Understory Diversity And Biomass Of Polar-Birch Secondary Forest And Larch Plantation In Over-cutting Forest Area Of Changbai Mountains

The study object in this paper is Polar-Birch secondary forest and Larch plantation. Species diversities were analyzed by using Gleason abundance index,Shannon index,Simpson index and Pielou eveness index and the differences between these two different forest types were compared,10 common species of understory shurb were sampled, crown area(Ac),project volume(Vc), ground diameter square times of height(D2H) were used as variables in component biomass models, then tree-like(single trunked) mixed models and shurb-like(multi-stemmed or low branching) mixed models were built according to the growth forms. The shrub biomass along with the distribution of it in different species and components were investigated by using the best-fit models which were judged by high R2 and low SEE, lastly the correalations beween understory biomass and stand characteriscs, species divesties were analyzed, main conclusions are as follows:(1) Shrub diversity indexes were higer than herb diversity indexes in these two forest types,but there were huge differences between two different forest types and the same forest types with different stand densities or ages,the results show that the shrub diversities indexes in Polar-Birch secondary forest were higher than those in Larch plantation,but the herb diversities indexes in Polar-Birch secondary forest were lower than those in Larch plantation.In Polar-Birch secondary forest, shrub species number is the most when canopy densites is 0.8,the shrub diversity and eveness as long as the herb number and diversity are the best when canopy densites is 0.6, but herb eveness index is highest when canopy densities is 0.8.The diversties were increased as the age grows in Larch Platation after canopy closure.(2)The forms of best-fit shrub biomass models are mainly cubic or power equations, variables in these models were D2H or Vc, the mixed model of tree-like plants has higher R2 than that of shurb-like plants, stem and root models have higher R2 than leave and branch models in tree-like plants, and stem and branch models have higher R2 than leave and root models in shrub-like plants,most species-specific component models have higher R2 than mixed-species component models.(3) The understory biomass is 7327.67 kg·hm-2 in Polar-Birch secondary forest,35863.17 kg·hm-2 in Larch plantation,the two forests understory biomass mainly stored in shrub layer,however there were huge differences between different stand densities or ages in these two different forest types, understory biomass as along as shrub biomass is the most when canopy densites is 0.8,least when the canopy densites is 1.0, when canopy densites reaches 0.6,the herb biomass reaches its peak.The understory biomass and biomass contribution of shrub layer in Larch Plantation grows as stand ages grows.(4) Shrub biomass of Polar-Birch secondary forest was the highest in stem, then root and branch, Shrub biomass of Larch Plantation was the highest in stem, then root.the biomass of Polar-Birch secondary forest mainly stored in tree-like plants,while biomass mainly stores in different species with different stand ages,the biomass of 39 years old Larch Plantation mainly stored in shrub-like plants such as Sorbaria sorbifolia, Padus racemosa etc, the biomass of 52 years old Larch Plantation mainly stored in tree-like plants like Acer ukurunduense, Syringa reticulata var. amurensis.The under-ground shrub biomass is bigger than below-ground biomass and under-ground herb biomass is lower than below-ground biomass in different stand densities in Polar-Birch secondary forest;The underground biomass of understory in Larch Plantation grows as the stand ages grows.(5) The understory biomass in Polar-Birch secondary forest was most affected by canopy densites,shrub bimass growth as the canopy densites grows,but in a certain time when canopy closed(canopy density=1.0),the shrub biomass declines in stead; herb biomass declines as the the canopy densites grows.The shrub ansd herb biomass grows as the stand ages and basal area per hecter grows.there are no significant correalations between shrub and herb biomass and diversity indexes in Polar-Birch secondary forest;while in Larch Plantation,the shrub biomass decease as diversity indexes grows,herb biomass grows as diversity indexes grows.