Changes in vegetation photosynthetic activity trends across the Asia–Pacific region over the last three decades

Abstract

The updated Global Inventory Modeling and Mapping Studies (GIMMS) third generation global satellite Advanced Very High Resolution Radiometer (AVHRR) Normalized Difference Vegetation Index (NDVI) dataset provides very detailed global information on the state of vegetation from 1982 to 2011. Using these data we investigated the changes in the vegetation photosynthetic activity in the Asia–Pacific (AP) (including Australia, South East Asia, China, and the Pacific Coast of North America) region, by discerning gradual changes into two key metrics: 1) the cumulative annual NDVI in each year and 2) the seasonality or variance in that index. We then assessed changes using break and turning points using three statistical models (least-square linear, expanded paired-consecutive linear and piecewise regression models). We found that the AP region overall experienced increasing NDVI from 1982 through 2011 with an average rate of 5.30×10−4NDVIyr−1 (0.13%yr−1). The annual NDVI increased from 1982 at a faster rate of 26.14×10−4NDVIyr−1 (0.65%yr−1) until a break in the trend after 1991 (after that the trend reduced to 5.78×10−4NDVIyr−1). In the Asia–Australia (AA) subarea of the AP, vegetation greening slowly increased at 8.71×10−4NDVIyr−1 before 2003 and then increased to 28.30×10−4NDVIyr−1 after 2003. In contrast, in the North America (NA) subarea NDVI rapidly increased initially at 18.72×10−4NDVIyr−1 before 1992 and then marginally increased (3.96×10−4NDVIyr−1) after 1992. The turning points were found to be 2008 and 1987 for the AA and NA subareas respectively. Analysis of monthly NDVI data showed that the trends were positive for most of the months of the study period, particularly during the growing season. Geospatial analyses demonstrated that cumulative annual NDVI and the variance or seasonality across the large AP region varied across the different subareas. As well, we found evidence for different spatial patterns of the NDVI changes with strong spatial heterogeneity in the patterns of the break and turning points. This suggests complex and nonlinear responses of vegetation photosynthetic activity to regional climatic changes and other drivers.