Fig 1.
Digital elevation model of the Xiangjiang River basin and its watershed characteristics.
(Source of base map was provided by Shuhan Wang. The map was generated by using the free and open source software QGIS version 3.16 (http://www.qgis.org/en/site/)).
Fig 2.
Spatial distribution of phenology in the Xiangjiang River Basin.
(A is SOS, B is EOS, and C is LEN. Source of base map was provided by Shuhan Wang. The map was generated by using the free and open source software QGIS version 3.16 (http://www.qgis.org/en/site/)).
Table 1.
Descriptive statistics of the vegetation phenological indicators.
Fig 3.
Variation of vegetation phenological indicators as a function of annual precipitation.
Fig 4.
Variation of vegetation phenology as a function of annual mean temperature.
Fig 5.
Areas corresponding to phenological turning points.
(A shows the areas with annual precipitation greater than 1600 mm; B shows the areas with a yearly average temperature lower than 16°C. The overlapping regions are concentrated in the southeastern part of the upper reaches, and the eastern part of the middle reaches (Luoxiao Mountains, zone I in the figure), and in the southern part of the upper reaches (Nanling Mountains, zone II in the figure). Source of base map was provided by Shuhan Wang. The map was generated by using the free and open source software QGIS version 3.16 (http://www.qgis.org/en/site/)).
Fig 6.
Variation of vegetation phenological indicators as a function of elevation intervals.
(In this study, the vertical accuracy of ASTER GDEM V2 is 20m. To analyze the detailed impact of elevation changes on the phenological indicators and also ensure that the data is effective and accurate, the minimum interval of the altitude zoning was set to 20m. The dashed red line represents the turning points of elevation on different phenological indicators; the shaded area shows the standard error of the mean).
Fig 7.
Spatial distribution of elevation zones corresponding to different vegetation phenological areas in the Xiangjiang River Basin.
(Numerically, the vegetation phenological zone with an elevation <230 m occupies 53.5% of the area, the zone from 230 to 520 m occupies 27.1% of the area, from 520 to 1700 m 19.3%, and >1700 m accounts for 0.1% of the total basin area. Source of base map was provided by Shuhan Wang. The map was generated by using the free and open source software QGIS version 3.16 (http://www.qgis.org/en/site/)).
Table 2.
Relationship between the geographies of five basic terrain types and elevation features.
Fig 8.
Box plots of different phenological indicators in the three identified vegetation phenological areas.
Table 3.
The linear fitting results and significance test between phenology and elevation.
Fig 9.
The relationship of the different phenological indicator values and monthly temperature/precipitation in the three identified vegetation phenological areas.
Table 4.
The contribution of factors spatially influencing phenology in the three identified zones.