*3.5. Zoning of EVI for Climatic Driving Forces*

The growth of vegetation was closely related to the climate and the environment. Climate conditions, especial changes in air temperature, relative humidity, and precipitation, would have a great influence on the distribution and growth of vegetation [53]. In this paper, air temperature, relative humidity, and precipitation were chosen to zone different driving forces for EVI (Table 1).

The zoning results of driving force for EVI change in the study area (Figure 9) show that the zones where EVI change was driven by air temperature were mainly located in the north and scattered in the central and southern parts, including northeastern Hulunbuir and western Xilingol League with an elevation of 600–1400 m. The air temperature driving zones account for 8% of the total area and the vegetation types were mainly typical steppe; and including deciduous broadleaf forests, deciduous coniferous forests, and desert steppe. The zones where relative humidity was the main driving force for EVI change were mainly distributed in the northern part of the study area, and scattered in the central and southern parts, involving Xilingol League, Chifeng, Tongliao, Baotou, and southeastern Hulunbuir, with an elevation from 200 to 1800 m, being 11.6% of the total area. The vegetation types mainly included evergreen coniferous forests, deciduous coniferous forests, deciduous broadleaf forests, and coniferous and broadleaf mixed forests. In the northeastern, central and western part of IMAR, precipitation driving areas scattered in the northwest of Hulunbuir and southern part of Hinggan League and the northern part of Tongliao, where the elevation was 300–1500 m, accounting for 21.8% of the area. EVI there was driven by precipitation, and the vegetation types were mainly evergreen coniferous forests, deciduous coniferous forest and typical steppe. Others include typical steppe, swamps, and desert steppe.


**Table 1.** The zoning rules of driving forces for EVI change.

<sup>1</sup> The GRG between EVI and air temperature; <sup>2</sup> The GRG between EVI and precipitation; <sup>3</sup> The GRG between EVI and relative humidity; <sup>4</sup> EVI change driven by air temperature; <sup>5</sup> EVI change driven by precipitation; <sup>6</sup> EVI change driven by relative humidity; <sup>7</sup> EVI change driven by both air temperature and precipitation; <sup>8</sup> EVI change driven by both air temperature and relative humidity; <sup>9</sup> EVI change driven by both precipitation and relative humidity; <sup>10</sup> EVI change driven by air temperature, relative humidity and precipitation.

The zones where EVI change was driven by both air temperature and precipitation were mainly distributed in the southeastern Hulunbuir with an elevation of 400–1000 m, accounting for 2.7% of the total area. The vegetation types were mainly meadow steppe, desert steppe, and typical steppe. The zones where air temperature and relative humidity co-driving EVI change were mainly located in the eastern Hulunbuir, the elevation from 500 to 1000 m, accounting for 3.1% of the total area. The vegetation types were mainly deciduous coniferous forests and deciduous broadleaf forests. The zones where precipitation and relative humidity co-driving EVI change were mainly located in the northern Hulunbuir, the elevation from 600 to 1100 m, accounting for 3.8% of the total area. The vegetation types mainly include evergreen coniferous forests, deciduous broadleaf forests. and meadow steppe. The zones where EVI change was driven by air temperature, precipitation and relative humidity were mainly distributed in the northeastern Hulunbuir, the elevation from 300 to 800 m, accounting for 0.93% of the total area. The vegetation types were mainly evergreen coniferous forests, deciduous broadleaf forests, and typical steppe. The weak driving force of climatic factors made little contribution to the study, so the authors will not further analyze it.

The vegetation in different zones relied on water, heat, or both to different degrees. The typical steppe, coniferous forests, and cultivated plants in east-central and northwestern parts of the study area clearly showed that water was a dominant condition for vegetation growth. However, in the typical steppe area where there was a remarkable joint drive of air temperature and precipitation, it indicated that the growth of typical steppe was more dependent on the collective effect of water and heat. In the swamps, broadleaf forests, and desert steppe of the west-central part, as well as southeastern region of the northern part of the study area, air temperature and relative humidity were the main driving forces, indicating that these zones were more dependent on air temperature and humidity than on water. In the coniferous and broadleaf mixed forests of the northeastern part of the study area, where EVI was driven by air temperature, relative humidity and precipitation, it indicated that the vegetation had greater demand for air temperature, relative humidity, and precipitation.

**Figure 9.** Areas of precipitation drive, air temperature drive, and relative humidity drive in the study area.
