Comparative Analysis Of NPP Spatial-temporal Variation And Its Climate Response In Tropical Forests

Tropical forest is an important part of the global carbon cycle,and its carbon sink effect is affected by global change as well as gives feedback to it.Studying temporal and spatial variation of carbon sinks and their climatic responses of tropical forests not only can help us to further understand the relationship between tropical forest and climate change but also can broaden our knowledge of the mechanism of carbon sequestration in global tropical forests.Net primary productivity(NPP)is a net source of plant photosynthesis organic matter.As a key parameter of terrestrial ecological processes,NPP is an important part to understanding the terrestrial carbon cycle.Many studies have analyzed and explored the interaction between tropical forests and climate change,but there is still a lack of systematic regional comparative analysis of forest changes and its climate response as well as the analysis about the spatial distribution pattern of tropical forest carbon sequestration.Based on these problems,this paper uses MODIS data and climate data during 2001-2013 to compare the temporal-spatial variation of NPP and its influencing factors of different regions by means of time series analysis,landscape pattern analysis and correlation analysis.The main contents and conclusions of this thesis are as follows:(1)The temporal and spatial characteristics of carbon sequestration in tropical forests were studied by using time series analysis and landscape pattern analysis.The results show that the NPP of the western Amazon basin study area and Southeast Asian study area is significantly weakened from 2001 to 2013,while the NPP of the southern Congo basin study area is significantly increased.Forests with NPP unit area higher than 1800 gC/m2 are mainly distributed in the eastern side of the Andes and east of Madagascar;forests with NPP less than 600 gC/m2 are mainly distributed in the southwest of the Amazon basin study area,Africa Guinea highlands and the western Indian Peninsula.The total NPP of tropical forest was declining during the period from 2001 to 2013,with the highest in 2004(about 16.13 PgC),the lowest in 2005(about 14.83 PgC).There are significant reductions of total NPP in 2006-2007 and 2009-2010,and the total NPP shows an increasing trend since 2010.Forests with a more severe reduction of NPP(<-20 gC/(m2·a))are mainly distributed in the western central Amazon basin study area and Southeast Asia study area;forests with a more significant increase of NPP are mainly(>20 gC/(m2·a))distributed in the southern part of the Congo basin.(2)Based on single factor correlation analysis and multi-factor partial correlation analysis,the forest carbon sequestration intensity and its influencing factors were compared in the three tropical forest areas.The results of temporal and spatial analysis show that NPP is higher and stable in the Amazon study area,and the Southeast Asian is lower and unstable.NPP of the Amazon study area is mainly influenced by temperature,the Congo study area is largely affected by tree cover while the Southeast Asia is mostly influenced by PAR.The Amazon forest has the higest NPP per unit area and the total NPP;the Congo study area has the lowest total NPP;and the Southeast Asia has the lowest NPP per unit area.From the landscape pattern analysis,the NPP patches in the Amazon study area have a higher degree of aggregation and better forest stability;NPP patches in the Southeast Asian study area have a higher degree of fragmentation and poor forest stability.NPP changes in the Amazon study area were less affected by tree coverage and climatic factors,and the NPP was negatively correlated with temperature and PAR in the main forest distribution area.The Congo study area has a lower temperature and a higher PAR level.The change of NPP in this area was greatly affected by tree cover and positively correlated to temperature and PAR.Southeast Asia study area has high precipitation and humid climate.Forest NPP in this study area is negatively correlated with precipitation,positively correlated with PAR,and significantly affected by climate factors.(3)Using the time series analysis and correlation analysis method,the temporal and spatial changes of forest carbon sequestration and its influencing factors of 11 countries,including five tropical humid climate zone countries and six tropical dry climate zone countries,in Southeast Asia from 2001 to 2013 were compared and analyzed.From 2001 to 2013,the forest carbon sequestration in 11 countries in Southeast Asia was significantly weakened,and the change of tree coverage was small.The changes of NPP and the influencing factors were different in different countries.The tropical arid regions were mainly affected by temperature,while the tropical wet regions mostly influenced by PAR.There is little change of tree coverage in most countries of Southeast Asia while the NPP shows a decreasing trend and the tropical wet regions have a relatively obvious reduction of NPP.According to the distribution and trend of NPP,the 11 countries can be divided into 4 groups: high NPP with fluctuating,low NPP with fluctuating,NPP with steep drop from 2005 to 2008 and NPP with soft drop from 2001 to 2013.NPP in the third group is most sensitive to climate response and NPP in the fourth group is sensitive to TC change.Tropical monsoon forest NPP is dominated by temperature,and tropical rain forest NPP is dominated by PAR.