Study On The Variation And Influencing Factors Of Vegetation Phenology In Protected Areas And Lighting Areas

In the context of climate change,the world is facing a severe situation of global warming,the change of precipitation pattern and the increase of extreme climate events.Because of a large number of industrial heat and large area of impervious water in urban areas,the warming situation is particularly significant in urban area.Under such circumstances,protected areas become increasingly important,not only to protect the ecological environment and biological resources,but also to mitigate climate change.Vegetation phenology which is a good indicator of climate change is very sensitive to climate change.At the same time,it is of great significance to the relationship between biological species and the water,heat and carbon cycle of the soil-vegetationatmosphere system.Therefore,this paper uses DMSP/OLS night light data to explore the difference of nightlight level in and around different types of protected areas from 1992 to 2013,to determine whether the protected area has resisted interference from human activities.Next,the characteristics of changes of vegetation phenology in global protected areas are studied.In order to compare the characteristics of vegetation phenology in protected areas with an area under strong human activities,this paper uses DMSP/OLS nightlight data to extract lighting areas as control areas.Then,from the pixel scale,intercontinental scale and different latitude zones,we catch the characteristics of vegetation phenology changes in protected areas and lighting areas and the differences between protected areas and lighting areas.Finally,16 factors(including digital elevation,latitude,longitude,night light,surface temperature,land cover type,cloud cover,daily temperature range,ground frost frequency,near ground temperature and the highest temperature near the ground)related to climate,vegetation,geography and human activities are selected to study the driving mechanism of vegetation phenology on the global,hemispheric,and intercontinental scales by geographic detectors and Pearson correlation coefficients.The purpose of this study is to explore the human pressure faced by protected areas,and the characteristics and differences of phenological changes of protected areas and lighting area at various scales,and the main influencing factors of phenology.These works are of significance in providing a basis for the managing work of protected areas,to enhance the protection value and ecological significance of the protected area,and in better grasping the law of phenological changes,to provide ecological basis for climate change,and in providing a theoretical basis and a novel way for the impact of human activities on vegetation phenology.The main conclusions are as follows:(1)The nightlight level in every type of protected area is significantly lower than that in the surrounding area,which means that the boundary of the protected area effectively prevents the interference of human activities.But the interior of the protected area is not completely dark,there is still a certain artificial light.From 1992 to 2013,the average nightlight level in European protected areas was the highest,followed by Asia,North America,South America,Africa and Oceania.The nightlight change trend from 1992 to 2013 ranking was same as the ranking of nightlight level.From 1992 to 2013,the nightlight level in and around each type of protected area is getting larger and larger.The areas with the highest nightlight level around the protected areas of Ia,II,III,IV and V are generally in the 1-25 km buffer,but of Ib and VI are 50-100 km buffer which is farer from the boundary of protected area.The nightlight levels of different types of protected areas are different.The ranking from high to low is V> IV> III> VI> II> Ia> Ib.By comparing typical sample protection areas,it is found that protected areas of the same type under different social and economic conditions will exhibit different lighting characteristics due to different geographical locations.(2)Among the global protected areas,the most changed ones are SOS,followed by EOS and LOS.SOS of protected areas shows a stronger advance trend,and EOS is showing a stronger postponement trend,and LOS shows a stronger extension trend.For SOS of vegetation in protected areas,15.93% of the 17220 protected areas in the global scale have a significant trend of SOS change,and 73.86% of them show a significant trend of advance.Europe is the continent with the largest number of protected areas,and 78.45% of protected areas with changing trends show a delayed trend.Europe is the continent with the largest number of protected areas of which EOS is with a changing trend,and 78.45% of protected areas with changing trends show a delayed trend.11.34% of the protected areas has a significant change trend in LOS,and 89.25% of the protected areas with a significant change trend show a significant extension trend.The European is with the largest number of protected areas with LOS change,and 97.41% of the protected area with LOS change show a delayed trend.(3)On the pixel scale,20.51% of the pixel SOS in the global protected area shows a changing trend,of which 55.90% shows an early trend,and 27.78% of the pixel SOS in the lighting area has a changing trend,of which 71.54% reflects the early trend,which is 10.91% higher than the protected area.The changing rate(the number of pixels with significant change in SOS / total number of pixels of protected area)of SOS in the lighting area in Europe,Asia,Africa,Oceania is higher than the changing rate of SOS in the protected area,while in North America and South America protected areas The changing rate of SOS is higher than that of the lighting area.In Europe,Africa,South America,and Oceania,the SOS in lighting areas show an earlier trend than the protected areas.In Asia and North America,on the contrary,the SOS of protected areas is stronger than lighting areas.The advance rate(number of pixels with significantly advanced SOS / number of pixels with a changing trend of SOS)of SOS of vegetation pixels in the European protected area reached 88.69%,and the lighting area reached 90.37%,significantly higher than the advance rate of any other continent.The proportions of vegetation pixels in protected areas and lighting areas that have significant changes in EOS are 24.89% and 24.75%,respectively.The changing rate of EOS in protected areas is slightly higher than that in the lighting area.43.97% of the changed pixels of EOS in protected areas show a delayed trend,and 61.34% of the changed pixels of EOS in lighting areas show a delayed trend.At the intercontinental scale,protected areas in Europe,Asia,Africa,North and South America have a larger proportion of pixels with significant change trend of EOS than lighting area.Only Oceania is on the opposite,protected areas have a larger proportion of pixels with significant change trend of EOS than lighting area.EOS in lighting area of Asia,Europe,North America and Oceania shows a stronger postponement trend than EOS in protected areas.The changing rate of LOS of vegetation pixels in lighting areas is 27.76%,of which 69.04% shows a prolonged trend,which is higher than the changing rate of 22.51% and 63.65% with postponement trend in protected area.In Asia and Europe,the change rate of LOS of lighting area is higher than that in the protected area.the other four continents are opposite,and the change rate of the LOS in protected areas is higher than that in the lighting area.(4)The change trend of phenological indicators of different vegetation types on the same continent will be different,and the phenological indicators of the same vegetation type will also be different in different continents.This difference is manifested by the opposite trend of the indicator change,or different degrees of change trend,though the direction of the change trend is the same.In general,the change trend of SOS in the protected areas and lighting areas are continent.The SOS in Africa and North America shows a delayed trend,and in Asia and Europe shows an early trend.The change trend of EOS of the same vegetation type shows different trends in protected areas and lighting areas.The LOS of most vegetation types shows a prolonged trend in the lighting areas and protected areas on all continents.(5)Vegetation phenology shows a certain pattern in the latitude zone,and different vegetation types show a similar pattern.The patterns of SOS,EOS and LOS vary with latitude,and the patterns of protected and lighting areas are also different.For SOS,the SOS of vegetation in the protected area and lighting area in the middle and high latitudes of the northern hemisphere shows a significant advance trend,and there was a delay trend in the low latitudes area.The advance trend of SOS in the lighting area is stronger than that in the protected area.In the southern hemisphere,most vegetation's SOS in the protected area showed a delayed trend.Most vegetation types in lighting areas exhibited a delayed trend at 5 °S-20 °S and an early trend at 30 °S-35 °S.The trend of EOS of global vegetation is more complicated than SOS.The EOS of different vegetation types is obviously different,and the same vegetation type also shows huge differences in different latitudes.At 0-20 °N,the EOS of most types of vegetation in protected areas showed a delayed trend,however,the EOS in lighting areas at this latitude zone has no change trend.At 20-65 °N,the change trend of vegetation EOS in protected areas and lighting areas is more complicated,and there is large difference between different vegetation types.At 65-80 °N,almost all vegetation types with change trend in protected areas and lighting areas show an early trend EOS.At 0-35 °N,LOS of most vegetation types in both protected areas and lighting areas showed a shortening trend.The LOS shortening trend in protected areas was slightly stronger than that in lighting areas;At 35 °N-80 °N,the extension trend of LOS is more obvious in middle and high latitudes,and the extension trend of LOS in lighting areas is stronger than that in protected areas.Most of the vegetation in the southern hemisphere does is not with an obvious trend,and the vegetation with an obvious trend is mainly concentrated at 30 °S-35 °S,all of which shows an extended trend of LOS.(6)According to the results of the geographical detectors and the Pearson correlation coefficient,it can be seen that at the global,hemispheric,and intercontinental scales,latitude,land surface temperature,ground frost frequency,nearsurface temperature,and near-surface maximum temperature are the main factors affecting vegetation phenology in the lighting area and protected area,followed precipitation,wet day frequency and longitude.And the interaction of each two factors will enhance the impact on vegetation phenology,that is,the q value of the two factors acting together is greater than the q value of any one of the factors alone.Generally these factors have a larger q value in protected areas than in the lighting areas.There are no particularly prominent driving factors in lighting areas,and there are no very prominent driving force differences between different lighting areas.In protected areas,these 16 factors have a stronger driving effect on the SOS distribution pattern than the EOS.However,the difference in lighting areas is not obvious.