The Effect Of Patched Vegetation Pattern On Plant Regeneration In Loess Hilly And Gully Regions

The Hill-gullied Loess Plateau region is one of the regions with the most serious soil erosion and vulnerable ecological environment in China.And the region also is the key and difficult area for ecological management.In arid and semi-arid areas,patched vegetation pattern is a common and relatively stable landscape type and it is a result of vegetation adapting to the climate and environments.The patched vegetation pattern directly affects the redistribution of resources within the community,which in turn affects the spatial pattern of plant populations.Studying the effects of vegetation patches on plant regeneration can better explore the structural characteristics of plant communities,and provide a theoretical basis for scientific prediction of the development direction of vegetation structure and vegetation construction in the study region.In this study,the Yanhe basin was the study area.Three typical watersheds(Liandao Bay,Ansai,Haiyan Gully)were chosen according to the precipitation gradient.And three typical plant communities(Bothriochloa ischaemum,Sophora viciifolia and Artemisia gmelinii)were selected as the research object.The soil seed bank,seedling and standing vegetation species composition,abundance and s pecies diversity characteristics in both time and space scales in plant patches and bare land patches were studied based on the quadrat survey and indoor germination experiment.And then,the relationships between soil seed bank,seedling and standing vegetation were analyzed.The main results are as follows:(1)In this study,108 species were recorded in standing vegetation and 81 species were recorded in of seedlings,in the field survey,and 45 species were identified by soil seed bank germination experiments.Gramineae,Leguminosae,Gramineae took largest part among the vegetation composition.Among all these species,perennial herbs accounted for the largest proportion,followed by annual and biennial herbs,then by shrubs and subshrub species,and few species of trees.(2)The patchy distribution pattern of vegetation made the spatial distribution of soil seed banks and seedlings difference in species composition,density and diversity between plant patches and bare patches.In plant pactches,the soil seed bank density ranged from 262 to 3868 seed/m2,seedling density ranged from 15 to 133 seed/m2,while in the bare patches,soil seed bank density ranged from 83 to 2549 seed/m2,seedling density ranged from 8 to 73 seed/m2.The species number,density,diversity of the soil seed bank and seedlings were all higher in plant patches than bare patches.The seeds were mainly distributed in 0-2 cm soil layers,and the soil seed bank density that persisted in 2-5 cm soil layers were relatively small.Along rainfall gradients,the density and diversity of soil seed banks and seedlings in the three communities did not increase with the increase of precipitation.It indicated that the gradient of rainfall in this study does not change much,and it is not the main factor affecting the soil seed banks seedlings species diversity.(3)The density and diversity of soil seed bank and seedling bank showed seasonal changes.The density and species diversity of soil seed bank were all showing the followed change trend:April>August>October.About the seedling,the largest seedling density were recorded in August and the lowest seedling density were recorded in April.And the largest species diversity was recorded in October and the lowest species diversity was recorded in April.(4)The proportion of common species in the soil seed bank,seedling bank and aboveground plants exceeded 73%.The results showed that seed regeneration was the main strategy approach in the process of vegetation regeneration in this region.The Sorensen index of soil seed bank and seedlings,seed bank and standing vegetation,seedlings and standing vegetation of the three communities was generally plant patches>bare patches,and there was no significant difference between the two patches.Sorensen index was between soil seed bank and seedling bank>was higher than it between seedling bank and standing vegetation>ang then higher than it between soil seed bank and standing vegetation,but the Sorensen index is was lower than 0.52,and the similarity is was low.(5)To sum up,in the study area,in during the slope vegetation natural restoration process of slope vegetation in the study area,patchedy of vegetation pattern gradually formed,and the relationship of sink and source was existed between plant patches and bare patches.Plant patches can effectively increase the interception and preservation of soil seed bank,and increase the species diversity and density.At the same time,in plant patches,the combination of the meliorative improvement of microhabitat by plant patches and the rich soil seed bank promoted the germination and survival of seedlings,and standing vegetation played an active positive nursery role in the germination and survival of seedlings.Therefore,compared with bare plaquespatches,plant plaques patches have higher success rate of seedling regeneration and plant restoration,which provides guarantee for the maintenance and stability of plant patches,and makes the patchy pattern of slope vegetation more stable,and have a more profound impact on the hydrological process and soil erosion process.