## 1 Introduction
However, area change analysis only captures the total space of urban coverage and cannot reveal interior changes of urban environments [21]. Landscape patterns, known as spatial metrics, can objectively measure the pattern and structure of an urban environment. Landscape indices were usually used to detect and describe the change in urban landscape patterns, which can quantify and classify complicated landscapes into recognizable patterns and reveal some ecosystem properties that are not readily visible. Moreover, urban landscape pattern describes the spatial interaction among landscape factors in urban areas, which has the potential to provide a more detailed analysis of the spatio-temporal patterns of the urbanization process. Combining the application of urban landscape indices and remote sensing, though still under-used, can map the landscape patterns of urban green spaces and explore urban vegetation fragmentation. Such a combination will help better illustrate and understand the heterogeneous characteristics of urban regions and the effects of urbanization on the surrounding environment. It is worth mentioning that urbanization has effected water, heat, soil quality, and carbon cycle, and has gradually become an important factor affecting vegetation growth [22]. Apart from the necessity to depict and comprehend the spatial diversity in land use patterns, it is also vital to assess the impact of urbanization on plant growth. To investigate the response of vegetation to urbanization, a variety of vegetation indexes have been utilized. [PERSON] et al. (2013) explored the impacts of urbanization on vegetation growth using an enhanced vegetation index (EVI). Previous studies found that vegetation production is decreased in urban areas using net primary production (NPP) data derived from process-based models and data-driven models ([PERSON] et al., 2013; [PERSON] et al., 2014; [PERSON] et al., 2015). However, as a key quantitative factor of vegetation growth, the spatiotemporal dynamics of the fractional vegetation coverage (FVC) under rapid urbanization have been studied rarely and, hence, are not yet fully understood. Here, FVC was generally defined as the ratio of the vertical projection of above-ground vegetation organs on the ground to the entire calculated area, it can be independent of the noise of NDVI or EVI extremes, and better reflects the vegetation change process than vegetation indices ([PERSON] et al., 2014; [PERSON] et al., 2014). [PERSON] et al. detected the dynamic change of urban FVC using multi-temporal remote sensing images and revealed the influence intensity and direction of the urban sprawl on vegetation coverage ([PERSON] et al., 2014). Moreover, because of the high rates of urbanization and obvious ecological impacts, metropolitan areas often serve as the ideal places to study the ecological effects of urbanization. Most previous studies on the effects of urbanization have focused on mega-temperate cities in southern regions ([PERSON] et al., 2013; [PERSON] et al., 2014). However, few studies have been published specifically regarding how urbanization affects vegetation in relatively cold regions in China. As the largest city in China by area, Harbin is the capital of China's northeast province Heilongjiang, it is a typical industrial city with recent rapid urbanization in the cold temperate of northeastern China. Harbin experienced a significant loss of green space as a result of implementation of the revitalization of the old industrial base of Northeast China's urban development strategy and the rapid urbanization process ([PERSON] et al., 2014). Since 2014, the Harbin government has formulated a series of development strategies including the Harbin Urban Master Plan (HUMP, 2004-2020), which had direct guidance for the development of urban green space and strived to be an ecological garden city ([PERSON] et al., 2014). Therefore, Harbin is a typical and unique area to study urban expansion and greening.