Biology | Free Full-Text | Predicting the Potential Distribution of Haloxylon ammodendron under Climate Change Scenarios Using Machine Learning of a Maximum Entropy Model

3.3. Potentially Suitable Area under Current and Future Scenarios

The Maxent model was employed to forecast the suitable regions for H. ammodendron in the current climate, as depicted in Figure 4. The highly suitable area spans 489,800 km², constituting 5.10% of China’s total land area. The moderately suitable area includes 562,600 km², equivalent to 5.86% of China’s land area. The marginally suitable area covers 780,700 km², accounting for 8.13% of China’s land area. These regions include Xinjiang, Gansu, Ningxia, Inner Mongolia, Tibet, Qinghai, and other parts of China.

In the future high-emission scenario (SSP126), the extent of suitable areas within the country generally exhibits an upward trajectory when compared with the prevailing climatic conditions (Figure 5).

By 2030S, the area classified as highly suitable will include 564,200 km², while the moderately suitable area will span 578,700 km². The marginally suitable area will extend over 781,700 km², resulting in a total suitable area of 192.46 million km². In comparison with the range of suitable areas under current climatic conditions, there is an increase of 74,400 km² in the highly suitable areas and 16,100 km² in the moderately suitable areas. However, the marginally suitable areas have diminished by 35,000 km², resulting in an overall increment of 55,500 km².

By 2050S, the area of highly suitable area will cover 782,600 km², with the moderately suitable area spanning 431,400 km². The marginally suitable area will include 784,100 km², culminating in a total suitable area of 1.981 million km². In contrast with the range of suitable areas under current climatic conditions, the moderately suitable areas have reduced by 131,200 km², and the marginally suitable areas have shrunk by 32,600 km². Simultaneously, the highly suitable areas have expanded by 292,800 km², resulting in an overall increase of 12,900 km².

Regarding the 2070s, the highly suitable area is anticipated to span 873,000 km², with the moderately suitable area covering 429,000 km². The marginally suitable area is predicted to extend over 889,400 km², resulting in a total suitable area of 2,191,300 km². Compared with the range of suitable areas under the current climatic conditions, there is a considerable augmentation of 383,200 km² in the highly suitable areas and 72,700 km² in the marginally suitable areas. Conversely, the moderately suitable areas have contracted by 133,600 km², leading to a net increase of 322,200 km².

In the future medium-emission scenario (SSP245), the extent of suitable areas within the country generally follows an ascending trend compared with the current climatic conditions, as depicted in Figure 6.

By the 2030s, the highly suitable area is anticipated to include 554,000 km², with the moderately suitable area extending over 578,900 km². The marginally suitable area is projected to cover 787,700 km², resulting in a total suitable area of 1,913,600 km². In relation to the range of suitable areas under the current climatic conditions, there is an expansion of 64,200 km² in the highly suitable areas and 16,300 km² in the moderately suitable areas. However, the marginally suitable areas have contracted by 36,600 km², resulting in a net increase of 44,500 km².

Moving forward to the 2050s, the highly suitable area is expected to span 833,300 km², while the moderately suitable area will include 398,700 km². The marginally suitable area is predicted to cover 76,400 km², contributing to a total suitable area of 1.995 million km². In comparison with the range of suitable areas under the current climatic conditions, there is a decrease of 164,600 km² in the moderately suitable areas and 52,700 km² in the less suitable areas. Simultaneously, the highly suitable areas expanded by 343,500 km², resulting in an overall increase of 126,100 km².

Looking ahead to the 2070s, the highly suitable area is predicted to extend over 770,700 km², while the moderately suitable area will span 4410 km². The marginally suitable area is estimated to cover 681,300 km², resulting in a total suitable area of 1.88 million km². In comparison with the range of suitable areas under current climatic conditions, there is a reduction of 121,700 km² in the moderately suitable areas and 135,400 km² in the less suitable areas. Simultaneously, the highly suitable areas expanded by 270,900 km², leading to a net increase of 12,900 km².

In the future low-emission scenario (SSP585), the extent of suitable areas within the country is expected to initially increase and then decrease compared with the current climatic conditions, as illustrated in Figure 7.

By the 2030s, the highly suitable area is projected to span 523,100 km², with the moderately suitable area covering 617,700 km². The marginally suitable area is anticipated to extend over 837,500 km², resulting in a total suitable area of 1,978,300 km². In relation to the range of suitable areas under current climatic conditions, there is an expansion of 50,500 km² in the highly suitable areas and 20,800 km² in the medium suitable areas. The overall increase amounts to 109,200 km².

Moving forward to the 2050s, the highly suitable area is expected to cover 830,700 km², while the moderately suitable area will include 395,800 km². The marginally suitable area is projected to span 755,600 km², contributing to a total suitable area of 1,982,100 km². In comparison with the range of suitable areas under the current climatic conditions, there is a reduction of 61,000 km² in the low suitable areas and 166,900 km² in the medium suitable areas. Simultaneously, the highly suitable areas expanded by 340,900 km², resulting in an overall increase of 113,000 km².

Looking ahead to the 2070s, the highly suitable area is predicted to extend over 687,700 km², with the moderately suitable area spanning 407,100 km². The marginally suitable area is estimated to cover 637,700 km², leading to a total suitable area of 1,731,800 km². In relation to the range of suitable areas under the current climatic conditions, there is a decrease of 179,700 km² in the low suitable areas and 155,500 km² in the medium suitable areas. Simultaneously, the highly suitable areas expanded by 197,900 km², resulting in a net decrease of 137,300 km².

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