Vegetation Recovery Characteristics Under Different Spatial Scales In Loess Hilly And Gully Region

The Loess Hilly and Gully Region was known as an ecological fragile region by the serious soil and water loss which due to its special terrains,vegetation,soil and climate conditions.As the main measures to prevent and control soil and water loss,vegetation plays an important role in ecological construction.The implementation of “Green for Grain” has had an important impact on the vegetation restoration and ecological reconstruction in the Loess Hilly and Gully Region and the in what specific extent did vegetation restored has been paid high attention.Therefore,in this study,the vegetation restoration characteristics in Ansai County of Loess Hilly and Gully region was studied based on different data sources from different spatial scales(area scale,watershed scale and slope scale).The main findings are as follows:1)In area scale,the NDVI value increased significantly from 2000 to 2015.All the vegetation levels distributed more evenly in 2000,and vegetation levels patches at all periods mainly transferred to higher vegetation levels.Superior vegetation level(VI)was dominant in 2015.2)The agglomeration of superior vegetation level patches raised significantly from 2000 to 2005.Other vegetation levels distributed more evenly after 2015,which broke the reunion of superior vegetation level patch types.The landscape distribution became more even and diversified,vegetation restoration went well.3)The area of farmland decreased substantially from 2004 to 2015 in typical watersheds,while the area of forest land increased significantly.The farmland in three small watersheds was contiguously distributed in a large area in 2004,and a few forest lands distributed fragmentarily.Then the area of farmland reduced significantly,while forest land increased and agglomerated,all land use types mainly transferred to those types with higher vegetation coverage by 2015,in which time forest land and grassland were dominant land use types.4)The present circumstances of vegetation restoration in three watersheds are positive,as there are more than a half watershed area showed higher NDVI value(> 0.6),only less than 2% area of three watershed showed lower NDVI value(< 0.2).5)Artificial Robinia pseudoacacia forests and Caragana korshinskii shrubs went mature in the 20-30 years period.Artificial Hippophae rhamnoides shrubs went mature by 20 years.The species diversity of understory vegetation in artificial forests had no significant changes with the increase of time,while the species evenness increased.These three communities were all more stable in 20-30 years period.6)The coverage of natural vegetation increased significantly to 43% by the stage of Stipa bungeana and Lespedeza davurica communities,and reached maximum 57% at the stage of Bothriochloa ischaemum communities.The community stability and evenness of Artemisia gmelinii communities and Bothriochloa ischaemum communities were both higher than other communities.Therefore,Artemisia gmelinii communities and Bothriochloa ischaemum communities are more stable than others.