Vegetation Activities Of Tropical Rain Forests And Its Response To Climate Change

The paper studied the growth of vegetation and its response to climate change in the three tropical rainforest regions in the world based on the GLASS LAI data and remote sensing climatic data from 2001 to 2012.Using the combination of points and faces("big boundary,small plots"),correlation analysis and process analysis,the paper analyzed the vegetation growth of tropical rain forests and its response mechanism to climate change deeply.The main findings are as follows:(1)From 2001 to 2012,the vegetation growth(LAI)in the global tropical rainforest region showed a slow decline.Among them,LAI changes in the global tropical rain forest are dominated by regions with less fluctuating trends(54.7%of the area),supplemented by regions with significant fluctuations;Although the area of the upward trend is slightly more than the area of the downward trend in the regions where the LAI fluctuates markedly,the area with extremely significant downward trend is more than the area with extremely significant upward trend.As a result,the LAI in the rain forest area generally shows a slow downward trend.The LAI fluctuation of the unclear and upward trends in the 12 years is mainly distributed in the tropical rain forest core area,while the LAI decline area is mainly distributed in the edge of the rain forest,such as the southeast edge of the Amazon rainforest,the southern and northern edges of the African rainforest,and the rainforest north of the Asian rainforest.(2)The correlation between global tropical rainforest vegetation growth(LAI)and average annual temperature from 2001 to 2012 was mainly positive and weak(95.4%of total area),and the overall relationship between LAI and annual precipitation was weakly related(about 80%of the area).(3)From 2001 to 2012,the correlation between LAI and monthly average temperature of tropical rain forest vegetation was mainly positive and weak,and the area of negative correlation was relatively low(about 7.2%of area)and concentrated on the edge of the rain forest,such as the southeast edge of the Amazon rainforest and the northern edge of the rain forest in the African rainforest;The relationship between LAI and monthly precipitation is mainly weak and negative.The monthly correlation between vegetation growth and precipitation has a certain corresponding relationship with the spatial distribution of annual precipitation,namely:generally,high rainfall areas correspond to the weak correlation areas.the medium rainfall areas correspond to the negative correlation areas,and the low precipitation areas correspond to the positive correlation areas.(4)The study on the ecological response of rain forest vegetation growth to the month changes of temperature and precipitation shows that there are 9 different response scenarios in rain forest areas.Based on the distribution center of plot location and the average monthly value of LAI greater than 4,etc.,a total of 11 typical plots were selected,which mainly reflected 5 ecological response scenarios.They are:①LAI is positively correlated with temperature and negatively correlated with precipitation(symbol abbreviated as T+P-);② LAI is weakly correlated with temperature and negatively correlated with precipitation(TOP-);③LAI is weakly correlated with temperature and weakly related with precipitation(TOPO);④LAI is weakly correlated with temperature and positively correlated with precipitation(TOP+);⑤LAI is positively correlated with temperature and negatively correlated with precipitation(T+PO).There are three scenarios such as T+P-,TOPO,and TOP-in the Americas region,and two scenarios such as T+PO and TOP+ in the Africa region,and only TOPO in the Asian region.(5)From 2001 to 2012,the vegetation growth(LAI)of typical tropical rain forests showed a generally gentle fluctuation.The LAI values in the typical plots of the Americas are higher and the inter-annual variability are smaller.The LAI values of typical plots in the African and Asian rainforest regions are relatively lower and the inter-annual variability are larger.The changes of LAI during the year can be divided into two kinds of scenarios:double-peak fluctuations and single-peak fluctuations.The typical sample plots of African rain forests mainly exhibit double-peak fluctuations,and the typical sample plots of the American and Asian rain forests mainly show single-peak small fluctuations.There is a positive correlation between the magnitude of LAI fluctuations and the average monthly temperature with monthly precipitation during the year.The greater the correlation,the greater the LAI fluctuation during the year.(6)The study on the ecological response of LAI and temperature precipitation in typical rainforest plots during 2001-2012 shows that the annual precipitation,low monthly precipitation,and fluctuation direction of temperature and precipitation during the year are the main ecological indicators that affect the monthly correlation of LAI with temperature and precipitation.The performance is:T+P-and TOP-type response scenarios are mainly distributed in the America’s rain forest region where the annual precipitation is moderate(2200-2500mm),the annual precipitation fluctuation is relatively large(39-359mm),and exists 2-3 months relative dry season(3 9-90mm).The plots whose temperature and precipitation fluctuations were basically reversed during the year were mainly T+P-type responses.The plots with basically the same temperature and precipitation fluctuations during the year were mainly TOP-type responses.The T+PO and TOP+ response scenarios are mainly distributed in the African rain forest region where the annual precipitation is relatively low(1500-1900mm),the annual precipitation fluctuation is relatively small(53-238mm),and the temperature and precipitation fluctuations are not exactly in the same direction.The plots with no obvious dry season during the year were mainly T+PO-type response scenarios,and the plots with 2-3 months relative dry season(53-100 mm)were mainly represented as TOP+ response scenarios.TOPO-type response scenarios are mainly distributed in the American and Asian rain forest regions where annual precipitation is high(2700-4600mm),precipitation fluctuation is large(100-600mm),and temperature and precipitation are not in the same direction.(7)Further studies on the correlation between temperature,precipitation,and significant changes in the years of LAI in typical sites of rain forests from 2001 to 2012 show that:In the above T+P-and T0P-type response scenarios,the LAI during the significant LAI changes over the years is negatively correlated with the temperature and cumulative precipitation over the same period.In the two response scenarios of T+P0 and T0P+,the LAI during the significant changes of LAI during the year was weakly positively correlated with temperature,and there was a lagging and cumulative effect of previous precipitation on vegetation growth when there is sufficient rainfall for three consecutive months(accumulated precipitation is 400-600mm),LAI is negatively correlated with precipitation.When there is not enough precipitation for three consecutive months(the cumulative precipitation is about 330mm),LAI is positively correlated with precipitation.The correlation between the significant period of LAI changes during the year of the T0P0-type response scenario and the temperature and cumulative precipitation over the same period is more complex,but overall weaker.(8)The relationship between the monthly change response scenario and the significant phase change result during the year can be divided into 4 categories.The first is consistent with the relationship between temperature and precipitation,corresponding to T0P-type response scenarios;The second is that the temperature-related relationship is inconsistent,and the precipitation-related relationship is consistent,corresponding to the T+P-type response scenario;The third is that the correlations with temperature and precipitation are inconsistent,corresponding to T+P0 type;The fourth is that there is no obvious correlation between temperature and precipitation,which mainly corresponds to the T0P+ and T0P0 response scenarios.