Spatiotemporal Variation Of Phenology And Its Response In Qinling Mountains In The Context Of Climate Change

The study of plant phenology is of great significance for the in-depth exploration of the response relationship between global climate change and terrestrial ecosystems.The mountainous area is considered as the outpost of global change.The Qinling Mountain,as the “backbone of China”,has a unique geographical location and topographical features,which are more typical and representative to regional response to climate change.The warming of this climate sensitive area can be regarded as an early warning signal for China's climate change and even global warming.Therefore,the study of vegetation phenology in the Qinling Mountains is of far-reaching significance in revealing the response mechanism of the mountain vegetation ecosystem to climate change.This study was based on natural phenology observations from 1964 to 2015,combined meteorological observation data of the same period and vegetation remote sensing data since 2000,in order to study the spatiotemporal pattern variations of phenology and its response mechanism in Qinling Mountains in the context of climate change,to explore the possibility of using remote sensing phenology to represent ground observation phenology,to provide a theoretical basis for phenological application research and practice,and to provide data foundation and scientific basis for in-depth understanding of the facts of global change,and the response and adaptation of ecosystem,and other scientific issues.This study has obtained the following main conclusions and progress:(1)Based on observed phenological data analysis,it was found that the beginning and the end of the plant phenology has advanced and delayed,causing a significant prolongation of the growth season,over the past 52 years.There were differences of tree species and the northern & Southern slope.The abrupt change of plant phenology occurred in the mid-1980 s.and the response of the plant phenology to the climate change was more sensitive after the abrupt change.The plant phenology has advanced at a rate of 1.2 days decade-1,the end of the plant phenology has delayed at a rate of 3.5 days decade-1,and the growth season was a significant prolongation,over the past 52 years.The abrupt change of phenophase occurred in the 1980 s in Qinling area,the start of phenophase occurred in 1985 and the end of phenophase did in 1984.Before the abrupt change occurs,there was no significant change in the beginning of the phenology,but a significant advance in the end of the phenology.After the abrupt change occurs,plant phenological characteristics changed significantly,compared with abrupt change before,showing that the advanced rate in the start of phenophase was faster at a rate of 4.3 days decade-1,and the trend in the end of the phenophase turned into a very significant delay at a rate of 8.4 days decade-1,the rate of change and the significance at the end of the plant phenophase were higher than that at the beginning of the period.These changes in the beginning and end points of plant phenophases manifest as a "convergence effect".Interdecadal variations in phenology indicate that the rate of advance in the beginning of plant phenophases slowed from 2001 to 2005,and that the response of plants to climate change showed qualities of adaptability and hysteresis.The changes in phenophase varied by species,the advancement of the beginning of the phenophase promoted the prevalence of shrubs,trees,and vines,in this order,at the beginning of the phenophase,whereas the delay in the ending of the phenophase decreased the abundance of trees,shrubs,and vines,in this order,at the end.The plant responses to climate change in the Qinling Mountains differed along a north-south axis.The rate of advance in the beginning of the phenophase was higher in the northern slopes than in the southern slopes,whereas the rate of delay in ending of the phenophase was more severe in the southern slopes than in the northern slopes.(2)Based on the analysis of climatic growth season(CGS),it is found that the spatial distribution pattern of the CGS in the Qinling Mountains showed significant elevation sensitivity,and the location of the temperature belt has a significant vertical migration along the elevation,and the migration amplitude is more larger after abrupt change of temperature,the north subtropical,and the warm temperature zones on the southern slope and the northern slope increased by 297.71 m,326.06 m,and 334.82 m,respectively.Through the analysis of the spatial distribution and change trends of the GSS(the growth season start),GSE(the growth season end)and GSL(the growth season length)of the climate in the Qinling Mountains,it was found that the regional scope of the three were all extended to high-elevation areas.As an increase in 100 meters of elevation,it resulted in a GSS delay of 2.19 days,GSE advancement of 2.27 days,and GSL shortening of 4.45 days,after the abrupt change of the temperature.According to the “China Climate Regional New Plan”,the temperature zone is divided by the accumulated temperature days of ?10?,that is,the GSL(temperature threshold temperature of 10?)in the study.The warm temperate zone and the north subtropical zone correspond to 170-220 d and 220-240 d,respectively.The results showed that the 170 d and 220 d contours extracted from the GSL of the Qinling Mountains had changed,especially after abrupt changes of temperature.the north subtropical location moved northward by about 297.71 m,and the range expanded by about 28.35m;the warm temperate zone in the southern slope of Qinling Mountains,which the position movednorthward by 326.06 m,and the range expanded by approximately 54.93 m.And the warm temperate zone in the northern slope showed an upward trend along the elevation and the range narrowed,which was approximately 334.82 m and 74.8m respectively,after the temperature abrupt change.(3)Based on the phenological data of remote sensing,it was found that the threshold of EVI2(the enhanced vegetation index 2)in the starting and end of phenology in the Qinling Mountains were 0.28 and 0.26,respectively.The vertical belt of the vegetation with an increasing elevation gradient,the starting,end and growing season were all exchanged in the alpine meadow area between the northern and southern slopes,which shows that the northern slope is earlier,later and longer than the southern slope.The vertical belt of the vegetation from the low-altitude area to the high-altitude area,the starting of phenology occurred earlier in the southern slope than the northern slope,but it was earlier approximately 23.81 days and 1.96 days in the northern slope than the southern slope in the area of ?600m and the alpine meadow area;the end of phenology occurred later in the southern slope than the northern slope,but it was later approximately 7.58 days in the northern slope than the southern slope in the alpine meadow area;the growing season of phenology was longer in the southern slope than the northern slope,but it was longer approximately 6.58 days and 9.54 days in the northern slope than the southern slope in the area of ?600m and the alpine meadow area.The interannual variation trend in the vegetation vertical belt along the elevation also shows that the advanced amplitude of the starting phenology gradually increased,especially in the alpine meadow area on the north and south slopes;the delay amplitude of the end of phenology gradually weakened;while the growing season turned the weakening trend to a sharp increase,especially in the alpine meadow area on the northern slope.(4)There are differences in the degree of Phenological response to climatic factors and the response is more sensitive after the abrupt change.The start and end of phenophase were both comprehensively affected by the climatic factors such as temperature,sunshine,and precipitation,in which the air temperature was the predominant factor.Especially,the rise of the daily mean te mperature during the same period plays a dominant role in advancing the starting of phenophase and delaying the end of phenology.There is 1~3 months of a lag effect for the responses of the start and end of phenophase to climate change in varying degrees.The beginning and end of plant phenology is affected by the combined effects of temperature,sunshine,and precipitation,and there are differences in the contribution of climatic factors to the changes of the beginning and end of plant phenology,its ability to explain the change of the beginning of phenology is in the following order: average daily temperature > effective accumulated temperature > average daily sunshine > accumulated precipitation;and the impact on the end of phenology is daily average temperature > cumulative sunshine > effective accumulated temperature > cumulative precipitation > daily average daily sunshine.Temperature is the most important factor affecting the change of the plant phenology,in particular,the effect of daily average temperature over the same period has dominant control effect.And there is a difference in the contribution of climatic factors to the influence of the changes in the start and end of phenology.There is a lag effect for the responses of the start and end of phenophase to climate change.The time-lag was about 1-2 months for air temperature and about 1-3 months for the pre-period cumulated precipitation on the start of phenophase,respectively.Nolag effect on the start of phenophase was found for the sunshine hours.As related to the end of phenophase,the time-lag was about 1-3 months for the air temperature and about 1-2 months for the sunshine hours,repectively.Nolag effect on the end of phenophase was found for the precipitation.(5)The response of vegetation phenology in the Qinling Mountains to extreme climate changes has obvious spatial and temporal differences.The extreme low temperature in March and October has the greatest impact on the start and the end of phenology;the extreme high tempe rature in February and Septe mber has stronger influence,and the ENSO event has a certain degree of influence on the phenological period.For the correlations between the starting and the end of phenology and the extreme low temperatures during the same stage in the Qinling Mountains were negatively related(80.28%,75.00%);the correlation between the beginning of the phenology and the extreme low temperature in March was best(83.68%),the negative correlation between the end of phenology and the extreme low temperature in October was the best(85.79%).In terms of extreme high temperatures,the correlation between the beginning of phenology and the extreme high temperature during the same stage was negatively related(71.60%),and the negative correlation was particularly significant in the northern slope;the correlation between the end of the phenology and the extreme high temperature in the same period was mainly positively correlated(51.78%),the beginning of phenology was negatively related to the extreme high temperature in February(71.37%).The correlation with the extreme high temperature in March indicates that the “cold spring” weather has a certain influence on the beginning of phenology in the Qinling;.The highest positive correlation is high(69.40%) between the end of the phenology and extremes high temperature in September.The beginning shows ElNino year earlier than La Nina,and the latter is ElNino year later than La Nina.The ENSO index NOI,PDO and SOI have different degrees of influence on the phenological period.(6)In the future,there will be obvious differences in the north-south slope and elevation of vegetation phenology changes in the Qinling Mountains.However,whether in the whole area or in the north and south slopes,the future trends are still mainly in advanced of the beginning of phenology,delayed the end of phenology,and prolonged the growing season.In the future,the change trend of the beginning of phenology will fluctuations larger with an increasing altitude.The lower altitude areas of below 600 m and the elevations of 1800-3300 m will be mainly delayed.The areas with elevations of 700-1800 m and elevations of above 3300 m will be dominated by advance trends.The change trend of the end of phenology in the area above 2600 m will be predominant,while it was in advance in the higher altitude area of above 2600 m.The change trend of growing season was mainly the extended trend in the elevation of below 3100 m;while the altitude of above 3100 m was obvious shortening.The Hurst index at the begining of phenology was 0.55,0.58 at the northern slope,and 0.54 at the southern slope;the Hurst index at the end of phenology was 0.63,the north slope was 0.62,and the south slope was 0.63;the Hurst index at the growing season was 0.66,the north slope was 0.65,and the south slope was 0.66.(7)Over the past 16 years,the Larix chinensis Beissn and Abies fargesii Franch the typical tree species of the coniferous forest have shown an advance trend in the beginning of phenology,a delayed trend in the end of phenology,and an extended trend at the growing season of phenology.In the future,the Larix chinensis Beissn of the beginning,end,and growing season of phenology will be mainly postponed,postponed,and shortened,respectively;while the Abies fargesii Franch will be dominated by advances,delays,and extensions,respectively.The starting of phenology about the Larix chinensis Beissn mainly occurred in the first 100-140 day,its end of phenology was in the 280-300 day,and its growing season was approximately 140-200 days.The trend in its beginning and end of phenology was mainly advanced(81.39%,55.26%),and the growing season was mainly prolonged(63.54%);all three were mainly in advance and extended 0~10d/10 a.The starting of phenology about the Abies fargesii Franch mainly occurred in the first 90-140 day,its end of phenology was in the 270-300 day,and its growing season was approximately 130-190 days.the trend in its beginning and end of phenology was mainly advanced(82.94%,70.59%),and the growing season was mainly prolonged(51.33%);all three were mainly in advance and extended 0~10d/10 a.The Hurst indices of the starting,end,and growing season of phenology about the Larix chinensis Beissn were 0.47,0.39,and 0.46,respectively,while those of the Abies fargesii Franch were 0.51,0.43,and 0.51,respectively.