the shrub layer with dominantEricaceae in SF and Hamamelidaceae in PF, respectively. These community characteristics onthe whole showed a picture of a subtropical evergreen forest.(2) The disaster damage to SF and OF were up to84.24%and40.91%in mechanicaldamage, respectively. However, the mild damage was dominated and the damage to OF is lessthan to SF. Low frequency species were less destroyed in this disaster. Stem bending was themajor type of damages in SF, while top breadage was the major type of damages in OF. Stembending and normal trees were trees with diameter classes I andâ…¡, top breadage trees are thosewith diameter class â…£. The damage degree differed in variable dominant species. Fagaceaespecies were damaged slightly. Only the canopy structure changed a little and the wholecharacteristics of Fargesii did not change. (3) There were72gaps formed after the disaster in our five sampling plots. Small gapswere the majority in SF and big gaps were the majority in OF. Gap-maker trees were mainlycomposed by dominant species: uprooting trees in SF and top breakage trees in OF. For gapregeneration species, most of them were trees and bushes, followed by vines and grasses. Gapregeneration species and the original forest species had low similarity, and this would result inthe invasion of heliophilous species and then short-term changes in community composition.(4)The snow and freeze damage led to low mortality (6.81%-14.80%) in broad-leavedevergreen forests and the dead trees were mainly small ones almost with mechanical damages.Sprouting rates in broad-leaved evergreen forests were up to73.00%, and sprouting rates of OFwere bigger than those of SF. The sprouting rates of destroyed trees in SF were in the sequence:lodging> trunk breakage> top breakage> stem bending> uprooting; the sprout rates ofdestroyed trees in OF were listed: trunk breakage> stem bending> top breakage> lodging.Diameters at breast height (DBH) had certain correlation with the sprout number in SF (a linearcorrelation) and in PF (Power exponent correlation). The number and lengths of sprouts had nocorrelation, and the length of broken stem have no obvious impact on the number and lengthsof sprouts.(5)We firstly used phytogeography to study the response of Nanling broad-leavedevergreen secondary forests to the snow and freeze disaster. We found that their geographicalcomponents were similar with geographical components of mid-section of Nanling, which aredominated by China-Japan components. Among these geographical components, Jiangnandistribution and tropical Asia distribution accounted for the largest proportion in heavydamaged type; South China distribution and Nanling unique elements were less destroyed.Local originating species' ability to resisting damage was stronger than that of tropicaloriginating species. The regeneration of woody plants after the disaster mainly came fromTropical Asia, China-Japan and South China distribution. Though regeneration trees were lessfrom Nanling distribution, their sprouting rates were the highest.(6) Our results suggested that for a rational conclusion it is very important to chooseappropriate calculation or estimate methods for damage index and forest self-recovery potential and so forth. That is to say, to restore the damaged broad-leaved evergreen forests efficiently,we should choose indigenous trees or trees which are originated from Nanling, and at themeantime we should also strengthen the nurture of "target trees".