近20 a呼和浩特市城市化对植被物候的影响

了解植被物候与城市化之间的关系对于认识人类活动对生态系统的影响至关重要。基于呼和浩特市近20 a MODIS的两种植被指数数据，利用动态阈值法提取了植被物候，结合城市化指标，研究了2001—2020年呼和浩特市植被物候对城市化的响应。研究表明：森林和灌木地返青期（Start of growing season，SOS）发生较早（平均值第132 d），但其枯黄期（End of growing season，EOS）也较早（第265 d）。SOS较晚的是耕地（第168 d），EOS较晚的是草地（第275 d），表明研究区木本植物SOS和EOS均早于草本植物。人造地表植被物候年际变化较大，在SOS和EOS的物候变化率分别为每10 a提前4.1 d和推迟0.7 d。此外，以人造地表比率和城乡梯度信息（即从城市核心到周边农村地区的同心环）为城市化指标，探讨了呼和浩特市中心城区植被物候对城市化的响应。研究发现SOS随人造地表比率上升而提前，EOS则出现相反的趋势。从城乡梯度上看，在特定范围内，远离城市中心SOS波动上升，即距城市中心越远植被SOS越晚，而EOS逐渐下降，即距城市中心越远植被EOS越早。总之，不同的城市化指标显示了植被物候对城市化的非线性响应。

Effects of urbanization on vegetation phenology in Hohhot City in the recent 20 years

It is essential to understand the impact of human activities on ecosystems by analysing the relationship between vegetation phenology and urbanization. In this study, the vegetation phenology of Hohhot City, Inner Mongolia, China was extracted using a dynamic threshold method based on two vegetation indexes from MODIS in recent 20 years, and the response of vegetation phenology to urbanization in Hohhot City from 2001 to 2020 was investigated using the urbanization index. We found that the start of growing season (SOS) of forests and shrubs occurred earlier (132 days), and the end of growing season (EOS) also occurred earlier (265 days). The later SOS was in crops (168 days), and the later EOS was in grasslands (275 days), indicating that both SOS and EOS of woody plants were earlier than those of herbaceous plants in the study area. The phenological change rate of urban vegetation was 4.1 days earlier and 0.7 days later per decade in SOS and EOS, respectively. In addition, we explored the response of vegetation phenology to urbanization in Hohhot City, using the urban ratio and information about urban-rural gradients (concentric rings from the urban core to surrounding rural areas) as the urbanization indicators. We found that SOS was advanced with an increase in urban ratio, whereas EOS exhibited the opposite trend. From the perspective of the urban-rural gradient within a certain distance, SOS fluctuated, whereas EOS decreased at a distance from urban centres. That is, the farther away from the city center, the later SOS and the earlier EOS. In conclusion, different urbanization indicators reflect the nonlinear response of vegetation phenology to urbanization.