Research On The Spatial-Temporal Dynamics And The Driving Mechanisms Of Wetland Landscape In Honghe National Nature Reserve,Northeast China Over The Past 40 Years

The unique environmental conditions of wetlands give them a rich flow of material,energy and information,as well as providing habitat for a diverse range of organisms,and are considered to be among the most productive ecosystems in the world.The Heilongjiang Honghe National Nature Reserve(HNNR)plays an important role in protecting rare and endangered plant and animal resources and the wetland ecosystems on which they depend,and in maintaining biodiversity.However,due to human activities and natural factors,the marsh wetland ecosystem in the HNNR has been seriously degraded,and the quantity and quality of wetland resources have been drastically reduced,posing a great threat to wetland organisms.This study takes the HNNR as the research object,using Random Forest algorithm to extract wetland information from the long time series Landsat remote sensing images based on Google Earth Engine cloud platform,and obtain the landscape spatial distribution dataset of the HNNR from 1985 to 2021;using spatial analysis and other methods,the key indicators such as area change of landscape elements,transfer matrix,mass centre change and landscape pattern index are analysed to reveal the spatial and temporal dynamic characteristics of the landscape pattern of the HNNR;quantitatively analyze the relationship between landscape pattern change and various driving factors,and explore the driving mechanism affecting the change of wetland landscape pattern of the HNNR,with a view to providing theoretical and methodological reference for wetland ecology research,while the research results can also directly The results of the study can also be directly used for the scientific management of wetland ecosystems in protected areas.The main conclusions are as follows:(1)Based on the GEE cloud platform,the classification of Landsat series images using the Random Forest algorithm can achieve better results,effectively extracting the wetland information of the HNNR from 1985 to 2021,with overall classification accuracy above 80% and Kappa coefficients above 0.70,and constructing a spatial distribution dataset of the HNNR landscape with this.(2)From 1985 to 2021,the area of marsh wetlands in the HNNR increases overall,the area of meadows decreases significantly,the area of woodlands and water increases significantly,and the area of arable land increases first and then decreases sharply after conversion to abandoned land.Among them,from 1985 to 2008,the area of marsh wetlands in the HNNR showed a general downward trend,an upward and then downward trend in the area of meadows,a downward and then upward trend in the area of woodlands,and a continuous increase in the area of arable lands;the landscape change in this time period was mainly from marsh wetlands to meadows,and meadows to woodlands and arable lands.From 2008 to 2021,the area of marsh wetlands in the HNNR gradually rises and reaches a stable state,the meadow area decreases significantly,the woodland areashows a steady rise,and the water area increases significantly and then stabilizes,the vast majority of the arable land area has been converted to abandoned land,and the landscape change in this phase is mainly from meadow to marsh wetland.The landscape index analysis shows that the landscape of the HNNR is always dominated by the marsh wetland,with woodland,arable land and water expanding their dominance by encroaching on the meadows.The marsh wetland became increasingly fragmented from 1985 to 2008,while the marsh wetland fragmentation improved significantly from 2008 to 2021.Meadow fragmentation continues to increase.At an overall level,the landscape shape of the HNNR becomes more complex,favouring wetland stability and increasing landscape heterogeneity.(3)Changes in hydrological conditions due to natural and human factors are the main drivers of the evolution of the wetland landscape in the HNNR.From 1985 to 2008,human activities such as construction of water conservancy projects and irrigation of arable land,coupled with a declining trend in precipitation,led to a decline in the surface water and groundwater levels in the HNNR,resulting in the degradation of the wetland habitat.From 2008 to 2021,due to the barrier dam constructed in the lower reaches of the Nongjiang River,the water level in the HNNR rises and both the area of the wetland and the area of the water rise,allowing the hydrological situation to recover and the wetland habitat to be restored.