| Larix principis-rupprechtii is one of dominant tree species in the middle and high mountain coniferous forest in North China.The understory regeneration of Larix principis-rupprechtii was poor,and litter was an important factor.In this paper,the natural secondary forest of L.principis-rupprechtii in Guandi mountain was selected as the research object,and three typical stands of L.principis-rupprechtii,including pure stand,mixed stand of Larix principis rupprechtii and Picea spp.,mixed stand of Larix principis-rupprechtii,Betula spp.and Populus spp.In this paper,quantity and distribution characteristics of regeneration of L.principisrupprechtii for above three stands were analyzed based on understory investigations of 12 square plots of 20 m × 20 m.We also collected understory litter distinguished decomposition state of each plot,set up indoor litter-covering experiment to explore the physical barrier effect,prepare litter extract solution to disclose the chemical effect of litter on seed germination and seedling growth.Based on above research results,litter was somewhat removed and seeds were added to the plot with no regeneration,in order to explore the changes of germination after removal of litter.The results were as follows:(1)The regeneration of L.principis-rupprechtii forest was poor.A few seedlings and saplings were clustered at the stand edge or gap.There were only 19 seedlings and 58 saplings in 12 plots,and the maximum regeneration density was 250 seedlings per hm2.Among the three types of L.principis-rupprechtii stands,the highest regeneration density was 187.50±52.04 per hm2 in mixed stand of L.principis-rupprechtii,Betula spp.and Populus spp.That of L.principis-rupprechtii pure stand was 136.46± 44.54 per hm2.The mixed stand of L.principis rupprechtii and Picea spp.was of the leaest regeneration density(90.63±78.64 per hm2).Among the three types of stands,L.principis-rupprechtii pure stand was of the best seedling growth,followed by the mixed stand of L.principis rupprechtii and Picea spp.,and the seedling growth of mixed stand of Larix principis-rupprechtii,Betula spp.and Populus spp.was the worst.(2)The initial germination time and germination rate of L.principis rupprechtii was both significantly affected by litter covering patters and thickness.The initial germination time of below-cover-litter treatment was significantly later than the above-cover-litter treatment.The germination rate of seeds covered by undecomposed and semi-decomposed litter above seeds was lower than that of litter only covered above seeds.In the same treatment,the thicker the litter,the lower the germination rate.The root length of seedlings of treatment of above-cover litter and below-cover litter was significantly less than that of seedlings only above covered.There was no significant difference of stem length among treatments.(3)Litter water extract significantly inhibited seedling growth of L.principis-rupprechtii.The inhibition effect of litter of pure L.principis-rupprechtii stand was the weakest(IR=-0.12),followed by mixed stand of L.principis rupprechtii and Picea spp.stand(IR=-0.21),and that of mixed stand of Larix principisrupprechtii,Betula spp.and Populus spp.was the strongest(IR=-0.27).Litter decomposition degree had a markable effect on seed germination,seedling growth and biomass(P<0.05).The inhibition effect of undecomposed litter of pure L.principis rupprechtii stand and L.principis rupprechtii and Picea spp.was the weakest,the inhibition effect was gradually increased with the deepening of litter decomposition degree.The inhibition effect of undecomposed litter in mixed stand of Larix principis-rupprechtii,Betula spp.and Populus spp.was the strongest,the inhibition effect of litter was weakened with the deepening of litter decomposition degree.(4)It was found that the regeneration of L.principis-rupprechtii was significantly affected by the thickness of undecomposed layer and the thickness uniformity of each litter layer.When each litter layer was of 2~4 thickness,it was beneficial to the regeneration of L.principis rupprechtii.In the quadrat of no regeneration,the germination rate of L.principis-rupprechtii significantly increased by removing semidecomposed litter and adding seeds.In conclusion,the regeneration of L.principis-rupprechtii forest is poor,and litter was a limit factor.Before the seed falling in autumn,removal of litter above the decomposed layer could significantly improve the germination and seedling growth of L.principis rupprechtii,thus promoting the regeneration of natural secondary forest of L.principis rupprechtii. |
