Study On Ecological Characteristics Of Coarse Woody Debris In Three Typical Forest Types In Tianbaoyan National Nature Reserve

With the method of adjacent-grids,the study on the input way,the storage,the diameter distribution , height/length structure , spatial distribution pattern of CWD and the characteristics of its decay class,and the water and soil conservation function of CWD and so on were carried out in Rhododendron simiarum forests,Tsuga longibracteata forests and Crytomeria fortunei forests in Tianbaoyan National Nature Reserve,which aimed to provide references for the management of Coarse Woody Debris(CWD),and the full display of ecological functions of those CWD in forest ecosystems in Tianbaoyan National Nature Reserve.The results showed that:⑴The input ways of CWD in these three types of forests were of different kinds,in the major forms of fallen trees,snags and stumps,thereinto,fallen trees existed in three forms,namely breakage on trunk,breakage at trunk base and uprooting.In addition,the reasons causing the death of fallen trees,snags and stumps were different,and the death were mainly resulted from the individual death and the disturbance;⑵The fallen trees and snags in these three types of forests,mainly belonged to small-diametered CWD,that is,they mainly distributed at the range of 0～20cm,and the number of small-diametered CWD > middle > big , however , the proportion of small-diametered CWD in Rhododendron simiarum forests and Tsuga longibracteata forests increased with the elevations,while that in Crytomeria fortunei forests displayed the opposite trend with the elevations;⑶In terms of elevations,the height/length of fallen trees and snags in these types of forests at high- and mid- and low elevations distributed at the range of 1～3m,and at the same elevation,the amount of fallen trees of this range was more than that of snags with the height/length of 1～3m;in the light of stands,the height/length structure of these three types of forests all centered around 1～3m,and what's more,the number of fallen trees and sangs in the three forests decreased with the increase of height/length class;⑷Generally speaking,the spatial distribution pattern of CWD in these three types of forests,were aggregated or random.Different kinds of CWD in the same forests had different spatial patterns with the changes of elevations as well;⑸In terms of forest types,the total storage of CWD in Rhododendron simiarum forests in Tianbaoyan National Nature Reserve(45.2664 t/hm^-2)>Tsuga longibracteata forests(32.5526 t/hm^-2)>Crytomeria fortunei(28.4368 t/hm^-2);considering the types of CWD,the total storage of fallen trees(37.8617 t/hm^-2)>snags(5.4263 t/hm^-2)>stumps (1.9784t/hm^-2)in Rhododendron simiarum forests,in Tsuga longibracteata forests was fallen trees(20.9994 t/hm^-2)>snags(10.6783 t/hm^-2)>stumps(1.875 t/hm^-2),and stumps>snags>fallen trees in Crytomeria fortunei forests;from the point of elevations,they showed the upward trend with the increase of elevations both in Rhododendron simiarum forests and Tsuga longibracteata forests,while the storage of CWD in Crytomeria fortunei forests changed with the increase of elevations and showed high(20.2192 t/hm^-2)>low(6.6074 t/hm^-2)>middle(1.6103 t/hm^-2);as for the decay class,the storage distribution among CWD of different decay classes in the three types of forests all was in line with normal distribution,namely the storage ofⅡ-class CWD andⅢ-class CWD were relatively more,andⅠ-,Ⅳ- andⅤ-class CWD were relatively less,and their specific order wasⅢ(16.2750 t/hm^-2)>Ⅱ(11.5384 t/hm^-2)>Ⅴ(9.9258t/hm^-2))>Ⅳ(5.0717t/hm^-2)>Ⅰ(2.4575 t/hm^-2)in Rhododendron simiarum forests,Ⅱ(14.9505 t/hm^-2)>Ⅲ(5.4095 t/hm^-2))>Ⅴ(4.5299 t/hm^-2)>Ⅰ(3.7513 t/hm^-2)>Ⅳ(3.7210 t/hm^-2)in Tsuga longibracteata forests,and the storage of CWD showedⅡ>Ⅲ>Ⅰ>Ⅴ>Ⅳin Crytomeria fortunei forests;the fallen trees,snags and stumps with different decay classes had a various contribution to the storage,and the storage they had was different even at the same elevation;⑹Generally speaking,Ⅱ-class CWD in Rhododendron simiarum forests and Tsuga longibracteata forests dominated,whileⅠ-class CWD in Crytomeria fortunei forests was more than CWD of any other decay classes.Thereinto,Ⅱ-class fallen trees,Ⅰ-class snags andⅤ-class stumps in Rhododendron simiarum forests were the most in quantity accourdingly;andⅡ-class fallen trees and snags accounted for the majority,andⅤ-class stumps in Tsuga longibracteata forests dominated;while the snags,fallen trees and stumps in Crytomeria fortunei forests all hadⅠ-class as the majority;⑺From the point of stands,the water-holding capacity of CWD in Rhododendron simiarum forests>Tsuga longibracteata forests>Crytomeria fortunei forests,so we can say that CWD in Rhododendron simiarum forests had the most powerful function of runoff and silt retardance,in fact,fallen trees,snags and stumps in those forests all had the function of runoff prevention in some measure,but their water-holding capacity varied.As a whole,the water-holding capacity of fallen trees>snags>stumps in Rhododendron simiarum forests and Tsuga longibracteata forests,and that of stumps>fallen trees>snags which might have something to do with the human disturbance.Generally speaking,the higher the decay class and the more the storage,the more the water-holding content and the water-holding content almost increased with the rise of elevations.